Investigation of entropy generation and thermohydraulics of forced and mixed convection of Al₂O₃-Cu/water in a parabolic trough receiver tube

Khfagi, Amir Mohamed Ibrahim (2023) Investigation of entropy generation and thermohydraulics of forced and mixed convection of Al₂O₃-Cu/water in a parabolic trough receiver tube. PhD thesis, University of Glasgow.

Abstract

Heat transfer has long been a vital part of human life. Many sources have focused on increased heat transfer. Various industries, such as solar water heating systems, solar chemistry, solar desalination plants, and concentrating solar power plants, food processing plants, petrochemical plants, refrigeration systems and air conditioning equipment, and condensing central heating exchangers, etc., face the challenges of effective utilisation, conservation, and recovery of heat. In modern times, increasing the rate of heat transfer in concentrating solar collectors such as parabolic troughs by using various passive approaches have proven to be very effective. When passive approaches are used, more pumping power is needed to move the fluid through the receiver. Manufacturing of parabolic trough receiver tubes requires a significant financial commitment due to the high expenses of both capital and operation. Therefore, it is essential to develop parabolic trough receivers that are efficient. Several methods, such as heat transfer enhancement and minimisation of entropy generation, are used to do this. The current investigation makes use of tube insert technology and nanoparticle flow to achieve optimal thermohydraulic and thermodynamic designs.

Previous research on fluid flow and heat transfer in a regular pipe (PT) and a pipe equipped with an elliptical-cut twisted tape insert (TECT) and a traditional twisted tape insert (TPT) has not been conducted, particularly emphasizing the utilization of hybrid nanofluid as the working medium. However, previous works on water and nanofluid do exist. In addition, the Bejan number and the generation of total entropy are not examined on tubes supplied with an elliptical-cut and classical twisted tape insert for different fluids. Hence, in this study, heat transfer and entropy generation in a turbulent flow of an Al₂O₃-Cu/water hybrid nanofluid in a plain tube with classical and elliptical-cut twisted tape inserts are investigated numerically.

The current study focuses on the heat transmission augmentation and thermodynamic irreversibility of steady and unsteady turbulent flows through pipes with elliptical-cut and classical twisted tape introduced under uniform or non-uniform well heat flux for water, hybrid-nanofluids (Al₂O₃-Cu/water), and nanofluids (CuO/water). This work uses Star-CCM+ for numerical simulations. The realizable k-ℇ model is employed to simulate the turbulent flow computationally. The findings are utilised to determine which type of tube and fluid provides the highest performance by quantifying gains in steady state (friction factor, heat transfer, and thermal performance factor) and unsteady state (transient heat transfer). The total entropy generation has been examined in this PhD study to determine the type of tube and fluid that reduces entropy generation.

The results indicate that the heat transfer augmentation and thermal performance factor provided by the tube fitted with elliptical-cut twisted tape are greater than those provided by the tube supplied with classical twisted tape and the ordinary tube. This is because the pipe supplied with elliptical-cut twisted tape mixes the fluids better than the tube supplied with traditional twisted tape and the ordinary tube. Also, when the number of nanoparticles increases, heat transmission and thermal performance factors increase. Furthermore, TECT, hybrid nanofluids, and mass concentrations of nanoparticles affect the rate of total entropy production.

The mixed convection of Al₂O₃-Cu/water hybrid nanofluid is also investigated in a vertical pipe supplied with elliptical-cut twisted tape inserts. Further, the local and total entropy production as well as Bejan number of the system are calculated. The results clearly demonstrate the effect of mixed convection on heat transfer, thermal performance factor, and entropy production. Where the factor of thermal performance and the rate of heat transfer increase of pipe systems under mixed convection exceed those under forced convection. Moreover, mixed convection has a significant impact on the minimisation of the total entropy production.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Supported by funding from the Libyan government and Ministry of Higher Education.
• Subjects: T Technology > T Technology (General)
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Supervisor's Name: Paul, Professor Manosh, Karimi, Dr. Nader and Hunt, Dr. Graeme
• Date of Award: 2023
• Depositing User: Theses Team
• Unique ID: glathesis:2023-83735
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 27 Jul 2023 10:51
• Last Modified: 27 Jul 2023 11:05
• Thesis DOI: 10.5525/gla.thesis.83735
• URI: https://theses.gla.ac.uk/id/eprint/83735

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