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A practical method for improving the COP of an air-cooled chiller is pre-cooling the entering air of its condenser via a water mist system. This article studies a water mist system with hollow-cone spray nozzles and investigates the effects of water flow rate, water droplet diameter and the number of spray nozzles on system performance. Simulations were run by software FLUENT applying Eulerian-Lagrangian method. Solution grid independency was obtained and it was validated with experimental data. According to the results, in a constant air flow rate of 8.3 (kg/s), with increasing the water flow rate from 0.05 to 0.4 (kg/s), percent increase of COP increases from 3 to about 14, but the percentage of evaporated water decreases from 12.13 to 7.62 (however the value of evaporated water increases). Besides, decreasing the water droplets’ diameter from 200 to 50 micrometer, results in percent increase of COP from 4 to 24. Due to less water evaporation in higher flow rates, the number of spray nozzles was raised in a constant total flow rate that according to the results, increasing the number of nozzles improves the system performance. Also with other simulations it was observed that increasing the number of nozzles is more effective in higher flow rates and less drop diameters. Finally by the case study, it was demonstrated using sufficient number of nozzles, it is possible to achieve higher COPs in lower flow rates and therefore in addition to energy consumption decline, the water consumption could be lowered.

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With recent developments in sprinkler technology, water mist system is becoming more and more useful in fire suppressions. The computational method is an efficient way to investigating effect of Nozzle parameter of water mists and optimize them. In this research, a open source fire dynamic simulator (FDS) is used to numerically investigating the different nozzle parameter on the fire suppression and extinguishment mechanism.The range of droplet size was determined based on the NFPA 750 standard. Extinguishing mechanisms in water mist systems and their effect on extingushing time and nozzle parameter such as droplet size, water flow rate and spray cone angle were investigated. The simulation concluded that droplet sizes I hollow cone angle smaller than 121 μm and larger than 600 μm were appropriate for fire extingushment. With a full cone angle nozzle and 1/5 flowrate compared with hollow cone nozzle, fire extingush time reduce from 26 second to 7.4 second. Spray cone angle in fine droplets does not much affect the duration of fire extinguishing, however, for large droplets, the desired result can be achieved by reducing the spary cone angle. So with recognition of nozze parameter and its effects on fire extingushing time could rich the optimum design.
Keywords
m design.