A calculation method for a gravity-flow parallel heat exchanger

Abstract

The present invention discloses a calculation method for a gravity-flow parallel heat exchanger. According to the known total hot-side flow rate, first assume the hot-side flow rate of heat exchanger one to obtain the hot-side flow rate of heat exchanger two. Then, conduct a check calculation on the two parallel heat exchangers to obtain the hot-side flow resistances of the two heat exchangers, and compare the relationship between the hot-side flow resistances and the hot-side flow rates of the two heat exchangers. Through iterative calculation, continuously allocate the hot-side flow rates of the two heat exchangers until the requirements are met. The design method of the present invention can accurately and efficiently solve the problems of hot-side flow rate distribution and thermal calculation of the gravity-flow parallel heat exchanger. Moreover, the calculation method of the gravity-flow parallel heat exchanger of the present invention conducts iterative allocation of the hot-side flow rate through the bisection method, with better convergence and more convenient calculation.

Description

Technical Field

[0001] The present invention relates to a calculation method for heat exchangers, and particularly to a calculation method for gravity-flow parallel heat exchangers. Background Art

[0002] In a gravity-flow parallel heat exchange system, the hot-side flow rate distribution between two heat exchangers is determined only by the hot-side flow resistances of the two heat exchangers, and the ratio of their hot-side flow rates is equal to the inverse ratio of the hot-side flow resistances. For two gravity-flow parallel heat exchangers, their thermodynamic parameters affect each other. When the hot-side flow resistance of one changes, it will cause the hot-side flow rate distribution of the two heat exchangers to change and re-match.

[0003] Due to the mutual influence between the two heat exchangers in a gravity-flow parallel heat exchange system, it is difficult for traditional heat exchanger calculation methods to accurately perform thermodynamic calculations on the two heat exchangers, especially difficult to solve the problem of hot-side flow rate distribution. Therefore, it is necessary to develop a new calculation method to solve the flow rate distribution problem of gravity-flow parallel heat exchangers and accurately perform thermodynamic calculations on the two gravity-flow parallel heat exchangers. Summary of the Invention

[0004] The purpose of the present invention is to provide a calculation method for gravity-flow parallel heat exchangers, which can accurately and efficiently solve the problems of hot-side flow rate distribution and thermodynamic calculation of gravity-flow parallel heat exchangers.

[0005] The technical solution adopted by the present invention includes the following steps:

[0006] 1) Given the structural parameters of two gravity-flow parallel heat exchangers and the cold-side working fluid inlet parameters, and given the total hot-side working fluid inlet parameters, including the inlet temperature Th h,in of the hot-side working fluid, the total inlet mass flow rate qmh h,total of the hot-side working fluid, the inlet pressure ph h,in of the hot-side working fluid, and a relatively large initial hot-side flow rate iteration value Δqm is given.

[0007] Wherein:

[0008] T - temperature, K;

[0009] qm - mass flow rate, kg·s -1 ;

[0010] Δqm - flow rate iteration value;

[0011] Subscript h - hot side;

[0012] Subscript in - inlet;

[0013] Subscript total - all;

[0014] 2) For gravity-flow parallel heat exchangers, assume the hot-side flow rate qm of heat exchanger one h,1, the hot-side flow rate qm of the second heat exchanger can be obtained based on the flow relationship h,2 . According to the inlet parameters of the working fluids on the cold and hot sides of the two heat exchangers, a check calculation is performed on the two heat exchangers, and the hot-side flow resistance Δp of the two heat exchangers can be obtained h,1 , Δp h,2 .

[0015] Where:

[0016] Δp - heat exchanger flow resistance;

[0017] Subscript 1 - the first heat exchanger;

[0018] Subscript 2 - the second heat exchanger;

[0019] 3) Determine whether the hot-side flow resistance and hot-side flow rate of the two heat exchangers meet the conditions. If not, increase the iteration amount Δqm of the hot-side flow rate qm of the first heat exchanger, and repeat step 2). h,1 Increase the iteration amount Δqm, and repeat step 2).

[0020] 4) When the hot-side flow resistance and hot-side flow rate of the two heat exchangers meet the conditions, determine whether the current flow iteration value Δqm meets the accuracy requirement. If not, change the hot-side flow rate of the first heat exchanger to the value of the previous cycle, and at the same time change the flow iteration value Δqm to half of the original value, and repeat steps 2) and 3).

[0021] 5) Output the parameters of the two heat exchangers, the ratio of the hot-side flow resistances of the two heat exchangers Δp h,1 / Δp h,2 , the inverse ratio of the hot-side flow rates of the two heat exchangers qm h,2 / qm h,1 , and determine the matching degree of the hot-side flow resistance and hot-side flow rate of the two heat exchangers. Thus, the calculation is completed, and the problem of hot-side flow rate distribution and heat exchanger thermal calculation of self-flow parallel heat exchangers is solved accurately and efficiently.

[0022] In step 2), it is assumed that the initial hot-side flow rate qm of the first heat exchanger h,1 = 0.1 and iteration is performed for increase.

[0023] In step 3), the hot-side flow resistance and hot-side flow rate of the two heat exchangers need to satisfy that the ratio of the hot-side flow resistances is greater than the inverse ratio of the hot-side flow rates, that is, (Δp h,1 / Δp h,2 ) > (qm h,2 / qm h,1 ).

[0024] In step 4), the flow iteration amount Δqm needs to satisfy Δqm < ε, where ε represents the calculation accuracy of the hot-side flow rate, and the smaller the value of ε, the higher the calculation accuracy.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] The existing calculation methods for heat exchangers are difficult to accurately perform thermal calculations on gravity-flow parallel heat exchangers, especially difficult to solve the problem of the hot-side flow rate distribution of two heat exchangers. The calculation method for gravity-flow parallel heat exchangers proposed by the present invention can accurately and efficiently solve the problems of hot-side flow rate distribution and thermal calculation of gravity-flow parallel heat exchangers. Moreover, the calculation method for gravity-flow parallel heat exchangers of the present invention performs iterative distribution of the hot-side flow rate through the bisection method, with better convergence and more convenient calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of a gravity-flow parallel heat exchanger.

[0028] Figure 2 is a flow chart of the calculation method for the gravity-flow parallel heat exchanger provided by the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] As Figure 1 shown, the hot sides of the two gravity-flow parallel heat exchangers have the same incoming flow, with a total mass flow rate of qm h,total , and the flow rates qm h,1 , qm h,2 of the two heat exchangers are only determined by the hot-side flow resistances Δp h,1 , Δp h,2 of the two heat exchangers, and the ratio of their hot-side flow rates is equal to the inverse ratio of the hot-side flow resistances.

[0030] As Figure 2 shown, it specifically includes the following steps:

[0031] 1) Given the structural parameters of the two gravity-flow parallel heat exchangers and the cold-side working fluid inlet parameters, and given the total hot-side working fluid inlet parameters, including the inlet temperature T h,in of the hot-side working fluid, the total inlet mass flow rate qm h,total of the hot-side working fluid, the inlet pressure p h,in of the hot-side working fluid, and a relatively large initial hot-side flow rate iteration value Δqm is given.

[0032] Wherein:

[0033] T - temperature, K;

[0034] qm - mass flow rate, kg·s -1 ;

[0035] Δqm - flow rate iteration value;

[0036] Subscript h - hot side;

[0037] Subscript in - inlet;

[0038] Subscript total - all;

[0039] 2) For the gravity-flow parallel heat exchanger, assume the hot-side flow rate \(q_{m1}\) of Heat Exchanger 1 h,1 , according to the flow rate relationship, the hot-side flow rate \(q_{m2}\) of Heat Exchanger 2 can be obtained h,2 . Based on the inlet parameters of the working fluids on the cold and hot sides of the two heat exchangers, a check calculation is performed on the two heat exchangers, and the hot-side flow resistances \(\Delta p_1\) h,1 , \(\Delta p_2\) h,2 can be obtained.

[0040] Where:

[0041] \(\Delta p\) - heat exchanger flow resistance;

[0042] Subscript 1 - Heat Exchanger 1;

[0043] Subscript 2 - Heat Exchanger 2;

[0044] 3) Determine whether the hot-side flow resistances and hot-side flow rates of the two heat exchangers meet the conditions. If not, increase the iteration quantity \(\Delta q_m\) for the hot-side flow rate \(q_{m1}\) of Heat Exchanger 1 and repeat step 2). h,1

[0045] 4) When the hot-side flow resistances and hot-side flow rates of the two heat exchangers meet the conditions, determine whether the flow rate iteration value \(\Delta q_m\) meets the accuracy requirements. If not, change the hot-side flow rate of Heat Exchanger 1 to the value of the previous cycle, and at the same time change the flow rate iteration value \(\Delta q_m\) to half of the original value, and repeat steps 2) and 3).

[0046] 5) Output the parameters of the two heat exchangers, the ratio of the hot-side flow resistances of the two heat exchangers \(\Delta p_1\) h,1 / \(\Delta p_2\) h,2 , the inverse ratio of the hot-side flow rates of the two heat exchangers \(q_{m2}\) h,2 / \(q_{m1}\) h,1 , and judge the matching degree of the hot-side flow resistances and hot-side flow rates of the two heat exchangers. Thus, the calculation is completed, and the problem of hot-side flow rate distribution and heat exchanger thermal calculation of the gravity-flow parallel heat exchanger is solved accurately and efficiently.

[0047] In step 2), it is assumed that the initial hot-side flow rate \(q_{m1}\) of Heat Exchanger 1 h,1 = 0.1 and iterative increase is carried out. For a heat exchanger with determined structural parameters, under the condition that all the inlet parameters on the cold side, the hot-side inlet temperature, and the inlet pressure are determined, its hot-side flow resistance is positively correlated with the hot-side flow rate. The greater the hot-side flow rate, the greater the hot-side flow resistance. As the hot-side flow rate \(q_{m1}\) h,1 of Heat Exchanger 1 iteratively increases from the initial value, the ratio of the hot-side flow resistances of the two heat exchangers \(\Delta p_1\) h,1 / \(\Delta p_2\) h,2 continuously increases from the minimum value, and the inverse ratio of the hot-side flow rates \(q_{m2}\) h,2 / \(q_{m1}\) h,1 continuously decreases from the maximum value.

[0048] In step 3), the hot-side flow resistance and hot-side flow rate of the two heat exchangers should satisfy that the ratio of the hot-side flow resistances is greater than the inverse ratio of the hot-side flow rates, i.e., (Δp h,1 / Δp h,2 ) > (qm h,2 / qm h,1 ).

[0049] In step 4), the flow rate iteration amount Δqm should satisfy Δqm < ε, where ε represents the calculation accuracy of the hot-side flow rate. The smaller the value of ε, the higher the calculation accuracy.

Claims

1. A calculation method for a gravity-flow parallel heat exchanger, characterized in that By assuming the hot-side flow rate of Heat Exchanger 1 and performing calculations, the bisection method is used for iterative allocation of the hot-side flow rates of the two heat exchangers until the hot-side flow rates and hot-side flow resistances of the two heat exchangers meet the requirements. The specific steps are as follows: 1) Given the structural parameters of two self-flow parallel heat exchangers and the cold-side working fluid inlet parameters, and given the total hot-side working fluid inlet parameters, including the inlet temperature T h,in of the hot-side working fluid, the total inlet mass flow rate qm h,total of the hot-side working fluid, the inlet pressure p h,in of the hot-side working fluid, and given a relatively large initial hot-side flow iteration value Δqm; Where: T - temperature, K; qm - mass flow rate, kg·s -1 ; Δqm - flow rate iteration value; Subscript h - hot side; Subscript in - inlet; Subscript total - all; 2) For the gravity-flow parallel heat exchanger, assuming the hot-side flow rate qm of heat exchanger 1 h,1 , the initial qm h,1 = 0.

1. According to the flow rate relationship, the hot-side flow rate qm of heat exchanger 2 can be obtained h,2 . Based on the inlet parameters of the hot and cold working fluids of the two heat exchangers, a check calculation is carried out on the two heat exchangers, and the hot-side flow resistance Δp of the two heat exchangers can be obtained h,1 , Δp h,2 ; Where: Δp - Flow resistance of the heat exchanger; Subscript 1 - Heat Exchanger 1; Subscript 2 - Heat Exchanger 2; 3) Determine whether the hot side flow resistance and hot side flow of the two heat exchangers meet the conditions. The judgment condition is (Δp h,1 / Δp h,2 )>(qm h,2 / qm h,1 ), if not satisfied, the hot side flow rate qm of heat exchanger 1 h,1 Increase the iteration amount Δqm and repeat step 2); 4) When the hot-side flow resistances and hot-side flow rates of the two heat exchangers meet the conditions, determine whether the current flow rate iteration value Δqm meets the accuracy requirement, and the accuracy requirement is Δqm < ε. If not, change the hot-side flow rate of Heat Exchanger 1 to the value in the previous cycle, and at the same time change the flow rate iteration value Δqm to half of the original value, and repeat steps 2) and 3). 5) Output the parameters of the two heat exchangers, the hot side flow resistance ratio Δp of the two heat exchangers h,1 / Δp h,2 , the hot side flow of the two heat exchangers is inversely proportional to qm h,2 / qm h,1 , determine the matching degree between the hot side flow resistance and the hot side flow of the two heat exchangers. At this point, the calculation is completed, and the hot side flow distribution of the gravity parallel heat exchanger and the thermal calculation problem of the heat exchanger are solved accurately and efficiently.

Images