Experimental Study of Electrohydrodynamic Induction Pumping of a Dielectric Micro Liquid Film in External Horizontal Condensation Process

2002 ◽  
Author(s):  
K. Brand ◽  
J. Seyed-Yagoobi
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Flux ◽  
Liquid Film ◽  
Phase Change ◽  
Traveling Wave ◽  
Change Process ◽  
Change Processes ◽  
Condensation Process ◽  
Flow Management

Electrohydrodynamic induction pumping of a dielectric micro condensation film is experimentally investigated in an external horizontal configuration. The pumping and its effect on heat transfer are explored by varying the voltage and frequency of the electric traveling wave, as well as the condensation heat flux. The induced pumping impacts the phase change process, but it provides first and foremost a tool for effective flow management. This is of significant importance in phase-change processes.

Experimental Study of Electrohydrodynamic Induction Pumping of a Dielectric Micro Liquid Film in External Horizontal Condensation Process

2003 ◽  
Vol 125 (6) ◽  
pp. 1096-1105 ◽  
Author(s):  
K. Brand ◽  
J. Seyed-Yagoobi
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Flux ◽  
Liquid Film ◽  
Phase Change ◽  
Electric Conductivity ◽  
Traveling Wave ◽  
Condensation Process ◽  
Liquid Motion ◽  
Fundamental Understanding

Electrohydrodynamic (EHD) induction pumping is based on charges induced in a dielectric liquid and delayed at a gradient or discontinuity of the electric conductivity. A traveling electric wave (AC) attracts or repels these induced charges, leading to liquid motion. EHD induction pumping of a dielectric micro condensation film, in an external horizontal configuration, is investigated experimentally. The pumping and its effect on heat transfer are explored by varying the voltage and frequency of the electric traveling wave, as well as the condensation heat flux. This study provides a fundamental understanding of induction pumping of micro liquid film and illustrates its potential for managing the flow and enhancing the heat transfer in the presence of phase change.

Numerical Analysis on Evaporation Assisted Convective Cooling: Effect of Surface Morphology

2019 ◽  
Author(s):  
Sudipta Saha ◽  
Amitav Tikadar ◽  
Jamil Khan ◽  
Tanvir Farouk
Keyword(s):  
Heat Flux ◽  
Thermal Resistance ◽  
Liquid Film ◽  
Phase Change ◽  
Surface Structure ◽  
Change Process ◽  
Cooling System ◽  
Structure Modification ◽  
Convective Cooling ◽  
Cooling Method

Abstract With an escalating need to find ways to reduce the water consumption in industrial cooling system, on-demand hybrid cooling has been a topic of great interest. The main concept of this cooling method is centered upon the utilization of huge exchange of enthalpy associated with phase change process in a conventional convective cooling system. In this study, a multidimensional multi-physics model has been employed to study a system that undergoes this dual mode cooling process where both convection and evaporation contribute to the heat transfer process. The computational domain considered is comprised of a thin liquid film that undergoes evaporation with constant heat flux provided from the bottom and a convective loading of laminar air flow above it. Evaporation takes place at the liquid-gas interface and the evaporated mass is being carried away by the incoming air, hence augmenting the convective cooling through the phase change process. This is an extension of our prior work where the surface structure modification (i.e. undulated surface) on the performance of this proposed hybrid cooling method is numerically investigated. Array of hemispherical structures have been introduced as the surface introducing the heat flux to the liquid film. The objective is to increase the surface to volume ratio and decrease the thermal resistance across the liquid film. The predictions indicate that with the increase in the height of the undulated surface the thermal resistance across the liquid film tends to decrease. Results from these simulations show that a ∼50% reduction in the thermal resistance can be achieved by the surface structure modification while the net evaporation flux can be doubled compared to a flat film configuration.

Experimental Study on Thermal Characteristics of Finned Coil LHSU Using Paraffin as Phase Change Material

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Guansheng Chen ◽  
Nanshuo Li ◽  
Huanhuan Xiang ◽  
Fan Li
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Phase Change ◽  
Phase Change Material ◽  
Water Flow ◽  
Water Flow Rate ◽  
Thermal Characteristics ◽  
Heat Transfer Fluid ◽  
Latent Heat Storage ◽  
Change Material

It is well known that attaching fins on the tubes surfaces can enhance the heat transfer into and out from the phase change materials (PCMs). This paper presents the results of an experimental study on the thermal characteristics of finned coil latent heat storage unit (LHSU) using paraffin as the phase change material (PCM). The paraffin LHSU is a rectangular cube consists of continuous horizontal multibended tubes attached vertical fins at the pitches of 2.5, 5.0, and 7.5 mm that creates the heat transfer surface. The shell side along with the space around the tubes and fins is filled with the material RT54 allocated to store energy of water, which flows inside the tubes as heat transfer fluid (HTF). The measurement is carried out under four different water flow rates: 1.01, 1.30, 1.50, and 1.70 L/min in the charging and discharging process, respectively. The temperature of paraffin and water, charging and discharging wattage, and heat transfer coefficient are plotted in relation to the working time and water flow rate.

Experimental Study on Heat Transfer Augmentation for High Heat Flux Removal in Rib-Roughened Narrow Channels

1998 ◽  
Vol 35 (9) ◽  
pp. 671-678 ◽  
Author(s):  
Md. Shafiqul ISLAM ◽  
Ryutaro HINO ◽  
Katsuhiro HAGA ◽  
Masanori MONDE ◽  
Yukio SUDO
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Flux ◽  
High Heat ◽  
High Heat Flux ◽  
Narrow Channels ◽  
Heat Transfer Augmentation ◽  
Rib Roughened

Heat Transfer Enhancement in Compact Phase Change Microchannel Heat Exchangers for High Flux Laser Diodes

2018 ◽  
Author(s):  
Jensen Hoke ◽  
Todd Bandhauer ◽  
Jack Kotovsky ◽  
Julie Hamilton ◽  
Paul Fontejon
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Phase Change ◽  
Flow Boiling ◽  
Laser Diodes ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Maximum Heat ◽  
Average Maximum

Liquid-vapor phase change heat transfer in microchannels offers a number of significant advantages for thermal management of high heat flux laser diodes, including reduced flow rates and near constant temperature heat rejection. Modern laser diode bars can produce waste heat loads >1 kW cm−2, and prior studies show that microchannel flow boiling heat transfer at these heat fluxes is possible in very compact heat exchanger geometries. This paper describes further performance improvements through area enhancement of microchannels using a pyramid etching scheme that increases heat transfer area by ∼40% over straight walled channels, which works to promote heat spreading and suppress dry-out phenomenon when exposed to high heat fluxes. The device is constructed from a reactive ion etched silicon wafer bonded to borosilicate to allow flow visualization. The silicon layer is etched to contain an inlet and outlet manifold and a plurality of 40μm wide, 200μm deep, 2mm long channels separated by 40μm wide fins. 15μm wide 150μm long restrictions are placed at the inlet of each channel to promote uniform flow rate in each channel as well as flow stability in each channel. In the area enhanced parts either a 3μm or 6μm sawtooth pattern was etched vertically into the walls, which were also scalloped along the flow path with the a 3μm periodicity. The experimental results showed that the 6μm area-enhanced device increased the average maximum heat flux at the heater to 1.26 kW cm2 using R134a, which compares favorably to a maximum of 0.95 kw cm2 dissipated by the plain walled test section. The 3μm area enhanced test sections, which dissipated a maximum of 1.02 kW cm2 showed only a modest increase in performance over the plain walled test sections. Both area enhancement schemes delayed the onset of critical heat flux to higher heat inputs.

scholarly journals Capillary-Limited Evaporation From Well-Defined Microstructured Surfaces

2013 ◽  
Author(s):  
Solomon Adera ◽  
Rishi Raj ◽  
Evelyn N. Wang
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Heat Flux ◽  
Phase Change ◽  
Thermal Management ◽  
Latent Heat ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Microstructured Surfaces ◽  
Latent Heat Of Vaporization

Thermal management is increasingly becoming a bottleneck for a variety of high power density applications such as integrated circuits, solar cells, microprocessors, and energy conversion devices. The performance and reliability of these devices are usually limited by the rate at which heat can be removed from the device footprint, which averages well above 100 W/cm2 (locally this heat flux can exceed 1000 W/cm2). State-of-the-art air cooling strategies which utilize the sensible heat are insufficient at these large heat fluxes. As a result, novel thermal management solutions such as via thin-film evaporation that utilize the latent heat of vaporization of a fluid are needed. The high latent heat of vaporization associated with typical liquid-vapor phase change phenomena allows significant heat transfer with small temperature rise. In this work, we demonstrate a promising thermal management approach where square arrays of cylindrical micropillar arrays are used for thin-film evaporation. The microstructures control the liquid film thickness and the associated thermal resistance in addition to maintaining a continuous liquid supply via the capillary pumping mechanism. When the capillary-induced liquid supply mechanism cannot deliver sufficient liquid for phase change heat transfer, the critical heat flux is reached and dryout occurs. This capillary limitation on thin-film evaporation was experimentally investigated by fabricating well-defined silicon micropillar arrays using standard contact photolithography and deep reactive ion etching. A thin film resistive heater and thermal sensors were integrated on the back side of the test sample using e-beam evaporation and acetone lift-off. The experiments were carried out in a controlled environmental chamber maintained at the water saturation pressure of ≈3.5 kPa and ≈25 °C. We demonstrated significantly higher heat dissipation capability in excess of 100 W/cm2. These preliminary results suggest the potential of thin-film evaporation from microstructured surfaces for advanced thermal management applications.

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