Influence of spray parameters and thermal environments under convection heat transfer on the application of spray cooling technology in deep-buried high-temperature building tunnel

Abstract

Spray cooling technology is an effective and sustainable cooling method that is frequently used in hot environments, both indoors and outdoors. This paper studied the theory of droplet evaporation under convection heat transfer and established a model of tunnel construction under high-temperature. The results of the field measurements were used to determine the boundary conditions for the model. After that, the cooling effect under various spray conditions (spray pressure Pn and water temperature Tw) was explored. Next, it was discussed how the tunnel's thermal environment affected the droplet evaporation, and a suitable layout of nozzles was chosen. The results showed that, firstly, the droplet group produced by spraying was in an irregularly cone-shaped distribution, with most droplets falling within the particle size range of 30–40 μm. Secondly, when the spray pressure (Pn) was increased, the break-up of droplets was better, which would improve the evaporation flow of droplets. However, the evaporative ratio of the droplets exhibited a peak value. When Pn = 4 MPa, the droplet evaporation ratio reached its maximum at 82.7 %. Thirdly, in a high-humidity environment, the evaporation ratio of droplets would decrease, and the average evaporation time of a single droplet would increase, leading to the reduction of the spray cooling effect. When D increased from 5 g/kg to 25 g/kg, the average evaporation time rose at 5.7 s. Fourthly, when constructing in the tunnel's high-temperature zone, the number of nozzles (N) could be raised to achieve the cooling effect; and the cooling effect was optimal when the spacing between nozzles (Δx) was 20–30 m. The research results enriched the study of spray parameters and thermal environments on the cooling effect of droplet evaporation, which could provide a reference for applying spray cooling technology in the tunnel.