Date of Award

January 2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

First Advisor

Clement Tang

Abstract

Sudden area expansions and contractions in channels are encountered in numerous engineering applications such as pipeline, cooling systems, and heat exchangers. Over the last several decades, numerous studies have been done on this subject. However, there is still a lack of proper investigations, especially on quantifying the viscous pressure loss at the singularity as a function of flow rate along the channel with abrupt area expansion or contraction.

In this study, the investigation was done on the behavior of static pressure of water and 9.58% volume concentration silicon dioxide nanofluid in channels with sudden area expansion and contraction. The main parameters studied are area ratio (σ = 0.0625 and 0.140), axial length of the channel, static pressure, pressure loss at the singularity, and loss coefficient. These parameters were analyzed at various mass flow rates ranging from 5 to 30 g/s.

The static pressure data were measured and were used to compute the pressure drop and loss coefficient. Results proved that static pressure and pressure drop increase with increasing mass flow rate for sudden expansion and contraction. For sudden area expansion with water, the loss coefficient increases with increasing mass flow rate and reaches an optimum value. The opposite trend was observed for sudden expansion with nanofluid and sudden area contraction with both fluids. In this case, loss coefficient decreases with increasing mass flow rate.

Because loss coefficient varies with the flow rate, the conventional Carnot equation for sudden expansion/contraction could not be used to predict the results. For this reason, new expressions were derived and used to quantify the loss coefficients.

The comparative study between the behavior of water and nanofluid showed that the pressure drop due to sudden expansion or contraction increases as a result of addition of nanoparticles in water. However, the percentage increase in pressure drop is greatly reduced at higher flow rates as a result of the increase in turbulence. For the area ratio of 0.0625 at 7.92 g/s, nanofluid pressure drop due to sudden area change is approximately 129% higher than water pressure drop. This percentage drops to approximately 16.5% at 25.7 g/s.

For nanofluid, the increase in the area ratio showed an impact on the pressure drop. For sudden area expansion, the pressure drop decreases with increasing area ratio; whereas it increases with the increasing area ratio for sudden area contraction. The behavior of the pressure drop, in channel with sudden area contraction with respect to the area ratio, was attributed to the decrease in the corrected dynamic pressure, which is the subtractive term in the overall sudden area contraction pressure drop.

For practical applications, it is recommended that this type of nanofluid be used for systems that require higher flow rates (turbulent flow).

There are number of ways by which this work can be improved in order to make sure, that the subjects covered meet well intended practical applications. In order to gain more insight on silicon dioxide nanofluid thermal performance, there is a desire to investigate heat transfer in channels with sudden area change. The results of the heat transfer investigation can be compared with the results of pressure drop provided by this work. Moreover, silicon dioxide nanofluid with lower nanoparticles concentration should be experimented in order to understand more the effect of nanoparticles addition on fluid flow in complex geometry

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