Intro to Refrigeration Enthalpy & Gas Laws Flashcards
Charles 1 st Law
p1 x T2 = p2 x T1
Volume is constant
Increase in absolute temperature of an ideal gas whose volume is constant will also result in a proportional increase in pressure of that gas.
Charles 2nd Law
V1 x T2 = V2 x T1
Pressure is constant
That increase in the absolute temperature of an ideal gas whose pressure is constant will result in a proportional increase in the volume of that gas
Boyles Law
p1 x V1 = p2 x V2
Temperature is constant
That increase in absolute pressure of an ideal gas from which temperature is constant will result in a proportional decrease in the volume of that gas.
Bernoulli’s Law
That an increase in the fluid flow results in a decrease in the lateral or static pressure applied by that fluid.
Pascal’s Law
Pascals las states that in a closed loop system, a change in fluid pressure results in an equal change in pressure applied through the fluid at a given level
Dalton’s Law
That the total pressure of a mixture of gases is the sum of each individual gas pressure.
Absolute zero pressure in gauge pressure?
29.92 “hgv
Psia ?
PSIG + 14.7
What is the ideal gas law formula?
pV=mRT
m= mass
p= Pressure
R= the gas constant
T= Temperature
V= volume
General or Combined gas law
p1 x V1 x T2 = p2 x V2 x T1
Pressure
Volume
Temperature
Convert formula to Kelvin
K = Deg Celsius + 273
Convert to Rankine
Deg R = Deg F + 460
kPag to Kapaa
kPa= kPag + 101.3
What is heat ?
Energy in a form of molecules in motion.
Latent heat
The hidden heat added or removed during a change is state or phase.
Specific heat?
The amount of heat in a unitary mass of a substance
Sensible heat ?
The visible heat added or removed during a change in temperature.
Enthalpy
The amount of heat in one pound of a substance starting from a zero-base point and at universally accepted temperature. The base point of refrigerants is -40 Deg F or C
Entropy
A measure of change in a refrigerants molecular activity without a change in molecular structure while passing a vapour through a compressor. Useless heat.
Pressure
Force applied over an area
Specific Volune
The volume per unit mass of a substance
Subcooled
A liquid refrigerant at a lower temperature than it’s saturation temperature for a given saturation pressure
Superheat
A refrigerant vapour at a higher temperature than it’s saturation temperature for a given saturation pressure
What is Net Refrigeration Effect
Is the amount of heat gained in the evaporator during a refrigeration cycle.
NRE = evaporator outlet enthalpy - metering device inlet enthalpy
NRE = h3-h1
Heat of Compression (HOC)
Is the amount of heat added by the compressor and the compression process during the refrigeration cycle.
HoC = Compressor outlet enthalpy - Compressor Inlet Enthalpy
NRE= h5-h4
Heat of Rejection. (HOR)
Is the amount of heat rejected by the condensing process during refrigeration cycle.
HOR = Compressor Outlet Enthalpy - Metering device inlet Enthalpy
HOR = h5-h1
Mass flow rate
Is the velocity of the refrigerant flowing through the refrigeration system.
m = system capacity / NRE or
200 btu/min / NRE
Coefficient of Performance
Is a positive value used to rate the refrigeration system. Higher COP value results in effective system performance.
CoP = NRE / HoC
Compression Ratio
Compression ratio is a positive value used to rate a refrigeration system. Lower CR value results in greater system performance
CR = Saturated Discharge Absolute Pressure / Saturated Suction Absolute Pressure
Critical point
Is referred to as a refrigerants condition where it’s liquid and vapour form coexist and cannot change state.
