CN106404829A - CHF measuring method based on heat flux correction - Google Patents

Abstract

The present invention provides a CHF measurement method based on heat flow correction, comprising: Step 1: analyzing the heat leakage link of the heating body, by arranging thermocouples at the heating surface, monitoring the measured temperature value at the heat leakage link of the heating body, and Obtain the leakage heat loss through the heat leakage link; step 2: use the measured value or estimated temperature at the heat leakage link of the heating body as the boundary condition, carry out three-dimensional modeling and numerical simulation calculation of the heating body, and compare the calculated temperature with The measured temperature of the thermocouple arranged in the heating body is compared; step 3: the correction factor C of the heat flow is estimated by the ratio of the actual peak heat flow to the theoretical peak heat flow, and the critical heat flux is calculated. The method of the invention can be used to obtain the critical heat flux density in the non-uniform heating boiling heat transfer of a large-scale engineering test bench, and can effectively improve the accuracy of measurement results.

Description

CHF Measurement Method Based on Heat Flow Correction

technical field

The present invention relates to a critical heat flux measurement method, in particular to a CHF measurement method based on heat flow correction.

Background technique

Boiling heat transfer is widely used in nuclear power, chemical industry, microelectronics and other fields. For boiling heat transfer, boiling heat transfer coefficient (HTC) and critical heat flux (CHF) are two very critical parameters. HTC represents the heat transfer capacity between the fluid and the solid surface. CHF is the maximum heat flux density that can be achieved before the boiling heat transfer surface reaches the critical boiling point. Once the heat flux density exceeds CHF, the boiling heat transfer surface will dry up and burn. It is of great significance to protect the performance and safety of equipment.

Based on the principle of heat balance, the total power input to the heating body is equal to the sum of the leakage heat of the heating body and the heat transfer of the boiling heat exchange surface. Assuming that the input capacity of the body is P ₁ , the body leaks heat through other surfaces except the boiling heat exchange surface, and the leakage heat P ₂ of these surfaces can be measured by arranging thermocouples. The area of the boiling heat transfer surface can be obtained by measurement, and it is set as S. Now the general critical heat flux measurement calculation formula is:

where η is the thermal efficiency of the system,

According to the second law of thermodynamics, wherever there is a temperature difference, heat energy will spontaneously transfer from the high temperature area to the low temperature area. Obviously, formula (1) is not suitable for non-uniform heating and boiling heat transfer, and it is not accurate enough for uniform heating and boiling heat transfer. In non-uniform heating and boiling heat transfer, there will be heat diffusion inside the heating body. Equation (1) only considers the problem of heat balance and does not include thermal diffusion. Therefore, the CHF calculated by only using Equation (1) is too large .

The critical heat flux measurement method based on computational fluid dynamics and heat balance can solve the heat diffusion problem in non-uniform heating boiling heat transfer while considering the system heat balance problem, and improve the measurement accuracy of CHF.

Contents of the invention

In view of the defects in the prior art, the purpose of the present invention is to provide a CHF measurement method based on heat flow correction.

The CHF measurement method based on heat flow correction provided by the present invention comprises the following steps:

Step 1: Analyze the heat leakage link of the heating body, monitor the measured temperature value at the heat leakage link of the heating body by arranging thermocouples on the heating surface, and obtain the heat leakage loss through the heat leakage link;

Step 2: Using the measured value or estimated temperature at the heat leakage link of the heating body as the boundary condition, carry out three-dimensional modeling and numerical simulation calculations on the heating body, and put the calculated temperature at the same position as the thermocouple measurement into the heating body The measured temperature of the arranged thermocouple is compared;

If the error of the calculated temperature relative to the measured temperature is less than or equal to 1%, it is considered that the thermal efficiency of the heating body calculated by three-dimensional modeling and numerical simulation is consistent with the actual thermal efficiency of the copper strip, and the upper limit of the thermal efficiency of the heating body is determined; if the error is greater than 1%, adjust the heat transfer coefficient of the boiling heat transfer surface, recalculate and compare with the measured temperature of the thermocouple;

Step 3: Estimate the correction factor C of the heat flow by the ratio of the actual peak heat flow to the theoretical peak heat flow, and calculate the critical heat flow.

Preferably, it also includes: a heat flow distribution uniformity analysis step, based on the three-dimensional heat conduction numerical simulation results, evaluating the heat flow distribution uniformity on the heating surface, evaluating and determining whether the method of calculating the average heat flow on the heating surface from the heating power is applicable, if the heating body is in the It is not applicable if the heat flow distribution in the width direction is not uniform, and it is considered suitable if the heat flow distribution in the width direction is uniform.

Preferably, the critical heat flux measurement calculation formula in the step 3 is as follows:

In the formula: P ₁ represents the highest input power where the critical heat flux CHF occurs, S represents the boiling heat transfer surface area corresponding to the highest input power, and C represents the heat flow correction factor.

Preferably, the estimation formula of the correction factor C of the heat flow in the step 3 is as follows:

In the formula: q _B represents the maximum boiling heat transfer heat flow, P _max represents the maximum input power, and S ₁ is the boiling heat transfer surface area corresponding to P _max .

Compared with the prior art, the present invention has the following beneficial effects:

1. The CHF measurement method based on heat flow correction provided by the present invention can be used to obtain the critical heat flux density in non-uniform heating and boiling heat transfer of large-scale engineering test benches, effectively improving the accuracy of measurement results.

2. The CHF measurement method based on heat flow correction provided by the present invention can solve the thermal diffusion problem in non-uniform heating and boiling heat transfer while considering the system heat balance problem, and improve the measurement accuracy of CHF.

Description of drawings

Other characteristics, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

Fig. 1 is the thermal balance analysis diagram of the heating block of the test body;

Fig. 2 is a schematic flow chart of the CHF measurement method based on heat flow correction provided by the present invention.

detailed description

The present invention will be described in detail below in conjunction with specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

According to the CHF measurement method based on heat flow correction provided by the present invention, using computational fluid dynamics (CFD) software, the heat leakage to the environment and the heat diffusion problem inside the system are coupled, and a CHF measurement method is proposed, aiming at improving CHF The measurement accuracy provides a reference for testing and engineering.

When critical boiling occurs, the heat transfer coefficient of the boiling heat transfer surface will drop sharply, and at this time the temperature of the boiling heat transfer surface will rise sharply. Therefore, when measuring CHF by boiling heat transfer, thermocouples are generally arranged near the boiling heat transfer surface to monitor the occurrence of CHF and prevent burning.

Specifically, analyze various possible heat leakage links of the heating body, monitor the measured temperature values (steady-state values) at the typical positions of each heat leakage link of the test body by arranging thermocouples on the heating surface, and determine the temperature of each heat leakage link Leakage heat loss. Then use the measured data or (conservative) estimation of the heating body leakage heat as the boundary condition, carry out three-dimensional modeling and numerical simulation calculation on the test body, compare the calculated temperature with the measured temperature of the thermocouple arranged in the heating body, when When the two are roughly the same, it can be considered that the thermal efficiency of the calculation model is consistent with the actual thermal efficiency of the copper strip, and the upper limit of the thermal efficiency of the test body can be determined; at the same time, based on the results of the three-dimensional heat conduction numerical simulation, the uniformity of the heat flow distribution on the heating surface is evaluated, and then the Determine the applicability of the method of calculating the average heat flow on the heating surface from the heating power.

In addition, since the thermal diffusion effect of the heating body can be considered by using the three-dimensional heat conduction numerical simulation, the correction factor C (correction factor) of the local heat flow can be estimated from the ratio of the actual peak heat flow to the theoretical peak heat flow.

The critical heat flux measurement calculation formula is:

Where P ₁ is the highest input power where CHF occurs, S is the boiling heat transfer surface area corresponding to the highest input power, and C is the heat flow correction factor.

The focus of this measurement method is to obtain the heat flow correction factor C. In order to determine the heat flow correction factor _C (or determine the actual heat flow qc at the peak heat flow), the heat balance of the test body must first be analyzed and measured in detail. Take the IVR test bench as an example ,As shown in Figure 1. The corresponding (lumped) heat balance relationship is:

∑P _i ＝∑ _s q _sw +∑ _s q _uw +∑ _s q _stw +∑ _s q _B +∑(q _l +q _r )

In the above heat balance relationship of the body heating block:

The heat leakage heat flow q _uw on the upper surface, the heat leakage heat flow q _sw on the side (including the heat leakage through the side branch), and the heat leakage heat flow q _stw to the water tank (including the heat leakage through the gasket, the gantry frame, etc. ): The temperature (gradient) can be measured by the set heat balance monitoring thermocouple, estimated by Fourier's law (heat leakage through the gasket) or numerical calculation (heat leakage through the gantry frame); Circumferential heat conduction q _l , q _r of the unit: estimated from the temperature difference measured by the solid wall thermocouple between the upper sections of the body; input heat flow of the heating rod group: known under specific test conditions.

These can be used as the boundary conditions and source items for the calculation of the 3D heat conduction of this section of the body. In this way, in order to understand the temperature field in the section of the heating body and the heat flow on the wall, it is only necessary to determine the remaining boundary condition, that is, the boiling heat transfer heat flow q _B of the heating surface facing downwards in this section.

However, the boiling heat transfer is more complicated and not very clear. Fortunately, there are three rows of solid-wall temperature measuring points a, b, and c on the solid wall of the body, so the boiling heat transfer boundary conditions can be assumed (the test results of SBLB are selected as the initial test value here), and the boiling temperature can be continuously adjusted. The heat transfer boundary conditions make the deviation _εi between the calculated temperature at the temperature measurement point of the three rows of thermocouples and the measured temperature meet the specific "acceptance" criterion, and the three-dimensional numerical results in this case are used as the comparison between the actual temperature field of the test body and the actual temperature. Best estimate of thermal flow field. With the actual temperature field (and the corresponding heat flow field), the heat flow correction factor C can be estimated according to the actual surface heat flow (q _c ) at the peak heat flow point on the body,

Among them: q _B is the maximum boiling heat transfer heat flow of the model in this section, P _max is the maximum input power of the model in this section, and S ₁ is the boiling heat transfer surface area corresponding to P _max .

The critical heat flux measurement calculation formula is:

Where P ₁ is the highest input power where CHF occurs, S is the boiling heat transfer surface area corresponding to the highest input power, and C is the heat flow correction factor.

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. In the case of no conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims (4)

1. A CHF measurement method based on heat flow correction, is characterized in that, comprises the steps: Step 1: Analyze the heat leakage link of the heating body, monitor the measured temperature value at the heat leakage link of the heating body by arranging thermocouples on the heating surface, and obtain the heat leakage loss through the heat leakage link; Step 2: Using the measured value or estimated temperature at the heat leakage link of the heating body as the boundary condition, carry out three-dimensional modeling and numerical simulation calculations on the heating body, and put the calculated temperature at the same position as the thermocouple measurement into the heating body The measured temperature of the arranged thermocouple is compared; If the error of the calculated temperature relative to the measured temperature is less than or equal to 1%, it is considered that the thermal efficiency of the heating body calculated by three-dimensional modeling and numerical simulation is consistent with the actual thermal efficiency of the copper strip, and the upper limit of the thermal efficiency of the heating body is determined; if the error is greater than 1%, adjust the heat transfer coefficient of the boiling heat transfer surface, recalculate and compare with the measured temperature of the thermocouple; Step 3: Estimate the correction factor C of the heat flow by the ratio of the actual peak heat flow to the theoretical peak heat flow, and calculate the critical heat flow. 2. The CHF measurement method based on heat flow correction according to claim 1, further comprising: a heat flow distribution uniformity analysis step, based on the three-dimensional heat conduction numerical simulation results, evaluating the heat flow distribution uniformity on the heating surface, evaluating and determining Whether the method of calculating the average heat flow on the heating surface from the heating power is applicable. If the heat flow distribution of the heating body in the width direction is not uniform, it is not applicable. If the heat flow distribution in the width direction is uniform, it is considered applicable. 3. the CHF measurement method based on heat flow correction according to claim 1, is characterized in that, in described step 3, critical heat flux measurement formula is as follows: ${\mathrm{<span\; class="notranslate">\; q</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; S</span>}}\mathrm{<span\; class="notranslate">\; C</span>}$ In the formula: P ₁ represents the highest input power where the critical heat flux CHF occurs, S represents the boiling heat transfer surface area corresponding to the highest input power, and C represents the heat flow correction factor. 4. the CHF measurement method based on heat flow correction according to claim 1, is characterized in that, the estimation formula of the correction factor C of heat flow in described step 3 is as follows: $\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; q</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}$ In the formula: q _B represents the maximum boiling heat transfer heat flow, P _max represents the maximum input power, and S ₁ is the boiling heat transfer surface area corresponding to P _max .