Air enters an evaporative (or swamp) cooler at 14.7 psi, 95^∘ F, and 20 percent relative humidit

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Air enters an evaporative (or swamp) cooler at 14.7 psi,...

Air enters an evaporative (or swamp) cooler at 14.7 psi, $95^{\circ} \mathrm{F}$, and 20 percent relative humidity, and it exits at 80 percent relative humidity. Determine $(a)$ the exit temperature of the air and $(b)$ the lowest temperature to which the air can be cooled by this evaporative cooler.

Key Concepts

Evaporative Cooling

This concept involves the cooling of air through the evaporation of water. When water evaporates, it absorbs latent heat from its surroundings, thereby lowering the temperature of the air in contact with it. This principle is used in devices such as swamp coolers where the addition of moisture reduces the sensible heat of incoming dry air.

Psychrometrics

Psychrometrics is the study of the thermodynamic properties of moist air, including its temperature, humidity, and the amount of water vapor it contains. It provides tools such as psychrometric charts which help in understanding how air properties change during processes like heating, cooling, humidifying, and dehumidifying.

Dry-Bulb and Wet-Bulb Temperatures

The dry-bulb temperature is the temperature of air measured by a regular thermometer, while the wet-bulb temperature is measured using a thermometer with a wetted wick over its bulb. The difference between these two temperatures is significant in determining cooling limits and the amount of moisture the air can absorb, making them crucial in evaporative cooling calculations.

Relative Humidity

Relative humidity is a measure of the current amount of water vapor in the air relative to the maximum amount it can hold at a given temperature. It is expressed as a percentage. Changes in relative humidity affect the air's capacity to absorb additional moisture and are essential for predicting the outcomes of evaporative cooling processes.

Adiabatic Saturation Process

This process refers to the condition where air comes into contact with water and is allowed to reach a state of saturation without any heat exchange with its surroundings. In evaporative cooling, the air is cooled as it gains moisture, moving towards its wet-bulb temperature, which represents the theoretical limit of cooling under saturated conditions.

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