DATUM LEVEL REFRIGERATION

DATUM LEVEL REFRIGERATION

ASSUMED DATUM LEVEL FOR VARIOUS VAPOR REFRIGERANTS

FPS units(–40F) mks units( 0C) SI units (-40C)
   hl=0

sl=0

  hl=100 k cal/kg

sl=1.0 k cal/kg C

  hl=0

sl=0

Where hl is enthalpy of liquid and sl is entropy of liquid respectively.

FOR WATER, ASSUMED DATUM LEVEL  IN SI UNITS

DATUM LEVEL IS 0C

hl = 0  enthalpy of liquid

sl= 0     Entropy of liquid

                PROPERTIES GIVEN IN THE TABLES 

(i) SATURATED LIQUID SPECIFIC PROPERTIES   

(ii) SPECIFIC PROPERTIES OF SATURATED VAPOR

              PROPERTIES READ FROM THE CHARTS

(i) SUB-COOLED LIQUID SPECIFIC PROPERTIES 

(ii) SPECIFIC PROPERTIES OF SATURATED LIQUID

(iii) WET VAPOR SPECIFIC PROPERTIES  

(iv) SPECIFIC PROPERTIES OF SATURATED VAPOR 

(v) SUPER HEATED VAPOR SPECIFIC PROPERTIES  

VALUES OF VARIOUS CONSTANTS IN REFRIGERATION

Rair = 0.287 k J/kg K

Runiversal = 8.313 k J/kg mol K

p air= 1.005 k J/kg K

v air= 0.718 k J/kg K

Theoretical Compression index = γair = 1.4=Theoretical Expansion Index

Actual Compression index n air = 1.0 to 1.4= Actual Expansion Index

Specific heat at constant pressure  C p water       = 4.184 k J/kg K

At constant volume                        C v water       = 4.184 k J/kg K

For Water vapor,                              C p water vapor= 1.885 k J/kg K

Ice specific heat                               C p ice          = 1.94 k J/kg K

One unit of Pressure                         1 atm       = 760 mm of Hg

Second unit of pressure                     1 ata         = 736 mm of Hg

Third unit of pressure                         1 bar         = 751 mm of Hg

Fourth unit of pressure                        1 torr        = 1 mm of Hg

Power       1 HP          = 736 W = 736 J/s

1 kWh        = 3600 k J

1 k J/kg      = 0.239 k cal

One Ton of refrigeration=211 k J/min = 50 k cal/min

= 200 BTU/min = 3.5167 kW

NOTE

  1.  Newton is smaller than kgf
  2. k J is smaller than k cal
  3. Bar is smaller than atmospheric pressure
  4. SI HP is smaller than British HP
  5. 1 US Ton (2000 lbs) is smaller than 1 British ton (2240 Lbs)

IMPORTANT PARAMETERS OF COMMONLY USED REFRIGERANTS

Refrigerant Normal B.P.C Critical   temperature C Critical Pressure, bar Freezing point C Index’ γ’
Water 100 374.15 218.3 0.0 1.27
Ammonia -33.35 132 112 1.31
Carbon Dioxide -78.52 31.00 73.7
R22 -41 96 50 1.18
Air -191 -140.2 1.4
Oxygen -183 -118.8 -218.8
Nitrogen -196 -147 -210
Hydrogen -253 -240 -259
Helium -269 -268 -269.7