A performance calculation method for partition wall heat exchanger based on energy average temperature

Abstract

The present invention discloses a performance calculation method of a partition-type heat exchanger based on energy average temperature, comprising the following steps: inputting the working conditions of the partition-type heat exchanger; according to the flow mode of the working fluid, taking the heat capacity flow rate of the fluid on both sides as the weight, weighting the inlet temperatures on both sides to calculate the energy average temperature; calculating the convective heat transfer coefficient according to the convective heat transfer characteristic database on both sides of the heat transfer unit; calculating the convective heat transfer thermal resistance between the wall and the fluid on both sides and the thermal conductivity thermal resistance of the solid wall of the partition-type heat exchanger according to the convective heat transfer coefficient on both sides, and calculating the total heat transfer coefficient; redefining the number of heat transfer units and calculating; calculating the outlet temperature of the fluid on both sides and the temperature distribution along the process according to the number of heat transfer units and the energy average temperature, and calculating the total heat transfer. The present invention realizes the non-iterative direct calculation of the heat transfer performance of the partition-type heat exchanger, improves the design calculation efficiency, obtains the heat transfer performance of the partition-type heat exchanger more precisely, and provides a new idea for the design calculation of the partition-type heat exchanger.

Description

Technical Field

[0001] The invention belongs to the technical field of heat exchangers, and in particular relates to a performance calculation method of a partition-type heat exchanger based on energy average temperature. Background Art

[0002] As a widely used component in traditional industries, heat exchangers are carriers of energy exchange between fluids and play a key role in many fields such as refrigeration and air conditioning, electricity, ships, gas turbines, and aerospace. Especially in the field of gas turbines and aerospace, heat exchangers are used in many occasions such as fuel cooling of drones, intercooling and heat recovery of large ground gas turbines, and fuel and air cooling inside aircraft engines. They are key components for solving thermal problems and improving energy utilization. Therefore, heat exchanger technology is also a bottleneck technology for the development of the above fields. The performance of heat exchangers is directly related to the final performance of the equipment. In recent years, with the continuous development of heat exchanger design and manufacturing technology, heat exchangers have gradually developed in the direction of refinement, compactness, and lightness. Technological innovations in various industrial directions have put forward more complex and stringent flow heat exchange requirements for heat exchangers. Accordingly, it is necessary to develop heat exchanger performance calculation methods based on traditional heat exchanger design calculation methods.

[0003] The logarithmic mean temperature difference method is a traditional heat exchanger design calculation method that has been used for nearly a hundred years. This method is used in the design of heat exchangers with almost all flow and structural forms. Taking the downstream type as an example, the expression of this method is

[0004]

[0005] Q=LMTDKA

[0006] Wherein, LMTD is the logarithmic mean temperature difference, t is the temperature, K is the total heat transfer coefficient, and A is the total heat transfer area. The logarithmic mean temperature difference method can calculate the average heat transfer temperature difference in the heat exchanger from the known inlet and outlet temperatures of the fluids on both sides, and then calculate the heat transfer according to Newton's cooling law; the equilibrium relationship between the heat transfer and the enthalpy difference of the inlet and outlet fluids requires iterative solution of the fluid outlet temperature. This method can accurately solve the performance of the heat exchanger, and its reliability has been verified in a large number of engineering applications. The performance calculation method proposed in the present invention can omit the iterative solution in the calculation process, improve the calculation efficiency, and obtain more detailed and comprehensive heat transfer performance information.

[0007] In view of this, the present invention is proposed. Summary of the invention

[0008] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for calculating the performance of a partition-type heat exchanger based on the energy average temperature. To solve the above technical problem, the basic concept of the technical solution adopted by the present invention is:

[0009] A method for calculating the performance of a partitioning heat exchanger based on energy average temperature comprises the following steps:

[0010] Step 1: input the working conditions of the partitioning heat exchanger according to the thermal environment of the partitioning heat exchanger;

[0011] Step 2: Calculate the energy average temperature of the two fluids. According to the working medium flow mode and the heat capacity flow rate of the fluids on both sides, take the heat capacity flow rate of the fluids on both sides as the weight to perform a weighted average of the inlet temperatures on both sides and calculate the energy average temperature.

[0012] Step 3: Calculate the convective heat transfer coefficient. According to the convective heat transfer characteristic database on both sides of the heat transfer unit, obtain the convective heat transfer coefficient of the fluid working medium on both sides of the partition wall heat exchanger.

[0013] Step 4: Calculate the total heat transfer coefficient of the partition wall heat exchanger, calculate the convection heat transfer thermal resistance between the wall and the fluid on both sides according to the convection heat transfer coefficient on both sides, and the thermal conductivity thermal resistance of the solid wall of the partition wall heat exchanger, and calculate the total heat transfer coefficient;

[0014] Step 5, define and calculate the number of heat transfer units. The number of heat transfer units is defined as the product of the sum of the inverse of the heat capacity flow rate of the fluid working medium on both sides, the total heat transfer coefficient and the total heat transfer area;

[0015] Step 6: Calculate the fluid outlet temperature and temperature distribution along the fluid on both sides according to the number of heat transfer units and the average energy temperature to further obtain the total heat transfer.

[0016] Furthermore, the partition-type heat exchanger is an integral downstream heat exchanger or an integral countercurrent heat exchanger.

[0017] Furthermore, the working conditions of the intermediate wall heat exchanger in step 1 include: inlet flow, temperature, pressure; physical property parameters of the fluid working medium on both sides; structural form and structural parameters of the intermediate wall heat exchanger.

[0018] Furthermore, the calculation formula for the energy average temperature of the downstream heat exchanger in step 2 is:

[0019] t ave =(W1t 1,in +W2t 2,in ) / (W1+W2),

[0020] The energy average temperature calculation formula of the counterflow heat exchanger is:

[0021] t ave =(W1t 1,in -W2t 2,out ) / (W1-W2),

[0022] Where t is the temperature and W is the heat capacity flow rate, which is the product of specific heat capacity and mass flow rate.

[0023] Furthermore, in step three, the basic heat transfer unit form is obtained through the working conditions input in step one, the empirical correlation formula used to calculate the heat transfer characteristics of the fluids on both sides is determined according to the unit heat transfer form, and the convective heat transfer coefficients of the fluid working medium on both sides and the wall of the partition heat exchanger are calculated according to the Reynolds number range.

[0024] Furthermore, the calculation formula for the number of heat transfer units redefined in step 5 is:

[0025] NTU=(1 / W1+1 / W2)KA,

[0026] The expression for the number of heat transfer units of a counterflow heat exchanger is:

[0027] NTU=(1 / W1-1 / W2)KA,

[0028] Among them, K is the total heat transfer coefficient and A is the total heat transfer area of ​​the partition wall heat exchanger.

[0029] Furthermore, in step 6, the outlet temperature of the downstream heat exchanger is expressed as

[0030] t i,out =t ave +e -NTU (t i,in -t ave ),

[0031] The expression for the outlet temperature of a counterflow heat exchanger is:

[0032] t 1,out =t ave +e -NTU (t 1,in -t ave ), t 2,out =t ave +e NTU (t 2,in -t ave ).

[0033] Furthermore, the energy average temperature expression of the counterflow heat exchanger in step 2 is re-derived so that it can be directly calculated by the input parameters, and the obtained expression is:

[0034] t ave =(e -NTU W1t 1,in -W2t 2,in ) / (e -NTU W1-W2).

[0035] Furthermore, the temperature distribution of the fluids on both sides can be obtained by calculation, and the expression is:

[0036] For co-current heat exchanger: t i (x) = t ave +e -NTU[0→x] (t i,in -t ave );

[0037] Countercurrent heat exchanger: Wherein, t1 represents the temperature of the fluid along the counterflow heat exchanger with the same flow direction as the coordinate axis, t2 represents the temperature of the fluid along the counterflow heat exchanger with the opposite flow direction to the coordinate axis, L represents the total flow length, and x represents the fluid flow distance; NTU[0→x] represents the number of heat transfer units from position 0 to position x, that is, the number of heat transfer units corresponding to the heat transfer area from position 0 to position x.

[0038] Furthermore, the total heat transfer formula is Q = W1 | t 1,out -t 1,in |=W2|t 2,out -t 2,in |.

[0039] Furthermore, the heat transfer unit forms include equal-section channels, finned tube bundles, smooth tube bundles, etc.

[0040] After adopting the above technical scheme, the present invention has the following beneficial effects compared with the prior art.

[0041] The present invention realizes non-iterative direct calculation of the heat transfer performance of the partition wall heat exchanger through inputting the working conditions of the partition wall heat exchanger, calculating the average temperature of the energy of two fluids, analyzing the convective heat transfer performance of the fluids on both sides, calculating the total heat transfer coefficient of the partition wall heat exchanger, defining and calculating the number of heat transfer units of the partition wall heat exchanger, and calculating the outlet temperatures of the fluids on both sides and the total heat transfer of the partition wall heat exchanger, thereby improving the calculation efficiency, obtaining the heat transfer performance of the partition wall heat exchanger in a more precise manner, and providing new ideas for the design and calculation of the partition wall heat exchanger.

[0042] The present invention introduces a performance calculation method in the field of heat exchanger optimization, which can more objectively identify structural shortcomings, effectively increase structural optimization efficiency, and improve the convergence of optimization design.

[0043] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The accompanying drawings are part of this application and are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an improper limitation of the present invention. Obviously, the drawings described below are only some embodiments. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0045] Figure 1 It is a schematic diagram of the calculation method of the present invention;

[0046] Figure 2 is a simplified schematic diagram of the heat transfer process in an embodiment of the present invention;

[0047] Figure 3 Schematic diagram of temperature distribution curve along the process in an embodiment of the present invention;

[0048] Figure 4 It is a schematic diagram of the residual error of iterative calculation in the comparative example of the present invention.

[0049] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but are intended to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0051] In the description of the present invention, it should be noted that the directions or positional relationships indicated by terms such as “upper”, “lower”, “front”, “back”, “left”, “right”, “vertical”, “inside” and “outside” are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0052] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0053] like Figure 1-4As shown, the present invention provides a method for calculating the performance of a partition wall heat exchanger based on energy average temperature, comprising the following steps:

[0054] Step 1: input the working conditions of the partitioning heat exchanger according to the thermal environment of the partitioning heat exchanger;

[0055] Step 2: Calculate the energy average temperature of the two fluids. According to the working medium flow mode and the heat capacity flow rate of the fluids on both sides, take the heat capacity flow rate of the fluids on both sides as the weight to perform a weighted average of the inlet temperatures on both sides and calculate the energy average temperature.

[0056] Step 3: Calculate the convective heat transfer coefficient. According to the convective heat transfer characteristic database on both sides of the heat transfer unit, obtain the convective heat transfer coefficient of the fluid working medium on both sides of the partition wall heat exchanger.

[0057] Step 4: Calculate the total heat transfer coefficient of the partition wall heat exchanger. Calculate the convection heat transfer thermal resistance between the specific wall and the fluids on both sides according to the convection heat transfer coefficient, as well as the thermal conductivity resistance of the solid wall of the partition wall heat exchanger to calculate the total heat transfer coefficient.

[0058] Step 5, define and calculate the number of heat transfer units. The number of heat transfer units is defined as the product of the sum of the inverse of the heat capacity flow rate of the fluid working medium on both sides, the total heat transfer coefficient and the total heat transfer area;

[0059] Step six: Calculate the fluid outlet temperature and temperature distribution along the fluid on both sides according to the number of heat transfer units and the average energy temperature to further obtain the total heat transfer.

[0060] Based on the thermal environment of the partition heat exchanger, in step 1, input the inlet flow, temperature and pressure of the fluid working medium on both sides; input the physical parameters of the fluid working medium on both sides or the law of change of the physical parameters with temperature and pressure; give the structural form and structural parameters of the partition heat exchanger. According to the heat exchange requirements of the partition heat exchanger and the reliable working temperature range of the fluid working medium, determine the outlet temperature limit of the fluid working medium on both sides. The inlet temperature of the fluid working medium on both sides is a known quantity, while the outlet temperature is an unknown quantity, which meets the input boundary of the general heat exchanger performance calculation.

[0061] The energy average temperature of the two fluids is calculated, where the partition wall heat exchanger is an integral co-current heat exchanger or an integral counter-current heat exchanger. For the co-current heat exchanger, the energy average temperature is calculated by weighting the heat capacity flow rate of the fluids on both sides to average the inlet temperatures on both sides, that is, t ave =(W1t 1,in +W2t 2,in) / (W1+W2), where t is temperature and W is heat capacity flow rate. The inlet temperatures on both sides are replaced by the outlet temperatures at the same time. For counterflow heat exchangers, the energy average temperature is calculated by taking the heat capacity flow rate of the fluid on both sides as the weight to average the inlet temperature on one side and the outlet temperature on the other side. The heat capacity flow rate weight of the fluid on the side opposite to the coordinate axis is taken as a negative value, that is, t ave =(W1t 1,in -W2t 2,out ) / (W1-W2), the inlet / outlet temperature of the fluid on both sides is replaced by the outlet / inlet temperature. The above two expressions of energy average temperature do not change along the process, and the temperature in the formula can be taken as the fluid temperature on both sides corresponding to any flow position. That is, the temperature distribution along the process of the fluid on both sides can be obtained through the formula.

[0062] According to the proposed structure of the partition wall heat exchanger input in step 1, the basic heat transfer unit form of the fluid channels on both sides is obtained, including but not limited to equal-section channels, finned tube bundles, smooth tube bundles, etc. According to the type of heat transfer unit, the empirical correlation formula to be used for calculating the heat transfer characteristics of the fluids on both sides is determined, and the convective heat transfer coefficient between the fluid working medium on both sides and the wall of the partition wall heat exchanger is calculated according to the Reynolds number range. The convective heat transfer thermal resistance between the wall and the fluids on both sides is calculated based on the convective heat transfer coefficient on both sides, and the thermal conductivity resistance of the solid wall of the partition wall heat exchanger is further considered. The sum of the three is the total heat transfer thermal resistance between the fluids on both sides of the partition wall heat exchanger, so as to calculate and obtain the total heat transfer coefficient K of the partition wall heat exchanger.

[0063] Based on the above-calculated total heat transfer coefficient K and the total heat transfer area A of the intermediate wall heat exchanger, the number of heat transfer units of the intermediate wall heat exchanger is redefined. The number of heat transfer units defined in the present invention is clearly distinguished from the number of heat transfer units in the traditional "heat transfer effectiveness-heat transfer unit number method". For the co-current heat exchanger, the number of heat transfer units in the present invention is defined as the product of the sum of the inverses of the heat capacity flow rates of the fluid working fluids on both sides, the total heat transfer coefficient K and the total heat transfer area A, and its expression is NTU = (1 / W1 + 1 / W2) KA; while for the counter-current heat exchanger, the heat capacity flow rate of the fluid working fluid on the side opposite to the coordinate axis should take a negative value. In the present invention, fluid working fluid 2 may be taken as a reverse flow working fluid, and the expression for the number of counter-current heat transfer units is NTU = (1 / W1-1 / W2) KA.

[0064] Based on the defined energy average temperature and the number of heat transfer units, the outlet temperature of the fluid on both sides of the partition heat exchanger is directly calculated. For a co-current heat exchanger, the expression for the outlet temperature is t i,out =t ave +e -NTU (t i,in -t ave ); For a counter-flow heat exchanger, for fluid 1 flowing in the same direction as the coordinate axis, the outlet temperature expression is t1,out =t ave +e -NTU (t 1,in -t ave ), for fluid 2 flowing in the opposite direction to the coordinate axis, its outlet temperature expression is t 2,out =t ave +e NTU (t 2,in -t ave ). Accordingly, the total heat transfer of the partition wall heat exchanger can be obtained from the outlet temperature result. Therefore, the present invention provides a method for calculating the outlet temperature and total heat transfer of heat exchangers with two basic flow forms, namely, overall co-current flow and overall counter-current flow. This method can accurately and simply calculate the performance of the partition wall heat exchanger.

[0065] Preferably, in the energy average temperature calculation method of the counterflow heat exchanger, the expression of the energy average temperature is t ave =(W1t 1,in -W2t 2,out ) / (W1-W2), where t 2,out is an unknown quantity, so the energy average temperature cannot be directly solved. In order to make the solution more convenient, the expression of the countercurrent energy average temperature is re-derived and rewritten as t ave =(e - NTU W1t 1,in -W2t 2,in ) / (e -NTU W1-W2). In the formula, the number of countercurrent heat transfer units can be obtained from known quantities, and the other variables are all known quantities. Therefore, the rewritten expression can directly solve the countercurrent energy average temperature.

[0066] Analogous to the solution method and conclusion of the above outlet temperature, the analytical solution of the temperature along the fluid on both sides of the intermediate wall heat exchanger can be directly written. For the downstream heat exchanger, the expression of the temperature along the two sides is t i (x) = t ave +e -NTU[0→x] (t i,in -t ave );For the counter-flow heat exchanger, the expressions of the temperatures along the two sides are t1(x)=t ave +e -NTU[0→x] (t 1,in -t ave ) and t2(x)=t ave +e NTU[x→L] (t 2,in -t ave), where t1 represents the temperature of the fluid along the counterflow heat exchanger with the same direction as the coordinate axis, t2 represents the temperature of the fluid along the counterflow heat exchanger with the opposite direction to the coordinate axis, L represents the total length of the flow direction, and x represents the flow distance of the fluid; NTU[0→x] represents the number of heat transfer units from 0 to x, that is, the number of heat transfer units corresponding to the heat transfer area from 0 to x. Therefore, this method gives an analytical solution to the temperature distribution of the fluid along the two sides, and improves the temperature field information of the heat transfer process of the partition wall heat exchanger with a brief conclusion.

[0067] The important feature of the performance calculation method of the partition wall heat exchanger based on the energy average temperature is that the heat exchanger performance can be directly solved according to the known quantity. Compared with the traditional logarithmic mean temperature difference method, the outlet temperature iteration step is omitted. This method can be applied to the structural optimization design of the partition wall heat exchanger, effectively simplifying the performance calculation process of the optimization design, increasing the efficiency of structural optimization, and improving the convergence of the optimization design algorithm.

[0068] Embodiment 1

[0069] like Figures 1 to 4 As shown, the performance calculation method of a partitioning heat exchanger based on energy average temperature described in this embodiment takes a counterflow heat exchanger as an example and performs the following steps:

[0070] Step 1: According to the thermal environment of the partition heat exchanger, input the inlet flow, temperature and pressure of the fluid working medium on both sides of the partition heat exchanger; input the physical parameters of the fluid working medium on both sides or the law of change of physical parameters with temperature and pressure; give the structural form and structural parameters of the partition heat exchanger. The specific input parameters are shown in Table 1, and the heat transfer process diagram is as follows: Figure 2 As shown, the operating parameters are given with reference to the water-cooled air heat exchanger;

[0071] Step 2: According to formula t ave =(e -NTU W1t 1,in -W2t 2,in ) / (e -NTU W1-W2) calculates the energy average temperature of the two fluids, and calculates the energy average temperature by taking the heat capacity flow rate of the fluids on both sides as the weight and performing weighted average of the inlet temperatures on both sides according to the working medium flow mode and the heat capacity flow rate of the fluids on both sides;

[0072] Step 3: Calculate the convective heat transfer coefficient. According to the convective heat transfer characteristic database on both sides of the heat transfer unit, obtain the convective heat transfer coefficient of the fluid working medium on both sides of the partition wall heat exchanger.

[0073] Step 4: Calculate the total heat transfer coefficient of the partition wall heat exchanger. Calculate the convection heat transfer resistance between the specific wall and the fluid on both sides according to the convection heat transfer coefficient, as well as the thermal conductivity resistance of the solid wall of the partition wall heat exchanger. Calculate the total heat transfer coefficient. This section only demonstrates the calculation process and method. It is assumed that the total heat transfer coefficient is 800W / (m 2 K) and total heat transfer area 1m 2 , as shown in Table 1;

[0074] Step 5: Calculate the number of heat transfer units according to NTU = (1 / W1 - 1 / W2)KA, and the calculated value is -1.0084;

[0075] Step 6: According to formula t 1,out =t ave +e -NTU (t 1,in -t ave ), calculate the outlet temperature of the fluid 1 whose flow direction is consistent with the coordinate axis; according to the formula t 2,out =t ave +e NTU (t 2,in -t ave ) Calculate the outlet temperature of the fluid 2 whose flow direction is opposite to the coordinate axis.

[0076] The expression of the energy average temperature in step 2 is t ave =(W1t 1,in -W2t 2,out ) / (W1-W2), where t 2,out is an unknown quantity, which makes it impossible to solve directly. In order to facilitate the solution, the formula t 2,out =t ave +e NTU (t 2,in -t ave ) into t ave =(W1t 1,in -W2t 2,out ) / (W1-W2), the energy average temperature of the counterflow heat exchanger is obtained by re-deriving it as t ave =(e -NTU W1t 1,in -W2t 2,in ) / (e -NTU W1-W2), according to Table 1, the known quantities are substituted into the formula to obtain T ave 265.16K, t 1,out 341.90K, t 2,out is 322.79K; the total heat transfer formula is Q = W1|t 1,out -t 1,in |=W2|t 2,out-t 2,in |, further calculation shows that the total heat exchange Q is 40.95kW.

[0077] Table 1

[0078] <![CDATA[t 1,in ]]> <![CDATA[m1]]> <![CDATA[c p,1 ]]> <![CDATA[t 2,in ]]> <![CDATA[m2]]> <![CDATA[c p,2 ]]> 293.15K 0.2kg / s 4200J / (kg·K) 423.15K 0.4kg / s 1020kJ / (kg·K) <![CDATA[W1]]> <![CDATA[W2]]> K A NTU <![CDATA[T ave ]]> 840W / K 408W / K <![CDATA[800W / (m 2 ·K)]]> <![CDATA[1m 2 ]]> -1.0084 265.16K <![CDATA[t 1,out ]]> <![CDATA[t 2,out ]]> Q 341.90K 322.79K 40.95kW

[0079] The embodiment uses a specific heat transfer process case to demonstrate the entire process of the method proposed in the present invention, and completes the performance calculation of the partition wall heat exchanger in a sequential calculation method without iteration. According to conventional input, boundary conditions give the inlet fluid parameters on both sides and the total heat transfer capacity of the partition wall heat exchanger, that is, the total heat transfer coefficient K and the total heat transfer area A, and the outlet temperature and temperature distribution of the fluid on both sides are directly given in the form of analytical solutions. The present invention clarifies the mathematical model of the heat transfer process and simplifies the performance calculation process of the partition wall heat exchanger.

[0080] Comparative Example 1

[0081] like Figures 1 to 4 As shown, in order to further illustrate the advantages of the method of the present invention compared with the traditional heat exchanger performance calculation method based on logarithmic mean temperature difference, the input parameters of the above embodiment are solved using the traditional method.

[0082] The brief process of the traditional method is as follows: Assume that the outlet temperature of fluid 1 is t within a reasonable range. 1,out , calculate the outlet temperature t of fluid 2 according to the energy conservation relationship of the fluids on both sides 2,out , substitute the inlet and outlet temperatures of the fluids on both sides into the logarithmic mean temperature difference calculation formula:

[0083] LMTD=[(t 1,out -t 2,in )-(t 1,in -t 2,out )] / ln[(t 1,out -t 2,in ) / (t 1,in -t 2,out )]

[0084] Calculate the average heat transfer temperature difference and compare the heat transfer calculated by the heat transfer equation Q1 = LMTD KA with the fluid inlet and outlet enthalpy difference Q2 = c p,1 m1|T 1,out -T 1,in |Compare, if the difference between Q1 and Q2 is within the allowable range, the iteration converges, otherwise the aforementioned assumed "fluid 1 outlet temperature" is adjusted according to the difference and size relationship between the two, and the above process is repeated until convergence.

[0085] Using the fast gradient-based iterative method, the residual of the iterative calculation is as follows Figure 4As shown, the residual is defined as (Q2-Q1) / Q2. Under the input parameter conditions of Example 1, the residual can be reduced to 10-4 after about 120 steps, achieving a relatively accurate convergence. The fluid outlet temperatures on both sides after convergence are 341.89K and 322.80K, respectively, which still have a deviation of the second decimal place from the exact value calculated by the method of the present invention.

[0086] This comparative example illustrates that the traditional method and the method of the present invention can obtain basically the same heat transfer results, but compared with the precise analytical solution of the present invention, the traditional iterative solution can only obtain a numerical solution, and there is a certain degree of deviation; the traditional method needs to undergo a certain order of magnitude of iterations, and the comparative example iterates 120 times, and the calculation is relatively cumbersome, while the method of the present invention can obtain the heat transfer performance calculation results without iteration by executing it in the order of the process, and only requires 1 calculation. In addition, the iterative process of the traditional method will be affected by factors such as initial values ​​and boundary conditions, and the convergence of its iterative process requires certain means to ensure, which further increases its workload. Therefore, the method of the present invention can effectively improve the computational efficiency of the traditional heat transfer calculation method, eliminate iterations to simplify the calculation process, and improve stability.

[0087] Without loss of generality, the above-mentioned embodiment 1 uses a counter-flow heat exchanger as an example to illustrate the method of the present invention. The method can be similarly substituted into a co-flow heat exchanger example to obtain the same conclusion as above.

[0088] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment, it is not used to limit the present invention. Any technician familiar with this patent can make some changes or modify the technical contents suggested above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the solution of the present invention.

Claims

1. A method for calculating the performance of a partition wall heat exchanger based on energy average temperature, characterized in that: The steps include: Step 1: input the working conditions of the partitioning heat exchanger according to the thermal environment in which the partitioning heat exchanger is located; the partitioning heat exchanger is an integral downstream heat exchanger or an integral countercurrent heat exchanger; the working conditions of the partitioning heat exchanger include: inlet flow, temperature, pressure; physical property parameters of the fluid working medium on both sides; structural form and structural parameters of the partitioning heat exchanger; Step 2: Calculate the energy average temperature of the two fluids. According to the working medium flow mode and the heat capacity flow rate of the fluids on both sides, take the heat capacity flow rate of the fluids on both sides as the weight to perform weighted average of the inlet temperatures on both sides and calculate the energy average temperature. The energy average temperature calculation formula of the downstream heat exchanger is t ave =(W1t 1,in +W2t 2,in ) / (W1+W2), the energy average temperature calculation formula of the counterflow heat exchanger is t ave =(W1t 1,in -W2t 2,out ) / (W1-W2), where t is temperature and W is heat capacity flow rate; Step 3: Calculate the convective heat transfer coefficient. Obtain the basic heat transfer unit form through the working conditions input in step 1. Determine the empirical correlation formula used to calculate the heat transfer characteristics of the fluids on both sides according to the heat transfer unit form. Calculate the convective heat transfer coefficient between the fluid working medium on both sides and the wall of the partition heat exchanger according to the Reynolds number range. Step 4: Calculate the total heat transfer coefficient of the partition wall heat exchanger, calculate the convection heat transfer thermal resistance between the wall and the fluid on both sides according to the convection heat transfer coefficient on both sides, and the thermal conductivity thermal resistance of the solid wall of the partition wall heat exchanger, and calculate the total heat transfer coefficient; Step 5, define and calculate the number of heat transfer units. The number of heat transfer units is defined as the product of the sum of the inverse of the heat capacity flow rate of the fluid working medium on both sides, the total heat transfer coefficient and the total heat transfer area; the redefined calculation formula for the number of heat transfer units includes: the heat transfer unit expression of the downstream heat exchanger is NTU = (1 / W1 + 1 / W2) KA, and the heat transfer unit expression of the countercurrent heat exchanger is NTU = (1 / W1 - 1 / W2) KA, where K is the total heat transfer coefficient and A is the total heat transfer area of ​​the partition wall heat exchanger; Step 6: Calculate the outlet temperature of the fluid on both sides and the temperature distribution along the process according to the number of heat transfer units and the energy average temperature, and further calculate the total heat transfer; the outlet temperature expression of the downstream heat exchanger is t i,out =t ave +e -NTU (t i,in -t ave ), the expression of the outlet temperature of the counterflow heat exchanger is t 1,out =t ave +e -NTU (t 1,in -t ave ), t 2,out =t ave +e NTU (t 2,in -t ave ); The calculation expression of the temperature distribution along the process is: for the downstream heat exchanger: i (x) = t ave +e -NTU[0→x] (t i,in -t ave ) Countercurrent heat exchanger: Wherein, t1 represents the temperature of the fluid along the counterflow heat exchanger with the same flow direction as the coordinate axis, t2 represents the temperature of the fluid along the counterflow heat exchanger with the opposite flow direction to the coordinate axis, L represents the total flow length, and x represents the fluid flow distance; NTU[0→x] represents the number of heat transfer units from position 0 to position x, that is, the number of heat transfer units corresponding to the heat transfer area from position 0 to position x.

2. The method for calculating the performance of a partitioning heat exchanger based on energy average temperature according to claim 1, characterized in that: The energy average temperature expression of the counter-flow heat exchanger in step 2 is re-derived to obtain the expression t ave =(e -NTU W1t 1,in -W2t 2,in ) / (e -NTU W1-W2).

3. The method for calculating the performance of a partition wall heat exchanger based on energy average temperature according to claim 1, characterized in that: The heat transfer unit forms include equal-section channels, finned tube bundles, and smooth tube bundles.

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