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 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