Dissertations / Theses on the topic 'Evaporative Coolers'

Thesis (MEng.) -- Stellenbosch University, 1988.<br>ENGLISH ABSTRACT: In this report various mathematical models for the thermal evaluation of evaporative coolers and condensers are presented. These models range from the exact model based on the work by Poppe [84P01] to the simplified logarithmic models based on the work of McAdams [54Mcl] and Mizushina et al. [67MI1], [68MI1]. Various computer programs were written to perform rating and selection calculations on cross-flow and counterflow evaporative coolers and condensers. Experimental tests were conducted on a cross-flow evaporative cooler to determine the governing heat and mass transfer coefficients. The experimentally determined coefficients were cqrrelated and these correlations are compared to the existing correlations. The two-phase pressure drop across the tube bundle was also measured and a correlation for two-phase pressure drop across a tube bundle is presented.

2 pp.<br>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.

In developing countries about 40 % of the food-waste is due to post-harvest losses, such as improper storage. The Zeer-pot is an evaporative cooler, which cools the inside by convective heat transfer, and can be used to keep fruits and vegetables fresh longer. This is typically convenient in hot rural areas without access to electricity and is more efficient in non-humid areas. This study will investigate if there is a correlation between the temperature decrease inside the pot and the wind velocity, how the efficiency of the Zeer-pot is affected by hanging it in the air to additionally expose the underside to the airflow and also how the efficiency is affected from glazing of the inner pot, to prevent the food from getting damaged from high humidity. It will also consider the feasibility of combining the Zeer-pot with a solar dryer, also to improve its efficiency. The evaporation is increased by higher wind velocity due to forced convection. A solar dryer can create an airflow when the heated air rises along the surface of the solar collector and creates a temperature difference between the upper and the lower part. A design for a solar dryer that could be appropriately integrated with a Zeer-pot to achieve a greater airflow around it is modelled in CAD and presented. The tests on the pots took place in a climate chamber where the ambient temperature was controllable. In the climate chamber a fan and a dehumidifier was installed in order to create wanted conditions. One pot was tested only for wind velocities and the other only for the cases of the pot hanging in the air and being glazed on the inside. A reference case was designed and tested for the second pot in order to compare the glazed and hanging pot in the same conditions. The relative humidity was not controllable in this setup, and thereof a way to compare these results was to calculate the final temperature the pot achieved relative to the lowest possible theoretical temperature, the wet bulb temperature. For the first pot an almost linear correlation between the time it took to reach the final temperature depending on the wind velocities could be observed, apart from two values. A rather nice coherent curve, also apart from two values, was found for how close to the wet bulb temperature the final temperature was depending on the wind velocity. For the second pot the cooling capacity was enhanced for both the hanging construction and the glazed pot. For the hanging pot this was expected, but for the glazed one it was not. If a solar dryer is combined with the Zeer-pot, a wind velocity around 3-3.5 m/s is guaranteed to improve the Zeer-pots cooling capacity. A lower wind velocity could probably make a large difference too, but the experiments in this study is insufficient to make any conclusions.<br>I utvecklingsländer beror cirka 40 % av matavfallet på förluster efter skörd, till exempel felaktig förvaring. En Zeer-pot är en evaporativ kylare som kyls med hjälp av konvektion och kan användas för att öka livslängden på frukter och grönsaker. Den är användbar i områden utan tillgång till elektricitet där klimatet är varmt och behovet för kylning är stort. Kyleffekten förbättras i ett klimat med låg luftfuktighet. Denna studie kommer att undersöka om det finns ett samband, mellan temperatursänkningen och vindhastigheten. Ett sätt att förbättra kyleffekten skulle kunna vara att konstruera någon form av stöd för att göra det möjligt för krukan att hänga i luften, detta för att även undersidan ska utsättas för luftflödet. För att inte låta fukten som skapas vid evaporationen komma in i innerkrukan där maten förvaras kan innersidan glaseras. Hur mycket dessa justeringar kommer att påverka kylkapaciteten undersöks också i denna studie. Krukan kyls med hjälp av evaporation av vatten och denna ökar vid en högre vindhastighet på grund av påtvingad konvektion. Ett sätt att skapa ett större luftflöde runt krukan är att integrera en soltork med den så kallade Zeer-poten. Soltorken skapar ett luftflöde då en temperaturskillnad mellan den övre och den undre delen får värmen att stiga upp från ytan av solfångaren. En hypotetisk modell av en lämplig soltork modelleras i CAD och presenteras. För att se en korrelation för hur ökade vindhastigheter påverkar temperatursänkningen i grader och hur fort sluttemperaturen uppnås gjordes tester på samma kruka i så i övrigt konstanta förhållanden som praktiskt var möjligt. Testen för de olika krukorna ägde rum i en klimatkammare där luftens temperatur gick att kontrollera. En fläkt och en avfuktare var installerade. Den ena krukan testades för fallet med olika vindhastigheter och den andra för den upphängda krukan och för glaseringen på insidan. Ett referensfall gjordes även för att jämföra den andra krukans två fall separat. Den relativa fuktigheten gick inte att kontrollera i klimat-kammaren och därav fick resultaten jämföras genom en framräknad procentsats. Procentsatsen visade hur långt testets sluttemperatur hade sjunkit i förhållande till den våta temperaturen. En nästan linjär korrelation, med undantag för två värden, mellan tiden det tog att nå sluttemperaturen i förhållande till vindhastigheten kunde observeras. Ett tydligt samband, också undantaget från två värden, kunde observeras mellan den våta temperaturen och den uppnådda temperaturen för olika hastigheter. För den andra krukan ökade kylkapaciteten för både den hängande konstruktionen samt den glaserade krukan. Det var väntat för den hängande konstruktionen, men inte för den glaserade. Om en soltork kombineras med Zeer-poten i syfte att märkbart förbättra dess kylkapacitet, skulle ett luftflöde med en vindhastighet kring 3-3,5 m/s garanterat fungera. Lägre vindhastigheter lär även de kunna påverka krukan nästan lika mycket, men tyvärr är resultaten från experimenten inte tillräckliga för att dra några slutsatser om detta.

The aims of the research work described in this thesis were to use computational fluid dynamics (CFD) to investigate the factors affecting the performance of a multi-stage downdraught evaporative cooling device for low-energy cooling of buildings developed from a novel prototype device described by Erell et al. (2008) and Pearlmutter et al. (2008); and to model and explore the performance of the device when integrated within a hypothetical, but representative, building in a hot dry climate. The research work was carried out with initial objectives of: understanding and modelling water spray evaporation using CFD methods; verifying the CFD model of water spray evaporation using published experimental data; modelling and examining the spray characteristics of the nozzles used in the work by Erell et al. and Pearlmutter et al.; creating a detail model of the prototype multi-stage downdraught evaporative cooling device described by Erell et al. and Pearlmutter et al.; carrying out a series of CFD simulations of the prototype device under wind-driven operation with and without water sprays and comparing the results obtained with available experimental data. Following completion of these initial studies, a detailed investigation of the factors affecting the performance of a multi-stage cooling device derived from the prototype device was carried out. This involved carrying out simulations: to select the most effective wind catcher geometry; to optimize the number and arrangement of water spray nozzles; and to select a range of geometrical parameters. Following completion of these additional studies a model of a two-floor hypothetical building with an integrated multi-stage downdraught evaporative cooling device of optimum geometry and a wind catcher was created, and simulations to investigate the performance under varying wind speeds and environmental conditions were carried out. All simulations were carried out using ANSYS CFX, versions 12.0, or 12.1 or 13.0. The results obtained indicated that comfortable conditions within the cooled space could be achieved over almost all of the range the wind speeds and environmental conditions studied. Some recommendations for future work are given.

Asthma is the leading chronic illness in children in the United States. Since children in the U.S. spend a majority of their time indoors there is an increased need to understand key sources of daily asthma triggers in the home. Bacterial endotoxin, dust mite allergens and β-D-glucan have been shown to be potent inducers of asthma attacks, and high levels of these allergens in homes can trigger attacks in those with asthma. We aim to better understand the risks to those with asthma that might be associated with evaporative cooler (EC) use in low-income homes. ECs are often promoted because of their low energy consumption and decreased environmental impact compared to central air conditioning (AC). Because of their lower cost, ECs are more widely used in low-income homes. ECs use evaporation to cool the air, which leads to higher indoor relative humidity. This may create an ecological niche for house dust mites in semi-arid climates where they are normally absent. EC sump water also provides an ideal environment for bacteria and fungi to grow, possibly resulting in EC loading the air with more potential asthma triggers than central air conditioning. We sampled low-income homes around Utah county with central air and evaporative cooling and tested them for the presence of dust mite allergens, β-D-glucan and endotoxin. There were significantly higher levels of endotoxins and β-(1→3)-D-glucans in the EC homes compared to the AC homes, with increased odds of dust mite allergen prevalence but not at clinically significant levels. These findings suggest that in semi-arid environments, endotoxin and β-(1→3)-D-glucan levels in homes with evaporative coolers are more elevated than dust mite allergens.

Proton Exchange Membrane Fuel Cells (PEMFCs) present a promising alternative to the conventional internal combustion engine for automotive applications because of zero harmful exhaust emissions, fast refuelling times and possibility to be powered by hydrogen generated through renewable energy. However, several issues need to be addressed before the widespread adoption of PEMFCs, one such problem is the removal of waste heat from the fuel cell electrochemical reaction at high ambient temperatures. Automotive scale fuel cells are most commonly liquid cooled, evaporative cooling is an alternative cooling method where liquid water is added directly into the fuel cell flow channels. The liquid water evaporates within the flow channel, both cooling and humidifying the cell. The evaporated water, along with some of the product water, is then condensed from the fuel cell exhaust, stored, and re-used in cooling the fuel cell. This work produces a system level model of an evaporatively cooled fuel cell vehicle suitable for the study of water balance and heat exchanger requirements across steady state operation and transient drive cycles. Modelling results demonstrate the ability of evaporatively cooled fuel cells to self regulate temperature within a narrow region (±2°C) across a wide operating range, provided humidity is maintained within the flow channels through sufficient liquid water addition. The heat exchanger requirements to maintain a self sufficient water supply are investigated, demonstrating that overall heat exchange area can be reduced up to 40% compared to a liquid cooled system due to the presence of phase change within the vehicle radiator improving heat transfer coefficients. For evaporative cooling to remain beneficial in terms of heat exchange area, over 90% of the condensed liquid water needs to be extracted from the exhaust stream. Experimental tests are conducted to investigate the condensation of water vapour from a saturated air stream in a compact plate heat exchanger with chevron flow enhancements. Thermocouples placed within the condensing flow allow the local heat transfer coefficient to be determined and an empirical correlation obtained. The corresponding correlation is used to produce a heat exchanger model and study the influence different heat exchanger layouts have on the overall required heat transfer area for an evaporatively cooled fuel cell vehicle. A one-dimensional, non-isothermal model is also developed to study the distribution of species, current density and temperature along the flow channel of an evaporatively cooled fuel cell using different methods of liquid water addition. Results show that good performance can be achieved with cathode inlet humidities as low as 20%, although some anode liquid water addition may be required at high current densities due to increased electro-osmotic drag. It is also demonstrated that both good membrane hydration and temperature regulation can be managed by uniform addition of liquid water across the cell to maintain a target exhaust relative humidity.

Worldwide energy demand in buildings represents about 40-50% of the total energy consumption. In hot climates, such as Middle East and North Africa (MENA) countries, about 30% of the national power demand is used for HVAC applications in buildings. This has led to escalation in power demand in buildings for indoor air-cooling and high energy bills. This is exacerbated further by the widespread adoption of energy intensive and commercially dominant vapour compression air conditioning systems as the technology of choice. This research aims to address the potential of novel designs of evaporative cooling systems for space cooling and thermal comfort in buildings with reduced water and energy consumption, and low environmental impact as an alternative to vapour compression where climatically is suitable. High water consumption rates and low cooling effectiveness are some of the issues affecting the performance of existing Indirect Evaporative Coolers (IEC). A new configuration of IEC combining heat pipe heat exchanger and porous ceramic tubes is investigated in this work. The proposed cooler configuration is based on the concept of regenerative IEC system, this system incorporates heat pipes as passive heat transfer elements and porous ceramic tubes as wet medium mounted on the condenser side of the exchanger. The design of the cooler was carried out with consideration for size of the airflows channels, heat pipes for heat transfer, and porous ceramic tubes properties for water evaporation. A mathematical formulation of heat and mass transfer equations was used to develop a computer model to design and optimise the cooling system. Furthermore, a test rig was built to test a laboratory scale cooling unit, evaluate the performance and validate the simulation. The simulation results reveal that the Wet-bulb (WB) effectiveness of the cooler ranged from 0.524 to 1.053, the COP ranged from 6.33 to 17.01, and water consumption rates of the cooler were around 0.875-1.55 (l/kWh) of cooling capacity. Whereas, the experimental performance parameters of the cooler show the WB effectiveness was in the range of 0.422-0.908 for all test conditions, the COP was 4.62-13.16, and water consumption rates varied 0.841-2.82 (l/kWh) of cooling capacity. A good agreement was obtained between the experiments data and numerical results, the maximum errors between measured and computed results was around 3.94% and 4.51% of supply air temperature and humidity, respectively, while the discrepancy was in the range of 8.67-12.90% of the WB effectiveness. The impact of operational and design parameters on the cooler performance was evaluated in a parametric study using the developed numerical model. It was found that increasing the inlet air temperature, decreasing the inlet air flow rate, and/or increasing the working-to-inlet air flow ratio, results in improving the effectiveness and supply air temperature. Whereas, increasing the inlet air wet-bulb temperature depression, increasing the inlet air flow rate, and/or minimising the working-to-inlet air flow ratio leads to enhancing the cooling output and COP of the cooler. Additionally, increasing the thickness and/or the radius of ceramic tube causes a decline of cooler thermal performance. Therefore, it is recommended to operate the cooler at inlet air velocity of 2-2.5 m⁄s, 50% flow ratio of working-to-inlet air, and inlet air relative humidity below 35% for best results of supply air temperature, WB effectiveness, and COP. Whereas, for desert climate conditions, it is recommended to increase the number of heat pipe rows to 20 to insure sufficient cooling effectivity and performance that meet comfort levels. Finally, a brief economic assessment of the cooler annual operational performance for a case study was carried out, this IEC system provide sufficient cooling effectiveness to the conditioned space with significantly low power consumption compared to traditional air conditioner with annual saving of 77.60% of operational costs, and also substantially contribute to minimise CO2 emissions by saving about 86% of electricity consumption.

The polymer electrolyte membrane fuel cell is being proposed for a number of power generation systems. With regard to replacing conventional technologies, they offer many advantages including quiet operation with low emissions. However, the key issue for the success of fuel cell system will be a superior operational efficiency. The associated subsystems for controlling fuel cell stack thermal and water management contribute significantly to the reduction in stack weight and volume and increase the associated operational parasitic losses. In this thesis a novel fuel cell operational method has been proposed which utilises a combined humidification and cooling mechanism based on the direct injection of liquid water to the cathode flow-field. Several analyses were performed to investigate critical issues for the workable concept of such an EC, or evaporatively cooled, fuel cell system.

This diploma thesis deals with the use of adiabatic cooling for the improvement of microclimate of large-scale tents in Czech climatic conditions, specifically in city of Rožnov pod Radhoštěm. First part thesis is the design of a universal calculation tool for calculating the heat load of two types of large-scale tents. This tool was used to design and construct the suitable mobile trickle adiabatic cooler. The experimental part is focused on the finding of suitable material to be used to as filling of trickle adiabatic cooler and further testing it.

Increasing energy use has caused many environmental problems including global warming. Energy use is growing rapidly in developing countries and surprisingly a remarkable portion of it is associated with consumed energy to keep the temperature comfortable inside the buildings. Therefore, identifying renewable technologies for cooling and heating is essential. This study introduced applications of steel sheets integrated into the buildings to save energy based on existing technologies. In addition, the proposed application was found to have a considerable chance of market success. Also, satisfying energy needs for space heating and cooling in a single room by using one of the selected applications in different Köppen climate classes was investigated to estimate which climates have a proper potential for benefiting from the application. This study included three independent parts and the results related to each part have been used in the next part. The first part recognizes six different technologies through literature review including Cool Roof, Solar Chimney, Steel Cladding of Building, Night Radiative Cooling, Elastomer Metal Absorber, and Solar Distillation. The second part evaluated the application of different technologies by gathering the experts’ ideas via performing a Delphi method. The results showed that the Solar Chimney has a proper chance for the market. The third part simulated both a solar chimney and a solar chimney with evaporation which were connected to a single well insulated room with a considerable thermal mass. The combination was simulated as a system to estimate the possibility of satisfying cooling needs and heating needs in different climate classes. A Trombe-wall was selected as a sample design for the Solar Chimney and was simulated in different climates. The results implied that the solar chimney had the capability of reducing the cooling needs more than 25% in all of the studied locations and 100% in some locations with dry or temperate climate such as Mashhad, Madrid, and Istanbul. It was also observed that the heating needs were satisfied more than 50% in all of the studied locations, even for the continental climate such as Stockholm and 100% in most locations with a dry climate. Therefore, the Solar Chimney reduces energy use, saves environment resources, and it is a cost effective application. Furthermore, it saves the equipment costs in many locations. All the results mentioned above make the solar chimney a very practical and attractive tool for a wide range of climates.

Terracotta vessels are about understanding how we can store food by using a new product solution and how we could use less energy and waste less food in doing so. This project is an attempt to minimise the energy usage in our homes but also to gain greater understanding about the food we choose to bring into our homes and what we can do to avoid throwing it away.

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.

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.

碩士<br>國立臺北科技大學<br>能源與冷凍空調工程系<br>106<br>This study investigates the heat and mass transfer and pressure drop performance characteristics of an evaporative cooler using elliptic tube, and compare with circular tube one. From the experimental results, correlations for the water film heat transfer coefficient and air-water mass transfer coefficient are developed. The circular tube is 15.88 mm o.d., and the elliptic tube (axis ratio 0.5) is formed from a 15.88 mm o.d. circular tube whose perimeter is the same. Both tubes are investigated under the same operating conditions. The air inlet velocity varied from 0.94 to 3.73 m/s, and the spray water flow rate varied from 10 to 40 L/min on a tube bundle of 600mm long by 266mm wide cross section. The inlet hot water temperature is 45℃, and the hot water flow rate is 23.7 L/min. The experimental results show that the pressure drop of elliptic tube is lower than the circular one at various spray water flow rates. The lower contraction ratio of circular tube bundle results in higher air velocity between the bundle, and increases the fluid film waviness with water spraying outside the tubes. Consequently, it also affects the heat and mass transfer performance. The surge of pressure drop at the air velocity about 2.7 m/s is more obvious at the circular tube bundle than the elliptic one. Both the water film heat transfer coefficient and air-water mass transfer coefficient of elliptic tube and circular tube increase with increasing air Reynolds number. The heat and mass transfer performance of the circular tube bundle is better than the elliptic one. However, comparing the thermal-hydraulic performance of elliptical tube with circular tube, the elliptic shows higher j/f. At a fixed spray water flow rate of 25 LPM, the j/f of elliptic tube is 1.38 to 2.54 times of circular tube at various fan frequency.

Submitted in fulfilment of the requirements of the egree of Master of Technology: Chemical Engineering, Durban University of Technology, 2011.<br>The South African electroplating industry generates large volumes of hazardous waste water that has to be treated prior to disposal. The main source of this waste water has been the rinse system. Conventional end-ofpipe waste water treatment technologies do not meet municipality standards. The use of technologies such as membranes, reverse osmosis and ion exchange are impractical, mainly due to their cost and technical requirements. This study identified source point reduction technologies, close circuiting of the electroplating process, specific to the rinse system as a key development. Specifically the application of a low flow counter current rinse system for the recovery of the rinse water in the plating bath was selected. However, the recovery of the rinse tank water was impeded by the low rates of evaporation from the plating bath, which was especially prevalent in the low temperature operating plating baths. This master’s study proposes the use of an induced draft evaporative cooling tower for facilitation of evaporation in the plating bath. For total recovery of the rinse tank water, the rate of evaporation from the plating bath has to be equivalent to the rinse tanks make up water requirements. A closed circuit plating system mathematical model was developed for the determination of the mass evaporated from the plating bath and the cooling tower for a specified time and the equilibrium temperature of the plating bath and the cooling tower. The key criteria in the development of the closed circuit plating system model was the requirement of minimum solution specific data as this information is not readily available. The closed circuit plating system model was categorised into the unsteady state and steady state temperature regions and was developed for the condition of water evaporation only. The closed circuit plating system model was programmed into Matlab and verified. The key factors affecting the performance of the closed circuit plating system were identified as the plating solution composition and operational temperature, ambient air temperature, air flow rate and cooling tower iv packing surface area. Each of these factors was individually and simultaneously varied to determine their sensitivity on the rate of water evaporation and the equilibrium temperature of the plating bath and cooling tower. The results indicated that the upper limit plating solution operational temperature, high air flow rates, low ambient air temperature and large packing surface area provided the greatest water evaporation rates and the largest temperature drop across the height of the cooling tower in the unsteady state temperature region. The final equilibrium temperature of the plating bath and the cooling tower is dependent on the ambient air temperature. The only exception is that at low ambient air temperatures the rate of water evaporation from the steady state temperature region is lower than that at higher ambient air temperatures. Thus the model will enable the electroplater to identify the optimum operating conditions for close circuiting of the electroplating process. It is recommended that the model be validated against practical data either by the construction of a laboratory scale induced draft evaporative cooling tower or by the application of the induced draft evaporative cooling tower in an electroplating facility.

碩士<br>國立臺北科技大學<br>能源與冷凍空調工程系<br>107<br>In this study, respective mathematical models are built through simulating the thermal mass transfer characteristics of the elliptic tube and the round tube evaporative cooler, and further compare the deviations of the total heat load. Discuss the effect of the main variables on temperature changes and trends between the pipe arrays within the closed cooling tower, such as: the external air temperature, the spray flow rate, and the hot water flow in the tube. The simulation results showed that the Total Thermal Load Deviations between prediction and experiment fell in 10% to 20% regardless of the wind speed. Compare different parameter effects – it shows that either parameters of the external air inlet temperature influences the air temperature, the spray temperature, and the water temperature inside the tube, regardless of it is a circular tube or an elliptical tube array. The air temperature outside the pipe and the temperature of the spray water will affect the ratio of sensible heat to latent heat, which carries the heat load from within the pipe as the inlet air temperature rises. When the inlet temperature is high, the heat load within the pipe is carried away through the latent heat by heat absorbing. From the results we can understand that due to less spacing of the round pipe arrays comparing to elliptic pipe arrays, the sprinkling water tends to stay on the outer wall of the tube array for a longer period of time when the inlet wind speed is ≥ 2.7 m/s, therefore resulting in a higher pressure loss and the better mass transfer effect when the round pipe array is chosen. The same trend is as well proven through the simulation.

碩士<br>國立臺北科技大學<br>能源與冷凍空調工程系碩士班<br>95<br>This study investigates the evaporation phenomena of a cross-flow evaporative cooler, in which the wet durable honeycomb paper, having 8.777 mm hydraulic diameter, constitutes as packing material. The evaporative cooling system is expected to act as both humidifier and cooler to create a comfortable indoor environment. Heat transfer rates and mass transfer coefficients are experimentally obtained for the evaporative cooling process at various packing thickness and frontal area, water and air flow rates. The air side Reynolds number varies between 220 and 1600, and the water mass velocity varies between 0.25 and 0.52 kg/sm2. The experimental results show that for the embient air dry ball temperature at about 30℃ the evaporative cooler reduces the air dry-ball temperature by about 7~11℃ and the relative humidity increases approximately 20~33%. The mass transfer coefficient increases as the air flow rate or water flow rate increases. The effectiveness of the evaporative cooler increases as increasing air flow rate, and it decreases as the water flow rate increases. These data are nondimensionalized and curve fitted to yield a correlation of the mass transfer coefficient, which fits the present data within +-20%.

碩士<br>國立臺北科技大學<br>能源與冷凍空調工程系碩士班<br>101<br>Retrofitting of a mist device in the air-cooled air conditioning system has the most direct effect on energy conservation. This study investigated the overall performance of applying the air-cooled variable refrigerant flow system in evaporative cooling and air cooling. Under the experimental conditions, this study compared the evaporative cooling, the air cooling and other cooling methods. It also analyzed the power consumption, system operational effect and COP to confirm the system operational effect and output performance. The results showed that the application of water mist for evaporative cooling in the multi-joint variable refrigerant system can effectively reduce the compressor discharge temperature, and extend compressor life. Moreover, the evaporative cooling can make the target evaporation temperature more consistent with the actual evaporation temperature of the multi-joint variable refrigerant system to ensure the cooling capacity needed for the overall operation and thus make the system operation more stable. In terms of the overall power consumption performance, the evaporative cooling can reduce the system compressor power consumption by 10.78% and overall power consumption by 9.02%, and increase the overall COP by 6.09%. Hence, the application of evaporative cooling in the multi-joint variable refrigerant system can improve operational efficiency, reduce energy consumption, extend compressor service life and reduce the cost of use.

Energy is a basic necessity shared by all living things on the planet, much like water, food, and shelter so we need to save energy and protect our mother earth. The recent increase in awareness of global warming has rekindled the hunt for environment friendly refrigerants that have a lower impact on global warming and zero ozone depletion effect. The aim of this study is to examine how a spray evaporative cooling system can improve the efficiency of an air-cooled scroll chiller in a tropical climate region. To achieve this, the study involves the design selection and simulation of a fin and tube type heat exchanger, as well as theoretical investigation that combines a spray evaporative cooling system with the air-cooled scroll chiller in the Fin and tube type heat exchanger. According to the theoretical results, the addition of the spray evaporative cooling system to the air-cooled chiller led to a reduction in compressor power consumption and an increase in the COP (Coefficient of Performance) of the chiller, ranging from 6.25% to 18.66%. Additionally, the use of the spray cooling system resulted in power savings of 6.36% to 17.26% in air-cooled chiller systems. To further improve the COP of the air cooled chiller, it is suggested to use a more appropriate spray evaporative cooling mode, such as adjusting the water flows based on the cooling capacity and positioning the cooling pads at appropriate distance from condenser. Certain design constraints are addressed, as well as several methods for improving system functionality for future optimization.

碩士<br>國立臺北科技大學<br>能源與冷凍空調工程系碩士班<br>98<br>In the present study, we retrofitted an indirect device module with air conditioning facilities to conduct an experiment. Analyzing the experimental results, we investigated the heat transfer efficiency and saturation efficiency of device module, and compared it with operating efficiency of air-cooling. This experiment was divided into two modules, and discussed the influence of the front nozzle pressure and row quantity of tubes heat transfer efficiency and saturation efficiency. The water pressures of the front nozzle are 0.15、0.2 and 0.3MPa,respectively,and the row quantities of tube row Nozzle are 1 ~ 3 rows. The experimental results show that higher pressure in front nozzle induces higher heat transfer and saturation efficiency, and condenser inlet temperature is decrease, which enhances the capacity of the condenser. Moreover, the power consumption of cross-flow is lower than that of air-cooled by 12.5~36.1%, the Condensing capacity of cross-flow is higher than that of air-cooled by 13.6~55.0%, the COP of cross-flow is higher than that of air-cooled by 16.9~66.9%, the power consumption of reverse-flow is lower than that of air-cooled by 9.4~38.0%, the Condensing capacity of reverse-flow is higher than that of air-cooled by 6.5~36.1%, and the COP of reverse-flow is higher that than air-cooled by 9.3~72.9%.

碩士<br>國立臺北科技大學<br>冷凍與低溫科技研究所<br>100<br>In this study, heat and mass transfer analysis by air and water, and ε-NTU method were used to analyze the performance of the loofah fiber modules applied to indirect evaporatively cooled device. The thickness of respectively, the modules were 5, 10 and 15 cm. Because the loofah fiber module can absorb water and keep its surface moist, it can cause heat and mass transfer phenomenon by the pressure of water molecules and the temperature difference as air flow through the indirect evaporatively-cooled device. The module was installed in front of an air-cooled condenser for energy improvement experiment. Water was sprayed on different thickness of materials. As air flow though it, the module caused evaporative cooling, and heat and mass transfer phenomenon, so that the air temperature decreased. As the air entered the fin tube condenser immediately, the condenser performance was improved, and air conditioning power consumption was reduced. In the measurement results, 15 cm thick of loofah fiber module had better performance, with maximum temperature difference of 2.95 ℃ in a day, effectiveness of ε (cooling efficiency) of 55%, and number of transfer(NTU) of 0.8%; the next was 10 cm thick loofah fiber module. In actual measurement and ε-NTU calculation, the heat transfer coefficient(h_C), mass transfer coefficient(h_m), the total area of the material wet (A_s)and all kinds of heat transfer data was obtained. By analyzing the actual measurement to analyze the performance of the different thickness of loofah fiber module, the best design and size were obtained in this study.