RAC4

In a vapour compression refrigeration plant, the enthalpy values at different points are:

(i) Enthalpy at exit of the evaporator = 350 kJ/kg

(ii) Enthalpy at exit of the compressor 375 kJ/kg

(iii) Enthalpy at exit of the condenser = 225 kJ/kg

The refrigerating efficiency of the plant is 0·8. What is the power required per kW of

cooling to be produced?

• 0·25 kW

• 4·0 kW

• 12·5 kW

• 11 kW

Replacing a water-cooled condenser with an air-cooled one in a vapour compression

refrigeration system with constant evaporator pressure results in

• increase in condensation pressure

• decrease in pressure ratio

• increase in pressure ratio

• increase in condensation temperature

In a vapour compression refrigeration plant, the refrigerant leaves the evaporator at135 kJ/kg and the condenser at 65 kJ/kg. For 2 kg/s of refrigerant, what is the refrigeration effect?

• 70 KW

• 100 KW

• 130 KW

• 140 KW

A single-stage vapour compression refrigeration system cannot be used to produce ultra low temperatures because

• refrigerants for ultra-low temperatures are not available

• lubricants for ultra-low temperatures are not available

• volumetric efficiency will decrease considerably

• heat leakage into the system will be excessive

Ideal refrigeration mixture is one which

• Obeys Raoult's law in liquid phase and does not obey Dalton's law in vapour phase

• Does not obey Raoult's law in liquid phase and does not obey Dalton's law in vapour phase

• Obeys Raoult's law in liquid phase and obeys Dalton's law in vapour phase

• (Does not obey Raoult's law in liquid phase and obeys Dalton's law in vapour phase

Ozone depletion by CFCs occurs by breakdown of

• chlorine atoms from refrigerant by UV radiation and reaction with ozone in troposphere

• fluorine atoms from refrigerant by UV radiation and reaction with ozone in troposphere

• chlorine atoms from refrigerant by UV radiation and reaction with ozone in stratosphere

• fluorine atoms from refrigerant by U V radiation and reaction with ozone in stratosphere

Refrigerant R-717 has Chemical constituent

• Trichlorotrifluroethane (CCl₂FCClF₂)

• . Difluoro monochloro methane (CHF₂CI)

• . Ammonia (NH₃)

• Difluoro dichloro methane (CCl₂F₂)

Refrigerant CCl₂F₂ has designated as

• R 22

• R 12

• R 13

• R134