Prediction of Heat Transfer Coefficient in Saturated Flow Boiling Heat Transfer in Parallel Rectangular Microchannel Heat Sinks: An Experimental Study

2016 ◽  
Vol 38 (16) ◽  
pp. 1415-1428 ◽  
Author(s):  
Burak Markal ◽  
Orhan Aydin ◽  
Mete Avci
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Heat Sinks ◽  
Saturated Flow ◽  
Rectangular Microchannel ◽  
Flow Boiling Heat Transfer

Experimental Investigation of Flow Boiling Heat Transfer Characteristics of FC-72 in Cross-Linked Microchannel Heat Sinks Using Thermochromatic Liquid Crystals

2009 ◽  
Author(s):  
Ayman Megahed ◽  
Ibrahim Hassan ◽  
Kristina Cook
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Heat Sinks ◽  
Heat Transfer Characteristics ◽  
Flow Boiling Heat Transfer ◽  
Boiling Heat Transfer Coefficient

The present study investigates the effect of cross-links on flow boiling heat transfer characteristics in rectangular microchannel heat sinks, using FC-72 as the working fluid. The silicon test section consists of 45 cross-linked microchannels, measuring 16 mm in length, with a hydraulic diameter of 248 μm. The parameters investigated include mass flux, heat flux, and exit quality, ranging from 99–275 kg/m2s, 7.2–88.8 kW/m2, and 0.01–0.71, respectively. Thermochromatic liquid crystals have been used in the present study as full-field surface temperature sensors to map the temperature distribution on the heat sink surface. The flow boiling heat transfer coefficient shows a different trend in the cross-linked design relative to the straight microchannel design. The flow boiling heat transfer coefficient increases with increasing exit quality at a constant mass flux, which is caused by the domination of the nucleation boiling mechanism in the cross-link region. The predictions obtained from the existing heat transfer correlations found in the literature significantly under-estimate the present heat transfer measurements, except for the Yu et al. (2002) correlation.

Analytical Modeling of Annular Flow Boiling Heat Transfer in Mini- and Microchannel Heat Sinks

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
A. Megahed ◽  
I. Hassan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Analytical Model ◽  
Boiling Heat Transfer ◽  
Annular Flow ◽  
Flow Boiling ◽  
Heat Sinks ◽  
Flow Boiling Heat Transfer ◽  
The Heat Transfer Coefficient

An analytical model is proposed to predict the flow boiling heat transfer coefficient in the annular flow regime in mini- and microchannel heat sinks based on the separated model. The modeling procedure includes a formulation for determining the heat transfer coefficient based on the wall shear stress and the local thermophysical characteristics of the fluid based on the Reynolds’ analogy. The frictional and acceleration pressure gradients within the channel are incorporated into the present model to provide a better representation of the flow conditions. The model is validated against collected data sets from the literature produced by different authors under different experimental conditions, different fluids, and with mini- and microchannels of hydraulic diameters falling within the range of 92–1440 μm. The accuracy between the experimental and predicted results is achieved with a mean absolute error of 10%. The present analytical model can correctly predict the different trends of the heat transfer coefficient reported in the literature as a function of the exit quality. The predicted two-phase heat transfer coefficient is found to be very sensitive to changes in mass flux and saturation temperature. However, it is found to be mildly sensitive to the change in heat flux.

Experimental Investigation of Saturated Flow Boiling Heat Transfer of Vertical Narrow Rectangular Channel

2008 ◽  
Author(s):  
De-Qi Chen ◽  
Liang-Ming Pan ◽  
De-Wen Yuan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Operating Conditions ◽  
Least Square ◽  
Saturated Flow ◽  
Flow Boiling Heat Transfer

Narrow rectangular channel has been widely used at evaporator of cryogenic engineering and electronics cooling. At present paper, saturated flow boiling heat transfer at vertical narrow rectangular channel with gaps of 1.0, 1.5 and 2.5 was experimentally investigated, the heat transfer characteristics at various operating conditions were tested and discussed, and the correlation of saturated boiling heat transfer coefficient was regressed used Least Square Method according to experimental results. It shows that heat transfer coefficient decreases at wider gaps and higher inlet pressure, and it increases at higher flow rate, heat flux and increased vapor quality. Compared with traditional correlation for ordinary channel, the discrepancy is significant. Considering the size effects, a new correlation was proposed to estimate the heat transfer coefficient. The error of the regressed correlation is within ±12%.

A Fundamental View of the Flow Boiling Heat Transfer Characteristics of Nano-Refrigerants

2012 ◽  
Author(s):  
Lorenzo Cremaschi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Phase ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Working Fluid ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow Boiling Heat Transfer

Driven by higher energy efficiency targets and industrial needs of process intensification and miniaturization, nanofluids have been proposed in energy conversion, power generation, chemical, electronic cooling, biological, and environmental systems. In space conditioning and in cooling systems for high power density electronics, vapor compression cycles provide cooling. The working fluid is a refrigerant and oil mixture. A small amount of lubricating oil is needed to lubricate and to seal the sliding parts of the compressors. In heat exchangers the oil in excess penalizes the heat transfer and increases the flow losses: both effects are highly undesired but yet unavoidable. This paper studies the heat transfer characteristics of nanorefrigerants, a new class of nanofluids defined as refrigerant and lubricant mixtures in which nano-size particles are dispersed in the high-viscosity liquid phase. The heat transfer coefficient is strongly governed by the viscous film excess layer that resides at the wall surface. In the state-of-the-art knowledge, while nanoparticles in the refrigerant and lubricant mixtures were recently experimentally studied and yielded convective in-tube flow boiling heat transfer enhancements by as much as 101%, the interactions of nanoparticles with the mixture still pose several open questions. The model developed in this work suggested that the nanoparticles in this excess layer generate a micro-convective mass flux transverse to the flow direction that augments the thermal energy transport within the oil film in addition to the macroscopic heat conduction and fluid convection effects. The nanoparticles motion in the shearing-induced and non-uniform shear rate field is added to the motion of the nanoparticles due to their own Brownian diffusion. The augmentation of the liquid phase thermal conductivity was predicted by the developed model but alone it did not fully explain the intensification on the two-phase flow boiling heat transfer coefficient reported in previous work in the literature. Thus, additional nano- and micro-scale heat transfer intensification mechanisms were proposed.

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