Construction method of heat transfer calculation model of multi-layer nested brazing milling groove type heat exchanger

Abstract

The invention relates to a construction method of a heat transfer calculation model of a multi-layer nested brazing milling groove type heat exchanger. The technical problems that in the prior art, the heat transfer calculation accuracy of the multi-layer nested brazing milling groove type heat exchanger is low, and the calculation period is long are solved. The invention provides a construction method of a heat transfer calculation model of a multilayer nested brazing milling groove type heat exchanger. The construction method comprises the following steps: step 1, constructing an initial heat transfer calculation model; 2, performing parameter initialization on the initial heat transfer calculation model; 3, on the basis of the heat transfer calculation model after parameter initialization, according to different heat exchange modes of the submodules, corresponding heat transfer calculation infinitesimal elements are adopted for calculation, and the heat exchange amount of the heat exchanger is obtained; and 4, carrying out iterative calculation on the heat exchange amount of the heat exchanger, and when the difference value between the heat exchange amount obtained by each round of iteration and the heat exchange amount before the current round of iteration meets the convergence requirement, completing the construction of the heat transfer calculation model of the multilayer nested brazing milling groove type heat exchanger.

Description

Technical Field

[0001] The invention relates to a gas heat exchanger for liquid rocket engine tank pressurization, and in particular to a method for constructing a heat transfer calculation model of a multi-layer nested brazing milled groove heat exchanger. Background Art

[0002] In liquid rocket engine thrust chamber cooling systems and hypersonic vehicle thermal management systems, heat exchangers must operate efficiently under extreme conditions such as high temperature and high pressure, while also meeting requirements for compact structure, lightweight, and high heat transfer efficiency. Multi-layer nested brazed milled groove heat exchangers offer advantages such as compact structure, small size, large heat transfer area, high heat transfer efficiency, strong pressure bearing capacity, and high structural reliability.

[0003] With the growing demand for high-thrust, high-thrust-to-weight ratio liquid rocket engines in space missions such as lunar exploration and deep space exploration, lightweight, miniaturized and efficient gas booster heat exchangers have become an inevitable requirement for the design of rocket tank booster systems.

[0004] The multi-layer nested brazed milled groove heat exchanger has a complex structure and the flow channel size is generally small. Three-dimensional numerical methods are usually used for fluid-solid coupling heat transfer calculations. However, due to the large number of grids during heat transfer calculations, the accuracy of the heat transfer calculations is low and the calculation cycle is long. Summary of the Invention

[0005] The purpose of the present invention is to solve the technical problems of low accuracy and long calculation cycle in the existing heat transfer calculation method of multi-layer nested brazed milled groove heat exchanger, and to provide a method for constructing a heat transfer calculation model of a multi-layer nested brazed milled groove heat exchanger.

[0006] To achieve the above objectives, the technical solutions provided by the present invention are as follows:

[0007] A method for constructing a heat transfer calculation model for a multi-layer nested brazed milled groove heat exchanger is special in that it includes the following steps:

[0008] Step 1: Divide the heat exchanger into multiple submodules according to a predetermined division rule, construct a heat transfer calculation element for each submodule, and construct an initial heat transfer calculation model based on the heat transfer calculation element;

[0009] Step 2: Initializing parameters of the initial heat transfer calculation model;

[0010] Step 3: Based on the heat transfer calculation model after parameter initialization, according to the different heat exchange modes of the submodules, corresponding heat transfer calculation micro-element is used to calculate and obtain the heat exchange capacity of the heat exchanger;

[0011] Step 4: Iteratively calculate the heat transfer rate of the heat exchanger and determine whether the difference between the heat transfer rate obtained in each round of iteration and the heat transfer rate before the current round of iteration meets the convergence requirements. If so, the heat transfer calculation model of the multi-layer nested brazed milled groove heat exchanger is constructed. If not, optimize the heat transfer calculation model parameters and perform a new round of iteration until the difference meets the convergence requirements, completing the construction of the heat transfer calculation model of the multi-layer nested brazed milled groove heat exchanger.

[0012] Furthermore, in step 3, the heat exchange mode of the submodule is two-sided / two-phase flow heat exchange, and the specific calculation steps of the corresponding heat transfer calculation element are as follows:

[0013] Step 3.11: Calculate the two-phase heat transfer coefficient h at a given node in the two-phase flow region. tpf :

[0014] h tpf =X·h V +(1-X)·h L

[0015] Where: subscript tpf represents the two-phase flow point; h V is the gas heat transfer coefficient, h L is the liquid heat transfer coefficient, both of which can be derived through the Sieder-Tate experimental correlation formula; X is the dryness, which is calculated using the following formula:

[0016]

[0017] Where: E is the enthalpy value, subscript L is the enthalpy value of the liquid saturation state at a given pressure and temperature, subscript V is the enthalpy value of the gas saturation point at a given pressure and temperature, E c is the enthalpy of the two-phase flow point at the calculation node;

[0018] Step 3.12: Calculate the heat transfer Q between the fluid and the solid wall f,w :

[0019] Q f,w =h tpf ·A f,w ·(t f -t w )

[0020] Where A f,w is the heat exchange area between the fluid and the solid wall, in m 2 , t f is the fluid temperature, t w is the solid wall temperature; the subscript w represents the solid wall, and f represents the fluid;

[0021] Step 3.13: Calculate the heat transfer Q of the solid wall w :

[0022]

[0023] Where, δ w is the thickness of the heat exchange wall, in m, λ w is the average thermal conductivity of the solid wall, unit is w / (m·K), A w is the heat conduction area of the solid wall, in m 2 , t w.g is the solid wall temperature on the hot fluid side, t w.c is the solid wall temperature on the cold fluid side, subscript c represents the cold fluid, and subscript g represents the hot fluid;

[0024] Step 3.14: Calculate the heat transfer Q of the cold and hot fluids f :

[0025] Q f =K·A f ·(t g -t c )

[0026] Where A f is the fluid heat transfer area, unit: m 2 , t g is the temperature of the hot fluid, t c is the temperature of the cold fluid, K is the total heat transfer coefficient between the cold and hot fluids, and K is derived from the following formula:

[0027]

[0028] Where: w is the thickness of the heat exchange wall, in m, λ w is the thermal conductivity of the heat exchange wall, unit is w / (m·K), ξ is the conversion coefficient of the outer rib efficiency to the inner rib efficiency, A w is the solid wall heat transfer area, A g is the heat transfer area of the hot fluid, A c is the heat transfer area of the cold fluid, h g is the heat transfer coefficient of the thermal fluid, which can be derived from the Sieder-Tate experimental correlation formula, η is the total rib efficiency, and ψ is the conversion coefficient of the outer rib efficiency;

[0029] Step 3.15: Calculate the rib top temperature T rib_top :

[0030]

[0031] Where, t f Fluid temperature, t w is the solid wall temperature, ch is the symbol of the hyperbolic cosine function, and m·H is derived and calculated using the following formula:

[0032]

[0033] Where λ w,r is the average thermal conductivity of the ribs, in units of w / (m·K), b is the rib width, in units of m, and H is the rib height, in units of m;

[0034] Calculate the rib top temperature T when heat exchange occurs on both sides at the pre-distribution height rib_top , if the two rib top temperatures T rib_top If the difference between the two calculated values is greater than the set value, correct the rib height distribution and return to step 3.11 until the two calculated differences meet the set value.

[0035] Furthermore, in step 3, the heat exchange mode of the submodule is double-sided / single-phase flow heat exchange, and the specific calculation steps of the corresponding heat transfer calculation element are as follows:

[0036] Step 3.21. Calculate the heat transfer Q between the fluid and the solid wall f,w :

[0037] Q f,w =h f,w ·A f,w ·(t f -t w )

[0038] Where h f,w is the heat transfer coefficient, which can be derived from the Sieder-Tate experimental correlation formula;

[0039] Step 3.22: Calculate the heat transfer Q of the solid wall w :

[0040]

[0041] Step 3.23: Calculate the heat transfer Q of the cold and hot fluids f :

[0042] Q f =K·A f ·(t g -t c )

[0043] Where K is the total heat transfer coefficient between the cold and hot fluids. The K value is derived from the following formula:

[0044]

[0045] Where h c is the heat transfer coefficient of the cold fluid, which can be derived from the Sieder-Tate experimental correlation formula;

[0046] Step 3.24, calculate the rib top temperature Trib_top :

[0047]

[0048] In the formula, m·H is derived and calculated using the following formula:

[0049]

[0050] Where h f is the fluid heat transfer coefficient, which can be derived from the Sieder-Tate experimental correlation formula;

[0051] Calculate the rib top temperature T when heat exchange occurs on both sides at the pre-distribution height rib_top , if the two rib top temperatures T rib_top If the difference between the two calculated values is greater than the set value, correct the rib height distribution and return to step 3.21 until the two calculated differences meet the set value.

[0052] Furthermore, in step 3, the heat exchange mode of the submodule is single-side / two-phase heat exchange, and the specific calculation steps of the corresponding heat transfer calculation element are as follows:

[0053] Step 3.31: Calculate the two-phase heat transfer coefficient h at a given node in the two-phase flow region. tpf :

[0054] h tpf =X·h V +(1-X)·h L

[0055] Where: X is the dryness, calculated using the following formula:

[0056]

[0057] Step 3.32: Calculate the heat transfer Q between the fluid and the solid wall f,w :

[0058] Q f,w =h tpf ·A f,w ·(t f -t w );

[0059] Step 3.33: Calculate the heat transfer Q of the solid wall w :

[0060]

[0061] Step 3.34: Calculate the heat transfer Q of the cold and hot fluids f :

[0062] Q f =K·Af ·(t g -t c );

[0063] Where K is derived from the following formula:

[0064]

[0065] Furthermore, in step 3, the heat exchange mode of the submodule is single-side / single-phase heat exchange, and the specific calculation steps of the corresponding heat transfer calculation element are as follows:

[0066] Step 3.41. Calculate the heat transfer Q between the fluid and the solid wall f,w :

[0067] Q f,w =h f,w ·A f,w ·(t f -t w );

[0068] Step 3.42: Calculate the heat transfer Q of the solid wall w :

[0069]

[0070] Step 3.43: Calculate the heat transfer Q of the cold and hot fluids f :

[0071] Q f =K·A f ·(t g -t c )

[0072] Wherein, the K value is derived from the following formula:

[0073]

[0074] Furthermore, the step 1 is specifically as follows:

[0075] Step 1.1, obtaining the structure of each brazing component and the flow channel structure parameters of each milling groove part in the multi-layer nested brazing milling groove heat exchanger, and obtaining the flow organization form of the cold and hot fluids in the heat exchanger;

[0076] Step 1.2: Select one of the cold and hot fluids as the reference fluid. Based on the flow organization of the cold and hot fluids obtained in step 1.1, divide the multi-layer nested brazed milled groove heat exchanger into multiple submodules with a single flow direction in each milled groove layer to facilitate heat transfer calculation.

[0077] Step 1.3: In the submodules divided in step 1.2, establish heat transfer calculation micro-elements along the axial and radial directions of the multi-layer nested brazed milled groove heat exchanger;

[0078] Step 1.4: Based on the multiple heat transfer calculation elements established in step 1.3, construct an initial heat transfer calculation model.

[0079] Furthermore, in step 2, the parameters include inlet parameters of each calculation element in the multiple heat transfer calculation elements and outlet parameters of the last calculation element. The inlet parameters and outlet parameters include the type, flow rate, temperature, pressure, and physical property values of the hot and cold fluids. The calculation process of the temperature parameter in the outlet parameter is as follows:

[0080] The outlet temperature of the cold fluid is T c,e The calculation method is as follows:

[0081]

[0082] Where, T c,i is the inlet temperature of the cold fluid, T g,i is the inlet temperature of the thermal fluid;

[0083] The outlet temperature of the hot fluid T g,e The calculation method is as follows:

[0084]

[0085] Where m c is the flow rate of the cold fluid, C pc,e is the specific heat capacity of the cold fluid at the outlet temperature, m g is the flow rate of the thermal fluid, C pg,i is the specific heat capacity at the inlet temperature of the hot fluid, T c,e is the outlet temperature of the cold fluid, T c,i is the inlet temperature of the cold fluid.

[0086] Furthermore, h in step 3.11 V 、h L , h in step 3.14 g , h in step 3.21 f,w , h in step 3.23 c , h in step 3.24 f , the formula derived from the Sieder-Tate experimental correlation is as follows:

[0087]

[0088] Where, subscript x is any one of v, l, g, f, w, c, f, λ xis the thermal conductivity of the fluid, in units of w / (m·K), d is the equivalent diameter of the heat exchange channel, and Nu is the Nusselt number, which is n is a constant determined by experimental data and is calculated as 0.027, Re is the fluid Reynolds number, Pr is the fluid Prandtl number, ζ f is the dynamic viscosity of the fluid, in Pa·s, ζ w It is the dynamic viscosity of the fluid at the heat transfer wall temperature, in Pa·s.

[0089] Furthermore, the conversion coefficient ψ of the outer rib efficiency in step 3.14 is calculated using the following formula:

[0090]

[0091] Where N is the number of heat transfer elements on the heat transfer wall (assuming that the entire outer surface is distributed with the same milling groove structure as the heat transfer calculation module being calculated); N runner is the number of milling channels on the thermal wall (assuming that the entire outer surface is distributed with the same milling groove structure as the heat transfer calculation module being calculated); the subscripts "o" and "i" represent the outer surface and inner surface, respectively.

[0092] Furthermore, the total rib efficiency η in step 3.14 is calculated using the following formula:

[0093]

[0094] Where a is the width of the milling groove, unit is m, b is the rib width, unit is m, η rib is the rib efficiency, and the corresponding η g and η c , where η rib The value of is different, which is calculated using the following formula:

[0095]

[0096] In the formula, m is derived and calculated using the following formula:

[0097]

[0098] Beneficial effects of the present invention:

[0099] 1. The present invention provides a method for constructing a heat transfer calculation model for a multi-layer nested brazed milled groove heat exchanger. This method takes into account the structural and fluid characteristics of the multi-layer nested brazed milled groove heat exchanger to construct a heat transfer calculation model, thereby improving the accuracy of the heat transfer calculation and reducing the heat transfer calculation cycle.

[0100] 2. The present invention provides a method for constructing a heat transfer calculation model for a multi-layer nested brazed milled groove heat exchanger, which improves the accuracy of heat transfer calculations during phase change heat transfer by optimizing the two-phase flow heat transfer coefficient;

[0101] 3. The present invention provides a method for constructing a heat transfer calculation model for a multi-layer nested brazed milled groove heat exchanger. By calculating the rib top temperature and optimizing the rib height, the accuracy of heat transfer calculations during bilateral heat exchange is improved.

[0102] 4. The present invention provides a method for constructing a heat transfer calculation model for a multi-layer nested brazed milled groove heat exchanger, which correctly converts the efficiency of the ribs on both sides into the heat transfer calculation element, thereby improving the accuracy of the heat transfer calculation.

[0103] 5. The present invention provides a method for constructing a heat transfer calculation model for a multi-layer nested brazed milled groove heat exchanger, which accelerates convergence by formulating a suitable calculation process and iterative method, thereby reducing the heat transfer calculation cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0104] Figure 1 This is a simplified structural diagram of a multi-layer nested brazed milled groove heat exchanger in an embodiment of a method for constructing a heat transfer calculation model of a multi-layer nested brazed milled groove heat exchanger according to the present invention;

[0105] Figure 2 This is a schematic diagram of a double-sided heat exchange submodule model using the cold fluid as the reference fluid, after dividing the multi-layer nested brazed milled slot heat exchanger into multiple submodules in step 2 of an embodiment of the present invention;

[0106] Figure 3 This is a flow chart of an embodiment of a method for constructing a heat transfer calculation model for a multi-layer nested brazed milled groove heat exchanger according to an embodiment of the present invention;

[0107] The following are the descriptions of the reference numerals:

[0108] 1- pressurized medium channel, 2- gas channel, 3- cold fluid, 4- hot fluid, 5- brazing assembly. DETAILED DESCRIPTION

[0109] The present invention will be further described below with reference to the accompanying drawings and exemplary embodiments.

[0110] The schematic diagram of the milling groove heat exchanger is as follows Figure 1As shown, the heat exchange assembly is the main heat exchange component of the heat exchanger. It is made of two cylinders with milled grooves on the outer wall, brazed together. One of the cold and hot fluids is selected as the reference fluid, and the other is the heat exchange fluid. In this embodiment, the cold fluid is used as the reference fluid and the hot fluid is used as the heat exchange fluid. The cold and hot fluids flow in the pressurized medium channel 1 and the gas channel 2 respectively. The cold fluid may flow in one direction or reciprocatingly in the same heat exchange assembly, and the hot fluid may also flow in the same direction. Figure 1 The cold fluid in the middle heat exchange component is heat exchanged on both sides, and the hot fluid is heat exchanged on one side. If another heat exchange component is added, the hot fluid between the two heat exchange components is also heat exchanged on both sides.

[0111] Take any complete pressurized medium heat exchange channel 1 (flow channel + half of the rib width 5 on both sides) and the corresponding gas channels 2 on the inner and outer sides as the heat exchange microelement section, and establish a heat transfer microelement physical model along the flow direction, as shown in the following example: Figure 2 As shown; when the heat exchanger is working, the hot fluid 3 in the pressurized medium channel 1 and the cold fluid 4 in the gas channels 2 on both sides simultaneously exchange heat.

[0112] This embodiment proposes a method for constructing a heat transfer calculation model for a multi-layer nested brazed milled groove heat exchanger. The heat transfer calculation model is established for the complex fluid flow and heat exchange process inside the heat exchanger:

[0113] A method for constructing a heat transfer calculation model for a multi-layer nested brazed milled groove heat exchanger comprises the following steps:

[0114] Step 1: According to the structure of each brazing component and the flow channel structural parameters of each milling groove part, the flow organization form of the cold and hot fluids is obtained. The flow channel structural parameters include: determining the flow channel layout of each layer of milling groove parts, the structural parameters of the rib / groove structure, and the circumferential relative position of each milling groove layer.

[0115] Step 2: Use the cold fluid as the reference fluid and the hot fluid as the heat exchange fluid, and obtain the flow organization forms of the cold and hot fluids according to step 1. Divide the multi-layer nested brazed milled groove heat exchanger into multiple sub-modules that are convenient for heat transfer calculations, and each milled groove layer has a single flow direction.

[0116] Step 3: Within the submodules divided in Step 2, establish heat transfer calculation elements along the axial and radial directions of the multi-layer nested brazed milled groove heat exchanger. The specific establishment process is as follows: number each fluid layer along the radial direction of the heat exchanger, and divide the heat exchanger into multiple equidistant or unequally spaced one-dimensional heat transfer calculation nodes along the axial direction of the heat exchanger and number them. At this point, each heat transfer calculation module is divided into multiple continuous heat transfer calculation elements. The fluid layers of each element can be identified by a two-dimensional array consisting of fluid layer numbers and calculation node numbers, which facilitates heat transfer calculations for the calculation elements and data transmission between calculation elements. In principle, the more axial nodes, the more accurate the calculation results, but the corresponding computational workload also increases significantly.

[0117] Step 4: Establish an initial heat transfer calculation model based on the heat transfer calculation element established in step 3.

[0118] Step 5: Initialize the parameters of the initial heat transfer calculation model;

[0119] Initialize the heat transfer calculation model established in step 4. The initialization parameters (inlet parameters) on each calculation element include the type, flow rate, temperature, pressure, and physical property values of the hot and cold fluids.

[0120] Without loss of generality, assume that the outlet temperature of the cold fluid is T c,e , which is calculated as follows:

[0121]

[0122] Where T is the temperature of the fluid in K, subscript c represents the cold fluid, subscript g represents the hot fluid, subscript i represents the inlet temperature of the calculation element, subscript e represents the outlet temperature of the calculation element, T c,i is the inlet temperature of the cold fluid, T g,i is the inlet temperature of the thermal fluid;

[0123] The outlet temperature of the heat transfer fluid is T g,e The calculation method is as follows:

[0124]

[0125] Where m c is the flow rate of the cold fluid, m g is the flow rate of the thermal fluid, in kg / s, C pc,e is the specific heat capacity of the cold fluid at the outlet temperature, C pg,e is the specific heat capacity at the outlet temperature of the hot fluid, in kJ / s, T c,e is the outlet temperature of the cold fluid, T c,i is the inlet temperature of the cold fluid;

[0126] The initial outlet temperatures of the cold and hot fluids of each calculation element are preset to be T c,e and T g,e The initial outlet pressure of each calculation element can be preset to the inlet pressure value, and the heat transfer value of each calculation element is preset to 0. For brazed components with double-sided heat exchange, there is a minimum or maximum temperature point at the height of the interlayer ribs. The rib heights on both sides of this point belong to the heat exchange walls on both sides, and the initial height preset value is half the rib height.

[0127] Under steady-state heat transfer conditions, heat transfer from hot fluid to cold fluid undergoes three processes and the heat transfer amount Q is equal, namely:

[0128] Q=Q g，w =Q w =Q c，w

[0129] Where, the subscript "w" represents the heat exchange wall, Q g，w is the convective heat transfer between the hot fluid and the solid wall, Q w Q is the heat transfer from the hot fluid side to the cold fluid side of the solid wall; c，w It is the convective heat transfer between the solid wall and the cold fluid.

[0130] Step 6: Determine whether the heat transfer mode of each calculation element in the heat transfer calculation model is unilateral heat transfer or bilateral heat transfer with the reference fluid as the research object. If it is unilateral heat transfer, execute step 7; if it is bilateral heat transfer, execute step 10.

[0131] Step 7: Determine whether each calculation element in the heat transfer calculation model is single-phase heat exchange or two-phase heat exchange. If it is single-phase heat exchange, execute step 8; if it is two-phase heat exchange, execute step 9;

[0132] Step 8: Single-side / single-phase heat flow calculation;

[0133] Step 8.1. Calculate the heat transfer Q between the fluid and the solid wall f,w :

[0134] Q f,w =h f,w ·A f,w ·(t f -t w )

[0135] Where, subscript w represents the heat exchange wall, f represents the fluid, and t f is the fluid temperature, t w is the solid wall temperature; A f,w is the heat exchange area between the fluid and the solid wall, in m 2 , h f,w is the heat transfer coefficient between fluid and solid wall, unit is w / (m 2K), derived and calculated from the Sieder-Tate experimental correlation:

[0136]

[0137] Where λ f,w is the thermal conductivity of the fluid, in units of w / (m·K), d is the equivalent diameter of the heat exchange channel, and Nu is the Nusselt number, which is n is a constant determined by experimental data and is calculated as 0.027, Re is the fluid Reynolds number, Pr is the fluid Prandtl number, ζ f is the dynamic viscosity of the fluid, unit: Pa·s, ζ w is the dynamic viscosity of the fluid at the heat exchange wall temperature, unit: Pa·s;

[0138] Step 8.2: Calculate the heat transfer Q of the solid wall w :

[0139]

[0140] Where, δ w is the thickness of the heat exchange wall, unit: m, λ w is the average thermal conductivity of the solid wall, A w is the heat conduction area of the solid wall, in m 2 , t w.g is the solid wall temperature on the hot fluid side, t w.c is the solid wall temperature on the cold fluid side, subscript c represents the cold fluid, and subscript g represents the hot fluid;

[0141] Step 8.3: Calculate the heat transfer Q of the cold and hot fluids f :

[0142] Q f =K·A f ·(t g -t c )

[0143] Where A f is the fluid heat transfer surface area, unit: m 2 , t g is the temperature of the hot fluid, t c is the temperature of the cold fluid, K is the total heat transfer coefficient between the cold and hot fluids, and the K value is derived from the following formula:

[0144]

[0145] Where, δ w is the thickness of the heat exchange wall, in m, λ wis the thermal conductivity of the heat exchange wall, w / (m·K), η is the total rib efficiency, ξ is the conversion coefficient of the outer rib efficiency to the inner rib efficiency, A w is the solid wall heat transfer area, A g is the heat transfer area of the hot fluid, A c is the heat transfer area of the cold fluid, h g is the heat transfer coefficient of the thermal fluid, h c is the heat transfer coefficient of the cold fluid, ψ is the conversion coefficient of the outer rib efficiency, and is calculated using the following formula:

[0146]

[0147] Where N is the number of heat transfer elements on the heat transfer wall (assuming that the entire outer surface is distributed with the same milling groove structure as the heat transfer calculation module being calculated); N runner is the number of milling channels on the thermal wall (assuming that the entire outer surface is distributed with the same milling groove structure as the heat transfer calculation module being calculated); the subscripts "o" and "i" represent the outer surface and inner surface, respectively;

[0148] For the milled groove heat transfer structure described in this article, the influence of ribs on heat transfer must also be considered. The influence on heat transfer can be expressed by the total rib efficiency. This is not a general example of rectangular ribs. Other rib structures are treated with corresponding methods: the total heat transfer coefficient K between the hot and cold fluids is derived using the formula η g and η c Use the following formula to calculate, for η g and η c , where η r The values of are different:

[0149]

[0150] Where a is the width of the milling groove, unit is m, b is the rib width, unit is m, H is the rib height, unit is m, η rib is the rib efficiency, which is calculated using the following formula:

[0151]

[0152] In the formula, m is derived and calculated using the following formula:

[0153]

[0154] In the above formula, λ w,r is the average thermal conductivity of the ribs, unit is w / (m·K), h f Fluid heat transfer coefficient;

[0155] Step 9: One-side / two-phase heat transfer calculation;

[0156] For heat transfer processes with phase change, due to the complexity of two-phase flow heat transfer and influencing factors, if there is no experimental correlation formula with the same or similar experimental conditions available, a simplified algorithm can be used for calculation. Since the length of the two-phase flow heat transfer zone is relatively short, it will not introduce large calculation errors. The present invention adopts a simplified two-phase flow zone convective heat transfer solution method: the Sieder-Tate experimental correlation formula is used to calculate the convective heat transfer coefficient at the liquid saturation state and the gas saturation state at both ends of the two-phase flow. The convective heat transfer coefficient at a given point in the two-phase flow region is the weighted value of the dryness X at that point and the convective heat transfer coefficient at both ends, where the dryness is calculated using the following formula:

[0157]

[0158] Where: E is the enthalpy value, subscript L is the enthalpy value of the liquid saturation state at a given pressure and temperature, subscript V is the enthalpy value of the gas saturation point at a given pressure and temperature, E c is the enthalpy of the two-phase flow point at the calculation node;

[0159] The two-phase heat transfer coefficient h at a given node in the two-phase flow region tpf Use the following formula to calculate:

[0160] h tpf =X·h V +(1-X)·h L

[0161] Where: subscript tpf represents the two-phase flow point; h V is the gas heat transfer coefficient, h L is the liquid heat transfer coefficient, both of which can be derived through the Sieder-Tate experimental correlation formula;

[0162] Step 9.1. Calculate the heat transfer between the fluid and the solid wall:

[0163] Q f,w =h tpf ·A f,w ·(t f -t w )

[0164] Where A f,w is the heat exchange area between the fluid and the solid wall, in m 2 , t f is the fluid temperature, t w is the solid wall temperature; the subscript w represents the solid wall, and f represents the fluid;

[0165] Step 9.2: Calculate the heat transfer of the solid wall:

[0166]

[0167] Where, δw is the thickness of the heat exchange wall, in m, λ w is the average thermal conductivity of the solid wall, unit is w / (m·K), A w is the heat conduction area of the solid wall, in m 2 , t w.g is the temperature of the hot fluid side wall, t w.c is the temperature of the cold fluid side wall;

[0168] Step 9.3, calculate the heat transfer of cold and hot fluids:

[0169] Q f =K·A f ·(t g -t c )

[0170] Where A f is the fluid heat transfer area, unit: m 2 , t g is the temperature of the hot fluid, t c is the temperature of the cold fluid, K is the total heat transfer coefficient between the cold and hot fluids, and K is derived from the following formula:

[0171]

[0172] Where: δ w is the thickness of the heat exchange wall, in m, λ w is the thermal conductivity of the heat exchange wall, unit is w / (m·K), η is the total rib efficiency, ξ is the conversion coefficient of the outer rib efficiency to the inner rib efficiency, A w is the solid wall heat transfer area, A g is the heat transfer area of the hot fluid, A c is the heat transfer area of the cold fluid, h g is the heat transfer coefficient of the thermal fluid, which can be derived from the Sieder-Tate experimental correlation formula, ψ, η g , η c The derivation process is the same as that in step 8.3;

[0173] Step 10: Determine whether each calculation element in the heat transfer calculation model is a single-phase flow heat exchange. If it is a single-phase flow heat exchange, execute step 11; if it is a two-phase flow heat exchange, execute step 12;

[0174] Step 11: Calculate double-sided / single-phase heat flow;

[0175] Step 11.1. Calculate the heat transfer Q between the fluid and the solid wall f,w :

[0176] Q f,w =h f,w ·A f,w·(t f -t w )

[0177] Where h f,w is the heat transfer coefficient between the fluid and the solid wall, which can be derived from the Sieder-Tate experimental correlation formula;

[0178] Step 11.2: Calculate the heat transfer Q of the solid wall w :

[0179]

[0180] Step 11.3. Calculate the heat transfer Q of the cold and hot fluids f :

[0181] Q f =K·A f ·(t g -t c )

[0182] Where K is the total heat transfer coefficient between the cold and hot fluids. The K value is derived from the following formula:

[0183]

[0184] Where h c is the heat transfer coefficient of the cold fluid, which can be derived from the Sieder-Tate experimental correlation formula;

[0185] Step 11.4: Determine whether the top temperatures of the ribs of the heat exchange interlayers on both sides of the brazing assembly are equal;

[0186] In this example, when calculating the double-sided heat exchange, the height of the sandwich ribs belonging to the heat exchange wall on both sides is different at each node. The distribution of the sandwich rib height on both sides requires repeated iterative calculations. First, calculate the rib top temperature T when the heat exchange is carried out on both sides at the pre-distributed height. rib_top If the two temperatures are not equal, the rib height distribution is corrected and recalculated until the difference between the two calculations meets the set value. The rib top temperature T rib_top The calculation formula is as follows:

[0187]

[0188] Where, t f Fluid temperature, t w is the solid wall temperature, and m is derived and calculated using the following formula:

[0189]

[0190] In the above formula, λ w,r is the average thermal conductivity of the ribs, unit is w / (m·K), hf Convective heat transfer coefficient;

[0191] Calculate the rib top temperature T when heat exchange occurs on both sides at the pre-distribution height rib_top , if the two rib top temperatures T rib_top If the difference between the two calculated values is greater than the set value, correct the rib height distribution and return to step 11.1 until the two calculated differences meet the set value.

[0192] Step 12: Double-sided / two-phase heat transfer calculation;

[0193] Step 12.1. Calculate the two-phase heat transfer coefficient h at a given node in the two-phase flow region. tpf :

[0194] h tpf =X·h V +(1-X)·h L

[0195] Where: subscript tpf represents the two-phase flow point; h V is the gas heat transfer coefficient, h L is the liquid heat transfer coefficient, both of which can be derived through the Sieder-Tate experimental correlation formula; X is the dryness, which is calculated using the following formula:

[0196]

[0197] Where: E is the enthalpy value, subscript L is the enthalpy value of the liquid saturation state at a given pressure and temperature, subscript V is the enthalpy value of the gas saturation point at a given pressure and temperature, E c is the enthalpy of the two-phase flow point at the calculation node;

[0198] Step 12.2: Calculate the heat transfer Q between the fluid and the solid wall f,w :

[0199] Q f,w =h tpf ·A f,w ·(t f -t w )

[0200] Where A f,w is the heat exchange area between the fluid and the solid wall, in m 2 , t f is the fluid temperature, t w is the solid wall temperature; the subscript w represents the solid wall, and f represents the fluid;

[0201] Step 12.3. Calculate the heat transfer Q of the solid wall w :

[0202]

[0203] Where, δ w is the thickness of the heat exchange wall, in m, λ w is the average thermal conductivity of the solid wall, unit is w / (m·K), A w is the heat conduction area of the solid wall, in m 2 , t w.g is the solid wall temperature on the hot fluid side, t w.c is the solid wall temperature on the cold fluid side, subscript c represents the cold fluid, and subscript g represents the hot fluid;

[0204] Step 12.4: Calculate the heat transfer Q of the cold and hot fluids f :

[0205] Q f =K·A f ·(t g -t c )

[0206] Where A f is the fluid heat transfer area, unit: m 2 , t g is the temperature of the hot fluid, t c is the temperature of the cold fluid, K is the total heat transfer coefficient between the cold and hot fluids, and K is derived from the following formula:

[0207]

[0208] Where: δ w is the thickness of the heat exchange wall, in m, λ w is the thermal conductivity of the heat exchange wall, unit is w / (m·K), ξ is the conversion coefficient of the outer rib efficiency to the inner rib efficiency, A w is the solid wall heat transfer area, A g is the heat transfer area of the hot fluid, A c is the heat transfer area of the cold fluid, h g is the heat transfer coefficient of the thermal fluid, which can be derived from the Sieder-Tate experimental correlation formula, η is the total rib efficiency, and ψ is the conversion coefficient of the outer rib efficiency;

[0209] Step 12.5: Calculate the rib top temperature T rib_top :

[0210]

[0211] Where, t f Fluid temperature, t w is the solid wall temperature, ch is the symbol of the hyperbolic cosine function, and m·H is derived and calculated using the following formula:

[0212]

[0213] Where λ w,r is the average thermal conductivity of the ribs, in units of w / (m·K), b is the rib width, in units of m, and H is the rib height, in units of m;

[0214] Calculate the rib top temperature T when heat exchange occurs on both sides at the pre-distribution height rib_top , if the two rib top temperatures T rib_top If the difference between the two calculated values is greater than the set value, the rib height distribution is corrected and the process returns to step 12.1 until the two calculated differences meet the set value.

[0215] Step 13: Determine whether all calculation elements of the heat transfer calculation model have been calculated. If not, continue the calculation until all calculation elements are calculated. If all calculation elements are calculated, execute step 14.

[0216] Step 14: Determine whether the calculated heat transfer values meet the convergence requirements. If so, the calculation is completed. If not, for single-phase flow scenarios, optimize the heat transfer coefficient and other related calculation parameters, and re-iterate the calculation. For two-phase flow scenarios, optimize the heat transfer coefficient, rib top temperature and other related calculation parameters, and re-iterate the calculation.

[0217] The iterative process is as follows:

[0218] Starting from the reference fluid inlet point, the calculation calculates the outlet temperature, pressure, heat transfer capacity, wall temperature, rib height distribution, and other parameters of the cold and hot fluids at the first calculation element based on their flow rate, temperature, and pressure. These outlet parameters are then used as the inlet parameters for the next calculation element, progressing point by point to complete a round of heat transfer calculations for the entire heat exchanger. Within each calculation round, different heat transfer calculation methods are used based on the flow organization of the cold and hot fluids within the heat transfer calculation module corresponding to each calculation element, the structure of each brazed component, and the flow channel structure of each milled groove part.

[0219] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for constructing a heat transfer calculation model for a multi-layer nested brazed milled groove heat exchanger, characterized in that: The following steps are involved: Step 1: Divide the heat exchanger into multiple submodules according to a predetermined division rule, construct a heat transfer calculation element for each submodule, and construct an initial heat transfer calculation model based on the heat transfer calculation element; Step 2: Initializing parameters of the initial heat transfer calculation model; Step 3: Based on the heat transfer calculation model after parameter initialization, according to the different heat exchange modes of the submodules, corresponding heat transfer calculation micro-element is used to calculate and obtain the heat exchange capacity of the heat exchanger; Step 4: Iteratively calculate the heat transfer rate of the heat exchanger and determine whether the difference between the heat transfer rate obtained in each round of iteration and the heat transfer rate before the current round of iteration meets the convergence requirements. If so, the heat transfer calculation model of the multi-layer nested brazed milled groove heat exchanger is constructed. If not, optimize the heat transfer calculation model parameters and perform a new round of iteration until the difference meets the convergence requirements, completing the construction of the heat transfer calculation model of the multi-layer nested brazed milled groove heat exchanger.

2. The method for constructing a heat transfer calculation model of a multi-layer nested brazed milled groove heat exchanger according to claim 1, characterized in that: In step 3, the heat exchange mode of the submodule is two-sided / two-phase flow heat exchange, and the specific calculation steps of the corresponding heat transfer calculation element are as follows: Step 3.11: Calculate the two-phase heat transfer coefficient h at a given node in the two-phase flow region. tpf : h tpf =X·h V +(1-X)·h L Where: subscript tpf represents the two-phase flow point; h V is the gas heat transfer coefficient, h L is the liquid heat transfer coefficient, both of which can be derived through the Sieder-Tate experimental correlation formula; X is the dryness, which is calculated using the following formula: Where: E is the enthalpy value, subscript L is the enthalpy value of the liquid saturation state at a given pressure and temperature, subscript V is the enthalpy value of the gas saturation point at a given pressure and temperature, E c is the enthalpy of the two-phase flow point at the calculation node; Step 3.12: Calculate the heat transfer Q between the fluid and the solid wall f,w : Q f,w =h tpf ·A f,w ·(t f -t w ) Where A f,w is the heat exchange area between the fluid and the solid wall, in m 2 , t f is the fluid temperature, t w is the solid wall temperature; the subscript w represents the solid wall, and f represents the fluid; Step 3.13: Calculate the heat transfer Q of the solid wall w : Where, δ w is the thickness of the heat exchange wall, in m, λ w is the average thermal conductivity of the solid wall, unit is w / (m·K), A w is the heat conduction area of the solid wall, in m 2 , t w.g is the solid wall temperature on the hot fluid side, t w.c is the solid wall temperature on the cold fluid side, subscript c represents the cold fluid, and subscript g represents the hot fluid; Step 3.14: Calculate the heat transfer Q of the cold and hot fluids f : Q f =K·A f ·(t g -t c ) Where A f is the fluid heat transfer area, unit: m 2 , t g is the temperature of the hot fluid, t c is the temperature of the cold fluid, K is the total heat transfer coefficient between the cold and hot fluids, and K is derived from the following formula: Where: δ w is the thickness of the heat exchange wall, in m, λ w is the thermal conductivity of the heat exchange wall, unit is w / (m·K), ξ is the conversion coefficient of the outer rib efficiency to the inner rib efficiency, A w is the solid wall heat transfer area, A g is the heat transfer area of the hot fluid, A c is the heat transfer area of the cold fluid, h g is the heat transfer coefficient of the thermal fluid, which can be derived from the Sieder-Tate experimental correlation formula, η is the total rib efficiency, and ψ is the conversion coefficient of the outer rib efficiency; Step 3.15: Calculate the rib top temperature T rib_top : Where, t f Fluid temperature, t w is the solid wall temperature, ch is the symbol of the hyperbolic cosine function, and m·H is derived and calculated using the following formula: Where λ w,r is the average thermal conductivity of the ribs, in units of w / (m·K), b is the rib width, in units of m, and H is the rib height, in units of m; Calculate the rib top temperature T when heat exchange occurs on both sides at the pre-distribution height rib_top , if the two rib top temperatures T rib_top If the difference between the two calculated values is greater than the set value, correct the rib height distribution and return to step 3.11 until the two calculated differences meet the set value.

3. The method for constructing a heat transfer calculation model of a multi-layer nested brazed milled groove heat exchanger according to claim 1, characterized in that: In step 3, the heat exchange mode of the submodule is double-sided / single-phase flow heat exchange, and the specific calculation steps of the corresponding heat transfer calculation element are as follows: Step 3.

21. Calculate the heat transfer Q between the fluid and the solid wall f,w : Q f,w =h f,w ·A f,w ·(t f -t w ) Where h f,w is the heat transfer coefficient between the fluid and the solid wall, which can be derived from the Sieder-Tate experimental correlation formula; Step 3.22: Calculate the heat transfer Q of the solid wall w : Step 3.23: Calculate the heat transfer Q of the cold and hot fluids f : Q f =K·A f ·(t g -t c ) Where K is the total heat transfer coefficient between the cold and hot fluids. The K value is derived from the following formula: Where h c is the heat transfer coefficient of the cold fluid, which can be derived from the Sieder-Tate experimental correlation formula; Step 3.24, calculate the rib top temperature T rib_top : In the formula, m·H is derived and calculated using the following formula: Where h f is the fluid heat transfer coefficient, which can be derived from the Sieder-Tate experimental correlation formula; Calculate the rib top temperature T when heat exchange occurs on both sides at the pre-distribution height rib_top , if the two rib top temperatures T rib_top If the difference between the two calculated values is greater than the set value, correct the rib height distribution and return to step 3.21 until the two calculated differences meet the set value.

4. The method for constructing a heat transfer calculation model of a multi-layer nested brazed milled groove heat exchanger according to claim 1, characterized in that: In step 3, the heat exchange mode of the submodule is one-side / two-phase heat exchange, and the specific calculation steps of the corresponding heat transfer calculation element are as follows: Step 3.31: Calculate the two-phase heat transfer coefficient h at a given node in the two-phase flow region. tpf : h tpf =X·h V +(1-X)·h L Where: X is the dryness, calculated using the following formula: Step 3.32: Calculate the heat transfer Q between the fluid and the solid wall f,w : Q f,w =h tpf ·A f,w ·(t f -t w ); Step 3.33: Calculate the heat transfer Q of the solid wall w : Step 3.34: Calculate the heat transfer Q of the cold and hot fluids f : Q f =K·A f ·(t g -t c ); Where K is derived from the following formula:

5. The method for constructing a heat transfer calculation model of a multi-layer nested brazed milled groove heat exchanger according to claim 1, characterized in that: In step 3, the heat exchange mode of the submodule is single-side / single-phase heat exchange, and the specific calculation steps of the corresponding heat transfer calculation element are as follows: Step 3.

41. Calculate the heat transfer Q between the fluid and the solid wall f,w : Q f,w =h f,w ·A f,w ·(t f -t w ); Step 3.42: Calculate the heat transfer Q of the solid wall w : Step 3.43: Calculate the heat transfer Q of the cold and hot fluids f : Q f =K·A f ·(t g -t c ) Wherein, the K value is derived from the following formula:

6. The method for constructing a heat transfer calculation model of a multi-layer nested brazed milled groove heat exchanger according to claim 1, characterized in that: The step 1 is specifically as follows: Step 1.1, obtaining the structure of each brazing component and the flow channel structure parameters of each milling groove part in the multi-layer nested brazing milling groove heat exchanger, and obtaining the flow organization form of the cold and hot fluids in the heat exchanger; Step 1.2: Select one of the cold and hot fluids as the reference fluid. Based on the flow organization of the cold and hot fluids obtained in step 1.1, divide the multi-layer nested brazed milled groove heat exchanger into multiple submodules with a single flow direction in each milled groove layer to facilitate heat transfer calculation. Step 1.3: In the submodules divided in step 1.2, establish heat transfer calculation micro-elements along the axial and radial directions of the multi-layer nested brazed milled groove heat exchanger; Step 1.4: Based on the multiple heat transfer calculation elements established in step 1.3, construct an initial heat transfer calculation model.

7. The method for constructing a heat transfer calculation model for a multi-layer nested brazed milled groove heat exchanger according to claim 1, characterized in that: In step 2, the parameters include the initial values preset for each heat transfer calculation element and the outlet parameters of the last calculation element. The inlet and outlet parameters include the type, flow rate, temperature, and pressure of the hot and cold fluids. The temperature parameter in the outlet parameters of the last calculation element is calculated as follows: The outlet temperature of the cold fluid is T c,e The calculation method is as follows: Where, T c,i is the inlet temperature of the cold fluid, T g,i is the inlet temperature of the thermal fluid; The outlet temperature of the hot fluid T g,e The calculation method is as follows: Where m c is the flow rate of the cold fluid, C pc,e is the specific heat capacity of the cold fluid at the outlet temperature, m g is the flow rate of the thermal fluid, C pg,i is the specific heat capacity at the inlet temperature of the hot fluid, T c,e is the outlet temperature of the cold fluid, T c,i is the inlet temperature of the cold fluid.

8. The method for constructing a heat transfer calculation model for a multi-layer nested brazed milled groove heat exchanger according to claim 2 or 3, characterized in that: h in step 3.11 V 、h L , h in step 3.14 g , h in step 3.21 f,w , h in step 3.23 c , h in step 3.24 f , the formula derived from the Sieder-Tate experimental correlation is as follows: Where, subscript x is any one of v, l, g, f, w, c, f, λ x is the thermal conductivity of the fluid, in units of w / (m·K), d is the equivalent diameter of the heat exchange channel, and Nu is the Nusselt number, which is n is a constant determined by experimental data and is calculated as 0.027, Re is the fluid Reynolds number, Pr is the fluid Prandtl number, ζ f is the dynamic viscosity of the fluid, in Pa·s, ζ w It is the dynamic viscosity of the fluid at the heat transfer wall temperature, in Pa·s.

9. The method for constructing a heat transfer calculation model for a multi-layer nested brazed milled groove heat exchanger according to claim 2, characterized in that: The conversion coefficient ψ of the outer rib efficiency in step 3.14 is calculated using the following formula: Where N is the number of heat transfer elements on the heat transfer wall (assuming that the entire outer surface is distributed with the same milling groove structure as the heat transfer calculation module being calculated); N runner is the number of milling channels on the thermal wall (assuming that the entire outer surface is distributed with the same milling groove structure as the heat transfer calculation module being calculated); the subscripts "o" and "i" represent the outer surface and inner surface, respectively.

10. The method for constructing a heat transfer calculation model of a multi-layer nested brazed milled groove heat exchanger according to claim 9, characterized in that: The total rib efficiency η in step 3.14 is calculated using the following formula: Where a is the width of the milling groove, unit is m, b is the rib width, unit is m, η rib is the rib efficiency, and the corresponding η g and η c , where η rib The value of is different, which is calculated using the following formula: In the formula, m is derived and calculated using the following formula:

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