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.

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.

Three-Dimensional Modelling of Heat Transfer in Micro-Channels With Synthetic Jet

2010 ◽  
Author(s):  
Ann Lee ◽  
Victoria Timchenko ◽  
Guan H. Yeoh ◽  
John A. Reizes
Keyword(s):  
Heat Transfer ◽  
Silicon Substrate ◽  
Three Dimensional ◽  
Synthetic Jet ◽  
Numerical Results ◽  
Maximum Temperature ◽  
Complex Conjugate ◽  
Two Dimensional ◽  
Flow And Heat Transfer ◽  
Micro Channels

An in-house computer code is developed and applied to investigate the effect of a synthetic jet on heat transfer rates in forced convection of water in silicon micro-channels etched in the rear side of the silicon substrate. To account for the deflection of the membrane located at the bottom of the actuator cavity, a moving mesh technique to solve the flow and heat transfer is purposefully adopted. The governing equations are transformed into the curvilinear coordinate system in which the grid velocities evaluated are then fed into the computation of the flow in the cavity domain thus allowing the conservation equations of mass, momentum and energy to be solved within the stationary computational domain. The fully three-dimensional model considers the SIMPLE method to link the pressure and velocity. A heat flux of 1 MW/m2 is applied at the surface of the top of the silicon wafer and the resulting complex, conjugate heat transfer through the silicon substrate is included. The hydrodynamics feature of the flow is validated against existing experimental results and verified against numerical results from commercial package ANSYS CFX 11.0. Good agreement has been achieved. To track the development of the flow and heat transfer when the actuator is switched on, numerical results of 20 full cycles of the actuator are simulated. When the actuator is switched on, noticeable temperature drop is observed at all points in the substrate from those which existed when there has been a steady water flow in the channel. At the end of 20th cycle of actuation, the maximum temperature in the wafer has reduced by 5.4 K in comparison with the steady flow values. In comparison with the two-dimensional study which account for 17K reduction, it indicates that synthetic jet has only smaller beneficial cooling and has been over-estimated in the previous two-dimensional study.

Numerical Study of Nozzle Design on Cadmium Quenching Process in Thermochemical Splitting of Water

2009 ◽  
Author(s):  
Jianhu Nie ◽  
Yitung Chen ◽  
Bunsen Wong ◽  
Lloyd C. Brown
Keyword(s):  
Heat Transfer ◽  
Hydrogen Production ◽  
Gas Flow ◽  
Numerical Study ◽  
Three Dimensional ◽  
Maximum Velocity ◽  
Numerical Results ◽  
Nozzle Design ◽  
Flow And Heat Transfer ◽  
Quenching Process

Three-dimensional liquid-gas flow with condensation during cadmium quenching process for hydrogen production was numerically simulated in order to effectively guide the design of solar decomposer and vapor quencher. The mixture model was selected for modeling the multiphase flow, and the two-equation RNG k-ε model was used to model the turbulent flow and heat transfer. Numerical results including velocity, temperature, pressure, and mole fraction distributions were obtained for different nozzle designs. Numerical results showed that flow is relatively low in the decomposer and close to the bottom and the top inlets. The maximum velocity develops in the region near the entrance of the quenching nozzle as the nozzle angle is small. As the nozzle angle is large, the maximum velocity appears in the exit tube. Temperature, pressure and cadmium vapor distributions are also directly affected by the nozzle angle.

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.

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.

Numerical Study on the Effect of Inner Tube Position on Heat Transfer Process in Self-Recuperative Radiant Tube

2011 ◽  
Vol 228-229 ◽  
pp. 676-680 ◽  
Author(s):  
Ye Tian ◽  
Xun Liang Liu ◽  
Zhi Wen
Keyword(s):  
Heat Transfer ◽  
Transfer Process ◽  
Numerical Study ◽  
Flame Temperature ◽  
Three Dimensional ◽  
Mathematic Model ◽  
Heat Transfer Process ◽  
Bulk Temperature ◽  
Radiant Tube ◽  
Peak Value

A three-dimensional mathematic model is developed for a 100kw single-end recuperative radiant tube and the simulation is performed with the CFD software FLUENT. Also it is used to investigate the effect of distance between combustion chamber exit and inner tube on heat transfer process. The results suggest that the peak value of combustion flame temperature drops along with the increasing of distance, which leads to low NOX discharging. Also radiant tube surface bulk temperature decreases, which causes radiant tube heating performance losses.

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