Author

Neil Sullivan

Date of Award

7-2021

Document Type

Dissertation - Open Access

Degree Name

Doctor of Philosophy in Aerospace Engineering

Department

Aerospace Engineering

Committee Chair

Dr. Mark Ricklick

Committee Co-Chair

Dr. Sandra Boetcher

First Committee Member

Dr. John Ekaterinaris

Second Committee Member

Dr. Scott Martin

Third Committee Member

Dr. Bertrand Rollin

Abstract

A detailed study of the local heat transfer behavior of supercritical carbon dioxide (sCO2) is performed. Flows relevant to heat transfer devices, such as sCO2 heaters, recuperators, and internally cooled turbine blades are studied, with particular attention paid to data reduction methodology, and the use of appropriate reference quantities, nondimensionalizations, and correlations. Additionally, a semi-intrusive temperature measurement technique capable of obtaining highly spatially resolved temperature distributions is adapted for use in the challenging conditions of supercritical (SC) flow. SC fluids have proven difficult to study both experimentally and numerically due to dramatically changing thermodynamic and transport properties near the critical point. It is clear from the existing literature that the heat transfer processes within a SC flow vary from those of a subcritical flow, particularly near the pseudo-critical line. Poor predictions of heat transfer rates may lead to unexpected pinch-points in heat exchangers or heat transfer degradation. Existing experimental research of SC flow heat transfer has largely been limited to spatially averaged trends and/or simplified geometries. There remains a gap between the techniques used in the subcritical regime, and the needs of the supercritical fluids industries and sciences. Numerical simulations that are benchmarked against experimental sCO2 heat transfer data evaluate the ability of existing correlations to predict heat transfer in the SC regime, both away from and very near the critical point and pseudocritical line. As it is desired to harness the advantages arising from the peaks in K and Ср along this line, a study is performed assessing the applicability of a reducedorder model to this effect. Semi-intrusive temperature measurement is achieved, using proper calibration and coating, with accuracy approximating (uncalibrated) type-T thermocouple uncertainty. The benchmarked numerical simulations give good agreement with experimental HTC data, suggesting the use of commercial RANS code is suitable as a building block for the study of the physics of these flows. New, modified heat transfer correlations are obtained for sCO2 turbine blade cooling geometry. Additionally, experimental uncertainty for calculated heat transfer quantities is quantified for the first time in the near-critical region, where fluid properties see very large gradients.

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