4363-120-RAC | Refrigeration | Relative Humidity

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TE Mechanical Pune University Question Papers for May-2013 Exam!
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  Page 1 of  8   [Total No. of Questions: 12] [Total No. of Printed Pages:8] UNIVERSITY OF PUNE[4363]-120 T. E.(MECHANICAL) May Examination - 2013 REFRIGERATION AND AIRCONDITIONNING(302051) (2008 Course)[Time: 3 Hours] [Max. Marks: 100]Instructions: 1 Answers to the two sections should be written in separateanswer-books. 2 Black figures to the right indicate full marks. 3 Your answer will be valued as a whole4 Neat diagrams must be drawn wherever necessary. 5Use of electronic pocket refrigeration tables, calculator and  steam tables is allowed. Psychometric chart.6  Assume suitable data, if necessary. 7  Answer any three questions from Section I and any threequestions from Section II  SECTION  –  I Q.1 A) State (minimum four) different application of refrigeration and explain any one of them.[3]B) Refrigerator working on reversed Carnot cycle withinthe temperature limits 36 o C and -20 o C has R 152a vapor as a working medium. Find work of compression, work of expansion, refrigerating effect, heat rejected per kg of refrigerant and COP of the cycle. Show the cycle on P-h,T-s diagram with parameters. If actual refrigerator hasCOP of 0.78 of the maximum how much will be power consumption per ton of refrigeration capacity? Usefollowing R 125a data.[8]  Page 2 of  8   t o C p bar v g m 3 /kg h f  kJ/kg h g kJ/kg s f  kJ/kgk s g kJ/kgk -20 1.211 0.2514 168.43 493.26 0.8768 2.159936 8.159 -- 264.19 529.8 1.2251 2.0842 C) With a schematic diagram explain the working of Vortextube. State its applications.[5]OR Q.2 A) Explain deviation of actual / practical VCC from simplesaturated VCC with P-h, T-s diagrams.[6]B) Domestic refrigerator of 1/8 ton refrigeration (TR)capacity has COP half that of Carnot COP. Outside air temperature is 40 o C while freezer is maintained at  –  10 o C. Assuming 5 o C temperature difference is requiredon both sides determine the power consumption.[6]C) State and explain the limitations of reversed Carnotcycle with vapor and gas as working medium.[4]Q. 3 A) Sketch actual vapor compression cycle on P-h and T-sdiagram and explain all processes briefly.[8]B) Simple saturated VCC using R134a has capacity of 2TR.Evaporator and condenser temperatures are  –  18 o C and40 o C respectively. Calculate mass flow rate of refrigerant, COP of system, heat rejected in condenser and power consumption. What will be effect on COPand power consumption if liquid vapor heat exchanger is placed in the system? Vapor enters the heat exchanger asdry saturated and leaves at 12 o C. Use following[10]  Page 3 of  8    properties. Specific heat of R 134a vapor is 0.823kJ/kgK and specific heat R 134a liquid is 1.145 kJ/kgK .Show the cycle on P-h and T-s diagram with important parameters. t o C P bar v g m/kg h f  kJ/kg h g kJ/kg s f  kJ /kgK s g kJ /kgK -18 1.446 0.13592 176.23 387.79 0.9104 1.739640 10.166 -- 256.41 419.43 1.1905 1.7111 OR Q. 4 A) In a simple saturated vapor compression cycle using R22condenser and evaporator temperatures are 40 o C and 0 o Crespectively. For the refrigerating capacity of 15 TR,calculatei)   mass flow rate (kg/s)ii)    power consumption (k W)iii)   COPiv)   volume flow rate (m 3 / s)v)   discharge temperature ( o C)vi)   condenser capacity (k W). Show cycle on P-hand T-s diagram.Use following properties. Specific heat of R22 vapor is0.67 kJ/ kgK. t o C P bar v g m 3 /kg h f  kJ/kg h g kJ/kg s f  kJ/kgK s g kJ/kgK  0 4.976 0.0471 200.0 405.36 1.000 1.751840 15.335 0.151 249.08 415.95 1.1666 1.6995[10]B) Describe with sketch working of single effect ammonia-water vapor absorption system[8]Q. 5 A) Comment on the following properties of refrigerant assection criteria-1) Condenser and evaporator pressure 2)[6]  Page 4 of  8    Normal boiling point 3) Action with water, oil and other material used 4) Thermal conductivity.B) R-22 plant has two evaporators 1) at -30 o C, refrigeratingcapacity 30,000 kJ/h and 2) at -25 o C refrigeratingcapacity 45,000 kJ/h. Vapor leaves the evaporator with 6degree of superheat. Condenser temperature is 35 o C andthere is no sub-cooling. The vapors are superheated by10 degree in suction line. A single acting for cylinder compressor has Speed 930rpm, volumetric efficiency =72% and bore / stroke ratio 1.25. Calculate thedimensions of cylinder, power consumption and COP.Use Chart. Show cycle on P-h diagram with parameters.[10]OR Q. 6 A) What are different alternative refrigerants for R12 andR22? Why do they need replacement?[6]B) R-22 plant of capacity 150 kW is working between thecondenser and evaporator temperatures 40 o C and -30 o Crespectively. There is no sub-cooling of the refrigerantand vapor enters the compressor in dry saturated state.Find power consumption, COP, and mass flow ratei)   when one stage is used andii)   when two stage compression with flash inter cooling is used. Use Chart[10] SECTION II Q. 7 A) Explain the followings :i)   Relative humidity[6]
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