CN111189879A - Horizontal pipe external condensation heat exchange test device and test method - Google Patents
Horizontal pipe external condensation heat exchange test device and test method Download PDFInfo
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Abstract
The invention relates to a horizontal pipe external condensation heat exchange test device and a test method, and belongs to the technical field of heat exchange. The low-temperature storage tank of the device enters a first pipe and a second pipe which are positioned in a cavity of an intermediate medium vaporizer and have different pipe external roughness in two ways; the lower part of the cavity of the intermediate medium vaporizer is provided with a lower tube bundle for circulating a heat supply medium; the first pipe and the second pipe are respectively provided with corresponding inlet pressure transmitter, inlet temperature transmitter, outlet pressure transmitter and outlet temperature transmitter probes; the cavity of the intermediate medium vaporizer is provided with a cavity temperature transmitter and a cavity pressure transmitter probe; the inlet and the outlet of the lower tube bundle are respectively provided with an inlet temperature transmitter and an outlet temperature transmitter probe; the probe signal output ends of each flowmeter and each transmitter are respectively in communication connection with a computer host through a PLC. The invention can realize the comparison test of a plurality of groups of heat exchange tubes with different roughness in the same time, and accurately calculate the specific numerical value of the heat transfer coefficient outside the tubes with different roughness.
Description
Technical Field
The invention relates to a condensation heat exchange test device, in particular to a horizontal pipe external condensation heat exchange test device, and also relates to a corresponding test method, belonging to the technical field of heat exchange.
Background
Droplet condensation is the process with the highest heat transfer coefficient in existing heat transfer models. The essential requirement for the liquid formed by condensation to be in the form of drops rather than films at the hot and cold interfaces is that the interfaces have a low surface energy.
The surface energy is generated microscopically because the state of particles (ions, atoms, or molecules) on the surface of an object is different from that inside the object. The particles in the interior are uniformly acted by the surrounding particles to show a stress equilibrium state. However, the coordination number of the particles on the surface is reduced, so that the acting force is unbalanced, namely, an unsaturated force field exists on the surface. The particles at the surface have a tendency to be drawn inward causing a reduction in surface energy, thereby creating surface tension. The stronger the interparticle interaction, the higher the surface energy. The metal bond is a strong bonding action, so the metal surface is generally a high energy surface. Since industrial condensers are often made of metal materials, film condensation is a common phenomenon in the field of heat exchange technology.
In order to improve the heat exchange effect, when designing a heat exchanger, it is desirable to convert film-like condensation into drop-like condensation, and the drop-like condensation needs to reduce the surface energy of the heat exchange tube surface. The reduction mode is various, and the simplest and most effective mode is to change the surface state of the surface of the heat exchange tube, such as mechanical polishing, electrochemical polishing, hydrochloric acid soaking and the like. Due to the complexity of heat transfer, namely the flow rate, temperature, pressure, medium characteristics, heat exchange tube materials and specifications of the medium in the tube can influence the heat transfer effect, the same is true outside the tube. Due to a plurality of influencing factors, no research report is found.
The device comprises a heat exchange inner pipe, a condensation section shell, a material outlet pipeline, a first two-way rotary joint, a steam outlet pipeline, a second two-way rotary joint, a steam inlet pipeline, a sealing washer, an internal thread sleeve head, a material inlet pipeline, a fixed base, a pipe wall surface thermocouple, an in-pipe fluid thermocouple and an out-pipe steam thermocouple, wherein the heat exchange inner pipe, the condensation section shell, the material outlet pipeline, the first two-way rotary joint, the steam outlet pipeline, the second two-way rotary joint, the steam inlet pipeline, the sealing washer, the internal thread sleeve head, the material inlet pipeline, the fixed; the test and research on the temperature data of the condensation heat exchange outside the heat exchange pipe can be realized, and the total heat exchange coefficient and the condensation heat exchange characteristic of the condensation heat exchange under the free rotation load condition can be obtained. However, the device was studied with the direction of free rotation on the effect of condensation heat transfer and no comparison was made in a single experiment. And small differences in flow, pressure and temperature of each test may have an effect on the test.
In addition, chinese patent application No. 200610010400.6, publication No. CN 101126609a, discloses a condenser tube liquid guide for use in a shell-and-tube heat exchanger, and a liquid guide plate for reducing the thickness of a condensed liquid film outside the heat exchanger tube. The device comprises a liquid guide groove, wherein a planar continuous drainage plate is arranged at the upper part of the curved liquid guide groove, and the liquid guide groove and the drainage plate are fixed on a condensation pipe through a snap spring and a pin. However, the application range is limited, because the heat exchange tubes in the common heat exchanger are tightly arranged to form a tube bundle, and the heat exchange effect in unit volume is reduced on the contrary because the 'condensation tube liquid guide' cannot be tightly arranged.
Disclosure of Invention
The invention aims to: the horizontal pipe external condensation heat exchange test device capable of reducing interference factors to the greatest extent is provided, and meanwhile, a corresponding test method is provided, so that quantitative test data of heat transfer coefficients reflecting the influence of different roughness on condensation heat transfer outside the pipe along the length direction can be obtained, and a scientific foundation is laid for improving heat exchange efficiency research.
In order to achieve the purpose, the horizontal pipe external condensation heat exchange test device comprises a low-temperature storage tank for storing cold media, wherein the low-temperature storage tank is branched into two paths after passing through a main regulating valve and a buffer tank, one path of the low-temperature storage tank enters a first pipe in a pipe bundle of a cavity of an intermediate medium vaporizer through an upper flow meter and an upper regulating valve, and the other path of the low-temperature storage tank enters a second pipe in the pipe bundle of the cavity of the intermediate medium vaporizer through a lower flow meter and a lower regulating valve; the first tube and the second tube are parallel to each other and have different tube external roughness;
a liquid intermediate medium is contained in a cavity of the intermediate medium vaporizer, a lower tube bundle for circulating a heat supply medium is arranged at the lower part of the cavity, and the heat supply medium passes through a tube bundle flowmeter;
the inlet end and the outlet end of the first pipe are respectively provided with a first inlet pressure transmitter, a first inlet temperature transmitter, a first outlet pressure transmitter and a first outlet temperature transmitter probe; the inlet end and the outlet end of the second pipe are respectively provided with a second inlet pressure transmitter, a second inlet temperature transmitter, a second outlet pressure transmitter and a second outlet temperature transmitter probe; the cavity of the intermediate medium vaporizer is provided with a cavity temperature transmitter and a cavity pressure transmitter probe; the inlet and the outlet of the lower tube bundle are respectively provided with an inlet temperature transmitter and an outlet temperature transmitter probe;
and the probe signal output ends of each flowmeter and each transmitter are respectively connected with the corresponding access ends of a PLC in the test control system, and the PLC is in communication connection with a computer host.
The corresponding test method of the invention is that the computer host in the test control system operates according to the following steps:
the method comprises the following steps of firstly, calculating and comparing heat quantity, namely receiving corresponding data signals transmitted by each flowmeter and a transmitter probe and transmitted by a PLC, obtaining heat quantity released by a heat medium and heat quantity absorbed by a cold medium flowing through an intermediate medium vaporizer according to the following equations, judging whether the difference between the heat quantity and the heat quantity absorbed by the cold medium is within a preset tolerance range, if so, carrying out the next step, and if not, carrying out the test after the adjustment through a corresponding regulating valve:
Q1＝F311×(T312-T311)×Cpc1
Q2＝F321×(T322-T321)×Cpc2
Qc＝Q1+Q2
Qh＝F101×(T101-T102)×Cph
in the formula:
Q1、Q2respectively absorbing heat by cold media flowing through the first pipe and the second pipe, wherein the unit is W;
Qc、Qhrespectively absorbing heat by cold medium flowing through the intermediate medium vaporizer and emitting heat by hot medium, unit W;
f311, F321 and F101 are respectively flow data received from an upper flowmeter, a lower flowmeter and a tube bundle flowmeter and are in units of kg/s;
t311, T312, T321, T322, T101 and T102 are temperature data received from a first inlet temperature transmitter, a first outlet temperature transmitter, a second inlet temperature transmitter, a second outlet temperature transmitter, an inlet temperature transmitter and an outlet temperature transmitter respectively, and the unit is;
Cpc1、Cpc2、Cph1the specific heat of the medium flowing through the first pipe, the second pipe and the lower pipe bundle respectively is unit J/(kg DEG C);
calculating heat transfer coefficients, namely calculating the heat transfer coefficients of the first pipe and the second pipe through the following formula, calculating the maximum relative difference value of the first pipe and the second pipe, judging whether the absolute value of the relative difference value is greater than a preset value, if so, reporting an abnormality, and if not, performing the next step;
K1＝Q1/(A1×△tm1)
K2＝Q2/(A2×△tm2)
△tm1＝(△t11-△t21)/ln(△t11/△t21)
△tm2＝(△t12-△t22)/ln(△t12/△t22)
△t11＝T201-T311
△t21＝T201-T312
△t12＝T201-T321
△t22＝T201-T322
in the formula:
K1、K2the heat transfer coefficients of the first tube and the second tube, respectively, in W/(m)2·℃)；
A1、A2The external surface areas of the first tube and the second tube, respectively, in m2；
△tm1Is the logarithmic mean temperature difference in units of the first tube;
△tm2is the log mean temperature difference in units of the second tube;
△t11the temperature difference between the cold and the hot ends of the first pipe is large, and the unit is;
△t21the temperature difference is the small end of the cold and hot temperature difference of the first pipe, and the unit is;
△t12the temperature difference is the large end of the cold and hot temperature difference of the second pipe, and the unit is;
△t22the temperature difference is the small end of the cold and hot temperature difference of the second pipe, unit ℃;
thirdly, establishing an iterative calculation formula of the heat transfer coefficient outside the tube, namely equally dividing the heat exchange tube into n (n is a natural number which is more than or equal to three) sections, and establishing the following relational expression from the beginning to the ith (1< i < n) section of the heat exchange tube length:
Qinner i＝QPipe i
QPipe i＝QOuter i
QInner i＝QOuter i
QInner i＝αni×Ani×(tni-ti)
QOuter i＝D×αwi×Awi×(td-twi)
QPipe i＝2π×Lz×λi×(twi-tni)/ln(dw/dn)
Ani＝2π×dn×Lz
Awi＝2π×dw×Lz
In the formula:
Qinner i、QPipe i、QOuter iRespectively measuring the length of the ith segment, the heat flux in the tube wall and the heat flux outside the tube in a unit W;
Ani、Awithe length of the ith segment is the internal surface area of the tube, the external surface area of the tube, and the unit m2；
αni、αwiThe length of the ith segment is the convection heat transfer coefficient in the tube and the convection heat transfer coefficient outside the tube respectively in units of W/(m)2·℃)；
ti、tni、twThe temperature of the medium in the tube, the temperature of the inner wall of the tube and the temperature of the outer wall of the tube are respectively the ith section length, and the unit is;
tdthe temperature of the medium outside the pipe is T201 in unit ℃;
pnthe medium pressure in the pipe is expressed in kpa;
pwthe pressure of medium outside the pipe is P201, and the unit is kpa;
d is an external pipe correction coefficient and is dimensionless;
Lzis the length of the ith segment, in m;
unithe flow speed of the medium in the length pipe of the ith section is in m/s;
dw、dnrespectively the outer diameter of the pipe and the inner diameter of the pipe in m;
f is medium flow in the pipe, the first pipe is substituted into F311, the second pipe is substituted into F321, and the unit kg/s is obtained;
g is the acceleration of gravity, and has a value of 9.80, units of m/s2；
λi、λni、λwThe heat conductivity coefficient of the ith section of the pipe, the heat conductivity coefficient of the medium in the pipe and the heat conductivity coefficient of the medium outside the pipe are respectively as follows: W/(m.DEG C);
γwthe unit is J/kg of condensation latent heat of saturated steam of a medium outside the pipe;
ρni、ρwthe density of the i-th section of the medium inside the pipe and the density of the medium outside the pipe are respectively in kg/m3；
cpni、cpwThe specific heat of the i-th section of the medium inside the pipe and the medium outside the pipe respectively has the unit J/(kg DEG C);
μni、μwrespectively the section length of the ith section of the external medium and the viscosity of the external medium in Pa & s;
fourthly, obtaining the distribution data of the heat transfer coefficient outside the tube along the length of the tube through iteration
Step one, substituting td、pw、pn、Lz、dw、dn、F、λw、ρw、cpw、μw、γw；
Step two, setting the initial value of the external correction coefficient D of the pipe and the temperature t of the external wall of the pipew1An initial value of (t)1+td)/2；
Step three, calculation is carried out from the first section to obtain αw1、αn1And QInner 1And calculate QFirst pipe＝2π×Lz×λ1×(tw1-tn1)/ln(dw/dn)；
Step four, judging QInner 1And QFirst pipeIf the relative difference is greater than the preset tolerance, if so, returning to the step two to reset twiIf otherwise, look at tw1If the assumption is correct, recording the total length L of the first section of the heat exchange tube1External tube heat transfer coefficient αw1Heat flux parameter QInner 1；
Step five, according to QInner 1Calculating the absorption Q of the cold medium in the tubeInner 1The temperature of the medium t in the length of the second section of heat exchange tube is obtained by the change of the rear temperature2Respectively obtaining the corresponding in-tube temperature, the total length of the heat exchange tube, the heat transfer coefficient outside the tube and the heat flux parameter from the second section to the ith section according to the third step and the fourth step;
step six, when the temperature t of the medium in the pipe isiIf the difference between the calculated length of the heat exchange tube and the actual length of the heat exchange tube is larger than the tolerance, returning to the step III, if the difference is smaller than the tolerance, judging whether the relative difference between the calculated length of the heat exchange tube and the actual length of the heat exchange tube is smaller than the preset tolerance, and if not, returning to the step II, and resetting the correction coefficient D; if yes, the result is recorded as D1And recording the distribution of the heat transfer coefficient outside the tube along the length of the first tube heat exchange tube;
the analysis result of the heat transfer coefficient test data of the second tube obtained by referring to the above steps is marked as D2And recording the distribution of the heat transfer coefficient outside the tube along the length of the second tube heat exchange tube.
The test method of the invention is further perfected by comprising the following steps:
fifthly, verifying the correctness of the test result by judging the reasonability of the test result, namely judging (K)2-K1)/K1}×{(D2-D1)/D1Whether is greater than0, if so, judging that the test result is reasonable, and further verifying the correctness of the test result; if not, judging that the test result is not reasonable, and carrying out the test again.
Summarizing, the invention has the following remarkable beneficial effects:
1. the device can realize the contrast test of a plurality of groups of heat exchange tubes with different roughness at the same time in the same device, and effectively inhibit the errors of parameters such as flow, pressure, temperature and the like, thereby better reflecting the influence of the roughness outside the tubes on the heat exchange performance.
2. The process flow, the instrument and electric control and the test main body are all optimally designed, the flow consistency of a plurality of groups of heat exchange tubes can be ensured, and the method is embodied as follows:
a. a buffer tank and a valve adjusting valve are additionally arranged between the cold medium storage tank and the heat exchange device in the process flow, so that the influence of cold medium vaporization on flow fluctuation is eliminated, and the stable pressure and the stable flow of the total flow are realized;
b. the primary flow primary regulation and the secondary fine regulation are controlled by the instrument and the electric controller, so that multilayer cascade regulation is realized, and the consistency of inlet flow, temperature and pressure of cold media in the first pipe and the second pipe before entering the heat exchange device is ensured;
c. in the structural design of the test main body, the first pipe and the second pipe share a shell pass, and the external environments of the two pipes are consistent, so that the temperature t of an intermediate medium outside the pipes is ensureddiThe consistency is achieved;
3. the specific values of the heat transfer coefficients outside the pipe with different roughness can be accurately obtained.
Drawings
Fig. 1 is a schematic structural diagram of an embodiment of the present invention.
Fig. 2 is a partial perspective view of the adapter tube of the embodiment of fig. 1.
Fig. 3, 4 and 5 are circuit diagrams of the test circuit of the embodiment of fig. 1.
FIG. 6 is a flowchart of the iterative operation of the fourth step of data analysis in the embodiment of FIG. 1.
FIG. 7 is a graph of the results of the tests performed on the embodiment of FIG. 1.
Detailed Description
Example one
As shown in fig. 1 and 2, a low-temperature storage tank 1 for storing a cold medium is branched into two paths after passing through a main regulating valve 2 and a buffer tank 3, one path enters a first pipe 6-1 in a pipe bundle of a cavity of an intermediate medium vaporizer 6 through an upper flow meter 5 and an upper regulating valve 4, and the other path enters a second pipe 6-1 ' in the pipe bundle of the cavity of the intermediate medium vaporizer 6 through a lower flow meter 5 ' and a lower regulating valve 4 '. The first tube 6-1 and the second tube 6-1' are U-shaped tubes parallel to each other and have different tube external roughness.
The liquid intermediate medium is contained in the cavity of the intermediate medium vaporizer 6, the lower part of the cavity is provided with a lower tube bundle 6-2 through which the heat supply medium flows, and the heat supply medium passes through a tube bundle flow meter 7. The inlet end of the first tube 6-1 is equipped with a first inlet pressure transmitter P311, a first inlet temperature transmitter T311, while the outlet end is equipped with a first outlet pressure transmitter P312, a first outlet temperature transmitter T312 probe. The inlet end of the second pipe is provided with a second inlet pressure transmitter P321 and a second inlet temperature transmitter T321, and the outlet end is provided with a second outlet pressure transmitter P322 and a second outlet temperature transmitter T322 probe. The cavity of the intermediate medium vaporizer 6 is provided with a cavity temperature transmitter T201 and a cavity pressure transmitter probe P201; the inlet and outlet of the lower tube bundle 6-2 are respectively provided with an inlet temperature transmitter T101 and an outlet temperature transmitter T102 probe. The signal output ends of the probes of the flow meters and the transmitters are respectively connected with the corresponding access ends of the PLC in the test control system and then are in communication connection with a computer host through the PLC.
In this embodiment, the cold medium is liquid nitrogen, the heat medium is factory water, the intermediate medium is propane, and the heat exchange tube is made of SS304 stainless steel. The low-temperature storage tank 1 stores low-temperature liquid nitrogen at the temperature of-190 ℃, the low-temperature liquid nitrogen enters the buffer tank 3 through the regulating valve 2 after being gasified, the flow rate of the nitrogen is regulated through the regulating valve 4, the low-temperature nitrogen is divided into two paths, the two paths of low-temperature nitrogen respectively enter the two heat exchange tubes 6-1 and 6-1 'of the upper tube bundle of the intermediate medium vaporizer 6, the roughness of the first tube 6-1 is Ra 0.2 mu m, the roughness of the second tube 6-1' is Ra 0.02 mu m, the reading F311 of the flowmeter is 0.00829kg/s and the reading F321 of the flowmeter is 0.00kg/s through the combined cascade control of primary regulation and secondary regulation, the inlet temperature T311 and the inlet temperature T321 are the same, the inlet temperature range is-100 ℃ to 10 ℃, and the inlet pressure P311 and. The temperature of the used water as the heat medium was 30 ℃ and the pressure was 0.2MPa, the flow rate F101 was controlled at 0.27778kg/s by the flow meter 7, the water entered the lower tube bundle 6-2 of the intermediate medium vaporizer 6, the inlet temperature T101 was 30 ℃, and the outlet temperature after passing through the lower tube bundle 6-2 was denoted as T102. Liquid intermediate medium B adopts propane in the 6 cavitys of intermediate medium vaporizer, prevents that intermediate medium from freezing after meeting cold nitrogen gas, and propane constantly is evaporated for gas by circulating water heating during the platform operation, then rises to the last back of tubes and is fallen into lower tube bank by low temperature nitrogen condensation for liquid again to realize the purpose of circulating water indirect heating low temperature nitrogen gas. The propane pressure P201 was 935.7kpa and the propane temperature T201 was 24.37 ℃.
When the heat medium A runs, the heat medium A enters the lower tube bundle 6-2 of the intermediate medium vaporizer 6 to heat the intermediate medium liquid outside the tubes of the lower tube bundle 6-2, the intermediate medium is gasified into gas after being heated, the tubes of the upper tube bundle 6-1 and 6-1' are filled with the intermediate medium C, the gaseous intermediate medium B and the cold medium C exchange heat due to the fact that the tubes of the upper tube bundle are filled with the cold medium C, the cold medium C is heated out of the upper tube bundle 6-1, the gaseous intermediate medium B is condensed to be liquid outside the tubes and falls into the bottom of the intermediate medium vaporizer 6 again, the lower tube bundle 6-2 is immersed, the two tubes of the upper tube bundle influence the condensation heat exchange coefficient outside the tubes due to different roughness, the outlet temperatures T312 and T322 of the cold medium C are further influenced, and the influence factors of the different roughness outside the tubes of the upper tube bundle.
The split type structural design is actually adopted to the intermediate medium vaporizer of this embodiment, consequently can be convenient dismantle the U-shaped pipe of changing different roughness levels to install the sight glass, thereby can observe gas condensation and hang the membrane process.
Theoretically, the first pipe and the second pipe are made of the same material and have the same specification, and the inlet state (temperature, pressure and flow) of nitrogen in the pipe and the external propane environment are the same, so that the condensation influence number of the roughness of the outer surfaces of the first pipe and the second pipe can be calculated through the difference of the outlet temperature of the nitrogen in the pipe, the device and the test method of the embodiment can be established, the independent variable number of heat transfer is reduced as much as possible through real-time comparison, quantitative analysis and calculation are made possible, and a test basis is laid for researching the specific influence and the specific condensation quantity of the condensation effect of natural circulation media outside the pipe caused by different roughness outside the horizontal pipe.
In the PLC circuit portion of the present embodiment, as shown in fig. 3, 4 and 5, 002UC is the analog input module of the PLC, 003UC and 004UC are the analog input/output modules of the PLC, the analog input is represented by AI, and the analog output is represented by AO. The specific connection and signal transmission relationship is as follows:
1)002UC passes through a safety gate to acquire a current signal of a mass flow meter (FT) in real time according to a sampling period, wherein the FT311 measures the medium flow passing through a second pipe, the medium flow passing through 0+ and 0-of the 002UC is accessed, the FT321 measures the medium flow passing through a first pipe, the medium flow passing through 1+ and 1-of the 002UC is accessed, the FT101 measures the flow passing through a heat medium inlet, the medium flow passing through 2+ and 2-of the 002UC is accessed, and the flow is in units of kg/s.
2)002UC is subjected to real-time acquisition of platinum thermal resistance signals according to a sampling period through a Temperature Transmitter (TT), wherein TT101 measures the temperature of a thermal medium inlet, 3+ and 3-of 002UC is accessed, TT102 measures the temperature of a thermal medium outlet, 4+ and 4-of 002UC is accessed, TT201 measures the temperature of an intermediate medium, 5+ and 5-of 002UC is accessed, TT202 measures the temperature of the intermediate medium, 6+ and 6-of 002UC is accessed, TT311 measures the temperature of a second pipe cold medium inlet, 7+ and 7-of 002UC is accessed, and the temperature is unit ℃.
3) The 003UC collects the platinum thermal resistance signal in real time according to the sampling period by a Temperature Transmitter (TT), wherein T321 measures the temperature at the cold medium inlet of the first pipe, the temperature is connected to 0+ and 0-of the 003UC, T312 measures the temperature at the cold medium outlet of the first pipe, the temperature is connected to 1+ and 1-of the 003UC, T322 measures the temperature at the cold medium inlet of the first pipe, the temperature is connected to 2+ and 2-of the 003UC, and the temperature is in unit ℃.
4) The 003UC collects the opening feedback signal of the electric regulating valve FV301 in real time according to the sampling period, and is connected to 3+ and 3-of the 003UC, and simultaneously outputs the opening signals of the electric regulating valves FV311 and FV321 which are respectively connected to 0M, 0 and 1M, 1 of the 003UC, and the opening is unit percent.
5) The 004UC collects opening feedback signals of the electric control valves FV311 and FV321 in real time according to a sampling period, and respectively accesses 0+, 0-and 1+, 1-of the 004UC, and simultaneously outputs opening signals of the electric control valve FV301, which access 0M and 0 of the 004UC, wherein the opening is unit percent.
6)004UC collects current signals of a Pressure Transmitter (PT) in real time according to a sampling period through a safety barrier, wherein PT301 measures the pressure of a buffer tank, 2+ and 2-of 004UC is accessed, PT201 measures the pressure of a heat exchanger, 3+ and 3-of 004UC is accessed, and the unit of pressure kPa (a) is pressure.
The tests carried out with the apparatus of this example generally require:
1) preparing a low-temperature cold medium gas source, namely storing a liquid cold medium in a storage tank, discharging the liquid cold medium from a cold medium storage tank, gasifying the liquid cold medium by a gasifier, allowing the liquid cold medium to enter a buffer tank after passing through a pressure regulating valve, opening a valve behind the buffer tank after the pressure of the buffer tank reaches a preset pressure, maintaining the pressure in the buffer tank at the preset pressure by the pressure regulating valve, and allowing the temperature of the cold medium in the buffer tank to reach a preset low-temperature state after precooling is finished so as to finish primary regulation of the constant temperature requirement and the flow of the cold medium before entering a heat exchanger;
2) the flow of the low-temperature cold medium in each pipe is adjusted, namely a flow control program is started after the low-temperature cold medium reaches constant temperature and pressure, the flow is accurately controlled, at the moment, the low-temperature cold medium is discharged from a buffer tank and then enters a first pipeline and a second pipeline in two ways respectively, and the low-temperature cold medium passes through a corresponding mass flow meter, a corresponding regulating valve and a corresponding control system respectively, so that the two-stage accurate control of the flow of the two pipelines is realized, the temperature and the flow of the cold medium in the two pipelines are ensured to be consistent before entering an intermediate vaporizer, and the adverse effect on a test result;
3) after the hot medium pipeline is opened and the cold medium pipeline is prepared, the hot medium is introduced into the hot medium pipeline;
4) preparing an intermediate vaporizer, wherein an intermediate medium is filled in a cavity of the intermediate vaporizer to immerse a lower heat exchange tube (but not higher than the upper heat exchange tube), the two upper heat exchange tubes have the same specification and size and the same material, only the state of the outer surface of the tubes is adjusted by a single factor, one heat exchange tube is a common heat exchange tube, the outer surface of the tubes is not treated, the outer surface of the tubes is subjected to brightening treatment (after a group of tests are finished, the heat exchange tubes with other roughness can be replaced according to needs), and because the two heat exchange tubes are positioned in the same cavity, the external environment influence factors are consistent, namely, the external contact medium, the medium pressure and the;
5) after the heat exchanger is prepared, in order to ensure the accuracy of the test, the embodiment furthest ensures that the test conditions of the two heat exchange tubes are consistent from the aspects of the process flow, the control method and the structural design, can better judge the specific influence of the brightness of the tube outside on the heat exchange of the heat exchange tubes through the outlet temperature of the heat exchange tubes, and lays a foundation for accurately and quantitatively calculating the influence value;
6) the PLC of the test calculation-control system collects the temperature, pressure and flow parameter values of each pipeline and equipment in real time, and the influence values of the heat exchange tubes with different roughness grades on condensation can be obtained through computer analysis and calculation.
The test method of the present embodiment can be specifically exemplified by the following steps of operating the computer host in the test control system (see fig. 7):
first, heat quantity calculation and comparison
Receiving corresponding data signals transmitted by each flowmeter and the transmitter probe transmitted by the PLC, obtaining heat released by a heat medium and heat absorbed by a cold medium flowing through the intermediate medium vaporizer according to the following equations, and judging whether the difference between the heat released by the heat medium and the heat absorbed by the cold medium is within a preset tolerance range, if so, carrying out the next step, otherwise, carrying out the test after the adjustment of a corresponding regulating valve:
Q1＝F311×(T312-T311)×Cpc1
Q2＝F321×(T322-T321)×Cpc2
Qc＝Q1+Q2
Qh＝F101×(T101-T102)×Cph
in the formula:
Q1、Q2respectively absorbing heat by cold media flowing through the first pipe and the second pipe, wherein the unit is W;
Qc、Qhabsorbing heat and heat respectively for a cold medium flowing through an intermediate medium evaporatorHeat is released in units of W;
f311, F321 and F101 are respectively flow data received from an upper flowmeter, a lower flowmeter and a tube bundle flowmeter and are in units of kg/s;
t311, T312, T321, T322, T101 and T102 are temperature data received from a first inlet temperature transmitter, a first outlet temperature transmitter, a second inlet temperature transmitter, a second outlet temperature transmitter, an inlet temperature transmitter and an outlet temperature transmitter respectively, and the unit is;
Cpc1、Cpc2、Cph1the specific heat of the medium flowing through the first pipe, the second pipe and the lower pipe bundle respectively is unit J/(kg DEG C);
one set of experimental data in the experiment was:
tdthe temperature T201 of the medium outside the pipe is 24.37 ℃;
pwthe pressure of the medium outside the pipe P201 is 935.7kpa (a);
pnthe pressure of medium in the pipe is P311/P321 which is 200kpa (a);
Lzthe length of the ith section is 0.02 m;
outer diameter of tube dw0.016m, inner diameter d of pipen0.012m, and 2.52m for the actual length L of the heat exchange tube;
f is medium flow in the pipe, the first pipe F311 is 0.00829kg/h, and the second pipe F321 is 0.00828 kg/h;
g is the acceleration of gravity, with a value of 9.80, in m/s 2;
t1the temperature of the medium in the pipe is the temperature of the medium in the pipe of the 1 st segment, namely the inlet temperature T311/T312 of the medium in the pipe, wherein T311 is-46.2 ℃, and T312 is-46.1 ℃;
tnthe temperature of the medium in the pipe is the temperature of the medium in the n-th section, namely the outlet temperature T321/T322 of the medium in the pipe, wherein T321 is 14.1 ℃, and T322 is 15.2 ℃;
the specific calculation result of the energy balance calculation of the first tube is as follows:
Q1＝F311×(T312-T311)×Cpc1
＝0.00829×(14.1-(-46.2))×1038W＝518.99W
Q2＝F321×(T322-T321)×Cpc2
＝0.00828×(15.2-(-46.1))×1038W＝526.67W
Qc＝Q1+Q2
＝518.99W+526.67W＝1045.66W
Qh＝F101×(T101-T102)×Cph
＝0.27778×(30-29.1)×4180W＝1040.57W
the tolerance is (Q)c-Qh)/QhThe heat exchange energy balance principle is met, and the data of the group can be used.
Calculating heat transfer coefficients, namely calculating the heat transfer coefficients of the first pipe and the second pipe through the following formula, calculating the maximum relative difference value of the first pipe and the second pipe, judging whether the absolute value of the relative difference value is greater than 25% of a preset value, if so, reporting an abnormality, and otherwise, performing the next step;
the significance of this step is: theories and tests show that the heat transfer coefficient which visually reflects the heat exchange capacity of the heat exchange tube is limited by the influence of the roughness of the outside of the tube, the change of the heat transfer coefficient is usually not more than +/-25 percent, and the exceeding means that test data is distorted, and the test is stopped to search for reasons in time so as to avoid the iterative calculation with complicated subsequent steps and long time consumption; the calculation result of the step which is not out of range can be used as the evidence of the final result;
K1＝Q1/(A1×△tm1)
K2＝Q2/(A2×△tm2)
△tm1＝(△t11-△t21)/ln(△t11/△t21)
△tm2＝(△t12-△t22)/ln(△t12/△t22)
△t11＝T201-T311
△t21＝T201-T312
△t12＝T201-T321
△t22＝T201-T322
in the formula:
K1、K2the heat transfer coefficients of the first tube and the second tube, respectively, in W/(m)2·℃)；
A1、A2The external surface areas of the first tube and the second tube, respectively, in m2；
△tm1Is the logarithmic mean temperature difference in units of the first tube;
△tm2is the log mean temperature difference in units of the second tube;
△t11the temperature difference between the cold and the hot ends of the first pipe is large, and the unit is;
△t21the temperature difference is the small end of the cold and hot temperature difference of the first pipe, and the unit is;
△t12the temperature difference is the large end of the cold and hot temperature difference of the second pipe, and the unit is;
△t22the temperature difference is the small end of the cold and hot temperature difference of the second pipe, unit ℃;
the calculation result after substituting the corresponding specific numerical value is as follows:
△t11＝T201-T311＝24.37-(-46.2)＝70.57℃
△t21＝T201-T312＝24.37-14.1＝10.27℃
△t12＝T201-T321＝24.37-(-46.1)＝70.47℃
△t22＝T201-T322＝24.37-15.2＝9.17℃
△tm1＝(△t11-△t21)/ln(△t11/△t21)＝31.29℃
△tm2＝(△t12-△t22)/ln(△t12/△t22)＝30.36℃
K1＝(A1×△tm1)/Q1＝128.55W/m2·℃
K2＝(A2×△tm2)/Q2＝136.86W/m2·℃
(K2-K1)/K1＝6.46％
thirdly, establishing an iterative calculation formula of the heat transfer coefficient outside the pipe
Because the heat flux transferred from inside to outside of each section of heat exchange tube is the same, the heat exchange tube is equally divided into n sections (n is a natural number which is more than or equal to three), and the length from the beginning to the ith (1< i < n) section of the heat exchange tube
QInner i＝QPipe i
QPipe i＝QOuter i
QInner i＝QOuter i
QInner i＝αni×Ani×(tni-ti)
QOuter i＝D×αwi×Awi×(td-twi)
QPipe i＝2π×Lz×λi×(twi-tni)/ln(dw/dn)
Ani＝2π×dn×Lz
Awi＝2π×dw×Lz
In the formula:
Qinner i、QPipe i、QOuter iRespectively measuring the length of the ith segment, the heat flux in the tube wall and the heat flux outside the tube in a unit W;
Ani、Awithe length of the ith segment is the internal surface area of the tube, the external surface area of the tube, and the unit m2；
αni、αwiThe length of the ith segment is the convection heat transfer coefficient in the tube and the convection heat transfer coefficient outside the tube respectively in units of W/(m)2·℃)；
ti、tni、twThe temperature of the medium in the tube, the temperature of the inner wall of the tube and the temperature of the outer wall of the tube are respectively the ith section length, and the unit is;
tdthe temperature of the medium outside the pipe is T201 in unit ℃;
pnthe medium pressure in the pipe is expressed in kpa;
pwthe pressure of medium outside the pipe is P201, and the unit is kpa;
d is an external pipe correction coefficient and is dimensionless;
Lzis the length of the ith segment, in m;
unithe flow speed of the medium in the length pipe of the ith section is in m/s;
dw、dnrespectively the outer diameter of the pipe and the inner diameter of the pipe in m;
f is medium flow in the pipe, the first pipe is substituted into F311, the second pipe is substituted into F321, and the unit kg/s is obtained;
g is the acceleration of gravity, and has a value of 9.80, units of m/s2；
The following are respectively the medium thermal physical properties only related to the medium itself, the medium temperature and the medium pressure, and can be obtained by looking up a table from a related handbook of thermal physical properties of fluid (published by Ningjing History, China petrochemical Press), or by calling special software NIST/HTRI/HYSYS, specifically comprising
λi、λni、λwThe heat conductivity coefficient of the ith section of the pipe, the heat conductivity coefficient of the medium in the pipe and the heat conductivity coefficient of the medium outside the pipe are respectively as follows: W/(m.DEG C);
γwthe unit is J/kg of condensation latent heat of saturated steam of a medium outside the pipe;
ρni、ρwthe density of the i-th section of the medium inside the pipe and the density of the medium outside the pipe are respectively in kg/m3；
cpni、cpwSpecific heat of the i-th section of the medium inside the pipe and the medium outside the pipe respectivelySite J/(kg. DEG C.);
μni、μwrespectively the section length of the ith section of the external medium and the viscosity of the external medium in Pa & s;
fourthly, obtaining the distribution data of the heat transfer coefficient outside the tube along the length of the tube by iteration
Step one, substituting td、pw、pn、Lz、dw、dn、F、λw、ρw、cpw、μw、γw；
Step two, setting an initial value of the external correction coefficient D of the pipe, normally setting the initial value to 0.5, and setting the external wall temperature t of the pipew1An initial value of (t)1+td)/2，；
Step three, calculation is carried out from the first section to obtain αw1、αn1And QInner 1And calculate QFirst pipe＝2π×Lz×λ1×(tw1-tn1)/ln(dw/dn)；
Step four, judging QInner 1And QFirst pipeIf the relative difference is greater than the preset tolerance (0.1%), if so, returning to step two to reset twi(due to t)iRepresenting the temperature of the cooling medium in the tube, tdRepresenting the temperature of the medium outside the tube, the wall t of the tubewAt temperature t onlyiAnd tdThe heat transfer principle is met, so the iteration range is ti-td) If otherwise, look at tw1If the assumption is correct, recording the total length L of the first section of the heat exchange tube1External tube heat transfer coefficient αw1Heat flux parameter QInner 1；
Step five, according to QInner 1Calculating the absorption Q of the cold medium in the tubeInner 1The temperature of the medium t in the length of the second section of heat exchange tube is obtained by the change of the rear temperature2 
Respectively obtaining the corresponding in-tube temperature, the total length of the heat exchange tube, the heat transfer coefficient outside the tube and the heat flux parameter from the second section to the ith section according to the third step and the fourth step;
step six, when the temperature t of the medium in the pipe isiAnd when the corresponding outlet temperature (T312 or T322) is greater than the tolerance (0.1%), returning to the step three, and when the corresponding outlet temperature (T312 or T322) is less than the tolerance (0.1%), judging the calculated length L of the heat exchange pipe at the momentCALWhether the relative difference value with the actual heat exchange tube length L is less than the tolerance (1%), wherein LCAL＝i×LZIf not, returning to the step two, resetting a correction coefficient D, wherein the iteration range is 0-1, the iteration method is a dichotomy, the iteration method has multiple modes and mainly comprises a Newton method, a conjugate iteration method, a dichotomy, a genetic algorithm, simulated annealing and the like, the dichotomy is simple in operation and high in iteration speed, the iteration range A-B is selected firstly, the range median C is selected for the first iteration to be (A + B)/2, the new range median D is selected to be (A + C)/2 or D is (C + B)/2 according to the iteration result, and the iteration process is finished by analogy; if yes, the result is recorded as D1And recording α along the length of the first tube heat exchange tubewiThe distribution of (a);
the analysis result of the heat transfer coefficient test data of the second tube obtained by referring to the above steps is marked as D2And recording the distribution of the heat transfer coefficient outside the tube along the length of the second tube heat exchange tube;
the iterative calculation of the heat transfer coefficient outside the pipe with specific values substituted in the embodiment is as follows:
① will test t in the datad＝24.37℃、pw＝935.7kpa(a)、pn＝200kpa(a)、Lz＝0.02m、L＝2.52m、dw＝0.016m、dn＝0.012m、F＝0.00829kg/s、g＝9.8m/s2As input, according to t in the constant valued、pwSubstituting into HYSYS software to obtain lambdaw＝0.0188W/(m·℃)、ρw＝20.24kg/m3、cpw＝1886J/(kg·℃)、μw＝8.61Pa·s、γw＝3.4E05J/(kg·℃)；
② assuming the external correction coefficient D of the first tube, the initial value is set to 0.5;
③ start the calculation of segments, i is 1to n, starting from the first segment, at which t is calculated1Substitution into tiAccording to t1＝-46.2℃、pnSubstituting 200kpa (a) into HYSYS software to obtain λn1＝0.0207W/(m·℃)、ρn1＝2.98kg/m3、cpn1＝1033.7J/(kg·℃)、μn1＝14.8Pa·s
Assuming a tube outer wall temperature tw1：
tw1＝(t1+td)/2＝(-46.2+24.37)/2＝-10.915℃
αw1＝207.84W/(m2℃)
QOuter 1＝D1×αw1×Awi×(td-tw1)
QOuter 1＝D1×αw1×2π×dw×Lz×(td-tw1)
＝1x207.84x6.28x0.016x0.02x35.285＝14.74W
QInner 1＝QOuter 1＝14.74W
λ1Substituted into HYSYS calculation software to obtain 16.5W/(m ℃)
QFirst pipe＝2π×Lz×λ1×(tw1-tn1)/ln(dw/dn)
＝2x3.14x0.02x16.5x(-9.095)/ln(0.016/0.0128)
＝-84.50W
(QInner 1-QFirst pipe)/QFirst pipeRe-iterating t greater than a specified value, -117.44%w1，
When t is after 12 iterationsw1Q is obtained at ③ deg.C under-5.56458 deg.CInner 1＝13.027W，QFirst pipe＝13.021W；
④, judging that (Q in 1-Q first tube)/Q first tube is 0.05% and is smaller than a specified value, finishing the first-stage iterative computation, and starting to perform the second-stage iterative computation;
⑤ carry out t2And (3) calculating:
according to t2The calculated temperature is substituted into the step ④ again to complete iterative calculation of the second section of heat exchange tube, and t2, t3, ti and the like are obtained in sequence according to the step ④ and the step ⑤;
⑥ the program iterates for 14200 times according to steps ④ and ⑤ to obtain t14200＝14.112℃
(t14200-T312)/T312When the ratio of (14.115-14.1)/14.1 is 0.085%, and the tolerance is less than 0.1%, the calculation of the calculated length of the heat exchange tube is completed:
LCAL＝i*LZ＝14200*0.02m＝284m
(LCALand (L)/L (284-2.52)/2.52 (11169%) which is larger than the tolerance (1%), wherein the calculated length of the heat exchange tube is inconsistent with the actual length of the heat exchange tube, and the step ③ is returned to repeat the step D:
d takes a new value of 0.25, and then after 122 iterations when D is 0.00725, LCAL＝2.524m。
(LCALAnd L/L is (2.524-2.52)/2.52 is 0.159%, the calculated length of the heat exchange tube is consistent with the actual length of the heat exchange tube, and the calculated length of the heat exchange tube is consistent with the actual length of the heat exchange tube, so that the correction coefficient D outside the tube of the first tube is 0.00725, which is assumed to be correct and is recorded as D1Recording α along the length of the first tube heat exchange tubewiDistribution of (2). The distribution situation of the heat transfer coefficient outside the tube in the length direction of the heat exchange tube in the graph of fig. 7 is visualized through graphic representation, and the variation trend of the heat transfer coefficient outside the tube in the length direction of different heat exchange tubes is objectively reflected.
If necessary, carrying out a fifth step: verifying the correctness of the test result by judging the reasonability of the test result, namely judging { (K)2-K1)/K1}×{(D2-D1)/D1Judging whether the test result is reasonable if the result is larger than 0, and further verifying the correctness of the test result; if not, judging that the test result is not reasonable, and carrying out the test again.
The derivation of the above formula in the fifth step is as follows:
according to
α thereinn、αwThe average convection heat transfer coefficient in the full-length pipe and the average convection heat transfer coefficient outside the pipe are respectively unit W/(m)2DEG C.,. lambda.is the average thermal conductivity unit W/(m DEG C.) of the full length pipe
Is provided with
Substituted into the above formula to obtain
Is composed of (K)2-K1)/K1>0,K1>0 to get
K2>K1
D2>D1
I.e. (D)2-D1)/D1>0
The same principle can prove when (K)2-K1)/K1＜0,K1>Time 0 (D)2-D1)/D1＜0
Thus demonstrating { (K)2-K1)/K1}×{(D2-D1)/D1Always larger than 0.
The above experiments in this example show that the first and second tubes have an outside tube heat transfer coefficient of α along the length of the heat exchange tubewiAs shown in fig. 7, illustrates a higher outside-tube heat transfer coefficient of the second tube, with a specific improvement value of (D)2-D1)/D150.07% for (0.01088-0.00725)/0.00725. Furthermore, according to (K)2-K1)/K16.46%, indicating a higher heat transfer coefficient for the second tube, and { (K)2-K1)/K1}×{(D2-D1)/D1}＝6.46％×50.07％＝3.23％>And 0, the analysis result conforms to the heat exchange principle, and the correctness of the calculation result of the heat transfer coefficient outside the tube is proved.
In addition, the experiment shows that the embodiment has the following remarkable advantages:
1) the influence variables can become quantitative by accurately controlling various factors influencing heat exchange conditions, so that the interference of test results is reduced, and the heat exchange performance of the heat exchange tubes with different roughness can be conveniently calculated according to the difference of a single target variable.
2) Meanwhile, 2 groups of heat exchange pipe tests are carried out, so that the consistency of the propane environment outside the pipe and the consistency of the state of the cold medium inlet inside the pipe are ensured, the influence of other factors on test data is reduced to the greatest extent, and the temperature difference of outlets of two pipes can be directly compared due to the simultaneous implementation, so that the intuition is strong.
3) The method comprises the steps of achieving primary pre-adjustment of the flow of two pipes through a pressure valve, and then accurately adjusting the flow of the two pipes through an adjusting valve, wherein the primary adjustment and the secondary adjustment are in cascade treatment in a control program, and the two adjustments are mutually coordinated, so that the flow of media in the two pipes is consistent.
4) The condensing medium outside the upper tube bundle exists in the cavity of the intermediate medium vaporizer, belongs to a closed space, does not need a pump to make the condensing medium circulate forcibly, and can realize natural circulation of evaporation-condensation through the heat medium of the lower tube bundle.
In addition to the above embodiments, the present invention may have other embodiments, such as the selection of the intermediate medium, the selection of the material of the heat exchange tube, the selection of the different heat medium and the cold medium, etc., which are equivalent to form the technical solutions, and all fall into the protection scope of the present invention.
Claims (7)
1. The utility model provides a heat transfer test device is congealed outward to horizontal pipe which characterized in that: the system comprises a low-temperature storage tank (1) for storing cold media, wherein the low-temperature storage tank is branched into two paths after passing through a main regulating valve (2) and a buffer tank (3), one path enters a first pipe (6-1) in a pipe bundle of a cavity of an intermediate medium vaporizer (6) through an upper flow meter (5) and an upper regulating valve (4), and the other path enters a second pipe (6-1 ') in the pipe bundle of the cavity of the intermediate medium vaporizer through a lower flow meter (5 ') and a lower regulating valve (4 '); the first tube and the second tube are parallel to each other and have different tube external roughness;
a liquid intermediate medium is contained in a cavity of the intermediate medium vaporizer, a lower tube bundle (6-2) through which a heat supply medium flows is arranged at the lower part of the cavity, and the heat supply medium passes through a tube bundle flowmeter (7);
the inlet end and the outlet end of the first pipe are respectively provided with a first inlet pressure transmitter (P311), a first inlet temperature transmitter (T311), a first outlet pressure transmitter (P312) and a first outlet temperature transmitter (T312) probe; the inlet end and the outlet end of the second pipe are respectively provided with a second inlet pressure transmitter (P321), a second inlet temperature transmitter (T321), a second outlet pressure transmitter (P322) and a second outlet temperature transmitter (T322) probe; the cavity of the intermediate medium vaporizer is provided with a cavity temperature transmitter (T201) and a cavity pressure transmitter probe (P201); the inlet and the outlet of the lower tube bundle are respectively provided with an inlet temperature transmitter (T101) probe and an outlet temperature transmitter (T102) probe;
and the probe signal output ends of each flowmeter and each transmitter are respectively connected with the corresponding access ends of a PLC in the test control system, and the PLC is in communication connection with a computer host.
2. The horizontal out-of-tube condensation heat exchange test device of claim 1, wherein: the first tube and the second tube are U-shaped tubes which are parallel to each other.
3. The horizontal out-of-tube condensation heat exchange test device of claim 2, wherein: the intermediate medium vaporizer is of a split structure and is provided with a sight glass for observing gas condensation and a film hanging process.
4. The horizontal out-of-tube condensation heat exchange test device of claim 3, wherein: the cold medium is liquid nitrogen, the heat medium is water, and the intermediate medium is propane.
5. The test method of the horizontal pipe external condensation heat exchange test device of any one of claims 1to 4 is characterized in that a computer host in the test control system operates according to the following steps:
the method comprises the following steps of firstly, calculating and comparing heat quantity, namely receiving corresponding data signals transmitted by each flowmeter and a transmitter probe and transmitted by a PLC, obtaining heat quantity released by a heat medium and heat quantity absorbed by a cold medium flowing through an intermediate medium vaporizer according to the following equations, judging whether the difference between the heat quantity and the heat quantity absorbed by the cold medium is within a preset tolerance range, if so, carrying out the next step, and if not, carrying out the test after the adjustment through a corresponding regulating valve:
Q1＝F311×(T312-T311)×Cpc1
Q2＝F321×(T322-T321)×Cpc2
Qc＝Q1+Q2
Qh＝F101×(T101-T102)×Cph
in the formula:
Q1、Q2respectively absorbing heat by cold media flowing through the first pipe and the second pipe, wherein the unit is W;
Qc、Qhrespectively absorbing heat by cold medium flowing through the intermediate medium vaporizer and emitting heat by hot medium, unit W;
f311, F321 and F101 are respectively flow data received from an upper flowmeter, a lower flowmeter and a tube bundle flowmeter and are in units of kg/s;
t311, T312, T321, T322, T101 and T102 are temperature data received from a first inlet temperature transmitter, a first outlet temperature transmitter, a second inlet temperature transmitter, a second outlet temperature transmitter, an inlet temperature transmitter and an outlet temperature transmitter respectively, and the unit is;
Cpc1、Cpc2、Cph1the specific heat of the medium flowing through the first pipe, the second pipe and the lower pipe bundle respectively is unit J/(kg DEG C);
calculating heat transfer coefficients, namely calculating the heat transfer coefficients of the first pipe and the second pipe through the following formula, calculating the maximum relative difference value of the first pipe and the second pipe, judging whether the absolute value of the relative difference value is greater than a preset value, if so, reporting an abnormality, and if not, performing the next step;
K1＝Q1/(A1×△tm1)
K2＝Q2/(A2×△tm2)
△tm1＝(△t11-△t21)/ln(△t11/△t21)
△tm2＝(△t12-△t22)/ln(△t12/△t22)
△t11＝T201-T311
△t21＝T201-T312
△t12＝T201-T321
△t22＝T201-T322
in the formula:
K1、K2the heat transfer coefficients of the first tube and the second tube, respectively, in W/(m)2·℃)；
A1、A2The external surface areas of the first tube and the second tube, respectively, in m2；
△tm1Is the logarithmic mean temperature difference in units of the first tube;
△tm2is the log mean temperature difference in units of the second tube;
△t11the temperature difference between the cold and the hot ends of the first pipe is large, and the unit is;
△t21the temperature difference is the small end of the cold and hot temperature difference of the first pipe, and the unit is;
△t12the temperature difference is the large end of the cold and hot temperature difference of the second pipe, and the unit is;
△t22the temperature difference is the small end of the cold and hot temperature difference of the second pipe, unit ℃;
thirdly, establishing an iterative calculation formula of the heat transfer coefficient outside the tube, namely equally dividing the heat exchange tube into n (n is a natural number which is more than or equal to three) sections, and establishing the following relational expression from the beginning to the ith (1< i < n) section of the heat exchange tube:
Qinner i＝QPipe i
QPipe i＝QOuter i
QInner i＝QOuter i
QInner i＝αni×Ani×(tni-ti)
QOuter i＝D×αwi×Awi×(td-twi)
QPipe i＝2π×Lz×λi×(twi-tni)/ln(dw/dn)
Ani＝2π×dn×Lz
Awi＝2π×dw×Lz
In the formula:
Qinner i、QPipe i、QOuter iRespectively measuring the length of the ith segment, the heat flux in the tube wall and the heat flux outside the tube in a unit W;
Ani、Awithe length of the ith segment is the internal surface area of the tube, the external surface area of the tube, and the unit m2；
αni、αwiThe length of the ith segment is the convection heat transfer coefficient in the tube and the convection heat transfer coefficient outside the tube respectively in units of W/(m)2·℃)；
ti、tni、twThe temperature of the medium in the tube, the temperature of the inner wall of the tube and the temperature of the outer wall of the tube are respectively the ith section length, and the unit is;
tdthe temperature of the medium outside the pipe is T201 in unit ℃;
pnthe medium pressure in the pipe is expressed in kpa;
pwthe pressure of medium outside the pipe is P201, and the unit is kpa;
d is an external pipe correction coefficient and is dimensionless;
Lzis the length of the ith segment, in m;
unithe flow speed of the medium in the length pipe of the ith section is in m/s;
dw、dnrespectively the outer diameter of the pipe and the inner diameter of the pipe in m;
f is medium flow in the pipe, the first pipe is substituted into F311, the second pipe is substituted into F321, and the unit kg/s is obtained;
g is the acceleration of gravity, and has a value of 9.80, units of m/s2；
λi、λni、λwThe heat conductivity coefficient of the ith section of the pipe, the heat conductivity coefficient of the medium in the pipe and the heat conductivity coefficient of the medium outside the pipe are respectively as follows: W/(m.DEG C);
γwthe unit is J/kg of condensation latent heat of saturated steam of a medium outside the pipe;
ρni、ρwthe density of the i-th section of the medium inside the pipe and the density of the medium outside the pipe are respectively in kg/m3；
cpni、cpwThe specific heat of the i-th section of the medium inside the pipe and the medium outside the pipe respectively has the unit J/(kg DEG C);
μni、μwrespectively the section length of the ith section of the external medium and the viscosity of the external medium in Pa & s;
fourthly, obtaining the distribution data of the heat transfer coefficient outside the tube along the length of the tube through iteration
Step one, substituting td、pw、pn、Lz、dw、dn、F、λw、ρw、cpw、μw、γw；
Step two, setting the initial value of the external correction coefficient D of the pipe and the temperature t of the external wall of the pipew1An initial value of (t)1+td)/2，；
Step three, calculation is carried out from the first section to obtain αw1、αn1And QInner 1And calculate QFirst pipe＝2π×Lz×λ1×(tw1-tn1)/ln(dw/dn)；
Step four, judging QInner 1And QFirst pipeIf the relative difference is greater than the preset tolerance, if so, returning to the step two to reset twiIf otherwise, look at tw1If the assumption is correct, recording the total length L of the first section of the heat exchange tube1External tube heat transfer coefficient αw1Heat flux parameter QInner 1；
Step five, according to QInner 1Calculating the absorption Q of the cold medium in the tubeInner 1The temperature of the medium t in the length of the second section of heat exchange tube is obtained by the change of the rear temperature2Refer to step three and step fourSequentially obtaining corresponding in-tube temperature, total length of the heat exchange tube, heat transfer coefficient outside the tube and heat flux parameters from the second section to the ith section;
step six, when the temperature t of the medium in the pipe isiIf the difference between the calculated length of the heat exchange tube and the actual length of the heat exchange tube is larger than the tolerance, returning to the step III, if the difference is smaller than the tolerance, judging whether the relative difference between the calculated length of the heat exchange tube and the actual length of the heat exchange tube is smaller than the preset tolerance, and if not, returning to the step II, and resetting the correction coefficient D; if yes, the result is recorded as D1And recording the distribution of the heat transfer coefficient outside the tube along the length of the first tube heat exchange tube;
the analysis result of the heat transfer coefficient test data of the second tube obtained by referring to the above steps is marked as D2And recording the distribution of the heat transfer coefficient outside the tube along the length of the second tube heat exchange tube.
6. The test method of the horizontal tube outside condensation heat exchange test device according to claim 5, further comprising:
fifthly, verifying the correctness of the test result by judging the reasonability of the test result, namely judging (K)2-K1)/K1}×{(D2-D1)/D1Judging whether the test result is reasonable if the result is larger than 0, and further verifying the correctness of the test result; if not, judging that the test result is not reasonable, and carrying out the test again.
7. The test method of the horizontal pipe external condensation heat exchange test device according to claim 6, wherein: the iteration method is one of a Newton method, a conjugate iteration method, a dichotomy method and a genetic algorithm.
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| CN111984044A (en) * | 2020-07-21 | 2020-11-24 | 航天晨光股份有限公司 | Double-pipe flow and outlet pressure cooperative control method in horizontal pipe external condensation heat exchange test |
| CN115096628A (en) * | 2022-06-27 | 2022-09-23 | 镇江东方电热有限公司 | Method for calculating heating performance and tube surface temperature of tubular electric heater based on HTRI |
| CN117168864A (en) * | 2023-11-02 | 2023-12-05 | 天津市热电有限公司 | Monitoring management method and system for heat exchange station of heat supply network |
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| CN117968415A (en) * | 2024-04-01 | 2024-05-03 | 苏州杜尔气体化工装备有限公司 | Device for increasing heat exchange efficiency of vaporizer by using circulating water spray |
| CN117968415B (en) * | 2024-04-01 | 2024-07-02 | 苏州杜尔气体化工装备有限公司 | Device for increasing heat exchange efficiency of vaporizer by using circulating water spray |
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