Periods Of Heat Generation Rate Research Articles

Transient Heat Transfer Characteristics of Twisted Structure Heated by Exponential Heat Flux

This study was conducted to investigate the transient heat transfer characteristics of a twisted structure. The twisted structure was heated according to exponential function (Q=Q0×exp(t/τ), where Q0 is the initial heat generation rate, W/m3; t is time, s; and τ is the period of heat generation rate). A wide range of τ from 37 ms to 14 s was applied for the experimental study. A platinum plate with five pitches (each was 180° twisted with 20 mm in length) was used in the experiment. Helium gas with inlet temperature of 298 K under 500 kPa was used as the coolant. The heat transfer coefficient is found to increase with the decrease of τ, and the transition point was estimated to be at τ≈1s, which means that, when the increasing ratio of heat generation rate satisfies dQdt≥Q0⋅et, the heat transfer enhancement phenomenon will be observed. The response analysis for transient heat transfer at fluid-solid interface was conducted by applying the concept of penetration depth. It is considered that, when the penetration depth is smaller than the thermal boundary thickness, the heat transfer from the interface (wall surface) to the fluid domain is not fully developed during the disturbance.

Transient forced convection heat transfer for nitrogen gas flowing over plate heater with exponentially increasing heat input

The transient forced convection heat transfer of plate heater for nitrogen gas due to exponentially increasing heat input was investigated experimentally and numerically. The platinum ribbon with a thickness of 0.1mm and a width of 4.0mm was used as the test heater. The heat generation rate of the test heater was raised with exponential function. The inlet flow velocity was ranged from 2 to 4m/s for the gas temperature of 313K under the system pressure of 500kPa. The period of heat generation rate was ranged from 45ms to 8s. Experimental results indicate that the surface temperature difference and heat flux increased exponentially as the heat generation rate increased through an exponential function. It was clarified that the heat transfer coefficient was divided into the two regions for the period ranging from 45ms to 8s. The numerical results were compared with experimental data. The numerical simulation was in agreement with the experimental data.

Experimental study on transient heat transfer enhancement from a twisted plate in convection flow of helium gas

The knowledge of heat transfer enhancement using a heater with twisted configuration is important for the high performance design of high temperature thermal systems such as very high temperature reactors (VHTR). In this study, forced convection transient heat transfer for helium gas at various periods of exponential increase of heat input to a twisted plate was experimentally studied. 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 transient heat transfer experimental data were measured for the periods ranged from 46ms to 17s and at gas temperatures of 303K and 313K under 500kPa. The flow velocities ranged from 4m/s to 10m/s. The pitches of the twisted plates were 20mm, 25mm, and 30mm. The surface temperature and heat flux increased exponentially with the time. It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period longer than about 1s, and it becomes higher for the period shorter than about 1s. An enhancement in the heat transfer performance for the twisted plate was clarified. Based on the experimental data, empirical correlation of heat transfer for twisted plate was obtained. Furthermore, the mechanism of heat transfer enhancement due to twisted plate was stated in detail.

Width effect and local transient heat transfer characteristics for helium gas flowing over a twisted plate

Forced convection transient heat transfer for helium gas at various periods of exponential increase of heat input to a short twisted plate with various helix angles was experimentally studied. Twisted plates were made of platinum plate with a thickness of 0.1 mm and width of 2 and 4 mm. The heat generation rates of the heater was raised with exponential function, , where t is time, and τ is period of heat generation rate. 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 to 10 m/s. In the experiments, the twisted plates with different width were tested. The local mean heat transfer coefficients have been tested as well. An enhancement in the heat transfer coefficient for the twisted plate with different width was clarified. 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.

Transient heat transfer for forced flow of helium gas along a horizontal plate with different widths

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 plate heaters with different widths under various pressures inside a circular channel have been tested for forced convective flow. The heat generation rate of the plate 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 0.1mm and widths of 2mm, 4mm and 6mm. 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, widths of plate and periods of heat generation rate. It was clarified that the heat transfer coefficient approaches the quasi-steady-state value when the period is more than around 1s and it becomes higher when the period is shorter than around 1s. It was found that the heat transfer coefficient becomes higher with the increase of gas pressure under the same velocity and period of heat generation rate. It was also found that the widths have a great influence on the heat transfer coefficient: the heat transfer coefficients of narrow heaters are much higher than those of wide ones under the same velocity and the same pressure. Based on the experimental data, empirical correlations were obtained for both quasi-steady state heat transfer and transient state one at various plate-widths.

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

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. The twisted platinum ribbon 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 exponentially. Transient heat transfer coefficients increase with increasing gas flow velocity. The heater configuration of twisted heater in this study shows a large effect on the heat transfer coefficient. Empirical correlations for quasi-steady-state heat transfer were obtained based on the experimental data.

Transient Forced Convection Heat Transfer due to Exponentially Increasing Heat Input for Helium Gas Flowing on a Narrow Plate

Steady and transient forced convection transient 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 not only in a high temperature gas cooled reactor (HTGR) due to an accident in excess reactivity but also in high heat flux gas cooling devices such as a gas turbine and a rocket engine. In this research, forced convection transient heat transfer for helium gas at various periods of exponential increase of heat input (Q0 exp(t/τ)) to a horizontal narrow plate was numerically solved based on a turbulent flow model. The platinum plate with a length of 50 mm was used as test heater. The 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 8.6 s. The values of numerical solutions for surface temperature and heat flux were compared and discussed with authors’ experimental values. It was obtained that the surface temperature difference and heat flux increase exponentially as the heat generation rate increases with the exponential function. Then the temperature within the boundary layer also increases with the increase of the surface temperature. It is understood that the gradient of the temperature distribution near the wall of the plate is higher at a higher surface temperature difference. 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. And also, heat transfer coefficients at the velocity of 6 m/s agree well with the experimental data, though they show some differences at other velocities. They agree within 15% at various periods and velocities.Copyright © 2008 by ASME

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

Transient heat transfer coefficients for helium gas flowing over a horizontal plate (ribbon) were measured under wide experimental conditions. The platinum plate with a thickness of 0.1 mm was used as the test heater and heated by electric current. The heat generation rate was exponentially increased with a function of Q0 exp(t/τ). The gas flow velocities ranged from 4 to 10 m/s, the gas temperatures ranged from 290 to 353 K, and the periods of heat generation rate, τ, ranged from 50 ms to 17 s. The surface superheat and heat flux increase exponentially as the heat generation rate increases with the exponential function. It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period τ longer than about 1 s, and it becomes higher for the period shorter than around 1 s. Empirical correlation for transient heat transfer was also obtained based on the experimental data.

1811 増加熱入力による気流中の水平平板発熱体過渡熱伝達(G06-2 伝熱(2),G06 熱工学)

Forced convection transient heat transfer for helium gas at various periods of exponential increase in 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. The gas flow velocities ranged from 4 to 10m/s, the gas temperatures ranged from 313 to 353K, and the periods of heat generation rate, τ, ranged from 46ms to 17s. 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.

Transient Forced Convection Heat Transfer for Helium Gas Flowing Over a Horizontal Plate

Transient heat transfer coefficients for helium gas flowing over a horizontal plate (ribbon) were measured under wide experimental conditions. The 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 Q{sub 0}exp(t/t). 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, t, ranged from 50 ms to 17 s. The surface superheat and heat flux increase exponentially as the heat generation rate increases with the exponential function. It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period t longer than about 1 s, and it becomes higher for the period shorter than around 1 s. The dependence of transient heat transfer on the gas flowing velocity becomes weaker when the period becomes very shorter. The gas temperature in this study shows little influence on the heat transfer coefficient. Empirical correlation for quasi-steady-state heat transfer was obtained based on the experimental data. (authors)