Selection and effectiveness evaluation of spray nozzles for spray cooling system in dairy cattlehousing

摘要

Heat stress negatively impacts on dairy cattle production including feed intake, milk production, and reproduction. Techniques to alleviate heat stress of the cows are widely developed and adopted in practice. At high temperature and humid days, evaporative cooling has been demonstrated to be one of the most effective methods, in which the spray nozzle plays an important role. In dairy cattle housing in China, water sprayer combined with mixing fan is typically used in summer. However, there is no standardized method for design and configuration of the evaporative system, which often leads to a poor system performance. In particularly, improper selection and installation of the commercial spray nozzles in practice could inhibit the system to achieveexpected cooling effect, and may adversely result in leaking and wetting the lying area of the cattle. The method to evaluate effectiveness of the sprayers is highly needed as well. The aim of the study is to screen out the suitable nozzles and figure out its installation scheme. Based on an investigation of the currently used nozzles in dairy farm, 19 types of nozzles were selected and their performances on flow rates, particle sizes and spray strengths were tested. Water distributions of the sprayersin different mounting heights (50cm, 60cm and 70cm) were measured using a 10*10 mesh net. Based on the date, the spray intensity at different net point was superposed at varied mounting spaces from 1.0 m to 2.4 m to calculate the combined spray intensities and the combined uniform coefficients. The nozzles suited to the spray cooling system were identified accordingly. The flow rates of nozzles varied from 10.0+0.4 ml/s to 126.6±4.9 ml/s with Rainbird RB15 having the highest flow rate. Water droplet diameters of the nozzles changes from 129.4 pm to 1289.5 pm, and Teejet nozzle had the largest particle size among all the nozzles. Water distributions of these nozzles were mainly within the area beneath the nozzles with a length of 1.2m except for the 2Rainbird nozzles. The results of combined uniform coefficients showed that most of the nozzles had a uniform spray coefficient above 40%, which might be selected as a standard value to judge the uniformity of the nozzles. Finally, Teejet, HTZS, and 3 other types of nozzles were screened out. Finally, the installation methods were suggested to achieve good effectiveness.