Gyuwan Hwang

Elongating axial conduction path design to enhance performance of cryogeinc compact pche (printed circuit heat exchanger)

PCHE (Printed Circuit Heat Exchanger) is one of the promising cryogenic compact heat exchangers due to its compactness, high NTU and robustness. The essential procedure for fabricating PCHE is chemical etching and diffusion bonding. These technologies can create sufficiently large heat transfer area for a heat exchanger with numerous micro channels (Dh<1 mm). However, PCHE shows disadvantages of high pressure drop and large axial conduction loss. Axial conduction is a critical design issue of a cryogenic heat exchanger when it is operated with a large temperature difference. Elongating the heat conduction path is implemented to reduce axial conduction in PCHE in this study. Two PCHEs with identical channel configuration are fabricated, for comparison, one of which is modified to have longer heat conduction path. Both heat exchangers are tested in cryogenic environment (300~70 K), and the modified PCHE shows better performance with significantly reduced axial conduction. The experimental results indicate t...

DEVELOPMENT OF THE HYBRID JT‐EXPANDER CYCLE FOR NG LIQUEFACTION CYCLE

Two liquefaction cycles for LNG (liquefied natural gas) production are compared in this paper. One is a well known MR (mixed refrigerant) JT cycle with two phase separators and four heat exchangers. Another one is the novel concept of hybrid cycle, which is to replace the last stage JT expansion with a turbine expander. The inlet flow to the turbine expander is deliberately warmed up by NG (natural gas) stream to guarantee superheated vapor phase and increase useful work. The turbine expander is to extract pressure exergy and reduce entropy generation by producing work and alleviating work requirement in the compressor. This paper describes the detailed processes of hybrid JT‐expander cycle and the quantitative comparison results by HYSYS simulation under some realistic physical constraints.

ESTIMATION OF FREEZING POINT OF HYDROCARBON AND HYDROFLUOROCARBON MIXTURES FOR MIXED REFRIGERANT JT CRYOCOOLER

Estimating the freezing point of refrigerant is an essential part in designing an MR JT (Mixed refrigerant Joule‐Thomson) cryocooler to prevent itself from clogging and to operate with stability. There were researches on estimating freezing point, but some of them resulted in the wrong prediction of clogging. In this paper, the freezing point of the MR is precisely estimated with caution of clogging. The solubility of HC (hydrocarbon) and HFC (hydrofluorocarbon) mixture components are obtained with their activity coefficients, which represent the molecular interaction among the components. The freezing points of the MR JT cryocooler are systematically investigated in the operating temperature range from 70 K to 90 K.

BUFFERED ROTARY VALVE SYSTEM OF GM-TYPE PULSE TUBE REFRIGERATOR

The buffered rotary valve system was invented to make a valved refrigeration system more efficient. This paper introduces its basic design and operation process, and describes the experimental performance results. The mass flow rate was reduced and the coldhead temperature at no load condition became lower than that of the conventional rotary valve system even though the improvement was not so much as we expected. The experimental results are discussed with the effect of the orifice reservoir of double inlet PTR (Pulse Tube Refrigerator), and the prospect of buffered rotary valve system is suggested.