All ETDs from UAB

Advisory Committee Chair

Hessam Taherian

Advisory Committee Members

David L Littlefield

Roy P Koomullil

Document Type

Thesis

Date of Award

2016

Degree Name by School

Master of Science in Mechanical Engineering (MSME) School of Engineering

Abstract

Heat exchangers are vital devices and are used in many specific applications such as air conditioning, power production, and waste heat recovery. Throughout the year, a large amount of energy is wasted in air conditioning and refrigeration systems in residential and commercial sectors. At the same time, a huge amount of energy (natural gas and electricity) is used in order for water heating to be supplied to our buildings. The present research project is heat transfer analysis of triple-concentric tube heat exchanger as a component of refrigeration cycle in HVAC systems. This novel design will replace conventional air-cooled condenser and consequently provide heat recovery that results in significant energy saving in the system. Phase change processes are efficient ways of heat removal, as the latent heat of condensation and evaporation provides high heat transfer coefficients. Condensation heat transfer plays a dominant role in many industrial applications. In this study, the condensation heat transfer of R-134a to air and water in the tubes as parallel and counter flow was investigated. In order to predict fluid dynamics behavior in the tubes, a detailed numerical modeling and three-dimensional transient simulation has been conducted by means of Computational Fluid Dynamics (CFD). The Volume of Fluid (VOF), Mixture and Eulerian frameworks have been employed to simulate phase change of R-134a in the annulus. A mechanistic model with physical basis (Lee model) and Thermal Phase Change model (two-resistance approach) are used to solve liquid-vapor mass transfer equations. In addition, - and -ɛ models have been used to simulate turbulent flow of air, water, R-134a in the tubes.

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