Evaporative cooling is an alternative and efficient method of cooling in dry climates. When a liquid evaporates into the surrounding gas, the energy required for the change of phase produces a cooling effect. The wet bulb depression is the measure of potential for evaporative cooling. Greater the wet bulb depression greater is the cooling effect, and vice versa. The residential desert cooler, apart from cooling the air increases the humidity of the air in the room by absorbing moisture from the water supplied to the cooler. This may result in an undesirable increase in humidity level. Allergies is an additional problem with direct evaporative coolers. Indirect evaporative cooling does not have these two drawbacks. In the present work a small indirect evaporative cooler is developed with a cross flow heat exchanger and the performance of the cooler is evaluated under controlled environmental conditions. The results are compared with the results of an analytical model developed by assuming constant water film temperature on the external wall of the heat exchanger tube. The experimental results of the cooler show a satisfactory agreement with the analytical values. Design calculations are presented to show the performance characteristics of indirect evaporative coolers under different temperature and humidity conditions of the ambient. It has been shown that reducing the heat exchanger tube diameter to around 2 mm results in better cooling effect. Climatic conditions of different Indian cities are discussed with respect to the expected effectiveness of indirect evaporative coolers.

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Eskom provides 98% of South Africa’s ever increasing electricity demand. The mining sector is a vital contributor to the economy, but also consumes vast amounts of electricity. This sector is responsible for almost 15% of the country’s electricity usage. Mines heavily depend on the supply of cold water and air. Refrigeration systems are therefore constantly operational and can account for 25% of a mine’s electricity costs. The need therefore exists to investigate possible energy savings initiatives. Refrigeration systems are typically used to lower the temperature of water and air. Bulk Air Coolers (BACs) are used to produce cold air. The aim of this study is to investigate possible electricity cost savings in a mine refrigeration system. This can be achieved by enabling equipment to dynamically adapt to changes in their environment. Electricity usage reduction has the greatest financial impact if it occurs during Eskom peak periods. Time-dependent schedules of operation are therefore used to achieve this objective. Due to the lack of such a controller in the mining industry, the focus of this study is a BAC control system. A BAC controller would be able to follow guidelines that could lead to electricity cost savings. It was therefore developed and incorporated in the Real-time Energy Management System (REMS). The BAC controller combines various inputs and constraints to determine the output. An electricity usage reduction during the Eskom evening peak period was consequently achieved. The BAC controller was implemented on three sites. Electrical energy usage during the evening peak period was reduced via the load shifting method. This aids Eskom in their effort to reduce the peak period demand. Air temperature and dam levels were closely monitored during the peak period. If any preset condition was violated, the load shifting was abandoned for that day. It was shown that a total power reduction of 7 MW is possible between the three sites. The electricity savings occurred in the evening peak period. A calculation was made to determine the possible annual savings by using the achieved daily cost savings. The winter months were not included in the calculation. An annual cost saving of R1 166 694.41 is therefore possible without having to reduce output quantities. / MIng(Computer and Electronic Engineering), North-West University, Potchefstroom Campus, 2015

Eskom provides 98% of South Africa’s ever increasing electricity demand. The mining sector is a vital contributor to the economy, but also consumes vast amounts of electricity. This sector is responsible for almost 15% of the country’s electricity usage. Mines heavily depend on the supply of cold water and air. Refrigeration systems are therefore constantly operational and can account for 25% of a mine’s electricity costs. The need therefore exists to investigate possible energy savings initiatives. Refrigeration systems are typically used to lower the temperature of water and air. Bulk Air Coolers (BACs) are used to produce cold air. The aim of this study is to investigate possible electricity cost savings in a mine refrigeration system. This can be achieved by enabling equipment to dynamically adapt to changes in their environment. Electricity usage reduction has the greatest financial impact if it occurs during Eskom peak periods. Time-dependent schedules of operation are therefore used to achieve this objective. Due to the lack of such a controller in the mining industry, the focus of this study is a BAC control system. A BAC controller would be able to follow guidelines that could lead to electricity cost savings. It was therefore developed and incorporated in the Real-time Energy Management System (REMS). The BAC controller combines various inputs and constraints to determine the output. An electricity usage reduction during the Eskom evening peak period was consequently achieved. The BAC controller was implemented on three sites. Electrical energy usage during the evening peak period was reduced via the load shifting method. This aids Eskom in their effort to reduce the peak period demand. Air temperature and dam levels were closely monitored during the peak period. If any preset condition was violated, the load shifting was abandoned for that day. It was shown that a total power reduction of 7 MW is possible between the three sites. The electricity savings occurred in the evening peak period. A calculation was made to determine the possible annual savings by using the achieved daily cost savings. The winter months were not included in the calculation. An annual cost saving of R1 166 694.41 is therefore possible without having to reduce output quantities. / MIng(Computer and Electronic Engineering), North-West University, Potchefstroom Campus, 2015

Corrosion problems of copper waffle coolers are experienced in Platinum Group Metals (PGM’s) smelting furnaces. The copper cooler wear mechanism was studied through a post-mortem analysis of the refractory corrosion products that were removed from a PGM smelter. Post-mortem samples were characterised using Scanning Electron Microscopy (SEM), X-Ray Fluorescence Spectroscopy (XRF) and X-Ray Powder Diffraction (XRD). On visual inspection of the refractory wall it was observed that at the slag-feed interface the front refractory (mag-chrome) brick was completely corroded and only the freeze lining (frozen slag) formed a barrier between the copper cooler and the feed. At the bottom section of the slag zone the front refractory brick was still intact. Base metal sulphides and element sulphur were the major phases observed at the copper cooler-freeze lining interface while at the copper cooler-front brick interface only covellite (CuS) and element sulphur were observed. It was concluded that wear proceeded through two mechanisms: Reaction of copper with base metal sulphides which infiltrated the freeze lining and gaseous attach of copper by sulphur forming covellite. Front mag-chrome refractory bricks are replaced by graphite blocks in the latest furnace wall designs. A post-mortem graphite block was analysed with SEM, XRD and Inductively Coupled Plasma (ICP) to determine the phases associated with copper cooler corrosion. Base metal sulphides were observed at the copper cooler-graphite block (cold face) interface. Good agreement was found between the phases in the graphite block and the phases in the post-mortem sample where the refractory brick was used. Laboratory experiments were carried out to determine the effect of corrosive gas composition and copper cooler surface temperature on the corrosion rate and morphology of the corrosion products. Tests were performed on copper foils at temperatures from 80°C to 140°C. Corrosive gases included H2S, S2 and S2 with HCl. It was found that when a copper foil is exposed to sulphur the sulphides that form are covellite at 80°C, covellite and yarrowite (Cu9S8) at 110°C, yarrowite and digenite (Cu1.8S) at 140°C. Linear corrosion rate behaviour was observed between 80°C and 110°C since the sulphide scales are not passivating and they poorly adhere to the copper foil. Average corrosion rates of copper foil by sulphur vapour was 54 mm/y at 80°C and 80 mm/y at 110°C, above 112°C the corrosion rate decreased to 5 mm/y. Additions of HCl enhance the corrosion rate at temperatures above the melting point of sulphur (112°C). Chalcocite (Cu2S) forms when copper is exposed to H2S. It was concluded that the corrosion rate and the morphology of the corrosion product are functions of temperature and the corrosive gas composition. Copyright / Dissertation (MSc)--University of Pretoria, 2010. / Materials Science and Metallurgical Engineering / unrestricted

Carbon dioxide (CO2) is a natural, low cost refrigerant with good thermo-physical properties. CO2 is a good alternative for replacing HFC refrigerants that possess high global warming potential and reducing the direct impacts of refrigeration systems on the environment. However, CO2 refrigeration systems operate at relatively high condenser/gas cooler pressures and this imposes special design and control considerations. The gas cooler is a very important part of the system and can have significant influence on its performance. In sub-critical operation, good gas cooler/condenser design can reduce the condenser pressure and delay switching to supercritical operation which increases system efficiency. In supercritical operation optimum design and control can enable the system to operate at pressures that maximise system efficiency. In air cooled systems, gas coolers/condensers are of the finned-tube type. This type of heat exchanger is well established in the HVAC and refrigeration industries. The large changes in the CO2 properties in the gas cooler, however, during supercritical operation impose special design and manufacturing considerations. This research project considered the influence of the unique heat transfer characteristics of CO2 on the design and performance of finned tube air cooled condensers/gas coolers for CO2 refrigeration applications. A combined experimental and modelling approach using Computational Fluid Dynamics (CFD) was employed. A CO2 condenser/gas cooler test facility was developed for the experimental investigations. The facility employs a ‘booster’ hot gas bypass CO2 refrigeration system, with associated condenser/gas cooler test rig and evaporator load simulation facility. A series of experimental tests were carried out with two gas coolers which incorporated horizontal and horizontal-vertical slit fins and was obtained adequate experimental data concerning gas cooler performance. CFD modelling was used to study the performance of the gas coolers. The model was validated against test results and was shown to predict the air outlet temperature and heat rejection of the gas cooler with an accuracy of within ±5%. The model was subsequently used to evaluate the effect of a fin slit between the 1st and 2nd row of tubes of the gas cooler as well as a vertical slit on the 1st row before the last tube of the section. The results showed a 6%-8% increase in the heat rejection rate of the gas cooler compared to the performance without the horizontal slit. The vertical slit in the fin of the last tube has resulted in an additional increase in heat rejection over and above that for the horizontal slit of 1%-2%. CFD modelling was also used to investigate the variation of the refrigerant side, air side and overall heat transfer coefficient along the heat exchanger. The results showed that the refrigerant heat transfer coefficient increases with the decreasing of bulk refrigerant temperature and reaches its maximum when the specific heat of the refrigerant is highest. Furthermore, increasing the refrigerant mass flux, increases the refrigerant side heat transfer coefficient and heat rejection. This can reduce the size of the gas cooler for a given capacity at the expense of higher pressure drop and compressor power consumption. Air side and overall heat transfer coefficient correlations were developed for the specific gas cooler designs which were investigated and showed the heat transfer coefficients increase with increasing Reynolds Number.

2 pp. / In the semi-arid climate of southern AZ, evaporative cooling systems are commonly used and very effective for cooling homes (swamp coolers), outdoor areas (misters), and for greenhouses used for commercial and horticultural plant production (pad-and-fan, high-pressure-fog). The purpose of this brochure is to educate users about strategies they can employ to save water and improve the performance of evaporative cooling systems. Principles of operation, a list of advantages and disadvantages, and a comparison of common systems is also included, to help users decide the best system for them.

A cold fiber solid phase microextraction device was designed and constructed based on the use of a thermoelectric cooler (TEC). A three-stage thermoelectric cooler was used for cooling a copper rod coated with a polydimethylsiloxane (PDMS) hollow fiber, which served as the SPME fiber. The copper rod was mounted on a commercial SPME plunger and exposed to the cold surface of the TEC, which was enclosed in a small aluminum box. A heat sink and a fan dissipated the generated heat at the hot side of the TEC. By applying an appropriate DC voltage to the TEC, the upper part of the copper rod, which was in contact to the cold side of the TEC, was cooled and the hollow fiber reached a lower temperature through heat transfer. A thermocouple was embedded in the cold side of the TEC for indirect measurement of the fiber temperature. A portable cold fiber SPME device was made by using a car battery as the power supply. The cold fiber SPME device with thermoelectric cooling was applied in quantitative analysis of off-flavors in rice. Hexanal, nonanal, and undecanal were chosen as three test analytes in rice. These analytes were identified according to their retention times and analyzed with a GC/FID instrument. Headspace extraction conditions (i.e. extraction temperature and extraction time) were optimized. Standard addition calibration graphs were obtained at the optimized conditions and the concentrations of the three analytes were calculated. The developed method was compared to a conventional solvent extraction method. The applicability of the portable cold fiber SPME with TEC for field sampling was tested. The effect of cooling on extraction recovery and the reproducibility of extraction were examined for extractions from an n-alkane flow through system. It was found that the extraction recoveries were significantly higher when the fiber was cooled. To further investigate the effect of cooling on the sensitivity of SPME in field sampling, the portable cold fiber SPME was used for extraction of volatile components from living wisteria flowers. Both the number of identified compounds and the related peak areas increased for extractions with cold PDMS fiber relative to without cooling and commercial PDMS and PA fibers. The portable cold fiber SPME device was also used for field sampling of volatile components of living lily-of-the-valley flowers and the extracted compounds were analyzed with GC/MS. The desorption kinetics of hydrophobic organic compounds (HOCs) from environmental solid matrices was investigated using cold fiber SPME with CO2 cooling. Polycyclic aromatic hydrocarbons (PAHs) and selected volatile organic compounds (i.e. toluene, ethylbenzene, o-xylene) were used as test analytes. Sand, silica gel, and clay were used as laboratory model solid matrices and were contaminated by the test analytes. Certified sediments were used as naturally contaminated samples. In this approach, the organic compounds, released from contaminated solid samples at different elevated temperatures, were exhaustively extracted with cold fiber SPME over different extraction times. The extraction data were used to obtain desorption and Arrhenius plots. The rate constants of desorption and activation energies of desorption were measured for each contaminant using these plots. The results were comparable to those reported in the literature.

A cold fiber solid phase microextraction device was designed and constructed based on the use of a thermoelectric cooler (TEC). A three-stage thermoelectric cooler was used for cooling a copper rod coated with a polydimethylsiloxane (PDMS) hollow fiber, which served as the SPME fiber. The copper rod was mounted on a commercial SPME plunger and exposed to the cold surface of the TEC, which was enclosed in a small aluminum box. A heat sink and a fan dissipated the generated heat at the hot side of the TEC. By applying an appropriate DC voltage to the TEC, the upper part of the copper rod, which was in contact to the cold side of the TEC, was cooled and the hollow fiber reached a lower temperature through heat transfer. A thermocouple was embedded in the cold side of the TEC for indirect measurement of the fiber temperature. A portable cold fiber SPME device was made by using a car battery as the power supply. The cold fiber SPME device with thermoelectric cooling was applied in quantitative analysis of off-flavors in rice. Hexanal, nonanal, and undecanal were chosen as three test analytes in rice. These analytes were identified according to their retention times and analyzed with a GC/FID instrument. Headspace extraction conditions (i.e. extraction temperature and extraction time) were optimized. Standard addition calibration graphs were obtained at the optimized conditions and the concentrations of the three analytes were calculated. The developed method was compared to a conventional solvent extraction method. The applicability of the portable cold fiber SPME with TEC for field sampling was tested. The effect of cooling on extraction recovery and the reproducibility of extraction were examined for extractions from an n-alkane flow through system. It was found that the extraction recoveries were significantly higher when the fiber was cooled. To further investigate the effect of cooling on the sensitivity of SPME in field sampling, the portable cold fiber SPME was used for extraction of volatile components from living wisteria flowers. Both the number of identified compounds and the related peak areas increased for extractions with cold PDMS fiber relative to without cooling and commercial PDMS and PA fibers. The portable cold fiber SPME device was also used for field sampling of volatile components of living lily-of-the-valley flowers and the extracted compounds were analyzed with GC/MS. The desorption kinetics of hydrophobic organic compounds (HOCs) from environmental solid matrices was investigated using cold fiber SPME with CO2 cooling. Polycyclic aromatic hydrocarbons (PAHs) and selected volatile organic compounds (i.e. toluene, ethylbenzene, o-xylene) were used as test analytes. Sand, silica gel, and clay were used as laboratory model solid matrices and were contaminated by the test analytes. Certified sediments were used as naturally contaminated samples. In this approach, the organic compounds, released from contaminated solid samples at different elevated temperatures, were exhaustively extracted with cold fiber SPME over different extraction times. The extraction data were used to obtain desorption and Arrhenius plots. The rate constants of desorption and activation energies of desorption were measured for each contaminant using these plots. The results were comparable to those reported in the literature.

M. Tech. Engineering: Mechanical. / Determines the highest energy savings which could be achieved by using variable air ventilation (VAV) strategy in cool processing, without affecting the performance of the cold room.