Experimental Study and Model on Critical Heat Flux of Refrigerant-123 and Water in Microchannels

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Wai Keat Kuan ◽  
Satish G. Kandlikar
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Flow Instabilities ◽  
Cross Sectional ◽  
Rectangular Channels ◽  
Boiling Process ◽  
Parallel Microchannels ◽  
Surface Tension Forces

The present work is aimed toward understanding the effect of flow boiling stability on critical heat flux (CHF) with Refrigerant 123 (R-123) and water in microchannel passages. Experimental data and theoretical model to predict the CHF are the focus of this work. The experimental test section has six parallel microchannels, with each having a cross-sectional area of 1054×157μm2. The effect of flow instabilities in microchannels is investigated using flow restrictors at the inlet of each microchannel to stabilize the flow boiling process and avoid the backflow phenomena. This technique resulted in successfully stabilizing the flow boiling process. The present experimental CHF results are found to correlate best with existing correlations to overall mean absolute errors (MAEs) of 33.9% and 14.3% with R-123 and water, respectively, when using a macroscale rectangular equation by Katto (1981, “General Features of CHF of Forced Convection Boiling in Uniformly Heated Rectangular Channels,” Int. J. Heat Mass Transfer, 24, pp. 1413–1419). A theoretical analysis of flow boiling phenomena revealed that the ratio of evaporation momentum to surface tension forces is an important parameter. A theoretical CHF model is proposed using these underlying forces to represent CHF mechanism in microchannels, and its correlation agrees with the experimental data with MAE of 2.5%.

Critical Heat Flux Measurement and Model for Refrigerant-123 Under Stabilized Flow Conditions in Microchannels

2006 ◽  
Author(s):  
Wai Keat Kuan ◽  
Satish G. Kandlikar
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
High Speed ◽  
Flow Boiling ◽  
Flux Measurement ◽  
Absolute Error ◽  
Cross Sectional ◽  
Boiling Process ◽  
Parallel Microchannels

The present work is aimed toward understanding the effect of flow boiling stability on critical heat flux (CHF) with Refrigerant-123 (R-123) in microchannel passages. Experimental data and theoretical model to predict the CHF are the focus of this work. The experimental test section has six parallel microchannels with each having a cross sectional area of 1054 × 157 μm2. The effect of flow instabilities in microchannels is investigated using flow restrictors at the inlet of each microchannel to stabilize the flow boiling process and avoid the backflow phenomena. This technique resulted in successfully stabilizing the flow boiling process as seen through a high-speed camera. The present CHF result is found to correlate to mean absolute error (MAE) of 24.1% with a macroscale empirical equation by Katto [13]. A theoretical analysis of flow boiling phenomena revealed that the ratio of evaporation momentum to surface tension forces is an important parameter. For the first time, a theoretical CHF model is proposed using these underlying forces to represent CHF mechanism in microchannels, and its correlation agrees with the experimental data with MAE of 2.5%.

Effect of Cross-Sectional Perturbation on Critical Heat Flux Criteria in Microchannels

2013 ◽  
Vol 135 (10) ◽  
Author(s):  
Mark J. Miner ◽  
Patrick E. Phelan
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Phase Velocity ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Channel Diameter ◽  
Cross Sectional ◽  
Growing Body ◽  
Circular Microchannel ◽  
Expanding Channel

A variety of predictive correlations for critical heat flux (CHF) are examined in light of the growing body of work exploring enhanced flow boiling CHF via cross-sectional expansion. The analysis considers the effect of a small perturbation of the diameter of a circular microchannel on the predictions made by the selected criteria, and seeks to demonstrate an optimum rate of expansion. It is demonstrated that a nonzero diameter expansion necessarily improves performance under several criteria for critical heat flux, and an optimum expansion rate exists for many of these criteria. CHF relations are seen to follow a few distinct types, and those relations which contemplate effects which may directly influence CHF, such as pressure and phase velocity, tend to better reflect the experimentally demonstrated effect of the expanding channel diameter on CHF. Experimental data are examined from several investigators, including the authors' group, and the validity of both the criteria and the analysis is compared to the data.

Experimental Study on Saturated Flow Boiling Critical Heat Flux in Microchannels

2006 ◽  
Author(s):  
Wai Keat Kuan ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Quantitative Information ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Saturated Flow ◽  
Cross Sectional ◽  
Parallel Microchannels ◽  
Cartridge Heater

The saturated flow boiling critical heat flux in microchannels is investigated using water as the working fluid. The experimental test section has six parallel microchannels with each having a cross sectional area of 1054 × 157 micrometers. The mass flow rate, inlet temperature of the working fluids, and the electric current supplied to the resistive cartridge heater are controlled to provide quantitative information near the CHF condition in microchannels. The trends in present CHF with mass flux and quality are similar to those obtained by Qu and Mudawar [1] and earlier investigators.

scholarly journals A Study of Critical Heat Flux During Flow Boiling in Microchannel Heat Sinks

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Tailian Chen ◽  
Suresh V. Garimella
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Rate ◽  
Heat Input ◽  
Heat Sink ◽  
Flow Boiling ◽  
Strong Dependence ◽  
Heat Fluxes ◽  
Abrupt Decrease ◽  
Parallel Microchannels

The cooling capacity of two-phase transport in microchannels is limited by the occurrence of critical heat flux (CHF). Due to the nature of the phenomenon, it is challenging to obtain reliable CHF data without causing damage to the device under test. In this work, the critical heat fluxes for flow boiling of FC-77 in a silicon thermal test die containing 60 parallel microchannels were measured at five total flow rates through the microchannels in the range of 20–80 ml/min. CHF is caused by dryout at the wall near the exit of the microchannels, which in turn is attributed to the flow reversal upstream of the microchannels. The bubbles pushed back into the inlet plenum agglomerate; the resulting flow blockage is a likely cause for the occurrence of CHF which is marked by an abrupt increase in wall temperature near the exit and an abrupt decrease in pressure drop across the microchannels. A database of 49 data points obtained from five experiments in four independent studies with water, R-113, and FC-77 as coolants was compiled and analyzed. It is found that the CHF has a strong dependence on the coolant, the flow rate, and the area upon which the heat flux definition is based. However, at a given flow rate, the critical heat input (total heat transfer rate to the coolant when CHF occurs) depends only on the coolant and has minimal dependence on the details of the microchannel heat sink (channel size, number of channels, substrate material, and base area). The critical heat input for flow boiling in multiple parallel microchannels follows a well-defined trend with the product of mass flow rate and latent heat of vaporization. A power-law correlation is proposed which offers a simple, yet accurate method for predicting the CHF. The thermodynamic exit quality at CHF is also analyzed and discussed to provide insights into the CHF phenomenon in a heat sink containing multiple parallel microchannels.

On the Nature of Critical Heat Flux in Microchannels

2005 ◽  
Vol 127 (1) ◽  
pp. 101-107 ◽  
Author(s):  
A. E. Bergles ◽  
S. G. Kandlikar
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Flow Distribution ◽  
High Heat ◽  
Operating Conditions ◽  
High Heat Flux ◽  
Clear Understanding ◽  
Wide Range ◽  
Parallel Microchannels

The critical heat flux (CHF) limit is an important consideration in the design of most flow boiling systems. Before the use of microchannels under saturated flow boiling conditions becomes widely accepted in cooling of high-heat-flux devices, such as electronics and laser diodes, it is essential to have a clear understanding of the CHF mechanism. This must be coupled with an extensive database covering a wide range of fluids, channel configurations, and operating conditions. The experiments required to obtain this information pose unique challenges. Among other issues, flow distribution among parallel channels, conjugate effects, and instrumentation need to be considered. An examination of the limited CHF data indicates that CHF in parallel microchannels seems to be the result of either an upstream compressible volume instability or an excursive instability rather than the conventional dryout mechanism. It is expected that the CHF in parallel microchannels would be higher if the flow is stabilized by an orifice at the entrance of each channel. The nature of CHF in microchannels is thus different than anticipated, but recent advances in microelectronic fabrication may make it possible to realize the higher power levels.

Flow boiling in microgravity: Part 2 – Critical heat flux interfacial behavior, experimental data, and model

2015 ◽  
Vol 81 ◽  
pp. 721-736 ◽  
Author(s):  
Christopher Konishi ◽  
Hyoungsoon Lee ◽  
Issam Mudawar ◽  
Mohammad M. Hasan ◽  
Henry K. Nahra ◽  
...  
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Interfacial Behavior

Correlation for Flow Boiling Critical Heat Flux in Thin Rectangular Channels

2009 ◽  
Vol 131 (12) ◽  
Author(s):  
Futoshi Tanaka ◽  
Takashi Hibiki ◽  
Kaichiro Mishima
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Rectangular Channels ◽  
Hydraulic Design ◽  
Wide Range ◽  
Outlet Flow ◽  
Triggering Mechanisms ◽  
Small Channels ◽  
Heated Length

The effect of heated length on critical heat flux (CHF) in thin rectangular channels under atmospheric pressure has been studied. CHF in small channels has been widely studied in the last decades but most of the studies are based on flow in round tubes and number of studies focused on rectangular channels is relatively small. Although basic triggering mechanisms, which lead to CHF in thin rectangular channels, are similar to that of tubes, applicability of thermal hydraulic correlations developed for tubes to rectangular channels are questionable since heat transfer in rectangular channels are affected by the existence of nonheated walls and the noncircular geometry of channel circumference. Several studies of CHF in thin rectangular channels have been reported in relation to thermal hydraulic design of research reactors and neutron source targets and correlations have been proposed, but the studies mostly focus on geometrical conditions of the application of interest and therefore effect of channel parameters exceeding their interest is not fully understood. In his study, CHF data for thin rectangular channels have been collected from previous studies and the effect of heated length on CHF was examined. Existing correlations were verified with data with positive quality outlet flow but none of the correlations successfully reproduced the data for a wide range of heated lengths. A new CHF correlation for quality region applicable to a wide range of heated lengths has been developed based on the collected data.

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