Month: December 2022

Air conditioning is the process whereby the condition of air, as defined by its temperature and moisture content, is changed as per requirement. In practice other factors should also be taken into account especially cleanliness, odour, velocity, and distribution pattern. Comfort is a very subjective matter. The engineer aims to ensure comfort for most people…

An air washer is a device for conditioning air. In an air washer air comes in direct contact with a spray of water and there will be an exchange of heat and mass (water vapour) between air and water. The outlet condition of air depends upon the temperature of water sprayed in the air washer.…

Mixing of air streams at different states is commonly encountered in many processes, including in air conditioning. Depending upon the state of the individual streams, the mixing process can take place with or without condensation of moisture. Mixing Without Condensation: Figure 8.14 shows an adiabatic mixing of two moist air streams during which no condensation of moisture…

This process can be achieved by using a hygroscopic material, which absorbs or adsorbs the water vapour from the moisture. If this process is thermally isolated, then the enthalpy of air remains constant, as a result the temperature of air increases as its moisture content decreases as shown in Figure 8.13. This hygroscopic material can be a…

As the name implies, during this process, the air temperature drops and its humidity increases. This process is shown in Figure 8.12. As shown in the figure, this can be achieved by spraying cool water in the air stream. The temperature of water should be lower than the DBT of air but higher than its DPT to…

During winter it is essential to heat and humidify the room air for comfort. As shown in Figure 8.11, this is normally done by first sensibly heating the air and then adding water vapour to the air stream through steam nozzles as shown in the figure. Figure 8.11 Heating and Humidification Process Mass balance of water vapour for…

It is defined as the ratio of sensible to total heat transfer rate (Qt), i.e.,   SHF = Qs/ Qt = Qs/(Qs + Q1)   From the above equation, we can observe that a SHF of 1.0 corresponds to no latent heat transfer and a SHF of 0 corresponds to no sensible heat transfer. A SHF of 0.75−0.80 is quite common in…

When moist air is cooled below its dew point by bringing it in contact with a cold surface, some of the water vapour in the air condenses and leaves the air stream as liquid, as a result both the temperature and humidity ratio of air decreases as shown. This is the process air undergoes in…

During this process, the moisture content of air remains constant but its temperature decreases as it passes over a cooling coil. To keep the moisture content constant, the surface of the cooling coil should be dry and its surface temperature should be greater than the dew point temperature (DPT) of air. If the cooling coil…

8.8.1  Psychrometric Chart A view of psychrometric chart is shown in Figure 8.6. The different psychrometric process are shown in Figure 8.7. Figure 8.6 Psychrometric Chart Figure 8.7 Psychrometric Processes