Two-Phase Flow and Heat Transfer in Pin-Fin Enhanced Micro-Gaps With Non-Uniform Heating

2013 ◽  
Author(s):  
Steven A. Isaacs ◽  
Yogendra Joshi ◽  
Yue Zhang ◽  
Muhannad S. Bakir ◽  
Yoon Jo Kim
Keyword(s):  
Heat Transfer ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Phase Flow ◽  
Two Phase ◽  
Pin Fin ◽  
Flow And Heat Transfer ◽  
Imaging Results

In modern microprocessors, thermal management has become one of the main hurdles in continued performance enhancement. Cooling schemes utilizing single phase microfluidics have been investigated extensively for enhanced heat dissipation from microprocessors. However, two-phase fluidic cooling devices are becoming a promising approach, and are less understood. This study aims to examine two-phase flow and heat transfer within a pin-fin enhanced micro-gap. The pin-fin array covered an area of 1cm × 1cm and had a pin diameter, height and pitch of 150μm, 200μm and 225μm, respectively, (aspect ratio of 1.33). Heating from two upstream heaters was considered. The working fluid used was R245fa. The average heat transfer coefficient was evaluated for a range of heat fluxes and flow rates. Flow regime visualization was performed using high-speed imaging. Results indicate a sharp transition to convective flow boiling mechanism. Unique, conically-shaped two-phase wakes are recorded, demonstrating 2D spreading capability of the device. Surface roughness features are also discussed.

Proposed Correlation for Forced Convection Boiling Heat Transfer in Mini and Micro Channels With CO2 as a Fluid

2014 ◽  
Author(s):  
Mayank I. Vyas ◽  
Salim A. Channiwala ◽  
Mitesh N. Prajapati
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Working Fluid ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Boiling Heat Transfer ◽  
Micro Channels

After reviewing the available literature on flow boiling heat transfer in mini/micro tubes and channels, it is felt that there is need for predictive correlations which is applicable over wide range of parameters. In present work a new correlation for two-phase flow boiling heat transfer coefficient is developed, which has considered nucleate boiling and convective boiling heat transfer effect. To develop this correlation we have considered total 651 data points, which have been collected from the open available literature covering different operational conditions and different dimensions of channels. We have selected CO2 as a working fluid because it does not contain chlorine, hence an efficient and environmentally safe refrigerant and would be potential replacement for R-22. CO2 has unusual heat transfer and two-phase flow characteristics, and is very different from those of conventional refrigerant. Also a comparison of present correlation with the best published correlation for CO2 is done. The results of this comparison indicate that the new developed correlation is superior to published best correlation for CO2. Present correlation is also compared with best published correlation for all fluids and with the correlation developed by using CO2 data. The results of these both case, indicate that the present correlation is superior.

Heat Transfer Mechanism and Flow Pattern During Flow Boiling of Water in a Vertical Narrow Channel: Experimental Results

2006 ◽  
Author(s):  
Ewelina Sobierska ◽  
Rudi Kulenovic ◽  
Rainer Mertz
Keyword(s):  
Heat Transfer ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Transfer Mechanism ◽  
Phase Flow ◽  
Fluid Temperature ◽  
Heat Transfer Mechanism ◽  
Two Phase ◽  
Mass Fluxes

Experimental investigations on flow boiling phenomena in a vertical narrow rectangular microchannel with the hydraulic diameter dh = 0.48 mm were carried out. The experiments were performed under fluid-inlet subcooling conditions with deionised and degassed water for different mass fluxes. Investigations on pressure drop and heat transfer during single-and two-phase flow have been carried out. Moreover, flow visualisation of the two-phase flow patterns along the channel was performed using a digital high-speed video camera. The present work outlines local heat transfer coefficients for three mass fluxes (200, 700 and 1500 kg/m2s) and heat fluxes (30–110, 35–150 and 65–200 kW/m2, respectively) during two-phase flow. The fluid temperature at the inlet was about 50 °C what corresponds to inlet subcooling, depending on flow pressure conditions, from 34 °C to 57 °C. The visual observations were used to obtain a better insight about the heat transfer mechanism.

Experimental Investigation of Flow Boiling in a Vertical Narrow Channel

2005 ◽  
Author(s):  
Ewelina Sobierska ◽  
Klaudia Chmiel ◽  
Rudi Kulenovic ◽  
Rainer Mertz
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Experimental Investigations ◽  
Flow Visualisation ◽  
Phase Flow ◽  
Two Phase

Experimental investigations on thermofluid-dynamic phenomena in a vertical narrow rectangular microchannel with the hydraulic diameter dh = 0.27 mm were carried out. The experiments are performed under fluid-inlet subcooling conditions with de-ionised and degassed water for different mass fluxes (50–2000 kg/m2s) and heat fluxes (2–150 kW/m2). Moreover, flow visualisation of the two-phase flow patterns along the channel is performed using a digital high-speed video camera. Investigations on pressure drop during single- and two-phase flow have been carried out. The present work is concentrated on two-phase heat transfer. The mean heat transfer coefficient and the local heat transfer coefficient at saturated conditions were calculated and the latter ones was compared with available correlations.

Flow Boiling Heat Transfer and Pressure Drops of R1234ze(E) in a Silicon Micro-pin Fin Evaporator

2017 ◽  
Vol 139 (3) ◽  
Author(s):  
C. Falsetti ◽  
M. Magnini ◽  
J. R. Thome
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Phase Flow ◽  
Two Phase ◽  
Pressure Drops ◽  
Pin Fin ◽  
The Heat Transfer Coefficient

The development of newer and more efficient cooling techniques to sustain the increasing power density of high-performance computing systems is becoming one of the major challenges in the development of microelectronics. In this framework, two-phase cooling is a promising solution for dissipating the greater amount of generated heat. In the present study, an experimental investigation of two-phase flow boiling in a micro-pin fin evaporator is performed. The micro-evaporator has a heated area of 1 cm2 containing 66 rows of cylindrical in-line micro-pin fins with diameter, height, and pitch of, respectively, 50 μm, 100 μm, and 91.7 μm. The working fluid is R1234ze(E) tested over a wide range of conditions: mass fluxes varying from 750 kg/m2 s to 1750 kg/m2 s and heat fluxes ranging from 20 W/cm2 to 44 W/cm2. The effects of saturation temperature on the heat transfer are investigated by testing three different outlet saturation temperatures: 25 °C, 30 °C, and 35 °C. In order to assess the thermal–hydraulic performance of the current heat sink, the total pressure drops are directly measured, while local values of heat transfer coefficient are evaluated by coupling high-speed flow visualization with infrared temperature measurements. According to the experimental results, the mass flux has the most significant impact on the heat transfer coefficient while heat flux is a less influential parameter. The vapor quality varies in a range between 0 and 0.45. The heat transfer coefficient in the subcooled region reaches a maximum value of about 12 kW/m2 K, whilst in two-phase flow it goes up to 30 kW/m2 K.

Flow and heat transfer in a closed loop thermosyphon. Part I – theoretical simulation

2007 ◽  
Vol 18 (4) ◽  
pp. 32-40 ◽  
Author(s):  
R.T. Dobson ◽  
J.C. Ruppersberg
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Closed Loop ◽  
Two Phase Flow ◽  
Working Fluid ◽  
Phase Flow ◽  
Two Phase ◽  
Operating Modes ◽  
Flow And Heat Transfer ◽  
Control Volumes

A natural circulation, closed loop thermosyphon can transfer heat over relatively large distances without any moving parts such as pumps and active controls. Such loops are thus considered suitable for nuclear reactor cooling applications where safety and high reliability are of paramount importance. A theoretical basis from which to predict the flow and heat transfer performance of such a loop is present-ed. A literature survey of the background theory is undertaken and the theoretical equations describing the single and two-phase flow as well as heat trans-fer behaviour are given. The major assumptions made in deriving these equations are that the work-ing fluid flow is quasi-static and that its single, two-phase flow and heat transfer behaviour may be cap-tured by dividing the working fluid in the loop into a number of one dimensional control volumes and then applying the equations of change to each of these control volumes. Theoretical simulations are conducted for single phase, single and two-phase and heat pipe operating modes, and a sensitivity analysis of the various variables is undertaken. It is seen that the theoretical results capture the single and two-phase flow operating modes well for a loop that includes an expansion tank, but not for the heat pipe operating mode. It is concluded that the theo-retical model may be used to study transient and dynamic non-linear effects for single and two-phase modes of operation. To more accurately predict the heat transfer rate of the loop however, loop specific heat transfer coefficients need to be determined experimentally and incorporated into the theoretical model.

Numerical Simulation on the Organic Fluid Two-Phase Flow and Heat Transfer in the PEMFC Cooling Plate for Waste Heat Recovery

2017 ◽  
Author(s):  
Lili Yu ◽  
Weilin Zhuge ◽  
Yangjun Zhang ◽  
Jie Peng
Keyword(s):  
Heat Transfer ◽  
Fuel Cell ◽  
Heat Recovery ◽  
Waste Heat Recovery ◽  
Two Phase Flow ◽  
Waste Heat ◽  
Working Fluid ◽  
Phase Flow ◽  
Two Phase ◽  
Flow And Heat Transfer

The proton exchange membrane fuel cell (PEMFC) system is becoming one of the most potential power systems for automotive applications in the future. Though the efficiency of PEMFC is high, almost half of the hydrogen energy is taken away by coolant without being utilized. Organic Rankine Cycle (ORC) could be used for the waste heat recovery of PEMFC. The working fluid of ORC flows directly into the fuel cell stack and cool the stack as the same time. In this paper, the feasibility of R245ca as the coolant of PEMFC and working fluid of ORC is studied. A simulation model of the fluid flow and heat transfer of R245ca in PEMFC cooling plates is set up with the CFD software package FLUENT. The Volume of Fluid (VOF) model is used to simulate the two-phase flow. Results show that R245ca can efficiently remove the waste heat and ensure uniform temperature distribution in PEMFC.

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