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.

The backbone of the expanding Information and Communication Technology (ICT)-sector are data centers. In these, Information Technology (IT) equipment is housed which provides computational power for e.g. cloud computing and internet services. Data centers consume massive amount of electricity, estimated to 1% of the global demand. All this power is however not used directly by the IT equipment, to keep the operating conditions in the desired range 21-61% of the electricity is used by the cooling solution. This is mainly due to the extensive use of vapor-compression refrigeration systems (VCRS) which provide a dependable cooling solution that works independent of climate conditions. To get around VCRS the concept of free cooling has been utilized in data centers, this can be done in many ways but the main idea is to introduce a natural cooling source without compromising the operating environment. Previous studies have showed that direct airside economization, i.e. using outdoor air directly in the data center have potential to reduce the energy demand of the cooling solution. This is however directly dependent on the outdoor conditions, by combining direct airside economization with direct evaporative cooling and recirculation of hot air from the IT equipment the cooling solution can handle a wider range of weather conditions and still keep the operating environment in desired conditions. Simulations of similar cooling solutions have been been done by Endo et al. and Ham et al. and showed promising results, but no study of an experimental setup have been published. To test how direct airside economization with direct evaporative cooling technology performs and find its characteristics an experimental setup was constructed, coolers with direct airside economziation and direct evaporative cooling was installed in a data center module at RISE SICS North data center ICE. The setup consisted of 12 racks of OCP Winterfell servers in a hot and cold aisle setup with containment, ducts on the ceiling connected the hot aisle to the coolers and made recirculation of hot air possible. A test schedule was developed to test the cooling solution in two of its four operating modes where the IT-load and setpoint temperatures where adjusted in predefined steps. The IT equipment consumed between 60 - 100kW and the facility power varied between 1.5 - 7kW, which results in a power usage effectiveness (PUE) value between 1.02 and 1.08. Compared to traditional VCRS systems these are very low values. By running the coolers in evaporative cooling mode the PUE was consistently lower compared to ventilation mode, the supply air temperature drop was up to 10°C while in cooling mode. The water consumption, and the corresponding water usage effectiveness (WUE) value was not measured or calculated due to limitations of the test rig that made long tests unstable. Direct airside economization with direct evaporative cooling is not the cooling solution for all data centers in all climates. But if the right conditions are present it is a simple cooling solution that without VCRS or heat exchangers (HEX) shows impressive PUE capabilities. Due to the psychical limitations of the system it can not handle high temperature and/or humidity levels, the data center either needs to be shut down, operated in undesirable conditions or complemented with a separate cooling system to operate in these conditions. To find the limits for this system supply air alteration and removal of exhaust air needs to be implemented. Due to the natural limitations of evaporative cooling combined with the ASHRAE guidelines the technology needs to be further researched to find what climate conditions it can handle. The water consumption which according to previous studies can be substantial also needs to be further studied.

Thesis (Master of Engineering in Electrical Engineering)--Cape Peninsula University of Technology, 2018. / Gas turbines have achieved widespread popularity in industrial fields. This is due to the high power, reliability, high efficiency, and its use of cheap gas as fuel. However, a major draw-back of gas turbines is due to the strong function of ambient air temperature with its output power. With every degree rise in temperature, the power output drops between 0.54 and 0.9 percent. This loss in power poses a significant problem for utilities, power suppliers, and co-generations, especially during the hot seasons when electric power demand and ambient temperatures are high. One way to overcome this drop in output power is to cool the inlet air temperature. There are many different commercially available means to provide turbine inlet cooling. This disserta-tion reviews the various technologies of inlet air cooling with a comprehensive overview of the state-of-the-art of inlet fogging systems. In this technique, water vapour is being used for the cooling purposes. Therefore, the water quality requirements have been considered in this thesis. The fog water is generally demin-eralized through a process of Reverse Osmosis (RO). The drawback of fogging is that it re-quires large amounts of demineralized water. The challenge confronting operators using the fogging system in remote locations is the water scarcity or poor water quality availability. However, in isolated hot areas with high levels of radiation making use of solar PV energy to supply inlet cooling system power requirements is a sustainable approach. The proposed work herein is on the development of a photovoltaic (PV) application for driv-ing the fogging system. The design considered for improved generation of Acaica power plant in Cape Town, South Africa. In addition, this work intends to provide technical infor-mation and requirements of the fogging system design to achieve additional power output gains for the selected power plant.

Research is performed to assess the potential of surface moisture evaporative cooling from composite plates as a means of reducing the external temperature of military aircraft. To assess the feasibility of evaporative cooling for this application, a simplified theoretical model of the phenomenon is formulated. The model consists of a flat composite plate at an initial uniform temperature, T0. The plate also possesses an initial moisture (molecular water) content, M0. The plate is oriented vertically and at t=0 s, one surface is exposed to a free stream of air at an elevated temperature. The other surface is exposed to stagnant air at the same temperature as the plate’s initial temperature. The equations associated with energy and mass transport for the model are developed from the conservation laws per the continuum mechanics hypothesis. Constitutive equations and assumptions are introduced to express the two nonlinear partial differential equations in terms of the temperature, T, and the partial density of molecular water, ρw. These equations are approximated using a weak form Galerkin finite element formulation and the α–family of time approximation. An algorithm and accompanying computer program written in the Matlab programming language are presented for solving the nonlinear algebraic equations at successive time steps. The Matlab program is used to generate results for plates possessing a variety of initial moisture concentrations, M0, and diffusion coefficients, D. Surface temperature profiles, over time, of moisture bearing specimens are compared with the temperature profiles of dry composite plates. It is evident from the results that M0 and D affect the surface temperature of a moist plate. Surface temperature profiles are shown to decrease with increasing M0 and/or D. In particular, dry and moist specimens are shown to differ in final temperatures by as much as 30°C over a 900 s interval when M0 = 30% and D is on the order of 10–8m2/s (T0 = 25°C, h = 60 W/m2°C, T∞ = 90°C).

Water is abundant on earth and in the atmosphere and the most crucial liquid for life as we know it. It has been subject to rather intense research since more than a century and still holds secrets about its molecular structure and dynamics, particularly in the supercooled state, i. e. the metastable liquid below its melting point.  This thesis is concerned with different aspects of water and is written from a theoretical perspective. Simulation techniques are used to study structures and processes on the molecular level and to interpret experimental results. The evaporation kinetics of tiny water droplets is investigated in simulations with focus on the cooling process associated with evaporation. The temperature evolution of nanometer-sized droplets evaporating in vacuum is well described by the Knudsen theory of evaporation. The principle of evaporative cooling is used in experiments to rapidly cool water droplets to extremely low temperatures where water transforms into a highly structured low-density liquid in a continuous and accelerated fashion. For water at ambient conditions, a structural standard is established in form of a high precision radial distribution function as a result of x-ray diffraction experiments and simulations. Recent data even reveal intermediate range molecular correlations to distances of up to 17 Å in the bulk liquid. The barium fluoride (111) crystal surface has been suggested to be a template for ice formation because its surface lattice parameter almost coincides with that of the basal plane of hexagonal ice. Instead, water at the interface shows structural signatures of a high-density liquid at ambient and even at supercooled conditions. Inelastic neutron scattering experiments have shown a feature in the vibrational spectra of supercooled confined and protein hydration water which is connected to the so-called Boson peak of amorphous materials. We find a similar feature in simulations of bulk supercooled water and its emergence is associated with the transformation into a low-density liquid upon cooling. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 4: Manuscript.</p>

Water availability is a common concern in semi-arid regions, such as Southern Arizona, USA. Hydroponic greenhouse crop production greatly reduces irrigation water use, but the study of water use by evaporative cooling has been limited.This project investigated water use by two evaporative cooling systems: pad-and-fan and high-pressure-fog with fan ventilation. All studies were performed in a double-layer polyethylene film-covered greenhouse (28 x 9.8 x 6.3 m) with mature tomato plants (2.9 plants m-2). Water use efficiency (WUE, kg yield per m3 water use) was calculated daily according to ventilation rate, as well as for a 6-month croppipng period, which used temperature-controlled pad-and-fan cooling.Pad-and-fan water use was 3.2, 6.4, 8.5, and 10.3 L m-2 d-1 for ventilation rates of 0.016, 0.034, 0.047, 0.061 m3 m-2 s-1, respectively. High-pressure-fog water use with a single central, overhead line was 7.9, 7.4, and 9.3 L m-2 d-1 for ventilation rates of 0.01, 0.016, 0.034 m3 m-2 s-1, respectively. For pad-and-fan ventilation rates less than 0.034 m3 m-2 s-1, total greenhouse WUE (20 - 33 kg m-3) was similar to field drip irrigation. For the temperature-controlled high-pressure-fog system, total greenhouse WUE (14 - 17 kg m-3) was similar to field sprinkler irrigation.For the 6-month crop cycle, combining water use by closed irrigation and pad-and-fan systems produced a total WUE of 15 kg m-3. Pad-and-fan WUE increased during monsoon conditions due to lower water use rates.Evaporative cooling water use and air temperature were well-predicted by the energy balance model. Predictions of air temperature improved when outside climate the measured conditions at one greenhouse location. Wind tunnel and full-scale studies of natural ventilation demonstrated the value of knowing airflow patterns when designing and operating a high-pressure-fog systemIt is possible for greenhouse tomato production to have a higher WUE than field production, if ventilation rates are not excessive, if closed irrigation is used, and if control methodologies are improved. Water use can be minimized by knowing how the evaporative cooling system affects greenhouse climate and plant responses.

Doctor of Philosophy / Department of Animal Sciences and Industry / Micheal J. Brouk / Four studies were conducted that focused either on silage quality parameters or heat abatement systems to improve cow comfort. Study 1 evaluated the effects of treating whole-plant corn at harvest with a dual-purpose commercial silage inoculant containing Lactobacillus buchneri and Lactococcus lactis O224 on fermentation and aerobic stability of corn silage through 32 d of ensiling. Inoculating silage to be fed after minimal storage time (≤ 32 d post-harvest) had no effect (P > 0.05) on the chemical composition, fermentation variables, aerobic stability or rise in temperature post-harvest. Study 2 was designed to develop a berry processing score (BPS) for sorghum silage as well as evaluate the change in starch digestibility as the level of berry processing increased. A method to evaluate the level of processing in sorghum silage was successfully developed by measuring the percent of starch passing through a 1.7 mm screen. This provides the industry with a standardized method to measure the level of processing in sorghum silage. As BPS increased from 26.28 to 55.05 ± 0.04%, 7-h in situ starch digestibility increased from 50.54 to 82.07 ± 4.94% for unprocessed and heavily processed sorghum silage, respectively (R² = 0.43). By processing sorghum silage during harvest and measuring the extent of processing, sorghum silage starch digestibility can be enhanced and may serve as a viable alternative to corn silage in the diet of lactating dairy cows in areas of the country where corn silage is a high-risk forage crop due to lack of water. Study 3 evaluated the effects of 2 heat stress abatement systems on barn temperature, micro-environmental temperature, core body temperature (CBT), respiration rate, rear udder temperature, and lying time in lactating dairy cows. The systems evaluated were: direct cooling via feedline soakers and fans, or evaporative cooling via a fan and fog system. The evaporative cooling system was effective (P = 0.04) in reducing respiration rates (52.0 vs. 57.9 ± 2.2 breaths per min; P < 0.01) and rear udder temperatures (33.2 vs. 34.5 ± 0.3ºC; P < 0.01), and increased daily lying time (11.8 vs. 10.8 ± 0.3 h/d; P < 0.01) due to differences in barn THI and airflow. No treatment differences (P = 0.79) were detected for CBT, likely due to cooler ambient conditions during the study. Study 4 assessed the effects of the same evaporative and direct cooling systems as in Study 2 but were applied in the holding area prior to afternoon milking, where effects on CBT and micro-environmental temperature in lactating dairy cows were measured in addition to water usage by each system. No significant differences (P > 0.05) between direct cooling and evaporative cooling were detected for micro-environmental THI. However, the evaporative cooling system reduced the consumption of water in the holding area while maintaining CBT < 39.0ºC. Future research should be conducted under greater ambient THI to determine if an evaporative cooling system is able to maintain CBT < 39.0ºC, while also comparing CBT and water usage to a soaker system in the holding area.

Orientador: Vivaldo Silveira Junior / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-24T19:17:01Z (GMT). No. of bitstreams: 1 Oliveira_CintiaCarlaMelgacode_M.pdf: 2012386 bytes, checksum: 17e9e513690eaa1341a66b69e6b22a64 (MD5) Previous issue date: 2014 / Resumo: A busca por equipamentos de refrigeração eficientes e acessíveis é crescente no mercado. Grandes empresas buscam instalar termoacumuladores, armazenamento de energia a baixa temperatura, em suas instalações por fatores econômicos. Com isso, este processo pode ser efetuado em horários fora de pico de energia e ser usado em horário de maior demanda energética, projetando-se então, equipamentos menores para acoplar ao sistema principal e melhorar o dimensionamento do espaço físico. Atualmente, um dos meios utilizado no sistema de resfriamento evaporativo é o uso de bomba de vácuo ou ejetores. Este trabalho tem como objetivo construir e avaliar energeticamente um sistema de resfriamento evaporativo com uso de ejetor, tendo água como fluido que circulará no seu interior, permitindo ser instalado em locais com abundância de água em circulação, perante a substituição ao sistema de resfriamento com uso de dispositivos mecânicos ou geradores. Ejetores são dispositivos usados para arrastar amostras por um jato de um fluido auxiliar, que constam essencialmente de um tubo aspirador e um bocal convergente, alimentando um compartimento convergente-divergente. Após a montagem mecânica e elétrica do sistema, estudou o comportamento do mesmo perante a mudança da vazão volumétrica e da temperatura da água de circulação, temperatura da água de reposição, presença de cavitação e avaliou o coeficiente de desempenho de acordo com as diferentes potências térmicas aplicadas no reservatório de resfriamento. O maior vácuo obtido no reservatório de resfriamento foi de 8,5 kPa nas condições operacionais nominais de 4,1 ± 0,1 m³/h e 5 ± 0,5 °C da água de circulação, atingindo 9,7 ± 0,5 °C a água de resfriamento. Não houve presença de cavitação no bocal do hidroejetor pois a pressão atingida no mesmo não foi inferior a pressão de saturação da água nas condições operacionais da água de circulação. A perturbação gerada, tipo pulso, no reservatório de resfriamento com a reposição da água de resfriamento em diferentes momentos de funcionamento do sistema, não resultou em mudanças expressivas quanto a desestabilidade do vácuo ou do aumento de temperatura no reservatório de resfriamento. O coeficiente de desempenho (COP), avaliado no sistema na maior inserção de potência térmica, 92,27 W pela água de resfriamento, foi de 0,077, sendo subestimado devido a possíveis problemas de eficiência da bomba. O sistema em estudo não foi ideal para resfriamento de fluido a baixas temperaturas nas condições operacionais estudadas, mas pode ser muito bom quando utilizado para resfriamento de fluido a patamares de temperatura maior, podendo ser complementar aos sistemas de refrigeração principal / Abstract: The search for efficient and affordable cooling equipment is increasing in the market. Big companies are always seeking to use thermal storage as a way to storage energy at low temperatures in their facilities due to economic factors. Therefore, this process can be done in off-peak energy periods and the energy stored can be used in times of high demand. This allows the design of smaller equipment, which can be coupled to the main system, improving the design of the physical space. Currently, evaporative cooling is conducted through the use of vacuum pumps or ejectors. This work aimed to construct and evaluate energy evaporative cooling system using an ejector, using water as the inner circulating fluid, which allows it to be installed in places plenty of water circulation, through the replacement of the cooling system using generators or mechanical devices by ejectors systems. Ejectors are devices used to drag samples by a jet of an auxiliary fluid, built essentially with a sniffer and a converging nozzle, which feeds a convergent-divergent compartment. After mechanical and electrical assembly of the system, the behavior of the system was evaluated by changing the volumetric flow rate and temperature of the circulation water, temperature of makeup water and cavitation water. The performance coefficient was also evaluated according to the different thermal inputs applied in the reservoir cooling. The higher vacuum obtained in the cooling tank was 8.5 kPa in a nominal volumetric flow rate of 4.1 ± 0.1 m³/h and circulating water at 5 ± 0.5 °C. In situation, the cooling water reached 9.7 ± 0.5 °C. There was no cavitation observed in hidroejector nozzle, since the pressure reached was not less than the saturation pressure of water in the operating conditions of the circulating water. The disturbance generated, like pulse, in the cooling reservoir with the replacement of the cooling water at different times, did not result in significant changes in vacuum destabilization or in the temperature rising in the cooling reservoir. The coefficient of performance (COP), evaluated at the greater inclusion of thermal power for cooling water (92.27 W) was 0.077. This value was underestimated due to problems of pump efficiency. The system studied was not ideal for cooling fluids at low temperatures the studied operating conditions, but it can be good enough when used for cooling fluids with higher temperatures, which may be complementary to the main refrigeration systems / Mestrado / Engenharia de Alimentos / Mestra em Engenharia de Alimentos

The sample used for evaporative cooling system is Fabric defender 750 with Shelltite finish. From the experimental data and equations we have diffusion coefficient of 20.9 ± 3.71 x 10-6 m2/s for fabric with one layer with 17%-20% fluctuations from the theory, 27.8 ± 4.5 x 10-6 m2/s for fabric with two layers with 6%-14% fluctuations from the theory and 24.9 ± 4.1 x 10-6 m2/s for fabric with three layers with 13%-16% fluctuations from the theory. Since the thickness of the fabric increases so the mass transport rate decreases so the mass transport resistance should be increases. The intrinsic mass resistances of Fabri-1L, Fabri-2L and Fabri-3L are respectively 104 ± 10.2 s/m, 154 ± 23 s/m and 206 ± 26 s/m from the experiment.

In Gulf Cooperation Council (GCC) countries, a lack of freshwater, poor soil quality, and ambient temperatures unsuitable for cultivation for parts of the year hinders domestic agriculture. The result is a reliance on a fluctuating supply of imported fresh produce which may have high costs and compromised quality. There are agricultural technologies available such as hydroponics and controlled environment agriculture (CEA) that can allow GCC countries to overcome poor soil quality and ambient temperatures unsuitable for cultivation, respectively. Evaporative cooling is the most common form of cooling for CEA and requires a significant amount of water. In water-scarce regions, it is desirable for sea or brackish water to be used for evaporative cooling. Unfortunately, in many coastal desert regions, evaporative cooling does not provide enough cooling due to the high wet-bulb temperature of the ambient air during hot and humid months of the year. A liquid desiccant dehumidification system has been proven to lower the wet-bulb temperature of ambient air in the coastal city of Jeddah, Saudi Arabia to a level that allows for evaporative cooling to meet the needs of heat-sensitive crops. Much of the past research on the regeneration of the liquid desiccant solution has been on configurations that release water vapor back to the atmosphere. Studies have shown that the amount of water captured by the liquid desiccant when used to dehumidify a greenhouse can supply a significant amount of the water needed for irrigation. This thesis studied the regeneration of a magnesium chloride (MgCl2) liquid desiccant solution from approximately 20 to 31wt% by direct contact membrane distillation and explored the possibility of using the recovered water for irrigation. Two microporous hydrophobic PTFE membranes were experimentally tested and modeled when the bulk feed and coolant temperature difference was between 10 and 60°C. In eight experiments, the salt rejection was higher than 99.97% and produced permeate suitable for irrigation with a concentration of MgCl2 less than 94 ppm.