On the importance of upstream compressibility in microchannel boiling heat transfer

Experimental data for flow boiling of water and n-hexane in microchannels of diameters 0.90 and 2.00 mm have been studied for mass fluxes ranging from 60 to 180 kg m−2 s−1, heat fluxes from 20 to 465 kW m−2, operating pressures of 100–200 kPa and exit vapour qualities from 0.0 to 0.8. Two different single-channel test sections having very different thermal time constants (<1 s and 200 s) have been employed. Results have been obtained over a wide range of inlet compressibility provided by a specified volume of gas introduced into a side branch upstream of the test section. Introduction of even minute levels of inlet compressibility led to the establishment of steady oscillations in pressure, mass flow and wall temperature. The frequency of these oscillations is very well predicted by a mass-spring model and it is concluded that the oscillations are a resonant phenomenon that say nothing about the boiling process itself. Inlet compressibility is accompanied by a change in the magnitude and behaviour of the boiling heat transfer coefficient. Most strikingly, for a “hard” inlet (no upstream compressibility) the heat transfer coefficient (h) is found to depend on mass flux but not on wall heat flux whereas for sufficiently “soft” inlet, h depends on heat flux but not mass flux. These results shed new light on the diversity of behaviours reported in the literature for microchannel boiling. Control and specification of the upstream compressibility condition is essential to proper characterisation of conditions.

[1]  M. Kim,et al.  Flow pattern transition instability during flow boiling in a single microchannel , 2007 .

[2]  Yoav Peles,et al.  Pressure effects on flow boiling instabilities in parallel microchannels , 2009 .

[3]  T. Karayiannis,et al.  Examination of heat transfer correlations and a model for flow boiling of R134a in small diameter tubes , 2007 .

[4]  S. Garimella,et al.  Review and Comparative Analysis of Studies on Saturated Flow Boiling in Small Channels , 2008 .

[5]  P. Cheng,et al.  An experimental study of flow boiling instability in a single microchannel , 2008 .

[6]  Albert Mosyak,et al.  Fluid flow in micro-channels , 2005 .

[7]  G. M. Lazarek,et al.  Evaporative heat transfer, pressure drop and critical heat flux in a small vertical tube with R-113 , 1982 .

[8]  Akira Inoue,et al.  極狭間流路における気液二相流の熱流動特性 : 沸騰二相流の摩擦損失, 熱伝達特性および狭間内二相流のモデル化 , 1992 .

[9]  John R. Thome,et al.  A heat transfer model for evaporation of coalescing bubbles in micro-channel flow , 2010 .

[10]  J. Thome,et al.  Mechanisms Of Boiling In Microchannels: Critical Assessment , 2010 .

[11]  R. Shah,et al.  Laminar Flow Forced Convection in Ducts: A Source Book for Compact Heat Exchanger Analytical Data , 2014 .

[12]  Mohammad Faghri,et al.  Heat transfer with laminar pulsating flow in a pipe , 1979 .

[13]  M. Gundogdu,et al.  Present State of Art on Pulsatile Flow Theory : Part 1:Laminar and Transitional Flow Regimes , 1999 .

[14]  M. Cooper.  SATURATION NUCLEATE POOL BOILING - A SIMPLE CORRELATION , 1984 .

[15]  John R. Thome,et al.  State-of-the-Art Overview of Boiling and Two-Phase Flows in Microchannels , 2006 .

[16]  John R. Thome,et al.  Micro-channel flow boiling heat transfer of R-134a, R-236fa, and R-245fa , 2009 .

[17]  M. W. Wambsganss,et al.  Boiling Heat Transfer in a Horizontal Small-Diameter Tube , 1993 .

[18]  John R. Thome,et al.  Heat Transfer Model for Evaporation in Microchannels, Part II: Comparison with the Database , 2004 .

[19]  T. Karayiannis,et al.  Flow boiling and flow regimes in small diameter tubes , 2004 .

[20]  A. E. Bergles,et al.  On the Nature of Critical Heat Flux in Microchannels , 2003 .

[21]  Jürgen Schmidt,et al.  Experimental investigation of transient boiling heat transfer in microchannels , 2007 .

[22]  A. Mosyak,et al.  Periodic boiling in parallel micro-channels at low vapor quality , 2006 .

[23]  S. Kandlikar.  Nucleation characteristics and stability considerations during flow boiling in microchannels , 2006 .

[24]  K. Sefiane,et al.  Hydrodynamics and heat transfer during flow boiling instabilities in a single microchannel , 2009 .

[25]  A. Bontemps,et al.  Vertical flow boiling of refrigerant R134a in small channels , 2005 .

[26]  B. C. Taylor,et al.  Experimental correlations to predict fluid resistance for simple pulsatile laminar flow of incompressible fluids in rigid tubes , 1994 .

[27]  D. Fletcher,et al.  Flow boiling heat transfer of Freon R11 and HCFC123 in narrow passages , 2000 .

[28]  David F. Fletcher,et al.  LOCAL FLOW BOILING HEAT TRANSFER COEFFICIENTS IN NARROW CONDUITS , 2000 .

[29]  Tassos G. Karayiannis,et al.  Confined bubble growth during flow boiling in a mini/micro-channel of rectangular cross-section Part I: Experiments and 1-D modelling , 2011 .

[30]  John R. Thome,et al.  Heat Transfer Model for Evaporation in Microchannels, Part I: Presentation of the Model , 2004 .

[31]  J. Thome,et al.  Mechanisms of Boiling in Micro-Channels: Critical Assessment , 2010 .

[32]  John R. Thome,et al.  Heat Transfer Model for Evaporation of Elongated Bubble Flows in Microchannels , 2002 .

[33]  A. Walton,et al.  Two-phase flow instabilities in a silicon microchannels heat sink , 2009 .

[34]  David F. Fletcher,et al.  Subcooled flow boiling heat transfer in narrow passages , 2003 .