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The term 'psychrometric properties' refers to the various parameters used to describe moist air conditions in thermodynamics. These include temperature, pressure, relative humidity, specific enthalpy, and humidity ratio.

In the given exercise, we need to work with these properties to track how air changes as it flows through the dehumidifier. Psychrometric charts or tables can provide the necessary values. Here's a breakdown:

• Saturation pressure \(\text{P}_s\): The pressure at which air becomes saturated with moisture at a given temperature.


• Humidity ratio \( \text{W} \): The mass of water vapor per mass of dry air.


• Specific enthalpy \( \text{h} \): The total heat content of the moist air per unit mass.

By using these properties, we can determine how much energy is transferred and how much water vapor condenses during the dehumidification process.

An energy balance is used to account for all energy entering and leaving a system. In this exercise, the dehumidifier's change in energy is due to cooling the moist air and condensing water vapor.

The energy balance equation can be written as:
\[\text{Energy removed} = (\text{dry air flow rate}) \times (h_1 - h_2) + (\text{condensate flow rate}) \times h_f \]
This equation means that the total energy removed from the air is the sum of:

• The energy due to cooling the dry air, which is the difference between the specific enthalpy of the inlet and outlet air multiplied by the dry air flow rate.


• The energy due to condensing water vapor, which is the flow rate of the condensate multiplied by the enthalpy of the liquid water at 15°C \( h_f \).

Ignoring heat transfer between the dehumidifier and surroundings simplifies the calculation and focuses solely on the main energy transactions within the dehumidifier.

Calculating the humidity ratio is crucial to understanding the amount of water vapor in the air. This in turn helps in determining the mass of condensate produced.

The initial and final humidity ratios (\text{W}\text{_1} and \text{W}\text{_2}) can be obtained from psychrometric charts or tables.

Using these values, the mass of condensate produced can be found by:
\[\text{m}_{\text{condensate}} = \text{W}_{1} - \text{W}_{2} \]
This equation calculates the difference between the initial and final humidity ratios, effectively giving us the total mass of water vapor that condenses out of the air.

The exact values of \text{W}_{1} and \text{W}_{2} are derived from the given conditions of the inlet and outlet air, which ensures accurate calculation of the condensate mass.

The refrigerant flow rate is key in determining the efficiency of the dehumidifier. The refrigerant absorbs heat as it passes through the cooling coil, indicated by an increase in specific enthalpy.

According to the exercise, the specific enthalpy of the refrigerant increases by 100 kJ/kg. Using this information along with the energy balance, we can find the refrigerant flow rate.

The formula is:
\[\text{Energy removed} = (\text{Refrigerant flow rate}) \times (100 \text{kJ/kg}) \]

Setting the energy removed from the air equal to the energy absorbed by the refrigerant and solving for the refrigerant flow rate:

\[( \text{dry air flow rate}) \times (h_1 - h_2) + ( \text{condensate flow rate}) \times h_f = (\text{Refrigerant flow rate}) \times (100 \text{kJ/kg}) \]
Doing this will give you the refrigerant flow rate per kg of dry air.