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Psychrometrics – Lecture 3

This lecture series by Dr. C. L. Jones focuses on the principles of psychrometrics, essential for managing water vapor in air and materials. Key topics include calculating properties of air-water vapor mixtures, such as wet bulb temperature, dry bulb temperature, and relative humidity. The course also covers practical applications like cooling and heating systems, drying processes, and the impact of ventilation rates on animal housing. Real-world examples illustrate how to maintain ideal conditions for greenhouse plants and livestock, emphasizing the importance of energy balance and moisture control in agricultural engineering.

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Psychrometrics – Lecture 3

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  1. Psychrometrics – Lecture 3 Dr. C. L. Jones Biosystems and Ag. Engineering

  2. Lecture 1 and 2 Review • This is all about removing and adding water from materials and from air-water vapor • Knowing 2 of the properties of a state point, we can find the other 5 properties • Wet Bulb T, Dry Bulb T, Dew Point, RH, enthalpy h, humidity ratio H, specific volume v Dr. C. L. Jones Biosystems and Ag. Engineering

  3. Lecture 1 and 2 Review • Cooling and heating without changing amount of moisture: moves along a horizontal line (humidity ratio H stays the same…everything else changes) • In a mixing process (2 air streams at different state points)…resultant state point will lay on a line between the two initial stages Dr. C. L. Jones Biosystems and Ag. Engineering

  4. Lecture 1 and 2 Review • Product drying process using air: adiabatic…follows the enthalpy line…wet bulb stays the same, enthalpy stays the same, everything else changes Dr. C. L. Jones Biosystems and Ag. Engineering

  5. Psychrometric Processes: Addition of Water at any state • Changes enthalpy and humidity ratio…and everything else, Figure 9.12 • Mass of water: (eqtn 9.100) • Energy balance: (eqtn 9.101) • Example 9.14 Dr. C. L. Jones Biosystems and Ag. Engineering

  6. Psychrometric Processes: Addition of Water at any state • Greenhouse plants like to be kept at 30°C and 95% rh. • To achieve this condition, steam at 160°C is injected into the ventilation air stream (20°C, 30% rh). • Mass flow rate of the air stream is 1800 kg/min and the mass flow rate of the steam is 5 kg/min. • Will this system achieve the ideal conditions for the plants? Dr. C. L. Jones Biosystems and Ag. Engineering

  7. Psychrometric Processes: Animal Housing • What ventilation rate is needed in a swine finishing confinement building with a solid floor and 140 head of 150 lb pigs for outside temperatures from -10F to 50F? • Assume inside conditions of 60F and 80%RN and outside RH of 80% Dr. C. L. Jones Biosystems and Ag. Engineering

  8. Psychrometric Processes: Animal Housing • What ventilation rate is needed in a poultry confinement building with hanging cages over pits and 690 4-lb laying hens for outside temperatues from -10 to 50F? • Assume inside conditions of 60F and 70%RN and outside RH of 80%. Dr. C. L. Jones Biosystems and Ag. Engineering

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