Effects of fixed - point air supply cooling system on airflow and temperature around sows and convective heat transfer of sows

Ventilation and cooling have been highly required in large-scale lactating pig houses, particularly in areas of high temperature and high humidity. This study aims to evaluate the effects of different inlet diameters, air speed, and temperature on the airflow and temperature field around lactating sows, as well as the heat dissipation of lactating sows under the fixed-point air supply cooling system using computational fluid dynamics (CFD) numerical simulation. The length, width, and height of the pig house were set as 2.5, 1.8, and 6 m, respectively, all the same as the experimental and simulation. The temperature and humidity at six points were measured on Z=0.53 m plane. The results showed that the air speed of each measuring point after the second point was less than 0.5 m/s at the different inlet air speeds when the air inlet temperature was constant and the inlet diameter was 8 cm. The air speed of each measuring point after the fourth point was less than 0.5 m/s when the inlet diameter was 12 cm and the inlet air speed was 6 m/s. The air speed of the sixth measuring point was less than 0.5 m/s when the inlet diameter was 16 cm and the inlet air speed was 4 m/s. There was about a 1.7 ℃ temperature difference between each measuring point under the conditions of the same inlet air temperature and different inlet diameters. The average temperature of the second to sixth measuring points corresponding to the three air inlet diameters was lower than 27 ℃, when the inlet air temperature was 23 ℃. There was about a 1.8 ℃ temperature difference between each measuring point, under the conditions of the same inlet diameter and different inlet air temperatures. The average temperature of the second to sixth measuring points was lower than 27 ℃when the inlet diameter was 16 cm and the inlet air temperatures were 23 ℃ and 25 ℃. The convective heat-transfer coefficient of sows significantly increased with the increase of inlet diameter and inlet air speed, whereas, there was no significant effect from the inlet temperature. Once the diameter of the air inlet was 12 cm, the air speed and temperature in the area around the sows had fully met the needs of suckling piglets, where the sows behaved the high convective heat dissipation. Therefore, the air inlet of 12 cm was recommended in this case for the actual production. Specifically, the inlet air speed increased by 1 m/s, and the convective heat transfer of sows increased by 28.76 W, where the inlet diameter was 12 cm and the inlet temperature was 25 ℃. Furthermore, the inlet air temperature decreased by 1 ℃, and the convective heat transfer of sows increased by 16.61W, where the inlet diameter was 12 cm and the inlet air speed was 6 m/s. Therefore, the fixed-point air supply cooling system posed a great impact on the air speed and temperature distribution in the activity area of piglets, together with the convective heat transfer of sows. The finding can provide the theoretical basis for the cooling mode in the lactating sow houses.