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This study compared experimental and Computational Fluid Dynamics (CFD) results for heating and cooling in a packed bed (N=5.33). The experimental data was compared between heating and cooling, and was also used to validate the CFD model. The validated models were used to compare theoretical heat transfer parameters. For the experiments, it was found that the effective thermal conductivity was comparable for heating and cooling, and the wall Nusselt number for heating was higher. For the CFD results, it was found that both the wall Nusselt number and effective thermal conductivity were comparable for heating and cooling. The wall Nusselt number was slightly higher for cooling, however this difference decreased as the Reynolds number increased.

This study compared experimental and Computational Fluid Dynamics (CFD) results for heating and cooling in a packed bed (N=5.33). The experimental data was compared between heating and cooling, and was also used to validate the CFD model. The validated models were used to compare theoretical heat transfer parameters. For the experiments, it was found that the effective thermal conductivity was comparable for heating and cooling, and the wall Nusselt number for heating was higher. For the CFD results, it was found that both the wall Nusselt number and effective thermal conductivity were comparable for heating and cooling. The wall Nusselt number was slightly higher for cooling, however this difference decreased as the Reynolds number increased.

Enhancement of condensation heat transfer by wrapping of fine WIres on a condenser tube and Marangoni condensation of binary mixtures have been studied. For wire-wrapped tubes enhancement is due to modification of the profile of the condensate surface which leads to axially-directed pressure gradients and local thinning of the condensate film. Approximate theories do not agree well with limited available data prior to the present work. A systematic experimental investigation has been conducted using three fluids with widely different properties. Five wire diameters and a range of winding pitch have been used. Maximum heat-transfer enhancement ratios of 3.7, 2.2 and 2.3 for R-I13, ethylene glycol and steam respectively were obtained. The effect of inundation for steam condensation on wire-wrapped tubes has also been investigated. Extensive data exist for Marangoni condensation of steam-ethanol mixtures on small plane ve.rtical surfaces. Here the practically more relevant case C?f a horizontal tube has been studied. Apparent differences between the vertical plate and horizontal tube data are shown to be due to circumferential variation of tube surface temperature. Enhancement ratios up to around 3.7 have been obtained with as little as 0.05% mass fraction of ethanol in the boiler feed. For wire-wrapped tube and Marangoni condensation, a copper condenser tube (outside diameter 12.2 mm) fitted with four embedded wall thermocouples was cooled internally by water using a wide range of flow rates. The coolant temperature rise was measured to within 0.01 K using a ten-junction thermopile while the coolant temperature rise ranges were 0.11 to 0.77 K, 0.89 to 9.28 K and 1.00 to 6.98 K for the wire-wrap tests with R-I13, ethylene glycol and steam respectively and 1.24 to 29.1 K for Marangoni condensation. The effect on the boiler performance for water-ethanol mixtures has also been investigated.

Cooling channels with a developing flow entrance condition and aspect ratios of 1:4 and 2:1 were studied. The range of the rotation number and buoyancy parameter for the selected AR channels was extended. The maximum Ro and Bo for the 1:4 channel was 0.67 and 1.9, respectively. For the 2:1 channel, these values were 0.45 and 0.85, respectively. The effect of rib spacing and rib height on heat transfer in the 1:4 channel is investigated. Three rib spacing configurations were considered: P/e=2.5, 5, 10 with a constant e/Dh ratio of 0.078. To investigate the effect of rib height, a rib configuration with an e/Dh ratio of 0.156 and P/e ratio of 10 was considered. For the 2:1 channel, a smooth channel surface condition was studied. For each channel aspect ratio and surface condition, five Reynolds numbers were studied up to 40K. At each Re, five rotational speeds are considered up to 400 rpm. The results of this research work indicate that rotation can cause a significant increase in heat transfer on the first pass trailing surface of both aspect ratio channels. The leading surface in ribbed channels has shown a dramatic decrease in heat transfer with rotation in the first pass. Reductions in heat transfer by as much as 50% were observed. In the second pass, the leading and trailing surfaces with ribs showed very similar effects of rotation. Also, the effect of rotation seems to vary with the rib spacing. The strength of rotation showed to be greater in the tight rib spacing of P/e=2.5. The rib height in the 1:4 channel had minimal impact due to the large distance between the leading and trailing surfaces. The tip cap heat transfer for both channels showed large increases with rotation. This is very beneficial since tip cooling is an important part of maintaining the life a turbine blade. Finally, the buoyancy parameter proved to be very useful in predicting heat transfer in rotating conditions. The correlations developed showed very acceptable accuracy when compared to the experimental data.

Vacuum frying is an alternative processing method for producing high quality snacks with the advantages of lower processing temperature, enhanced organoleptic quality, and reduced acrylamide content. Vacuum frying (1.33 kPa), with the aid of a deoiling mechanism, was used to produce low-fat potato chips. The kinetics of oil absorption and oil distribution in the potato chips (total, internal, and surface oil content) was studied so that effectiveness of the de-oiling system could be established. An analysis of product quality attributes (PQA) such as moisture content, oil content, microstructure, diameter shrinkage, and thickness expansion, as well as, bulk density, true density, and porosity of chips fried at different temperatures (120, 130, and 140 degrees C) was performed in order to evaluate the effect of process temperature on the product. Moreover, heat capacity of the chips and convective heat transfer coefficient at the oil-chip interface were determined for the same temperature range. The final oil content of the potato chips was 0.072±0.004, 0.062±0.003, and 0.059±0.003 g/g solid for frying temperatures of 120, 130, and 140 degrees C, respectively. These values are lower (80-85 percent less) than those found in traditionally-fried potato chip which indicates that the de-oiling mechanism is crucial in vacuum frying processing. A significant difference (P<0.05) was observed in oil content and oil distribution within temperatures. It was found that the rate of change in PQAs is greatly affected by temperature; however, the final values of moisture content, bulk density, true density, porosity, diameter shrinkage, and thickness expansion were not affected by temperature. During vacuum frying, the specific heat of potato chips decreased with time as water decreases. The convective heat transfer coefficient changed considerably as frying progresses; moreover, it increased with temperature reaching a maximum between 2,200 and 2,650 W/m2K depending on frying temperature.

This study investigates the turbulent heat transfer and friction in a trapezoidal channel with opposite walls roughened with transverse and v-shaped ribs. The roughened channel depicts the internal cooling passage of an aerofoil near the trailing edge. The various configurations investigated for this study are smooth channel, channel with 90° transverse ribs and channel with v-shaped ribs angled at 45°. The pitch-toheight ratio (P/e), rib height-to-hydraulic diameter ratio (e/Dh) and the aspect ratio (W/e) were maintained at 12, 0.1906 and 1, respectively. The configuration was tested for Reynolds number ranging from 7,000 to 40,000. The 45° rib was found to produce the maximum heat transfer and minimum pressure loss.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 182-186). Also available on the Internet.