Category: Air-Conditioning and Psychrometrics

The psychrometric processes by which the state of moist air can be altered are shown in Fig. 20.7. These processes are: Figure 20.7 Basic psychrometric processes 1 Sensible Heating or Cooling Process The heating/cooling of air without any change in its specific humidity is known as sensible heating/cooling. The process of sensible heating (line 1-2) or cooling…

The psychrometric chart is a graphical representation of the complete thermodynamic properties of moist air and psychrometric analysis of air-conditioning processes. The chart most commonly used is the w-td chart, which specifies specific humidity (ω) or water vapour pressure (pv) along the ordinate and the dry bulb temperature (td) along the abscissa. The chart is normally constructed…

The thermodynamic wet bulb temperature or AST is the temperature at which the air can be brought to saturation state adiabatically by the evaporation of water in the flowing air. A schematic representation of this process, called the adiabatic saturation process, is shown in Fig. 20.3. It consists of an adiabatic enclosure containing adequate quantity of…

Eq. (20.16) can be written as, h= (cpa + wcpv)td + w(hfg)0°C is termed as the humid specific heat. It is the specific heal of moist air (1 + w) kg per kg of dry air. At low temperatures of air-conditioning the value of w is very small. An approximate value of cp of 1.0216 kJ/(kg d.a.).K may be taken for nil practical purposes Example…

The temperature-entropy diagram is shown in Fig. 20.2. Enthalpy of moist air = Enthalpy of dry air + Enthalpy of water vapour associated with dry air h = ha + whv per kg of dry air where ha = cpa td = 1.005 td kJ/kg cpa = 1.005 kJ/kg. K td = DBT of air in °C. hv = cpw tdp +[(hfg)dp + cpv (td −tdp)]kJ/kg = 4.1868tdp + (hfg)dp +1.88(td −tdp) where cpw = 4.1868 kJ/kg K is the specific heat of…

The psychrometry is that branch of engineering which deals with the study of moist air i.e. dry air mixed with water vapour. Dry air: The dry air consists of O2 = 0.2099, N2 = 0.7803, Ar = 0.0094, CO2 = 0.0003 and H2 = 0.0001 parts by volume. Molecular weight of air = 28.966 Gas constant, Ra = 0.287 kJ/kg K Density of…

The air-conditioning is that branch of engineering which deals with the study of supplying and maintaining desirable internal room atmospheric conditions of air for human comfort. The four important factors for human comfort are: temperature, humidity, purity and motion of air. The working substance for air-conditioning is moist air, which a mixture of two gases.…