# GAS REFRIGERATION CLASS NOTES FOR MECHANICAL ENGINEERING

## AIR AS REFRIGERANT IN AIRCRAFT’S

### NECESSITY OF AIRCRAFT COOLING

#### Air cycle refrigeration COP is less because of sensible cooling.

BELL COLEMAN CYCLE

### replaces the evaporator.

Fig. Line Diagram Bell Coleman Cycle

Fig. Bell Coleman Cycle on p-V Chart

### DISADVANTAGES OF BELL COLEMAN CYCLE

#### (iii) Mass of air required per ton of refrigeration is large as compared to other systems of refrigeration. Hence size of the system is large.

TYPES OF AIR REFRIGERATION CYCLES

### Purpose of boot strap compressor

##### COP Of Air Refrigeration Cycle

COP = Cooling effect/ Net work input

Net work input = Work in compressor –Work from Turbine

Normally COP of Air Refrigeration Cycle is less than 1.

VARIOUS EXPRESSIONS FOR COP OF AIR REFRIGERATION

(i) Firstly compression and expansion are isentropic

COP = (T1—T4)/[(T2—T1)—(T3—T4)]

(ii) Secondly compression is isentropic and expansion is poly-tropic

COP = (T1—T4)/[(T2—T1)—(n/(n-1)((γ—1)/γ)(T3—T4)]

(iii)  Thirdly compression is poly-tropic and expansion is isentropic

COP = (T1—T4)/[ (n/(n-1)((γ—1)/γ)( (T2—T1)— T3—T4)]

(iv)  Fourthly both compression and expansion are poly-tropic

COP = (T1—T4)/[(n/(n-1)((γ—1)/γ)] [  (T2—T1)— (T3—T4)]

Normally it is less than 1.

Differences between Air Refrigeration and Vapor Compression Refrigeration

#### Vapor compression Refrigeration

##### There is work of expansion in turbine.
There is no turbine.

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