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.

Enhancement of Forced Convection Heat Transfer Using Twisted Heater With Exponential Heat Inputs

2013 ◽  
Author(s):  
Makoto Shibahara ◽  
Qiusheng Liu ◽  
Katsuya Fukuda
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Heat Generation ◽  
Swirling Flow ◽  
Generation Rate ◽  
Transient Heat Transfer ◽  
Heat Generation Rate ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Plate Heater

Forced convection transient heat transfer coefficients have been measured for nitrogen gas flowing over a twisted heater due to exponentially increasing heat inputs (Q0exp(t/τ)). And then, the effect of heater configuration on transient heat transfer by a twisted heater has been investigated comparing to that of the plate heater. In the experiment, the platinum ribbon with a thickness of 0.1 mm and a width of 4.0 mm was used as a test heater. For heat transfer enhancements in single-phase flow, it was twisted at the central part of the heater with an angle of 90 degrees with respect to the upper part of the heater. The heat generation rate was exponentially increased with a function of Q0exp(t/τ). The gas flow velocity ranged from 1 to 4 m/s for the gas temperatures of 313K. The periods of heat generation rate ranged from 46 ms to 17 s. The surface temperature difference and heat flux increased exponentially as the heat generation rate increased with the exponential function. The heat transfer coefficients for twisted heater have been compared to those of the plate heater. They were 24 % higher than those of the plate one. The geometric effect (twisted effect) of heater in this study showed an enhancement on the heat transfer coefficient. It was considered that the heat transfer coefficients are affected by the change in the flow due to swirling flow on the twisted heater. Finally, the empirical correlations for quasi-steady-state heat transfer and transient one have been obtained 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.

A Study of Forced Convection Direct Air Cooling in the Downstream Vicinity of Heat Sinks

1990 ◽  
Vol 112 (3) ◽  
pp. 234-240 ◽  
Author(s):  
G. L. Lehmann ◽  
S. J. Kosteva
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Heat Sink ◽  
Convection Heat Transfer ◽  
Heat Sinks ◽  
Air Cooling ◽  
Transfer Coefficients ◽  
Packaging System ◽  
Transfer Rates ◽  
Heat Transfer Coefficients

An experimental study of forced convection heat transfer is reported. Direct air cooling of an electronics packaging system is modeled by a channel flow, with an array of uniformly sized and spaced elements attached to one channel wall. The presence of a single or complete row of longitudinally finned heat sinks creates a modified flow pattern. Convective heat transfer rates at downstream positions are measured and compared to that of a plain array (no heat sinks). Heat transfer rates are described in terms of adiabatic heat transfer coefficients and thermal wake functions. Empirical correlations are presented for both variations in Reynolds number (5000 < Re < 20,000) and heat sink geometry. It is found that the presence of a heat sink can both enhance and degrade the heat transfer coefficient at downstream locations, depending on the relative position.

Effect of Heater Configurations on Transient Heat Transfer for Various Gases Flowing Over a Twisted Heater

2009 ◽  
Author(s):  
Makoto Shibahara ◽  
Qiusheng Liu ◽  
Katsuya Fukuda
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Generation ◽  
Gas Flow ◽  
Generation Rate ◽  
Transient Heat Transfer ◽  
Heat Generation Rate ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Forced convection transient heat transfer coefficients were measured for helium gas and carbon dioxide gas flowing over a twisted heater due to exponentially increasing heat input (Q0exp(t/τ)). The twisted platinum plate with a thickness of 0.1 mm was used as test heater and heated by electric current. The heat generation rate was exponentially increased with a function of Q0exp(t/τ). The gas flow velocities ranged from 1 to 10 m/s, the gas temperatures ranged from 313 to 353 K, and the periods of heat generation rate ranged from 46 ms to 17 s. The surface temperature difference and heat flux increase exponentially as the heat generation rate increases with the exponential function. Transient heat transfer coefficients increase with increasing gas flow velocity. The geometric effect of twisted heater in this study shows an enhancement on the heat transfer coefficient. Empirical correlation for quasi-steady-state heat transfer was obtained based on the experimental data. The data for heat transfer coefficient were compared with those reported in authors’ previous paper.

Enhanced Heat Transfer for Various Gases Flowing Over a Twisted Heater Due to Exponentially Increasing Heat Input

2010 ◽  
Author(s):  
Makoto Shibahara ◽  
Qiusheng Liu ◽  
Katsuya Fukuda
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Generation ◽  
Heat Input ◽  
Swirling Flow ◽  
Generation Rate ◽  
Heat Generation Rate ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Forced convection transient heat transfer coefficients were measured for various gases (helium, nitrogen, argon and carbon dioxide gas) flowing over a twisted heater due to exponentially increasing heat input (Q0exp(t/τ)). The platinum ribbon with a thickness of 0.1 mm and a width of 4.0 mm was used as the test heater. It was twisted at the center of the heater with an angle of 45 and 90 degrees with respect to the upper part of the heater. The heat generation rate was exponentially increased with a function of Q0exp(t/τ). The gas flow velocities ranged from 1 to 10 m/s, the gas temperatures ranged from 313 to 353 K, and the periods of heat generation rate ranged from 45 ms to 17 s. The surface temperature difference and heat flux increase exponentially as the heat generation rate increases with exponential function. The heat transfer coefficients for twisted heater were compared with those of a plate heater. They are 13 ∼ 28% higher than those of the plate one. The geometric effect (twisted effect) of heater in this study shows an enhancement on the heat transfer coefficient. This is because the heat transfer coefficients are affected by the change in the flow due to swirling flow on the twisted heater. And also, it was understood that heat transfer coefficient increase with the angle of twisted heater due to swirl motion and raised turbulence intensity. Empirical correlations for quasi-steady-state heat transfer and transient one were obtained based on the experimental data.

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