Briefly describe the principle of circulating water cooling?

Answer: ① The cooling of circulating water occurs through the contact between water and air, as a result of the combined effects of evaporation-based heat dissipation, conduction-based heat dissipation, and radiation-based heat dissipation； ②Evaporative cooling: In water-cooling systems, small water droplets or extremely thin water films are formed, which increases the contact area between the water and air as well as the duration of this contact. This enhances the evaporation of water, allowing water vapor to carry away the heat required for vaporization, thereby cooling the water ； ③Contact heat dissipation: Conduction and convection heat transfer are referred to as contact heat transfer ； ④ Radiative cooling: Radiative cooling does not require a heat transfer medium; it relies on electromagnetic waves for heat transfer, and it is only effective in large cooling surfaces.

The water temperature in a naturally cooled ventilation tower is generally 5-6 degrees lower than the ambient temperature, and it is also influenced by the environmental humidity and the wind speed over the packing. This temperature is called the wet-bulb temperature. When the humidity remains constant, evaporation and condensation reach equilibrium. Condensation releases heat, which is carried away by the air flowing from bottom to top; this is the hyperbolic suction effect of the tower. Evaporation, on the other hand, absorbs heat, and the heated water rises upward; as a result, its temperature naturally drops below that of the surrounding environment.

The cooling of circulating water occurs through the contact between water and air, as a result of the combined action of three processes: evaporative heat loss, convective heat loss, and radiative heat loss. (1) The water evaporated and dispersed forms larger or smaller water droplets, or extremely thin water films, within the cooling device; this increases the contact area between the water and air as well as the duration of contact, thereby enhancing water evaporation. The water vapor carries away the heat required for vaporization from the water, thus cooling it. (2) Contact heat dissipation occurs through conduction and convection, and is known as contact heat dissipation. When the water surface comes into contact with air at a lower temperature, the temperature difference causes heat from the hot water to transfer to the air, resulting in a decrease in the water temperature. The greater the temperature difference, the better the heat transfer effect. (3) Radiative heat dissipation: Radiative heat dissipation does not require the presence of a heat transfer medium; rather, it is a phenomenon in which thermal energy is transferred in the form of electromagnetic waves. Radiative heat dissipation is effective only in large cooling pools. In other types of cooling equipment, radiative heat loss can be neglected. The role of these three heat dissipation processes in water cooling varies depending on the physical properties of the air. During spring, summer, and autumn, the outdoor temperatures are high, and surface evaporation plays a major role. In the hottest months of summer, evaporation accounts for over 90% of the total heat loss; as a result, the amount of water lost through evaporation is greatest, and the amount of water that needs to be replenished is also the highest. In winter, as temperatures drop, the effect of heat loss through contact increases, rising from 10–20% in summer to 40–50%; in extremely cold weather, it can even reach around 70%. As a result, the amount of water lost through evaporation decreases during the cold seasons, and accordingly, the amount of water that needs to be replenished also decreases.