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2003 Course Refrigeration & Air Conditioning

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Total No. of Questions : 12] P1185 [Total No. of Pages : 6 [3664]-143 B.E. (Mech. SW) REFRIGERATION AND AIR CONDITIONING (2003 Course) Time : 3 Hours] [Max. Marks : 100 Instructions to the candidates: 1) 2) 3) 4) 5) 6) Answer any three questions from each section. Answers to the two sections should be written in separate books. Neat diagrams must be drawn wherever necessary. Figures to the right indicate full marks. Use of logarithmic tables, slide rule, Mollier charts, electronic pocket calculator and steam tables is allowed. Assume suitable data, if necessary. SECTION - I Q1) a) Explain Steam Jet refrigeration system with neat sketch. [8] b) Explain Reduced ambient air-refrigeration cycle. Why it is called reduced ambient? [8] OR Q2) a) Define the terms COP, EER, SEER, IPLV. [8] b) A reversed cycle has refrigerating COP of 4, [8] i) Determine the ratio T1/T2. ii) If the work done on the cycle is 10 kW, determine the maximum refrigerating effect in TR. iii) If this cycle is used as heat pump, determine the COP and heat delivered. Q3) a) Define the following : i) ODP ii) GWP. iii) TEWI. [4] b) What is difference between retrofitting and drop in. What are the modifications made in R-12 system to make it suitable for HFC-134a refrigerant? [4] P.T.O. c) Differentiate between dry compression and wet compression. Why expansion device is used in VCC instead of expander. Discuss with the help of P-V and T-S diagram. [8] OR Q4) a) Discuss various losses occurred in actual vapour compression cycle.[8] b) A vapour compression refrigerator works between the pressures of 5.3 bar and 2.1 bar. The vapour is superheated at the end of compression; its temperature being 37 C. The vapour is superheated by 5 C before entering the compressor. The specific heat at constant pressure for superheated vapour is 0.63 kJ/kgK. Find the COP of the plant. Use the data given below. [8] Pressure (bar) Temp. C hf (kJ/kg) hfg (kJ/kg) 5.3 2.1 15.5 -14.0 56.15 25.12 144.9 158.7 Q5) a) What is necessity of multi staging? Explain the analysis of two stage compression system with flash gas chamber as a gas removal. [8] b) A refrigeration system using R-12 as refrigerant has three evaporators of capacities 30TR at - 10 C, 20 TR at 5 C and 10 TR at 10 C. The refrigerant leaving the evaporator is dry and saturated. The system is provided with compound compression, individual expansion valves and flash intercoolers. The condenser temperature is 40 C. Assuming isentropic compression in each compressor, find the power required to run the system and COP of the system when the liquid refrigerant leaving the refrigerant is saturated. [10] OR Q6) a) Compare VAC and VCC. [4] b) Explain construction and working of Electrolux refrigerator system. [8] c) Explain with neat sketch Cascade refrigeration system. Why CO2 is a suitable refrigerant for this system. [6] SECTION - II Q7) a) Prove Enthalpy of moist air (h) = cpm Td + w (hfg) at 0 C . Where cpm = humid specific heat, Td = DBT, w = humidity ratio, hfg is enthalpy of evaporation. [4] b) Sketch comfort chart and show on it the comfort zone . [6] [3664]-143 2 c) The sling psychrometer reads 40 C DBT and 28 C WBT. Calculate the following : [6] i) Specific humidity. ii) Relative humidity. iii) Vapour density of air. iv) Dew-point temperature. v) Enthalpy of the mixture per kg of dry air. Assume atmospheric pressure to be 0.95 bar. OR Q8) a) State and explain the factors affecting human comfort. [4] b) Explain the different psychometric processes with the help of Air washer. [4] c) Room air at 20 C DBT and 50% RH is mixed with outdoor air at 40 C DBT and 30% RH in the ratio of 4 : 1. The mixture is passed through a cooling coil whose temperature is maintained constant at 10 C whose by pass factor is 0.2. Determine the following : [8] i) Condition of air before entering the cooling coil, ii) Condition of air leaving the coil and iii) Refrigeration load on cooling coil when 250m3/min of air is supplied to the room. Q9) a) Describe the procedure to estimate load on air-conditioning system with the help of psychometric chart and block diagram. Explain both cases, mixing of air before and after cooling coil. [10] b) Explain air-water air-conditioning system with neat sketch. [6] OR Q10) a) Enumerate main types of condensers in use with specific application of [6] each type. b) Compare D-X and flooded type evaporators and explain construction and working of any one flooded type evaporator. [6] c) Explain the procedure of charging of refrigerant in the system. Q11) a) Explain pressure losses in duct. [4] [6] b) Why the ducts are used in an air-conditioning system. Classify ducts.[4] [3664]-143 3 c) A rectangular duct section 500 mm 350 mm size carries 1.25 m3/s of air having density of 1.15 kg/m3. Determine the equivalent diameter of a circular duct if [8] i) the quantity of air carries in both cases is same. ii) and velocity of air in both cases is same. If f = 0.001 for sheet metal, find the pressure loss per 100m length of duct. OR Q12) a) Discuss various applications of cryogenics. [8] b) Explain construction and working of linde system liquefaction of gas.[10] [3664]-143 4 [3664]-143 5 [3664]-143 6

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