Evaporative Heat Transfer From Ten-Micron Micro-Channels

2005 ◽  
Author(s):  
T. A. Quy ◽  
D. A. Carpenter ◽  
C. D. Richards ◽  
D. F. Bahr ◽  
R. F. Richards
Keyword(s):  
Heat Transfer ◽  
Electrical Power ◽  
Ccd Camera ◽  
Working Fluid ◽  
Sensible Heat ◽  
Silicon Membrane ◽  
Long Distance ◽  
Liquid Front ◽  
Micro Channels ◽  
Evaporative Heat Transfer

Evaporative heat transfer from ten-micron square open-top micro-channels is investigated experimentally. The channels are fabricated by spinning ten microns of SU-8 on a two micron thick silicon membrane and using a photolithography process to create micro channels in radial and annular patterns. The working fluid, FC77, is pumped by capillary forces into the channels from a reservoir at the edge of the silicon membrane. Electrical power is dissipated in a thin-film heater in the center of the membrane. The liquid front of working fluid in the channels is visualized with a long-distance microscope and CCD camera. Sensible heat conducted radially out of the membrane is measured with two concentric annular PRT’s. The mass of working fluid evaporated from the micro-channels is determined gravimetrically. A global energy balance including latent and sensible heat transfer out of the system is then tabulated. The study shows that only five to ten percent of the power going into the membrane is carried away by evaporation while the remaining ninety to ninety-five percent of the power is conducted out along the membrane.

Experimental and Numerical Study of Evaporative Heat Transfer From Ten- Micro Microchannels

2006 ◽  
Author(s):  
Hoki Lee ◽  
T. A. Quy ◽  
C. D. Richards ◽  
D. F. Bahr ◽  
R. F. Richards
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Latent Heat ◽  
Numerical Study ◽  
Electrical Power ◽  
Three Dimensional ◽  
Working Fluid ◽  
Silicon Membrane ◽  
Transfer Rates ◽  
Evaporative Heat Transfer

Experimental and numerical results are presented for evaporative heat transfer from ten-micron square open-top channels. The radial channels are fabricated in epoxy photoresist on a two micron thick silicon membrane. The working fluid is pumped by capillary forces from a reservoir at the edge of the silicon membrane into the channels where it evaporates. The electrical power dissipated in a thin-film heater in the center of the membrane, the conduction heat transfer rate radially out of the membrane, and the rate of evaporation of the working fluid are measured. A three-dimensional finite difference, time-domain integration is used to predict sensible and latent heat transfer rates. Only 5-10% of the energy dissipated as heat in the thin film heater is carried away as latent heat by the evaporating working fluid. Computed temperatures and heat transfer rates are shown to match the experimental results.

Simulation on the Flow and Heat Transfer Characteristics of Confined Bubbles in Micro-Channels

2012 ◽  
Author(s):  
Qingming Liu ◽  
Björn Palm ◽  
Henryk Anglart
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Phase Interface ◽  
Working Fluid ◽  
Initial Shape ◽  
Thin Film Evaporation ◽  
Flow And Heat Transfer ◽  
Vof Model ◽  
Micro Channels

3D simulations on confined bubbles in micro-channels with diameter of 1.24 mm were conducted. The working fluid is R134a with a mass flux range from 125kg/m2s to 375kg/m2s. The VOF model is chosen to capture the 2 phase interface while the geo-construction method was used to re-construct the 2-phase interface. A heated boundary wall with heat flux varying from 15kW/m2 to 102kW/m2 is supplied. The wall temperature was calculated. The effects of mass flux and heat flux are studied. The shape of the bubble was predicted by the simulation successfully and the results show that they are independent of the initial shape. Both thin film evaporation and micro convection enhance the heat transfer. However, the micro convection which is caused by bubble motion has greater contribution to the total heat transfer at the stage of bubble growth studied.

Effects of Dented Roughness on Laminar Flow and Heat Transfer in Microchannels

2010 ◽  
Author(s):  
Hui Miao ◽  
Yong Huang ◽  
Fa Xie ◽  
Haigang Chen ◽  
Fang Wang
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Working Fluid ◽  
Heat Transfer Characteristics ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Micro Channels ◽  
Planar Area ◽  
Poiseuille Number ◽  
Energy Equations

Liquid laminar flow and heat transfer characteristics for parallel plate micro-channels consisting of many triangle shape hollows to fit with the etching surfaces are investigated numerically in the present paper. The height of the channel is 50μm, with three different relative depths, three relative spacing, and three oblique angles of the triangle surface, respectively. The 2D N-S and energy equations are solved using a commercial CFD code FLUENT6.3. Water is used as the working fluid, and the Reynolds number ranges from 100 to 1500. The global Poiseuille number and average Nusselt number are obtained. It is shown that the dented shapes cause a modest influence in Poiseuille number, but a greater impact on the Nusselt numbers. In addition, both of Po and Nu increase modestly with Re. The local Nusselt numbers are always lower in dented area and larger in planar area of dented roughness microchannels, than that of conventional smooth value. Finally, geometry parameters have modest impact on heat transfer for dented roughness.

An Experimental Study of Two Phase Flow in Impinging Micro Channels

2013 ◽  
Author(s):  
Liang-Han Chien ◽  
Han-Yang Liu ◽  
Wun-Rong Liao
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Rate ◽  
Heat Sink ◽  
Heat Transfer Performance ◽  
Experimental Result ◽  
Working Fluid ◽  
Transfer Performance ◽  
Two Phase ◽  
Micro Channels

A heat sink integrating micro-channels with multiple jets was designed to achieve better heat transfer performance for chip cooling. Dielectric fluid FC-72 was the working fluid. The heat sink contained 11 micro-channels, and each channel was 0.8 mm high, 0.6 mm wide, and 12 mm in length. There were 3 or 5 pores on each micro-channel. The pore diameters were either 0.24 or 0.4 mm, and the pore spacing ranged from 1.5 to 3 mm. In the tests, the saturation temperature of cooling device was set at 30 and 50°C, and the volume flow rate ranged from 9.1 to 73.6 ml/min per channel (total flow rate = 100∼810 ml/min). The experimental result showed that heat transfer performance increased with increasing flow rate for single phase heat transfer. For heat flux between 20 and 100 kW/m2, the wall superheat decreases with increasing flow rate at a fixed heat flux. However, the influence of the flow rate diminished when the channels are in two phase heat transfer regime. Except for the lowest flow rate (9.1 ml/min), the heat transfer performance increased with increasing jet diameter/spacing ratios. The best surface had three nozzles of 0.4 mm diameter in 3.0 mm jet spacing. It had the lowest thermal resistance of 0.0611 K / W in the range of 200 ∼ 240 W heat input.

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.

Experimental and Numerical Study of Evaporating Flow Heat Transfer in Micro-Channel

2007 ◽  
Author(s):  
HoKi Lee ◽  
C. D. Richards ◽  
R. F. Richards
Keyword(s):  
Heat Transfer ◽  
Latent Heat ◽  
Numerical Study ◽  
Three Dimensional ◽  
Contact Angles ◽  
Numerical Results ◽  
Working Fluid ◽  
Micro Channels ◽  
Flow Heat ◽  
Domain Integration

Experimental and numerical results are presented for steady evaporating flow heat transfer from open top square micro-channels. Radial channels, 40 microns high, and 35, 50 and 70 microns wide with 5 micron wide SU-8 walls are considered. The channels are filled with Fluorinert FC77 working fluid pumped by capillary forces from a reservoir at the outer circumference of the radial channels. An energy balance on the radial channels including heat into the channels, conduction heat transfer radially along the channels and latent heat transfer via evaporation of the working fluid from the channels is experimentally determined. Microphotography is used to visualize the working fluid and the meniscus contact angles in the channels. A three-dimensional finite difference time-domain integration is used to predict sensible heat transfer rates and latent heat transfer/ evaporation rates. Experimental measurements are compared to the numerical results to extract estimates of the liquid thickness in the channels.

Effect of nano-fluid types on the improvement of heat transfer in a micro-channel with regular hexagonal pattern

2020 ◽  
Vol 234 (6) ◽  
pp. 657-664
Author(s):  
S Emami ◽  
MH Dibaei Bonab ◽  
M Mohammadiun ◽  
H Mohammadiun ◽  
M Sadi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Cross Section ◽  
Transfer Rate ◽  
Nano Particles ◽  
Working Fluid ◽  
Micro Channel ◽  
Hexagonal Cross Section ◽  
Micro Channels ◽  
Nano Fluids

Micro channels are widely used in different industries. The investgations on heat transfer improvments of these instruments are of significant inportance. At hte present study, the influence of different nano-fluids and geometrical charectrestics on the thermal performance of a heat sink which is especially for for micro-channels are investigated. In the present study, the authors investigated the Nusselt number and pressure drop in differential geometries and Reynolds numbers (Re). Then the micro-channel was investigated with different heat flux (q).In the first step, the micro-channel was examined and the final numerical results showed that the hexagonal cross-section can improve heat transfer about 9%. At the second step and after selecting appropriate parameters, the effect of three nano-particles (Al2O3 - CuO- TiO2) were studied. The results presented that aluminum oxide (Al2O3) has the best heat transfer rate among the mentioned nano-fluids. With the presence of nano-particles (Al2O3, φ = 4%) an increment of 40% in heat transfer rate, for the hexagonal cross section was achieved compare to rectangular cross section with water as working fluid.

Influence of Thermo-Physical Properties on the Flow and Heat Transfer in Rectangular Micro-Channels

2011 ◽  
Vol 347-353 ◽  
pp. 2640-2644 ◽  
Author(s):  
Xue Tao Duan ◽  
Bin Xu ◽  
Hao Luo
Keyword(s):  
Heat Transfer ◽  
Physical Properties ◽  
Flow Direction ◽  
Three Dimensional ◽  
Working Fluid ◽  
Fluid Temperature ◽  
Flux Boundary Condition ◽  
Flow And Heat Transfer ◽  
Friction Factors ◽  
Micro Channels

This paper investigated the behaviors of flow and heat transfer of single-phase in rectangular micro-channels with three-dimensional numerical analysis. The single micro-channel is 200μm deep, 50μm wide. Deionized water was used as the working fluid. The fluid physical properties varying with temperature and Re number were studied. Comparisons were made among the results obtained from experiments, numerical simulations, and from those in the literature. The results indicated that the friction factors decreasing along the flow direction were ascribed to the fluid temperature rising under the unified heat flux boundary condition. It was found that influence of viscosity variation with temperature and viscous dissipation effect could be too significant to be neglected.

Numerical simulation of forced convection in a bi-disperse porous medium channel by creating new porous micro-channels inside the porous macro-blocks

2019 ◽  
Vol 29 (11) ◽  
pp. 4142-4166 ◽  
Author(s):  
Behnam Rajabzadeh ◽  
Mohammad Hojaji ◽  
Arash Karimipour
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Pressure Drop ◽  
System Performance ◽  
Stokes Equations ◽  
Simple Algorithm ◽  
Numerical Code ◽  
Working Fluid ◽  
Content Type ◽  
Micro Channels

Purpose Porous medium has always been introduced as an environment for increasing heat transfer in cooling systems. However, increase in heat transfer and resolving pressure drop in the fluid flow have been focused on by researchers.The purpose of this paper is to study the effects of creating porous micro-channels inside porous macro-blocks to optimize system performance in channels. Design/methodology/approach To simulate flow field, a developed numerical code that solves Navier–Stokes equations by finite volume method and semi-implicit method for pressure linked equations (SIMPLE) algorithm will be used together with bi-disperse porous medium (BDPM) method. Working fluid is air with Pr = 0.7 in laminar state. Influence of permeability changes by creation of micro-channels containing porous medium in vertical, horizontal and cross-shape patterns will be investigated. Findings By creating porous micro-channels inside macro-blocks, not only does the heat transfer increase significantly but the pressure also drops remarkably. Increase in performance evaluation criteria (PEC) is more evident in lower Reynolds numbers that can increase the PEC to 75 per cent by creating cross-shape micro-channels. By changing the permeability of micro-channels, PEC will increase by reducing the pressure drop but it has minor changes in Nu. Research limitations/implications The current work is applicable to optimizing system performance by decreasing the pressure drop and increasing the heat transfer. Practical implications The developed patterns are useful in increasing the system performance including the increase in heat transfer and decrease in pressure drop in systems such as air coolers required in electrical circuits. Originality/value Development and optimization of system performance by new patterns using BDPM in comparison to the previous patterns.

Mass and Heat Transfer Characteristics of a Single-High Aspect Ratio Microchannel Absorber

2012 ◽  
Author(s):  
Yunshan Liu ◽  
Ebrahim Al Hajri
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Flow Rate ◽  
Working Fluid ◽  
Transfer Performance ◽  
Micro Channel ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Micro Channels ◽  
Mass And Heat Transfer

Recently, study on a microscale-based absorption refrigeration system has sprung up motivated by the need of efficient energy utilization. Heat-driven absorption systems offer a possibility of generating both power and cooling with environment friendly refrigerants, such as ammonia/water and LiBr/water. However, these systems are often large in size and low in COP especially in single stage absorption systems. These characteristics of absorptions systems make them unattractive in most cases. This work introduces the utilization of micro-channel enhanced surfaces as heat exchangers to enhance the component and system performance, to reduce the system size and to reduce the cost of the system as well. In this work, a new concept of enhancing heat and mass transfer processes is applied in the absorber part of the absorption cycle by using a single micro-channel. Due to its merit of high area to volume ratio, microchannel technology has been well theoretically validated to be a very effective and potential choice for enhancing heat transfer performance. But there is a lack of research work on the mass transfer performance in micro-channels. This work investigated simultaneous mass and heat transfer characteristics of a novel microchannel absorber that uses LiBr/water as the working fluid. A microchannel with hydraulic diameter of 0.7mm is employed in this characterization study. Velocity distribution, pressure drop, concentration and temperature profile inside the microchannel as well as effects of the inlet absorbent concentration, flow rate and temperature together with the refrigerant flow rate on the heat/mass transfer are predicted. Investigations on the optimum inlet angle design of a single channel absorber are also presented in the end of this work. Feasibility of this novel absorber design was proved via this numerical simulation as the mass transfer taking place inside the mixing channel was observed to achieve the identical performance but with a size reduction by 1/27 compared to a conventional falling film absorber. A 7 times enhancement of the heat transfer coefficient was also achieved with the comparison of a macro-scale based absorber configuration.

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