Transient Heat Transfer for Helium Gas at Various Flow Decay Time Constants and Heat Generation Rates

2018 ◽  
Author(s):  
Qiusheng Liu ◽  
Ayumi Kitano ◽  
Katsuya Fukuda ◽  
Makoto Shibahara
Keyword(s):  
Heat Transfer ◽  
Heat Generation ◽  
Flow Rate ◽  
Transient Heat Transfer ◽  
Rate Condition ◽  
Initial Flow ◽  
Time Constants ◽  
Loss Of Coolant Accident ◽  
Helium Gas ◽  
Loss Of Coolant

Knowledge of the heat transfer phenomenon under flow decay transient condition is important for the safety assessment of a very high temperature reactor (VHTR) during a loss of coolant accident. In this study, transient heat transfer from a horizontal cylinder to helium gas under exponentially decreasing flow rate condition was experimentally investigated. The experiment was conducted by using a forced convection heat transfer experimental apparatus. A flow control value with its control system was used to realize a flow decay condition. Helium gas was used as a coolant, and a platinum cylinder with a diameter of 1 mm was used as the test heater. A uniform heat generation rate was added to the cylinder by a power source. The cylinder temperature was maintained at an initial value under a definite initial flow rate of the helium gas. Subsequently, the flow rate of the helium gas began to exponentially decrease with different time constants ranging from 3 s to 15 s. The initial flow velocity ranged from 7 m/s to 10 m/s. The surface temperature, heat flux, and heat transfer coefficient were measured during the flow decay transient process under a wide range of experimental conditions such as heat generation rates and flow decay time constants. The results indicated that the temperature of the test heater exhibits a rapid increase during this process, and the increasing rate of the temperature is higher for a lower time constant. An increase in the heat generation rate leads to a higher increase in the surface temperature. Therefore, the heat generation rates of the fuel rods are high when a VHTR operates at high power, and it is more challenging to implement passive safety design to ensure the temperature limitation of the fuel rods during a loss-of-coolant accident. Moreover, the heat transfer coefficient relative to time during the flow rate decreasing process was also obtained. The transient heat transfer process during exponentially decreasing flow rate condition was examined based on the experimental data.

Forced Convection Heat Transfer for Helium Gas Under Exponentially Decreasing Flow Condition

2017 ◽  
Author(s):  
Qiusheng Liu ◽  
Li Wang ◽  
Makoto Shibahara ◽  
Katsuya Fukuda
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Forced Convection ◽  
Flow Rate ◽  
Convection Heat Transfer ◽  
Convection Heat ◽  
Rate Condition ◽  
Initial Flow ◽  
Helium Gas

Knowledge of the heat transfer phenomenon during flow decay transient condition is important for the safety assessment of very high temperature reactor (VHTR) during the loss of coolant accident. In this study, transient heat transfer from a horizontal cylinder to helium gas under exponentially decreasing flow rate condition was experimentally studied. The experiment was performed by using a forced convection heat transfer test loop. A flow control value with its control system was used to realize the flow decay condition. Helium gas was used as coolant and platinum cylinder with 1 mm in diameter was used as the test heater. A uniform heat generation rate was added to the cylinder by a power source. The cylinder temperature was maintained at an initial value under a definite initial flow rate of the helium gas. Then, the mass flow rate of the helium gas starts to decrease exponentially with different time constants ranged from 4.3 s to 15.4 s. The initial flow velocity ranged from 10 m/s to 4 m/s. The surface temperature, heat flux, and heat transfer coefficient were measured during the flow decay transient process under wide experimental conditions such as initial flow rate, flow decay time constant. It was found that the temperature of the test heater shows rapid increase during this process, the increasing rate of the temperature is higher for a shorter time constant. The heat transfer coefficient versus time during the flow rate decreasing process was also obtained. The transient heat transfer process during exponentially decreasing flow rate condition was clarified based on the experimental data.

Experimental Study on Transient Heat Transfer for Helium Gas Flowing in a Minichannel

2020 ◽  
Author(s):  
Feng Xu ◽  
Qiusheng Liu ◽  
Satoshi Kawaguchi ◽  
Makoto Shibahara
Keyword(s):  
Heat Transfer ◽  
Heat Generation ◽  
Heat Transfer Process ◽  
Test Tube ◽  
Generation Rate ◽  
Transient Heat Transfer ◽  
Heat Generation Rate ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Helium Gas

Abstract The blanket modules of first wall need bear tremendous heat flux due to the very high temperature of plasma in the nuclear fusion reactor. Therefore, it is significant to clarify the knowledge of transient heat transfer process for helium gas flowing in the tubes installed in the blanket modules. In this research, the transient heat transfer process of turbulent forced convection for helium gas flowing in a horizontal minichannel was experimentally investigated. The test tube made of platinum with the inner diameter of 1.8 mm, the wall thickness of 0.1 mm and the effective length of 90 mm was heated by a direct current from power source. The heat generation rate of the test tube, Q̇, was raised with an exponential function, Q̇ = Q0 exp(t/τ), where Q0 is the initial heat generation rate, t is time, and τ is e-folding time of heat generation rate. The heat generation rates of the test tube were controlled and measured by a heat input control system. The flow rates were adjusted by the bypass of gas loop and measured by the turbine flow meter. The experiment was conducted under the e-folding time of heat generation rate ranged from 40 ms to 15 s. Based on experimental data, it is obvious that the heat flux and temperature difference between surface temperature of test tube and bulk temperature of helium gas increased with the exponentially increasing of heat generation rate. At the same flow velocity, the heat transfer coefficients approached constant values when the e-folding time is longer than about 1 s (quasi-steady state), but increased with a decrease of e-folding time when the e-folding time is smaller than about 1 s (transient state). The heat transfer coefficients increased with the increase in flow velocities but showed less dependent on flow velocities at shorter e-folding time. Furthermore, the Nusselt number under quasi-steady and transient condition was affected by the Reynolds number and the Fourier number.

Experimental Study on Transient Heat Transfer Enhancement for Helium Gas Flowing Over a Thin Twisted Plate

2014 ◽  
Author(s):  
Zhou Zhao ◽  
Qiusheng Liu ◽  
Katsuya Fukuda
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Heat Generation ◽  
Heat Input ◽  
Convection Heat Transfer ◽  
Transient Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Helium Gas ◽  
The Heat Transfer Coefficient

Transient forced convection heat transfer due to exponentially increasing heat input to a heater is important as a database for safety assessment of the transient heat transfer process in a Very High Temperature Reactor (VHTR). The knowledge of heat transfer enhancement using a heater with twisted configuration is also important for the high performance design of intermediate heater exchanger (IHX) in VHTR system. In this study, forced convection transient heat transfer for helium gas at various periods of exponential increase of heat input to a short thin twisted plate with various helix angles was experimentally studied. A forced convection heat transfer experimental apparatus was used to measure the experimental data. The test heater was mounted horizontally along the center part of a circular test channel. Twisted plates were made of thin platinum plate with a thickness of 0.1 mm and width of 2 mm and 4 mm. The heat generation rates of the heater were controlled and measured by a heat input control system. The heat generation rate, Q̇, was raised with exponential function, Q̇ = Q0exp(t/τ). Where, t is time, and τ is period of heat generation rate. The mean temperature of the test heater was measured by resistance thermometry. The heat flux was obtained by the energy conservation equation. The test heater surface temperature was calculated from heat conduction equation of the heater. The transient heat transfer experimental data were measured for the periods ranged from 80 ms to 17 s and at a gas temperature of 303 K under 500 kPa. The flow velocities ranged from 4 m/s to 10 m/s. In the experiments, the twisted plates with different width were tested. The surface temperature and heat flux are increasing exponentially with the time. It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period longer than about 1 s, and it becomes higher for the period shorter than about 1 s. The heat transfer coefficients for total length of the twisted plate were compared with the values of flat plate which has the same width and thickness with the twisted one. The local mean heat transfer coefficients have been tested as well. The heat transfer coefficients of twisted plate are about 10% for 2 mm-width one and15% for 4 mm-width one higher than those of flat plate with same width at the quasi-steady state. And also, the heat transfer coefficients for the first half pitch are 24% higher than that for the total length of the same twisted plate. Therefore, an enhancement in the heat transfer coefficient for the twisted plate was clarified.

Numerical Simulation of the Transient Phase Change Heat Transfer in a Pressurized Water Reactor Core During a Loss-of-Coolant Accident

2011 ◽  
Author(s):  
Soo W. Jo ◽  
Yong K. Lee ◽  
Jong C. Jo
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Transient Heat Transfer ◽  
Coolant Temperature ◽  
Pressurized Water Reactor ◽  
Pressurized Water ◽  
Water Reactor ◽  
The Core ◽  
Loss Of Coolant Accident ◽  
Loss Of Coolant

Temperature of pressurized water reactor (PWR) core is a key parameter used widely for judging the initiation of emergency operating procedures and severe accident management. Since direct measurement of the fuel cladding surface temperature using thermocouples is not practicable currently, the coolant temperature at the core exit locations is monitored instead. Several experimental researches showed that the CET rise during a loss of coolant accident (LOCA) and its magnitudes were always lower than the actual fuel rod cladding temperature at the same time. In this regard, a theoretical analysis of the transient heat transfer of coolant flow in a PWR core is needed to confirm the findings from the previous experimental works. This paper addresses numerical simulation of the transient boiling-induced multiphase flow through a simplified PWR core model during a LOCA by a commercial computational fluid dynamics (CFD) code. The calculated results are discussed to understand the transient heat transfer mechanism in the core and to provide useful technical information for reactor design and operation.

Transient Heat Transfer for Parallel Flow of Helium Gas Over a Horizontal Plate

2007 ◽  
Author(s):  
Qiusheng Liu ◽  
Katsuya Fukuda ◽  
Makoto Shibahara ◽  
Shingo Kikumoto
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Steady State ◽  
Heat Generation ◽  
Transient Heat Transfer ◽  
Quasi Steady State ◽  
Horizontal Plate ◽  
Heat Generation Rate ◽  
Helium Gas

Forced convection transient heat transfer for helium gas at various periods of exponentially increase of heat input to a horizontal plate (ribbon) was experimentally and theoretically studied. In the experimental studies, the authors measured heat flux, surface temperature, and transient heat transfer coefficients for forced convection flow of helium gas over a horizontal plate under wide experimental conditions. The gas flow velocities ranged from 4 to 10 m/s, the gas temperatures ranged from 313 to 353 K, and the periods of heat generation rate, τ, ranged from 46 ms to 17 s. The pressures were from 400 to 800 kPa. It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period longer than about 1 s, and it becomes higher for the period shorter than around 1 s. Empirical correlations for quasi-steady-state heat transfer and transient heat transfer were obtained based on the experimental data. In the theoretical study, transient heat transfer was numerically solved based on a turbulent flow model. It was obtained that the surface superheat and heat flux increase exponentially as the heat generation rate increases with the exponential function. The values of numerical solutions for surface temperature and heat flux at the velocity of 6 m/s agree well with the experimental data, though they show some differences at other velocities.

Transient Heat Transfer for Helium Gas Flowing Over a Horizontal Flat-Plate With Different Widths

2013 ◽  
Author(s):  
Zhou Zhao ◽  
Qiusheng Liu ◽  
Katsuya Fukuda
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Heat Generation ◽  
Generation Rate ◽  
Transient Heat Transfer ◽  
Quasi Steady State ◽  
Heat Generation Rate ◽  
Helium Gas ◽  
The Heat Transfer Coefficient

This study is aimed to clarify transient heat transfer process between the surface of solid and the neighboring helium gas in Very High Temperature Reactor (VHTR) or intermediate heat exchanger (IHX). In this paper a series of platinum heaters with different widths under different pressures inside a circular channel have been tested for forced convection flow. The heat generation rate of the platinum heater was increased with a function of Q0exp(t/τ) (where t is time and τ is period of heat generation rate or e-fold time). The heaters were platinum plates with a thickness of 0.1 mm and widths of 2 mm, 4 mm and 6 mm. In the present study, the heat flux, surface temperature, and transient heat transfer coefficients were measured for helium gas passing by horizontal plates under wide experimental conditions such as velocities, pressures and periods of heat generation rate. It was clarified that the heat transfer coefficient approaches the quasi-steady-state when the period is more than around 1 s and it becomes higher when the period shorter than around 1 s. Based on the experimental data, empirical correlations for both quasi-steady-state heat transfer and transient state one at various plate-widths were obtained. It was also found that the heat transfer coefficient becomes higher with the increases of gas pressure.

Transient Heat Transfer for Helium Gas Flowing Over a Horizontal Cylinder Under Flow Decay Conditions

2016 ◽  
Author(s):  
Qiusheng Liu ◽  
Li Wang ◽  
Makoto Shibahara ◽  
Katsuya Fukuda
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Heat Removal ◽  
Horizontal Cylinder ◽  
Heat Transfer Process ◽  
Transient Heat Transfer ◽  
Transient Condition ◽  
Decay Heat ◽  
Helium Gas ◽  
The Heat Transfer Coefficient

The Very High Temperature Reactor (VHTR) is a new reactor that uses helium gas as primary coolant for conventional graphite matrix, coated fuels. It enables the achievements of high thermal efficiency and can supply heat with a high temperature of about 900–1000 °C. During the loss of coolant process, the fuel hot spot temperature should not get over a criteria value due to the temperature limitation of the fuel assembly. Traditionally, the VHTRs are designed to deal with loss of forced circulation conditions by using a passive mode decay heat removal system for the cavity cooling. However, even passive systems may experience some failure due to multiple undesired conditions even though the possibility is extremely low. Therefore, the VHTRs are now expected to be designed as naturally safe reactors with inherent safety features. Which means the decay heat removal is fully dependent on natural convection and radiation. To accomplish the tough task, a clear understanding of the heat transfer process during flow decay transient condition is quite necessary. This study was conducted to investigate the transient heat transfer process between the solid surface and coolant (helium gas) in VHTR under flow decay conditions. Forced convection transient heat transfer for a horizontal cylinder under flow decay transient condition was experimentally studied. The experiment was conducted by using the helium gas as coolant. A uniform heat generation rate was added to the heater. With a certain flow rate of the helium gas, the heater temperature was maintained at a designed value. Then, the flow rate of the helium gas starts to decrease according to designed linear functions with different decreasing speed. Platinum cylinder with 1 mm in diameter was used as the test heater. The heat transfer coefficient and surface temperature were measured during the flow decay transient process under wide experimental conditions such as initial flow rate, flow decay time. It was found that the temperature of the test heater increases in curve shape with different gradients during this process, with a shorter flow decay time the increasing rate of heater surface temperature would be higher. The heat transfer coefficient versus time during the flow rate decreasing process was also obtained.

Characteristics Analysis of SCWR During Partial Loss of Reactor Coolant Flow Transient

2012 ◽  
Author(s):  
Juan Chen ◽  
Tao Zhou ◽  
Zhousen Hou ◽  
Canhui Sun
Keyword(s):  
Flow Rate ◽  
Transient Analysis ◽  
Coolant Flow ◽  
Partial Loss ◽  
Initial Flow ◽  
Reactor Coolant ◽  
Loss Of Coolant ◽  
Characteristics Analysis ◽  
And Control ◽  
Supercritical Water Cooled Reactor

Partial loss of reactor coolant flow is one of the most important transients for safety analysis of supercritical water-cooled reactor (SCWR). Taking the super LWR concept provided by Japan as research object, transient analysis of partial loss of coolant flow rate is given by coupled neutronics and thermal hydraulics calculation method. The results show that, when 5% partial loss of coolant flow is happening, maximum cladding temperature would increase firstly with the decreasing of fuel channel inlet coolant flow. Then followed with the neutronic feedback and control operation, maximum cladding temperature decreases and finally return to normal. When 50% partial loss of coolant flow is happening, a scram signal will be given to ensure system safety, but the maximum cladding temperature still shows a significant increase early. On this basis, sensitivity analysis is performed considering the influence of core power and main coolant flow. It is found that maximum peaking value increases significantly following the initial flow rate decreasing, but shows a very little increase caused by core power increasing.

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