Temperature distributions in fins with uniform and non-uniform heat generation and non-uniform heat transfer coefficient

1987 ◽  
Vol 30 (7) ◽  
pp. 1465-1477 ◽  
Author(s):  
H.C. Ünal
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Generation ◽  
Temperature Distributions ◽  
Uniform Heat

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.

Non-Intrusive Heat Transfer Coefficient Determination in a Packed Bed of Spheres

2010 ◽  
Author(s):  
David J. Geb ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Generation ◽  
Packed Bed ◽  
Computational Procedure ◽  
Spherical Particles ◽  
Average Heat Transfer Coefficient ◽  
Heat Generation Rate ◽  
Average Heat

Non-intrusive measurements of the internal average heat transfer coefficient [1] in a randomly packed bed of spherical particles are made. It is desired to establish accurate results for this simple geometry so that the method used can then be extended to determine the heat transfer characteristics in any porous medium, such as a compact heat exchanger. Under steady, one-dimensional flow the spherical particles are subjected to a step change in volumetric heat generation rate via induction heating. The fluid temperature response is measured. The average heat transfer coefficient is determined by comparing the results of a numerical simulation based on volume averaging theory with the experimental results. More specifically, the average heat transfer coefficient is adjusted within the computational procedure until the predicted values of the fluid outlet temperature match the experimental values. The only information needed is the basic material properties, the flow rate, and the experimental data. The computational procedure alleviates the need for solid and fluid phase temperature measurements, which are difficult to make and can disturb the solid-fluid interaction. Moreover, a simple analysis allows us to proceed without knowledge of the heat generation rate, which is difficult to determine due to challenges associated with calibrating an inductively-coupled, sample specific, heat generation system. The average heat transfer coefficient was determined, and expressed in terms of the Nusselt number, over a Reynolds number range of 20–600. The results compared favorably to the work of Whitaker [2] and Kays and London [3]. The success of this method, in determining the average heat transfer coefficient in a randomly packed bed of spheres, suggests that it can be used to determine the average heat transfer coefficient in other porous media.

Analytical Solution of Nonequilibrium Heat Conduction in Porous Medium Incorporating a Variable Porosity Model With Heat Generation

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
M. Nazari ◽  
F. Kowsary
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Heat Transfer Coefficient ◽  
Heat Conduction ◽  
Analytical Solution ◽  
Transfer Coefficient ◽  
Heat Generation ◽  
Conductivity Ratio ◽  
Variable Porosity ◽  
Porosity Model

This paper is concerned with the conduction heat transfer between two parallel plates filled with a porous medium with uniform heat generation under a nonequilibrium condition. Analytical solution is obtained for both fluid and solid temperature fields at constant porosity incorporating the effects of thermal conductivity ratio, porosity, and a nondimensional heat transfer coefficient at pore level. The two coupled energy equations for the case of variable porosity condition are transformed into a third order ordinary equation for each phase, which is solved numerically. This transformation is a valuable solution for heat conduction regime for any distribution of porosity in the channel. The effects of the variable porosity on temperature distribution are shown and compared with the constant porosity model. For the case of the exponential decaying porosity distribution, the numerical results lead to a correlation incorporating conductivity ratio and interstitial heat transfer coefficient.

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.

CFD Analysis Prediction of Heat Transfer Coefficient in Rotating Cavities With Radial Outflow

2006 ◽  
Author(s):  
Charles Wu ◽  
Boris Vaisman ◽  
Kevin McCusker ◽  
Roger Paolillo
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Test Data ◽  
Wall Temperature ◽  
Turbulence Models ◽  
Velocity Profiles ◽  
Transfer Coefficients ◽  
Reynolds Analogy ◽  
Temperature Distributions

This paper documents two related investigations. The first investigation was to benchmark commercial CFD code Fluent in rotating cavities for velocity profiles and beat transfer coefficients. The second investigation was to evaluate the methods of extracting heat transfer coefficients from CFD solution with direct method and Reynolds analogy approach. The rotating cavities examined include rotor-stator, contra-rotating and co-rotating disks. The velocity profiles benchmark was conducted prior to heat transfer coefficient benchmark. Several turbulence models were compared for closed rotating cavity flows. The comparisons between test data and CFD results of tangential and radial velocity profiles showed that the SST k-ω turbulence model performed the best among turbulence models tested. Hence, the SST k-ω model was chosen for heat transfer coefficient benchmarking. The comparisons of heat transfer coefficients between test data and CFD results were presented in the form of local Nusselt number. The thermal wall boundary conditions applied to all the computations were curved-fitted wall temperature distributions from available test data. The wall temperature distributions include approximately constant, positive and negative profiles. It was found that the accurate information of the thermal wall temperature distribution was critical to the benchmark and that only the CFD results with well defined information of wall temperature distributions matched well with test data. The Nusselt number extracted from the CFD solution with the Reynolds analogy approach tends to over predict the heat transfer coefficient on the higher radii and only matched test data at low Reynolds number with positive wall temperature profile. The error increases with higher Reynolds number and decreases with larger flow rate.

scholarly journals Consideration on Local Heat Transfer Measurement of Plate Heat Exchanger with the Aid of Simulation

2020 ◽  
Vol 3 (1) ◽  
pp. 1-9
Author(s):  
Thiha Tun ◽  
Keishi Kariya ◽  
Akio Miyara
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Plate Heat Exchanger ◽  
Local Heat Transfer Coefficient ◽  
Plate Heat ◽  
Temperature Distributions ◽  
Set Up

Abstract In this study, the local heat transfer coefficient of boiling and condensation were obtained by an experimental set up using vertical stainless-steel type brazed plate heat exchanger. A series of 8 vertical brazed plates are used as the major components of the test section of experimental set up and are fabricated into layers so that flow channels are formed between the plates through which water and refrigerants are flowing through. The experiments are carried out at the mass flux of 10, 20 and 50 kg/(m2žs). In order to measure the local heat transfer coefficient, flat stainless-steel plates of 10 mm in thickness are installed attached to the vertical plates onto which the thermocouples are positioned to measure the temperature distributions at the surface of the plates. By performing the experiment, the direction of the heat flux across the plate tends to deviate downward especially at the lower part of the plate due to the non-uniform temperature distributions across the plate. The results are analyzed and validated at the mass flux of 10 kg/(m2žs) by the aid of the simulation tool by using ANSYS FLUENT 19.1 to estimate the local heat transfer coefficient and the heat flux across the plate. The analysis result shows that the simulation model can assist to track the deviation of the direction of the heat flow from the horizontal direction across the plate and the experimental results of the local heat transfer coefficient have similar trends with that of the simulation results.

Experimental Modeling of Heat Transfer in a Continuous Casting Mould Model

2014 ◽  
Author(s):  
R. Kalter ◽  
B. W. Righolt ◽  
S. Kenjereš ◽  
C. R. Kleijn ◽  
M. J. Tummers
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Continuous Casting ◽  
Transfer Coefficient ◽  
Cooling Water ◽  
Working Fluid ◽  
Water Interface ◽  
Temperature Distributions ◽  
Air Water Interface ◽  
Continuous Casting Mould

Temperature distributions in a thin continuous casting mould model have been studied experimentally, using water as a working fluid. The mould model consists of two narrow walls and two broad walls. One of the broad walls of the mould model was cooled with cooling water of a fixed temperature. Inflow of two turbulent jets with a constant high temperature was from a bifurcated nozzle, submerged to a depth of 0.1 m below the air/water interface. The temperature drop over the mould was measured as a function of the temperature difference between the liquid flowing into the mould and the cooling water temperature. From these measurements the overall heat transfer coefficient and heat transfer coefficient due to convection in the mould were calculated. Temperature distributions at the cooled wall have been measured using thermochromic liquid crystal sheets, which have a specific color depending on the temperature. The shear layers of the two jets hit the cooled wall, leading to hot spot formation. The jets show a self-sustained oscillating behavior, leading to a non stationary temperature distribution at the cooled wall. Between the jets and the air/water interface, recirculation zones occur where the liquid cools down significantly, leading to large wall temperature differences in the mould.

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