Flow boiling visualization and heat transfer in metal-foam-filled mini tubes – Part II: Developing predictive methods for heat transfer coefficient and pressure drop

2016 ◽  
Vol 98 ◽  
pp. 868-878 ◽  
Author(s):  
Gholamreza Bamorovat Abadi ◽  
Chanhee Moon ◽  
Kyung Chun Kim
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Metal Foam ◽  
Flow Boiling ◽  
Predictive Methods ◽  
Foam Filled

Flow Boiling Heat Transfer in a Silicon Microchannel Heat Sink Using Liquid Crystal Thermography

2008 ◽  
Author(s):  
Ayman Megahed ◽  
Ibrahim Hassan ◽  
Tariq Ahmad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Microchannel Heat Sink

The present study focuses on the experimental investigation of boiling heat transfer characteristics and pressure drop in a silicon microchannel heat sink. The microchannel heat sink consists of a rectangular silicon chip in which 45 rectangular microchannels were chemically etched with a depth of 295 μm, width of 254 μm, and a length of 16 mm. Un-encapsulated Thermochromic liquid Crystals (TLC) are used in the present work to enable nonintrusive and high spatial resolution temperature measurements. This measuring technique is used to provide accurate full and local surface-temperature and heat transfer coefficient measurements. Experiments are carried out for mass velocities ranging between 290 to 457 kg/m2.s and heat fluxes from 6.04 to 13.06 W/cm2 using FC-72 as the working fluid. Experimental results show that the pressure drop increases as the exit quality and the flow rate increase. High values of heat transfer coefficient can be obtained at low exit quality (xe < 0.2). However, the heat transfer coefficient decreases sharply and remains almost constant as the quality increases for an exit quality higher than 0.2.

Experimental Study on Flow Boiling of HFC134a in a Multi-Port Extruded Tube

2004 ◽  
Author(s):  
Ken Kuwahara ◽  
Shigeru Koyama ◽  
Kengo Kazari
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Large Diameter ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Inlet Temperature

In the present study, the local heat transfer and pressure drop characteristics are investigated experimentally for the flow boiling of refrigerant HFC134a in a multi-port extruded tube of 1.06mm in hydraulic diameter. The test tube is 865mm in total length made of aluminum. The pressure drop is measured at an interval of 191 mm, and the local heat transfer coefficient is measured in every subsection of 75mm in effective heating length. Experimental ranges are as follows: the mass velocity of G = 100–700 kg/m2s, the inlet temperature of Tin = 5.9–11.4 °C and inlet pressure of about 0.5 MPa. The data of pressure drop are compared with a few previous correlations for small diameter tubes, and the correlations can predict the data relatively good agreement. The data of heat transfer coefficient is compared with the correlations of Yu et al. proposed for relatively large diameter tubes. It is found that there are some differences about two phase multiplier factor of convective heat transfer between the circular channel and rectangular channel.

Finned Metal Foam Heat Sinks for Electronics Cooling in Forced Convection

2002 ◽  
Vol 124 (3) ◽  
pp. 155-163 ◽  
Author(s):  
A. Bhattacharya ◽  
R. L. Mahajan
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Forced Convection ◽  
Metal Foam ◽  
Experimental Results ◽  
Heat Sinks ◽  
The Heat Transfer Coefficient

In this paper, we present recent experimental results on forced convective heat transfer in novel finned metal foam heat sinks. Experiments were conducted on aluminum foams of 90 percent porosity and pore size corresponding to 5 PPI (200 PPM) and 20 PPI (800 PPM) with one, two, four and six fins, where PPI (PPM) stands for pores per inch (pores per meter) and is a measure of the pore density of the porous medium. All of these heat sinks were fabricated in-house. The forced convection results show that heat transfer is significantly enhanced when fins are incorporated in metal foam. The heat transfer coefficient increases with increase in the number of fins until adding more fins retards heat transfer due to interference of thermal boundary layers. For the 20 PPI samples, this maximum was reached for four fins. For the 5 PPI heat sinks, the trends were found to be similar to those for the 20 PPI heat sinks. However, due to larger pore sizes, the pressure drop encountered is much lower at a particular air velocity. As a result, for a given pressure drop, the heat transfer coefficient is higher compared to the 20 PPI heat sink. For example, at a Δp of 105 Pa, the heat transfer coefficients were found to be 1169W/m2-K and 995W/m2-K for the 5 PPI and 20 PPI 4-finned heat sinks, respectively. The finned metal foam heat sinks outperform the longitudinal finned and normal metal foam heat sinks by a factor between 1.5 and 2, respectively. Finally, an analytical expression is formulated based on flow through an open channel and incorporating the effects of thermal dispersion and interfacial heat transfer between the solid and fluid phases of the porous medium. The agreement of the proposed relation with the experimental results is promising.

Microchannel Size Effects on Two-Phase Local Heat Transfer and Pressure Drop in Silicon Microchannel Heat Sinks With a Dielectric Fluid

2007 ◽  
Author(s):  
Tannaz Harirchian ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Heat Sinks ◽  
Dielectric Fluid ◽  
Two Phase ◽  
Microchannel Heat Sinks ◽  
The Heat Transfer Coefficient

Two-phase heat transfer in microchannels can support very high heat fluxes for use in high-performance electronics-cooling applications. However, the effects of microchannel cross-sectional dimensions on the heat transfer coefficient and pressure drop have not been investigated extensively. In the present work, experiments are conducted to investigate the local flow boiling heat transfer in microchannel heat sinks. The effect of channel size on the heat transfer coefficient and pressure drop is studied for mass fluxes ranging from 250 to 1600 kg/m2s. The test sections consist of parallel microchannels with nominal widths of 100, 250, 400, 700, and 1000 μm, all with a depth of 400 μm, cut into 12.7 mm × 12.7 mm silicon substrates. Twenty-five microheaters embedded in the substrate allow local control of the imposed heat flux, while twenty-five temperature microsensors integrated into the back of the substrates enable local measurements of temperature. The dielectric fluid Fluorinert FC-77 is used as the working fluid. The results of this study serve to quantify the effectiveness of microchannel heat transport while simultaneously assessing the pressure drop trade-offs.

Heat Dissipation Beyond 1 kW/cm2 With Low Pressure Drop and High Heat Transfer Coefficient for Flow Boiling Using Open Microchannels With Tapered Manifold

2016 ◽  
Author(s):  
Ankit Kalani ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Dissipation ◽  
Flow Boiling ◽  
Low Pressure ◽  
High Heat ◽  
High Heat Transfer ◽  
High Heat Transfer Coefficient

Heat dissipation beyond 1 kW/cm2 accompanied with high heat transfer coefficient and low pressure drop using water has been a long-standing goal in the flow boiling research directed toward electronic cooling application. In the present work, three approaches are combined to reach this goal: (a) a microchannel with a manifold to increase critical heat flux (CHF) and heat transfer coefficient (HTC), (b) a tapered manifold to reduce the pressure drop, and (c) high flow rates for further enhancing CHF from liquid inertia forces. A CHF of 1.07 kW/cm2 was achieved with a heat transfer coefficient of 295 kW/m2°C with a pressure drop of 30 kPa. Effect of flow rate on CHF and HTC is investigated. High speed visualization to understand the underlying bubble dynamics responsible for low pressure drop and high CHF is also presented.

Research on the Flow Boiling and Heat Transfer of Ethanol in a Corrugated Mini-Channel

2011 ◽  
Vol 66-68 ◽  
pp. 876-881
Author(s):  
Wei Chang ◽  
Shu Sheng Zhang ◽  
Shuai Tian ◽  
Meng Jia Huo
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Phase Interface ◽  
Experimental Studies ◽  
Heating Wall ◽  
Heat And Mass Exchange ◽  
System Pressure

Based on the establishment of a two-dimensional model, a numerical simulation was conducted in this paper to study the flow boiling and heat transfer characteristics of ethanol in a corrugated mini-channel. User defined functions were employed to describe the key processes of heat and mass exchange at the phase interface. Bubble growth profile was monitored over time and its influence on system pressure drop and heat transfer coefficient was also analyzed. The simulation result shows that the nucleation sites tend to distribute near the internal peaks of the heating wall due to the enhanced local turbulence. The system pressure drop increases over the heating time and fluctuates within a certain range. The heat transfer coefficient decreases with increasing quality, and this trend is consistent with the result of similar experimental studies.

Evaluation of Pressure Drop Performance During Enhanced Flow Boiling in Open Microchannels With Tapered Manifolds

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Ankit Kalani ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
High Surface ◽  
Heat Removal ◽  
Electronics Cooling ◽  
Successful Implementation ◽  
Efficient Operation

Boiling can provide several orders of magnitude higher performance than a traditional air cooled system in electronics cooling applications. It can dissipate large quantities of heat while maintaining a low surface temperature difference. Flow boiling with microchannels has shown a great potential with its high surface area to volume ratio and latent heat removal. However, flow instabilities and low critical heat flux (CHF) have prevented its successful implementation. A novel flow boiling design is experimentally investigated to overcome the above-mentioned disadvantages while presenting a very low pressure drop. The design uses open microchannels with a tapered manifold (OMM) to provide stable and efficient operation. The effect of tapered manifold block with varied dimension is investigated with distilled, degassed water at atmospheric pressure. Heat transfer coefficient and pressure drop results for uniform and tapered manifolds with plain and microchannel chips are presented. The OMM configuration yielded a CHF of over 500 W/cm2 in our earlier work. In the current work, a heat transfer coefficient of 277.8 kW/m2 °C was obtained using an OMM design with an inlet gap of 127 μm and an exit gap of 727 μm over a 10 mm flow length. The OMM geometry also resulted in a dramatic reduction in pressure drop from 158.4 kPa for a plain chip and 62.1 kPa for a microchannel chip with a uniform manifold, to less than 10 kPa with the tapered OMM design. A tapered manifold (inlet and exit manifold heights of 127 and 727 μm, respectively) with microchannel provided the lowest pressure drop of 3.3 kPa.

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