Organisation : University of Kerala
Exam : B.Tech Degree Examination
Document Type : Model Question Paper
Category or Subject : Refrigeration & Air Conditioning
Year : November 2016
Website : http://www.keralauniversity.ac.in/downs
Download Question paper : http://www.pdfquestion.in/uploads/9741-refregration.pdf
Refrigeration & Air Conditioning Model Question Paper :
Time: 3 Hours Marks: 100
Part-A : (Answer all questions; each question carries 2 marks)
1. Why a heat pump is preferred to an electric heater for room heating application?
2. Why air cycle refrigeration is preferred for air craft to vapour compression system, even though the COP is very less?
Related : University of Kerala Machine Tool Design Model Question Paper : www.pdfquestion.in/9737.html
3. Two refrigerator manufacturers claim that they developed a new model, working between -10°C and 40°C. First one claims a COP of 7.0, while the second manufacturer claims a COP of 8.0. Which one you will prefer? Why?
4. What is the effect of a LSHE in a VCRS?
5. What is the effect of change in evaporation temperature on COP of a VCRS?
6. Why low specific heat in liquid state is rated better in selection of refrigerants?
7. Why cooling turbine or expander is not used in VCRS?
8. How the function of a compressor in a vapour compression system is carried out in VARS?
9. Differentiate between specific humidity and relative humidity.
10. Which are the different methods for duct sizing? (10×2 = 20 marks)
(Answer any one question from each module; each carries 20marks)
Module – I :
11. a) What are the limitations of reversed Carnot cycle?
b) For a simple air craft refrigeration system, the work output of the cooling turbine is 80 kJ/kg with isentropic efficiency of 0.8 and temperature at its inlet as 45°C.The cabin is maintained at 25°C and 1 bar. The ram air temperature is 27°C and the compression efficiency is 85%.
12. a) Explain the working of a cooling system most suitable for a supersonic air craft.
b) Refrigerator working on reversed Joule’s cycle operates between pressure limits of 1.05 bar and 8.5 bar. Air is drawn from the cold chamber at 10°C, compressed and, hen it is cooled to 30°C before entering the expansion cylinder. Determine the theoretical C.O.P of the system. If the expansion and compression follows the law PV1.3 = Constant, what will be the change in COP?
Module – II :
13. a) (i) Which are the situations where multi pressure systems are used?
(ii) What are the advantages of multiple compression systems?
b) A 5 ton Freon-12 refrigeration plant has saturated suction temperature of (-5) °C. The condensation takes place at 40°C and there is no undercooling of refrigerant liquid. Assuming isentropic compression find (i) COP (ii) Mass flow rate of refrigerant and (iii) power required to drive the compressor in kW. What will be the bore of compressor cylinder, if speed is 3000 rpm, number of cylinders 2 and stroke length is 100 mm?
14. a) What are the deviations in an actual vapour compression cycle compared to a simple saturation cycle?
b) Calculate the power needed to compress 20 kg/min of Ammonia from saturated vapour at 1.4 bar to a condensing pressure of 10 bar by two stage compression with intercooling by liquid refrigerant at 4 bar. Assume saturated liquid to leave the condenser and dry saturated vapour to leave the evaporator.