Mindblown: a blog about philosophy.
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PSYCHROMETRIC CHART
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…
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THERMODYNAMIC WET BULB TEMPERATURE OR ADIABATIC SATURATION TEMPERATURE (AST)
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…
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HUMID SPECIFIC HEAT
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…
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ENTHALPY OF MOIST AIR
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…
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PSYCHROMETRIC RELATIONS
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PRINCIPLES OF PSYCHROMETRY
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…
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INTRODUCTION
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.…
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COMPARISON OF AMMONIA-WATER AND LITHIUM BROMIDE-WATER ABSORPTION SYSTEMS
The comparison of ammonia-water and lithium bromide-water systems are given m Table 19.2 Table 19.2 Comparison of ammonia-water and lithium bromide-water systems Exercises 19.1. The evaporator and condenser temperatures in an NH3 refrigeration system are –10°C and 40°C respectively. Determine per TR basis: (a) mass flow rate; (b) compressor work, (e) condenser heat rejection; (d) C.O.P.; and…
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LITHIUM BROMIDE-WATER VAPOUR ABSORPTION SYSTEM (LIBR-H2O)
In the LiBr-water system, water is the refrigerant and LiBr the absorber. The lithium bromide solution has a strong affinity for water vapour because of its very low vapour pressure. The lithium bromide-water vapour absorption system is shown in Fig. 19.25. The evaporator and absorber are placed in one shell which operates at the same low…
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AMMONIA-WATER (OR PRACTICAL) VAPOUR ABSORPTION SYSTEM (NH3 – H2O)
In the NH3 − H2O vapour absorption system, ammonia is the refrigerant and water is the absorber. An analyser, a rectifier and two heat exchangers are added to the simple vapour absorption system. The complete schematic diagram of ammonia-water absorption system is shown in Fig. 19.24. The functions of various accessories are:
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