{"title":"Flow Visualization, Critical Heat Flux Enhancement, and Transient Characteristics in Pool Boiling Using Nanofluids","authors":"R. Hegde, S. Rao, R. Reddy","doi":"10.1520/JAI104443","DOIUrl":null,"url":null,"abstract":"This paper presents the experimental outcome of a study of the pool boiling heat transfer characteristics of alumina and CuO nanofluid in distilled water using a 0.19 mm diameter NiCr wire. A series of experiments were conducted in order to visualize the flow, critical heat flux (CHF) enhancement, and transient characteristics of nanofluid. The boiling phenomenon was visualized using a 0.1 g/l concentration of alumina nanofluid. The average bubble diameter was measured and was found to increase with increased heat flux. The average bubble contact angle decreased from 69° during the initial stages of boiling to 33° at CHF. Massive vapour bubbles were observed on the test heater surface near the CHF, inducing vapour blankets and forming hot/dry spots. The increase in the CHF could be well explained by the hot/dry spot theory. Pool boiling experiments conducted using low volume concentrations of CuO-water nanofluid at atmospheric pressure in distilled water showed an increase in the CHF by 30 % at a 0.3 g/l concentration. The transient behaviour of nanofluid, examined by exposing the heater surface at a constant heat flux of 700 kW/m2, indicated CHF enhancement of 5.21 % to 6.77 % for the two time durations. Based on the experimental investigations, it was concluded that the CHF enhancement is due to nanoparticle coating, which changes the thickness of the surface as a function of time and surface wettability and corroborates the hot/dry spot theory.","PeriodicalId":15057,"journal":{"name":"Journal of Astm International","volume":"5 1","pages":"104443"},"PeriodicalIF":0.0000,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"3","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Astm International","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.1520/JAI104443","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 3
Abstract
This paper presents the experimental outcome of a study of the pool boiling heat transfer characteristics of alumina and CuO nanofluid in distilled water using a 0.19 mm diameter NiCr wire. A series of experiments were conducted in order to visualize the flow, critical heat flux (CHF) enhancement, and transient characteristics of nanofluid. The boiling phenomenon was visualized using a 0.1 g/l concentration of alumina nanofluid. The average bubble diameter was measured and was found to increase with increased heat flux. The average bubble contact angle decreased from 69° during the initial stages of boiling to 33° at CHF. Massive vapour bubbles were observed on the test heater surface near the CHF, inducing vapour blankets and forming hot/dry spots. The increase in the CHF could be well explained by the hot/dry spot theory. Pool boiling experiments conducted using low volume concentrations of CuO-water nanofluid at atmospheric pressure in distilled water showed an increase in the CHF by 30 % at a 0.3 g/l concentration. The transient behaviour of nanofluid, examined by exposing the heater surface at a constant heat flux of 700 kW/m2, indicated CHF enhancement of 5.21 % to 6.77 % for the two time durations. Based on the experimental investigations, it was concluded that the CHF enhancement is due to nanoparticle coating, which changes the thickness of the surface as a function of time and surface wettability and corroborates the hot/dry spot theory.