RAC

1. Branch : ME –D1
Prepared by: MEHUL VORA (140120119249)
Submitted to: Prof. MRUGESH KHATRI
Refrigeration and Air ConditioningRefrigeration and Air Conditioning
(2161908)(2161908)
PSYCHROMETIC PROCESS

2. Content of presentation
• Heating and dehumidification
• Heating and humidification
• Cooling and dehumidification
• Cooling and humidification

3. Heating dehumidification
• Removal of water from air is called
dehumidification
• In this method moisture is absorbed by chemical
like NaCl, LiBr, CaCl2, brine, ethyl glycol or silica.
• This process takes place along WBT line from 1-2.
• In this process latent heat released by moisture
is taken as sensible heat by air.
• In some cases reaction heat is also released so
process will flow along 1-3.
• So enthalpy difference is equal to additional heat.
• Absorption capacity of chemical is low at high
temperature.

4. Heating dehumidification
• Practically air can’t absorb all the heat so the chemical from the
sump is cooled and then recirlculated for spraying.
• Than the process would be 1 - 4 and the enthalpy difference h2- h4 or
h3- h4 is the heat absorbed by the chemical which is removed before
recirculation.

5. Heating humidification
• If the air is passed over heated water whose temperature is above
the DBT of air, the air will be simultaneously heated and humidified.
• Thus in this case supply air to the room needs to be heated and
humidified. It is carried out in 2 stages.
• Air is first sensibly heated in a heating coil and than passed through a
spray of water for adiabatic humidification process.
• Efficiency of humidification t2- t 1 / t2- twb
• It is used in winter AC to warm and humidify the air.

6. Cooling dehumidification
• It is possible if air is passed over a cooling coil which is at a
temperature below the dew temperature of air.
• The extent of moisture condensation from air would depends upon
coil temperature.
• Since water vapor condense out the coil surface temperature in the
process is called the apparatus dew point
• Under ideal condition the air coming out of the coil will be at its ADP
temperature, but it is never possible due to inefficiency of cooling
coil.
• Assume that a part of air passes over the coil to reach the ADP
temperature and the remainder air is bypassed.

7. • So, bypass factor as the ratio of air which is unaffected by the coil to
the total air quantity passing over the coil.
• BF is also depends on number of rows of coil and air velocity
• Efficiency = 1 – BF
• The cooling coil in this process absorbs sensible heat to reduce
temperature and also absorbs latent heat to reduce moisture
content
• SHF = Sensible heat absorbed / total heat absorbed
• SHF of a process in one way represent slope of the line representing
process on chart
• Cooling capacity = mass rate of flow * h1- h2 kW
• Capacity = 0.02 * m3
/min h1- h2 kW

8. Cooling humidification
• This process takes place when hot unsaturated air flow over water
surface. The air looses sensible heat to water and water vapor
formed is carried away by same stream. Thus in this process air
losses Sensible heat and gains latent heat with no heat transfer with
surrounding so it is called adiabatic cooling process in this process
DBT reduces.
• The water surface could be in the form of water spray to expedite
evaporation and cooling.
• Since the process is adiabatic the enthalpy of air remains same. Thus
the process is along constant enthalpy line.

9. • The lowest temperature possible by this process is the twb of the air
being cooled. But just as in the case of coil it is uneconomical to
provide large number of banks to spray to get the cooling to twb so air
gets cooled to t2temperature higher than twb and the efficiency is
given by t1- t2/ t1- twb.
• The water is recirculated after collection in a pan at the bottom. The
water lost by evaporation is made up by adding water to pan
periodically. The make up water is also known as humidify duty
• humidify duty in liter/hour = mass rate of dry air in kg/m * (w2–w1)*

10. • This is the process used in dessert/air coolers. Efficiency is depends
upon thickness and uniform distribution of fibers in a pad.
• Since the humidity of air increased in the process.
• The extent of cooling is depends on DB and WB temperature
• It is necessary that large air movement should be ensured in the
room
• This process is also used in cooling towers for cooling of condenser
water.

11. Numerical