Study of Heat Transfer Enhancement in Microchannels using
Computational Fluid Dynamics (CFD) Models

Abstract

Microchannel heat transfer operations involve reaction chamber whose sizes are typically in the range of
micrometers (μm) with volumetric capacity in the range of micro liters (μL).While electronics now provide the
„brains‟ to the electrical world, microchannel devices act as „sensors and actuators‟ to the outside world
providing the same benefits as the microchips provide to the electronics. Their high surface to volume ratio,
highly efficient heat and mass transfer characteristics and greatly improved fluid mixing allow precision control
of reaction with enhanced conversions, selectivity and yields of desired products, easily repairable tendency
have resulted in their increasing demand and they are the key components in automobile airbags, ink-jet
printers, projection display systems, aircrafts etc. They can even perform reactions on a very small scale to
determine the potential for dangerous situations. Reverse-flow action is used to utilize the thermal energy inside
a reactor.

The present study emphasizes on the enhancement of heat transfer in microchannnels by using vortex
promoters. The effects on thermal and hydrodynamic behaviour produced by vortex promoters of various
shapes in a 2D, laminar flow in a microchannel are studied.The liquid is assumed to be a Newtonian fluid
(water) and a Non-Newtonian fluid (Banana puree/CMC solution) .It is desired to obtain a suitable design
criteria of microcooling systems, which should be both thermally efficient and not expensive in terms of the
pumping power. Three reference cross sections, namely circular, rectangular, triangular are considered. The
effect of the blockage ratio, the Reynolds number, and the relative position and orientation of the obstacle are
also studied. The plots of Surface Nusselt Number vs Length of rectangular channel are studied to find the most
heat efficient design. In addition to this, a microchannel with no obstacle is taken and the effect on heat transfer
by reducing the height of the channel is also studied. Some design guidelines based on the above plots ,which
could be used in an engineering environment are provided. The geometry of the problem and meshing of the
problem have been made in ANSYS Workbench.The models have been solved by ANSYS Fluent 13.0 solver.