Confinement and vapour production rate influences in closed two-phase reflux thermosyphons Part A: Flow regimes. (April 2018)

• Record Type: Journal Article
• Authors: Smith, K.; Kempers, R.; Robinson, A.J.
• Is Part Of: International journal of heat and mass transfer. Volume 119(2018)
• Page Start: 907
• Page End: 921
• Publication Date: 2018-04
• Subjects: Thermosyphon -- Flow maps -- Flow regimes -- Two phase flow -- Confinement -- Reflux thermosyphon -- Flow pattern map; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2017.10.049
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: A thermally conductive and fully transparent reflux thermosyphon test apparatus has been constructed. Two phase heat and mass transport within the thermosyphon is investigated for varying levels of confinement and heat fluxes. Results show that confinement and vapour production rate strongly influence the flow regime. A flow regime map is suggested for predicting the expected flow regime for varying system parameters. Abstract: This study investigates the boiling regimes in a small diameter (D = 8 mm) transparent thermosyphon. The influence of confinement on the boiling regimes was studied using a range of fluids. The confinement of the vapour phase leads to boiling regimes that differ from those traditionally described for thermosyphon evaporator boiling physics, widely considered as a combination of pool boiling and film evaporation. The boiling behaviour of small dimension thermosyphons was investigated by designing and constructing a fully transparent thermosyphon, enabling simultaneous thermal and visual analysis. Three working fluids, water, ethanol and HFE-7000, were used to characterise the thermosyphon behaviour with varied characteristic bubble length scales. The observed flow regimes could be characterised in terms of the degree of confinement and rate of vapour production. A flow regime map was developed based on these observations to predict thermosyphon flow in terms of both confinement and the rate of vapour production. It was determined that for low confinement and high rates of vapour production, the boiling regimes resemble those of pool boiling. In contrast, at high levels of confinement and high heat flux, an unsteady regime exists where relatively large bubbles and vapour generation rates result in a pulsatile geyser-type flow regime.