Heat transfer coefficient measuring method and system based on nonlinear heat flux density reconstruction

Abstract

The invention is suitable for the technical field of heat exchange measurement, and provides a heat exchange coefficient measurement method and system based on nonlinear heat flux density reconstitution, and the method comprises the following steps: respectively measuring heat exchange temperature differences of a working medium and cooling water at an inlet, a middle position and an outlet of a test section, and obtaining an inlet temperature difference, a middle temperature difference and an outlet temperature difference; based on a preset analytical formula, according to the inlet temperature difference, the middle temperature difference and the outlet temperature difference, reconstructing nonlinear distribution of heat flux density in the test section; and calculating the heat exchange coefficient of any position in the test section based on the nonlinear distribution of the heat flux density. According to the method provided by the invention, the nonlinear distribution of the heat flux density can be reconstructed with high precision and the heat exchange coefficient can be accurately calculated only by three on-way temperature measuring points, so that the technical contradiction that the precision, the cost and the implementation difficulty cannot be considered in the prior art is solved.

Description

Technical Field

[0001] This invention belongs to the field of heat transfer measurement technology, and in particular relates to a method and system for measuring heat transfer coefficient based on nonlinear heat flux density reconstruction. Background Technology

[0002] Accurate measurement of the heat transfer coefficient is crucial for evaluating and designing heat exchange equipment. Reconstructing the heat flux distribution helps identify areas within the heat exchanger where heat transfer is good and where it is poor, thus providing guidance for optimizing the heat exchange structure, system matching, and regulation. The heat transfer coefficient is typically calculated using the following formula:

[0003]

[0004] In the formula, h is the heat transfer coefficient, W / (m³). 2 ·K); q is the heat flux density of the test section, W / m 2 ΔT is the temperature difference between the working fluid and the pipe wall in the test section, in °C.

[0005] In the above formula, the temperature difference ΔT can be directly measured, but the heat flux density q cannot be directly measured and needs to be calculated based on the measurement results of heat transfer-related parameters. A typical method for measuring the heat transfer coefficient is as follows: In a shell-and-tube heat exchanger, the working fluid flows through the inner tube, and the cooling water flows through the outer tube, forming a counter-current heat exchange. The measured parameters include the inlet and outlet temperatures of the working fluid, the water temperature, and the temperature of the heat exchange tube wall.

[0006] The traditional method for calculating heat flux density q is to take the overall average heat flux density of the test section (hereinafter referred to as the traditional averaging method), as shown in the following formula:

[0007]

[0008] In the formula, The average heat flux density is W / m³. 2 Q represents the total heat exchange of the test section, in W; A1 represents the heat exchange area of ​​the test section, in m². 2 .

[0009] The inherent drawback of this method is that when the heat transfer coefficient or heat transfer temperature difference varies significantly along the pipe length, the heat flux density exhibits a significant nonlinear distribution along the pipe length. In this case, using the average heat flux density will introduce a deviation. The magnitude of this deviation mainly depends on the degree of nonlinearity of the heat flux density.

[0010] To avoid this problem, there are two main existing improvement approaches:

[0011] 1. Using dense measurement points: Dozens of temperature sensors are densely arranged along the test section, and the actual heat flow distribution is approximated by piecewise integration. Although this method can improve accuracy, it significantly increases the cost of sensors, the complexity of the data acquisition system, and the difficulty of installation and maintenance, which is not conducive to engineering promotion.

[0012] 2. Controlling the nonlinearity of the test section: The changes in dryness or inlet / outlet temperature difference are controlled within a very small range to reduce the nonlinear characteristics along the flow path. However, this is particularly difficult for microchannel experiments because excessively small variation ranges result in excessively small heat transfer, increasing the measurement error of heat transfer and affecting accuracy. Furthermore, in engineering monitoring, the variation range within the heat exchanger is designed according to the process and cannot be controlled within a very small range; therefore, this method is completely impractical for this purpose.

[0013] In summary, the existing technology has the following problems:

[0014] 1. The traditional averaging method has limited accuracy: Under conditions where the heat flux density is significantly nonlinear, the measurement error is large and cannot meet the needs of high-precision design and research.

[0015] 2. High-precision solutions are costly: To achieve high-precision measurement of nonlinear heat flux density, existing methods use dense measurement points, which can improve accuracy, but the equipment cost is high, the system is complex, and it is difficult to apply in engineering.

[0016] 3. Narrow applicability of economical solutions: In order to achieve accurate measurement with fewer measuring points, only the degree of nonlinearity of the test section can be controlled. However, due to limitations of the process or measuring equipment, this is often impossible.

[0017] Therefore, there is an urgent need for a solution that can efficiently reconstruct the nonlinear distribution of heat flux and measure its heat transfer coefficient with high precision at a limited number of measurement points. Summary of the Invention

[0018] The purpose of this invention is to provide a method for measuring the heat transfer coefficient based on nonlinear heat flux density reconstruction, in order to solve the above-mentioned technical problems.

[0019] This invention is implemented as follows: a method for measuring the heat transfer coefficient based on nonlinear heat flux density reconstruction, comprising the following steps:

[0020] The heat exchange temperature difference between the working fluid and the cooling water was measured at the inlet, middle, and outlet of the test section to obtain the inlet temperature difference, middle temperature difference, and outlet temperature difference.

[0021] Based on the preset analytical formula, the nonlinear distribution of heat flux density in the test section is reconstructed according to the inlet temperature difference, intermediate temperature difference and outlet temperature difference;

[0022] Based on the nonlinear distribution of the heat flux density, the heat transfer coefficient at any location within the test section is calculated.

[0023] Furthermore, the analytical formula is as follows:

[0024] ;

[0025] In the formula, q is the heat flux density of the test section calculated based on the analytical formula; A is the inner surface area of ​​the pipe wall from the inlet of the test section to any position, in m³. 2 A0 represents the inner surface area of ​​the pipe wall from the inlet to the outlet of the test section, in meters. 2 Q tot The total heat exchange of the test section is expressed in W; ΔT in The outlet temperature difference, i.e., the heat exchange temperature difference between the working fluid and the cooling water at the outlet of the test section, is expressed in K; ΔT mid The intermediate temperature difference, i.e., the heat exchange temperature difference between the working fluid and the cooling water at the middle position of the test section, is expressed in K; ΔT out The inlet temperature difference, i.e., the heat exchange temperature difference between the working fluid and the cooling water at the inlet of the test section, is expressed in K.

[0026] Furthermore, the total heat exchange of the test section is calculated based on the inlet and outlet temperatures and flow rates of the cooling water.

[0027] Furthermore, the test section is a counter-current heat exchange structure, comprising an inner tube and an outer tube.

[0028] Furthermore, the working fluid flows in the inner pipe; the cooling water flows in the outer pipe.

[0029] Furthermore, the working fluid is a single-phase or two-phase working fluid, including pure working fluid or mixed working fluid.

[0030] Furthermore, the formula for calculating the heat transfer coefficient is as follows:

[0031]

[0032] In the formula, h is the heat transfer coefficient, W / (m³). 2 ·K); q is the heat flux density of the test section calculated based on the analytical formula, W / m. 2 ΔT is the temperature difference between the working fluid and the pipe wall in the test section, in °C.

[0033] Another object of the present invention is to provide a heat transfer coefficient measurement system based on nonlinear heat flux density reconstruction, for implementing the above-mentioned heat transfer coefficient measurement method, comprising:

[0034] The data measurement module is used to measure the heat exchange temperature difference between the working fluid and the cooling water at the inlet, middle and outlet of the test section, respectively, to obtain the inlet temperature difference, middle temperature difference and outlet temperature difference;

[0035] The data processing module is used to reconstruct the nonlinear distribution of heat flux density in the test section based on a preset analytical formula, according to the inlet temperature difference, intermediate temperature difference, and outlet temperature difference.

[0036] The results output module is used to calculate the heat transfer coefficient at any location within the test section based on the nonlinear distribution of the heat flux density.

[0037] The heat transfer coefficient measurement method based on nonlinear heat flux density reconstruction provided by this invention has the following beneficial technical effects compared with the prior art:

[0038] 1. Significantly improved measurement accuracy: By accurately reconstructing nonlinear heat flow, the theoretical error of the traditional averaging method is fundamentally overcome.

[0039] 2. Highly practical for engineering applications: Only three temperature measurement points are required. Compared with the "dense measurement point method", it significantly reduces sensor costs, data acquisition system complexity and installation and maintenance difficulty, making it easier to promote and apply in industrial field monitoring and laboratories.

[0040] 3. Overcomes operating condition limitations: There is no need to strictly limit the nonlinearity of the heat flux density of the test specimen to a very small range, making it more applicable.

[0041] 4. Efficiently reconstructing the heat flux density distribution helps to understand which locations within the heat exchanger have good heat transfer and which have poor heat transfer, thus providing guidance for heat exchange structure, system matching, and regulation optimization.

[0042] 5. Possesses theoretical universality: The method is based on rigorous heat transfer theory derivation, does not rely on specific working fluids or empirical "trial and error", and the results are reliable and reproducible, providing a new standard tool for heat transfer coefficient measurement. Attached Figure Description

[0043] Figure 1 This is a schematic flowchart of the heat transfer coefficient measurement method based on nonlinear heat flux density reconstruction provided in an embodiment of the present invention.

[0044] Figure 2 This is a schematic diagram of the heat exchange analysis principle.

[0045] Figure 3 This is a geometric model diagram of a shell-and-tube heat exchanger.

[0046] Figure 4 The graph shows the variation of heat flux density with pipe length under different cooling water inlet and outlet temperature differences.

[0047] Figure 5 This graph shows the variation of water temperature and wall temperature with pipe length under different inlet and outlet temperature differences of cooling water.

[0048] Figure 6 The figure shows a comparison of errors between the traditional averaging method and the new method proposed in this invention when the temperature difference between the inlet and outlet of the cooling water is 6.9K and the dryness difference between the inlet and outlet is 0.1. In the figure, (a) is a comparison of the formula values ​​of the heat transfer coefficient; (b) is a comparison of the relative errors.

[0049] Figure 7The figure shows a comparison of errors between the traditional averaging method and the new method proposed in this invention when the temperature difference between the inlet and outlet of the cooling water is 6.9K and the dryness difference between the inlet and outlet is 0.2. In the figure, (a) is a comparison of the formula values ​​of the heat transfer coefficient; (b) is a comparison of the relative errors.

[0050] Figure 8 The figure shows a comparison of errors between the traditional averaging method and the new method proposed in this invention when the temperature difference between the inlet and outlet of the cooling water is 6.9K and the dryness difference between the inlet and outlet is 0.3. In the figure, (a) is a comparison of the formula values ​​of the heat transfer coefficient; (b) is a comparison of the relative errors.

[0051] Figure 9 The figure shows a comparison of errors between the traditional averaging method and the new method proposed in this embodiment of the invention when the temperature difference between the inlet and outlet of the cooling water is 6.9K and the dryness difference between the inlet and outlet is 0.4. In the figure, (a) is a comparison of the formula values ​​of the heat transfer coefficient; (b) is a comparison of the relative errors.

[0052] Figure 10 The figure shows a comparison of errors between the traditional averaging method and the new method proposed in this invention when the temperature difference between the inlet and outlet of the cooling water is 6.9K and the dryness difference between the inlet and outlet is 0.5. In the figure, (a) is a comparison of the formula values ​​of the heat transfer coefficient; (b) is a comparison of the relative errors.

[0053] Figure 11 The figure shows a comparison of errors between the traditional averaging method and the new method proposed in this invention when the temperature difference between the inlet and outlet of the cooling water is 6.9K and the dryness difference between the inlet and outlet is 0.6. In the figure, (a) is a comparison of the formula values ​​of the heat transfer coefficient; (b) is a comparison of the relative errors.

[0054] Figure 12 This is a schematic diagram illustrating the monitoring principle of a conventional heat exchanger. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0056] In experimental measurements and engineering monitoring of heat transfer coefficients, the traditional averaging method introduces significant measurement errors when the heat flux density within the test section exhibits a markedly nonlinear distribution due to factors such as drastic changes in working fluid dryness or temperature difference along the path. In engineering applications, the nonlinear distribution of heat flux density increases monitoring errors, making it impossible to obtain accurate information about the internal heat transfer distribution. Current technologies for reducing these errors either rely on densely packed temperature measurement points, leading to high costs and complex implementation, or require strict control of the inlet / outlet dryness difference or temperature difference within an extremely small range. These factors significantly complicate accurate measurements, making implementation difficult.

[0057] This invention aims to provide a method and system for accurately reconstructing the nonlinear distribution of heat flux density and precisely calculating its heat transfer coefficient using only three temperature measurement points along the heat exchanger, thus resolving the technical contradiction of simultaneously achieving high accuracy, cost, and implementation difficulty. Specifically, the objectives are: 1. To achieve efficient reconstruction of nonlinear heat flux density and high-precision measurement of its heat transfer coefficient using a small number of measurement points, reducing the complexity and cost of the testing system; 2. To understand which locations within the heat exchanger have good heat transfer and which have poor heat transfer by reconstructing the heat flux density distribution, thereby providing guidance for heat exchange structure, system matching, and adjustment optimization.

[0058] Specifically, such as Figure 1 As shown, in one embodiment of the present invention, a method for measuring the heat transfer coefficient based on nonlinear heat flux density reconstruction is provided, comprising the following steps:

[0059] S1. At the inlet, middle and outlet of the test section, measure the heat exchange temperature difference between the working fluid and the cooling water to obtain the inlet temperature difference, middle temperature difference and outlet temperature difference.

[0060] S2. Based on the preset analytical formula, the nonlinear distribution of heat flux density in the test section is reconstructed according to the inlet temperature difference, intermediate temperature difference and outlet temperature difference;

[0061] S3. Based on the nonlinear distribution of the heat flux density, calculate the heat transfer coefficient at any location within the test section.

[0062] In a preferred embodiment of the present invention, in order to more accurately characterize the actual distribution of heat flux density, the present invention has developed a theoretical calculation formula based on three sets of temperature measurement points along the path to reconstruct the nonlinear change of heat flux density, which is the aforementioned preset analytical formula, as follows:

[0063] ;

[0064] In the formula, q is the heat flux density of the test section calculated based on the analytical formula; A is the inner surface area of ​​the pipe wall from the inlet of the test section to any position, in m³. 2 A0 represents the inner surface area of ​​the pipe wall from the inlet to the outlet of the test section, in meters. 2 Q tot The total heat exchange of the test section is expressed in W; ΔT in The outlet temperature difference, i.e., the heat exchange temperature difference between the working fluid and the cooling water at the outlet of the test section, is expressed in K; ΔT mid The intermediate temperature difference, i.e., the heat exchange temperature difference between the working fluid and the cooling water at the middle position of the test section, is expressed in K; ΔT out The inlet temperature difference, i.e., the heat exchange temperature difference between the working fluid and the cooling water at the inlet of the test section, is expressed in K.

[0065] In a preferred embodiment of the present invention, the derivation process of the above analytical formula is as follows:

[0066] like Figure 2 As shown, the working fluid and cooling water exchange heat in a counter-current manner. Three temperature measuring points are taken along the pipe length, located at the inlet, middle, and outlet. The heat exchange can be considered as a hypothetical single-phase heat exchange of the working fluid within a micro-element, based on thermal equilibrium.

[0067] ;

[0068] ;

[0069] In the formula, Q represents the heat exchanged (W); c p,w The specific heat capacity of cooling water at constant pressure, J / (kg·K); m w The mass flow rate of cooling water is kg / m²; T wa Where K is the cooling water temperature; c is the temperature of the cooling water. p,r The specific heat capacity of the working fluid at constant pressure is J / (kg·K); m r T represents the mass flow rate of the working fluid, in kg / m². f To test the fluid temperature, K;

[0070] Combining the above equations, we get:

[0071] ;

[0072] In the formula, k is the heat transfer coefficient, W / (m²). 2 ·K);

[0073] To simplify the expression of the equation, the coefficient B is defined as follows:

[0074] ;

[0075] Assuming that k varies linearly along the pipe length, and considering that the flow rate and specific heat are constants, the coefficient B can be considered to have a linear relationship with the pipe wall area A:

[0076] ;

[0077] Therefore:

[0078] ;

[0079] The general solution to this equation is:

[0080] ;

[0081] In the formula, C is the coefficient of the integral;

[0082] When A=0 (pipe inlet):

[0083] ;

[0084] In the formula, Tf,in The inlet temperature of the working fluid is K; T wa,out The outlet temperature of the cooling water, in K;

[0085] When A = A0 (pipe outlet):

[0086] ;

[0087] ;

[0088] In the formula, T f,out The outlet temperature of the working fluid, K; T wa,in The temperature at the cooling water inlet, in K;

[0089] When A = 0.5A0 (midpoint of the pipeline):

[0090] ;

[0091] ;

[0092] By combining the equations, we can obtain:

[0093] ;

[0094] ;

[0095] Therefore, the general solution is:

[0096] ;

[0097] ;

[0098] When A = A0, Q = Q tot We can obtain:

[0099] ;

[0100] Therefore, the formula for calculating the heat flux density of the pipe wall at any location (i.e., the preset analytical formula) can be obtained as follows:

[0101] .

[0102] The analytical formula derived above only requires three sets of temperature measurement points to reconstruct the nonlinear distribution of heat flux density within the test section, thus achieving a good balance between measurement accuracy and cost.

[0103] In a preferred embodiment of the present invention, the total heat exchange of the test section is calculated based on the inlet and outlet temperatures and flow rates of the cooling water.

[0104] In a preferred embodiment of the present invention, the test section is a counter-current heat exchange structure, including an inner tube and an outer tube; wherein the working fluid flows in the inner tube; and the cooling water flows in the outer tube.

[0105] In a preferred embodiment of the present invention, the working fluid is a single-phase or two-phase working fluid, including a pure working fluid or a mixed working fluid.

[0106] In a preferred embodiment of the present invention, the formula for calculating the heat transfer coefficient is:

[0107]

[0108] In the formula, h is the heat transfer coefficient, W / (m³). 2 ·K); q is the heat flux density of the test section calculated based on the analytical formula, W / m. 2 ΔT is the temperature difference between the working fluid and the pipe wall in the test section, in °C.

[0109] Another object of the present invention is to provide a heat transfer coefficient measurement system based on nonlinear heat flux density reconstruction, for implementing the above-mentioned heat transfer coefficient measurement method, comprising:

[0110] The data measurement module is used to measure the heat exchange temperature difference between the working fluid and the cooling water at the inlet, middle and outlet of the test section, respectively, to obtain the inlet temperature difference, middle temperature difference and outlet temperature difference;

[0111] The data processing module is used to reconstruct the nonlinear distribution of heat flux density in the test section based on a preset analytical formula, according to the inlet temperature difference, intermediate temperature difference, and outlet temperature difference.

[0112] The results output module is used to calculate the heat transfer coefficient at any location within the test section based on the nonlinear distribution of the heat flux density.

[0113] The following embodiments are applications of the present invention in actual measurement, and are only illustrative examples and are not limited thereto.

[0114] Example 1: Measurement of microchannel heat transfer coefficient

[0115] The heat flux density reconstruction and heat transfer coefficient calculation method based on three measuring points proposed in this invention has wide applicability. Its core principle is to analyze the nonlinear heat flux distribution through temperature difference data at a finite number of key points, and it is not limited to channels of specific sizes or a single heat transfer type. This method can be effectively applied to various scenarios with nonlinear heat flux density distribution characteristics, ranging from microchannels (<1mm) to conventional and large-scale engineering pipelines (>10mm), from pure working fluids to mixed working fluids, from single-phase to condensation and boiling, and from subcritical to supercritical fluid heat transfer.

[0116] The following detailed embodiment of pure working fluid condensation in a microchannel is used to fully demonstrate the specific implementation, technical details and significant effects of the present invention.

[0117] To evaluate the accuracy of the traditional averaging method and the new method provided by this invention, a typical condensation heat exchange condition was selected for theoretical analysis, and theoretical values ​​were used to evaluate the two methods.

[0118] Shell-and-tube heat exchangers are commonly used testing structures, such as... Figure 3 As shown, the inner tube has an inner diameter D1 = 1 mm, an outer diameter D2 = 3 mm, a wall thickness of 2 mm, and a sleeve diameter D3 = 6 mm. Neglecting the sleeve wall thickness, the effective heat exchange length L = 600 mm. The working fluid in the inner tube is environmentally friendly R1234ze(E), entering the heat exchanger through the left inlet. The cooling water in the outer tube flows counter-currently along the right end, forming an annular flow channel. Under steady-state conditions, the R1234ze(E) working fluid exchanges heat with the cooling water through the tube wall, ultimately achieving complete phase change condensation at the outlet. The cooling water maintains a single-phase forced convection state throughout the process, without undergoing a phase change. Pressure drop and heat dissipation to the environment are neglected.

[0119] The inlet mass flow rate was selected as Gr = 400 kg / (m³). 2 The pipe diameter is D1=1mm. Nonlinear characteristics of heat flux density under three different heat transfer temperature differences are analyzed, and calculations are performed for operating conditions with different dryness fractions. The inlet on the working fluid side is 40℃ R1234ze(E) saturated steam, and the inlet on the cooling water side is 20℃ liquid water at atmospheric pressure. The heat transfer coefficients under different operating conditions are calculated using the traditional averaging method, the proposed new method, and theoretical values, and error analysis is performed.

[0120] Based on the theoretical model, the working fluid mass flow rate is 400 kg / (m³). 2 ·s), temperature difference ΔT between different cooling water inlet and outlet wat The nonlinear distribution characteristics of heat flux density, heat transfer coefficient, and temperature under these conditions are analyzed, and the results are as follows: Figure 4 and Figure 5 As shown, the heat flux density exhibits a unimodal distribution along the pipe length, meaning it first rises to a peak and then decreases, but the magnitude of its variation varies significantly under different heat transfer temperature differences. The overall heat transfer coefficient decreases along the pipe length. Both the cooling water temperature and the pipe wall temperature decrease monotonically with pipe length, and under the same heat transfer temperature difference, their trends are basically consistent. The heat flux density exhibits obvious nonlinear characteristics, with the pipe wall temperature showing relatively less nonlinearity and the cooling water temperature showing the least nonlinearity. Under larger heat transfer temperature differences, the gradient of change increases, and the nonlinearity becomes more significant.

[0121] Under small temperature difference conditions (ΔT) watAt a temperature of 3.9 K, the heat flux density in the inlet region (L < 0.26 m) increases slowly with increasing pipe length; however, it decreases significantly once L > 0.26 m. Both the cooling water temperature and the pipe wall temperature continuously decrease, with the pipe wall temperature decreasing more non-linearly than the cooling water temperature. In ΔT... wat =6.9K and ΔT wat Under the condition of 13.7K, the overall trend of change is related to ΔT. wat Similar at 3.9K. When ΔT wat At 13.7 K, the heat flux density also exhibits a unimodal distribution of first increasing and then decreasing: it rises rapidly in the inlet section (L < 0.50 m), then decreases sharply after L > 0.50 m, and the rate of decrease is higher than the rate of increase in the inlet section. The cooling water temperature decreases continuously along the pipe length, with weak nonlinear characteristics; while the rate of decrease in pipe wall temperature gradually increases with pipe length.

[0122] like Figures 6-11 As shown, for a mass flow rate of 400 kg / (m³) 2 The working fluid R1234ze(E) was tested with inlet and outlet dryness difference (Δx) ranging from 0.1 to 0.6. The error between the heat transfer coefficient and the theoretical value of the traditional averaging method and the new method proposed in this embodiment of the invention was compared with different dryness fractions. The results show that the error generally increases with the increase of Δx. When Δx changes from 0.1 to 0.6, the error increases for both the traditional averaging method and the new method proposed in this embodiment of the invention, and the error of the traditional averaging method is greater than that of the proposed new method. Under the same Δx, the error increases with the decrease of dryness fraction. This is because the nonlinearity of heat flux density, cooling water temperature and pipe wall temperature is smaller under high dryness fraction conditions, so the error is also smaller. Under the same Δx conditions, the error of the traditional averaging method is always significantly higher than that of the new method proposed in this embodiment of the invention. The specific error data comparison is shown in Table 1.

[0123] Table 1

[0124]

[0125] It can be seen that when Δx is less than 0.2, the error of the traditional averaging method does not exceed 2.3%, but as Δx increases, the error of the traditional averaging method gradually increases, reaching a maximum of 10.6%. Such a large error is unacceptable for a calculation method. Therefore, the traditional averaging method is only applicable to small Δx values. In contrast, the new method proposed in this invention exhibits very small errors within the scope of the study, with a maximum error not exceeding 1.7%. Therefore, the accuracy and applicability of the new method proposed in this invention are far superior to the traditional averaging method.

[0126] Example 2: Monitoring of Conventional Heat Exchangers

[0127] The implementation principle of this embodiment is the same as that of the microchannel scenario in Embodiment 1, both based on the three-point heat flux density reconstruction technology. Specifically, as follows: Figure 7 As shown, the fluid temperatures inside the inner and outer jackets are simultaneously measured at three key cross-sections: the inlet, midpoint, and outlet of the heat exchanger tube. These measurements are then substituted into the analytical formula proposed in this embodiment of the invention to calculate the actual nonlinear heat flux density. To obtain the heat transfer coefficient, the heat flux density is divided by the heat transfer temperature difference.

[0128] In addition, other heat exchangers can also obtain nonlinear heat flux density distribution and heat transfer coefficient by installing measuring points at appropriate locations according to the ideas provided in the embodiments of the present invention and following the above method.

[0129] It should be noted that, according to the approach provided in the embodiments of the present invention, the number of measurement points can be reduced to two or increased to more. Reducing the number of measurement points helps to lower testing costs, but the accuracy decreases. Increasing the number of measurement points helps to further improve accuracy, but the cost increases. The approach and derivation process provided in the embodiments of the present invention can also be used to derive analytical formulas for other numbers of measurement points.

[0130] It should be understood that although the steps in the flowcharts of the various embodiments of the present invention are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the various embodiments may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least a portion of the sub-steps or stages of other steps.

[0131] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Furthermore, any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory.

[0132] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for measuring heat transfer coefficient based on nonlinear heat flux density reconstruction, characterized in that, Includes the following steps: The heat exchange temperature difference between the working fluid and the cooling water was measured at the inlet, middle, and outlet of the test section to obtain the inlet temperature difference, middle temperature difference, and outlet temperature difference. Based on the preset analytical formula, the nonlinear distribution of heat flux density in the test section is reconstructed according to the inlet temperature difference, intermediate temperature difference and outlet temperature difference; Based on the nonlinear distribution of the heat flux density, the heat transfer coefficient at any location within the test section is calculated.

2. The heat transfer coefficient measurement method based on nonlinear heat flux density reconstruction according to claim 1, characterized in that, The analytical formula is as follows: ； In the formula, q is the heat flux density of the test section calculated based on the analytical formula; A is the inner surface area of ​​the pipe wall from the inlet of the test section to any position, in m³. 2 ; A0 is the inner surface area of ​​the pipe wall from the inlet to the outlet of the test section, in meters. 2 Q tot The total heat exchange of the test section is expressed in W; ΔT in The outlet temperature difference, i.e., the heat exchange temperature difference between the working fluid and the cooling water at the outlet of the test section, is expressed in K; ΔT mid The intermediate temperature difference, i.e., the heat exchange temperature difference between the working fluid and the cooling water at the middle position of the test section, is expressed in K; ΔT out The inlet temperature difference, i.e., the heat exchange temperature difference between the working fluid and the cooling water at the inlet of the test section, is expressed in K.

3. The heat transfer coefficient measurement method based on nonlinear heat flux density reconstruction according to claim 2, characterized in that, The total heat exchange of the test section is calculated based on the inlet and outlet temperatures and flow rates of the cooling water.

4. The heat transfer coefficient measurement method based on nonlinear heat flux density reconstruction according to claim 1, characterized in that, The test section is a counter-current heat exchange structure, consisting of an inner tube and an outer tube.

5. The heat transfer coefficient measurement method based on nonlinear heat flux density reconstruction according to claim 4, characterized in that, The working fluid flows in the inner pipe; the cooling water flows in the outer pipe.

6. The heat transfer coefficient measurement method based on nonlinear heat flux density reconstruction according to claim 1 or 5, characterized in that, The working medium is a single-phase or two-phase working medium, including pure working medium or mixed working medium.

7. The heat transfer coefficient measurement method based on nonlinear heat flux density reconstruction according to claim 1 or 2, characterized in that, The formula for calculating the heat transfer coefficient is: ； In the formula, h is the heat transfer coefficient, W / (m³). 2 ·K); q is the heat flux density of the test section calculated based on the analytical formula, W / m. 2 ΔT is the temperature difference between the working fluid and the pipe wall in the test section, in °C.

8. A heat transfer coefficient measurement system based on nonlinear heat flux density reconstruction, used to implement the heat transfer coefficient measurement method according to any one of claims 1-7, characterized in that, include: The data measurement module is used to measure the heat exchange temperature difference between the working fluid and the cooling water at the inlet, middle and outlet of the test section, respectively, to obtain the inlet temperature difference, middle temperature difference and outlet temperature difference; The data processing module is used to reconstruct the nonlinear distribution of heat flux density in the test section based on a preset analytical formula, according to the inlet temperature difference, intermediate temperature difference, and outlet temperature difference. The results output module is used to calculate the heat transfer coefficient at any location within the test section based on the nonlinear distribution of the heat flux density.

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