TRANSIENT THERMAL PERFORMANCE ENHANCEMENT OF PHASE CHANGE MATERIALS THROUGH NOVEL PIN ARRANGEMENTS UNDER VARIED GRAVITY CONDITIONS

This thesis presents a comprehensive examination of encapsulation techniques and performance enhancement strategies for Phase Change Materials (PCMs) in the thermal management of spacecraft avionics. This research contributes to optimizing PCM applications in spacecraft through historical analysis, transient thermal performance enhancement, and computational studies.

The first chapter explains the significance of PCMs in passive thermal management since the beginning of space-age technology, it underlines the low thermal conductivity of PCMs and the necessity of incorporating materials with high thermal conductivity, such as metal foams, to improve heat transfer. It also discusses various advancements in PCM research for spacecraft thermal management applications like the shape-stabilized PCMs and also explains in details various encapsulations techniques for PCMs. This chapter also reflect upon the various efforts done by space agencies (NASA, ESA and ISRO) towards understanding the feasibility of phase change materials for spacecraft thermal management applications. It also examines the effect of various parameters such as direction of heat flow and orientation of PCM to obtain tailored heat transfer research which can be leveraged by phase change materials for effective thermal management of spacecraft avionics.

The subsequent chapter examines the transient thermal performance of a particular PCM, RT82, using novel pin arrangements. Through the strategic placement of fins, thermal conductivity and heat transfer surface area are enhanced. This study investigates numerically the melting characteristics under microgravity, terrestrial gravity, and hypergravity. This study focuses on the improvement in thermal performance brought about by fin integration under differing gravitational conditions.

The final chapter explores computational studies concentrating on the geometrical optimization of PCM encapsulation in Triplex Tube Heat Exchangers (TTHX) utilizing novel annular-fin configurations. This research examines the impact of fin shape, size, and positioning on the thermal characteristics of PCM. It identifies encapsulation geometries that facilitate vortex-like melting patterns, thereby accelerating PCM melting rates. In addition, it evaluates the heat transfer performance of these configurations under varying gravity conditions, elucidating the physics underlying the enhancement of melting performance.

In conclusion, this thesis demonstrates that judicious encapsulation techniques and geometric optimisation significantly enhance the thermal management effectiveness of PCMs in spacecraft. This research paves the way for innovation in spacecraft thermal management systems employing PCMs by interweaving historical context with performance enhancement strategies and computational insights.