Date of Award

Spring 2024

Access Type

Thesis - Open Access

Degree Name

Master of Science in Aerospace Engineering

Department

Aerospace Engineering

Committee Chair

Mark Ricklick

First Committee Member

Sandra Boetcher

Second Committee Member

Scott Martin

Third Committee Member

Neil Sullivan

College Dean

James Gregory

Abstract

Heat transfer of supercritical carbon dioxide (sCO2) was studied experimentally by commissioning a sCO2 flow loop featuring a horizontal tube-in-tube counterflow heat exchanger with a circular cross section. The main objective was to establish experimental heat transfer research capabilities for sCO2 at Embry-Riddle Aeronautical University’s (ERAU) Thermal Science Lab. sCO2 experiences a drastic change in thermophysical properties near its critical point that results in unique heat transfer characteristics. The high pressures at which sCO2 exists make the large gradients in thermophysical and transport properties difficult to study, experimentally and numerically. However, understanding the heat transfer characteristics and thermophysical behavior of sCO2 is essential in designs taking advantage of these improved heat transfer rates and efficiencies. Traditional correlations for heat transfer of single-phase fluids such as water or oil break down when the nonlinear thermophysical properties of sCO2 are taken into account. Thus, the fundamental characteristics of sCO2 heat transfer, as well as its sensitivity to inlet and boundary conditions, must be studied experimentally to validate computational models. The rig developed as part of this work was benchmarked and validated against previous work from the literature.

The designed test section comprised a 0.5 m long test section made up of a copper inner tube with an inner diameter of 6 mm and thickness of 1 mm containing the sCO2 which was cooled by a water jacket with an inner diameter of 12.7 mm. Temperature measurements were taken at 10 different axial locations along the test section, allowing for the calculation of local and average heat transfer coefficient under different boundary conditions. In addition to the experimental rig, a 1-D computational tool for pretest predictions was created. It was used to determine the operational parameters for the different subsystems in the loop to achieve a steady state, constant heat flux, cooling boundary condition; as well as making sure that the sCO2 remained within safe operational conditions governed by the capabilities of the flow loop. The designed rig allows for sCO2 experiments with testing conditions up to 1,500 psi (10.34 MPa) and 85°C (353.15 K). Cases at pressures between 4 and 9 MPa and mass fluxes up to 220 kg/m2s, where tested, with test section inlet temperature ranging between 20°C and 45°C. The experimental results are compared to the ones presented in the literature and the maximum difference for all cases is within 20%.

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