1 / 13

Psychrometrics – Lecture 2

Psychrometrics – Lecture 2. Dr. C. L. Jones Biosystems and Ag. Engineering . Psychrometrics. Mollier vs. Traditional charts. Dr. C. L. Jones Biosystems and Ag. Engineering . Psychrometrics – State Points. Example: 35 °C dry bulb and 17° C wet bulb

thuong
Download Presentation

Psychrometrics – Lecture 2

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Psychrometrics – Lecture 2 Dr. C. L. Jones Biosystems and Ag. Engineering

  2. Psychrometrics • Mollier vs. Traditional charts Dr. C. L. Jones Biosystems and Ag. Engineering

  3. Psychrometrics – State Points • Example: 35°C dry bulb and 17° C wet bulb • Find enthalpy, sp. vol., humidity ratio, rh, dewpoint • Enthalpy, h = 48 kJ/kg dry air • Sp. Vol. = 0.88 m^3/kg dry air • Humidity ratio = 0.0046 kg/kg dry air • Rh = 14 % • Dew point = 3° C Dr. C. L. Jones Biosystems and Ag. Engineering

  4. Psychrometrics – State Points • Example: 42°C dry bulb and 30% rh • Find enthalpy, sp. vol., humidity ratio, rh, dewpoint • Enthalpy, h = 83.5 kJ/kg dry air • Sp. Vol. = 0.915 m^3/kg dry air • Humidity ratio = 0.0156 kg/kg dry air • Dew point = 21° C • Wet bulb = 25.6° C Dr. C. L. Jones Biosystems and Ag. Engineering

  5. Psychrometrics • Mollier vs. Traditional charts Dr. C. L. Jones Biosystems and Ag. Engineering

  6. Psychrometric Processes Application: condensation A pallet containing cartons of strawberries are removed from a cooler. The cooler is kept at 4° C. The room temperature is 27° C with a relative humidity of 20%. Will condensation form on the cartons of berries? Dewpoint for 27° C and 20% rh is 2.5° C which is less than 4° C. Therefore, condensation will not condense. Rule: if the object coming into the warm area is at a temperature less than the dew point of the warm area, water will condense on the colder object. Dr. C. L. Jones Biosystems and Ag. Engineering

  7. Psychrometric Processes Application: power requirement for heating hog confinement system • 60 sows requiring 0.15 m^3/sec and 16°C • Air coming in: 10°C, 40% RH q = rate of heat transfer to air vapor mixture q = (Q/v) Δh Dr. C. L. Jones Biosystems and Ag. Engineering

  8. Psychrometric Processes: Mixtures • State Point of an air-vapor mixture from mixing 2 air streams at different state points lies on a line connecting the 2 initial state points. (proof on page 259) • Air stream #1: 20 °C, 90%RH, 5 m^3/s • Air stream #2: 40 °C 20%RH, 10 m^3/s Dr. C. L. Jones Biosystems and Ag. Engineering

  9. Psychrometric Processes: Adiabatic Process • Adiabatic: a procedure whereby there is a change from one state to another without heat exchange between system and surroundings • Follows the wet bulb line, H changes, h stays the same • Examples: evap. cooling, dehumidification by absorption Dr. C. L. Jones Biosystems and Ag. Engineering

  10. Psychrometric Processes: Adiabatic Process Example • Moisture content of a large container of coconut must be reduce by removing moisture from the container. • Air at 40°C, 25% rh will be passed through the container at 13 m^3/s. • What is the maximum rate of moisture removal? Dr. C. L. Jones Biosystems and Ag. Engineering

  11. Psychrometric Processes: Adiabatic Process Example • If the original weight and moisture content of the coconut was 500 kg at 75% (wb), what will be the moisture content after 15 minutes of aeration? Dr. C. L. Jones Biosystems and Ag. Engineering

  12. Psychrometric Processes: Addition of Water at any state • Changes enthalpy and humidity ratio • Mass of water: (eqtn 9.100) • Energy balance: (eqtn 9.101) Dr. C. L. Jones Biosystems and Ag. Engineering

  13. 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

More Related