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Call number: LD2668 .T4 1950 F86 / Master of Science

Call number: LD2668 .T4 1950 L56 / Master of Science

M.Ing. / In this study, alternative heat pump systems are compared for use in South African climatic conditions. Monthly heating/cooling capacities and coefficients of performance for air, vertical and several horizontal ground-source systems are calculated for Pretoria and Johannesburg. The desired type of heat exchanger is determined by considering economic factors such as the total costs, comprised of the capital and operating costs. The cost-effectiveness on investments of each system is calculated, with parameters such as the payback period, net present value and internal rate of return ...

Student Number : 9906314R - MSc dissertation - School of Pathology - Faculty of Science / Inappropriate use of antimicrobial agents has been shown to select for organisms with resistance mechanisms (eg. efflux pumps), which could lead to the development of antibiotic resistance. The objective of this study was to investigate a possible link between antibiotic resistant gastrointestinal pathogens and reduced susceptibility to anti microbial agents found in commonly used household disinfectants. Tetracycline and ofloxacin resistant and sensitive Salmonella and E.coli species were isolated from fresh poultry and clinical samples. Ethidium bromide accumulation assays were performed to assess the presence of active efflux pumps. Using spectrophotometric accumulation assays, the extrusion of the active components of commercial household agents by the efflux pumps was tested. To determine changes in the efficacy of these products, in-use disinfectant testing was performed. Active efflux pumps and extrusion of the active ingredients was observed in the resistant but not in the sensitive organisms. When the household products were used at the recommended concentrations, a significant reduction of both resistant and sensitive bacteria was observed after the in-use disinfectant testing procedure. However, if the household products were used at concentrations below the recommended concentration, the resistant bacteria were not eliminated as efficiently as the sensitive bacteria.

Water-source and ice-maker heat pumps share many characteristics. However, each presents different technical difficulties that have prevented them from being used more widely. In a water-source heat pump a very important consideration is to reduce water consumption, while in an ice-maker heat pump a major concern is to reduce the number of deicing cycles while keeping a high performance. Previous research by this author has indicated that the use of the flow reversal method (reversing periodically the water flow direction in the evaporator) has the effect of partly deicing the evaporator, reducing pressure drop and enhancing heat transfer. This thesis shows the development and application of analytical and numerical models to study the effect of different evaporator parameters on heat pump efficiency, as well as the possible advantages of using the flow reversal method in a water-source or ice-maker heat pump. The conclusion reached from these studies is that periodic water flow reversals inside an evaporator with freezing help improve the performance of a heat pump system in two different ways. First, periodic water flow direction reversals serve to enhance heat transfer in the evaporator. Second, reversing the water flow direction also delays ice blockage in the evaporator, or totally prevents blockage from happening. Delaying ice blockage represents a substantial improvement for ice-maker heat pumps, since these may then operate for a longer time without deicing. Preventing ice blockage represents a substantial improvement for water-source heat pumps, since these may then operate at lower water flow rates. Suggestions for future work include further testing of the flow reversal method for different evaporator geometries, as well as an experimental evaluation of the flow reversal method. / Graduation date: 1990

Thesis--PlanB (M.S.)--University of Wisconsin--Stout, 2004. / Includes bibliographical references.

Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Includes bibliographical references (leaves 50-51). Also available on the Internet.