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Microalgae feedstocks for aviation fuels
Published in Emily S. Nelson, Dhanireddy R. Reddy, Green Aviation: Reduction of Environmental Impact Through Aircraft Technology and Alternative Fuels, 2018
Mark Rumizen, Andre M. Coleman, Erik R. Venteris, Richard L. Skaggs
The water temperature within shallow microalgae cultivation ponds is bounded by the principle of the conservation of energy within a fluid volume and is thus influenced by pond water depth, water density (which varies by level of salinity), the specific heat of water, and net surface heat-flux, including net solar shortwave radiation, downward atmospheric longwave radiation, longwave back radiation, and heat flux due to evaporation and conduction, that are driven by meteorological variables including air temperature, wind, and relative humidity. Open pond systems are subject to dominant control from environmental conditions barring engineered solutions, such as industrial waste heat via heat exchangers during cool temperature months or the introduction of cool makeup water into the ponds during warm months to help keep pond temperatures at the optimum for the algae strain. As noted previously, the water temperature in an open pond will be impacted by large diurnal swings in air temperature but also by the degree to which evaporative cooling takes place. For example, in humid regions, evaporative cooling is much less effective due to the reduced ability of the air to absorb additional water vapor and thus creates a reduced rate of heat exchange through the liquid-to-gas phase change. Because of the thermal properties of water, the water temperature will respond to air temperatures with varying degrees of latency and dampening.
Passive Cooling Systems
Published in Pablo La Roche, Carbon-Neutral Architectural Design, 2017
In the broadest sense, the term evaporative cooling applies to all processes in which the sensible heat in an air stream is exchanged for the latent heat of water droplets or wetted surfaces. Evaporative cooling uses the local atmosphere as a heat rejection resource. The amount of heat absorbed in the process of water evaporation (its latent heat) is very high compared with the other modes of heat transfer, which are common in buildings. This process is adiabatic, which means that no energy is gained or lost. The sensible temperature is reduced with a gain in humidity. When moisture is added to the air, its absolute humidity increases while dry-bulb air temperature decreases. The evaporation of water is the basis of passive cooling systems such as the mechanical evaporative cooler, and on a psychrometric chart, this pattern follows the wet-bulb line upward to the left. There are several systems to produce evaporative cooling, and they usually involve a tower to produce the necessary height to evaporate the water and produce cool air or a pond. In hot and dry climates, evaporative cooling also increases thermal comfort because it brings the DBT closer to the comfort zone. In warm and humid climates, the increase in RH is not beneficial because conditions are then usually even more uncomfortable.
Environmental Functions of Roofs
Published in Simos Yannas, Evyatar Erell, Jose Luis Molina, Roof Cooling Techniques a Design Handbook, 2013
Simos Yannas, Evyatar Erell, Jose Luis Molina
A measure of the potential for evaporative cooling is the wet-bulb temperature depression. This is the difference between the dry-bulb and wet-bulb temperatures. Figure 1.18 shows the daily profile of this parameter for a typical summer day in Athens. Unlike the radiative cooling potential which peaks at night, evaporative cooling has its peak during the daytime whilst continuing to have a useful potential at night. Figure 1.19 illustrates the variation of 24-hour degree hours of wet-bulb depression for the summer period across parts of Europe. It can be seen that the largest potential is in the Mediterranean region. Clearly, the application of evaporative cooling is most appropriate in hot and dry climates.
Experimental investigation on use of alternative innovative materials for sustainable cooling applications
Published in International Journal of Sustainable Engineering, 2021
Sampath Suranjan Salins, S.V. Kota Reddy, Shiva Kumar
Evaporation trend for different mass flow rate is shown in Figure 10. Evaporation rate is defined as the rate at which material evaporates or vaporises. In other words, it is a change from liquid to vapour phase. Evaporative cooling happens when air encounters the liquid and liquid absorbs the latent heat there by converting into the vapour form. During this time, air temperature drops and hence it gets cooled. Figure 10 indicates that the evaporation rate is directly proportional to the mass flow rate of air. As there is an increase in mass flow rate, there is a rise in evaporation rate. From the experimental results, it is found that the evaporation rate is maximum in the case of coconut coir compared to wood shaving and standard cellulose packing in both counter and cross flow types. Cellulose exhibited the lowest evaporation rate. Inherent characteristics of wood shaving like long coiled porous structure compared to the long fibres with higher water holding capacity have made wood shaving as a better option for evaporative cooling pads. Increases in the evaporation rate with wood shaving and coconut coir are 54% and 47% with respect to Celdek packing under counter flow conditions. Similarly, these values are 63% and 51% higher for cross flow conditions. The low value of evaporation rate yielded high value of specific cooling capacity for cellulose and wood shaving type of packings. These figures will indicate the higher suitability of wood shaving as an alternative pad material in evaporative coolers as compared to Celdek material.
Utilization of an evaporative air cooler to achieve thermal comfort in Thailand
Published in Building Research & Information, 2021
In Thailand, energy consumption in residential buildings has increased by 22% since 2011 (Energy Policy and Planning Office, 2018), and air conditioning contributes to between 47% and 60% of total electrical energy used in buildings. An evaporative air cooler would be an effective alternative to air conditioning due to its low energy consumption. The feasibility of using evaporative cooling should be determined for individual location because thermal performance depends on climates and the specific nature of the application (El-Refaie & Kaseb, 2009). In Thailand, evaporative air coolers are rarely used in residential houses but are increasingly common in commercial malls, factories warehouses, and farms (Lertsatitthanakorn et al., 2006). Unreliable cooling performance depending on climatic conditions means that evaporative air coolers are unpopular.
A review of desiccant evaporative cooling systems in hot and humid climates
Published in Advances in Building Energy Research, 2021
Ismanizam Abd Manaf, Faisal Durrani, Mahroo Eftekhari
Another type of evaporative cooling system is indirect/indirect evaporative cooling. Conceptually, in the first stage, the primary air stream is cooled by indirect evaporative cooling. In the second stage, water used in first-stage cooling passes through the wetted side of a coil. Additional sensible heat is removed from the primary air stream, and no moisture is added to the primary air (illustrated in Figure 10). Another type of evaporative cooling is indirect evaporative cooling with DX back-up. In indirect evaporative cooling with DX back-up, the primary air stream is cooled first with indirect evaporative cooling. Basically, this cools the primary air stream to the desired temperature. But, when more cooling is required, the supplemental DX module cools the air further to reach the desired temperature. The schematic of indirect evaporative cooling with DX back-up is illustrated in Figure 11. A combined experimental/analytical study was conducted by Delfani et al. [6] in various climates with low humidity, in four cities of Iran, using indirect evaporative cooling as a pre-cooler to the packaged unit air-conditioner. Results showed a reduction in the cooling load of up to 75% during cooling seasons or summer time. Also, there was a 55% reduction in the electrical energy consumption of the packaged unit air-conditioner. We can therefore conclude that this type of IE can be used to reduce a mechanical cooling system's size, peak load and electrical energy consumption, especially in cooling season.