An experiment was performed to study the heat transfer characteristics of liquid flow through two multi-port extruded (MPE) micro-tubes with water

ethanol

acetone and ethanol/water mixtures. The cross-section geometries of two tubes were rectangular (approximate square) and circular

and with hydraulic diameters of 0.72 and 0.86 mm respectively. The results showed that at Reynolds number (Re) below 500

Nusselt number (Nu) decreased with increasing heat flux but Nu approached a minimum for increasing heat flux at Re > 500. Experimental results showed that such change was caused by the effect of entrance function and conjugate heat transfer. The experimental Nu of the circular multi-tube was higher than that of rectangular multi-tube. For ethanol

pressure drop decreased dramatically with increasing thermal resistance beginning at a low thermal resistance. Additionally

the higher the inlet temperature

the smaller the slope of pressure drop decrease against thermal resistanc. Further investigations of water

ethanol and acetone were conducted. Nu of ethanol were highest and those of water were the lowest among three solutions with the same heat flux and inlet temperature. Experiments of rectangular multi-tube

with different mixing ratios of ethanol/water showed that the trend of Nu against Re remained unchanged at low ethanol concentration. Furthermore

the higher the ethanol concentration

the faster the growth rate of Nu against Re and the greater the Nu difference between adjacent concentrations. Theoretical reasons for this remains to be further studied.