Evaporative Cooling as a Method of Reducing the Air Temperature and Increasing Humidity

Published: 2021-09-11 18:20:09
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Evaporative cooling is a potent solution and cost-friendly method of reducing the temperature of air and increasing humidity in an enclosed chamber where the humidity is quite low. Minimizing the degradation of fruits and vegetables enhances their shelf lives, implying that the produce will be available for longer periods; this would increase productivity and consequently reduce the instability of market supply and prices.
In this system, the temperature of the air passing through the pad is reduced thereby causing a cooling effect which is based on the principle of evaporative cooling. The extent to which the system can cool is dependent on the features of the pad (type of pad), air velocity through the fan, the degree of saturation of the pad which is a function of the water flow rate and the wetting smoothness of the pad.In a case where the flow rate of water through the pad is low, there would be mineral matter accumulation on the pad (calcification) and this would cause the pad to start deteriorating. Also, the mineral matter in the water gathers more because of evaporation of the whole water on the pad surface. This causes a reduction in the effectiveness of the system over time.
Some research have been carried out on evaporative cooling systems using various pads, some are summarized below.
Wiersma and Benham (1974) carried out a study for evaluating the optimum thickness and air flow rate of horizontally and vertically positioned pads made from poplar sawdust. Result showed that the most appropriate pad thickness was 7.5 cm and velocity of the air passing through the pad was 1.02m/s. Experiments carried out while the pads were horizontally placed showed the cooling efficiency increased about 5%. Although, there was no significant change in cooling efficiency when the air velocity increased to 1.27m/s on pads with 7.5cm and 12.5cm of thicknesses.
Buffington et al. (1978), made a comparative research on evaporative cooling pads made from four different materials in terms of cooling efficiency. The velocity of air passing through the pad was fixed at 0.75m/s. In this research, the maximum cooling efficiency was ascertained with cement-compounded sugar beet pulp pad. The cellulose-based pad had shown lower efficiency as compared to the compounded-sugar beet pulp pad. The rubberized pig bristles pad had achieved the lowest efficiency.
Vakis, (1981) developed a non-expensive cool store in Kenya. He used local grass for storage of vegetables. He kept the roof and walls wet by dripping water from the top of the roof. Evaporative cooling systems which operate on wind power to force air through wet pads, have also been designed and constructed, especially in some developing countries like India, China and Nigeria.
Rusten, (1985) carried out a research in the construction of different evaporative cooling systems using locally available absorbent materials. Mechanical fans were used in some of the designs which drew air through a continuously wetted pad. The continuous wetting of the pad was achieved by placing elevated water basins on the fabric material, which absorbed the water gradually and eventually got saturated.
Alebiowu, (1985) worked on the development of hexagonal wooden evaporative cooling systems and the system could be sub-divided into three parts head tank and pipe lines work ,the through and the frame work made of woods and its adjoins. The pipe line works at the top of the hexagonal frame supplied water constantly to wet the pad which is made of jute. Pressure from wind forces the air through the wetted jute pad. However, Limitation of this design is that the efficiency of the evaporative cooler depends on wind velocity.
Khurdiya et al. (1986) had constructed an evaporative cooler structure for storage of fruits and vegetables with a double wall made of baked bricks and the top of the storage space covered with khaskhas cloth in a bamboo framed structure.
Abdalla and Abdalla, (1995) worked on the development of a fan driven evaporative cooler. The research was study the suitability of using palm leaves as a wetted medium. This research was made possible due to the availability of palm leaves in Saudi Arabia. According to the research it was claimed that palm leaves could be used as the wetted media which is locally available to the masses.

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