Abstract
• Experiments on Two-phase loop thermosyphon (TPLT) studying influencing parameters. • Self-regulation compensates changes in heat load, height difference, mass flow rate. • Identification of optimal charge avoiding instabilities and critical temperatures. • Low-GWP refrigerants R1233zd(E) and R1224yd(Z) are suitable for thermosyphons. Two-phase loop thermosyphon (TPLT) is a promising technology looking at highly effective electronics cooling. Due to strong coupling between the internal and external parameters, in this study experimental tests in steady-state are carried out using R1233zd(E) and R1224yd(Z) as a working fluid to investigate the respective influences and resulting design requirements. The relationship between the governing thermal and flow equations is presented to facilitate the interpretation of the test results. The study shows a stable flow and cooling performance over a wide range of heat loads and recooling temperatures. The refrigerant charge is identified as one of the main influencing factors, with an optimum being between excessive subcooling and beginning dry-out. Both tested refrigerants lead to basically similar results, showing minor differences regarding thermal performance and system stability.
Highlights
Due to the strongly progressive electrification in many technical fields, thermal management has become one of the key challenges in engineering
This long-known technology has so far only been used widely in a few industries, such as power plants. This is because of the high sensitivity of the uncontrolled loop with regard to the boundary conditions, which makes the system design extremely difficult. For this reason there is a lot of research on the behavior of Two-phase loop thermosyphon (TPLT) under a wide range of operating conditions
Milanez and Mantelli (2010) confirmed the existence of an optimal refrigerant charge or rather heat transfer limit, when the downcomer is just fully filled with liquid during operation
Summary
Due to the strongly progressive electrification in many technical fields, thermal management has become one of the key challenges in engineering. Wu et al (1996) identified a strong dependency of oscillations on the heat load and subcooling using a low pressure TPLT This was observed by Khodabandeh and Furberg (2010) as well as Nayak and Vijayan (2008) at low power and pressure during the start-up process and defined as Density-wave instability (DWI) type I. Whereas this type is characterized by backflow due to low vapor fraction, type II occurs at high heat flux with local dry-out in the evaporator.
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