An experiment has been built and operated to investigate the pressure difference and the temperature variation through orifice plates in He II forced flow at bath temperatures between 1.7 K and 2.1 K. The flow of He II is generated with a bellows pump through a 1 m long, 73 mm inner diameter experimental channel containing the orifice plates: the ratios of orifice diameter to tube diameter are 10 % and 20 %. The mass flow rate is between 39 g/s and 186 g/s, corresponding Reynolds numbers between 3.0 × 106 and 1.2 × 107. The Reynolds numbers consist of the velocity at the orifice and the viscosity of normal fluid in He II. The experimental channel is instrumented with eight thermometers and two differential pressure transducers.
Pressure drops for adiabatic forced flow He II have been measured through the orifice plates and compared with correlations for classical fluids at high Reynolds number. No temperature dependence to the pressure drop has been observed within the bath temperature range for different orifice sizes. The measured discharge coefficient for the orifice size 10% looks to be larger than the corresponding value for classical fluids although it agrees reasonably well with previous results on a similar geometry in classical fluids. The measured discharge coefficient for the orifice size 20% is close to but slightly below the corresponding value for classical fluids. These results can be explained due to the similarity between the He II forced flow and the classical fluid flow. At the large mass flow for the experiment with the orifice size 10%, the pressure drops are unstable which is probably caused by cavitation in the downstream of the orifice.
A temperature increases through the orifice plate caused by the pressure drop has been observed. Due to the Joule-Thomson (JT) effect in He II forced flow, the temperature increases have been also compared with pipe flow data and predictions based on ideal isenthalpic expansion. The temperature increases measured is smaller than the predicted temperature increase. As comparing the temperature increase for the experiments of the orifice size 10% and 20%, the temperature increases for the experiment of the orifice size 20% is smaller. The disagreement is thought of as a contributing heat transfer mechanism due to thermal counterflow.
