Psychrometrics 2

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Author:
RJVan
ID:
238764
Filename:
Psychrometrics 2
Updated:
2016-01-16 13:28:02
Tags:
Water Moisture Humidity
Folders:
Mechanical Engineering
Description:
Mechanical Professional Engineering Exam Review
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  1. Which of these equations defines relative humidity?
    A.φ=ρwa
    B.φ=ρasat
    C.φ=ρwsat
    C.φ=ρwsat
    (this multiple choice question has been scrambled)
  2. Which of these equations defines relative humidity?
    A.φ=pw/pa
    B.φ=pa/pat
    C.φ=pw/psat
    C.φ=pw/psat
    (this multiple choice question has been scrambled)
  3. What is the humidity ratio, or specific humidity?
    a.ω=ρsata
    b.ω=ρwsat
    c.ω=ρwa
    c.ω=ρwa
  4. What is the definition of relative humidity (φ) in terms of pressures?
    φ=pw/psat (where pw is the partial pressure of water)
  5. What is the humidity ratio (ω) in terms of the partial pressures of water vapor and air?
    ω=0.622(pw/pa)
  6. What are two ways you can find the partial pressure of water (pw) based on the dry bulb and dew point temperatures?
    • pw = φpsat,db where psat,db is is the saturation pressure at the dry bulb temperature.
    • p= psat,dp   where psat,dp is the saturation pressure at the dew point.
  7. How can you find the partial pressure of water (pw) if you know the measured pressure (pt) and the humidity ratio (ω)?
    pw= ptω/(0.622+ω)
  8. How many grains are in a pound?
    7000 grains = 1 lbm
  9. What is the relationship between relative humidity  and humidity ratio  ?
  10. The wet bulb temperature is
    A. the equilibrium temperature that a regular thermometer measures if exposed to the air.
    B.the temperature at which water starts to condense when air is cooled at constant pressure.
    C.the temperature of air that has gone through an adiabatic saturation process.
    C.the temperature of air that has gone through an adiabatic saturation process.
    (this multiple choice question has been scrambled)
  11. When mixing two streams, what are the gravimetric fractions of flows mA and mB?


  12. How do you find the temperature of the mixture if you know GA, GB, TA and TB?
    • Tmixture=TA+GB(TB-TA)
    • Tmixture=TB+GA(TA-TB)
  13. What is the key concept for sensible cooling?
    • For sensible cooling there is no change in dew point. so 
    • q=ma(h2-h1)=ma(cp,a+ωcp,w)(T2-T1)
  14. What is the relationship that converts volume flow (cfm) to mass flow (lbm/hr)?
     
  15. What is the sensible heat ratio?


  16. What is the equation for latent heat added or removed from the air?
    ql=ma12)hfg
  17. What is the equation for the Bypass Factor (BF)?
  18. How is Bypass Factor related to coil efficiency?
    ηcoil=1-BF
  19. What are the steps in solving a problem with steam humidification?
    1) Set up conservation of energy and mass equations:


    2) Assume a value for steam mass flow, solve for ω2 and h2, and check if desired relative humidity (φ) has been achieved. 

    3) Iterate until solved.
  20. If airflow and beginning & final humidity ratios are known, how do you calculate the change in mass flow of water?
  21. If the mass flow rate, the moisture content, and the temperature change of air is known, how do you calculate the heat load?

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