No description available.

M.Ing. / Experiments are being conducted with regard to heat exchange systems. However, there are errors and uncertainties attached to each system. Journals, which publish articles concerning heat transfer experiments, require an estimate of this uncertainty. These uncertainties must be calculated in order to determine how valid a set of results is. The uncertainty describes to what level one may rely on a set of experimental results and conclusions. The uncertainty was calculated by the formulation of an uncertainty equation with the use of various statistical methods. Adjustments or modifications had to be made to the present uncertainty equations in order to calculate the uncertainty in heat transfer systems. Uncertainty based on a general uncertainty equation by Schultz and Cole (1979) enabled the derivation of the equations to calculate the necessary uncertainty factor for heat transfer systems. Implementation of the equations in various experimental set-ups was achieved. The uncertainty equations yielded results that seemed consistent with the subjective view of the experimenter. Therefore, the equations were considered valid.

M.Ing. / Since the promulgation of the Montreal Protocol many refrigerants needed to be phased out. R-22, which is a widely used refrigerant in refrigeration systems, was one of these. Many replacements have been found throughout the years but very few have the same refrigeration capacity without being penalised by an increase in pressure drop. R-407C is one of the refrigerants having the potential to replace R-22 as it has the same theoretical coefficient of performance and has a lower global warming potential. However, due to its zeotropic characteristics there is a degradation in heat transfer during evaporation and condensation attributed to mass transfer resistance. Thus, augmentation techniques are needed not only to increase the heat capacity, but also to achieve an increase without incurring an excessive pressure drop. One approach to cope with this problem is to make use of the recently developed herringbone micro-fin tubes. Unfortunately very little data exists for refrigerants undergoing condensation inside herringbone micro-fin tubes. There is also little pressure drop information available for this type of tube. An experimental set-up was designed to determine the characteristics of this type of tube due to the scarcity of information. With the aid of current literature, various techniques were used to determine the pressure drops inside the herringbone micro-fin tube. One of these techniques was the use of the Kattan-Thome-Favrat flow regime map which helped to identify the flow patterns inside the tube. Knowledge of the type of flow occurring inside the tube helped to clarify the behaviour of the pressure drop relationships. The type of refrigerant being used also affected the behaviour of the pressure drop curves. A low-pressure refrigerant had a higher pressure drop due to the high vapour velocities achieved. Another cause for excessive pressure drop is the friction created by the high velocity vapour and condensate inside the tube. Many relationships for the friction factor exist and these are used to analyse the experimental data.The experimental facility comprised of a vapour compression loop and a water loop. The vapour compression loop consisted of a hermetically sealed compressor with a cooling capacity of 9.6 kW, a manually operated expansion valve and an evaporator. Three condensers were tested, namely a smooth tube, a helical micro-fin tube, and a herringbone micro-fin tube. The condensers were of the tube-in-tube type with the refrigerant flowing in the inner tube and the water in counter flow in the annulus. The hot water loop was used as a source for the evaporator and a cold loop as a heat sink for the condenser. Three refrigerants were tested, namely R-22, R-134a, and R-407C, all operating at a nominal saturation temperature of 40°C and at mass fluxes between 300 and 800 kg/m 2s. Accurate sensors and transducers were used to measure the temperatures, pressures, and mass flows at predefined points. Video cameras were attached to sight glasses to aid in the identification of the type of flow regime. Data were captured using a computerised data acquisition programme designed specifically for use with the experimental study. The experimental results showed that transition between the annular and intermittent flow regimes occurred at around 25% vapour quality for the herringbone micro-fin tube, as opposed to 30% for the helical micro-fin tube and 50% for the smooth tube. Pressure drops for the herringbone micro-fin tube were higher than those for the smooth tube but slightly lower than those for the helical micro-fin tube when using refrigerants R-22 and R-134a. The correlation of Liebenberg was modified for the pressure drops inside the herringbone micro-fin tube and gave a mean deviation of 12%. The efficiency ratio for the herringbone tube using R-22 was 1.85 and 1.69 when compared with the helical micro-fin and smooth tube respectively. For R-134 the efficiency ratio was 2.02 and 2.13 when compared with the helical micro-fin and smooth tube respectively, while for R-407C it was 1.58 and 1.26 for the two respectively. It was also concluded that R-407C could be used as a replacement refrigerant for R-22when used with a herringbone micro-fin tube.

M.Ing. / The Montreal Protocol led to the phasing-out of ozone layer depleting refrigerants and replacing them with more environmentally friendly refrigerants, which in many cases caused heat transfer degradation in heat exchanger equipment. To make up for the heat transfer degradation, there was a need for the application of heat transfer enhancement techniques. One such technique is the use of micro-fin tubes as opposed to traditional smooth tubes. The purpose of this study is to develop a flow regime map for the condensation of R-22, R-407C and R-134a in a herringbone micro-fin tube. It was perceived that with the knowledge of flow patterns inside the tube and especially the annular-to-intermittent transition, it is possible to perform improved analyses of the heat transfer and pressure drop characteristics. Experimental and analytical work was performed to investigate the flow regimes during condensation of the refrigerants in smooth, helical micro-fin and herringbone micro-fin tubes at an average saturation temperature of 40oC, with mass fluxes ranging from 300 to 800 kg/m2s. Condensation occurred in tube-in-tube type condensers with cooling water flowing in the annulus and the refrigerant in the inner tubes. The condensers consisted of eight sub-sections to allow for the acquisition of sectional heat transfer and pressure data. Various criteria were considered in order to generate flow regime maps. The Thome flow regime transition criterion was used and complemented with visually-observed and photographic imaging, as well as the objective power spectral density distributions of the pressure signals of the condensing refrigerants. The observed flow regimes were mainly annular flow and intermittent flow. Stratified-wavy flow was observed at low mass fluxes and low vapour qualities. There were notable similarities in the flow pattern between the smooth and micro-fin tubes. However, the experimental results show that the transition from annular to intermittent flow regimes occurred at average vapour quality values of 0.26, 0.29 and 0.48 for the herringbone micro-fin, the helical micro-fin and smooth tubes respectively. The combined analyses assisted in adapting the helical micro-fin tube condensing flow pattern map, to ensure its application in accurately predicting herringbone micro-fin tube condensation. The new transition criterion effectively predicts the delay in transition from annular to intermittent flow for all three refrigerants, condensing in the herringbone micro-fin tube.

"Heat treatment is an important manufacturing process, which controls the mechanical property of metal parts, therefore contributes to the product quality. A Computerized Heat Treatment (CHT) system has been developed to model and simulate the heat transfer in furnace. When the part load and thermal schedule information is given with part and furnace specifications, the temperature profiles of parts in furnace can be calculated based on heat transfer principle. Therefore the part load and thermal schedule can be optimized to remove unnecessary delay time while the quality of heat treatment is ensured. In the thesis, the functions of CHT are enhanced with the capability of modeling and simulating the heat treatment processes with random part load and continuous furnaces. Methods to model random load and continuous furnace have been developed. Case studies with industry real data have been conducted to validate the system and to show effectiveness of the system. The system development is also introduced in the thesis."

Digitized by Kansas Correctional Industries

No description available.

A miniature reciprocating expander is being developed as part of a larger program to develop a heat actuated heat pump for portable applications. By utilizing the higher energy density of liquid hydrocarbon fuels relative to batteries, a heat actuated heat pump would be able to provide cooling for much longer than motor driven units of equal weight. A prototype expander has been constructed and demonstrated to produce up to 22 W of shaft power at 2500 rpm using 60 psig, room temperature nitrogen as the input. Assuming adiabatic conditions, the expander appears to operate at up to 80% isentropic efficiency. However, when heat inflow to the expander is accounted for, the resulting polytropic efficiency is about 10% lower. In addition to experimental results, models of expander performance with different loss mechanisms are presented. These mechanisms include over- and under-expansion, in-cylinder heat transfer, clearance volume, friction, and valve pressure drop. / Graduation date: 2005

Miniature energy and chemical systems (MECS) are miniature thermal, fluid, and chemical devices in the mesoscale size range between a sugar cube and a human fist. MECS take advantage of improved rates of mass and heat transfer that have been observed at the microscale. There are many potential applications for MECS, including manportable cooling and decentralized chemical processing. However, this potential has not been realized due to limitations in microfabrication. MECS devices require: 1) the fabrication of complex geometries incorporating microscale features; and 2) the thermal, mechanical and chemical properties of engineering metals. This thesis centers on developing a process for producing high-aspect-ratio, MECS devices in stainless steel. In order to achieve this goal, laser ablation and diffusion bonding were employed in a metal microlamination (MML) process. The process involves stacking and bonding a series of laminates with low-aspect-ratio features to produce a composite device with high-aspect-ratio features (20:1). Laser ablation was used to form many laminates of 0.003" 302 stainless steel. These laminates were then joined via diffusion bonding. The process developed in this thesis is unique in that it: 1) permits the MECS designer greater freedom in specifying microchannel widths; and 2) has produced microscale features in excess of 20:1 aspect ratio. Microchannels and microfins in excess of 20:1 aspect ratio were fabricated in stainless steel using this method. Resultant microchannels were tested by flowing air through them at various flow rates and measuring the resulting pressure drop. Experimental results were compared with theoretical calculations and other technical literature. Findings suggest that the preliminary efforts to build a MECS device resulted in significant air blockage in the microchannel passageways. Sources of this blockage include bent fins, warpage and misalignment among others. Further process refinements are needed to prove the economic viability of this process. / Graduation date: 1998

Described in this thesis is an investigation of the fully developed natural convection heat transfer in a vertical channel formed by two infinitely wide parallel plates maintained at a uniform wall temperature. Closed-form solutions for the velocity and temperature profiles are developed along with local and averaged Nusselt numbers. The local Nusselt number based on bulk temperature is found to be 3.77. This result is an analog corresponding to 7.60 for fully developed laminar forced convection in a parallel plate channel with uniform wall temperature boundary condition. The local Nusselt number based on the ambient temperature is deduced as a function of flowwise location. Results are compared with existing numerical and experimental data to find good agreement. / Graduation date: 1997