Author

Yang Chao

Date of Award

5-2020

Document Type

Thesis - Open Access

Degree Name

Master of Science in Aerospace Engineering

Department

Aerospace Engineering

Committee Chair

Dr. Mark Ricklick

First Committee Member

Dr. Sandra Boetcher

Second Committee Member

Dr. Magdy Attia

Abstract

Numerical investigation on thermodynamic characteristics of pure supercritical carbon dioxide (𝑆𝐢𝑂2) and mixtures of Helium and 𝑆𝐢𝑂2 in horizontal straight tubes with diameter of 6mm under cooling and heating conditions is carried out by using SST π‘˜ βˆ’ πœ” turbulence model. The computations are conducted at operating pressure of 8MPa with various operating conditions. Simulations are conducted by using the latest poly-hexcore mesh method in ANSYS FLUENT 19.2 and tetrahedral mesh method in CFX 19.2, results and solving time are compared. The effect of heat flux, mass flux, inlet temperature and buoyancy on heat transfer performance are studied, pressure drop and friction factor are analyzed and validated against previous correlations, the sensitivity of six different reference temperature settings in heat transfer coefficient calculation and five different lengths of adiabatic section after outlet are compared.

The results indicate that heat transfer coefficient increases with decreasing heat flux and increasing mass flux, wall temperature on the bottom surface decreases much faster than that on the top surface. Variations in heat transfer coefficient is about 10% between different reference temperature settings. Three buoyancy criteria is applied and compared in numerical results, which is not accurate enough to predict the onset of the buoyancy effect. There is no peak exist in heat transfer coefficient curve for Helium and 𝑆𝐢𝑂2 mixture, heat transfer coefficient increases with the increasing of Helium mass fraction. It is recommended to further investigate the influence in different reference temperature settings under various operating conditions and to improve the accuracy of current buoyancy effect criteria. It is recommended to further investigate the influence in different reference temperature settings under various operating conditions and to improve the accuracy of current buoyancy effect criteria.

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