1. In-depth analysis of thermodynamic exchange mechanism

The closed cooling tower achieves efficient cooling through "tube wall conduction + evaporative heat dissipation" two-stage heat exchange. Inside the closed coil, when the process fluid (such as water or ethylene glycol solution) below 90°C flows, the heat is first conducted to the outer wall through the copper tube or stainless steel tube wall. Taking the common 19mm outer diameter copper tube as an example, the thermal conductivity can reach 401W/(m·K) when the wall thickness is 1.5mm, and about 600W/m² of heat can be transferred for every 1°C decrease in the tube wall temperature difference.

The spray system evenly covers the cooling water on the outer surface of the coil to form a 0.5-1mm thick water film. When the axial flow fan passes through the tube bundle at a wind speed of 2.8-3.5m/s, forced evaporation occurs on the surface of the water film. According to Dalton's law of evaporation, 2260kJ of latent heat of vaporization is required for each kilogram of water evaporated. Under standard working conditions (wet bulb temperature 28℃), a heat dissipation of 350-450W can be achieved per square meter of heat exchange area.

2. Technical specifications of key components

The selection of coil material needs to comprehensively consider thermal conductivity and corrosion resistance. Industrial-grade copper tube C12200 is suitable for clean water with conductivity <500μS/cm, and the annual corrosion rate is <0.02mm in the pH range of 6.5-8.5. For coastal or chemical environments, SUS316L stainless steel tubes are required, and their molybdenum content of 2-3% can resist corrosion with chloride ion concentrations as high as 1000ppm.

The selection of spray nozzles directly affects the heat exchange efficiency. The spiral stainless steel nozzle can form a 60-90 degree conical fog field at a working pressure of 3bar, and the flow rate of a single nozzle is controlled at 1.2-1.8m³/h, ensuring that the surface coverage of the tube bundle is >95%. The water pump should be equipped with variable frequency control to automatically adjust the flow rate according to the outlet water temperature to achieve accurate temperature control of ±0.5℃.

III. Comparative analysis of measured energy efficiency

A certain automobile factory transformation case shows that after the open system is changed to a closed cooling tower: the circulating water conductivity is reduced from 1800μS/cm to 300μS/cm, and the annual water treatment agent cost is reduced by 850,000 yuan; after the fan adopts a permanent magnet motor, the energy consumption is reduced from 55kW to 38kW, and 149,000 degrees of electricity are saved annually; the 45℃ wastewater is heated to 60℃ for reuse through a heat recovery device, saving 160,000 US dollars in steam costs annually.