Convective heat transfer in supercritical flows of CO2 in tubes with and without flow obstacles

• Published in: Nuclear engineering and design 2017-03, Vol.313, p.162-176
• Main Authors: Eter, Ahmad, Groeneveld, Dé, Tavoularis, Stavros
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Convective heat transfer; Experimental data; Heat transfer deterioration; Obstacles; Supercritical pressure
• ISSN: 0029-5493; 1872-759X
• DOI: 10.1016/j.nucengdes.2016.12.016

•Measurements of supercritical heat transfer in tubes equipped with obstacles were obtained and compared with results in base tubes.•In general, flow obstacles improve supercritical heat transfer, but under certain conditions have a negative effect on it.•New correlations describing obstacle-enhanced supercritical heat transfer in the liquid-like and gas-like regimes are fitted to the data. Heat transfer measurements to CO2-cooled tubes with and without flow obstacles at supercritical pressures were obtained at the University of Ottawa’s supercritical pressure test facility. The effects of obstacle geometry (obstacle pitch, obstacle shape, flow blockage) on the wall temperature and heat transfer coefficient were investigated. Tests were performed for vertical upward flow in a directly heated 8mm ID tube for a pressure range from 7.69 to 8.36MPa, a mass flux range from 200 to 1184kg/m2s, and a heat flux range from 1 to 175kW/m2. The results are presented graphically in plots of wall temperature and heat transfer coefficient vs. bulk specific enthalpy of the fluid. The effects of flow parameters and flow obstacle geometry on supercritical heat transfer for both normal and deteriorated heat transfer are discussed. A comparison of the measurements with leading prediction methods for supercritical heat transfer in bare tubes and for spacer effects is also presented. The optimum increase in heat transfer coefficient was found to be for blunt obstacles, having a large flow blockage, and a short obstacle pitch.