CN109470741B - Oil scale thermal resistance measuring device and oil scale thermal resistance calculating method - Google Patents
Oil scale thermal resistance measuring device and oil scale thermal resistance calculating method Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 claims description 3
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- G—PHYSICS
- G01—MEASURING; TESTING
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Abstract
The invention discloses an oil scale thermal resistance measuring device, which comprises an oil supply pipe (13), wherein an oil inlet of the oil supply pipe (13) is connected with an oil outlet of an oil pump (14), an oil inlet of the oil pump (14) is connected with an oil outlet of an oil cooler (18), an oil inlet of the oil cooler (18) is connected with an oil outlet of an oil return pipe (17), an upper channel measuring section and a lower channel measuring section are connected in parallel between the oil inlet of the oil return pipe (17) and the oil outlet of the oil supply pipe (13), and a filter (12) and a total regulating valve are arranged on the oil supply pipe (13); a stop valve (16) is arranged on the oil return pipe (17). The invention also discloses a calculation method of the oil scale thermal resistance measuring device. According to the principle of heat transfer, the invention can simulate the working conditions of a horizontal pipe, a bent pipe and a vertical pipe, and has high measurement accuracy.
Description
Technical Field
The invention relates to an oil scale thermal resistance measuring device and an oil scale thermal resistance calculating method, and belongs to the technical field of thermal resistance measurement.
Background
The fuel oil supply and lubrication system relates to various heat exchangers, and the existence and accumulation of oil dirt over time influence the heat transfer coefficient, so that the heat exchange quantity is influenced, the oil temperature deviation and the pump consumption are increased when the fuel oil supply and lubrication system is light, the normal operation of production equipment is influenced, the metal overtemperature is caused when the fuel oil supply and lubrication system is heavy, the service life of the equipment is influenced, and even serious accidents are caused.
The thermal resistance measurement of oil dirt includes a direct measurement method and an indirect measurement method. The direct measurement method is to measure the thickness of the oil dirt and then calculate the thermal resistance of the oil dirt according to the thermal conductivity coefficient of the oil dirt, and the specific methods include an optical method, a radiation method, a pulse reflection method and the like, but the data are not ideal and have high cost; the indirect measurement method is usually a heat transfer coefficient method, and the existing measurement system has poor precision, poor data stability, insufficient consideration of the influence of oil speed and excessive complexity.
Disclosure of Invention
The invention aims to solve the technical problem of providing the oil scale thermal resistance measuring device which can simulate the working conditions of a horizontal pipe, a bent pipe and a vertical pipe according to the principle of heat transfer theory and has high measuring precision;
the invention also provides a method for calculating the oil scale thermal resistance of the oil scale thermal resistance measuring device, which considers the influence of the oil speed on the oil scale thermal resistance measuring precision, can simulate the working conditions of a horizontal pipe, a bent pipe and a vertical pipe, and has high measuring precision.
In order to solve the technical problems, the invention adopts the following technical scheme:
the oil scale thermal resistance measuring device comprises an oil supply pipe, wherein an oil inlet of the oil supply pipe is connected with an oil outlet of an oil pump, an oil inlet of the oil pump is connected with an oil outlet of an oil cooler, an oil inlet of the oil cooler is connected with an oil outlet of an oil return pipe, and an upper channel measuring section and a lower channel measuring section are connected in parallel between the oil inlet of the oil return pipe and the oil outlet of the oil supply pipe;
the oil supply pipe is provided with a filter and a total regulating valve;
a stop valve is arranged on the oil return pipe;
the upper channel measuring section and the lower channel measuring section both comprise branch regulating valves connected with the total regulating valve, the branch regulating valves are connected with an inlet pipe, the inlet pipe is connected with a flowmeter, the flowmeter is connected with an L-shaped bent pipe, the L-shaped bent pipe comprises a horizontal section, a bent pipe section and a vertical section which are integrally connected, and the horizontal section is connected with the flowmeter;
the horizontal section, the bent pipe section and the vertical section sequentially comprise an oil pipe, an insulating layer and a protective layer from inside to outside; heaters are arranged in the middle of the oil pipes of the horizontal section, the bent pipe section and the vertical section, and thermocouples and thermal resistors are arranged on the oil pipes of the horizontal section and the vertical section at two ends of the heaters;
the two vertical sections are connected with an oil return pipe through check valves;
the flowmeter, the thermocouple, the heater, the thermal resistor, the stop valve and the oil pump are all connected with a controller of the display instrument; the display instrument is provided with a liquid crystal screen, and the liquid crystal screen is connected with the controller. The liquid crystal screen displays mass flow (kg/min), oil speed c (m/s) and oil scale thermal resistance R x (m 2 ℃/W)。
The flow meter measures the volume flow, namely the flow meter reading flow V, the unit is L/min, the invention shows that the mass flow has higher practicability, and the mass flow is calculated according to the volume flow and the oil density of the flow meter.
The thermocouples and the thermal resistors are arranged on two sides of the diameter direction of the oil pipe, namely, the positions of the thermocouples and the thermal resistors at the same position correspond to each other.
The thermocouple is inserted into the oil pipe and used for measuring the oil temperature, and the thermocouple adopts an armored thermocouple produced by Dongtaixin Rui instruments, the model WRPK, the graduation number S, the measurement range is 0-1350 ℃, the allowable error is +/-0.5 ℃ and the outer diameter is 2mm.
The thermal resistor is stuck on the surface of the oil pipe and used for measuring the wall temperature of the oil pipe, the thermal resistor adopts Shanghai double-rising thin film type copper resistor, the model WZC is used, the measuring range is-50-150 ℃, and the allowable error is minus or plus (0.30+0.006t).
And the stop valve is respectively connected with check valves of the upper channel measuring section and the lower channel measuring section through three-way connectors.
The total regulating valve is respectively connected with the branch regulating valves of the upper channel measuring section and the lower channel measuring section through three-way connectors.
And the oil supply pipe, the oil return pipe and the oil pipe are all DN25 steel pipes. Except the horizontal section, the bent pipe section and the vertical section, other oil pipe parts are not insulated, and an oil passing passage is formed by the oil supply pipe, the oil return pipe and the oil pipe.
The heat insulation layer is made of foaming polyurethane.
The oil cooler is a coiled pipe type heat exchanger, is cylindrical and is at normal pressure, an oil inlet hole for inserting the oil return pipe is formed in the top end of the coiled pipe type heat exchanger, a cold water pipe is arranged in the oil cooler, and the cold water pipe is connected with tap water.
The oil supply pipe is led out from the bottom of the oil cooler and is provided with an oil pump, a filter and a total regulating valve which are respectively connected with branch regulating valves of the upper channel measuring section and the lower channel measuring section through three-way connectors. The oil return pipe is provided with a stop valve, and is respectively connected with check valves of the upper channel measuring section and the lower channel measuring section through a three-way joint, and finally enters the upper space of the oil cooler. In the oil cooler, the oil is cooled by a cold water pipe.
The flowmeter adopts an elliptic gear flow sensor produced by a combined fertilizer instrument general factory, the model LC, remote transmission, the precision +/-0.5%, DN25, the medium temperature-20-80 ℃ and the highest bearing pressure of 1.6MPa.
The heater adopts an insulating heating wire, is wound on the surface of the oil pipe, and is controlled by the display to heat and measure the electric heating power.
The oil pump is a gear oil pump manufactured by Quanta pump valve manufacturing company, and is made of a stainless steel material with the model WCB-75P, the flow rate of 75L/min, the pressure head of 30m, the electric power of 750W and the working oil temperature of not higher than 80 ℃.
The stop valve adopts Shanghai Tetong corrugated pipe stop valve, the temperature is 29 ℃ below zero to 350 ℃, the highest bearing pressure is 1.6MPa, and the caliber is 25mm.
The branch regulating valve adopts a T40 plunger type manual regulating valve of four-T in Shanghai and North, the highest bearing pressure is 1.6MPa, and the caliber is 25mm at the temperature of-29-150 ℃.
Obtaining the mass flow of the oil according to the readings of the flowmeter and the subsequent thermocouple readings; the total thermal resistance and the convective heat resistance can be calculated by measuring the electric heating power, the oil temperature rise and the average temperature of the outer wall of the oil pipe of the heater of the horizontal section, and the thermal resistance of the oil scale is finally calculated due to the fact that the thermal resistance of the heat conduction is fixed. The measurement principle of the bent pipe section and the vertical section is the same as that of the horizontal section.
A calculation method of oil scale thermal resistance of an oil scale thermal resistance measuring device comprises the following steps:
taking the horizontal section of the upper channel measuring section as an example, the calculation method of the oil scale thermal resistance of the horizontal section of the upper channel measuring section comprises the following steps:
adjusting the current of the heater on the horizontal section of the upper channel measuring section, and controlling the oil temperature rise delta t=t before and after the heater 2 -t 1 Wherein t is 2 Represents the temperature after temperature rise, where t 1 Representing the temperature before heating, deltat representing the heat transfer temperature difference, deltat not exceeding 10 ℃, and measuring the electric heating power N of the heater; the temperature of the outer wall of the oil pipe before and after the heater is respectively measured by thermal resistance and is respectively t W1 、t W2 The average temperature of the outer wall of the tube is t W ，t W ＝0.5(t W1 +t W2 ) The method comprises the steps of carrying out a first treatment on the surface of the The logarithmic average temperature difference at this time is:
in formula (1), subscript lm represents logarithmic average, Δt represents heat transfer temperature difference, (Δt) lm Representing logarithmic average heat transfer temperature difference, namely logarithmic average temperature difference for short, wherein the logarithmic average temperature difference is more in accordance with engineering practice than arithmetic average temperature difference;
because the length of the horizontal section and the heating area A are fixed, the heat conduction resistance R of the horizontal section 0 The heat transfer coefficient of the horizontal segment is K, and the total heat transfer resistance R can be calculated:
in the formula (2), R represents the total heat transfer resistance of the horizontal section; n represents the electrothermal power of the heater; r is R x Represents the thermal resistance of oil dirt; r is R α The convective heat transfer resistance of the horizontal section;
as can be seen from the formula (2), R, R is calculated α The thermal resistance R of the oil dirt can be known x The method comprises the steps of carrying out a first treatment on the surface of the r=1/K; r is calculated as follows α ；
According to the flow V read by the flowmeter, the unit is L/min, the unit is mm, the oil speed c is calculated, and the unit is m/s:
oil average temperature t=0.5 (t 1 +t 2 ) According to t, the oil density rho is obtained from an oil physical parameter table, wherein the rho unit is kg/L, the heat conductivity coefficient lambda, the kinematic viscosity and the Pr number; the channel flow m of the upper channel measurement section is calculated by adopting a formula of m=ρV, and the unit of m is kg/min; the reynolds number Re can be calculated from the known data, and the knoop number Nu can be calculated by the following formula (4):
Nu＝0.023Re 0.8 Pr 0.4 (4)
since nu=αd/λ, where α represents the convective heat transfer coefficient; therefore, the convection heat exchange thermal resistance R α Calculated by the following formula (5):
in the formula (5), alpha represents a convection heat transfer coefficient;
finally, the thermal resistance of oil dirt R x ＝R-R 0 -R α 。
Compared with the prior art, the invention has the beneficial effects that:
1. the thermal resistance of the oil dirt can be measured on line, the working conditions of a horizontal pipe, a bent pipe and a vertical pipe can be simulated, and the measuring precision is high.
2. The actual oil speed or other oil speeds can be used for measuring the thermal resistance of the oil scale and researching the change rule of the oil scale along with time.
3. The precise sensor is selected, measures are taken in various aspects to limit the measurement error, and the measurement method is proper.
4. When the oil scale thermal resistance measuring device is used for the first time, the oil scale thermal resistance is 0, and the oil scale thermal resistance measuring device can be used for calibrating a display instrument.
The measuring device and the measuring method can measure the oil scale thermal resistance of the horizontal pipe, the bent pipe and the vertical pipe with different flow rates, can be used for researching the increase rule of the oil scale thermal resistance along with time, and can meet the measuring and controlling requirements of thermal equipment because the measuring method is proper and various measures are taken to limit the measuring error, so that the measuring precision of the oil scale thermal resistance is higher.
Drawings
FIG. 1 is a schematic diagram of the structure of the present invention;
wherein, 1-branch regulating valve; 2-a flow meter; 3-thermocouple; 4-horizontal segment; 5-vertical segments; 6-check valve; 7-a heater; 8-bending a pipe section; 9-an inlet pipe; 10-a protective layer; 11-thermal resistance; 12-a filter; 13-an oil supply pipe; 14-an oil pump; 15-a cold water pipe; a 16-shut-off valve; 17-an oil return pipe; 18-an oil cooler; 19-display; 20-up channel button; 21-a down channel button; 22-a liquid crystal screen; 23-power button; 24-horizontal segment buttons; 25-bend section button; 26-vertical segment button.
Detailed Description
The invention will be further described with reference to the accompanying drawings.
The device for measuring the thermal resistance of oil dirt is shown in fig. 1, and consists of an oil supply pipe 13, a measuring section (which is divided into an upper channel measuring section and a lower channel measuring section and is symmetrically arranged), an oil return pipe 17, an oil cooler 18 and a display 19. The measuring section comprises a branch regulating valve 1, an inlet pipe 9, a flow meter 2, a horizontal section 4, a bent pipe section 8, a vertical section 5 and a check valve 6.
An oil inlet of the oil supply pipe 13 is connected with an oil outlet of the oil pump 14, an oil inlet of the oil pump 14 is connected with an oil outlet of the oil cooler 18, an oil inlet of the oil cooler 18 is connected with an oil outlet of the oil return pipe 17, and an upper channel measuring section and a lower channel measuring section are connected in parallel between the oil inlet of the oil return pipe 17 and the oil outlet of the oil supply pipe 13;
the filter 12 and the total regulating valve are arranged on the oil supply pipe 13;
the oil return pipe 17 is provided with a stop valve 16;
the upper channel measuring section and the lower channel measuring section both comprise branch regulating valves 1 connected with the total regulating valve, the branch regulating valves 1 are connected with an inlet pipe 9, the inlet pipe 9 is connected with a flowmeter 2, the flowmeter 2 is connected with an L-shaped bent pipe, the L-shaped bent pipe comprises a horizontal section 4, a bent pipe section 8 and a vertical section 5 which are integrally connected, and the horizontal section 4 is connected with the flowmeter 2;
the horizontal section 4, the bent pipe section 8 and the vertical section 5 sequentially comprise an oil pipe, an insulating layer and a protective layer 10 from inside to outside; the middle parts of the oil pipes of the horizontal section 4, the bent pipe section 8 and the vertical section 5 are respectively provided with a heater 7, and the oil pipes of the horizontal section 4 and the vertical section 5 at two ends of the heater 7 are respectively provided with a thermocouple 3 and a thermal resistor 11;
the two vertical sections 5 are connected with an oil return pipe 17 through a check valve 6;
the display 19 is internally provided with a controller, the flowmeter 2, the thermocouple 3, the heater 7, the thermal resistor 11, the stop valve 16 and the oil pump 14 are all connected with the controller, the display 19 is also provided with a liquid crystal screen 22, and the liquid crystal screen 22 is connected with the controller. LCD 22 displayMass flow (kg/min), oil velocity (m/s), thermal resistance of oil scale (m) 2 ℃/W)。
The oil supply pipe 13 is led out from the bottom of the oil cooler 18, is provided with an oil pump 14, a filter 12 and a total regulating valve, and is respectively connected with the branch regulating valves 1 of the upper channel measuring section and the lower channel measuring section through three-way connectors. The return line 17 is provided with a shut-off valve 16, which is connected via a three-way connection to the check valve 6 of the upper and lower measuring section, respectively, and finally into the upper space of the oil cooler 18. In the oil cooler 18, the oil is cooled down by the cold water pipe 15.
All oil pipes adopt DN25 steel pipes, and are not insulated except the horizontal section 4, the bent pipe section 8 and the vertical section 5. The left side of the inlet pipe 9 is connected with the branch regulating valve 1, and the right side is connected with the flowmeter 2. The L-shaped bent pipe is provided with an oil pipe, a foaming polyurethane heat insulation layer and a protection layer 10 from inside to outside, and the horizontal section 4 is provided with a thermocouple 3, a thermal resistor 11, a heater 7, the thermocouple 3 and the thermal resistor 11 in sequence from left to right.
The bend section 8 has a heater 7.
The vertical section 5 is similar to the horizontal section 4 in structure, and comprises a thermocouple 3, a thermal resistor 11, a heater 7, the thermocouple 3 and the thermal resistor 11 from bottom to top. To reduce the measurement error, the thermal resistor 11 and the thermocouple 3 are arranged as far as possible on both sides in the diameter direction of the oil pipe, i.e., the positions are preferably corresponding.
The thermocouple 3 and the thermal resistor 11 located on the right side of the horizontal section 4, and the thermocouple 3 and the thermal resistor 11 below the vertical section 5, respectively, can also be used for the measurement of the bent pipe section 8.
The thermocouple 3 is inserted into the oil pipe and used for measuring the oil temperature and the model WRPK;
the thermal resistor 11 is attached to the surface of the oil pipe and is used for measuring the wall temperature of the oil pipe.
Flow meter model 2 LC.
The heater 7 is an insulated heating wire wound on the surface of the oil pipe, and the display 19 controls heating and measures the electric heating power.
The oil pump 14 is WCB-75P, and is made of stainless steel.
The oil cooler 18 is a coiled heat exchanger, is cylindrical and has an oil inlet hole at normal pressure, is used for inserting an oil return pipe 17, and the cold water pipe 15 can be connected with tap water.
The tolerance temperature of the stop valve 16 is-29-350 ℃, the highest bearing pressure is 1.6MPa, and the caliber is 25mm.
The tolerance temperature of the branch regulating valve 1 is-29-150 ℃, the highest bearing pressure is 1.6MPa, and the caliber is 25mm.
The working process and principle of the invention are as follows:
when the thermal resistance of oil scale on the wall of the oil pipe is measured, the oil speed of the upper channel measuring section is controlled in the normal flow speed range, namely 2-3 m/s, and the oil speed of the lower channel measuring section is lower, namely about 1-1.5 m/s. The measuring device can simultaneously measure the oil scale thermal resistance of the horizontal section 4, the bent pipe section 8 and the vertical section 5 of the upper channel measuring section and the lower channel measuring section.
According to the readings of the flowmeter 2 and the subsequent thermocouple 3, the mass flow of the oil can be obtained; the total thermal resistance and the convective heat resistance can be calculated by measuring the electric heating power, the oil temperature rise and the average temperature of the outer wall of the oil pipe of the heater 7 of the horizontal section 4, and the thermal resistance of the oil scale is finally calculated due to the fact that the thermal resistance is fixed. The bent pipe section 8 and the vertical section 5 are the same as the measuring principle of the horizontal section 4.
The power button 23 of the display 19 is pressed, the total regulating valve and the stop valve 16 are opened, the oil pump 14 is started, the oil circuit starts to circulate, the cold water pipe 15 works, the flowmeter 2 works, and each temperature sensor works. Pressing the upper channel button 20, the liquid crystal screen 22 displays the accumulated working time (h), the upper channel mass flow rate (kg/min) and the oil speed (m/s), and the opening degree of the branch regulating valve 1 can be changed to regulate the oil speed; the liquid crystal display 22 displays the accumulated operating time, the mass flow rate of the lower channel (kg/min), and the oil velocity (m/s) by pressing the lower channel button 21, and the opening degree of the branch regulating valve 1 can be changed to regulate the oil velocity. The display 19 cannot display the data of the upper and lower channels at the same time.
When the upper channel button 20 is pressed, the horizontal section button 24, the bent section button 25 and the vertical section button 26 are pressed in sequence, and the liquid crystal screen 22 displays the 'horizontal section flow velocity oil scale thermal resistance' and the 'horizontal section flow velocity oil scale thermal resistance' respectively; the flow velocity oil scale thermal resistance of the bent pipe section and the flow velocity oil scale thermal resistance of the horizontal section; the flow velocity oil scale thermal resistance of the bend section; vertical section flow rate oil scale thermal resistance "; and a certain button is rebounded, and the corresponding display disappears. The lower channel is shown to be similar to the upper channel.
A calculation method of oil scale thermal resistance of an oil scale thermal resistance measuring device comprises the following steps:
taking the horizontal section 4 of the upper channel measuring section as an example, the calculation method of the oil scale thermal resistance of the horizontal section 4 of the upper channel measuring section comprises the following steps:
adjusting the current of the heater 7 on the horizontal section 4 of the upper channel measurement section, controlling the oil temperature rise Δt=t before and after the heater 7 2 -t 1 Wherein t is 2 Represents the temperature after temperature rise, where t 1 Representing the temperature before heating, deltat representing the heat transfer temperature difference, deltat not exceeding 10 ℃, and measuring the electric heating power N of the heater 7; the temperature of the outer wall of the oil pipe before and after the heater 7 is measured by a thermal resistor 11 respectively and is t respectively W1 、t W2 The average temperature of the outer wall of the tube is t W ，t W ＝0.5(t W1 +t W2 ) The method comprises the steps of carrying out a first treatment on the surface of the The logarithmic average temperature difference of horizontal segment 4 at this time is:
in formula (1), subscript lm represents logarithmic average, Δt represents heat transfer temperature difference, (Δt) lm Representing logarithmic average heat transfer temperature difference, namely logarithmic average temperature difference for short, wherein the logarithmic average temperature difference is more in accordance with engineering practice than arithmetic average temperature difference;
since the length and heating area A of the horizontal section 4 are fixed, the heat conduction resistance R of the horizontal section 4 0 The heat transfer coefficient of the horizontal segment 4 is K, and the total heat transfer resistance R can be calculated:
in the formula (2), R represents the total heat transfer resistance of the horizontal section 4; n represents the electrothermal power of the heater 7; r is R x Represents the thermal resistance of oil dirt; r is R α Representing the convective heat transfer resistance of horizontal segment 4;
as can be seen from the formula (2), R, R is calculated α The thermal resistance R of the oil dirt can be known x The method comprises the steps of carrying out a first treatment on the surface of the r=1/K; r is calculated as follows α ；
According to the flow V read by the flowmeter 2, the unit is L/min, the inner diameter d of the oil pipe is mm, and the oil speed c is calculated, wherein the unit is m/s:
oil average temperature t=0.5 (t 1 +t 2 ) According to t, the oil density rho is obtained from an oil physical parameter table, wherein the rho unit is kg/L, the heat conductivity coefficient lambda, the kinematic viscosity and the Pr number; the channel flow m of the upper channel measurement section is calculated by adopting a formula of m=ρV, and the unit of m is kg/min; the reynolds number Re can be calculated from the known data, and the knoop number Nu can be calculated by the following formula (4):
Nu＝0.023Re 0.8 Pr 0.4 (4)
since nu=αd/λ, where α represents the convective heat transfer coefficient; therefore, the convection heat exchange thermal resistance R α Calculated by the following formula (5):
in the formula (5), alpha represents a convection heat transfer coefficient;
finally, the thermal resistance of oil dirt R x ＝R-R 0 -R α 。
According to the oil scale thermal resistance measuring device and the oil scale thermal resistance calculating method, the heat conduction thermal resistance is small, so that the heat convection thermal resistance under actual conditions is considered, and meanwhile, a high-precision temperature sensor is adopted, so that the measuring precision is high. When the oil scale thermal resistance measuring device is used for the first time, the oil scale thermal resistance is 0, and the oil scale thermal resistance measuring device can be used for calibrating a display instrument; or, the oil scale thermal resistance measuring device is thoroughly alkaline washed after being used for a long time, and at the moment, the oil scale thermal resistance can be considered as 0 and can be used for calibrating the display instrument.
The foregoing is only a preferred embodiment of the invention, it being noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the present invention, and such modifications and adaptations are intended to be comprehended within the scope of the invention.
Claims (8)
1. The utility model provides an oil dirt thermal resistance measuring device which characterized in that: the oil feeding device comprises an oil feeding pipe (13), wherein an oil inlet of the oil feeding pipe (13) is connected with an oil outlet of an oil pump (14), an oil inlet of the oil pump (14) is connected with an oil outlet of an oil cooler (18), an oil inlet of the oil cooler (18) is connected with an oil outlet of an oil return pipe (17), and an upper channel measuring section and a lower channel measuring section are connected in parallel between the oil inlet of the oil return pipe (17) and the oil outlet of the oil feeding pipe (13);
a filter (12) and a total regulating valve are arranged on the oil supply pipe (13);
a stop valve (16) is arranged on the oil return pipe (17);
the upper channel measuring section and the lower channel measuring section both comprise branch regulating valves (1) connected with the total regulating valve, the branch regulating valves (1) are connected with an inlet pipe (9), the inlet pipe (9) is connected with a flowmeter (2), the flowmeter (2) is connected with an L-shaped bent pipe, the L-shaped bent pipe comprises a horizontal section (4), a bent pipe section (8) and a vertical section (5) which are integrally connected, and the horizontal section (4) is connected with the flowmeter (2);
the horizontal section (4), the bent pipe section (8) and the vertical section (5) sequentially comprise an oil pipe, an insulating layer and a protective layer (10) from inside to outside; the middle parts of the oil pipes of the horizontal section (4), the bent pipe section (8) and the vertical section (5) are respectively provided with a heater (7), and the oil pipes of the horizontal section (4) and the vertical section (5) at two ends of the heater (7) are respectively provided with a thermocouple (3) and a thermal resistor (11);
the two vertical sections (5) are connected with an oil return pipe (17) through check valves (6);
the flowmeter (2), the thermocouple (3), the heater (7), the thermal resistor (11), the stop valve (16) and the oil pump (14) are all connected with a controller of the display instrument (19); a liquid crystal screen (22) is arranged on the display instrument (19), and the liquid crystal screen (22) is connected with the controller;
the thermocouple (3) and the thermal resistor (11) are arranged on two sides of the oil pipe in the diameter direction, namely the thermocouple (3) and the thermal resistor (11) at the same position correspond to each other in position;
the oil supply pipe (13), the oil return pipe (17) and the oil pipe are all DN25 steel pipes.
2. The oil scale thermal resistance measuring apparatus according to claim 1, wherein: the stop valve (16) is connected with the check valves (6) of the upper channel measuring section and the lower channel measuring section respectively through three-way connectors.
3. The oil scale thermal resistance measuring apparatus according to claim 1, wherein: the total regulating valve is respectively connected with the branch regulating valves (1) of the upper channel measuring section and the lower channel measuring section through three-way connectors.
4. The oil scale thermal resistance measuring apparatus according to claim 1, wherein: the heat insulation layer is made of foaming polyurethane.
5. The oil scale thermal resistance measuring apparatus according to claim 1, wherein: the oil cooler (18) is a coiled pipe type heat exchanger, an oil inlet hole for inserting the oil return pipe (17) is formed in the top end of the coiled pipe type heat exchanger, a cold water pipe (15) is arranged in the oil cooler (18), and the cold water pipe (15) is connected with tap water.
6. The oil scale thermal resistance measuring apparatus according to claim 1, wherein: the model of the flowmeter (2) is LC.
7. The oil scale thermal resistance measuring apparatus according to claim 1, wherein: the heaters (7) are all insulated heating wires and are wound on the outer surface of the oil pipe.
8. The method for calculating the thermal resistance of oil dirt by using the thermal resistance measuring device for oil dirt according to any one of claims 1 to 7, characterized by comprising the steps of: the method comprises the following steps:
the calculation method of the oil scale thermal resistance of the horizontal section (4) of the upper channel measuring section comprises the following steps:
adjusting the current of the heater (7) on the horizontal section (4) of the upper channel measurement section, and controlling the oil temperature rise delta t=t before and after the heater (7) 2 -t 1 Wherein t is 2 Represents the temperature after temperature rise, where t 1 Representing the temperature before heating, deltat representing the heat transfer temperature difference, deltat not exceeding 10 ℃, and measuring the electrothermal power N of the heater (7); the temperature of the outer wall of the oil pipe before and after the heater (7) is respectively measured by a thermal resistor (11) and is respectively t W1 、t W2 The average temperature of the outer wall of the tube is t W ，t W =0.5（t W1 +t W2 ) The method comprises the steps of carrying out a first treatment on the surface of the The logarithmic average temperature difference of the horizontal section (4) at this time is:
（1）
in formula (1), subscript lm represents logarithmic average, Δt represents heat transfer temperature difference, (Δt) lm Representing logarithmic average heat transfer temperature difference, namely logarithmic average temperature difference for short, wherein the logarithmic average temperature difference is more in accordance with engineering practice than arithmetic average temperature difference;
because the length and the heating area A of the horizontal section (4) are fixed, the heat conduction resistance R of the horizontal section (4) 0 And (3) if the heat transfer coefficient of the horizontal section (4) is K, calculating the total heat transfer resistance R:
（2）
in the formula (2), R represents the total heat transfer resistance of the horizontal section (4); n represents the electrothermal power of the heater (7); r is R x Represents the thermal resistance of oil dirt; r is R α Represents the convective heat transfer resistance of the horizontal segment (4);
as can be seen from the formula (2), R, R is calculated α The thermal resistance R of the oil dirt can be known x The method comprises the steps of carrying out a first treatment on the surface of the r=1/K; r is calculated as follows α ；
According to the reading flow V of the flowmeter (2), the unit is L/min, the inner diameter d of the oil pipe is mm, and the oil speed c is calculated, wherein the unit is m/s:
（3）
oil average temperature t=0.5 (t 1 +t 2 ) According to t, the oil density rho is obtained from an oil physical parameter table, wherein the rho unit is kg/L, the heat conductivity coefficient lambda, the kinematic viscosity and the Pr number; the channel flow m of the upper channel measurement section is calculated by adopting a formula of m=ρV, and the unit of m is kg/min; the reynolds number Re can be calculated from the known data, and the knoop number Nu can be calculated by the following formula (4):
（4）
since nu=αd/λ, where α represents the convective heat transfer coefficient; therefore, the convection heat exchange thermal resistance R α Calculated by the following formula (5):
（5）
in the formula (5), alpha represents a convection heat transfer coefficient;
finally, the thermal resistance of oil dirt R x =R-R 0 -R α 。
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| CN102135511A (en) * | 2010-12-29 | 2011-07-27 | 浙江银轮机械股份有限公司 | Method and device for testing heat transfer performance of fin surface of plate-fin heat exchanger |
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