Refrigerater and Ac Repairing

DALTON’S LAW AND THE GIBBS-DALTON LAW  Dalton’s law shows that for a mixture of gases occupying a given volume at a certain temperature, the total pressure of the mixture is equal to the sum of the partial pressures of the constituents of the mixture, i.e., The partial pressure exerted by each constituent in the mixture is independent of the existence of other gases in the mixture. Figure 2.1 shows the variation of mass and pressure of dry air and water vapor, at an atmospheric pressure of 14.697 psia (101,325 Pa) and a temperature of 75°F (23.9°C). The principle of conservation of mass for nonnuclea r processes gives the following relationship: Applying Dalton’s law for moist air, we have Dalton’s law is based on experimental results. It is more accurate for gases at low pressures. Dalton’s law can be further extended to state the relationship of the internal energy, enthalpy, and entropy of the gases in a mixture as the Gibbs-Dalton law: ...

PSYCHROMETRICS Psychrometrics is the study of the thermodynamic properties of moist air. It is used extensively to illustrate and analyze the characteristics of various air conditioning processes and cycles. Moist Air The surface of the earth is surrounded by a layer of air called the atmosphere, or atmospheric air. From the point of view of psychrometrics, the lower atmosphere, or homosphere, is a mixture of dry air (including various contaminants) and water vapor, often known as moist air. The composition of dry air is comparatively stable. It varies slightly according to geographic location and from time to time. The approximate composition of dry air by volume percent is the following: The amount of water vapor present in moist air at a temperature range of 0 to 100°F (17.8 to 37.8°C) varies from 0.05 to 3 percent by mass. It has a significant influence on the characteristics of moist air. Water vapor is lighter than air. A cloud in the sky is composed of microscopic ...