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.

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.

A turbocharger’s performance is measured in a gas stand in order to provide information of the components characteristics. The measurement procedure is a very time consuming process and it is thus desired to make it more time-efficient. To allow for development of an enhanced control strategy used during the measurements, a 0D model of a gas stand is developed. The physical gas stand components are modeled and validated against measurements, all showing a reasonable result. Turbocharger heat transfers are investigated and modeled using a lumped capacitance approach. The heat transfer models shows approximative results when comparing with measurements which is explained by the lack of temperature measurement made on the bearing housing. When the complete gas stand model is validated against measurements, an improvement of the measurement procedure is examined. By adding an idealized heat source with the possibility to heat the compressor housing, it is possible to reduce the time it takes to reach an equilibrium when switching between two steady state operating points.

The k-distribution method for treating the spectral properties of and absorbing-emitting medium represents an alternative to line-by-line calculations which reduces the number of evaluations of the radiative transport equation from the order of a million to the order of ten without any significant loss of accuracy. For problems where an appropriate reference temperature can be defined, the k-distribution method is formally exact and consists only of a change of variables in the spectral domain. However, when no appropriate reference temperature can be defined such as for strongly non-isothermal media, the method results in errors. These errors are difficult to quantify. There have been several attempts to implement corrections to the k-distribution method to extend its application to inhomogeneous media by modeling the effects of temperature, pressure, and concentration gradient. The Multi-Source Full Spectrum K-Distribution Method (MSFSK) introduced here extends the k-distribution method to non-isothermal media without variations in pressure or concentration. The MSFSK method manages to attain this goal by applying the superposition principle to the original RTE before applying the k-distribution transformation to decompose the problem into a set of sub-problems each of which is able to be solved effectively via the ordinary or modified full spectrum k-distribution method. The concept behind this new Multi-Source Full Spectrum K-Distribution Method is to break up the problem domain into isothermal or nearly isothermal emission zones. For each zone, the heat flux and flux divergence are calculated considering only emission from that zone. The RTE is solved using the full spectrum k-distribution method. The k-distribution for each gas volume is generated using the temperature of the current emission zone as the reference temperature. This process is repeated for each emission zone and the heat flux and flux divergence are summed. This method is applied to a variety of one dimensional slab geometry problems are results are presented. It is shown that the MSFSK method provides very accurate results for the radiative heat flux and flux divergence in these geometries. The effect of different quadrature schemes for performing the spectral integration on solution accuracy. / text

Thermal contact conductance is highly important in a wide variety of applications, from the cooling of electronic chips to the thermal management of spacecraft. The demand for increased efficiency means that components need to withstand higher temperatures and heat transfer rates. Many situations call for contact heat transfer through nominally cylindrical interfaces, yet relatively few studies of contact conductance through cylindrical interfaces have been undertaken. This study presents a review of the experimental and theoretical investigations of the heat transfer characteristics of composite cylinders, presenting data available in open literature in comparison with relevant correlations. The present investigation presents a study of the thermal contact conductance of cylindrical interfaces. The experimental investigation of sixteen different material combinations offers an opportunity to develop predictive correlations of the contact conductance, in conjunction with an analysis of the interface pressure as a function of the thermal state of the individual cylindrical shells. Experimental results of the present study are compared with previously published conductance data and conductance models.

Computational Fluid Dynamics (CFD) is used in this study to assess the influence of temperature-dependent oil viscosity and density on the flow of oil up the well, and therefore the amount of insulation required. CFD is a difficult tool to apply to flows where the grid aspect ratio is as high as it needs to be to accommodate the full length of an oil well with a realistic number of grid points. Each model was therefore intensive in terms of computational effort and time. This study shows that by allowing oil viscosity and density to vary with temperature in a 2150 m vertical well with no insulation, the production output is significantly affected. The drop in production output is approximately 3% when oil viscosity varies with temperature, but when coupled with temperature-dependent density the loss in production increases to 22%. Ten CFD models, each with a different value of insulation heat transmission coefficient lying in the range 0.35 Wm^-2K^-1 to 16900 Wm^-2K^-1, are used to establish the temperature drop between riser inlet and outlet. The results obtained allow an operator to select an appropriate insulation based on the allowable temperature drop up the well, assuming all other properties are equal. The completion fluid region is situated outside the oil flow, tubing and insulation. The fluid is stationary which suggests that natural convection currents are present. Seven CFD models with annulus heights ranging from 1 m to 64 m are used to detect these currents, and assess the effectiveness of water as an insulating completion fluid. This thesis establishes that the natural convection currents do not split into multiple cells, but remain mono-cellular when the Grashof number is approximately 1x10⁸ and the Prandtl number is 2.3. This work also shows that heat loss due to natural convection from the completion fluid is an important contributory factor to the overall heat loss from a well, dependent on the well height.

No description available.

Regenerators are key components in many thermal devices such as Stirling cryocoolers, magnetic refrigeration devices etc. They act as temporal thermal energy storage and therewith separate two thermal reservoirs. Regenerators are typically made up of porous structures referred to as the packing material that can lead to complex flow pathways of the heat transfer fluid through the regenerator. The nonisothermal and periodically reversing flow type allows for thermal energy exchange with the packing material of the regenerator. The performance of such devices depends greatly on the geometry of the porous structure, itsmaterial properties, length scales involved as well as operating conditions. This thesis is a study of thermohydraulic properties of thermal regenerators under oscillating flow conditions. In the first part of this thesis, thermodynamic models are developed for the extraction of the friction factor and Nusselt number from an experiment based on a harmonic approximation technique. These models are verified using a two dimensional pore scale model that allows to calculate friction factor and Nusselt number on a theoretical basis independent from an experiment. The second part of this thesis is devoted to the application of the models presented in part one to an experiment. A test apparatus that allows to measure temperature and pressure drop for various types of regenerators is presented. The measurements for a microchannel and packed bed of spheres regenerator are characterized using spectral analysis. Friction factor and Nusselt numbers are evaluated and parametrized using the models derived in the first part of this thesis. Themethodology presented in this thesis reveals insights in the dynamic effects of oscillating flow type heat transfer. The theoretical findings are applied to experimentally obtained data for a correct interpretation of friction factor and Nusselt number. / Graduate