Numerical Investigation on Single Stage Co-Axial Pulse Tube Refrigerator

Abstract

Pulse tube cryocooler is the best medium to attain very low temperatures. These Cryocoolers have practical applications everywhere ranging from Space Rockets to house hold refrigeration, like in Industrial Field, the industrial gases liquid oxygen and liquid nitrogen produced from air are very important assets. They account for about one-third of all cryogenic activity (nearly about $4 billion) in sales per year in the U.S., In Space Application they are used to produce Vacuum Chambers at high altitude for testing and also provide cooling of Cryogenic engines with liquid helium to sustain the heat produced and the list goes on from Aeronautics field to Health etc. Pulse tube cryocooler can easily go up to 100K to 80K under no load or low load condition. Pulse tube cryocooler uses vapour compression cycle and have a pulsating compression to obtain desired refrigeration. Pulse tube are closed cycle where mass is not exchanged between system and surroundings. It has only one moving part i.e. oscillating valve for generating pulsating pressure. There are different types of pulse tube Cryocoolers available which ranges upon the application and size. The temperature at the cold tip and size determines the type of cryocooler to be used. One such Cryocooler which allured lot of consumers because of its compact size and performance is Co-Axial Pulse tube. There has not much analysis done on this type of cryocooler. So it’s very difficult to find literature survey for specifically for this cryocooler. Co-Axial Pulse tube are very compact and convenient for Practical Applications. Pulse tube has no moving parts at low temperature has a simple design, and its cold produces low vibration and low Electromagnetic Interference. It is always difficult to perform analysis on the system with dynamic parts. This cryocooler has moving pulsating compressor and the system involves acquisition of cryogenic fluid with movement around a complicated geometry. This increases the complexity and arises the need of thorough analysis. If numerical analysis is carried out with arbitrary assumptions will not give a worthy solution. A software given by ANSYS called Fluent can do these calculation considering real time scenario and give effective reliable results. So analysis is carried out with the CFD Modelling and experimental verification of SingleStage Inertance Tube Co-Axial Pulse Tube Cryocooler (CAPT) and studies various effect on CAPT. A two-dimensional axis-symmetric CFD model with the thermal non-equilibrium model is developed to simulate the internal process and the underlying mechanism of CAPT. This modeling will indicate the optimum frequency at which the CAPT should operate and simultaneously we will also keep a record of how quickly we are going to achieve it. Then the experimental verification of the obtained results will be done to get agreement between simulated and tested results. This Project has been carried out in two stages; First stage deals with the Validation with the previous obtained results of Authentic author then similar analysis is performed on slightly different models with particular physical changes and change in boundary conditions. In the second stage, these are applied to the current model to achieve a feasible model with increase in the efficiencies. The analysis includes checking of variables like frequency of the pulse tube, length of the inertance tube, reservoir volume and their effects on the final obtained temperatures. There has been ample of work and simulations carried out to predict the best possible values for different parameters i.e. inertance tube length, frequency, phasor relationship between mass flow rate and pressure etc. [math mode missing closing $]