Effect of Heat Source Geometry on the Transient Heat Transfer During Melting Process of a PCM

2016 ◽  
Author(s):  
Mohammad Bashar ◽  
Kamran Siddiqui
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Convective Heat Transfer Coefficient ◽  
Outer Region ◽  
Melting Process ◽  
Melting Rate ◽  
Transfer Coefficients ◽  
Heat Transfer Behavior ◽  
Transfer Behavior ◽  
Inner Region

Thermal energy storage (TES) systems using phase change materials (PCMs) are used in various engineering applications. TES is a means by which heat is ‘hold’ for a certain period of time for use at a later time. We report an experimental study which was conducted to investigate the melting process and associated heat transfer in a rectangular chamber with a cylindrical u-shaped heat source imbedded inside the PCM. The results showed that geometry and orientation of the heat source immensely influenced the heat transfer behavior during solid-liquid phase transition. The heat transfer behavior, interface movement and the heat transfer coefficients differed both axially and vertically inside the chamber as well as with the melting rate. The local convective heat transfer coefficient, hlocal in the inner region, enclosed by the U-tube, was observed to increase at a higher rate than the outer region. Stronger convective flow and a lower viscosity owing to higher temperature in the inner region is believed to have caused faster melting in this region. The melting rate was also found comparatively higher until approximately two-third of the PCM volume was melted before the rate declined.

Heat Transfer Characterizations of Heat Pipe in Comparison With Copper Pipe

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Chen-Ching Ting ◽  
Jing-Nang Lee ◽  
Chien-Chih Chen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Source ◽  
Heat Pipe ◽  
Heat Conductivity ◽  
Cooling Efficiency ◽  
Copper Pipe ◽  
Heat Transfer Behavior ◽  
Transfer Behavior ◽  
Large Heat

The article presents some significant experimental data for studying the heat transfer behavior of heat pipe, which will further help the cooling efficiency improvement of the heat pipe cooler. It is well known that the heat pipe owns the extreme large heat conductivity and is often integrated with cooling plates for CPU cooling. The heat pipe uses special heat transfer techniques to obtain extremely large heat conductivity, which are the inside liquid evaporation for heat absorption and the inside microstructural capillarity for condensation. These special techniques yield the instant heat transfer from the heat source to the remote side directly, but the special heat transfer behavior is changed due to the integration with cooling plates. The destroyed heat transfer behavior of the heat pipe causes the cooling efficiency of the heat pipe cooler to be not able to reach a predicted good value. To improve the cooling efficiency of the heat pipe cooler we recover the original heat transfer behavior of the heat pipe integrated with cooling plates. This work first built a CPU simulator in accordance with the ASTM standard for heating the heat pipe, then uses the color schlieren technique to visualize the sequent heat flux nearby the heat pipe and the infrared thermal camera for quantitative temperature measurements synchronously. The result shows that the heat flux first appears at the opposite side from the heat source and there exhibits also the highest temperature. This is different from the heat transfer behavior of the copper pipe. Another very interesting result is that the heat flux of the cooling plate nearest to the heat source is first viewed than the others, which is similar to the integration with the copper pipe.

Local Heat Transfer Behavior and Its Impact on a Single-Row, Annularly Finned Tube Heat Exchanger

1993 ◽  
Vol 115 (1) ◽  
pp. 66-74 ◽  
Author(s):  
X. Hu ◽  
A. M. Jacobi
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Convective Heat Transfer Coefficient ◽  
Experimental Studies ◽  
Finned Tube ◽  
Fin Efficiency ◽  
Tube Heat Exchanger ◽  
Heat Transfer Behavior ◽  
Finned Tube Heat Exchanger ◽  
Transfer Behavior

Experimental studies of the local mass transfer characteristics of annularly finned tubes in crossflow are presented. Variations due to boundary layer development, forward-edge separation, the tube wake, horseshoe vortices, and tip vortices are discussed. In addition, regularly located local maxima in mass transfer rates associated with the horseshoe vortex system are found, and conjecture as to their mechanism is offered. Inferring heat transfer behavior from the mass transfer results, we find that the true fin efficiency is always less than that obtained with an assumed constant convective heat transfer coefficient. The difference is 3–7 percent for high-conductivity materials such as aluminum alloys, and 9–17 percent for low-conductivity materials such as mild steels.

Development of Convective Heat Transfer Near Suddenly Heated, Vertically Aligned Horizontal Wires

1987 ◽  
Vol 109 (4) ◽  
pp. 912-918 ◽  
Author(s):  
J. R. Parsons ◽  
M. L. Arey
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Fluid Layer ◽  
Convective Motion ◽  
Transient Behavior ◽  
Temperature Fields ◽  
Heat Sources ◽  
Transfer Coefficients ◽  
Vertically Aligned ◽  
The Wire

Experiments have been performed which describe the transient development of natural convective flow from both a single and two vertically aligned horizontal cylindrical heat sources. The temperature of the wire heat sources was monitored with a resistance bridge arrangement while the development of the flow field was observed optically with a Mach–Zehnder interferometer. Results for the single wire show that after an initial regime where the wire temperature follows pure conductive response to a motionless fluid, two types of fluid motion will begin. The first is characterized as a local buoyancy, wherein the heated fluid adjacent to the wire begins to rise. The second is the onset of global convective motion, this being governed by the thermal stability of the fluid layer immediately above the cylinder. The interaction of these two motions is dependent on the heating rate and relative heat capacities of the cylinder and fluid, and governs whether the temperature response will exceed the steady value during the transient (overshoot). The two heat source experiments show that the merging of the two developing temperature fields is hydrodynamically stabilizing and thermally insulating. For small spacing-to-diameter ratios, the development of convective motion is delayed and the heat transfer coefficients degraded by the proximity of another heat source. For larger spacings, the transient behavior approaches that of a single isolated cylinder.

scholarly journals Heat transfer behavior of flat plate having 45° ellipsoidal dimpled surfaces

2014 ◽  
Vol 2 ◽  
pp. 67-74 ◽  
Author(s):  
Nopparat Katkhaw ◽  
Nat Vorayos ◽  
Tanongkiat Kiatsiriroat ◽  
Yottana Khunatorn ◽  
Damorn Bunturat ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Heat Transfer Behavior ◽  
Transfer Behavior

Heat Transfer and Friction in Channels With Very High Blockage 45° Staggered Turbulators

2003 ◽  
Author(s):  
Jeremy C. Bailey ◽  
Ronald S. Bunker
Keyword(s):  
Heat Transfer ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Flow Area ◽  
Test Technique ◽  
Heat Transfer Coefficients ◽  
Smooth Channel ◽  
Constant Pitch ◽  
Transfer Behavior ◽  
Very High

Heat transfer and friction coefficients have been measured within a rectangular passage of aspect ratio 0.4 containing 45-degree staggered turbulators of very high blockage. Using a constant pitch-to-height ratio of 10 for all geometries, turbulator height-to-channel hydraulic diameter ratios from 0.193 to 0.333 were investigated. This range of e/D creates actual channel blockage ratios e/H from 0.275 to 0.475, presenting significant flow area restrictions. A liquid crystal test technique is used to obtain both detailed heat transfer behavior on the surfaces between turbulators, as well as averaged fully developed heat transfer coefficients. Reynolds numbers from 20000 to 100000 were tested. Nusselt number enhancements of up to 3.6 were obtained over that of a smooth channel, with friction coefficient enhancements of as much as 65. In contrast to low-blockage turbulated channels, the 45-degree turbulated Nu is found to be lower than that at 90-degree orientation, given very similar e/D and e/H values.

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