CN102508958A - Optimal parameter determination method for plate-fin evaporator - Google Patents

Abstract

The invention provides an optimal design method for a plate-fin evaporator. The method has the following beneficial effects: based on the design theory of the heat exchanger, the heat exchange coefficient of the refrigerant side of the evaporator is used instead of the heat exchange coefficient of the single phase fluid and then the size of the evaporator core is obtained by solving the equation set; the evaporator designed by the method can meet the efficiency requirement and the fluid on the two sides can simultaneously meet the pressure drop requirement; and when the equation set is solved by an iterative method, the new iteration variable needs to be reasonably selected so as to ensure the numerical solution to converge faster.

Description

A kind of parameters optimization of plate-fin evaporator is confirmed method

Technical field

The parameters optimization that the present invention relates to a kind of plate-fin evaporator is confirmed method.

Background technology

Plate type finned heat exchanger has the heat transfer efficiency height; Compact conformation; Characteristics such as adaptability is strong; It not only divides on high, rare production of second and the synthetic ammonia petrochemical equipment at air and is used widely, and natural gas liquefaction with separate, also have great application prospect on aviation, automobile, diesel locomotive, hydrogen helium liquefaction, refrigeration and the air-conditioning equipment.Its designing and calculating generally comprises two types problem---and calculating of check property and designability are calculated.The calculating of check property is that the exchange capability of heat of existing heat interchanger is adjusted or variable working condition calculating; It is according to given condition of work and heat that designability is calculated, and confirms needed heat interchanging area, and then the concrete size of decision heat interchanger.

The requirement of electronic warfare is on the increase air environment, and thermal value constantly increases, and conventional air circulation refrigeration system can't satisfy the needs that the electronic equipment thermal value increases, can not guarantee the reliability and the security of electronic equipment fully.Having sweat cooling round-robin integrated thermal management system concurrently can address this problem, and this certainly will relate to novel evaporator so.This heat interchanger is a major equipment of taking away thermal force in the environmental control system; Civilian evaporator is because need not too much consider the needs of floor area; Volume is generally all bigger; Will consider weight and volume exactly and the environmental control system equipment on the aircraft is most important, and the advantage of plate-fin evaporator just in time can meet the volume and weight requirement well.

All the time, plate type finned heat exchanger mainly applies to the open type air circulation of aircraft environmental control system, mainly contains two kinds of forms: dry type (air of cold and hot both sides does not all have phase transformation), wet type (hot side air has phase transformation after being cooled, and promptly has condensate to produce).The designing and calculating of these two kinds of forms is all fairly simple; Detailed introduction has been arranged in many documents, relatively be applicable to dry type and the wet type heat interchanger mentioned just now, and for the evaporator of diabatic process more complicated; Parameter determination method needs to improve, so that make that design is more reasonable.

Summary of the invention

One embodiment of the present of invention have proposed a kind of method, and it confirms the parameter of evaporator core on the basis to the plate-fin evaporator modeling.Can satisfy the requirement of the refrigerating capacity and the pressure loss simultaneously with the evaporator of this method design.

According to an aspect of the present invention, a kind of parameter determination method of plate-fin evaporator of suitable two phase flow heat transfer is provided, has it is characterized in that comprising:

With hot side mass velocity and cold side mass velocity as iteration variable;

Confirm hot side heat transfer coefficient;

Confirm the cold side heat transfer coefficient;

According to hot side mass velocity, cold side mass velocity, hot side heat transfer coefficient and cold side heat transfer coefficient, confirm the heat interchanger size.

Description of drawings

Fig. 1 is that core body parameter according to an embodiment of the invention is confirmed synoptic diagram;

Fig. 2 is the process flow diagram that evaporator parameter according to an embodiment of the invention is confirmed.

Fig. 3 is a process flow diagram, has shown the step process of definite both sides heat transfer coefficient.

Embodiment

The method for designing of prior art mainly is suitable for the heat interchanger of gas flow; And along with industrial expansion; Compact heat exchanger such as plate type finned heat exchanger no longer have been confined to flowing of single phase gas, but are used as evaporator and condenser more and more, i.e. the heat exchange of two-phase fluid; Therefore this method is improved on the basis of gas compact heat exchanger method for designing, has proposed a kind of parameter determination method of plate-fin evaporator of suitable two phase flow heat transfer.

Parameter at the plate-fin evaporator of suitable two phase flow heat transfer according to an embodiment of the invention is confirmed

In the method, confirm to satisfy simultaneously the plate-fin evaporator mathematical model of pressure drop and efficient requirement earlier, its

In comprise:

-ignore the thermal resistance of cold and hot fluid heat transfer wall

The magnitude of wall thermal resistance is generally 10-6, and therefore the general 10-3 of the magnitude of both sides fluid thermal resistance compares with the both sides fluid thermal resistance, and the wall thermal resistance can be ignored;

-only consider the one dimension heat exchange on the flow direction

The fin equivalent diameter of plate-fin evaporator is 1～5mm, compares very for a short time with the flow channel length of hundreds of millimeter even thousands of millimeters, and the heat exchange convection cell effect of heat transfer of other directions is very little;

The known conditions of-introducing evaporator

Fluid parameter: allow maximum pressure drop, both sides working medium type, flow, inlet temperature and intake pressure;

Structural parameters: efficient, fin form, fin material, separator material, side plate material, strip of paper used for sealing material that requirement reaches;

-with distributary as the type of flow

Two very important characteristic index of evaporator are heat exchange efficiency and pressure drop, so this method confirms with above-mentioned four conditions to be known parameters, and to satisfy heat exchange efficiency and the pressure drop mathematical model as final goal.

If hot limit fluid (subscript is represented with h) length of flow is a, cold limit fluid (subscript is represented with c) length of flow b, non-current direction is of a size of the c (see figure 1).

The front face area of hot fluid (being the incoming flow cross-sectional area of fluid) is bc, and the front face area of cold fluid is ac.

The parameter determination method of the plate-fin evaporator of suitable two phase flow heat transfer according to an embodiment of the invention comprises:

A) both sides mass velocity G _hAnd G _cAs iteration variable (step 101).

With following approximation relation formula, calculate hot side mass velocity G respectively _hWith cold side mass velocity G _cFirst estimated value:

$G_h\≈\sqrt{{\left(\frac{\mathrm{St}{\mathrm{Pr}}^{2/3}}{f}\right)}_h\left(\frac{\mathrm{\Δ}{P}_h}{N_{\mathrm{tu}}}\right)\frac{g}{v_{\mathrm{mh}}{{\mathrm{Pr}}_h}^{2/3}}}---\left(1\right)$

$G_c\≈\sqrt{{\left(\frac{\mathrm{St}{\mathrm{Pr}}^{2/3}}{f}\right)}_c\left(\frac{\mathrm{\Δ}{P}_c}{N_{\mathrm{tu}}}\right)\frac{g}{\left(v_{\mathrm{mc}}{{\mathrm{Pr}}_c}^{2/3}\right)}}---\left(2\right)$

Wherein, (StPr ^2/3/ f) _h, (StPr ^2/3/ f) _cBe respectively hot side liquid, cold-side fluid heat transfer characteristic, all get 0.3; Δ P _h, Δ P _cBeing respectively hot side liquid allows maximum pressure drop, cold-side fluid to allow maximum pressure drop; v _Mh, v _McBe respectively the average specific volume of hot side liquid, the average specific volume of cold-side fluid; Pr _h, Pr _cBe respectively hot side liquid Prandtl constant, cold-side fluid Prandtl constant; N _TuBe the evaporator availability, its value is confirmed by heat exchange efficiency; G is an acceleration of gravity.

B) confirm both sides heat transfer coefficient k _hAnd k _c(step 102), this step detailed process is seen Fig. 3.Wherein the hot side liquid of evaporator is a monophasic fluid, the heat transfer coefficient k of this monophasic fluid _hConfirm that step comprises:

B 1) confirm hot side liquid reynolds number Re _h(step 201),

B 2) according to Re _hValue select corresponding formulas to calculate (step 202):

If 40＜Re _h＜800 (laminar flows):

Heat transfer factor $j_h=\frac{3.0}{{\mathrm{Re}}_h}---\left(3\right)$

Friction factor $f_h=\frac{14.0}{{\mathrm{Re}}_h}---\left(4\right)$

Coefficient K _h=j _hG _hc _Ph/ Pr _h ^2/3(5)

Wherein, c _PhBe hot side liquid specific heat capacity.

If 800≤Re _h＜10000 (transition flows):

Friction factor $f_h=0.0321{\left(\frac{{\mathrm{Re}}_h}{1000}\right)}^{-0.25}---\left(6\right)$

Nu Xieerte criterion numeral Nu _h=0.06Re _h ^2/3(7)

Heat transfer coefficient k _h=Nu _hλ _h/ de _h(8)

Wherein, λ _hBe hot side liquid coefficient of heat conductivity, de _hBe hot side fin equivalent diameter.

If Re _h>=10000 (turbulent flows):

Friction factor f _h=0.00128+0.1143Re _h ^-1/3.2145(9)

The Nu Xieerte criterion numeral ${\mathrm{Nu}}_h=\frac{f_h{\mathrm{Re}}_h{\mathrm{Pr}}_h}{2{(C+12.7(f_h/2)({\mathrm{Pr}}_h^{2/3}-1))}^{0.5}}---\left(10\right)$

Wherein, k _hConfirm by formula (8); Coefficient C=1.07+900/Re _h-0.63/ (1+10Pr _h).

The evaporator cold-side fluid is the two-phase flow state; Definite step of cold-side fluid heat transfer coefficient comprises:

B3) confirm liquid phase reynolds number Re in the cold-side fluid two-phase flow _Cl(step 201);

B4) establishing the evaporator heat flow density is q (step 203-1), confirms the coefficient of heat transfer k of liquid phase in the cold side two-phase flow _l

$k_l=\frac{{\mathrm{Re}}_{\mathrm{cl}}\·{\mathrm{Pr}}_{\mathrm{cl}}\·(f_c/2)\·{\mathrm{\λ}}_{\mathrm{cl}}}{{\mathrm{De}}_c[1.07+12.7({\mathrm{Pr}}_{\mathrm{cl}}^{2/3}-1){(f_{\mathrm{cl}}/2)}^{1/2}]}---\left(11\right)$

Wherein, Re _Cl, Pr _ClAnd λ _ClBe respectively Reynolds number, Prandtl criterion number and the coefficient of heat conductivity of liquid phase in the cold side two-phase flow; f _ClBe cold side fin friction factor; De _cBe cold side fin equivalent diameter;

B5) confirm the coefficient of heat transfer k of two-phase flow again _c(step 203-2)

$k_c=\left\{\begin{array}{c}{k}_l(0.6638\·{\mathrm{Co}}^{-0.2}\·f2{\mathrm{Fr}}_l+1058\·{\mathrm{Bo}}^{0.7}\·1.63){(1-\mathrm{Xm})}^{0.8}\\ k_l(1.136\·{\mathrm{Co}}^{-0.9}\·f2{\mathrm{Fr}}_l+667.2\·{\mathrm{Bo}}^{0.7}\·1.63){(1-\mathrm{Xm})}^{0.8}\end{array}\right.---\left(12\right)$

Wherein, liquid phase Fei Laode number

(g _mBe mass flow rate; ρ _lBe density of liquid phase); Coefficient $f2{\mathrm{Fr}}_l=\left\{\begin{array}{cc}{(25\&CenterDot;{\mathrm{Fr}}_l)}^{0.3}& {\mathrm{Fr}}_l<0.04\\ 1& \end{array}\right.;$ The convection current characteristic number

(ρ _gBe vapour phase density; Xm is the average quality void fraction); The boil feature number

(r is the cold-side fluid latent heat of vaporization).

C, confirm new heat flow density value (step 204) by both sides heat transfer coefficient value, with the q value of this value and first hypothesis relatively (step 205), as if close, finishing iteration (step 206) then; If difference is in the error allowed band (step 207), then with new heat flow density value substitution above-mentioned steps again, calculate successively again, up to obtaining final heat flow density value, and then confirm final two phase flow heat transfer coefficient.

D. confirm heat interchanger size (step 103)

After correlation parameter substitution equation group, unknown parameter is U _h, a, b, c, find the solution the equation group and can confirm the evaporator core size:

$\left\{\begin{array}{c}\frac{1}{U_h}=\frac{1}{{\mathrm{\&eta;}}_k{k}_h}+\frac{1}{{\mathrm{\&eta;}}_c{k}_c(A_c/A_h)}\\ {\mathrm{Nu}}_h=\frac{k_h{\mathrm{\&alpha;}}_h\mathrm{abc}}{W_{\min }}\\ w_h=G_h{\mathrm{\&sigma;}}_h\mathrm{ac}\\ w_c=G_c{\mathrm{\&sigma;}}_c\mathrm{bc}\end{array}\right.---\left(13\right)$

Wherein, U _hThe heat transfer coefficient of correspondence when being benchmark for hot side liquid total heat conduction area; η _h, η _cBe respectively heat, cold side fin efficiency; A _c/ A _hBe the ratio of cold side heat transfer area with hot side heat transfer area; Nu _hBe hot side availability; α _hBe the ratio of hot side heat transfer area with the evaporator cumulative volume; W _MinBe both sides fluid thermal capacity smaller value; w _h, w _cBe respectively heat, cold-side fluid mass rate; σ _h, σ _cBe respectively heat, cold side fin cell size.Known quantity in the system of equations is removed both sides mass velocity G _h, G _cHeat transfer coefficient k _h, k _cOutside being confirmed by steps A, B, all the other parameters all can be obtained by known conditions.

Parameter determination method according to the plate-fin evaporator of the suitable two phase flow heat transfer of a further embodiment of the present invention further comprises alternatively:

Whether checking procedure E., check institute design heat interchanger be in allowable pressure drop and weight range (step 104)

Pressure drop comprises two parts: loss of end cap additonal pressure and core body pressure drop.Pressure drop of trying to achieve and design allowable pressure drop are compared, judge then (step 105).If calculate the gained pressure drop in permissible value, then design of heat exchanger finishes (to step 106), otherwise readjusts both sides mass velocity G _h, G _cValue (step 107), get back to step 101 and continue to calculate.

F. by actual conditions adjustment size (optional step)

Just be designed to the single process distributary; If the size of evaporator direction has surpassed installation dimension, then can change this direction into multipaths, this moment, dimensional problem solved; But pressure drop not necessarily still meets the requirements fully, and the size that can adjust non-current direction this moment a little can meet the demands.

The useful achievement of the inventive method comprises:

1. existing plate type finned heat exchanger design is only applicable to monophasic fluid, and the proposition of this method has enlarged the scope of design of plate type finned heat exchanger;

2. the plate-fin evaporator design result of using this method to obtain can instruct its commercial production well, has reduced because of blindly processing data waste that causes and the economic loss of bringing thus;

3. the rational plate-fin evaporator of project organization has been arranged, just can promote its widespread use at aircraft industry.

Claims (8)

1. be fit to the parameter determination method of the plate-fin evaporator of two phase flow heat transfer, it is characterized in that comprising:

With hot side mass velocity (G _h) and cold side mass velocity (G _c) as iteration variable;

Confirm hot side heat transfer coefficient (k _h);

Confirm cold side heat transfer coefficient (k _c);

According to hot side mass velocity (G _h), cold side mass velocity (G _c), hot side heat transfer coefficient (k _h) and cold side heat transfer coefficient (k _c), confirm the heat interchanger size.

2. according to the method for claim 1, it is characterized in that further comprising:

Set the initial value of evaporator heat flow density (q),

By hot side heat transfer coefficient (k _h) and cold side heat transfer coefficient (k _c) value confirm the new value of evaporator heat flow density (q),

With evaporator heat flow density (q) should new value with said initial value relatively, as if its difference in a predetermined error allowed band, finishing iteration then; If difference is not in said error allowed band; Then with the new value substitution above-mentioned steps again of said evaporator heat flow density (q); Calculate successively again; In said predetermined error allowed band, and obtain the end value of heat flow density up to said difference, and then the final coefficient of heat transfer of definite two-phase flow.

3. according to the process of claim 1 wherein:

The thermal resistance of having ignored the cold and hot fluid heat transfer wall,

Only consider one dimension heat exchange along flow direction,

The efficient that reaches with permission maximum pressure drop, both sides working medium type, flow, inlet temperature and intake pressure, the requirement of evaporator, fin form, fin material, separator material, side plate material, strip of paper used for sealing material be as known conditions,

With distributary as the type of flow.

4. according to the method for claim 1, it is characterized in that the hot side mass velocity of said usefulness (G _h) and cold side mass velocity (G _c) further comprise as the step of iteration variable:

With following approximation relation formula, calculate the first estimated value of hot side mass velocity and cold side mass velocity respectively:

Wherein, (StPr ^2/3/ f) _h, (StPr ^2/3/ f) _cBe respectively hot side liquid, cold-side fluid heat transfer characteristic, all get 0.3; Δ P _h, Δ P _cBeing respectively hot side liquid allows maximum pressure drop, cold-side fluid to allow maximum pressure drop; v _Mh, v _McBe respectively the average specific volume of hot side liquid, the average specific volume of cold-side fluid; Pr _h, Pr _cBe respectively hot side liquid Prandtl constant, cold-side fluid Prandtl constant; N _TuBe the evaporator availability, its value is confirmed by heat exchange efficiency; G is an acceleration of gravity.

5. according to the method for claim 2, it is characterized in that the said hot side heat transfer coefficient (k of confirming _h) step further comprise: B 1) confirm hot side liquid Reynolds number (Re _h),

B 2) according to hot side liquid Reynolds number (Re _h) value select corresponding formulas to calculate.

6. according to the method for claim 5, it is characterized in that said according to hot side liquid Reynolds number (Re _h) the value step of selecting corresponding formulas to calculate further comprise:

If 40＜Re _h＜800, then:

Heat transfer factor

Friction factor

Heat transfer coefficient k _h=j _hG _hCp _h/ Pr _h ^2/3(5)

Wherein, c _PhBe hot side liquid specific heat capacity,

If 800≤Re _h＜10000, then:

Friction factor

Nu Xieerte criterion numeral Nu _h=0.06Re _h ^2/3(7)

Heat transfer coefficient k _h=Nu _hλ _h/ de _h(8)

Wherein, λ _hBe hot side liquid coefficient of heat conductivity, de _hBe hot side fin equivalent diameter;

If Re _h>=10000, then:

Friction factor f _h=0.00128+0.1143Re _h ^-1/3.2145(9)

Nu Xieerte criterion numeral

Wherein, k _hConfirm by formula (8); Coefficient C=1.07+900/Re _h-0.63/ (1+10Pr _h).

7. according to the method for claim 2, it is characterized in that the said cold side heat transfer coefficient (k of confirming _c) step further comprise:

B3) confirm liquid phase reynolds number Re in the cold-side fluid two-phase flow _Cl

B4) confirm the heat transfer coefficient k of liquid phase in the cold side two-phase flow _l:

Wherein, Re _Cl, Pr _ClAnd λ _ClBe respectively Reynolds number, Prandtl criterion number and the coefficient of heat conductivity of liquid phase in the cold side two-phase flow; f _ClBe cold side fin friction factor; De _cBe cold side fin equivalent diameter;

B5) confirm the heat transfer coefficient k of cold side two-phase flow _c:

Wherein,

Liquid phase Fei Laode number

G wherein _mBe mass flow rate, ρ _lBe density of liquid phase; Coefficient

Wherein convection current characteristic number

Be vapour phase density, Xm is the average quality void fraction;

Boil feature number

wherein r is the cold-side fluid latent heat of vaporization.

8. according to any one method among claim 1, the 5-7, it is characterized in that the step of said definite heat interchanger size further comprises

After correlation parameter substitution equation group, unknown parameter is U _h, a, b, c, find the solution the equation group and can confirm the evaporator core size:

Wherein,

U _hThe heat transfer coefficient of correspondence when being benchmark for hot side liquid total heat conduction area;

A is that hot limit fluid length of flow, b are that cold limit fluid length of flow, c are the height of evaporator;

η _h, η _cBe respectively heat, cold side fin efficiency;

A _c/ A _hBe the ratio of cold side heat transfer area with hot side heat transfer area;

Nu _hBe hot side availability;

α _hBe the ratio of hot side heat transfer area with the evaporator cumulative volume;

W _MinBe both sides fluid thermal capacity smaller value;

w _h, w _cBe respectively heat, cold-side fluid mass rate;

σ _h, σ _cBe respectively heat, cold side fin cell size.

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