Critical Heat Flux of R-123 in Silicon-Based Microchannels

2006 ◽  
Vol 129 (7) ◽  
pp. 844-851 ◽  
Author(s):  
Ali Koşar ◽  
Yoav Peles
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Heat Sink ◽  
Mass Velocity ◽  
Heat Fluxes ◽  
Microchannel Heat Sink ◽  
New Correlation ◽  
Mass Fluxes ◽  
System Pressure ◽  
Silicon Based

Critical heat flux (CHF) of R-123 in a silicon-based microchannel heat sink was investigated at exit pressures ranging from 227kPato520kPa. Critical heat flux data were obtained over effective heat fluxes ranging from 53W∕cm2to196W∕cm2 and mass fluxes from 291kg∕m2sto1118kg∕m2s. Flow images and high exit qualities suggest that dryout is the leading CHF mechanism. The effect of mass velocity, exit quality, and system pressure were also examined, and a new correlation is presented to represent the effect of these parameters.

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.

Experimental Investigation of Critical Heat Flux in Microchannels for Flow-Field Probes

2009 ◽  
Author(s):  
Ali Kos¸ar ◽  
Yoav Peles ◽  
Arthur E. Bergles ◽  
Gregory S. Cole
Keyword(s):  
Heat Flux ◽  
Experimental Investigation ◽  
Critical Heat Flux ◽  
Mass Velocity ◽  
Thermal Condition ◽  
Average Error ◽  
New Correlation ◽  
Hydraulic Conditions ◽  
Data Points ◽  
Heated Length

Critical heat flux (CHF) of water in circular stainless steel microchannels with inner diameters ranging from ∼127μm to ∼254 μm was investigated. Forty-five CHF data points were acquired over mass velocities ranging from 1,200 kg/m2s to 53,000 kg/m2s, heated lengths from 2 cm to 8 cm, and exit qualities from −0.2 to 0.15. Most of the exit qualities fell below 0.1. It was found that CHF conditions were more dependent on mass velocity and heated length than on exit thermal condition. The results were also compared to six CHF correlations, with a mean average error ranging from 22% to 261.8%. A new correlation was proposed to better predict the critical heat flux data under the thermal-hydraulic conditions studied in this investigation. In developing the correlation, 319 data points were added from two previous studies.

scholarly journals Critical heat flux enhancement of HFE-7100 flow boiling in a minichannel heat sink with saw-tooth structures

2017 ◽  
Vol 9 (2) ◽  
pp. 168781401668902 ◽  
Author(s):  
Ben-Ran Fu ◽  
Shan-Yu Chung ◽  
Wei-Jen Lin ◽  
Lei Wang ◽  
Chin Pan
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Heat Sink ◽  
Heat Dissipation ◽  
Flow Boiling ◽  
Convective Boiling ◽  
Tooth Structure ◽  
Flux Enhancement ◽  
System Pressure

A heat sink with convective boiling in micro- or mini-channels is with great potential to meet the requirement of the high heat dissipation of the electronic devices. This study investigates the flow boiling of HFE-7100, having a suitable boiling temperature at atmospheric pressure and dielectric property, in the minichannel heat sink with the modified surface (namely, the saw-tooth structure). The effect of the system pressure on the boiling characteristics was also studied. The results reveal that the critical heat flux can be significantly improved by introducing the saw-tooth structures on the channel surface or boosting the system pressure as well as by increasing the mass flux. Compared to the non-modified channel, the enhancements of the critical heat flux for the parallel and counter saw-tooth channels are 44% and 36%, respectively, at the small mass flux. The boiling visualization further indicates that the minichannels with the saw-tooth structures interrupt the boundary layer and restrain the coalescence of the bubble, which may be the reason for the critical heat flux enhancement. Moreover, the degree of the critical heat flux enhancement, contributed by the saw-tooth modification of the channel, decreases with an increase in the mass flux.

Critical Heat Flux of Water at Subatmospheric Pressures in Microchannels

2008 ◽  
Vol 130 (7) ◽  
Author(s):  
C.-J. Kuo ◽  
Y. Peles
Keyword(s):  
Heat Flux ◽  
Flow Visualization ◽  
Flow Pattern ◽  
Critical Heat Flux ◽  
Annular Flow ◽  
Hydraulic Diameter ◽  
Experimental Results ◽  
Rectangular Microchannels ◽  
Mass Fluxes ◽  
Silicon Based

Critical heat flux conditions for water at subatmospheric pressures in an array of silicon-based, 227μm hydraulic diameter, rectangular microchannels were experimentally studied. Experiments were conducted at exit pressures from 0.1atmto1atm, mass fluxes from 86kg∕m2sto303kg∕m2s, and an effective heat flux up to 444W∕cm2. The annular flow pattern revealed during flow visualization and the high exit qualities at CHF conditions suggest dryout to be the CHF mechanism. An analysis, based on the experimental results and known CHF characteristics, on the dependency of the critical heat flux on various variables was performed. It was found that the boiling number at the CHF condition was approximately a constant.

Investigation of Cooling Performance of a Swirl Microchannel Heat Sink by Numerical Simulation

2011 ◽  
Author(s):  
Yanfeng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Numerical Simulation ◽  
Heat Flux ◽  
Heat Sink ◽  
High Heat ◽  
Heat Fluxes ◽  
Maximum Temperature ◽  
Microchannel Heat Sink ◽  
Irreversible Damage ◽  
Cooling Performance ◽  
Large Heat

High heat fluxes have been created by the semiconductor devices due to the high power generation and shrank size. The large heat flux causes the circuit to exceed its allowable temperature and may experience both working efficiency loss and irreversible damage due to excess in their temperatures. In this paper, a swirl microchannel heat sink is designed to dissipate the large heat flux from the devices. The numerical simulation is carried out to investigate the cooling performance. Uniform heating boundary condition is applied and single phase water is selected as coolant. The present micro heat sink applies multiple swirl microchannels positioned in a circular flat plate to enhance the heat convection by creating the secondary flow at high Reynolds numbers. Copper is selected as the material of heat sink. The channel depth and width are fixed as 0.5 mm and 0.4 mm, respectively. The heat is injected into the system from the bottom of heat sink at the heat fluxes from 10 to 60 W/cm2. Flow is supplied from the top of micro heat sink through a jet hole with a diameter of 2 mm and enters swirl microchannels at the volume flow rates varying from 47 to 188 ml/min. The cooling performances of swirl microchannel heat sinks with different curvatures and channel numbers are evaluated based on the targets of low maximum temperature, temperature gradient and pressure drop.

Critical Heat Flux in Helically Coiled Tubes

1981 ◽  
Vol 103 (4) ◽  
pp. 660-666 ◽  
Author(s):  
M. K. Jensen ◽  
A. E. Bergles
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Mass Velocity ◽  
High Heat ◽  
Heat Fluxes ◽  
Tube Diameter ◽  
Coiled Tube ◽  
Coil Diameter ◽  
The Difference

A study of boiling R-113 in electrically heated coils of various diameters is reported. Subcooled critical heat flux (CHF) is lower with coils than with straight tubes. The difference increases as mass velocity and ratio of tube diameter to coil diameter (d/D) increases. On the contrary, quality CHF is enhanced and increases with d/D; CHF initially increases with increasing mass velocity, but decreases after a maximum is reached. Operational problems, in particular upstream dryouts, can occur if a coiled tube is operated with low to moderate subcooling near the inlet and with moderately high heat fluxes.

Pressure Drop Experiments of Liquid Sodium Flowing in a 7-Rod Bundle

2018 ◽  
Author(s):  
Yandong Hou ◽  
Liu Wang ◽  
Yingwei Wu ◽  
Wenxi Tian ◽  
Suizheng Qiu ◽  
...  
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Pressure Drop ◽  
Mass Velocity ◽  
Liquid Sodium ◽  
Average Temperature ◽  
Flux System ◽  
Rod Bundle ◽  
New Correlation ◽  
System Pressure

Pressure drop experiments was conducted for liquid sodium in an electrically heated 7-rod bundle. The electrically heated 7-rod bundle was placed in a hexagonal tube. In the experiment, the heat flux ranges from 0∼300 kw · m−2, mass velocity from 40∼450 kg · m−2 · s−1, system pressure from 10∼200 KPa and the average temperature of liquid sodium from 350∼650°C. The effects of the heat flux, system pressure and the average temperature of liquid sodium on the pressure drop was in-depth analyzed. A new correlation for pressure drop was developed based on the experimental data of liquid sodium in a 7-rod bundle.

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