CN102831302B - Performance calculating method of finned tube evaporator under frosting working condition - Google Patents

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 Calculation Methods for Performance 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, particularly the Calculation Methods for Performance of finned-tube evaporator under a kind of frozen condition.

Background technology

Frosting is one of modal phenomenon in Refrigeration Engineering and freezing and refrigeration field.Various big-and-middle-sized freezer, small-sized refrigerating plant (as instant freezer, refrigerator, refrigerator etc.), marine refrigerating plant, and there is the coil pipe frosting problem of refrigerating evaporator all bar none in marine refrigeration delivery container.The formation of frost can ventilate, and channel narrows, air quantity reduce, the pressure loss of air becomes large, and finally can block evaporator completely, the serious heat exchange hindered between air and refrigerant, reduces heat exchange amount; And the coefficient of heat conductivity of frost layer self is little, increase the heat transfer resistance of air side, can heat transfer be affected, the final overall heat transfer coefficient reducing evaporator.The performance prediction of evaporator comprises the refrigerating capacity of evaporator and the prediction of Frosting rate situation, at present the performance prediction of evaporator is adopted usually without frozen condition method for testing heat, then according to the experience of designer and the operating condition in conjunction with evaporator carries out certain correction to test result.But the performance impact of frozen condition to evaporator is larger, the method also more complicated of heat amount test.

At present, in the stage of designing and developing, the performance prediction of finned tube evaporator under frozen condition be mostly with reference to before experimental result and adopt the artificial method estimated, cause efficiency low, accuracy is not high, also make the performance of evaporator that designs and the required performance gap reached comparatively greatly simultaneously, cause raw-material waste more serious.

Summary of the invention

In order to solve shortcomings and deficiencies of the prior art, the present invention will propose a kind ofly can predict the refrigerating capacity of evaporator under frozen condition and the frost layer Calculation Methods for Performance 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 as follows: the Calculation Methods for Performance of finned-tube evaporator under a kind of frozen condition, comprises the steps:

A, determine the operating condition of evaporator: according to standard soft air physical characterization data establishment soft air Calculation of Physical Properties class, described soft air physical property 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 physical property comprises temperature, pressure, mass dryness fraction, density, enthalpy, entropy, coefficient of heat conductivity, specific volume and the latent heat of vaporization; According to evaporator wet air inlet parameter and the evaporating temperature of user's input, call the operating condition of soft air Calculation of Physical Properties class and refrigerant Calculation of Physical Properties class calculating evaporator, described evaporator wet air inlet parameter comprises temperature and relative humidity; Described operating condition comprise calculated by evaporator refrigerant temperature saturation pressure, enthalpy, refrigerant the latent heat of vaporization;

The defrosting cycle t of B, setting evaporator, computing time interval △ t and initial frost thickness, the default value of frost thickness is zero;

The structural parameters of C, setting evaporator and heat exchanger tube annexation: according to the input setting evaporation structure parameter of user, described structural parameters comprise caliber, tube pitch, fin shape, spacing of fin, and calculate the heat interchanging area of evaporator according to described structural parameters;

D, carry out the division of evaporator zoning according to the setting of user; Concrete division methods is by carrying out the pipe range segmentations such as zoning along refrigerant flow direction according to the heat exchanger tube of certain length;

E, calculating initialization: the operating condition of the evaporator that the zoning divided according to step D and steps A calculate, 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 entrance enthalpy of refrigerant, pressure; The water capacity of each zoning estimates the variable quantity of soft air water capacity by the enthalpy difference of supposition each zoning refrigerant and the temperature difference of air;

F, according to the fan static pressure family curve of user's setting and the air quantity of hydrostatic pressures losses determination evaporator of evaporator; Obtain according to evaporator frost thickness the hydrostatic pressures losses that air flows through evaporator, combine with the Static compression performance curve of described hydrostatic pressures losses and blower fan the air quantity solved when evaporator runs; Described fan static pressure family curve is provided by blower fan manufacturer or room records by experiment;

The computing formula of hydrostatic pressures losses is as follows:

$\begin{array}{c}{\mathrm{\Δp}}_a=5.88\×{10}^{-4}{N}_{\mathrm{rd}}\×\frac{\frac{2}{p_t}[S_2-\frac{\mathrm{\π}{(d_0+2{\mathrm{\δ}}_{\mathrm{fr}})}^2}{{4S}_1}]+\frac{\mathrm{\π}(d_0+2{\mathrm{\δ}}_{\mathrm{fr}})}{S_1}}{{S_2}^{0.3}}\\ {\×\left[\frac{p_t\·S_1}{[p_t-(t_f+2{\mathrm{\δ}}_{\mathrm{fr}})][S_1-(d_0+2{\mathrm{\δ}}_{\mathrm{fr}})]}\right]}^3\×{W_F}^{1.7}\end{array}$

In formula:

Δ p _a: air side hydrostatic pressures losses, unit Pa;

N _rd: pipe row;

D ₀: pipe external diameter, unit m;

δ _fr: frost thickness, unit m;

S ₁: pipe column pitch, unit m;

S ₂: pipe line space, unit m;

P _t: spacing of fin, unit m;

T _f: fin thickness, unit m;

W _f: face velocity, unit m/s;

Solving of the governing equation of G, single zoning i, subscript i represents the numbering of zoning;

G1, according to the import and export enthalpy difference of refrigerant and the heat exchange amount of mass flow calculation medium side:

$Q_{\mathrm{iref}}=\stackrel{.}{m}({\mathrm{hi}}_{\mathrm{out}}-{\mathrm{hi}}_{\mathrm{in}})$

In above formula, Q _ireffor the heat exchange amount of medium side in single zoning i, kW; for the mass rate of refrigerant, kg/s; Hi _out, hi _inbe respectively the outlet enthalpy of refrigerant in the i of zoning, import enthalpy, kJ/kg;

G2, the saturation temperature corresponding according to refrigerant pressure in single zoning i, assuming that single zoning i copper pipe wall surface temperature is T _iw0, and calculate refrigerant evaporation Local Condensing Heat Transfer Coefficients:

The evaporation Local Condensing Heat Transfer Coefficients computing formula of gas phase zone is

In above formula, a _irfor refrigerant evaporation Local Condensing Heat Transfer Coefficients in single zoning i, kW/ (m ²k); Re _gfor gas phase Reynolds number, Pr _gfor gas phase Prandtl number, l _lfor liquid phase coefficient of heat conductivity, d _ifor heat exchanger tube internal diameter, m;

The evaporation Local Condensing Heat Transfer Coefficients computing formula in vehicle repair major district is

a _ir＝Fa _cv+Sa _pb

A _cvfor forced convertion item, a _pbfor boiling item, F, S are respectively design factor;

G3, pass through heat conduction equation

Q _iref＝a _irA _i(T _iw-0.5*(T _irin+T _irout))

Recalculate single zoning i copper pipe tube wall surface temperature degree T _iw;

In above formula, Q _ireffor the heat exchange amount of medium side in single zoning i, kW; α _irfor the evaporation Local Condensing Heat Transfer Coefficients in vehicle repair major district, kW/ (m ²k); A _ifor heat interchanging area inside pipe in single zoning i, m ²; T _{ir, in}, T _{ir, out}be respectively refrigerant out temperature, K;

G4, repetition step G1-G3, until meet the condition of convergence of setting | T _iw0-T _iW| < 10 ^-4;

In H, the copper pipe wall surface temperature calculated according to step G and single zoning i, the dewpoint temperature of soft air judges whether frosting; Judge that simultaneously the condition of frosting meets following 2 conditions:

1) copper pipe wall surface temperature is lower than 0 DEG C;

2) dewpoint temperature of the soft air of single zoning i is higher than copper pipe wall surface temperature;

If I single zoning i frost-free, then calculate air side heat exchange amount Q according to dry cooling condition _a, computing formula is as follows:

Q _a＝KA△T _m

In above formula, K is the heat transfer coefficient in the single region of evaporator, kW/ (m ²k); A is the heat transfer area of the single zoning i of evaporator, m ²; Δ T _mfor log-mean temperature difference, K;

If the i frosting of single zoning, then perform following steps:

I1, supposition frost layer surface temperature are T _fr;

I2, calculate the heat exchange amount of air side in single zoning i, described heat exchange amount comprises latent heat heat exchange amount and sensible heat transfer amount;

The sensible heat transfer amount computing formula of air side is

$Q_{\mathrm{isen}}={\stackrel{.}{m}}_a{c}_{\mathrm{pa}}(T_{\mathrm{ai},\mathrm{in}}-T_{\mathrm{ai},\mathrm{out}})$

It is in above formula that the latent heat of air side changes heat Calculation formula, Q _isenfor the sensible heat transfer amount of air in single zoning i, kW; for the mass rate of air in single zoning i, kg/s; c _pafor the specific heat capacity at constant pressure of air, kJ/ (kgK); T _{ai, in}, T _{ai, out}be respectively inlet temperature, the outlet temperature of air in single zoning i, K;

$Q_{\mathrm{ilat}}={\stackrel{.}{m}}_a(d_{i,\mathrm{in}}-d_{i,\mathrm{out}})\&CenterDot;i_{\mathrm{sv}}$

In above formula, Q _ilatfor the latent heat heat exchange amount of air side in single zoning i, kW; for the mass rate of air in single zoning i, kg/s; i _svfor the latent heat of solidification of water, kJ/ (kgK); d _{i, in}, d _{i, out}be respectively the import water capacity of air in single zoning i, outlet water capacity, kg/kg _a;

Under frozen condition, the air side heat exchange amount of single zoning i is

Q _ia＝Q _isen+Q _ilat

I3, pass through heat conduction equation

Recalculate frost layer surface temperature T _fr0;

In above formula, T _ifrfor the frost layer surface temperature of single zoning i, T _iwfor the copper pipe wall surface temperature in single zoning i, Q is the heat exchange amount in single zoning i, m _irthe quality of the water increased for making frost density, i _svfor the latent heat of vaporization of water vapor, A _tfor the heat interchanging area of single zoning i, l _ifrfor the coefficient of heat conductivity of frost layer;

Repeat step I1-I3, until | T _fr-T _fr0| meet and calculate the condition of convergence 10 ^-4;

In above formula, T _frfor the frost layer surface temperature of hypothesis, T _fr0for the frost layer surface temperature calculated by zoning heat conduction equation;

The air side heat exchange amount Q that J, comparison step I calculate _awith the medium side heat exchange amount Q that step G calculates _iref, adjustment refrigerant exit enthalpy, repeat step G-I until | Q _ia-Q _iref|/Q _iameet the zoning condition of convergence 10 ^-4;

K, the heat exchange amount calculating single zoning i, Air Temperature Difference, frost thickness and frost density;

L, upgrade the calculating parameter of the zoning relevant to single zoning i; Described calculating parameter comprises the pressure of refrigerant, saturation temperature, enthalpy and mass dryness fraction, also comprises the temperature of soft air, the water capacity of soft air, frost thickness and frost density;

M, the order flowed according to refrigerant, calculate and solve all zonings, repeats step F-L, until

max|Dh _i-Dh _i0|/Dh _i0<e，

Then interval △ t calculating computing time terminates;

Dh in above formula _ifor single zoning i medium side imports and exports enthalpy difference calculated value, Dh _i0for single zoning i medium side imports and exports enthalpy difference default, e is iteration convergence condition, is defaulted as 10 ^-4;

N, preservation the result of calculation exported in this time step;

O, the frost thickness upgrading all zonings and frost density;

P, there is to block or arrive computing time when frost thickness calculated value is more than or equal to the half of spacing of fin and evaporator the defrosting cycle that user arranges, then calculate end, otherwise forward step F to.

The computing method of the refrigerant physical property class described in steps A of the present invention, use C++ programming language and OO programmed method, the refrigerant Data Base of Chemical Compound of encapsulation National Institute of Standards and Technology, and design interface class.

The computing method of the soft air physical property class described in steps A of the present invention, use C++ programming language and OO programmed method, the computing method of encapsulation U.S. heating, Refrigeration & Air-Conditioning society of engineers ASHRAE soft air physical property, and design interface class.

Setting heat exchanger tube annexation described in step C of the present invention, uses the annexation of one-dimension array statement heat exchanger tube, does not comprise interflow and the shunting of heat exchanger tube.

The division methods of the evaporator zoning described in step D of the present invention, by carrying out the pipe range segmentations such as zoning along refrigerant flow direction according to the heat exchanger tube of certain length, the inscape of each zoning is made up of refrigerant, soft air, frost layer and finned tube.

Evaporator described in step e of the present invention calculates initialized method, according to the zoning that 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.

Result of calculation store method described in step N of the present invention is form result of calculation exported as directly being processed by Microsoft Excel software, facilitates user to process result of calculation.

Compared with prior art, the present invention has following beneficial effect:

1, because the present invention adopts, evaporator is divided zoning according to certain pipe range, and solving of governing equation is carried out to each zoning, use computing machine supercomputing function, make to evaporator under setting working condition, performance prediction efficiency is high, accuracy is high.

2, because the present invention uses C++ programming language by the simulation calculation sequencing of evaporator, designer carries out configuration settings and the operating condition setting of evaporator by computing machine, and utilize the efficient computing velocity of computing machine, the experiment number of evaporator can be greatly reduced, shorten product development cycle.

3, the present invention uses the OO programmed method of C++ programming language, substantially increases the reusability of computation model.C Plus Plus is OO programming language, makes program layer aggregated(particle) structure 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 solve with the calculating that iterates of the C++ programming language establishment governing equation of simulation calculation program to each zoning, 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, arranges provide theoretical foundation to the defrost control of air-cooler.

Accompanying drawing explanation

The present invention has accompanying drawing 4 width, 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 schematic diagram of zoning division to evaporator, in order to the division methods of zoning to be described.In order to the component of division methods and single zoning that zoning of the present invention is described.

Fig. 3 is the schematic diagram that the present invention illustrates single zoning, in order to the constitution element of zoning to be described.

Fig. 4 is the schematic diagram of the present invention to single zoning fin, in order to zoning inner fin heat interchanging area to be described.

Embodiment

Understand for the ease of those skilled in the art and implement the present invention, below in conjunction with accompanying drawing, the present invention being explained in further detail.

Program flow diagram of the present invention, as shown in Figure 1, concrete steps are as follows:

A, input according to user, determine the operating condition of evaporator.

Initial parameter, evaporating temperature, the entrance state (pressure and enthalpy) of refrigerant, the entrance state (temperature and relative humidity) of soft air that input evaporator runs, and call other parameters of refrigerant Calculation of Physical Properties class and soft air Calculation of Physical Properties class determination refrigerant inlet.

Such as: selected refrigerant is R22, 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, note: (A, B are interface class);

Calculating density is 12.63kg/m ³; Temperature is 72.17 DEG C.

The pressure of known soft air is 101.325kPa, and dry-bulb temperature is-5 DEG C, and relative humidity is 60%.Calculate other parameters as follows: wet-bulb temperature is-6.64 DEG C, enthalpy is-1.33kJ/kg, water capacity 1.48g/kg, density 1.314kg/m ³.

The defrosting cycle t of B, setting evaporator, computing time interval △ t and initial frost thickness, the default value of frost thickness is zero;

Defrosting cycle t: whole evaporator from start working to carry out T.T. of defrosting.Example is set as 6 hours.

Computing time interval △ t: defrosting cycle t to be averaged division by user, wherein every portion be defined as one computing time interval △ t.This example is set as 5 minutes.

The structural parameters of C, setting evaporator and heat exchanger tube annexation.According to the structural parameters such as caliber, tube pitch, fin shape, spacing of fin of the input setting evaporator of user, and calculate the calculating parameters such as evaporator heat exchange area according to above-mentioned parameter; The evaporation structure parameter of user's input is in table 1:

Table 1 evaporation structure parameter is in 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 (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	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 the setting of user, such as set and heat exchanger tube is divided into 5 parts, as shown in Figure 2, the constitution element of zoning as shown in Figure 3 for the division methods of zoning;

E, calculating initialization: the zoning divided according to user and the operating condition of evaporator, arrange the initial value of each zoning of evaporator, first estimate the variable quantity of soft air water capacity by the enthalpy difference of supposition each zoning refrigerant and the temperature difference of air;

F, calculate the hydrostatic pressures losses of this moment evaporator, then combine with the Static compression performance curve of fan electromotor the air quantity solving evaporator, and be evenly distributed in each zoning calculating an air quantity.

G, the energy equation of single zoning i and solving of the equation of momentum;

First suppose the import and export enthalpy difference of refrigerant, and calculate the heat exchange amount of medium side; Evaporating temperature according to evaporator first supposes wall surface temperature, the import and export medial temperature determination refrigerant evaporation Local Condensing Heat Transfer Coefficients of wall surface temperature and refrigerant.Recalculate wall surface temperature by heat conduction equation, judge that whether the wall surface temperature calculated is consistent with hypothesis wall surface temperature; If inconsistent adjustment wall surface temperature, until wall surface temperature calculates convergence.

H, judge whether this zoning exists frosting situation according to above-mentioned calculating wall surface temperature, frosting decision condition is as follows:

1) wall surface temperature is lower than 0 DEG C;

2) dewpoint temperature of the soft air of zoning is higher than copper pipe wall surface temperature;

If I, zoning frost-free, calculate air side heat exchange amount Q according to dry cooling condition _ia; If zoning frosting, suppose frost layer surface temperature, calculate sensible heat and the latent heat of air side respectively.Recalculate frost layer surface temperature by heat conduction equation, judge to calculate frost layer surface temperature whether consistent with hypothesis frost layer surface temperature; If inconsistent adjustment frost layer surface temperature, until frost layer surface temperature calculates convergence, the fin heat interchanging area of single zoning is shown in Fig. 4.

The air side heat exchange amount of J, more above-mentioned calculating and medium side heat exchange amount, adjustment refrigerant exit enthalpy, repeat step until | Q _ia-Q _iref|/Q _iameet the zoning condition of convergence 10 ^-4;

K, calculate the heat exchange amount of this zoning, the parameters such as Air Temperature Difference, frost thickness, frost density;

L, to upgrade and the calculating parameter in i correlation computations region, zoning; The entrance enthalpy of such as refrigerant, the temperature in of soft air, water capacity, frost thickness and frost density etc.

M, the order flowed according to refrigerant, calculate and solve all zonings, until

Max|Dh _i-Dh _i0|/Dh _i0<e, then one computing time interval calculation terminate.

N, preservation the result of calculation exported in this time step, preservation form is Excel file;

O, the frost thickness upgrading all zonings and frost density;

P, calculating termination condition: frost thickness calculated value is greater than the half of spacing of fin, there is the defrosting cycle blocking or arrive computing time user's setting in evaporator, starts to defrost.

Claims (7)

1. the Calculation Methods for Performance of finned-tube evaporator under frozen condition, is characterized in that: comprise the steps:

A, determine the operating condition of evaporator: according to standard soft air physical characterization data establishment soft air Calculation of Physical Properties class, described soft air physical property 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 physical property comprises temperature, pressure, mass dryness fraction, density, enthalpy, entropy, coefficient of heat conductivity, specific volume and the latent heat of vaporization; According to evaporator wet air inlet parameter and the evaporating temperature of user's input, call the operating condition of soft air Calculation of Physical Properties class and refrigerant Calculation of Physical Properties class calculating evaporator, described evaporator wet air inlet parameter comprises temperature and relative humidity; Described operating condition comprise calculated by evaporator refrigerant temperature saturation pressure, enthalpy, refrigerant the latent heat of vaporization;

The defrosting cycle t of B, setting evaporator, computing time interval of delta t and initial frost thickness, the default value of frost thickness is zero;

The structural parameters of C, setting evaporator and heat exchanger tube annexation: according to the input setting evaporation structure parameter of user, described structural parameters comprise caliber, tube pitch, fin shape, spacing of fin, and calculate the heat interchanging area of evaporator according to described structural parameters;

D, carry out the division of evaporator zoning according to the setting of user; Concrete division methods is by carrying out the pipe range segmentations such as zoning along refrigerant flow direction according to the heat exchanger tube of certain length;

E, calculating initialization: the operating condition of the evaporator that the zoning divided according to step D and steps A calculate, 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 entrance enthalpy of refrigerant, pressure; The water capacity of each zoning estimates the variable quantity of soft air water capacity by the enthalpy difference of supposition each zoning refrigerant and the temperature difference of air;

F, according to the fan static pressure family curve of user's setting and the air quantity of hydrostatic pressures losses determination evaporator of evaporator; Obtain according to evaporator frost thickness the hydrostatic pressures losses that air flows through evaporator, combine with the Static compression performance curve of described hydrostatic pressures losses and blower fan the air quantity solved when evaporator runs; Described fan static pressure family curve is provided by blower fan manufacturer or room records by experiment;

The computing formula of hydrostatic pressures losses is as follows:

$\begin{array}{c}{\mathrm{\&Delta;p}}_a=5.88\&times;{10}^{-4}{N}_{\mathrm{rd}}\&times;\frac{\frac{2}{p_t}[S_2-\frac{\mathrm{\&pi;}{(d_0+{2\mathrm{\&delta;}}_{\mathrm{fr}})}^2}{{4S}_1}]+\frac{\mathrm{\&pi;}(d_0+{2\mathrm{\&delta;}}_{\mathrm{fr}})}{S_1}}{{S_2}^{0.3}}\\ \&times;{\left[\frac{p_t\&CenterDot;S_1}{[p_t-(t_f+{2\mathrm{\&delta;}}_{\mathrm{fr}})][S_1-(d_0+{2\mathrm{\&delta;}}_{\mathrm{fr}})]}\right]}^3\&times;{W_F}^{1.7}\end{array}$

In formula:

Δ p _a: air side hydrostatic pressures losses, unit Pa;

N _rd: pipe row;

D ₀: pipe external diameter, unit m;

δ _fr: frost thickness, unit m;

S ₁: pipe column pitch, unit m;

S ₂: pipe line space, unit m;

P _t: spacing of fin, unit m;

T _f: fin thickness, unit m;

W _f: face velocity, unit m/s;

Solving of the governing equation of G, single zoning i, subscript i represents the numbering of zoning;

G1, according to the import and export enthalpy difference of refrigerant and the heat exchange amount of mass flow calculation medium side:

$Q_{\mathrm{iref}}=\stackrel{\&CenterDot;}{m}({\mathrm{hi}}_{\mathrm{out}}-{\mathrm{hi}}_{\mathrm{in}})$

In above formula, Q _ireffor the heat exchange amount of medium side in single zoning i, kW; for the mass rate of refrigerant, kg/s; Hi _out, hi _inbe respectively the outlet enthalpy of refrigerant in the i of zoning, import enthalpy, kJ/kg;

G2, the saturation temperature corresponding according to refrigerant pressure in single zoning i, assuming that single zoning i copper pipe wall surface temperature is T _iw0, and calculate refrigerant evaporation Local Condensing Heat Transfer Coefficients:

The evaporation Local Condensing Heat Transfer Coefficients computing formula of gas phase zone is

In above formula, a _irfor refrigerant evaporation Local Condensing Heat Transfer Coefficients in single zoning i, kW/ (m ²k); Re _gfor gas phase Reynolds number, Pr _gfor gas phase Prandtl number, l _lfor liquid phase coefficient of heat conductivity, d _ifor heat exchanger tube internal diameter, m;

The evaporation Local Condensing Heat Transfer Coefficients computing formula in vehicle repair major district is

a _ir＝Fa _cv+Sa _pb

A _cvfor forced convertion item, a _pbfor boiling item, F, S are respectively design factor;

G3, pass through heat conduction equation

Q _iref＝a _irA _i(T _iw-0.5*(T _irin+T _irout))

Recalculate single zoning i copper pipe tube wall surface temperature degree T _iw;

In above formula, Q _ireffor the heat exchange amount of medium side in single zoning i, kW; α _irfor the evaporation Local Condensing Heat Transfer Coefficients in vehicle repair major district, kW/ (m ²k); A _ifor heat interchanging area inside pipe in single zoning i, m ²; T _{ir, in}, T _{ir, out}be respectively refrigerant out temperature, K;

G4, repetition step G1-G3, until meet the condition of convergence of setting | T _iw0-T _iW| < 10 ^-4;

In H, the copper pipe wall surface temperature calculated according to step G and single zoning i, the dewpoint temperature of soft air judges whether frosting; Judge that simultaneously the condition of frosting meets following 2 conditions:

1) copper pipe wall surface temperature is lower than 0 DEG C;

2) dewpoint temperature of the soft air of single zoning i is higher than copper pipe wall surface temperature;

If I single zoning i frost-free, then calculate air side heat exchange amount Q according to dry cooling condition _a, computing formula is as follows:

Q _a＝KAΔT _m

In above formula, K is the heat transfer coefficient in the single region of evaporator, kW/ (m ²k); A is the heat transfer area of the single zoning i of evaporator, m ²; Δ T _mfor log-mean temperature difference, K;

If the i frosting of single zoning, then perform following steps:

I1, supposition frost layer surface temperature are T _fr;

I2, calculate the heat exchange amount of air side in single zoning i, described heat exchange amount comprises latent heat heat exchange amount and sensible heat transfer amount;

The sensible heat transfer amount computing formula of air side is

$Q_{\mathrm{isen}}={\stackrel{\&CenterDot;}{m}}_a{c}_{\mathrm{pa}}(T_{\mathrm{ai},\mathrm{in}}-T_{\mathrm{ai},\mathrm{out}})$

It is in above formula that the latent heat of air side changes heat Calculation formula, Q _isenfor the sensible heat transfer amount of air in single zoning i, kW; for the mass rate of air in single zoning i, kg/s; c _pafor the specific heat capacity at constant pressure of air, kJ/ (kgK); T _{ai, in}, T _{ai, out}be respectively inlet temperature, the outlet temperature of air in single zoning i, K;

$Q_{\mathrm{ilat}}={\stackrel{\&CenterDot;}{m}}_a(d_{i,\mathrm{in}}-d_{i,\mathrm{out}})\&CenterDot;i_{\mathrm{sv}}$

In above formula, Q _ilatfor the latent heat heat exchange amount of air side in single zoning i, kW; for the mass rate of air in single zoning i, kg/s; i _svfor the latent heat of solidification of water, kJ/ (kgK); d _{i, in}, d _{i, out}be respectively the import water capacity of air in single zoning i, outlet water capacity, kg/kg _a;

Under frozen condition, the air side heat exchange amount of single zoning i is

Q _ia＝Q _isen+Q _ilat

I3, pass through heat conduction equation

Recalculate frost layer surface temperature T _fr0;

In above formula, T _ifrfor the frost layer surface temperature of single zoning i, T _iwfor the copper pipe wall surface temperature in single zoning i, Q is the heat exchange amount in single zoning i, m _irthe quality of the water increased for making frost density, i _svfor the latent heat of vaporization of water vapor, A _tfor the heat interchanging area of single zoning i, l _ifrfor the coefficient of heat conductivity of frost layer;

Repeat step I1-I3, until | T _fr-T _fr0| meet and calculate the condition of convergence 10 ^-4;

In above formula, T _frfor the frost layer surface temperature of hypothesis, T _fr0for the frost layer surface temperature calculated by zoning heat conduction equation;

The air side heat exchange amount Q that J, comparison step I calculate _awith the medium side heat exchange amount Q that step G calculates _iref, adjustment refrigerant exit enthalpy, repeat step G-I until | Q _ia-Q _iref|/Q _iameet the zoning condition of convergence 10 ^-4;

K, the heat exchange amount calculating single zoning i, Air Temperature Difference, frost thickness and frost density;

L, upgrade the calculating parameter of the zoning relevant to single zoning i; Described calculating parameter comprises the pressure of refrigerant, saturation temperature, enthalpy and mass dryness fraction, also comprises the temperature of soft air, the water capacity of soft air, frost thickness and frost density;

M, the order flowed according to refrigerant, calculate and solve all zonings, repeats step F-L, until

max|Dh _i-Dh _i0|/Dh _i0<e，

Then interval of delta t calculating computing time terminates;

Dh in above formula _ifor single zoning i medium side imports and exports enthalpy difference calculated value, Dh _i0for single zoning i medium side imports and exports enthalpy difference default, e is iteration convergence condition, is defaulted as 10 ^-4;

N, preservation the result of calculation exported in this time step;

O, the frost thickness upgrading all zonings and frost density;

P, there is to block or arrive computing time when frost thickness calculated value is more than or equal to the half of spacing of fin and evaporator the defrosting cycle that user arranges, then calculate end, otherwise forward step F to.

2. the Calculation Methods for Performance of finned-tube evaporator under a kind of frozen condition according to claim 1, it is characterized in that: the computing method of the refrigerant physical property class described in steps A, use C++ programming language and OO programmed method, the refrigerant Data Base of Chemical Compound of encapsulation National Institute of Standards and Technology, and design interface class.

3. the Calculation Methods for Performance of finned-tube evaporator under a kind of frozen condition according to claim 1, it is characterized in that: the computing method of the soft air physical property class described in steps A, use C++ programming language and OO programmed method, the computing method of encapsulation U.S. heating, Refrigeration & Air-Conditioning society of engineers ASHRAE soft air physical property, and design interface class.

4. the Calculation Methods for Performance of finned-tube evaporator under a kind of frozen condition according to claim 1, it is characterized in that: the setting heat exchanger tube annexation described in step C, use the annexation of one-dimension array statement heat exchanger tube, do not comprise interflow and the shunting of heat exchanger tube.

5. the Calculation Methods for Performance of finned-tube evaporator under a kind of frozen condition according to claim 1, it is characterized in that: the division methods of the evaporator zoning described in step D, by carrying out the pipe range segmentations such as zoning along refrigerant flow direction according to the heat exchanger tube of certain length, the inscape of each zoning is made up of refrigerant, soft air, frost layer and finned tube.

6. the Calculation Methods for Performance of finned-tube evaporator under a kind of frozen condition according to claim 1, it is characterized in that: the evaporator described in step e calculates initialized method, according to the zoning that 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 Calculation Methods for Performance of finned-tube evaporator under a kind of frozen condition according to claim 1, it is characterized in that: the result of calculation store method described in step N is form result of calculation exported as directly being processed by Microsoft Excel software, facilitates user to process result of calculation.