Refrigeration & Air Conditioning (ME-801) - Important Questions

A machine working on Carnot cycle operates between 305 K and 260 K. Determine the COP when it is operated as a refrigerator and as a heat pump. Also find the work input per TR if operated as a refrigerator.

State the limitations due to which it has not been possible to build a practical Carnot refrigeration system.

The temperature limits of an ammonia refrigerating system are 256C and -106C. If the gas is dry saturated at the end of compression, calculate the coefficient of performance of the cycle assuming no undercooling of the liquid. Use p-h chart / tables for ammonia.

Discuss the effect of change in suction (evaporator) and discharge (condenser) pressure on the performance of vapour compression refrigeration cycle.

Explain the working of a practical aqua-ammonia vapour absorption refrigeration system with a neat diagram, including properties of an ideal refrigerant-absorbent pair.

Explain the working of steam jet refrigeration system with neat sketch.

Explain the desirable thermodynamic, chemical, physical and other favourable properties of an ideal refrigerant.

Discuss the properties of Ammonia and R-22 as refrigerants and compare their suitability for different applications.

The amount of air supplied to an air-conditioned hall is 300 m3/min. The atmospheric conditions are 356C DBT and 55% RH. The required conditions are 206C DBT and 60% RH. Find out the sensible heat removed per minute, latent heat removed per minute and sensible heat factor.

Write a short note on comfort air conditioning and explain the factors affecting comfort.

Moist air enters a chamber at 56C DBT and 2.56C wet-bulb temperature at a rate of 90 cmm. While passing through the chamber the air absorbs 40.7 kW sensible heat and 40 kg/h saturated steam at 1106C. Determine the leaving dry-bulb and wet-bulb temperatures of air.

Explain the term tonne of refrigeration and discuss the advantages of dense air refrigeration system over open air refrigeration system.

In a cooling application, moist air enters a refrigeration coil at the rate of 100 kg of dry air per minute at 356C and 50% RH. The apparatus dew point of the coil is 56C and bypass factor is 0.15. Determine the outlet DBT, WBT and RH of air and the cooling capacity of the coil.

Write short notes on any four: (i) Grand sensible heat factor (ii) Production of dry ice (iii) Li-Br vapour absorption system (iv) Leak detection methods (v) Electrolux system.