Enhancement of pool boiling heat transfer with refrigerant based nanofluids
Date Issued
2008
Date
2008
Author(s)
Chung, Yang-Te
Abstract
Nanofluids is expected to be one of the most potential techniques for heat transfer enhancement in recent years. However, to date, there has been relatively little research conducted on boiling heat transfer regime, with refrigerants based are even bare reported. In addition, the varied characterization of suspension conditions in pool boiling causes the inconsistency between experimental results. Therefore, the aim of this article is to investigate the pool boiling heat transfer enhancement with refrigerant based Titania nanofluids. Using organic surface modification technique to produce nanoparticles with long-chain three-dimensional structure, cooperate with ultrasonic vibration to disperse nanoparticles effectively into refrigerants. Boiling experiments were conducted after suspension ability tests. Finally, the effect of suspension and concentration to boiling heat transfer of nanofluids are discussed.he result of suspension tests show, modified nanoparticles could be uniformly and steadily suspended in refrigerants. Boiling experiments reveals that 30% to 65% enhancement of convective heat transfer coefficient compare with unmodified nanofluids. One possible explanation for this is that the better suspension condition increases Brownian-motion-based mirco-convection heat transfer efficiency, which decreases the wall superheat, hence, enhances heat transfer. Boiling experiments of modified nanofluids under concentrations 0.001wt%、0.01wt%、0.1wt% found that, the heat transfer efficiency firstly increase and then decrease with increasing concentration. The highest enhancement of convective heat transfer coefficient is 65% compare with pure R-123 in concentration 0.01wt%. The possible reason is that, along with increasing concentration, the increasement of well-dispersed nanoparticles are favor to micro-convective mechanism, but too many nanoparticles would cause sedimentation on heating surface, which adds extra resistance of heat and decreases the boiling heat transfer. In addition, comparisons between the heat transfer data and the Rohsenow correlation indirectly affirm that the changed physical properties of the base liquid is not the main factor to performance, other mechanisms has to be considered. Further, correlations need to be proved by detail experiments and precisely theories.
Subjects
Heat transfer enhancemnet
Pool boiling
Nanofluids
Refrigerant
Titania
Type
thesis
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