CN-122019934-A - Natural convection heat transfer calculation method under radiation and convection coupling heat exchange condition

CN122019934ACN 122019934 ACN122019934 ACN 122019934ACN-122019934-A

Abstract

The application provides a natural convection heat transfer calculation method and a system under the radiation and convection coupling heat exchange condition, wherein the method comprises the steps of constructing an experimental device, wherein the experimental device comprises an passive waste heat discharge heat exchanger and an electric heating rod inserted into the interior of the passive waste heat discharge heat exchanger, a flow channel for cooling fluid to flow is arranged in the interior of the passive waste heat discharge heat exchanger, and a flow field interference device is not arranged in the flow channel; the method comprises the steps of measuring total heat exchange quantity transferred to cooling fluid by an electric heating rod and temperatures of all wall surfaces participating in radiation heat exchange in an experimental device, establishing a radiation heat exchange calculation model corresponding to the experimental device, calculating the radiation heat exchange quantity by taking the temperatures of all wall surfaces participating in radiation heat exchange as boundary input conditions by the radiation heat exchange calculation model, and subtracting the radiation heat exchange quantity from the total heat exchange quantity based on an energy conservation principle to obtain the convection heat exchange quantity. According to the application, through the 'half experiment-half simulation' integration thought, the precise separation of radiation heat exchange and convection heat exchange is realized under the condition of not interfering a flow field.

Inventors

CAI WENYI
QU WENHAI
LIU ZHAN
JIN DI
Hu Peizheng
FAN PU
ZHU YINGZI
CHEN ZHONGYUAN

Assignees

上海核工程研究设计院股份有限公司

Dates

Publication Date: 20260512
Application Date: 20260415

Claims (12)

1. A natural convection heat transfer calculation method under the radiation and convection coupling heat exchange condition is characterized by comprising the following steps: The method comprises the steps of building an experimental device, wherein the experimental device comprises an inactive waste heat discharge heat exchanger and an electric heating rod inserted into the inactive waste heat discharge heat exchanger, a flow channel for cooling fluid to flow is arranged in the inactive waste heat discharge heat exchanger, and a flow field interference device is not arranged in the flow channel; Measuring the total heat exchange amount transferred to the cooling fluid by the electric heating rod and the temperature of each wall surface participating in radiation heat exchange in the experimental device; Establishing a radiation heat exchange calculation model corresponding to the experimental device, wherein the radiation heat exchange calculation model takes the temperature of each wall surface participating in radiation heat exchange as a boundary input condition to calculate the radiation heat exchange quantity; And subtracting the radiation heat exchange amount from the total heat exchange amount based on an energy conservation principle to obtain the convection heat exchange amount.
2. The method of claim 1, wherein the radiant heat exchange calculation model calculates a radiant heat exchange amount comprising: discretizing each wall surface participating in radiation heat exchange, and dividing the wall surface into a plurality of sub-surfaces along the axial direction and the circumferential direction; Randomly sampling in each sub-surface to determine the emitting position and emitting direction of the ray, tracking the propagation path of the ray, and judging whether the ray intersects other wall surfaces or not; When the ray intersects with the wall surface, judging that the ray is absorbed or reflected according to the absorptivity of the wall surface, and recording the energy and the position of the absorbed ray; And counting the tracking results of all rays, calculating the angle coefficient between the wall surfaces based on the counting results, and further calculating the radiation heat exchange quantity.
3. The method of claim 2, wherein determining whether the ray intersects other walls comprises determining whether the ray intersects other walls by geometric intersection using a line-of-sight method and determining the location of the intersection.
4. A method according to claim 3, wherein determining whether a ray intersects other walls is performed by determining whether a ray and cylinder quadratic equation is positive real, the ray and cylinder quadratic equation being: , , ; Wherein, the method comprises the following steps of , ) Is the ray starting point coordinate , ) The component of the ray direction vector in the xy plane, R is the cylinder radius, and t is the distance along the ray direction.
5. The method of claim 2, wherein the sampling formula for the transmit location is: wherein z is the axial position under the cylindrical coordinate system, The circumferential position of the cylindrical coordinate system is L, the length of the electric heating rod is L, and the rand () is [0,1] uniform random number.
6. The method of claim 2, wherein the sampling of the transmit direction follows a diffuse transmit cosine distribution hypothesis, and wherein the sampling of the transmit direction is formulated as: Wherein, the In the form of a polar angle, the angle of the polar, For azimuth, rand () is a [0,1] uniform random number.
7. The method of claim 2, wherein determining whether radiation is absorbed or reflected based on the absorption of the wall surface comprises: generating a random number between 0 and 1, judging that the ray is absorbed and recording energy if the random number is smaller than the absorptivity of the wall surface, and resampling according to the diffuse reflection direction if the random number is not smaller than the absorptivity of the wall surface, and entering the next round of tracking; The ray terminates tracking under any condition that it is absorbed by the surface, escapes the calculation field or reaches a preset maximum number of reflections.
8. The method of claim 2, wherein the angular coefficient between the walls is calculated by the formula: Wherein, the The angular coefficient of wall i to wall j, To the number of rays emitted from wall i and absorbed by wall j, The total number of rays emitted for wall i.
9. The method of claim 2, wherein the radiant heat exchange amount is calculated based on an ash body radiant heat exchange network model: Wherein, the The heat exchange amount of the radiation of the wall surface i and the wall surface j, For the amount of heat exchange of the radiation, For the stefin-boltzmann constant, The temperature of the wall surface i is set to be the temperature of the wall surface i, For the temperature of the wall surface j, The area of the wall surface i is defined as, The area of the wall surface j is defined as, For the emissivity of the wall i, For the emissivity of the wall j, The angular coefficient of wall i to wall j.
10. The method of claim 1, further comprising, after obtaining the convective heat transfer amount: Based on the obtained convection heat exchange amount, calculating a convection heat exchange coefficient by combining the wall surface temperature and the fluid temperature which are measured by experiments and participate in radiation heat exchange, and fitting to obtain a natural convection heat exchange criterion association type: wherein Nu is natural convection Knoop number, gr is Gray dawn number, Is Planty number, C, n is constant, obtained by fitting experimental data.
11. The method of claim 1, further comprising the step of closed loop correction of the radiation heat exchange calculation model: And dynamically correcting boundary conditions of the radiation heat exchange calculation model by using the temperature of each wall surface participating in radiation heat exchange, and carrying out iterative calibration on the emissivity of the wall surface in the model by using experimental data under a reference working condition, so that the calculation error of the radiation heat exchange quantity is controlled within a preset range.
12. A natural convection heat transfer computing system, comprising: The experimental device comprises an inactive waste heat discharge heat exchanger and an electric heating rod inserted into the inactive waste heat discharge heat exchanger, wherein a flow channel for cooling fluid to flow is arranged in the inactive waste heat discharge heat exchanger, and a flow field interference device is not arranged in the flow channel; the data measuring unit is used for measuring the total heat exchange quantity transferred to the cooling fluid by the electric heating rod and the temperature of each wall surface participating in radiation heat exchange in the experimental device; The radiation heat exchange calculation model is used for calculating the radiation heat exchange quantity by taking the temperature of each wall surface participating in radiation heat exchange as a boundary condition; and the data fusion processing unit is used for subtracting the radiation heat exchange amount from the total heat exchange amount based on an energy conservation principle to obtain the convection heat exchange amount.

Description

Natural convection heat transfer calculation method under radiation and convection coupling heat exchange condition Technical Field The application mainly relates to the technical field of nuclear reactor thermodynamic hydraulic power and safety, in particular to a natural convection heat transfer calculation method and a natural convection heat transfer calculation system under radiation and convection coupling heat exchange conditions. Background The passive waste heat discharge system is the last barrier for ensuring the core of the nuclear reactor to maintain the core cooling under the accident condition of losing the hot trap. The passive waste heat discharging heat exchanger in the system is a key core component for realizing waste heat transfer, and horizontal tube bundles densely arranged inside the passive waste heat discharging heat exchanger form a heat transfer main body. Under the shutdown working condition, after the core waste heat is transferred to the surface of the tube bundle, the core waste heat is mainly transferred to cooling fluid in a natural convection and radiation heat exchange mode. The natural convection heat transfer characteristic directly determines the residual heat discharge capacity and long-term operation stability of the system, and is a core basis for heat exchanger structure optimization, thermodynamic and hydraulic model development and safety analysis. However, when the heat transfer characteristics of such heat exchangers are studied in the prior art, the radiation heat exchange and convection heat exchange share in the total heat exchange amount cannot be directly distinguished. In order to solve the problems, two main technical exploration schemes exist in the industry, but the defects that the technical exploration schemes are difficult to overcome exist. One type is a full experimental separation scheme, and attempts are made to directly measure radiant heat flow by adding a radiation shielding plate, a heat absorber or using a radiant heat flow meter. However, the direct measurement of radiant heat flow is interfered by multiple factors, namely, dynamic deviation of +/-50% exists in the wall emissivity affected by the oxidation degree, the calculation deviation of the angle coefficient can reach +/-15% due to mutual shielding among tube bundles, the calculation error of the total amount of radiant heat exchange after superposition is always more than 30%, and more importantly, the shielding device can change the geometric structure of the tube bundle flow channel, destroy the flow field form of natural convection, cause the measurement distortion of the convection heat exchange to exceed 50%, and completely lose the engineering reference value of experimental data. The other is a full simulation analysis scheme, which relies on CFD software to calculate radiation and convection heat exchange at the same time, but the scheme lacks effective verification of experimental data, wherein the scheme mainly adopts empirical values for input conditions such as wall emissivity, fluid physical parameters and the like, the deviation between a simulation result and an actual working condition can reach 35%, the conservation of a model cannot be ensured, and the rule requirement of nuclear safety equipment design is difficult to meet. Therefore, an experiment and calculation method capable of guaranteeing the reality of an experiment flow field and accurately separating the share of radiation heat exchange and convection heat exchange is needed, so as to solve the core heat transfer measurement problem of the passive waste heat discharge heat exchanger. Disclosure of Invention The application aims to solve the problems in the prior art, and provides a natural convection heat transfer calculation method and a natural convection heat transfer calculation system under the radiation and convection coupling heat transfer condition, which can realize the accurate separation of radiation heat transfer and convection heat transfer under the condition of not interfering a flow field. The application provides a natural convection heat transfer calculation method under radiation and convection coupling heat exchange conditions, which comprises the steps of constructing an experimental device, wherein the experimental device comprises an inactive waste heat discharge heat exchanger and an electric heating rod inserted into the inactive waste heat discharge heat exchanger, a flow channel for cooling fluid to flow is arranged in the inactive waste heat discharge heat exchanger, a flow field interference device is not arranged in the flow channel, measuring total heat exchange quantity transferred to the cooling fluid by the electric heating rod and wall surface temperatures participating in radiation heat exchange in the experimental device, establishing a radiation heat exchange calculation model of the experimental device, calculating radiation heat exchange quantity by taking the wall