Abstract
Spray cooling is widely used in relieving heat stress in dairy cows during summer, in which the cooling effect is highly correlated to the diameter of water droplet. To optimize the average diameter of spraying droplet (ADSD) in the process of heat transfer, a theoretical analysis was performed based on the enthalpy difference theory in this study. A platform was built to simulate the processes of spray cooling and its heat stress alleviation to dairy cows in field, and a field experiment was applied to verify the diameter of water droplets suitable for spray cooling. Heat exchange was calculated for eighteen different ADSD in three different environment conditions in the laboratory. The spraying droplets with eighteen diameters were formed by using six different nozzles under the combinations of three pressures and two wind speeds conditions, which were controlled by heaters. The relationship between the ADSD and heat exchange was established with the purpose to determine the appropriate diameter for practical production. In the field test, body temperature, rectal temperature, and respiratory rate of dairy cows were monitored, and the heat exchange was analyzed to verify the optimal diameter spraying cooling in summer. Results showed that the heat exchange generally increased as ADSD increased, and maximum heat exchanges were reached when the ADSD was averaged at 0.914 mm and 0.995 mm, under which the models of the corresponding nozzles were 9080 and 9010, respectively. After that, the heat exchange decreased as the ADSD continued to increase. Field experiment indicated that the best cooling effect could be achieved with the ADSD of 0.947 mm, and the water consumption for spray cooling was reduced by 22.8% under the scenario.
Highlights
With the increase demand of dairy milk, healthy and efficient farming of cows is getting more and more attention from both the producers and consumers
The current research results show that spray cooling can well alleviate heat stress in dairy cows, and this method is widely used in dairy farming production
18 kinds of spray average diameter of spraying droplet (ADSD) were analyzed in the laboratory using simulated dairy cows and laser precipitation monitor (LPM) tests
Summary
With the increase demand of dairy milk, healthy and efficient farming of cows is getting more and more attention from both the producers and consumers. High temperature and humid climate in summer is the main cause of heat stress in dairy cows, which may result in a decrease in feed intake, increase of incidence rate, and reduction of milk yield. Energies 2019, 12, 3637 form of small droplets and ventilation can significantly reduce the body temperature and effectively alleviate heat stress of the cows [3,4,5,6,7]. More research endeavors have been carried out on evaluating the cooling effect of spraying, determining proper spraying time and interval [12], and assessing the impact of spraying and ventilation combination on the rectal temperature and respiratory rate of the cows [13]. The effect of spray cooling on milk yield and cows’ health is always mostly concerned [14]
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