Numerical simulation of evaporation phenomena and heat transfer of liquid Hydrocarbon in a microtube

Evaporation and heat transfer is the key process that affects the performance of the portable liquid fuel system. The flow boiling of liquid n-heptane is studied numerically in a 0.2 mm microtube under non-uniform boundary conditions. At low fuel flow rate (5 μl/min) and low thermal gradient, the average value of heat transfer coefficient was 4000 W/m²-K, mean evaporation efficiency was 0.80, and low pressure drop oscillations of magnitude 600 Pa were observed. In addition, the flow pattern was stable with a dynamic liquid-vapor interface. At high flow rate (70 μl/min), the average value of heat transfer coefficient and pressure drop oscillations magnitude increases to 16000 W/m²-K and 2500 Pa respectively, whereas mean evaporation efficiency decreases to 0.65. The diameter and intensity of the nucleate bubble and the liquid droplets depends on flow rate and thermal gradients. At low fuel flow rate, high frequency low magnitude pressure drop fluctuation was obtained while at high low frequency high magnitude pressure drop fluctuation was obtained. Numerical calculations are also performed under several wall temperature profiles of the same temperature gradients that have shown smaller effect on evaporation efficiency.