EFFECTS OF LOW UNIFORM RELATIVE ROUGHNESS ON SINGLE-PHASE FRICTION FACTORS IN MICROCHANNELS AND MINICHANNELS

Nikuradse’s [1] work on friction factors focused on the turbulent flow regime in addition to being performed in large diameter pipes. Laminar data was collected by Nikuradse, however only low relative roughness values were examined. A recent review by Kandlikar [2] showed that the uncertainties in the laminar region of Nikuradse’s experiments were very high, and his conclusion regarding no roughness effects in the laminar region is open to question. In order to conclusively resolve this discrepancy, we have experimentally determined the effects of relative roughness ranging from 0-5.18% in micro and minichannels on friction factor and critical Reynolds numbers. Reynolds numbers were varied from 30 to 7000 and hydraulic diameters ranged from 198µm to 1084µm. There is indeed a roughness effect seen in the laminar region, contrary to what is reported by Nikuradse. The resulting friction factors are well predicted using a set of constricted flow parameters. In addition to higher friction factors, transition to turbulence was observed at decreasing Reynolds numbers as relative roughness increased. NOMENCLATURE � Aspect ratio

[1]  Zhi-Xin Li,et al.  EXPERIMENTAL STUDY ON FLOW CHARACTERISTICS OF LIQUID IN CIRCULAR MICROTUBES , 2003 .

[2]  W. Little,et al.  Measurement of the heat transfer characteristics of gas flow in fine channel heat exchangers used for microminiature refrigerators , 1984 .

[3]  Satish G. Kandlikar,et al.  Roughness effects at microscale - reassessing Nikuradse's experiments on liquid flow in rough tubes , 2005 .

[4]  Roland Baviere,et al.  An Experimental Study of Water Flow in Smooth and Rough Rectangular Micro-Channels , 2004 .

[5]  Gian Piero Celata,et al.  Water Single-Phase Fluid Flow and Heat Transfer in Capillary Tubes , 2003 .

[6]  G. Mala,et al.  Pressure-driven water flows in trapezoidal silicon microchannels , 2000 .

[7]  Gian Piero Celata,et al.  EXPERIMENTAL INVESTIGATION OF HYDRAULIC AND SINGLE-PHASE HEAT TRANSFER IN 0.130-MM CAPILLARY TUBE , 2002, Proceeding of Heat Transfer and Transport Phenomena in Microscale.

[8]  Dongqing Li,et al.  Flow characteristics of water in microtubes , 1999 .

[9]  Satish G. Kandlikar,et al.  ESTIMATING ROUGHNESS PARAMETERS RESULTING FROM VARIOUS MACHINING TECHNIQUES FOR FLUID FLOW APPLICATIONS , 2007 .

[10]  S. Kandlikar,et al.  Characterization of the effect of surface roughness and texture on fluid flow—past, present, and future , 2006 .

[11]  C F Colebrook,et al.  TURBULENT FLOW IN PIPES, WITH PARTICULAR REFERENCE TO THE TRANSITION REGION BETWEEN THE SMOOTH AND ROUGH PIPE LAWS. , 1939 .

[12]  X. Peng,et al.  FRICTIONAL FLOW CHARACTERISTICS OF WATER FLOWING THROUGH RECTANGULAR MICROCHANNELS , 1994 .

[13]  Jl L. Xu,et al.  Flow and heat transfer in microchannels with rough wall surface , 2006 .

[14]  Satish G. Kandlikar,et al.  Effect of Triangular Roughness Elements on Pressure Drop and Laminar-Turbulent Transition in Microchannels and Minichannels , 2006 .

[15]  Huiying Wu,et al.  An experimental study of convective heat transfer in silicon microchannels with different surface conditions , 2003 .

[16]  J. Welty,et al.  Pressure Drop Measurements in a Microchannel , 1998, Micro-Electro-Mechanical Systems (MEMS).

[17]  R. Shah,et al.  Handbook of single-phase convective heat transfer , 1987 .

[18]  W. Little,et al.  Measurement of friction factors for the flow of gases in very fine channels used for microminiature Joule-Thomson refrigerators , 1983 .

[19]  Gian Piero Celata,et al.  Hydrodynamic Behaviour and Influence of Channel Wall Roughness and Hydrophobicity in Microchannels , 2004 .

[20]  S. Kandlikar,et al.  Characterization of surface roughness effects on pressure drop in single-phase flow in minichannels , 2005 .

[21]  S. Kandlikar,et al.  Effect of Surface Roughness on Heat Transfer and Fluid Flow Characteristics at Low Reynolds Numbers in Small Diameter Tubes , 2003 .