Types of Steam

Specific Enthalpy, Entropy & IE

VCR Cycle

VCR Cycle

Heat Engine, Pump & Refrigerator

Types of Steam

Saturation points of steam and units of specific Enthalpy, Emtropy & IE

REFERIGERATION & AIR-CONDITIONING

REFRIGERATION

Science of providing and maintaining temperatures below that of surroundings.

· Deals with the chilling or freezing of a substance by removing some of its heat.

· Transfer of this heat to another system at high temperature.

· For this mechanical work must be performed to satisfy the second law of thermodynamics.

AIR CONDITIONING refers to simultaneous control of temperature, humidity, cleanliness and air motion within a confined region.

Separating Calorimeter

Separating & Throttling Calorimeter

Throttling Calorimeter

measuring quality of steam

Measurement of Quality of Steam

For pure substances –in-dependant properties such as pressure and temperature are needed (if pressure is known, temperature can be found)

We need specific volume, enthalpy or quality of mixture(liquid & vapour)

For measuring specific volume of mixture (quality) calorimeters are used.

a) Separating Calorimeter

b) Throttling Calorimeter

c) Separating & Throttling Calorimeter

d) Barrel Calorimeter

e) Electric Calorimeter

a) Separating Calorimeter:

Fig

X = M/ (M+m)

M=Mass of dry steam read from gauge of condenser

M=Mass of water separated in specified time interval

x= Dryness fraction or quality of steam

b) Throttling Calorimeter

Fig

x1= (h-hf1)/ hfg1

Let P1 = Initial Pressure

x1 = Dryness Fraction

hf1 = Enthalpy of water at P1

hfg1 = Enthalpy of vaporization

Cps = Sp heat of superheated steam after throttling..kJ/ kg

Tsat = Saturation temp at P2

During throttling process, the enthalpy remains constant.

Enthalpy of steam at P1 before throttling= Enthalpy of steam at P2 after throttling

hf1 + x1 hfg1 = hg2 + Cp (T2-Tsat)

x1 hfg1= hg2 + Cp (T2-Tsat) - hf1

x1= hg2 + Cp (T2-Tsat) - hf1/ hfg1

= h- hf1/ hfg1

h = sp enthalpy at state 2 from superheat read from table

MEASUREMENT OF QUALITY OF STEAM

Measurement of Quality of Steam

For pure substances –in-dependant properties such as pressure and temperature are needed (if pressure is known, temperature can be found)

We need specific volume, enthalpy or quality of mixture(liquid & vapour)

For measuring specific volume of mixture (quality) calorimeters are used.

a) Separating Calorimeter

b) Throttling Calorimeter

c) Separating & Throttling Calorimeter

d) Barrel Calorimeter

e) Electric Calorimeter

a) Separating Calorimeter:

Fig

X = M/ (M+m)

M=Mass of dry steam read from gauge of condenser

M=Mass of water separated in specified time interval

x= Dryness fraction or quality of steam

b) Throttling Calorimeter

Fig

x1= (h-hf1)/ hfg1

Let P1 = Initial Pressure

x1 = Dryness Fraction

hf1 = Enthalpy of water at P1

hfg1 = Enthalpy of vaporization

Cps = Sp heat of superheated steam after throttling..kJ/ kg

Tsat = Saturation temp at P2

During throttling process, the enthalpy remains constant.

Enthalpy of steam at P1 before throttling= Enthalpy of steam at P2 after throttling

hf1 + x1 hfg1 = hg2 + Cp (T2-Tsat)

x1 hfg1= hg2 + Cp (T2-Tsat) - hf1

x1= hg2 + Cp (T2-Tsat) - hf1/ hfg1

= h- hf1/ hfg1

h = sp enthalpy at state 2 from superheat read from table

CLAUSIUS STATEMENT OF SECOND LAW

▀Clausius Statement of second law:

It is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a system at low temperature to another system at high temperature.

Clausius statement points-out the essence of work input required in Refrigerators & Heat pumps

Fig

Heat can’t flow from low temperature to high temperature systems.

COP=Q/W=Q/0=∞.............(impossible)

It is impossible to construct a refrigerator, which operates without an input of work.

Fig

CLAUSIUS STATEMENT

▀Clausius Statement of second law:

It is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a system at low temperature to another system at high temperature.

Clausius statement points-out the essence of work input required in Refrigerators & Heat pumps

Fig

Heat can’t flow from low temperature to high temperature systems.

COP=Q/W=Q/0=∞.............(impossible)

It is impossible to construct a refrigerator, which operates without an input of work.

Fig