An Experimental Investigation of Pressure Drop in Expanding Microchannel Arrays

Abstract

The pressure effects of expanding the cross section of microchannels along the direction of flow are investigated across four rates of channel expansion in the flow boiling of R-134a. Prior investigation by the authors detailed the fabrication of four copper microchannel arrays and the pumped-loop apparatus developed to facilitate interchange of the microchannel specimens, allowing consistency across experiments. Significant beneficial pressure effects are observed to result from the expansion, including reduction by half of the pumping cost per flow rate at critical heat flux. The improvements are seen with small expansions, and greater expansion yields diminishing returns. The high pressure drops associated with microchannel evaporators are effectively reduced by expanding channel geometry, and the low-frequency system spectral response indicates that expanding channel arrays typically carry less energy in oscillations up to 2.5 Hz, suggesting amelioration of oscillatory instabilities. Results are discussed in light of a comparative force analysis, with the balance of these forces linked to the observed behavior of the pressure drop and heat flux relationship.

Force analysis and bubble dynamics during flow boiling in silicon nanowire microchannels

“…A number of research efforts on flow boiling in microchannels were focused on understanding the underlying mechanisms [20,[42][43][44][45][46][47]. Recently, Kandlikar [48] provides excellent discussion on the effects of different forces acting on liquid-vapor interface and settles on the inertia, surface tension, shear, buoyancy, and evaporation momentum forces as the candidates for significance.…”

Effect of taper on pressure recovery during flow boiling in open microchannels with manifold using homogeneous flow model

“…Providing a variable (increasing) flow cross-sectional area along the flow length, a concept introduced by Mukherjee and Kandlikar [10,11], has garnered a lot of attention. Diverging channels [12,13], stepped microchannels [14,15] and expanding microchannels [16] have all been investigated with promising results. Kandlikar et al [17] presented an open microchannel manifold concept which provided high heat dissipation of over 500 W/cm 2 (5 MW/m 2 ).…”

Transient force analysis and bubble dynamics during flow boiling in silicon nanowire microchannels

“…A number of research efforts on flow boiling in microchannels were focused on understanding the underlying mechanisms [4][5][6][7][8][9][10][11][12][13]. Zhang et al [4] investigated the bubble nucleation, flow patterns, heat transfer and pressure performances in silicon microchannels by varying surface roughness.…”

“…He concluded that surface tension and evaporation momentum forces played a dominant role at microscale. Miner et al [12] experimentally investigated the pressure drop in an expanding microchannels array. They discussed the results in light of a comparative force analysis and linked the observed behaviors of the pressure drop and heat flux relationship with the balance of these forces.…”