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

2021 ◽  
Vol 9 ◽  
Author(s):  
Li Wang
Keyword(s):  
Heat Transfer ◽  
Penetration Depth ◽  
Heat Generation ◽  
Generation Rate ◽  
Transient Heat Transfer ◽  
Inlet Temperature ◽  
Heat Generation Rate ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Wide Range

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.

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.

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.

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.

Transient Heat Transfer for Carbon Dioxide Flowing Over a Horizontal Plate With Exponentially Increasing Heat Input

2008 ◽  
Author(s):  
Makoto Shibahara ◽  
Qiusheng Liu ◽  
Katsuya Fukuda
Keyword(s):  
Heat Transfer ◽  
Surface Temperature ◽  
Heat Generation ◽  
Numerical Solutions ◽  
Generation Rate ◽  
Transient Heat Transfer ◽  
Horizontal Plate ◽  
Heat Generation Rate ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Transient heat transfer coefficients for carbon-dioxide gas flowing over a horizontal plate (ribbon) at various periods of exponentially increasing heat input was experimentally and theoretically studied. In the experimental studies, transient heat transfer coefficients were measured under various velocities and periods. 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 Q0exp(t/τ). The gas flow velocities ranged from 1 to 3 m/s, the gas temperatures ranged from 313 K to 353 K, and the periods of heat generation rate ranged from 46 ms to 17 s. The surface temperature 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 longer than about 1 s, and it becomes higher for the period shorter than around 1 s. In the theoretical study, forced convection transient heat transfer was numerically solved based on a conventional turbulent flow model. The temperature within the boundary layer around the heater 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 the heat fluxes agree well with the experimental data, though the numerical solutions for surface temperatures show some differences with the experimental data.

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.

Heat transfer characteristics of nanofluids from a sinusoidal corrugated cylinder placed in a square cavity

2021 ◽  
pp. 095440622110272
Author(s):  
Salaika Parvin ◽  
Nepal Chandra Roy ◽  
Litan Kumar Saha ◽  
Sadia Siddiqa
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Average Nusselt Number ◽  
Numerical Study ◽  
Heat Transfer Characteristics ◽  
Number Range ◽  
Transfer Characteristics ◽  
Wide Range

A numerical study is performed to investigate nanofluids' flow field and heat transfer characteristics between the domain bounded by a square and a wavy cylinder. The left and right walls of the cavity are at constant low temperature while its other adjacent walls are insulated. The convective phenomena take place due to the higher temperature of the inner corrugated surface. Super elliptic functions are used to transform the governing equations of the classical rectangular enclosure into a system of equations valid for concentric cylinders. The resulting equations are solved iteratively with the implicit finite difference method. Parametric results are presented in terms of streamlines, isotherms, local and average Nusselt numbers for a wide range of scaled parameters such as nanoparticles concentration, Rayleigh number, and aspect ratio. Several correlations have been deduced at the inner and outer surface of the cylinders for the average Nusselt number, which gives a good agreement when compared against the numerical results. The strength of the streamlines increases significantly due to an increase in the aspect ratio of the inner cylinder and the Rayleigh number. As the concentration of nanoparticles increases, the average Nusselt number at the internal and external cylinders becomes stronger. In addition, the average Nusselt number for the entire Rayleigh number range gets enhanced when plotted against the volume fraction of the nanofluid.

scholarly journals Conduction and convection heat transfer characteristics of water-based au nanofluids in a square cavity with differentially heated side walls subjected to constant temperatures

2014 ◽  
Vol 18 (suppl.1) ◽  
pp. 189-200 ◽  
Author(s):  
Primoz Ternik ◽  
Rebeka Rudolf
Keyword(s):  
Heat Transfer ◽  
Rayleigh Number ◽  
Base Fluid ◽  
Volume Fraction ◽  
Heat Transfer Characteristics ◽  
Square Cavity ◽  
Onset Of Convection ◽  
Transfer Characteristics ◽  
Wide Range ◽  
Water Based

The present work deals with the natural convection in a square cavity filled with the water-based Au nanofluid. The cavity is heated on the vertical and cooled from the adjacent wall, while the other two horizontal walls are adiabatic. The governing differential equations have been solved by the standard finite volume method and the hydrodynamic and thermal fields were coupled together using the Boussinesq approximation. The main objective of this study is to investigate the influence of the nanoparticles? volume fraction on the heat transfer characteristics of Au nanofluids at the given base fluid?s (i.e. water) Rayleigh number. Accurate results are presented over a wide range of the base fluid Rayleigh number and the volume fraction of Au nanoparticles. It is shown that adding nanoparticles in a base fluid delays the onset of convection. Contrary to what is argued by many authors, we show by numerical simulations that the use of nanofluids can reduce the heat transfer rate instead of increasing it.

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