Experimental Investigation of LN2 Pool Boiling Critical Heat Flux (CHF) and Development of New Correlation for All Cryogens, Accounting for Effects of Surface Material and Size, Pressure, Subcooling, and Surface Orientation

As the aerospace community prepares to establish humanity's permanence on the Moon and Mars, Cryogenic Fluid Management (CFM) technologies have proven themselves paramount to the established architecture of interplanetary travel. It will therefore be necessary to understand the two-phase physics inherent to cryogenic fluids. This study includes experimental investigation into saturated pool boiling critical heat flux (CHF) for liquid nitrogen (LN2). The obtained data aid in understanding effects of two important parameters which are underrepresented in the historical database: heated surface thermophysical properties and heated surface size. With a diameter of over 100 mm, the heated surfaces tested in this study are significantly larger than those adopted in prior studies and representative of 'infinitely' large surfaces for which theoretical CHF models have been constructed. This study also includes data for three surface materials: copper, aluminum, and stainless steel, and pressures ranging from 101 to 448 kPa. By comparing the present data with those from the historical database, it is shown that CHF increases with increases in both surface size and thermal conductivity but reaches an asymptotic level for large surfaces that is independent of both parameters. Using both the current LN2 and those of all cryogens from the historical database, a new correlation is developed which shows a MAE of 18.03% against 1181 datapoints across different cryogens, different heated surface materials and sizes, pressures, subcoolings, and surface orientations.