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.

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.

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.

Investigation of Transient Heat Transfer Coefficients in Quenching Experiments

1990 ◽  
Vol 112 (4) ◽  
pp. 843-848 ◽  
Author(s):  
A. M. Osman ◽  
J. V. Beck
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Temperature Response ◽  
Transient Heat Transfer ◽  
Transient Temperature ◽  
Empirical Correlations ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Inverse Heat Transfer

Methodological and experimental aspects of the estimation of transient heat transfer coefficients in quenching experiments, using inverse heat transfer methods, were addressed and investigated. Beck’s method was used for the estimation of the transient heat transfer coefficient history from interior transient temperature measurements during quenching. Experiments involved plunging a high-purity copper sphere into cooling baths without boiling. The sphere was instrumented with several interior thermocouples for measuring the transient temperature response during quenching. Water and ethylene glycol were investigated. The early transient values of the heat transfer coefficient history were found to be about 100–120 percent higher than the values predicted using well-known empirical correlations for free convection. The later time values were in good agreement with those predicted with empirical correlations. The transient inverse technique has the capability of estimating early transients and subsequent quasi-steady-state values of heat transfer coefficient in a single transient experiment.

Transient Heat Transfer From a Horizontal Plate in Forced Flow of Various Gases

2011 ◽  
Author(s):  
Qiusheng Liu ◽  
Makoto Shibahara ◽  
Katsuya Fukuda
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Gas Flow ◽  
Transient Heat Transfer ◽  
Quasi Steady State ◽  
Horizontal Plate ◽  
Heat Generation Rate ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
The Heat Transfer Coefficient

In this research, to obtain fundamental experimental data of transient heat transfer and to clarify the transient heat transfer process at wide experimental conditions for the safety assessment of very high temperature reactor (VHTR), forced convection transient heat transfer coefficients were measured for Helium, Carbon dioxide, Argon and Nitrogen gases flowing over a horizontal plate due to exponentially increasing heat input. The platinum ribbon with a thickness of 0.1 mm and a width of 4.0 mm was used as the test heater and heated by electric current. The heat generation rate was controlled and measured by a heat input control system, it was exponentially increased with a function of Q0exp(t/τ). The periods (e-fold times) of heat generation rate, τ, ranged from 46 ms to 17 s, the gas flow velocities ranged from 1 to 10 m/s, the pressures ranged from 400 kPa to 800 kPa, and the gas temperatures ranged from 290 to 353 K. 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. The heat transfer coefficient increases with the increases in pressure and velocity, and it shows some dependence on temperature at the experimental range of this research. The dependence of transient heat transfer on the gas flow velocity becomes weaker when the period becomes very shorter. Effect of gas thermal physical properties on heat transfer was investigated, and helium gas shows higher heat transfer coefficients than those of other gases due to its higher thermal conductivity. Empirical correlations for quasi-steady-state heat transfer and transient one for various gases were obtained based on 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.

scholarly journals Systematic heat transfer measurements in highly viscous binary fluids

2021 ◽  
Author(s):  
Ann-Christin Fleer ◽  
Markus Richter ◽  
Roland Span
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Volatile Component ◽  
Test Tube ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Low Viscosity ◽  
The Heat Transfer Coefficient

AbstractInvestigations of flow boiling in highly viscous fluids show that heat transfer mechanisms in such fluids are different from those in fluids of low viscosity like refrigerants or water. To gain a better understanding, a modified standard apparatus was developed; it was specifically designed for fluids of high viscosity up to 1000 Pa∙s and enables heat transfer measurements with a single horizontal test tube over a wide range of heat fluxes. Here, we present measurements of the heat transfer coefficient at pool boiling conditions in highly viscous binary mixtures of three different polydimethylsiloxanes (PDMS) and n-pentane, which is the volatile component in the mixture. Systematic measurements were carried out to investigate pool boiling in mixtures with a focus on the temperature, the viscosity of the non-volatile component and the fraction of the volatile component on the heat transfer coefficient. Furthermore, copper test tubes with polished and sanded surfaces were used to evaluate the influence of the surface structure on the heat transfer coefficient. The results show that viscosity and composition of the mixture have the strongest effect on the heat transfer coefficient in highly viscous mixtures, whereby the viscosity of the mixture depends on the base viscosity of the used PDMS, on the concentration of n-pentane in the mixture, and on the temperature. For nucleate boiling, the influence of the surface structure of the test tube is less pronounced than observed in boiling experiments with pure fluids of low viscosity, but the relative enhancement of the heat transfer coefficient is still significant. In particular for mixtures with high concentrations of the volatile component and at high pool temperature, heat transfer coefficients increase with heat flux until they reach a maximum. At further increased heat fluxes the heat transfer coefficients decrease again. Observed temperature differences between heating surface and pool are much larger than for boiling fluids with low viscosity. Temperature differences up to 137 K (for a mixture containing 5% n-pentane by mass at a heat flux of 13.6 kW/m2) were measured.

Experimental Study of Evaporation Heat Transfer Characteristics and Pressure Drops of R410A and R134a in a Multiport Mini-Channel

2009 ◽  
Author(s):  
Jatuporn Kaew-On ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
R 134A

The evaporation heat transfer coefficients and pressure drops of R-410A and R-134a flowing through a horizontal-aluminium rectangular multiport mini-channel having a hydraulic diameter of 3.48 mm are experimentally investigated. The test runs are done at refrigerant mass fluxes ranging between 200 and 400 kg/m2s. The heat fluxes are between 5 and 14.25 kW/m2, and refrigerant saturation temperatures are between 10 and 30 °C. The effects of the refrigerant vapour quality, mass flux, saturation temperature and imposed heat flux on the measured heat transfer coefficient and pressure drop are investigated. The experimental data show that in the same conditions, the heat transfer coefficients of R-410A are about 20–50% higher than those of R-134a, whereas the pressure drops of R-410A are around 50–100% lower than those of R-134a. The new correlations for the evaporation heat transfer coefficient and pressure drop of R-410A and R-134a in a multiport mini-channel are proposed for practical applications.

Calculation of Hourly Output of a Solar Still

1993 ◽  
Vol 115 (4) ◽  
pp. 231-236 ◽  
Author(s):  
V. B. Sharma ◽  
S. C. Mullick
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Balance ◽  
Solar Still ◽  
Balance Equations ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Hourly Output ◽  
The Heat Balance

An approximate method for calculation of the hourly output of a solar still over a 24-hour cycle has been studied. The hourly performance of a solar still is predicted given the values of the insolation, ambient temperature, wind heat-transfer coefficient, water depth, and the heat-transfer coefficient through base and sides. The proposed method does not require graphical constructions and does not assume constant heat-transfer coefficients as in the previous methods. The possibility of using the values of the heat-transfer coefficients for the preceding time interval in the heat balance equations is examined. In fact, two variants of the basic method of calculation are examined. The hourly rate of evaporation is obtained. The results are compared to those obtained by numerical solution of the complete set of heat balance equations. The errors from the approximate method in prediction of the 24-hour output are within ±1.5 percent of the values from the numerical solution using the heat balance equations. The range of variables covered is 5 to 15 cms in water depth, 0 to 3 W/m2K in a heat-transfer coefficient through base and sides, and 5 to 40 W/m2K in a wind heat-transfer coefficient.

Sign in / Sign up

Export Citation Format

Share Document