CN102831302A - Performance calculating method of finned tube evaporator under frosting working condition - Google Patents

Performance calculating method of finned tube evaporator under frosting working condition Download PDF

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CN102831302A
CN102831302A CN2012102775566A CN201210277556A CN102831302A CN 102831302 A CN102831302 A CN 102831302A CN 2012102775566 A CN2012102775566 A CN 2012102775566A CN 201210277556 A CN201210277556 A CN 201210277556A CN 102831302 A CN102831302 A CN 102831302A
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zoning
evaporator
heat
refrigerant
air
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CN102831302B (en
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秦海杰
朱卫英
夏梦心
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Bingshan Songyang Refrigerator System (Dalian) Co.,Ltd.
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Dalian Sanyo Compressor Co Ltd
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Abstract

The invention discloses a performance calculating method of a finned tube evaporator under the frosting working condition. The method comprises the following steps of: determining the operation working condition of the evaporator; setting the defrosting cycle t of the evaporator, the calculating time interval delta t and the initial frost layer thickness; dividing the evaporator calculating areas according to the user setting; calculating the initialization; solving a control equation of single calculating area i; judging whether frost is formed and calculating the surface temperature of the frost layer; updating the calculating parameter of the calculating area; updating the frost layer thickness and density of the calculating areas; and judging whether the calculation is ended or not. The calculating areas of the evaporator are divided based on a certain pipe length, the control equation in each calculating area is solved, and a high-speed calculating function of a computer is used, so that the performance predicating efficiency and accuracy are high under the preset working condition. By using the high-efficiency calculating speed of the computer, the frequency of experiments of the evaporator is greatly reduced, and the development cycle of the products is shortened.

Description

The performance computation method of finned-tube evaporator under a kind of frozen condition
Technical field
The present invention relates to the designing technique of evaporator in a kind of cooling system, the performance computation method of finned-tube evaporator under particularly a kind of frozen condition.
Background technology
Frosting is one of modal phenomenon in Refrigeration Engineering and the freezing and refrigeration field.Various big-and-middle-sized freezers, small-sized refrigerating plant (like instant freezer, refrigerator, refrigerator etc.), marine refrigerating plant, and all there is the coil pipe frosting problem of refrigerating evaporator bar none in the marine refrigeration delivery container.The formation of frost can ventilate, and channel narrows, air quantity reduce, the pressure loss of air becomes big, finally can stop up evaporator fully, seriously hinder the heat exchange between air and the refrigerant, reduce heat; And the coefficient of heat conductivity of frost layer self is little, has increased the heat transfer resistance of air side, can influence heat conduction, finally reduces the whole heat transfer coefficient of evaporator.The performance prediction of evaporator comprises the prediction of the refrigerating capacity and the white layer growth situation of evaporator; At present no frozen condition heat method of testing is adopted in the performance prediction of evaporator usually, again according to designer's experience and combine the operating condition of evaporator that test result is carried out certain correction.But frozen condition is bigger to the performance impact of evaporator, and the method for heat test is more complicated also.
At present; In the stage of designing and developing; The performance prediction of finned tube evaporator under frozen condition is the experimental result before the reference and adopts artificial estimation approach that cause efficient low, accuracy is not high mostly; Simultaneously also make the performance of evaporator and the required performance gap that reaches that design bigger, cause raw-material waste more serious.
Summary of the invention
For deficiency and the defective that solves prior art, the present invention will propose a kind of performance computation method that can predict refrigerating capacity and the frost layer of evaporator under frozen condition with the finned-tube evaporator of the upgrowth situation of working time accurately and efficiently.
To achieve these goals, technical scheme of the present invention is following: the performance computation method of finned-tube evaporator under a kind of frozen condition comprises the steps:
A, confirm the operating condition of evaporator: according to standard soft air physical characterization data establishment soft air Calculation of Physical Properties class, described soft air rerum natura comprises water capacity, enthalpy, density, specific volume, coefficient of heat conductivity and dewpoint temperature; According to refrigerant physical characterization data establishment refrigerant Calculation of Physical Properties class, described refrigerant rerum natura comprises temperature, pressure, mass dryness fraction, density, enthalpy, entropy, coefficient of heat conductivity, specific volume and the latent heat of vaporization; According to the evaporator soft air suction parameter and the evaporating temperature of user's input, call the operating condition that soft air Calculation of Physical Properties class and refrigerant Calculation of Physical Properties class are calculated evaporator, described evaporator soft air suction parameter comprises temperature and relative humidity; Described operating condition comprises the latent heat of vaporization by the saturation pressure of evaporator refrigerant temperature calculating, enthalpy, refrigerant;
B, the defrosting cycle t that sets evaporator, computing time be △ t and initial frost thickness at interval, and the default value of frost thickness is zero;
The structural parameters and the heat exchanger tube annexation of C, setting evaporator: the evaporation structure parameter is set in the input according to the user; Described structural parameters comprise caliber, tube pitch, fin shape, spacing of fin, and calculate the heat interchanging area of evaporator according to said structural parameters;
D, carry out the division of evaporator zoning according to user's setting;
E, calculate initialization: the zoning of dividing according to step D and the operating condition of the evaporator of steps A calculating; The initial value of each zoning of evaporator is set; The initial value of described each zoning comprises temperature in, the water capacity of soft air, the inlet enthalpy of refrigerant, pressure; The temperature difference of enthalpy difference and the air of the water capacity of each zoning through supposing each zoning refrigerant is inferred the variable quantity of soft air water capacity;
The air quantity of evaporator is confirmed in the static pressure loss of F, the fan static pressure family curve of setting according to the user and evaporator; Obtain airflow through the loss of the static pressure of evaporator according to the evaporator frost thickness, unite with the static pressure family curve of described static pressure loss and blower fan and find the solution the air quantity of evaporator when moving; Described fan static pressure family curve is provided by blower fan manufacturer or records through the laboratory;
The computing formula of static pressure loss is following:
Δ p a = 5.88 × 10 - 4 N rd × 2 p t [ S 2 - π ( d 0 + 2 δ fr ) 2 4 S 1 ] + π ( d 0 + 2 δ fr ) S 1 S 2 0.3
× [ p t · S 1 [ p t - ( t f + 2 δ fr ) ] [ S 1 - ( d 0 + 2 δ fr ) ] ] 3 × W F 1.7
In the formula:
Δ p a: the loss of air side static pressure, the Pa of unit;
N Ri: pipe row number;
d 0: external diameter of pipe;
δ Fr: frost thickness, the m of unit;
S 1: pipe column pitch, the m of unit;
S 2: pipe line space, the m of unit;
P t: spacing of fin, the m of unit;
t f: fin thickness, the m of unit;
W F: face velocity, the m/s of unit;
Finding the solution of the governing equation of G, single zoning i, subscript i representes the numbering of zoning;
G1, according to the import and export enthalpy difference of refrigerant and the heat of mass flow calculation refrigerant side:
Q iref = m · ( hi out - hi in )
In the following formula, Q IrefBe the heat of refrigerant side in the single zoning i, kW; Be the mass rate of refrigerant, kg/s; Hi Out, hi InBe respectively outlet enthalpy, the import enthalpy of refrigerant in the i of zoning, kJ/kg;
G2, the saturation temperature corresponding according to refrigerant pressure in the single zoning i suppose that single zoning i copper pipe wall surface temperature is t Iw0, and calculate the local coefficient of heat transfer of refrigerant evaporation:
The local coefficient of heat transfer computing formula of the evaporation of gas phase zone does
a ir = l l d i · 0.023 · Re g 0.8 · Pr g 0.4
In the following formula, a IrBe the local coefficient of heat transfer of refrigerant evaporation in the single zoning i, W/kg.k; Re gBe gas phase Reynolds number, Pr gBe gas phase Prandtl number, l lBe liquid phase coefficient of heat conductivity, d iBe internal diameter;
The local coefficient of heat transfer computing formula of the evaporation of vapour-liquid two-phase region does
a ir=Fa cv+Sa pb
a CvBe forced convertion item, a PbBe the boiling item, F, S is respectively design factor;
G3, pass through heat conduction equation
Q iref=a irA i(T iw-0.5*(T irin+T irout))
Recomputate single zoning i copper pipe tube wall surface temperature degree T Iw
In the following formula, Q IrefBe the heat of refrigerant side in the single zoning i, a IrBe the local coefficient of heat transfer of the evaporation of vapour-liquid two-phase region, A iBe intraductal heat exchange area in the single zoning i, T Irin, T IroutBe respectively the refrigerant out temperature;
G4, repeating step G1-G3, until | T Iw0-T Iw| satisfy the computational accuracy of setting 10 -4
The dewpoint temperature of soft air judges whether frosting in H, the copper pipe wall surface temperature that calculates according to step G and the single zoning i; The condition of judging frosting is to satisfy following 2 conditions simultaneously:
1) the copper pipe wall surface temperature is lower than 0 ℃;
2) dewpoint temperature of the soft air of single zoning i is higher than the copper pipe wall surface temperature;
If the single zoning of I i frost-free then calculates air side heat Q according to dry cooling condition a, computing formula is following:
Q a=KA△T m
In the following formula, K is the heat transfer coefficient in the single zone of evaporator, and A is the reference area of the single zoning i of evaporator, △ T mBe log-mean temperature difference;
If following steps are then carried out in the i frosting of single zoning:
I1, the white laminar surface temperature of supposition are T Fr
The heat of air side in I2, the single zoning i of calculating, described heat comprises latent heat heat and sensible heat transfer amount;
The sensible heat transfer amount computing formula of air side does
Q isen = m · a Cp a ( Ta iin - Ta iout )
In the following formula, Q IsenBe the sensible heat transfer amount of air in the single zoning i, kW;
Figure BDA00001979455000042
Be the mass rate of air in the single zoning i, kg/s; Cp aSpecific heat at constant pressure kJ/kg.K for air; Ta Iin, Ta IoutBe respectively inlet temperature, the outlet temperature of air in the single zoning i, degree centigrade;
The latent heat heat computing formula of air side does
Q ilat = m · a ( d iin - d iout ) i sv
In the following formula, Q IlatBe the latent heat heat of air in the single zoning i, kW;
Figure BDA00001979455000044
Be the mass rate of air in the single zoning i, kg/s; i SvBe the latent heat of solidification of water, kJ/kg.K; d Iin, d IoutBe respectively import water capacity, the outlet water capacity of air in the single zoning i, kg/kg;
Under the frozen condition, the air side heat of single zoning i does
Q ia=Q isen+Q ilat
I3, pass through heat conduction equation
T ifr = T iw + 2 Q - m ir · i sv 2 A T l ifr
Recomputate white laminar surface temperature T Fr0
In the following formula, T IfrBe the white laminar surface temperature of single zoning i, T IwBe the copper pipe wall surface temperature in the single zoning i, Q is the heat in the single zoning i, m IrFor making the quality of the water that frost layer density increases, i SvBe the latent heat of vaporization of water vapor, A TBe the heat interchanging area of single zoning i, l IfrCoefficient of heat conductivity for the frost layer;
Repeating step I1-I3, until | T Fr-T Fr0| satisfy and calculate the condition of convergence 10 -4
In the following formula, T FrBe the white laminar surface temperature of hypothesis, T Fr0Be the white laminar surface temperature of calculating by the zoning heat conduction equation;
The air side heat Q that J, comparison step I calculate aRefrigerant side heat Q with step G calculating Iref, the enthalpy of adjustment refrigerant exit, repeating step G-I is until | Q Ia-Q Iref|/Q IaSatisfy the zoning condition of convergence 10 -4
K, the heat of calculating single zoning i, the air temperature difference, frost thickness and frost layer density;
The calculating parameter of L, zoning that renewal is relevant with single zoning i; Described calculating parameter comprises pressure, saturation temperature, enthalpy and the mass dryness fraction of refrigerant, also comprises the temperature of soft air, water capacity, frost thickness and the frost layer density of soft air;
M, according to the order that refrigerant flows, calculate and find the solution all zonings, repeating step F-L, until
max|Dh i-Dh i0|/Dh i0<e，
The then computing time of △ t calculating end at interval;
Dh in the following formula iFor single zoning i refrigerant side is imported and exported enthalpy difference calculated value, Dh I0Import and export the enthalpy difference default for single zoning i refrigerant side, e is the iteration convergence condition, is defaulted as 10 -4
N, preservation are also exported the result of calculation in this time step;
O, the frost thickness that upgrades all zonings and frost layer density;
P, when the frost thickness calculated value more than or equal to half the, the evaporator cause clogging of spacing of fin or arrive the defrosting cycle that the user is provided with computing time, then calculate and finish, otherwise forward step F to.
The computing method of the described refrigerant rerum natura of steps A of the present invention are used C++ programming language and Object oriented programming method, the refrigerant physical data storehouse of encapsulation National Institute of Standards and Technology, and design interface class.
The described soft air Calculation of Physical Properties of steps A of the present invention method is used C++ programming language and Object oriented programming method, the computing method of encapsulation U.S. heating, the ASHRAE of Refrigeration & Air-Conditioning SE soft air rerum natura, and design interface class.
The described setting heat exchanger tube of step C of the present invention annexation uses one-dimension array to explain the annexation of heat exchanger tube, does not comprise the interflow and the shunting of heat exchanger tube.
The division methods of the described evaporator of step D of the present invention zoning is cut apart through carry out pipe ranges such as zoning according to the heat exchanger tube of certain-length along the refrigerant flow direction, and the inscape of each zoning is made up of refrigerant, soft air, frost layer and finned tube.
The described evaporator of step e of the present invention calculates initialized method, according to the zoning that the user divides, supposes the enthalpy difference of the refrigerant of each zoning according to average method; Suppose the temperature difference of air, calculate the difference of the water capacity of air according to law of conservation of energy.
The described result of calculation store method of step N of the present invention is that result of calculation is output as and can is made things convenient for the user that result of calculation is handled by the direct form of handling of Microsoft Excel software.
Compared with prior art, the present invention has following beneficial effect:
1, because the present invention adopts evaporator is divided the zoning according to certain pipe range; And each zoning carried out finding the solution of governing equation; The supercomputing function that uses a computer makes evaporator is being set under the working condition that performance prediction efficient is high, accuracy is high.
2, because the present invention uses the simulation calculation sequencing of C++ programming language with evaporator; The designer sets and the operating condition setting through the structure that computing machine carries out evaporator; And utilize computing machine computing velocity efficiently, can significantly reduce experiment number, the shortening product development cycle of evaporator.
3, the present invention uses the Object oriented programming method of C++ programming language, has improved the reusability of computation model greatly.C Plus Plus is an object oriented programming languages, makes that the program layer aggregated(particle) structure is clear, is convenient to safeguard and debugging.
4, the present invention uses finite volume method to set up the computation model of evaporimeter frosting operating mode; And with C++ programming language establishment simulation calculation program the governing equation of each zoning is iterated to calculate and find the solution; After gathering the result of calculation of each zoning the performance of evaporimeter frosting operating mode is predicted; Simulation reappears the frost layer situation of growth of whole evaporator, to the defrosting control setting of air-cooler theoretical foundation is provided.
Description of drawings
The present invention has accompanying drawing 4 width of cloth, wherein:
Fig. 1 is the process flow diagram that the present invention carries out evaporimeter frosting condition calculating method.
Fig. 2 is that the present invention carries out the synoptic diagram that the zoning is divided to evaporator, in order to the division methods of explanation zoning.In order to the division methods of explanation zoning of the present invention and the component of single zoning.
Fig. 3 is the synoptic diagram of the present invention to the explanation of single zoning, in order to the formation element of explanation zoning.
Fig. 4 is the synoptic diagram of the present invention to single zoning fin, in order to explanation zoning inner fin heat interchanging area.
Embodiment
Understand and embodiment of the present invention for the ease of those skilled in the art, the present invention is explained in further detail below in conjunction with accompanying drawing.
Program flow diagram of the present invention, as shown in Figure 1, concrete steps are following:
A, according to user's input, confirm the operating condition of evaporator.
The initial parameter of input evaporator operation, evaporating temperature, the entry state (pressure and enthalpy) of refrigerant, the entry state (temperature and relative humidity) of soft air, and call refrigerant Calculation of Physical Properties class and confirm other parameters that refrigerant enters the mouth with soft air Calculation of Physical Properties class.
For example: selected refrigerant is R22, and known pressure is 465kPa, and enthalpy is 220kJ/kg, A.Pk=465; A.H=220; LoaderMgr::getInstance (R22) .getLoader ()-getPHFL1 (A, B); ρ=B.RHOMOLL; T=B.Tk annotates: (A, B are interface class);
Calculating density is 12.63kg/m 3Temperature is 72.17 ℃.
The pressure of known soft air is 101.325kPa, and dry-bulb temperature is-5 ℃, and relative humidity is 60%.It is following to calculate other parameters: wet-bulb temperature is-6.64 ℃, and enthalpy is-1.33kJ/kg water capacity 1.48g/kg, density 1.314kg/m 3
B, the defrosting cycle t that sets evaporator, computing time be △ t and initial frost thickness at interval, and the default value of frost thickness is zero;
Defrosting cycle t: whole evaporator is from starting working to the T.T. that begins to defrost.Example is set at 6 hours.
Computing time is △ t at interval: by the user defrosting cycle t is averaged division, wherein each part is defined as the computing time of △ t at interval.This example is set at 5 minutes.
The structural parameters and the heat exchanger tube annexation of C, setting evaporator.Set the structural parameters such as caliber, tube pitch, fin shape, spacing of fin of evaporator according to user's input, and calculate calculating parameter such as evaporator heat interchanging area according to above-mentioned parameter; The evaporation structure parameter of user's input is seen table 1:
Table 1 evaporation structure parameter is seen table
Finned tube external diameter (mm): 9.52 Finned tube internal diameter (mm): 6.6
Finned tube columns (row): 6 Fin pattern: plain film
Finned tube row number (row): 18 Spacing of fin (mm): 10
Finned tube diverter branch number (individual): 9 Fin thickness (mm): 0.115
Finned tube effective length (mm): 1080 Fan electromotor quantity (individual): 2
Finned tube longitudinal pitch (mm): 25 The evaporator fan motor curve
Finned tube horizontal spacing (mm): 21.6 Fan electromotor power input: 460 (W/ platforms)
D, carry out the division of evaporator zoning according to user's setting, for example set heat exchanger tube is divided into 5 parts, the division methods of zoning is as shown in Figure 2, and the formation element of zoning is as shown in Figure 3;
E, calculate initialization: the zoning of dividing according to the user and the operating condition of evaporator, the initial value of each zoning of evaporator is set, at first the temperature difference of enthalpy difference through supposing each zoning refrigerant and air is inferred the variable quantity of soft air water capacity;
F, the static pressure loss of calculating this moment evaporator are united the air quantity of finding the solution evaporator with the static pressure family curve of fan electromotor then, and calculating an air quantity mean allocation in each zoning.
Finding the solution of the energy equation of G, single zoning i and the equation of momentum;
At first suppose the import and export enthalpy difference of refrigerant, and calculate the heat of refrigerant side; Evaporating temperature according to evaporator is supposed wall surface temperature earlier, and the import and export medial temperature of wall surface temperature and refrigerant is confirmed the local coefficient of heat transfer of refrigerant evaporation.Recomputate wall surface temperature through heat conduction equation, judge whether the wall surface temperature that calculates is consistent with the hypothesis wall surface temperature; If inconsistent adjustment wall surface temperature calculates convergence until wall surface temperature.
H, judge according to the aforementioned calculation wall surface temperature whether this zoning exists the frosting situation, and the frosting decision condition is following:
1) wall surface temperature is lower than 0 ℃;
2) dewpoint temperature of the soft air of zoning is higher than the copper pipe wall surface temperature;
If I, zoning frost-free calculate air side heat Q according to dry cooling condition IaIf white laminar surface temperature is supposed in the zoning frosting, calculate the sensible heat and the latent heat of air side respectively.Recomputate white laminar surface temperature through heat conduction equation, judge and calculate white laminar surface temperature and suppose whether white laminar surface temperature is consistent; If the white laminar surface temperature of inconsistent adjustment, until white laminar surface temperature computation convergence, the fin heat interchanging area of single zoning is seen Fig. 4.
The air side heat of J, comparison aforementioned calculation and refrigerant side heat, the enthalpy of adjustment refrigerant exit, repeating step is until | Q Ia-Q Iref|/Q IaSatisfy the zoning condition of convergence 10 -4
K, calculate the heat of this zoning, parameters such as the air temperature difference, frost thickness, frost layer density;
The calculating parameter in L, renewal and zoning i correlation computations zone; The inlet enthalpy of refrigerant for example, the temperature in of soft air, water capacity, frost thickness and frost layer density etc.
M, according to the order that refrigerant flows, calculate and find the solution all zonings, until max|Dh i-Dh I0|/Dh I0<e, then interval calculation end computing time.
N, preservation are also exported the result of calculation in this time step, and preserving form is the Excel file;
O, the frost thickness that upgrades all zonings and frost layer density;
P, calculating termination condition: the frost thickness calculated value is half the greater than spacing of fin, arrives evaporator cause clogging or computing time the defrosting cycle that the user is provided with, and begins to defrost.

Claims (7)

1. the performance computation method of finned-tube evaporator under the frozen condition is characterized in that: comprise the steps:
A, confirm the operating condition of evaporator: according to standard soft air physical characterization data establishment soft air Calculation of Physical Properties class, described soft air rerum natura comprises water capacity, enthalpy, density, specific volume, coefficient of heat conductivity and dewpoint temperature; According to refrigerant physical characterization data establishment refrigerant Calculation of Physical Properties class, described refrigerant rerum natura comprises temperature, pressure, mass dryness fraction, density, enthalpy, entropy, coefficient of heat conductivity, specific volume and the latent heat of vaporization; According to the evaporator soft air suction parameter and the evaporating temperature of user's input, call the operating condition that soft air Calculation of Physical Properties class and refrigerant Calculation of Physical Properties class are calculated evaporator, described evaporator soft air suction parameter comprises temperature and relative humidity; Described operating condition comprises the latent heat of vaporization by the saturation pressure of evaporator refrigerant temperature calculating, enthalpy, refrigerant;
B, the defrosting cycle t that sets evaporator, computing time be △ t and initial frost thickness at interval, and the default value of frost thickness is zero;
The structural parameters and the heat exchanger tube annexation of C, setting evaporator: the evaporation structure parameter is set in the input according to the user; Described structural parameters comprise caliber, tube pitch, fin shape, spacing of fin, and calculate the heat interchanging area of evaporator according to said structural parameters;
D, carry out the division of evaporator zoning according to user's setting;
E, calculate initialization: the zoning of dividing according to step D and the operating condition of the evaporator of steps A calculating; The initial value of each zoning of evaporator is set; The initial value of described each zoning comprises temperature in, the water capacity of soft air, the inlet enthalpy of refrigerant, pressure; The temperature difference of enthalpy difference and the air of the water capacity of each zoning through supposing each zoning refrigerant is inferred the variable quantity of soft air water capacity;
The air quantity of evaporator is confirmed in the static pressure loss of F, the fan static pressure family curve of setting according to the user and evaporator; Obtain airflow through the loss of the static pressure of evaporator according to the evaporator frost thickness, unite with the static pressure family curve of described static pressure loss and blower fan and find the solution the air quantity of evaporator when moving; Described fan static pressure family curve is provided by blower fan manufacturer or records through the laboratory;
The computing formula of static pressure loss is following:
&Delta; p a = 5.88 &times; 10 - 4 N rd &times; 2 p t [ S 2 - &pi; ( d 0 + 2 &delta; fr ) 2 4 S 1 ] + &pi; ( d 0 + 2 &delta; fr ) S 1 S 2 0.3
&times; [ p t &CenterDot; S 1 [ p t - ( t f + 2 &delta; fr ) ] [ S 1 - ( d 0 + 2 &delta; fr ) ] ] 3 &times; W F 1.7
In the formula:
Δ p a: the loss of air side static pressure, the Pa of unit;
N Ri: pipe row number;
d 0: external diameter of pipe;
δ Fr: frost thickness, the m of unit;
S 1: pipe column pitch, the m of unit;
S 2: pipe line space, the m of unit;
P t: spacing of fin, the m of unit;
t f: fin thickness, the m of unit;
W F: face velocity, the m/s of unit;
Finding the solution of the governing equation of G, single zoning i, subscript i representes the numbering of zoning;
G1, according to the import and export enthalpy difference of refrigerant and the heat of mass flow calculation refrigerant side:
Q iref = m &CenterDot; ( hi out - hi in )
In the following formula, Q IrefBe the heat of refrigerant side in the single zoning i, kW;
Figure FDA00001979454900022
Be the mass rate of refrigerant, kg/s; Hi Out, hi InBe respectively outlet enthalpy, the import enthalpy of refrigerant in the i of zoning, kJ/kg;
G2, the saturation temperature corresponding according to refrigerant pressure in the single zoning i suppose that single zoning i copper pipe wall surface temperature is t Iw0, and calculate the local coefficient of heat transfer of refrigerant evaporation:
The local coefficient of heat transfer computing formula of the evaporation of gas phase zone does
a ir = l l d i &CenterDot; 0.023 &CenterDot; Re g 0.8 &CenterDot; Pr g 0.4
In the following formula, a IrBe the local coefficient of heat transfer of refrigerant evaporation in the single zoning i, W/kg.k; Re gBe gas phase Reynolds number, Pr gBe gas phase Prandtl number, l lBe liquid phase coefficient of heat conductivity, d iBe internal diameter;
The local coefficient of heat transfer computing formula of the evaporation of vapour-liquid two-phase region does
a ir=Fa cv+Sa pb
a CvBe forced convertion item, a PbBe the boiling item, F, S is respectively design factor;
G3, pass through heat conduction equation
Q iref=a irA i(T iw-0.5*(T irin+T irout))
Recomputate single zoning i copper pipe tube wall surface temperature degree T Iw
In the following formula, Q IrefBe the heat of refrigerant side in the single zoning i, a IrBe the local coefficient of heat transfer of the evaporation of vapour-liquid two-phase region, A iBe intraductal heat exchange area in the single zoning i, T Irin, T IroutBe respectively the refrigerant out temperature;
G4, repeating step G1-G3, until | T Iw0-T Iw| satisfy the computational accuracy of setting 10 -4
The dewpoint temperature of soft air judges whether frosting in H, the copper pipe wall surface temperature that calculates according to step G and the single zoning i; The condition of judging frosting is to satisfy following 2 conditions simultaneously:
1) the copper pipe wall surface temperature is lower than 0 ℃;
2) dewpoint temperature of the soft air of single zoning i is higher than the copper pipe wall surface temperature;
If the single zoning of I i frost-free then calculates air side heat Q according to dry cooling condition a, computing formula is following:
Q a=KA△T m
In the following formula, K is the heat transfer coefficient in the single zone of evaporator, and A is the reference area of the single zoning i of evaporator, △ T mBe log-mean temperature difference;
If following steps are then carried out in the i frosting of single zoning:
I1, the white laminar surface temperature of supposition are T Fr
The heat of air side in I2, the single zoning i of calculating, described heat comprises latent heat heat and sensible heat transfer amount;
The sensible heat transfer amount computing formula of air side does
Q isen = m &CenterDot; a Cp a ( Ta iin - Ta iout )
In the following formula, Q IsenBe the sensible heat transfer amount of air in the single zoning i, kW;
Figure FDA00001979454900032
Be the mass rate of air in the single zoning i, kg/s; CP aSpecific heat at constant pressure kJ/kg.K for air; Ta Iin, Ta IoutBe respectively inlet temperature, the outlet temperature of air in the single zoning i, degree centigrade;
The latent heat heat computing formula of air side does
Q ilat = m &CenterDot; a ( d iin - d iout ) i sv
In the following formula, Q IlatBe the latent heat heat of air in the single zoning i, kW;
Figure FDA00001979454900034
Be the mass rate of air in the single zoning i, kg/s; i SvBe the latent heat of solidification of water, kJ/kg.K; d Iin, d IoutBe respectively import water capacity, the outlet water capacity of air in the single zoning i, kg/kg;
Under the frozen condition, the air side heat of single zoning i does
Q ia=Q isen+Q ilat
I3, pass through heat conduction equation
T ifr = T iw + 2 Q - m ir &CenterDot; i sv 2 A T l ifr
Recomputate white laminar surface temperature T Fr0
In the following formula, T IfrBe the white laminar surface temperature of single zoning i, T IwBe the copper pipe wall surface temperature in the single zoning i, Q is the heat in the single zoning i, m IrFor making the quality of the water that frost layer density increases, i SvBe the latent heat of vaporization of water vapor, A TBe the heat interchanging area of single zoning i, l IfrCoefficient of heat conductivity for the frost layer;
Repeating step I1-I3, until | T Fr-T Fr0| satisfy and calculate the condition of convergence 10 -4
In the following formula, T FrBe the white laminar surface temperature of hypothesis, T Fr0Be the white laminar surface temperature of calculating by the zoning heat conduction equation;
The air side heat Q that J, comparison step I calculate aRefrigerant side heat Q with step G calculating Iref, the enthalpy of adjustment refrigerant exit, repeating step G-I is until | Q Ia-Q Iref|/Q IaSatisfy the zoning condition of convergence 10 -4
K, the heat of calculating single zoning i, the air temperature difference, frost thickness and frost layer density;
The calculating parameter of L, zoning that renewal is relevant with single zoning i; Described calculating parameter comprises pressure, saturation temperature, enthalpy and the mass dryness fraction of refrigerant, also comprises the temperature of soft air, water capacity, frost thickness and the frost layer density of soft air;
M, according to the order that refrigerant flows, calculate and find the solution all zonings, repeating step F-L, until
max|Dh i-Dh i0|/Dh i0<e，
The then computing time of △ t calculating end at interval;
Dh in the following formula iFor single zoning i refrigerant side is imported and exported enthalpy difference calculated value, Dh I0Import and export the enthalpy difference default for single zoning i refrigerant side, e is the iteration convergence condition, is defaulted as 10 -4
N, preservation are also exported the result of calculation in this time step;
O, the frost thickness that upgrades all zonings and frost layer density;
P, when the frost thickness calculated value more than or equal to half the, the evaporator cause clogging of spacing of fin or arrive the defrosting cycle that the user is provided with computing time, then calculate and finish, otherwise forward step F to.
2. the performance computation method of finned-tube evaporator under a kind of frozen condition according to claim 1; It is characterized in that: the computing method of the described refrigerant rerum natura of steps A; Use C++ programming language and Object oriented programming method; The refrigerant physical data storehouse of encapsulation National Institute of Standards and Technology, and design interface class.
3. the performance computation method of finned-tube evaporator under a kind of frozen condition according to claim 1; It is characterized in that: the described soft air Calculation of Physical Properties of steps A method; Use C++ programming language and Object oriented programming method; The computing method of encapsulation U.S. heating, the ASHRAE of Refrigeration & Air-Conditioning SE soft air rerum natura, and design interface class.
4. the performance computation method of finned-tube evaporator under a kind of frozen condition according to claim 1; It is characterized in that: the described setting heat exchanger tube of step C annexation; Use the annexation of one-dimension array statement heat exchanger tube, do not comprise the interflow and the shunting of heat exchanger tube.
5. the performance computation method of finned-tube evaporator under a kind of frozen condition according to claim 1; It is characterized in that: the division methods of the described evaporator of step D zoning; Cut apart through carry out pipe ranges such as zoning according to the heat exchanger tube of certain-length along the refrigerant flow direction, the inscape of each zoning is made up of refrigerant, soft air, frost layer and finned tube.
6. the performance computation method of finned-tube evaporator under a kind of frozen condition according to claim 1; It is characterized in that: the described evaporator of step e calculates initialized method; According to the zoning that the user divides, suppose the enthalpy difference of the refrigerant of each zoning according to average method; Suppose the temperature difference of air, calculate the difference of the water capacity of air according to law of conservation of energy.
7. the performance computation method of finned-tube evaporator under a kind of frozen condition according to claim 1; It is characterized in that: the described result of calculation store method of step N is that result of calculation is output as and can is made things convenient for the user that result of calculation is handled by the direct form of handling of Microsoft Excel software.
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CN106403422A (en) * 2016-09-21 2017-02-15 广东工业大学 Defrosting start point judgment method and defrosting start point judgment system for multi-loop heat exchanger of air source heat pump
CN107244212A (en) * 2017-06-08 2017-10-13 南京协众汽车空调集团有限公司 Pump type heat electric automobile air conditioner defrosting control method based on humidity sensor technology
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CN110926093A (en) * 2019-12-06 2020-03-27 四方科技集团股份有限公司 On-demand defrosting method for air cooler
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CN111389471A (en) * 2020-04-10 2020-07-10 重庆苏试四达试验设备有限公司 Dehumidification evaporator for environmental test chamber
CN111811198A (en) * 2020-06-03 2020-10-23 珠海格力电器股份有限公司 Defrosting control method and device and electric equipment
CN112179040A (en) * 2020-09-21 2021-01-05 珠海格力电器股份有限公司 Defrosting control method and device for evaporator and refrigeration equipment
CN112504707A (en) * 2020-11-17 2021-03-16 中广核工程有限公司 Method for evaluating performance of heat exchanger of ventilation system, electronic equipment and storage medium
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CN104776884A (en) * 2015-04-17 2015-07-15 中国科学院工程热物理研究所 Method for obtaining outlet state parameters of plate-fin type aftercooler
CN104776884B (en) * 2015-04-17 2017-03-01 中国科学院工程热物理研究所 The method obtaining plate-fin aftercooler discharge state parameter
CN106403422A (en) * 2016-09-21 2017-02-15 广东工业大学 Defrosting start point judgment method and defrosting start point judgment system for multi-loop heat exchanger of air source heat pump
CN106403422B (en) * 2016-09-21 2019-03-01 广东工业大学 A kind of polycyclic pipeline heat exchanger defrosting starting point determination method of air source heat pump and system
CN107244212A (en) * 2017-06-08 2017-10-13 南京协众汽车空调集团有限公司 Pump type heat electric automobile air conditioner defrosting control method based on humidity sensor technology
CN108981019A (en) * 2018-06-20 2018-12-11 广东美的制冷设备有限公司 Air-conditioner outdoor unit and air conditioner with it
CN110926093B (en) * 2019-12-06 2021-07-23 四方科技集团股份有限公司 On-demand defrosting method for air cooler
CN110926093A (en) * 2019-12-06 2020-03-27 四方科技集团股份有限公司 On-demand defrosting method for air cooler
CN111330654A (en) * 2020-04-10 2020-06-26 重庆苏试四达试验设备有限公司 Refrigeration and dehumidification integrated evaporator for environmental test chamber
CN111389471A (en) * 2020-04-10 2020-07-10 重庆苏试四达试验设备有限公司 Dehumidification evaporator for environmental test chamber
CN111811198A (en) * 2020-06-03 2020-10-23 珠海格力电器股份有限公司 Defrosting control method and device and electric equipment
CN112179040A (en) * 2020-09-21 2021-01-05 珠海格力电器股份有限公司 Defrosting control method and device for evaporator and refrigeration equipment
CN112504707A (en) * 2020-11-17 2021-03-16 中广核工程有限公司 Method for evaluating performance of heat exchanger of ventilation system, electronic equipment and storage medium
CN112504707B (en) * 2020-11-17 2023-06-13 中广核工程有限公司 Method for evaluating performance of heat exchanger of ventilation system, electronic equipment and storage medium
CN114279110A (en) * 2022-03-01 2022-04-05 浙江乾丰智能科技有限公司 Intelligent defrosting device and method for air energy water heater
CN114279110B (en) * 2022-03-01 2022-05-20 浙江乾丰智能科技有限公司 Intelligent defrosting device and method for air energy water heater

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