Question 13.13: Latent and Sensible Cooling Process on Psychrometric Chart C......
Latent and Sensible Cooling Process on Psychrometric Chart
Consider an ideal process where moist air is cooled from 40°C (104°F) and 30% RH to 15°C (50°F). Does moisture condense? What are the values of the RH and the humidity ratio at the process endpoint?
Given: T_{db1} = 40°C, \phi_{1} = 0.30, and T_{db2} = 15°C
Figure: See Figure 13.15, process 1–3.
Find: W_{3} and \phi_{3}
The inlet conditions are identical to those in Example 13.10 while the air is cooled to a lower temperature.
The dew point is known to be 19°C for the moist air at the beginning of the process. Therefore, moisture condenses since the outlet temperature (= 15°C), for this case is below this dew point. This is a process where both sensible and latent cooling occur.
Inspection of process 1–3 in Figure 13.15 shows that the humidity ratio changes since moisture condensation has occurred. The saturated air at the exit temperature of 15°C has a humidity ratio of 0.0106 kg_{w}/kg_{a}. Finally, the relative humidity changes to the saturated value, i.e., RH of 100%, as shown in Figure 13.15.
This process can be viewed as a two-part process: (1) constant-humidity-ratio cooling until saturation and (2) constant-relative-humidity cooling with condensation of moisture. Figure 13.15 shows the process as it is displayed within the HCB software. Analysis of such problems is illustrated by the following example. However, some pertinent equations need to be introduced first.