Supercritical CO2 (sCO2) power cycle is an up-and-coming technology to produce electricity from various heat sources. Apart from power cycles, sCO2 can also be used as coolant in centralized cooling system and stand-alone cooling device. However, lack of accurate predication tools such as heat transfer coefficient correlations and insufficient knowledge behind fundamental heat transfer processes can hinder its practical realization in key energy and cooling systems. The overall objective of the study is to extend fundamental knowledge about heat transfer and fluid flow processes in conduits pertinent to sCO2 power cycle. The emphasis here is investigation of heat transfer effects of three testing parameters: heat flux, inlet mass flux and inlet temperature. Experimental setup for this heat transfer study is designed considering limitations due to high pressure rating requirements and thus follows unconventional approach to calculate heat transfer coefficient. Test section chosen is a horizontal stainless steel tubing of inner diameter of 9.4 mm and heated length of 1.23 m with uniform volumetric heat generation within tubing walls. The designed test apparatus and data reduction process are validated with high pressure air experiments. Nusselt numbers are calculated at top, bottom and side- wall locations to demonstrate effects of buoyancy. Enhancement of heat transfer at bot- tom wall surfaces and deterioration at top wall surfaces is observed as the main effect of buoyancy. It was observed that effects of buoyancy increase with heat flux and decrease with mass flux. Buoyancy effects are also decreased for fluid temperatures higher than pseudocritical temperature. Nusselt numbers calculated from experimental results are compared with Nusselt number from available correlations in literature. It is hinted that near critical region where property variations are significant, one correlation alone may not accurately predict heat transfer for different regimes of geometry, mass flux and heat flux.
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Doctor of Philosophy (Ph.D.)
College of Engineering and Computer Science
Mechanical and Aerospace Engineering
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Khadse, Akshay, "Supercritical CO2 Heat Transfer Study Near Critical Point in a Heated Circular Pipe" (2020). Electronic Theses and Dissertations, 2020-. 73.