Question

Solve the following using the psychrometric chart A filter-dryer exhaust is saturated air at 70 F.

This air is to be conditioned and then recycled back to the filter. To do this, the filter exhaust is
first heated in a heat exchanger and then passed through an adiabatic humidifier where it
reached 80% RH at the chamber exit. The chamber exit air is then reheated in a second heat
exchanger to the final desired conditions of 130 F dry bulb and 96 F wet bulb, after which it is fed
into the filter-dryer.

a. How much make-up water per hour will be needed for the humidifier, if the volumetric
exit is 5000 CFM?
b. What is the heat transferred in the second heat exchanger?

Answer 1

To solve this problem, we will use the psychrometric chart to determine the values for the different parameters at each stage of the process.

Step-by-step explanation:

To solve this problem, we will use the psychrometric chart to determine the values for the different parameters at each stage of the process.

For part a, we can use the psychrometric chart to find the specific humidity at 80% relative humidity and 80°F. From there, we can calculate the mass flow rate of the make-up water needed for the humidifier.

For part b, we need to determine the change in enthalpy between the conditions at the second heat exchanger inlet and outlet using the psychrometric chart. We can then calculate the heat transferred using the mass flow rate of the air and the change in enthalpy.

Answer 2

To solve the psychrometric chart problem, specific steps are followed on the chart, such as locating initial and final air conditions, and finding differences in enthalpy and moisture content to calculate makeup water and heat transfer. Exact numerical answers cannot be provided without using a chart or tools.

Step-by-step explanation:

Solution for the Psychrometric Chart Problem

To solve the given psychrometric chart problem, we need to apply the principles of thermodynamics and the properties of moist air. Unfortunately, without the use of an actual psychrometric chart or relevant software tools, providing exact numerical answers is not feasible. However, I can guide you on the process.

To determine the makeup water needed for the humidifier, you would follow these steps using the psychrometric chart:

1. 
   
3. Locate the initial condition of the filter-dryer exhaust air on the chart at 70°F and 100% relative humidity (RH).
4. 
   
6. Move along the line of constant enthalpy (since the air is heated without adding or removing moisture) to the higher temperature that the air reaches after the heat exchanger.
7. 
   
9. From the new temperature point, move vertically down to 80% RH to find the point where the humidification process ends.
10. 
    
12. Calculate the difference in moisture content between the two points to find the water added per pound of dry air.
13. 
    
15. Convert this to the make-up water needed per hour by multiplying with the air flow rate in cubic feet per minute (CFM), taking into account the density of air at the relevant conditions.

The heat transferred in the second heat exchanger can be calculated by:

1. 
   
3. Locating the point where the air exits the humidifier at 80% RH and the temperature noted in the previous steps.
4. 
   
6. Moving horizontally to the final desired condition of 130°F dry bulb and 96°F wet bulb temperature.
7. 
   
9. Comparing the enthalpy values at these two points to find the change in enthalpy per pound of dry air.
10. 
    
12. Multiplying the change in enthalpy by the airflow rate to get the total heat added.

This procedure shows how the moisture and heat transfer calculations would be performed using the psychrometric chart, although actual values are not provided.