Award Date

8-1-2015

Degree Type

Thesis

Degree Name

Master of Science in Engineering (MSE)

Department

Mechanical Engineering

First Committee Member

Samir Moujaes

Second Committee Member

Darrell Pepper

Third Committee Member

Brendan O’Toole

Fourth Committee Member

Samaan Ladkany

Number of Pages

101

Abstract

Heat exchanger devices are widely used in industries, air conditioning systems, refrigeration, etc. These devices have a major role in energy conservation; therefore, increasing the performance of heat exchangers helps save energy, costs and materials. The technique to increase the heat transfer performance is called heat augmentation, which can be applied to pipe surfaces and other surfaces which are used in heat exchangers to improve thermal performance. These techniques are categorized into 3 groups: passive, active and compound technique. In this study a helically machined rectangular groove on the inside of a 2.0 m tube with a diameter of 7.1mm was studied for the heat augmentation effect.

A Computational Fluid Dynamics (CFD) investigation has been carried out to study the heat transfer enhancement in a smooth tube and in four grooved tubes with different pitch sizes (7.1, 12.7, 50 and 130 (mm)). The simulations were performed in the Reynolds number range of 4000-20000. The current CFD predicted values were compared with previously collected experimental data . First, the CFD simulation was run for different groove pitches (203, 254 and 305) to compare them with the published experimental work. The results of these simulations for Nu numbers and friction factors showed good agreement with the experimental values. The primary focus of this study involves evaluating the effect of groove pitch on heat transfer and friction factors. A thermal enhancement factor is defined to evaluate the performance of the internally grooved tubes. By decreasing the pitch size from 130 to 7.1 (mm) at the same Reynolds number, both Nusselt number and friction factor increase. Also, by increasing the Reynolds number, the Nusselt number, as expected, becomes greater. The highest Nusselt number is obtained for smaller pitch size of 7.1 and 12.7 (mm) but at the penalty of a greater pressure drop compared to smooth tubes. It is observed that there is an optimum value of the enhancement factor (η) at about Re = 15,000 for all investigated grooves and enhancement up to 20% is obtained for grooved tubes with 7.1 mm pitch size.

The heat transfer properties of grooved tubes revealed that the CFD simulations can be used to improve future design considerations, which leads to improvement of performance in heat exchanger devices.

Keywords

Computational Fluid Dynamics; Friction Factor; Grooved Tube; Nusselt Number

Disciplines

Engineering | Mechanical Engineering

Language

English


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