To refresh air in a room, a counter flow heat exchanger, see...

To refresh air in a room, a counter flow heat exchanger, see Fig. P12.115, is mounted in the wall, drawing in outside air at $0.5^{\circ} \mathrm{C}, 80 \%$ relative humidity, and pushing out room air, $40^{\circ} \mathrm{C}$ $50 \%$ relative humidity. Assume an exchange of $3 \mathrm{kg} / \mathrm{min}$ dry air in a steady flow, and also assume that the room air exits the heat exchanger to the atmosphere at $23^{\circ} \mathrm{C}$. Find the net amount of water removed from the room, any liquid flow in the heat exchanger, and $(T, \Phi)$ for the fresh air entering the room.

Key Concepts

Counter Flow Heat Exchanger

A counter flow heat exchanger is a device that transfers thermal energy between two fluid streams flowing in opposite directions. In the context of air handling, it recovers heat from the outgoing (exhaust) air to preheat or cool the incoming (fresh) air, thereby conserving energy. This concept is pivotal when analyzing tasks that involve managing both temperature and humidity levels of air in a system.

Psychrometric Analysis

Psychrometric analysis involves studying the thermodynamic properties of air–water vapor mixtures. Key properties include dry bulb temperature, relative humidity, humidity ratio, and enthalpy. This analysis is essential for determining the moisture content of air, understanding how temperature changes affect relative humidity, and predicting condensation events in heating or cooling processes.

Dew Point and Condensation

The dew point is the temperature at which a given air–water vapor mixture becomes saturated, leading to condensation. Recognizing the dew point is critical when evaluating whether water will condense from air, as well as in designing systems to control indoor air moisture. It helps in determining potential water removal or liquid flows within heat exchangers.

Mass and Energy Balances

Mass and energy balance principles are used to account for the conservation of dry air, water vapor, and energy within a system. These balances are crucial when calculating the net amount of water removed from a space, as they ensure that both the mass of absorbed or condensed moisture and the heat transferred between streams are properly considered.

Transcript

Please give Ace some feedback