ANS:D - None of these

During evaporative cooling with recirculated water supply, the wet bulb temperature and the partial pressure of vapor decrease, while the relative humidity remains constant. Here's why:

1. Wet bulb temperature: During evaporative cooling, water evaporates into the air, which cools the air. As a result, the wet bulb temperature, which is the temperature measured by a thermometer with its bulb wrapped in a wet wick or cloth, decreases due to the cooling effect of evaporation.
2. Relative humidity: Relative humidity is the ratio of the partial pressure of water vapor in the air to the saturation vapor pressure at a given temperature. In an evaporative cooling process with recirculated water supply, the relative humidity remains constant because the amount of water vapor in the air does not change. However, since the temperature decreases, the saturation vapor pressure also decreases, keeping the relative humidity constant.
3. Partial pressure of vapor: The partial pressure of vapor decreases during evaporative cooling because as water evaporates into the air, it adds moisture to the air, increasing the total pressure. However, since the temperature decreases during the cooling process, the saturation vapor pressure also decreases, leading to a decrease in the partial pressure of vapor.