Flow Patterns During Convective Boiling in Microchannels
T. Harirchian and Dr. S. V. Garimella
NSF Cooling Technologies Research Center
School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907-2088

        To develop flow regime maps for convective boiling in microchannels and to propose flow pattern-based models to predict the corresponding heat transfer coefficients, a thorough understanding of the existing flow patterns and their transitions is necessary.  In the present study, high-speed photography is employed to observe the flow patterns in flow boiling of a dielectric liquid, FC-77, in parallel silicon microchannels of depth ranging from 100 to 400 μm and widths ranging from 100 to 5850 μm.  In each test, liquid mass flux (G) is constant and inlet subcooling is fixed at 5C, while the heat flux to the bottom of the heat sink is increased form zero to a value near the critical heat flux.  Temperature and pressure are measured at several locations.  A high-speed digital video camera is used to observe boiling patterns at frame rates ranging from 2000 to 24000 frames per second (fps).  The videos presented show a top view of the horizontal microchannels, at a location along the heat sink centerline and near the flow exit.

         To view flow patterns in a microchannel heat sink, select values of mass flux and heat flux for the corresponding microchannels from the drop-down menus in the table below and hit the view button; the visualization movie will play in a window at the bottom of the page.

          Reference: Harirchian, T. and Garimella, S. V., 2009. Effects of Channel Dimension, Heat Flux, and Mass Flux on Flow Boiling Regimes in Microchannels. International Journal of Multiphase Flow 35, 349-362.

 
 

  Schematic illustration of the microchannel heat sink

(not drawn to scale)

       

Photograph of the microchannel heat sink mounted on a printed circuit board, with integrated heaters and temperature sensors in the microchannel test piece.

 

Nominal Channel Width
w (m)
Nominal Channel Depth
d (m)
Nominal Fin Width

wf (m)
# of Channels

N
Hydraulic Diameter

Dh (m)
Aspect Ratio

w/d

Cross-Sectional Area
(mm2)
Mass Flux


G (kg/m2s)
Heat Flux/ Flow Regime


q"w (kW/m2)
 
100 220 100 63 134 0.45 0.021
100 400 100 60 159 0.27 0.037
250 400 100 35 291 0.64 0.089
 
400 100 100 25 111 6.12 0.026
 
400 220 100 25 264 2.03 0.079
 
400 400 100 24 379 1.08 0.144
 
1000 220 200 10 370 4.53 0.231
 
1000 400 200 10 541 2.62 0.366
 
2200 400 300 5 634 5.95 0.815
 
5850 400 300 2 707 15.55 2.201