Influence of wall material on nucleate pool boiling of liquid nitrogen

The wall material thermal conductivity k is one of the surface characteristics that influences the pool boiling heat transfer curve. The growth rate of vapor bubbles and their frequency are mechanisms affected by the thermal conductivity. But the wall material k affects the nucleate boiling curve only in the case of a limited number of nucleation sites. Previous experiments in fact concluded that for a rough surface that has a larger number of vapor generating centers, the wall thermal conductivity does not significantly affect the nucleate pool boiling curve. In this paper, nucleate pool boiling curves of saturated nitrogen under ambient pressure are experimentally obtained on a horizontal flat surface and the effect of three different wall materials (copper, aluminum, stainless steel) is evaluated. The tested surfaces are mechanically polished to avoid any roughness effect. Hysteresis behavior has been observed for the copper and aluminum surfaces, while the results for stainless steel are difficult to assess. The critical heat flux is also analyzed and compared by taking into account the thermal effusivity of the different materials. Finally, experimental results are compared against the most common empirical correlations for nucleate pool boiling heat transfer. (C) 2015 Elsevier Ltd. All rights reserved.