Experimental study on hydrodynamic characteristics of cyclohexane at trans- and supercritical pressures

Abstract

As an effective cooling method, the regenerative cooling technology using hydrocarbon fuel as coolant has been studied extensively in aircraft and space vehicles. Static flow instability, which is caused by multi-valued of hydrodynamic characteristics, often occurs under certain conditions affecting on the convection heat transfer process. The hydrodynamic characteristics of hydrocarbons naturally is attracted more attention on the regenerative cooling technology. In this paper, an experimental study on hydrodynamic characteristics of cyclohexane has been conducted at pressures ranging from 2.5 to 5.5 MPa, inlet temperature from 30.0 to 100.0°C and heat flux from 95 to 205 kW/m2. Some hydrodynamic characteristics curves are obtained in a horizontal stainless steel tube with 2.0 mm hydraulic diameter. In these experiments, the multi-valued characteristics of hydrodynamic characteristics curves existed for hydrocarbons were well-proved at trans- and supercritical pressures. Onset of the negative slope area of hydrodynamic characteristics was found when the fluid outlet temperature became slightly lower than its respective pseudo-critical temperature. And, the multi-valued tendency of test fluid was weakened with the increase of pressure and inlet temperature, however enhanced as the heat flux increased. Based on the experimental data, a formula for determining the onset of flow instability for cyclohexane was finally summed for the supercritical fluid.