Simulation method for friction heat generation and environment heat dissipation in nuclear power SCO2 pipe network model

Abstract

The invention relates to a method for simulating friction heat generation and environmental heat dissipation in a nuclear power SCO2 pipe network model, which comprises the following steps of: dispersing a nuclear power SCO2 pipe network system, determining nodes and streamlines of a target pipeline, acquiring original physical parameters, and acquiring friction pressure drop of fluid in the target pipeline by utilizing the original physical parameters; based on the friction pressure drop, the pipe wall friction acting heat absorption capacity and the fluid friction acting heat absorption capacity are obtained, and the fluid friction acting heat absorption capacity is introduced into an energy exchange item in the pipe network node energy conservation model. A pipe network heat dissipation model is established through the nodes, the pipe wall friction acting heat absorption capacity is added into the pipe network heat dissipation model, and the heat dissipation capacity of the nodes dissipating heat to the environment is obtained; and introducing the heat dissipating capacity into an energy exchange item, calculating a pipe network node energy conservation model after introduction, obtaining a specific enthalpy solving matrix, carrying out iterative operation on the specific enthalpy solving matrix, and obtaining friction heat generation and heat dissipation distribution results of all parts of the system under time step propulsion. According to the method, the simulation precision of the SCO2 pipe network is improved.

Description

Technical Field

[0001] The present invention relates to the field of simulation technology, in particular to a simulation method for frictional heat generation and environmental heat dissipation in a nuclear power SCO2 pipe network model. Background Art

[0002] In nuclear power plants, pipe network simulation technology is commonly used for the design, evaluation, operation, and training of primary and secondary circuit systems due to its system-level simulation capabilities and balanced computational speed and stability. In current nuclear power plant pipe network simulations, the heat dissipation losses at individual nodes are minimal, so the effects of heat dissipation between the pipes and the surrounding environment are often ignored. However, when applied to nuclear power plants such as deep space probes and unmanned underwater vehicles, where cabin space is small and compact, accurate calculation of heat dissipation is crucial for the design and control of cooling systems. This effect must be considered, especially for SCO2 pipe network systems with large total heat exchange area.

[0003] Supercritical carbon dioxide has a low density and a fast flow rate, and the frictional heat generated is usually between hundreds of watts and kilowatts. Frictional heat generation cannot be ignored. The existing nuclear power plant pipeline network simulation does not consider the impact of frictional heat generation. Specifically, it does not consider the heat dissipation from frictional heat generation to the environment, resulting in inaccurate calculation of the heat dissipation of the nuclear power SCO2 pipeline network, which brings difficulties to the prediction of the cabin heat load; secondly, it does not consider the frictional heat generation absorbed by the fluid. The above two situations will lead to the energy exchange term Q in the node energy conservation equation. i The calculated distance deviates from the actual one, which affects the solution of the node specific enthalpy in the SCO2 pipe network and reduces the simulation accuracy of the SCO2 pipe network. Summary of the Invention

[0004] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a simulation method for frictional heat generation and environmental heat dissipation in a nuclear power SCO2 pipe network model, thereby improving the simulation accuracy of the SCO2 pipe network.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A simulation method for frictional heat generation and environmental heat dissipation in a nuclear power SCO2 pipe network model includes:

[0007] Discrete the nuclear power SCO2 pipe network system, determine the nodes and streamlines of the target pipeline, and obtain the original physical parameters, and use the original physical parameters to obtain the friction pressure drop of the fluid in the target pipeline;

[0008] Based on the friction pressure drop, the amount of heat absorbed by the friction work of the pipe wall and the amount of heat absorbed by the friction work of the fluid are obtained, the amount of heat absorbed by the friction work of the fluid is introduced into the energy exchange term in the energy conservation model of the pipe network node, a pipe network heat dissipation model is established using the node, the amount of heat absorbed by the friction work of the pipe wall is added to the pipe network heat dissipation model, and the amount of heat dissipated from the node to the environment is obtained;

[0009] The heat dissipation is introduced into the energy exchange term, the energy conservation model of the pipe network node after the introduction is calculated, and the specific enthalpy solution matrix is ​​obtained. The specific enthalpy solution matrix is ​​iteratively calculated to obtain the frictional heat generation and heat dissipation distribution results of various locations in the SCO2 pipe network system under time step advancement, that is, the simulation results of frictional heat generation and environmental heat dissipation in the pipe network system.

[0010] Optionally, the original physical parameters include: specifications of the pipeline where the node is located, pipe wall material data, fluid parameters and streamline transport parameters;

[0011] The specifications of the pipe where the node is located include: length, diameter and thickness;

[0012] The pipe wall material data includes: density, thermal conductivity, heat capacity and absolute roughness of the pipe inner wall;

[0013] The fluid parameters include: fluid density, specific heat capacity at constant pressure, dynamic viscosity and thermal conductivity;

[0014] The streamline transport parameters include: mass flow, wind speed of the cabin air where the pipeline is located, ambient temperature and parameters of the pipeline insulation structure, air thermal conductivity, thermal conductivity of the reflective insulation layer and thermal conductivity of the interstitial working fluid glass wool fiber.

[0015] Optionally, obtaining the friction pressure drop of the fluid in the target pipeline includes:

[0016] The original physical parameters are used to obtain the Reynolds number of the fluid in the target pipe, and based on the Reynolds number, the friction coefficient between the fluid and the pipe wall is calculated to obtain the friction pressure drop.

[0017] Optionally, obtaining the amount of heat absorbed by the frictional work done by the pipe wall and the amount of heat absorbed by the frictional work done by the fluid includes:

[0018] Based on the friction pressure drop, node density and mass flow rate, the frictional heat generated by the fluid and the inner wall of the pipeline is obtained. The frictional heat absorption ratio is calculated through the thermal conductivity, density and specific heat capacity of the pipe wall material and the fluid respectively. Combined with the frictional heat generated, the frictional heat absorption of the pipe wall and the frictional heat absorption of the fluid are obtained.

[0019] Optionally, obtaining the amount of heat dissipated by the node to the environment includes:

[0020] A preset pipe inner wall temperature initial value is obtained, a pipe inner wall received convection heat exchange amount is obtained by combining the pipe inner wall temperature initial value with a fluid and pipe wall convection heat exchange thermal resistance, and the pipe inner wall received convection heat exchange amount and pipe wall friction work heat absorption amount are taken as a heat absorption amount of the pipe inner wall;

[0021] The heat absorption amount of the pipe inner wall is input into a heat balance equation for the pipe inner wall to obtain an iteratively converged pipe inner wall temperature, and a heat dissipation amount of the node to the environment is obtained based on the iteratively converged pipe inner wall temperature.

[0022] Optionally, the heat balance equation for the pipe inner wall comprises:

[0023]

[0024] Wherein, t w is a pipe inner wall temperature, ℃; t h is a cabin environment temperature, ℃; Q 对流 is a fluid and pipe inner wall convection heat exchange amount, Q f1 is a friction work heat absorption amount.

[0025] Optionally, the heat dissipation amount of the node to the environment comprises:

[0026]

[0027] Wherein, t0 is a fluid temperature, ℃; R1, R 2 , R 3 , R 4 , R 5 are respectively a fluid and pipe wall convection heat exchange thermal resistance per unit length, a pipe heat conduction thermal resistance, a thermal insulation layer inner wall gap glass wool fiber heat conduction thermal resistance, a metal reflective thermal insulation layer thermal resistance, and a thermal insulation layer and cabin air heat exchange thermal resistance, ℃ / kw.

[0028] Optionally, the method further comprises: visualizing and displaying a pipe network model parameter.

[0029] Wherein, the pipe network model parameter comprises: a target pipe inner fluid friction pressure drop, a fluid and pipe inner wall friction work heat generation amount, a pipe wall friction work heat absorption amount, a fluid friction work heat absorption amount, a node heat dissipation amount to the environment, a total heat dissipation amount of the pipe network, and a node specific enthalpy.

[0030] The present application has the following advantages:

[0031] The present application considers the SCO2 and pipe wall friction work heat generation, adds a heat dissipation term Q f2 of the pipe wall friction work heat absorption amount to the fluid friction work heat absorption amount Q wgBy coupling it into the node energy conservation equation, the specific enthalpy solution matrix is ​​obtained, and the corrected enthalpy value is solved, which improves the simulation accuracy of the SCO2 pipe network.

[0032] The present invention comprehensively considers the heat Q absorbed by the inner wall of the pipeline due to friction work f1 and convection heat transfer Q 对流 The heat dissipation of the pipe network is accurately calculated through the heat dissipation model, providing theoretical support for the cabin heat load prediction and the design of the heat dissipation system and heat dissipation control. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 This is a flow chart of a simulation method for frictional heat generation and environmental heat dissipation in a nuclear power SCO2 pipe network model according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0036] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] like Figure 1As shown, this embodiment discloses a simulation method for frictional heat generation and environmental heat dissipation in a nuclear power SCO2 pipe network model, including: discretizing the nuclear power SCO2 pipe network system, determining the nodes and streamlines of the target pipe, and obtaining original physical parameters, and using the original physical parameters to obtain the friction pressure drop of the fluid in the target pipe; based on the friction pressure drop, obtaining the heat absorption of the pipe wall friction work and the heat absorption of the fluid friction work, introducing the heat absorption of the fluid friction work into the energy exchange term in the energy conservation model of the pipe network node, establishing a pipe network heat dissipation model using the node, adding the heat absorption of the pipe wall friction work to the pipe network heat dissipation model, and obtaining the heat dissipation of the node to the environment; introducing the heat dissipation into the energy exchange term, calculating the introduced energy conservation model of the pipe network node, participating in subsequent coupled iterative operations of the SCO2 pipe network, supplementing the pipe network program output module with programs related to the frictional heat generation and heat dissipation, and outputting the frictional heat generation and heat dissipation distribution results at various locations in the SCO2 pipe network under time step advancement, so as to realize the simulation of frictional heat generation and environmental heat dissipation in the pipe network system.

[0038] Specifically, this embodiment discloses a simulation method for frictional heat generation and environmental heat dissipation in a nuclear power SCO2 pipeline network model, including: Step 1: Select a pipeline segment, determine the pipeline and pipeline insulation structure parameters, and the internal working fluid state parameters, and input the above parameters into the model; Step 2: Obtain the velocity of the fluid in the pipeline segment, calculate the Reynolds number of the fluid and the friction coefficient between the fluid and the pipeline wall, and obtain the friction pressure drop of the pipeline fluid; Step 3: Calculate the heat W generated by the friction work between the fluid and the inner wall of the pipeline f , the heat absorbed by the friction work of the tube wall Q f1 And the heat absorbed by the fluid friction work Q f2 ; Step 4: The fluid friction work done in step 3 absorbs heat Q f2 The energy exchange term Q added to the node energy conservation equation of the pipe network model i Step 5: Establish a pipe network heat dissipation model and convert the heat absorbed by the pipe wall friction work Q f1 Add it to the pipe network heat dissipation model to calculate the heat dissipation Q of the node to the environment wg , this step is applied to each node discretized from the actual system to obtain the total heat dissipation of the pipe network; Step 6: Substitute the node environmental heat dissipation Q calculated in step 5 wg The energy exchange term Q added to the node energy conservation equation i In the process, the energy conservation equation of the pipe network model is returned for calculation to obtain the specific enthalpy solution matrix, which is used for subsequent coupled iterative operations of the SCO2 pipe network. The frictional heat generation and heat dissipation related programs are supplemented in the pipe network program output module, and the frictional heat generation and heat dissipation distribution results of the SCO2 pipe network under time step advancement are output to realize the simulation of frictional heat generation and environmental heat dissipation in the pipe network model; Step 7: The parameters calculated in the above steps 2-6 are displayed to the external output to realize the output of the simulation results.

[0039] Furthermore, the original physical parameters include: specifications of the pipeline where the node is located, pipe wall material data, fluid parameters and streamline transport parameters; specifications of the pipeline where the node is located include: length, diameter and thickness; pipe wall material data include: density, thermal conductivity, heat capacity and absolute roughness of the inner wall of the pipeline; fluid parameters include: fluid density, constant pressure specific heat capacity, dynamic viscosity and thermal conductivity; streamline transport parameters include: mass flow rate, wind speed of the cabin air where the pipeline is located, ambient temperature and parameters of the pipeline insulation structure, air thermal conductivity, thermal conductivity of the reflective insulation layer and thermal conductivity of the interstitial working fluid glass wool fiber.

[0040] Specifically, step 1: Based on the macroscopic volume control method, the thermal system of a ship nuclear power plant is discretized. The volumetric and flow properties of the pipes in the thermal system are separated, resulting in nodes with volumetric properties and streamlines with flow properties. The nodes replace the volumetric properties of the pipes, possessing only volumetric parameters such as pressure, volume, temperature, and diameter, and these parameters are evenly distributed within the nodes. The streamlines replace the flow properties of the pipes, possessing only flow parameters such as flow rate and resistance, and these parameters are evenly distributed along the streamlines.

[0041] Select a pipe section, determine the nodes and streamlines representing the section, and clearly define the pipe, pipe insulation structure parameters, and internal working fluid state parameters, and input these parameters into the model. The pipe, pipe insulation structure parameters, and internal working fluid state parameters include:

[0042] (1) Specifications of the pipe where the node is located, such as length, diameter, thickness, etc.;

[0043] (2) 347 stainless steel was selected as the pipe wall material to obtain its density, thermal conductivity, heat capacity and absolute roughness of the pipe inner wall;

[0044] (3) Fluid parameters are obtained by calling SCO2 parameters, such as fluid density, constant pressure specific heat capacity, dynamic viscosity, thermal conductivity, etc.;

[0045] (4) The mass flow rate of streamline transport, the wind speed of the cabin air where the pipeline is located, the ambient temperature and the parameters of the pipeline insulation structure, the thermal conductivity of the air, the thermal conductivity of the reflective insulation layer and the thermal conductivity of the glass wool fiber in the gap. The thermal conductivity of the glass wool fiber is calculated by the segmented fitting method.

[0046] The thermal conductivity of the reflective insulation layer is:

[0047] λ=0.040705+0.000186t a (W / m·℃)

[0048] Among them, t a is the arithmetic mean of the Celsius temperatures of the inner and outer walls of the insulation layer, °C;

[0049] It is reasonable to assume that the outer wall temperature is 49° C. during the calculation of R4. The present invention also assumes that the outer wall temperature is 49° C. when calculating R4.

[0050] The calculation formula of thermal conductivity of glass wool fiber obtained by segmented fitting is as follows:

[0051] λ(T)=0.034+3×10 -5 ×(T-350)

[0052] In the formula, because the convection heat transfer thermal resistance R1 between the fluid and the inner wall of the pipe and the heat conduction thermal resistance R2 of the pipe are very small compared with other thermal resistances, the temperature T of the working medium in the gap when the fluid transfers heat is still close to the fluid temperature, ℃.

[0053] Furthermore, obtaining the friction pressure drop of the fluid in the target pipeline includes: using original physical parameters to obtain the Reynolds number of the fluid in the target pipeline, and based on the Reynolds number, calculating the friction coefficient between the fluid and the pipe wall to obtain the friction pressure drop.

[0054] Specifically, step 2: Based on the parameters of step 1, including mass flow rate, density, pipe size, etc., the velocity of the fluid in the pipe section is obtained, the Reynolds number of the fluid and the friction coefficient between the fluid and the pipe wall are calculated, and the friction pressure drop of the pipe fluid in the SCO2 pipe network model is obtained. The specific calculation process is as follows:

[0055] The SCO2 flow velocity and Reynolds number are calculated as follows:

[0056]

[0057] Where f is the mass flow rate, kg / s; d is the inner diameter of the pipe, m; v is the flow velocity, m / s; μ is the dynamic viscosity, Pa·s; ρ is the fluid density, kg / m 3 ;

[0058] The explicit form of the Colebrook-White equation of the Zigrang-Sylvester drag model is introduced:

[0059]

[0060] Where ε is the surface roughness, m; Re is the Reynolds number;

[0061] Introducing the Darcy-Weisbach formula:

[0062]

[0063] Where h f is the head loss due to friction, m; λ is the friction coefficient; L is the pipe length, m; v is the average flow velocity of the fluid, m / s; g is the acceleration due to gravity, m / s 2 ;

[0064] The friction pressure drop is calculated as follows:

[0065]

[0066] Where ΔP is the friction pressure drop.

[0067] Furthermore, obtaining the amount of heat absorbed by the frictional work done by the pipe wall and the amount of heat absorbed by the frictional work done by the fluid includes: obtaining the amount of heat generated by the frictional work done by the fluid and the inner wall of the pipe based on the friction pressure drop, node density and mass flow rate, calculating the proportion of frictional heat absorption through the thermal conductivity, density and specific heat capacity of the pipe wall material and the fluid respectively, and obtaining the amount of heat absorbed by the frictional work done by the pipe wall and the amount of heat absorbed by the frictional work done by the fluid in combination with the amount of heat generated by the frictional work.

[0068] Specifically, step 3: Based on the friction pressure drop of the fluid, calculate the heat W generated by the friction work between the fluid and the inner wall of the pipe in the SCO2 pipe network model. f , and then calculate the heat absorbed by the friction work of the tube wall Q f1 , the fluid friction work and heat absorption Q f2 ;

[0069] The friction between the fluid and the inner wall of the pipe generates heat W f for:

[0070]

[0071] The proportion of heat absorbed by friction between the inner wall of the pipe and the fluid is b:

[0072]

[0073] The heat absorbed by the inner wall of the pipe due to friction work Q f1 :

[0074]

[0075] Fluid friction work and heat absorption Q f2 :

[0076]

[0077] Among them, Q f1 is the heat absorbed by the friction work of the inner wall of the pipe, W; Q f2 is the heat absorbed by SCO2 due to frictional work, W; b is the fraction, a dimensionless number; W f is the heat generated by friction work in the pipe of length L, W;

[0078] Furthermore, step 4 converts the fluid friction work to heat absorption Q f2 The energy exchange term Q added to the node energy conservation equation i middle:

[0079] The energy conservation equation of the pipe network node is:

[0080]

[0081] Among them, E i is the energy in node i, kJ; M i is the mass of the fluid in node i, kg; h i is the specific enthalpy of the fluid in node i, kJ / kg; τ is the time, s; f in,i,j is the flow rate of the jth streamline flowing into node i, kg / s; h in,i,j is the specific enthalpy of the fluid on the jth streamline flowing into node i, kJ / kg; f out,i,j is the flow rate of the jth streamline out of node i, kg / s; Q i is other energy exchange quantity, including heat source, heat exchange, heat dissipation, etc., kW. i Including heat source term, heat transfer term, heat dissipation term, etc., the heat absorbed by the fluid friction Q f2 Join Q i middle.

[0082] Step 5: Based on certain assumptions, establish a pipe network heat dissipation model and convert the heat absorbed by the pipe wall friction work to Q f1 By adding the heat dissipation model to the pipe network, the heat dissipation from the SCO2 pipe network to the engine room can be calculated more accurately by considering the convective heat transfer between the fluid and the inner wall of the pipe and the heat generated by friction.

[0083] The basic assumptions of the heat dissipation model are as follows:

[0084] (1) The pipe is evenly filled with SCO2;

[0085] (2) The medium in the pipeline, insulation layer and gap is evenly distributed and relatively static;

[0086] (3) The pipe is made of stainless steel, and the only insulation layer outside the pipe is a metal reflective insulation layer;

[0087] (4) The interstitial medium between the pipe and the metal reflective protective layer is glass wool fiber;

[0088] (5) Assuming that the ambient temperature in the cabin is consistent with the cooling air temperature, the flow outside the insulation layer is mainly a mixture of forced convection and natural convection;

[0089] The heat dissipation model equation is as follows:

[0090]

[0091] The calculation formula for convective heat transfer is:

[0092]

[0093] Where t0 is the fluid temperature, °C; t w is the inner wall temperature of the pipe, °C; t h is the cabin ambient temperature, °C; Q wg is the heat dissipation from the node to the environment, W / m; h1 is the convection heat transfer coefficient between the fluid and the inner wall of the pipe, W / ℃·m 2 λ1, λ2, and λ3 are the thermal conductivity coefficients of the pipeline, the glass wool fiber in the gap between the pipeline and the insulation layer, and the reflective insulation layer, respectively, in W / m·℃; d 、h q They are the natural convection and forced convection heat transfer coefficients between the outer wall of the insulation layer and the cabin air, W / ℃·m 2 ; d is the inner diameter of the pipe, m; δ1, δ2, δ3 are the distance between the inner wall and the outer wall of the pipe, the distance between the outer wall of the pipe and the inner wall of the insulation layer, and the distance between the inner wall and the outer wall of the insulation layer, respectively, in m; R1, R2, R3, R4, R5 are the convective heat transfer thermal resistance between the fluid and the pipe wall, the heat conduction thermal resistance of the pipe, the heat conduction thermal resistance of the glass wool fiber in the gap between the inner wall of the insulation layer, the thermal resistance of the metal reflective insulation layer, and the convective heat transfer thermal resistance between the insulation layer and the cabin air, respectively.

[0094] Furthermore, obtaining the amount of heat dissipated from the node to the environment includes: presetting an initial value of the pipe inner wall temperature, obtaining the convective heat received by the pipe inner wall through the initial value of the pipe inner wall temperature combined with the convective heat transfer thermal resistance between the fluid and the pipe wall, and taking the sum of the convective heat and the heat absorbed by the pipe wall as the heat absorbed by the pipe inner wall; inputting the heat absorbed by the pipe inner wall into a heat balance equation for the pipe inner wall, and obtaining the pipe inner wall temperature after iterative convergence; and obtaining the amount of heat dissipated from the node to the environment based on the pipe inner wall temperature after iterative convergence.

[0095] Specifically, the total heat received by the inner wall of the pipe is:

[0096] Q suction = Q convection + Q f1

[0097] Given the pipe inner wall temperature t w Initial value, the convective heat transfer amount Q received by the inner wall of the pipe can be calculated through the convective heat transfer thermal resistance R1 between the fluid and the inner wall of the pipe 对流 , convective heat transfer Q 对流 Friction with the pipe wall does work and absorbs heat Q f1 The sum is the heat Q absorbed by the inner wall of the pipe 吸 , a heat balance equation is listed for the inner wall of the pipe. The heat balance equation is as follows: the heat absorbed by the inner wall of the pipe is equal to the heat released to the outside. The new inner wall temperature t is calculated by the heat balance equation. w , after iteration, we get t that meets the convergence condition w The subsequent idea is: the inner wall temperature of the pipe after convergence t wIt can be used to calculate the convection heat transfer resistance R1, the pipe heat transfer resistance R2, and the glass wool thermal fiber resistance R3 because the thermal conductivity of the materials is known. The thermal conductivity of the reflective metal insulation layer can be calculated with the help of the converged pipe inner wall temperature t w So the thermal resistance R4 of the reflective metal insulation layer can be calculated. The convection heat transfer resistance R5 between the insulation layer and the cabin air is known and can be calculated. So the fluid temperature t0 and the cabin air temperature t h Substituting the calculated thermal resistances into the heat dissipation model, the node heat dissipation can be solved. This node heat dissipation is accurate because the calculated thermal resistances are all calculated after thermal balance. As the time step of the SCO2 pipe network simulation progresses, the heat dissipation of the entire SCO2 pipe network system can be finally determined. The specific solution process is as follows:

[0098] The heat balance equation is:

[0099]

[0100] Among them, t w is the inner wall temperature of the pipe, °C; t h is the cabin ambient temperature, °C;

[0101] The inner wall temperature of the pipe is t w The initial value calculation obtains the convection heat transfer coefficient h1, and then the convection heat transfer thermal resistance R1 between the fluid and the tube wall is obtained. Q is calculated from the convection heat transfer thermal resistance R1 对流 The specific process is as follows:

[0102] The convective heat transfer coefficient between the fluid and the tube wall is calculated as follows, introducing the Gnielinski model for forced convection heat transfer of supercritical carbon dioxide:

[0103]

[0104] Where Nu is the Nusselt number; Re is the Reynolds number; Pr is the Prandtl number; d is the inner diameter of the flow channel m; L is the length of the inlet section m; t0 is the fluid temperature K; t w K represents the inner wall temperature of the pipe.

[0105] The applicable range of the Gnielinski model is: 2300 <Re<10 6 , 0.6 <Pr<10 5 .

[0106]

[0107] When calculating the convection heat transfer coefficient between the fluid and the tube wall, only t wIf unknown, it is used in an iterative calculation to determine the convection heat transfer resistance R1. The pipe material is 347 stainless steel, and its thermal conductivity is set to 18.35 W / (m·°C). The pipe thermal resistance R2 can be calculated. Based on the above formula for calculating the thermal conductivity of glass wool fibers, the invention assumes that the glass wool fiber temperature is the fluid temperature, and the thermal conduction resistance R3 of the glass wool fibers in the gap between the inner walls of the insulation layer can be calculated.

[0108] The method for solving the thermal resistance R4 of the metal reflective insulation layer is as follows: the heat balance equation is listed for the metal insulation layer. It is known that its thermal conductivity is only related to the inner wall temperature of the insulation layer in this invention. When t w After the initial value, the following formula only has t w1 Unknown, the temperature of the inner wall of the insulation layer t w1 It can be calculated. Assuming that the outer wall temperature is 49℃, t w1 The thermal conductivity of the metal insulation layer is calculated, and then R4 is calculated.

[0109]

[0110] λ3=0.040705+0.000186(t w1 +49)(W / m·℃)

[0111]

[0112] The thermal resistance R4 of the metal insulation layer is known, and the inner wall temperature t w1 Calculate the outer wall temperature of the insulation layer t w2 , outside the insulation layer, the heat transfer is a mixture of natural convection and forced convection between the air and the outer wall of the insulation layer. The heat transfer coefficient is solved as follows:

[0113]

[0114] Natural convection heat transfer coefficient formula:

[0115]

[0116] Where h z is the natural convection heat transfer coefficient of the outer surface of the outer protective tube, W / (m 2 ·K).

[0117] The forced convection heat transfer coefficient is as follows, where the air speed is 0.76m / s.

[0118]

[0119] Where Re is the Reynolds number of the ambient air; Pr is the Prandtl number of the ambient air; P is the density of the ambient air, kg / m 3 , take 1.205kg / m 3; v is the wind speed (take the measured average wind speed), m / s; μ is the dynamic viscosity of the ambient air, Pa·s, taken as 1.89x10 -5 Pa·s; according to Table A.2 of GB / T17357-2008, the Prandtl number of the ambient air can be determined to be 0.7.

[0120] Then the forced convection heat transfer coefficient outside the insulation layer is:

[0121]

[0122] Where h q is the forced convection heat transfer coefficient of the outer surface of the outer protective tube, W / (m·K); Nu is the Nusselt number of the ambient air; λ is the thermal conductivity of the ambient air, W / (m·K).

[0123] Substituting the above natural and forced convection heat transfer coefficients into the thermal resistance R5 can be calculated: During the iteration process, the thermal resistance of the heat dissipation model can be expressed as t w It is expressed as follows: after the heat balance equation is calculated for the inner wall of the pipe, the iterative convergence of t w The final temperature of the inner wall of the pipe is obtained. Therefore, the thermal resistance of the heat dissipation model is all known, the fluid temperature and the cabin air temperature are also known, and the heat dissipation Q of the node to the environment can be calculated by the heat dissipation model. wg .

[0124] The calculation equation for node heat dissipation is:

[0125]

[0126] Where t0 is the fluid temperature, °C.

[0127] This step is applied to each node discretized from the actual system, and the total heat dissipation of the SCO2 pipe network can be obtained by adding up the heat dissipation obtained by each node.

[0128] Step 6: Calculate the node environment heat dissipation Q based on step 5 wg The present invention takes into account the heat absorbed by the friction work of the pipe wall to calculate Q wg It's Q i The correction content in the Q i The heat dissipation term in the equation; the energy exchange term Q at this time i In addition to the original content, the fluid friction work and heat absorption term Q is added f2 , Fixed Q i In the heat dissipation item, Q iThe energy conservation equation of the pipe network model is returned to calculation, linear algebra equation groups of specific enthalpy of each node are established, a specific enthalpy solving matrix is obtained, the SCO2 pipe network is coupled and iterated, the friction heat and heat dissipation related program is supplemented in the pipe network program output module, the friction heat and heat dissipation distribution results of the SCO2 pipe network at each place under the output time step promotion are output, and the simulation of the friction heat and environmental heat dissipation in the pipe network model is realized.

[0129] Further, the method further comprises: visualizing and displaying the pipe network model parameters; wherein the pipe network model parameters comprise: friction pressure drop of the fluid in the target pipe, heat generated by friction work of the fluid and the inner wall of the pipe, heat absorbed by friction work of the pipe wall, heat absorbed by friction work of the fluid, heat dissipation of the node to the environment, total heat dissipation of the pipe network, and specific enthalpy of the node.

[0130] Specifically, the SCO2 pipe network model parameters calculated in steps 2-6 in step 7 mainly comprise:

[0131] friction pressure drop of the pipe fluid, heat generated by friction work of the fluid and the inner wall of the pipe W f , heat absorbed by friction work of the pipe wall Q f1 , heat absorbed by friction work of the fluid Q f2 , heat dissipation of the node to the environment Q wg , total heat dissipation of the pipe network, and specific enthalpy of the node.

[0132] The simulation results are output, and the simulation of the friction heat and environmental heat dissipation in the nuclear power SCO2 pipe network model is completed.

[0133] The above-described embodiments only describe the preferred modes of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements of the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A simulation method for frictional heat generation and environmental heat dissipation in a nuclear power SCO2 pipe network model, characterized in that: include: Discrete the nuclear power SCO2 pipe network system, determine the nodes and streamlines of the target pipeline, and obtain the original physical parameters, and use the original physical parameters to obtain the friction pressure drop of the fluid in the target pipeline; Based on the friction pressure drop, the amount of heat absorbed by the friction work of the pipe wall and the amount of heat absorbed by the friction work of the fluid are obtained, the amount of heat absorbed by the friction work of the fluid is introduced into the energy exchange term in the energy conservation model of the pipe network node, a pipe network heat dissipation model is established using the node, the amount of heat absorbed by the friction work of the pipe wall is added to the pipe network heat dissipation model, and the amount of heat dissipated from the node to the environment is obtained; The heat dissipation is introduced into the energy exchange term, the energy conservation model of the pipe network node after the introduction is calculated, and the specific enthalpy solution matrix is ​​obtained. The specific enthalpy solution matrix is ​​iteratively calculated to obtain the frictional heat generation and heat dissipation distribution results of various locations in the SCO2 pipe network system under time step advancement, that is, the simulation results of frictional heat generation and environmental heat dissipation in the pipe network system.

2. The simulation method for frictional heat generation and environmental heat dissipation in a nuclear power SCO2 pipe network model according to claim 1 is characterized in that: The original physical parameters include: specifications of the pipeline where the node is located, pipe wall material data, fluid parameters and streamline transport parameters; The specifications of the pipe where the node is located include: length, diameter and thickness; The pipe wall material data includes: density, thermal conductivity, heat capacity and absolute roughness of the pipe inner wall; The fluid parameters include: fluid density, specific heat capacity at constant pressure, dynamic viscosity and thermal conductivity; The streamline transport parameters include: mass flow, wind speed of the cabin air where the pipeline is located, ambient temperature and parameters of the pipeline insulation structure, air thermal conductivity, thermal conductivity of the reflective insulation layer and thermal conductivity of the interstitial working fluid glass wool fiber.

3. The simulation method for frictional heat generation and environmental heat dissipation in a nuclear power SCO2 pipe network model according to claim 1 is characterized in that: Obtaining the friction pressure drop of the fluid in the target pipeline includes: The original physical parameters are used to obtain the Reynolds number of the fluid in the target pipe, and based on the Reynolds number, the friction coefficient between the fluid and the pipe wall is calculated to obtain the friction pressure drop.

4. The simulation method for frictional heat generation and environmental heat dissipation in a nuclear power SCO2 pipe network model according to claim 1 is characterized in that: Obtaining the heat absorbed by the friction work of the pipe wall and the heat absorbed by the friction work of the fluid includes: Based on the friction pressure drop, node density and mass flow rate, the frictional heat generated by the fluid and the inner wall of the pipeline is obtained. The frictional heat absorption ratio is calculated through the thermal conductivity, density and specific heat capacity of the pipe wall material and the fluid respectively. Combined with the frictional heat generated, the frictional heat absorption of the pipe wall and the frictional heat absorption of the fluid are obtained.

5. The simulation method for frictional heat generation and environmental heat dissipation in a nuclear power SCO2 pipe network model according to claim 4 is characterized in that: Obtaining the amount of heat dissipated by the node to the environment includes: Preset an initial value of the pipe inner wall temperature, obtain the convective heat transfer amount received by the pipe inner wall by combining the initial value of the pipe inner wall temperature with the convective heat transfer thermal resistance between the fluid and the pipe wall, and use the sum of the convective heat transfer amount and the heat absorbed by the friction work of the pipe wall as the heat absorbed by the pipe inner wall; The heat absorbed by the inner wall of the pipeline is input into a heat balance equation for the inner wall of the pipeline to obtain the inner wall temperature of the pipeline after iterative convergence; based on the inner wall temperature of the pipeline after iterative convergence, the heat dissipation of the node to the environment is obtained.

6. The simulation method for frictional heat generation and environmental heat dissipation in a nuclear power SCO2 pipe network model according to claim 5 is characterized in that: The heat balance equation listed for the inner wall of the pipeline includes: Among them, t w is the inner wall temperature of the pipe, °C; t h is the cabin ambient temperature, °C; Q 对流 is the heat of convection heat transfer between the fluid and the inner wall of the pipe, Q f1 Friction does work and absorbs heat.

7. The simulation method for frictional heat generation and environmental heat dissipation in a nuclear power SCO2 pipe network model according to claim 5, characterized in that: Obtaining the amount of heat dissipated by the node to the environment includes: Where t0 is the fluid temperature, °C; R1, R2, R3, R4, and R5 are the convection heat transfer resistance between the fluid and the pipe wall, the heat conduction resistance of the pipe, the heat conduction resistance of the glass wool fiber in the gap between the insulation layer, the thermal resistance of the metal reflective insulation layer, and the heat transfer resistance between the insulation layer and the cabin air per unit length, respectively, (°C / kW).

8. The simulation method for frictional heat generation and environmental heat dissipation in a nuclear power SCO2 pipe network model according to claim 1 is characterized in that: The method further includes: visually displaying pipe network model parameters; Among them, the pipeline network model parameters include: the friction pressure drop of the fluid in the target pipeline, the heat generated by friction work between the fluid and the inner wall of the pipeline, the heat absorbed by friction work of the pipe wall, the heat absorbed by friction work of the fluid, the heat dissipated from the node to the environment, the total heat dissipation of the pipeline network and the node specific enthalpy.

Images