Optimal pulse-tube design using computational fluid dynamics

The pulse tube cryocooler (PTC) represents a reliable, compact, and efficient method for producing cryogenic refrigeration. In many ways, the PTC represents a straightforward extension of the more mature Stirling cryocooler. The key difference is the replacement of the displacer in the Stirling cryocooler with a pulse tube. The function of the displacer in the Stirling cryocooler is to transmit power from the cold end to the warm end of the machine; the pulse tube performs a similar function in the PTC. However, while the behavior of a displacer in a Stirling cycle is easily controlled, the behavior of the pulse tube in a PTC is not mechanically controlled and therefore one of the challenges associated with the design of a PTC is understanding the behavior of the pulse tube.;The overall objective of this thesis was to carry out fundamental research that will enable the deployment of high efficiency pulse tube cryocoolers by developing an experimentally verified and powerful CFD model that can be applied to the design of efficient pulse tubes and associated flow transitioning elements. A two-dimensional axisymmetric CFD model that captures the hydrodynamic and thermodynamic processes occurring in a pulse tube was developed using the commercial CFD code FLUENT. Post processing algorithms were developed in order to reduce the output of the CFD model (i.e., the temperature, velocity, pressure, etc. as a function of position and time) to the quantities of interest to a designer such as the enthalpy flow, acoustic power flow, and a figure of merit that is relevant to a PTC. An experimental test facility was designed and constructed to enable the experimental measurements of these quantities and allow the validation of the CFD model. The model was extended to allow for simulations at very low temperatures (4 K) by integrating a real gas equation of state with the CFD simulation. The outcome of this project is therefore a simulation that allows the designer to accurately predict the performance of low temperature pulse tubes.