A design method for a highly compact integrated radiator of a diesel generator set

Abstract

The invention discloses a design method for a highly compact integrated radiator of a diesel generator set, which belongs to the technical field of engines and comprises the following steps: step 1, calculating the heat capacity flow rate of each heat fluid; step 2, calculating the optimal allocation ratio of the heat dissipation area on the hot and cold sides of each heat fluid heat dissipation module; step 3, calculating the thermal resistance demand coefficient; step 4, multiplying the heat capacity flow rate of the heat fluid, the optimal allocation ratio of the heat dissipation area on the hot and cold sides, and the thermal resistance demand coefficient to calculate the heat exchange matching judgment parameter of each heat fluid heat dissipation module; step 5, determining the series-parallel state of each heat fluid heat dissipation module according to the heat exchange matching judgment parameter; step 6, arranging the cooling sequence of each heat fluid heat dissipation module connected in series, and distributing the cooling air volume of each heat fluid heat dissipation module connected in series; step 7, obtaining the final highly compact integrated radiator through the series-parallel selection of each heat fluid heat dissipation module in steps 1-6 and the distribution of the cooling air volume.

Description

Technical Field

[0001] The invention belongs to the technical field of engines, and in particular relates to a design method for a highly compact integrated radiator of a diesel generator set. Background Art

[0002] As the power of diesel engines continues to increase, the heat dissipation power increases synchronously, and the volume of the radiator increases accordingly. Data show that as the heat dissipation power increases, the heat dissipation area required for each kW of heat dissipation power rises sharply from 0.2㎡ to 0.7㎡, becoming the main factor limiting the improvement of the volume power density of high-power diesel engines.

[0003] Diesel-powered generator sets have the advantages of low fuel consumption and high compactness. There are many heat fluxes that need to be cooled, including engine boost air, lubricating oil, coolant, and generator cooling oil. The integrated radiator collects the heat fluxes and centrally cools them, which can effectively reduce the total volume of the radiator. However, the integrated radiator has design difficulties such as high heat flux density, multiple working media, wide flow span, and strong volume constraints, making it very challenging to achieve miniaturization.

[0004] Increasing the heat transfer temperature difference can reduce the heat dissipation area. However, the cooling medium flow is limited, and the temperature rise after absorbing heat is high, which cannot produce a sufficiently large heat transfer temperature difference with the heat flow medium. Connecting the heat dissipation modules of some heat flow mediums in series can increase the allocated cooling medium flow rate. Reasonable design of the series and parallel scheme of each heat dissipation module can increase the overall heat transfer temperature difference, reduce the required total heat dissipation area, and reduce the total volume of the radiator. The series-parallel design has become the core technology of highly compact integrated radiators. The traditional method lacks design criteria and relies on manual experience to determine the series-parallel design scheme, resulting in redundant design of the heat dissipation area of ​​some modules or substandard heat dissipation capacity, making the total volume of the radiator too large or the reflux temperature of some heat flow mediums exceeding the limit, causing the contradiction between high power and high power density of diesel generator sets. Summary of the invention

[0005] The purpose of the present invention is to provide a highly compact integrated radiator design method for a diesel generator set, so as to solve the problem that the conventional series-parallel scheme of integrated radiators designed by relying on experience in the prior art lacks design criteria, resulting in an excessively large total volume of the radiator, thus causing a contradiction between high power and high power density of the diesel generator set.

[0006] To achieve the above object, the present invention provides a method for designing a highly compact integrated radiator for a diesel generator set, comprising the following steps:

[0007] Step 1: Calculate the heat capacity flow rate C of each heat flow medium m ;

[0008] Step 2: Calculate the optimal distribution ratio α of the heat dissipation area on the hot and cold sides of each heat fluid heat dissipation module A ;

[0009] Step 3: Calculate the thermal resistance requirement coefficient R r ;

[0010] Step 4: The heat capacity flow rate C of the heat flow medium m , optimal distribution ratio of heat dissipation area on hot and cold sides α A , Thermal resistance requirement coefficient R r Multiply and calculate the heat exchange matching judgment parameter K of each heat fluid cooling module;

[0011] Step 5: Determine the series-parallel state of each heat-fluid cooling module according to the heat exchange matching judgment parameter K;

[0012] Step 6: Arrange the cooling sequence of each heat-fluid heat-dissipating module connected in series, and distribute the cooling air volume of each heat-fluid heat-dissipating module connected in series;

[0013] Step 7: Obtain a final highly compact integrated heat sink by selecting the series and parallel connections of the heat flux cooling modules in steps 1 to 6 and distributing the cooling air volume.

[0014] Preferably, in step 1, the heat capacity flow rate C of each heat flow medium is calculated m The specific expression is as follows:

[0015] C m =ρ*Q v *C p

[0016] Among them, C m is the heat capacity flow rate of the heat flux medium, in kW / K; ρ is the density of the heat flux medium, in kg / m 3 ;Q v is the volume flow rate of the heat working fluid, in m 3 / s;C p It is the specific heat capacity of the heat fluid at constant pressure, and its unit is kJ / (kg*K).

[0017] Preferably, in step 2, the optimal allocation ratio α of the heat dissipation area of ​​the hot and cold sides of each heat fluid heat dissipation module is calculated. A The specific expression is as follows:

[0018]

[0019] Among them, α A h is the optimal distribution ratio of the heat dissipation area on the hot and cold sides, dimensionless, defined as the ratio of the heat dissipation surface area on the hot flow side to the heat dissipation surface area on the cold flow side; h is the heat transfer coefficient, h c It is the cold transfer heat coefficient, and its unit is kW / (㎡*K). Its value is a design value related to the fin configuration and channel size. At this time, it can be estimated and determined based on empirical data.

[0020] Preferably, in step 3, the thermal resistance requirement coefficient R is calculated r The specific expression is as follows:

[0021]

[0022] Among them, R r is the thermal resistance demand coefficient, in K / kW; ΔT is the estimated average heat transfer temperature difference, in K, which is obtained by subtracting the cold flow inlet temperature from the average of the incoming and outgoing flow temperatures required by the hot flow working fluid; Q h It is the heat dissipation power required by the heat flow, and the unit is kW.

[0023] Preferably, the specific expression for calculating the heat exchange matching judgment parameter K of each heat fluid heat dissipation module in step 4 is as follows:

[0024] K=C m *α A *R r .

[0025] Preferably, in step 5, the heat exchange matching determination parameters K of the heat fluid cooling modules are close to each other and are arranged in series, while the heat exchange matching determination parameters K of the heat fluid cooling modules are far different from each other and are arranged in parallel.

[0026] Preferably, in step 6, the cooling order of each heat fluid cooling module connected in series is arranged from front to back according to the average temperature of the heat flow return flow from low to high, and the cooling air volume of each heat fluid cooling module is distributed according to the heat capacity flow rate of the cold and hot flows.

[0027] Therefore, the present invention adopts the above-mentioned design method of a highly compact integrated radiator for a diesel generator set, which has the following beneficial effects:

[0028] (1) The dimensionless heat transfer matching judgment parameter K is proposed as the design criterion for the series and parallel connection scheme of each heat dissipation module of the integrated heat sink, which breaks away from the traditional empirical design and is accurate and fast;

[0029] (2) The design principle of equal heat capacity flow rate on both sides of the hot and cold sides and minimum required heat dissipation area is proposed to solve the problem of cooling medium flow distribution of each series heat dissipation module;

[0030] (3) Using this method to design the series-parallel scheme of the integrated radiator can significantly reduce the required heat dissipation area and the total volume of the radiator, thus supporting the realization of high power density of high-power diesel generator sets;

[0031] (4) The formula is simple and does not require detailed design parameters such as fin configuration. It is completely isolated from the later detailed design stage and is suitable for the early overall design of the integrated heat sink.

[0032] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is an overall flow chart of a design method of a highly compact integrated radiator for a diesel generator set of the present invention;

[0034] Figure 2 This is a conceptual diagram of the design of an air-cooled integrated radiator for a certain type of 40kW diesel generator set with a 24kW heat dissipation power requirement according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] The following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] See also Figure 1-2 A design method for a highly compact integrated radiator of a diesel generator set is applied to the series-parallel design of each heat dissipation module of an integrated radiator of a certain type of 40kW diesel generator set, as shown in Table 1:

[0037] Table 1 Composition of integrated radiator module of a certain type of diesel generator set

[0038] Cooling module Thermal fluid Cold flow medium Intercooler module Pressurized air Cooling air Engine oil cooling module 10W-40 Engine Oil Cooling air Engine coolant cooling module eal5050 coolant Cooling air Generator cooling oil cooling module 45# Transformer Oil Cooling air

[0039] The integrated radiator includes an intercooler module for supercharged air cooling, an engine oil cooling module, a coolant radiator, and a generator oil cooling module. The working medium on the cooling side is air, and two electronic fans are used to transport and centrally cool the heat flow working medium in each of the four cooling modules. The specific steps are as follows:

[0040] Step 1: Calculate the heat capacity flow rate C of each heat flow medium m , the specific expression is as follows:

[0041] C m =ρ*Q v *C p (1)

[0042] Among them, C m is the heat capacity flow rate of the heat flux medium, in kW / K; ρ is the density of the heat flux medium, in kg / m 3 ;Q v is the volume flow rate of the heat working fluid, in m 3 / s;C pis the constant-pressure specific heat capacity of the heat fluid, and its unit is kJ / (kg*K). The calculation results are shown in Table 2, where the coolant volume flow rate, density, constant-pressure specific heat capacity are the highest, and the heat capacity flow rate is the highest, while the boost air volume flow rate, density, constant-pressure specific heat capacity are the lowest, and the heat capacity flow rate is the lowest.

[0043] Table 2 Heat capacity flow rate of heat flow medium

[0044]

[0045] The principle is that the heat transfer temperature difference between the hot and cold flows determines the heat dissipation area. The heat dissipation power requirement of the hot flow medium and the temperature of the return flow are given. When the type of the cold flow medium is determined, the cold flow volume flow rate determines the temperature rise after heat absorption, thereby determining the average heat transfer temperature difference between the hot and cold flows. According to the commonly used logarithmic average heat transfer temperature difference calculation formula, as shown in the following formula (2):

[0046]

[0047] Among them, Δt ln,m is the logarithmic average heat transfer temperature difference between the cold and hot streams, in K; Δt1 is the inlet temperature difference between the cold and hot streams, Δt2 is the outlet temperature difference between the cold and hot streams, both in K; ln() is the exponential logarithmic function.

[0048] In formula (2), the inverse of the logarithmic mean heat transfer temperature difference is the slope of the secant line between the inlet temperature difference Δt1 and the outlet temperature difference Δt2 of lnΔt. Since the derivative of lnΔt is monotonically decreasing over the entire domain and is a convex function, the secant line is always located below the function curve. Therefore, only when the secant line slope is equal to the tangent line slope of the original function at the point Δt2, the secant line slope can reach the minimum value, and at this time Δt1 approaches Δt2 infinitely. It can be concluded that when the inlet temperature difference Δt1 and the outlet temperature difference Δt2 are equal, the logarithmic mean heat transfer temperature difference is the largest and the required heat dissipation area is the smallest. To meet this temperature difference condition, the heat capacity flow rate of the cold and hot flows must be equal.

[0049] Because the cooling medium flow rates of several heat dissipation modules in series are equal, that is, the cold flow heat capacity flow rate is equal, the heat flow rate of the heat flow medium of several heat dissipation modules in series should be as close as possible to this equal cold flow heat capacity flow rate to ensure that the average heat transfer temperature difference of this series module is generally high. It is concluded that heat flow mediums with similar heat capacity flow rates are suitable for series connection, and those with far different heat capacity flow rates should be connected in parallel.

[0050] Step 2: Calculate the optimal distribution ratio α of the heat dissipation area on the hot and cold sides of each heat fluid heat dissipation module A , the specific expression is as follows:

[0051]

[0052] Among them, α Ah is the optimal distribution ratio of the heat dissipation area on the hot and cold sides, dimensionless, defined as the ratio of the heat dissipation surface area on the hot flow side to the heat dissipation surface area on the cold flow side; h is the heat transfer coefficient, h c is the cold transfer heat coefficient, and its unit is kW / (㎡*K). Its value is the design value related to the fin configuration and channel size. At this time, it can be estimated and determined based on empirical data. The calculation results are shown in Table 3. The heat transfer coefficients of various hot flow and cold flow working media are estimated based on commonly used data. Among them, the heat transfer coefficient of coolant is much higher than that of cooling air, so the required heat dissipation area allocation ratio on the coolant side is the smallest. The heat transfer coefficient of boost air is the least higher than that of cooling air, so the required heat dissipation area allocation ratio on the boost air side is the largest.

[0053] Table 3 Optimal distribution ratio of heat dissipation area on the hot and cold sides of each heat dissipation module

[0054]

[0055] The principle is that the total heat transfer resistance of the radiator determines the heat dissipation area, and the total heat transfer resistance is determined by the heat transfer coefficient and heat dissipation area on both sides. Under the premise that the total heat dissipation area on both sides is certain, due to the different heat transfer coefficients of the fluids on both sides, there should be an optimal distribution ratio of the heat dissipation area on both sides to minimize the total heat transfer resistance. The total heat transfer resistance calculation formula is shown in the following formula (4):

[0056]

[0057] Among them, h s is the total heat transfer coefficient, the unit is kW / (㎡*K); A h , A c , A s They are the heat dissipation area on the hot flow side and the cold flow side and the total heat transfer area, both in m2.

[0058] Assume that the heat dissipation area distribution ratio on both sides is Substituting into (4), we get the following formula (5):

[0059]

[0060] It can be seen from the above formula that the total heat transfer coefficient depends on the distribution ratio of the heat dissipation area on the hot and cold sides, and the calculation formula is shown in the following formula (6):

[0061]

[0062] For equation (6), calculate the heat dissipation area ratio α A The derivative of has a zero point, corresponding to the heat dissipation area ratio α A The total heat transfer coefficient at is the maximum value, and the area ratio calculation formula is the above formula (3).

[0063] It can be seen from the above formula (3) that when the heat transfer coefficient on the hot and cold sides is larger, the optimal heat dissipation area ratio to be allocated should be smaller, and the height of the fluid channel should be lower. In order to ensure that the cold flow medium flows smoothly through the cold flow channel formed after the series connection, the height of the cold flow channel of each heat dissipation module in series should be kept consistent. However, since the heat dissipation area is also related to factors such as the fin spacing, the optimal heat dissipation area ratio of each heat dissipation module in series can be kept as close as possible. In this way, the cold flow channel height matching is achieved on the one hand, and the overall heat transfer coefficient is also guaranteed to be high on the other hand.

[0064] Step 3: Calculate the thermal resistance requirement coefficient R r , the specific expression is as follows:

[0065]

[0066] Among them, R r is the thermal resistance demand coefficient, in K / kW; ΔT is the estimated average heat transfer temperature difference, in K, which is obtained by subtracting the cold flow inlet temperature from the average of the incoming and outgoing flow temperatures required by the hot flow working fluid; Q h is the heat dissipation power required by the heat flow, and the unit is kW. The calculation results are shown in Table 4. Although the heat dissipation power of the generator oil heat dissipation module is relatively low, the average temperature of the round-trip flow required by the heat flow is the lowest, so a very low thermal resistance is required. While the heat dissipation power of the intercooler module is the lowest, the average temperature of the round-trip heat flow is also the lowest, so a higher thermal resistance can also meet the design requirements.

[0067] Table 4 Thermal resistance requirement coefficients of each heat dissipation module

[0068]

[0069] The principle is that when considering the height matching of the cold flow channel, not only the optimal heat dissipation area allocation ratio on both sides of the hot and cold sides should be considered, but also the actual demand for the total heat dissipation area for the heat dissipation power of the hot fluid and the round-trip flow temperature should be considered. If the required allocation ratio of the heat dissipation area on the cold side is higher, but the heat dissipation power is lower or the round-trip temperature is higher, then the actual required cold flow channel height may not be high. This step 3 supplements the previous step 2.

[0070] Step 4: The heat capacity flow rate C of the heat flow medium m , optimal distribution ratio of heat dissipation area on hot and cold sides α A , Thermal resistance requirement coefficient R r The heat exchange matching judgment parameter K of each heat fluid cooling module is calculated by multiplication. The specific expression is as follows:

[0071] K=C m *α A *R r .

[0072] The calculation results are shown in Table 5:

[0073] Table 5 Heat exchange matching judgment parameters

[0074]

[0075]

[0076] The principle is to comprehensively consider all the factors in the above steps 1 to 3 to form an evaluation criterion for matching the heat transfer characteristics of the heat dissipation module.

[0077] Step 5, determine the series-parallel state of each heat-fluid cooling module according to the heat exchange matching judgment parameter K; specifically, each heat-fluid cooling module with a similar heat exchange matching judgment parameter K is set in series, and each heat-fluid cooling module with a relatively different heat exchange matching judgment parameter K is set in parallel. Specifically, the heat exchange matching judgment parameters of the intercooler module and the generator oil cooling module are similar, and the two should be connected in series. The heat exchange matching judgment parameters of the engine oil cooling module and the engine coolant cooling module are similar, and the two should be connected in series; the principle is that, considering the design requirements of the heat dissipation power and the return flow temperature on the heat dissipation area, the cold flow flow matching and the cold flow channel height matching of each heat dissipation module are comprehensively considered, and each heat dissipation module connected in series can make full use of the temperature difference with the cold flow for heat exchange, reduce the required heat dissipation area, and reduce the total volume of the radiator.

[0078] Step 6: Arrange the cooling sequence of each heat-fluid heat-dissipating module in series, and distribute the cooling air volume of each heat-fluid heat-dissipating module in series; specifically, the cooling sequence of each heat-fluid heat-dissipating module in series is arranged from front to back according to the average temperature of the heat flow in and out, and the cooling air volume of each heat-fluid heat-dissipating module is distributed according to the equal heat capacity flow rate of the cold and hot flows; since the average temperature of the generator cooling oil in and out is lower than the charge air, the generator cooling oil should be cooled first and then the charge air. The average temperature of the engine cooling oil in and out is lower than the engine coolant, so the engine cooling oil should be cooled first and then the engine coolant. The cooling air flow rate allocated to the generator cooling oil-intercooler series heat dissipation module can be less, and the heat capacity flow rate can be met at 0.082~0.680kW / K. The cooling air flow rate allocated to the engine cooling oil-engine coolant series heat dissipation module should be more, and the heat capacity flow rate must be met at 0.683~2.394kW / K. The principle is that in order to make full use of the temperature difference between the cold and hot flows for heat transfer, it has been determined that several heat fluid heat dissipation modules that need to be connected in series should first cool the ones with lower average temperatures and then cool the ones with higher average temperatures, so as to ensure that the heat transfer temperature difference of the entire heat fluid heat dissipation module is generally high. The cooling fluid flow rate required to be allocated to each series heat fluid heat dissipation module should ensure that the heat capacity flow rate of the cold flow is as close as possible to the heat capacity flow rate of the hot fluid, so as to ensure that the heat transfer coefficient of the entire heat dissipation module is generally high.

[0079] Step 7: Obtain a final highly compact integrated heat sink by selecting the series and parallel connections of the heat flux cooling modules in steps 1 to 6 and distributing the cooling air volume.

[0080] Therefore, the present invention adopts the above-mentioned high-compact integrated radiator design method for diesel generator sets, and proposes a dimensionless heat exchange matching judgment parameter, which is obtained by multiplying the heat capacity flow rate of the heat fluid, the optimal allocation ratio of the heat dissipation area on the hot and cold sides, and the thermal resistance demand coefficient. The heat exchange matching judgment parameters of the heat fluid cooling modules with similar parameters are connected in series, and those with large differences are connected in parallel. Then, the cooling sequence of the heat fluid cooling modules in series is arranged from front to back according to the average temperature of the heat flow in and out, and the cooling air volume of the heat fluid cooling modules in series is allocated according to the principle of equal heat capacity flow rates of cold and hot flows. In this way, the average heat transfer temperature difference and the improvement of the total heat transfer coefficient, the height matching of the cold flow channels of each heat fluid cooling module, the heat dissipation power and the design requirements of the in and out flow temperature are comprehensively considered, and the series and parallel schemes of each heat fluid cooling module can be accurately and quickly determined, the total volume of the radiator can be effectively reduced, and the realization of high power density of high-power diesel generator sets can be supported.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A design method for a highly compact integrated radiator of a diesel generator set, characterized in that: The following steps are involved: Step 1: Calculate the heat capacity flow rate C of each heat flow medium m ; Step 2: Calculate the optimal distribution ratio α of the heat dissipation area on the hot and cold sides of each heat fluid heat dissipation module A ; Step 3: Calculate the thermal resistance requirement coefficient R r ; Step 4: The heat capacity flow rate C of the heat flow medium m , optimal distribution ratio of heat dissipation area on hot and cold sides α A , Thermal resistance requirement coefficient R r Multiply and calculate the heat exchange matching judgment parameter K of each heat fluid cooling module; Step 5: Determine the series-parallel state of each heat-fluid cooling module according to the heat exchange matching judgment parameter K; Step 6: Arrange the cooling sequence of each heat-fluid heat-dissipating module connected in series, and distribute the cooling air volume of each heat-fluid heat-dissipating module connected in series; Step 7, obtaining a final highly compact integrated heat sink by selecting the series and parallel connection of each heat flow medium heat dissipation module and distributing the cooling air volume in steps 1 to 6; Calculate the heat capacity flow rate C of each heat flow medium in step 1 m The specific expression is as follows: C m =ρ*Q v *C p Among them, C m is the heat capacity flow rate of the heat flux medium, in kW / K; ρ is the density of the heat flux medium, in kg / m 3 ;Q v is the volume flow rate of the heat working fluid, in m 3 / s;C p is the specific heat capacity of the heat fluid at constant pressure, in kJ / (kg*K); In step 2, the optimal distribution ratio α of the heat dissipation area on the hot and cold sides of each heat fluid heat dissipation module is calculated. A The specific expression is as follows: Among them, α A h is the optimal distribution ratio of the heat dissipation area on the hot and cold sides, dimensionless, defined as the ratio of the heat dissipation surface area on the hot flow side to the heat dissipation surface area on the cold flow side; h is the heat transfer coefficient, h c is the cold transfer heat coefficient, the unit is kW / (㎡*K); Calculate the thermal resistance demand factor R in step 3 r The specific expression is as follows: Among them, R r is the thermal resistance demand coefficient, in K / kW; ΔT is the estimated average heat transfer temperature difference, in K, which is obtained by subtracting the cold flow inlet temperature from the average of the incoming and outgoing flow temperatures required by the hot flow working fluid; Q h is the heat dissipation power required by the heat flow, in kW; The specific expression for calculating the heat exchange matching judgment parameter K of each heat fluid heat dissipation module in step 4 is as follows: K=C m *a A *R r ; In step 5, the heat exchange matching determination parameters K of the heat fluid cooling modules are close to each other and are connected in series, while the heat exchange matching determination parameters K of the heat fluid cooling modules are far different from each other and are connected in parallel.

2. A design method for a highly compact integrated radiator of a diesel generator set according to claim 1, characterized in that: In step 6, the cooling order of each heat flow medium heat dissipation module connected in series is arranged from front to back according to the average temperature of the heat flow return flow from low to high, and the cooling air volume of each heat flow medium heat dissipation module is distributed according to the equal heat capacity flow rate of the cold and hot flows.

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