INVESTIGATION ON THE CAPACITANCE FLOWMETER & DEVELOPMENT OF VOID FRACTION SENSOR FOR CRYOGENIC TWO-PHASE FLOW

Abstract

Cryocoolers are devices that produce very low temperatures and provide adequate amount of cooling power at a specific location and hence can replace the conventional cryogenic fluids. The main difference between cryocoolers and cryogenic fluids is that cryocoolers can produce refrigeration at various low temperatures, while cryogenic fluids only provide refrigeration at specific temperatures, namely their boiling points. Cryocoolers can be classified into different types based on the heat exchangers used in them. They are regenerative and recuperative types. Regenerative type cryocoolers are further classified into three types namely, Stirling, Gifford McMahon (GM) and Pulse Tube. The CTI GM type cryocooler (Model: Cryodyne, Number:350C) had been chosen in our studies to understand its design, working and also to reverse engineer its development. One could learn the assembly of the system and also how it can be dismantled without damaging the components. After preparing the dimensional drawing of the displacer, Bakelite has been used for its fabrication, since it forms an equivalent substitute for the original Micarta material. The newly fabricated displacer housing was filled with the original regenerator materials and assembled into the coldhead housing. The temperature sensors were incorporated for the first and second stage cold heads. The system was tested for its performance to determine its lowest temperature reached. The regenerator materials and the sealings form the crucial components for the improved performance of the cryocooler. Both Teflon split rings and Rulon split rings have been used as sealings in our studies. Presently second stage temperature ~11.5K has been measured with lead as the regenerator material, with a water cooled 3kW helium compressor. On the other hand, with 1.5kW helium compressor, a temperature of 14.7K has been measured with lead as the regenerator material. With the same helium compressor, temperatures of 15.48K and 19.45K have been measured with Holmium copper and Erbium Nickel as regenerator materialrespectively. Since the above values are higher than those of with Lead as regenerator, we suspect the above regenerator materials have aged and are not performing satisfactorily. The first stage temperatures have been measured as 75.96 K and 58.93 K for Holmium copper and Erbium Nickel as second stage regenerator materials respectively. The first stage regenerator material used in the setup is copper meshes (< 200 mesh size). We have successfully designed and fabricated the displacer housing of the GM cryocooler system. Experiment have been performed using both labyrinth and non-labyrinth type housing. The performance of the system with indigenously designed displacer is quite satisfactory. Also, the theoretical analysis of the single stage GM Cryocooler has been attempted using the open-source regions software. By this analysis one can evaluate the cooling power, COP and inefficiency of the system as a function of various design and operational parameters. Following are the outcomes of the project. 1. Complete design drawings of the first and second stage displacer along with its housing. 2. Both Labyrinth type and non-labyrinth type displacers I have been designed, fabricated and tested. 3. Teflon silly rings are formed to perform better than the plastic sealing rings The results indicate that the performance of the regenerator materials such as Holmium Copper and Erbium Nickel is not satisfactory due to the aging effect and perhaps one should look for fresh regenerator materials.