ME300Lecture15

ME300Lecture15 - Lecture 15: Psychrometric Principles Moist...

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15.1 Lecture 15: Psychrometric Principles Moist air In typical HVAC processes, water vapor (moisture) is added or removed from the air (dry air), e.g., humidification, dehumidification, evaporative cooling Only the mass flow rate of water changes, the mass flow rate of dry air is constant Specific moist air properties are given per unit mass of dry air Two assumption are employed for air-water vapor properties : » Dalton’s law for non-reacting mixtures (each component in the mixture occupies entire volume at mixture temperature and partial pressure p = p a + p v » Air and water vapor are a mixture of ideal gases
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15.2 Continue Moist Air Properties For a single component: Need two independent, intrinsic properties to define the state point! For a two-component mixture (air-water vapor): Need three independent, intrinsic properties to define the state point! » Usually, temperature, pressure and concentration. » However, concentration is difficult to obtain for air-water vapor mixtures. » Therefore, we will use humidity ratio .
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15.3 Continue Moist Air Properties 1. Humidity ratio v v a av a a db v v v v v a a db a a db V m v v mass of water vapor V m mass of dry air v v
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ME300Lecture15 - Lecture 15: Psychrometric Principles Moist...

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