Numerical study of the effect of inlet constriction on bubble growth during flow boiling in microchannels
Abstract
Flow boiling through microchannels is characterized by
nucleation of vapor bubbles on the channel walls and their
rapid growth as they fill the entire channel cross-section. In
parallel microchannels connected through a common header,
formation of vapor bubbles often results in flow maldistribution
that leads to reversed flow in certain channels. The
reversed flow is detrimental to the heat transfer and leads to
early CHF condition. One way of eliminating the reversed flow
is to incorporate flow restrictions at the channel inlet. In the
present numerical study, a nucleating vapor bubble placed near
the restricted end of a microchannel is numerically simulated.
The complete Navier-Stokes equations along with continuity
and energy equations are solved using the SIMPLER method.
The liquid-vapor interface is captured using the level set
technique. The results show that with no restriction the bubble
moves towards the nearest channel outlet, whereas in the
presence of a restriction, the bubble moves towards the distant
but unrestricted end. It is proposed that channels with
increasing cross-sectional area may be used to promote
unidirectional growth of the vapor plugs and prevent reversed
flow.
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