Free expansion study of liquid nitrogen

Abstract

The phenomenas involved in the free expansion of liquid/superc ritical hydrogen are of great importance in many space applications. In this study, liquid nitrogen was substituted for hydrogen due to practical reasons. An experimental setup was designed to study the free expansion process when liquid/supercritical nitrogen is injected into an evacuated chamber. The effects of nozzle size, upstream pressure, and downstream pressure were studied. During the experiment, three different nozzle sizes were tested. When the pressure inside the expansion chamber was below the triple point, the nitrogen injected into the chamber solidified in two different forms. For the smallest nozzle, the solid formation occurred inside the nozzle, whereas, for the larger nozzles, the fluid solidified after being sprayed into the expansion chamber. No solidification was observed at chamber pressures higher than the triple point pressure. It was also found that supercritical nitrogen acts like a liquid in the free expansion process. Nomenclature Cd = coefficient of discharge d = nozzle orifice diameter g = gravitational acceleration L = length m = mass flow rate mN2 = mass of liquid nitrogen P = pressure Pc = critical pressure R = gas constant of nitrogen T = temperature t = time U = internal energy V = volume of the expansion chamber p = density