DATUM LEVEL IN REFRIGERATION

    DATUM LEVEL IN REFRIGERATION

ASSUMED DATUM LEVEL FOR VARIOUS VAPOR REFRIGERANTS

FPS units(–400 F)	mks units( 00 C)	SI units (-400 C)
hl=0 sl=0	hl=100 k cal/kg sl=1.0 k cal/kg 0 C	hl=0 sl=0

Where h_l is enthalpy of liquid and s_l is entropy of liquid respectively.

FOR WATER, ASSUMED DATUM LEVEL  IN SI UNITS

DATUM LEVEL IS 0⁰ C

h_l = 0  enthalpy of liquid

s_l= 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

R_air = 0.287 k J/kg K

R_universal = 8.313 k J/kg mol K

C _{p air}= 1.005 k J/kg K

C _{v air}= 0.718 k J/kg K

Theoretical Compression index = γ_air = 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 <  kg_f

2. k J < k Cal

3. Bar < atmospheric pressure

4. SI HP < British HP

5. 1 US Ton (2000 lb) < 1 British ton (2240 lb)

IMPORTANT PARAMETERS OF COMMONLY USED REFRIGERANTS

Refrigerant	Normal B.P.o C	Critical   temperature o C	Critical Pressure, bar	Freezing point o 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