UNIT-1 Q.1 Draw P-V and T-s diagram of Reversed Carnot cycle (2M-Apr./May-2009) Q.2 Define Ton of refrigeration and COP. (2M- Nov/Dec-2009) (2M-Apr./May-2011) Q.3 Differentiate between heat engine and refrigerator? (2M- Nov./Dec-09) Q.4 The following data refer to an air conditioning system of capacity50 tons. The heat transfer from the condenser operating at full capacity is 7500 KJ/min if the mechanical efficiency of the compressor is 0.8. Obtain COP, motor power, refrigerant flow rate through the system and compressor Swept Volume. The refrigerant used is R-22. The evaporator and condenser pressure are 4.38 bar and 15.27 bar assume dry compression and Vc /Vs = 30. Expansion index is 1.12. (14M-Nov/Dec-09) Q.5 With the help of schematic diagram and p-n diagram briefly explain Two stage compression system with flash inter-cooling.(4m-apr./may-2009) Q.6 A two stage refrigeration system works between pressure limits 9.634 and 1.826 bar. Saturation temperature 40 C and -15 C obtain the COP and capacity for the flow rate of 0.2 kg/s through the evaporator. The intermediate pressure is 4.238 bar compare the COP and capacity of two stage system with the corresponding single stage operating between the above pressure limits. The refrigerant used is R-12. (14M- Nov./Dec.-09) Q.7 An Ammonia ice plant operates between a condenser temperature of 35 C and an evaporator temperature of -15 C. It produces 10 tons of ice per day from water at 30 C to ice at -5 C. Assuming simple saturation cycle, determine: (i) The capacity of the refrigerating plant. (ii) The mass flow rate of refrigerant. (iii) The discharge temperature. (iv) The compressor cylinder diameter and stroke if its volumetric efficiency is η = 0.65, rpm N=1200, stroke/bore ratio L/D = 1.2 (v) The horsepower of the compressor motor if the adiabatic efficiency of the compressor η a =0.85 and mechanical efficiency η m = 0.95 (vi) The theoretical and actual COP.(10M-Apr./May-2009) Q.8 A standard Vapour Compression cycle developing 50 KW of refrigeration using 22 refrigerant operates with a condensing temperatures of 35 C and an evaporating temperature of -10 C.calculate: (i) The refrigerant effect in KJ/kg. (ii) The circulation rate of refrigerant in kg/sec. (iii) The power required by the compressor in KW. (iv) The coefficient of performance (v) The volume flow measured at the compressor suction (vi) The power per KW of refrigeration. (vii) The compressor discharge temperature.(10m-apr./may-2009) Q.9 An ammonia ice plant operate between temperature of 35 C and an evaporator temperature of -15 C it produces 5 tons of ice per day from water at 25 C to ice at -5 C. The ammonia enters the compressor as dry saturated vapour and leaves the condenser as saturated liquid. Determine a) The capacity of the refrigerating plant. b) Mass flow of refrigerant. c) Discharge temperature of NH 3 from the compressor d) Power of compressor motor if the isentropic efficiency of compressor is 85% and mechanical efficiency of compressor is 90% e) Relative efficiency Take latent heat of ice = 335kj/kg, specific heat of ice = 1.94 kj/kg-k, specific heat of water = 4.2 kj/kg-k Properties of ammonia are given below. (14M-Nov./Dec.-2010) 1
Saturation Temp. o C Enthalpy (KJ/kg.) Entropy (KJ/kg-K) Specific Heat (KJ/kg-K) - 15 112.3 1426 0.457 5.549 - - 35 347.5 1471 1.282 4.930 4.6 2.8 Q.10 A food storage refrigeration system uses NH 3 as refrigerant requires 12 tons capacity to maintain the food at -8 C. The condenser temperature is 30 c. The vapour leaving the evaporator is superheated by 6 C and liquid leaving the condenser is sub-cooled by 5 C. If clearance is 2%, L=1.5D, N=900rpm. Find: (i) COP (ii) power required (iii) bore and stroke of single acting one cylinder compressor (10M-Apr./May-2010) Q.11 What are the different methods of improving COP of vapour compression refrigeration system. Describe a cascade refrigeration system with figure. (14M- Nov./Dec.-2010) Q.12 List out the difficulties encountered in the production of low temperatures with the help of single or multi-stage vapour compression refrigeration system. Explain cascade refrigeration system with the help of suitable diagrams.(10m-apr./may-2010) Q.13 Draw the schematic diagrams and cycle diagrams on p-h chart for the refrigeration system using two evaporators,two expansion valve,one compressor and one pressure reducing valve (6M-Apr./May-2010) Q.14 A vapour compression refrigeration machine with Freon-12 as refrigerant, has a capacity of 12 tonne of refrigeration operating between -28 C and 26 C. the refrigerant is subcooled by 4 C before entering the expansion valve and the vapour is superheated by 5 C before leaving the evaporator. The machine has a 6 cyclinder, single acting compressor with stoke equal to 1.25 times the bore, it has a clearance of 3% of the stroke volume. Determine: (i) Theoretical power required (ii) COP (iv) (v) Volumetric η Bore and stroke of cylinder if the speed of the compressor is 1000 rpm,specific heat of liquid refrigerant = 0.963KJ/kg.k and the specific heat of superheated vapour = 0.615 KJ/kg-k. (10M-Apr./May-2011) Q.15 Calculate the power required 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 inter-cooling by liquid refrigerant at 4 bar. Assume saturated liquid to leave the condenser and dry saturated vapour to leave the evaporator. Determine also the power needed when inter-cooling is not employed. (10M-Apr./May-2011) Q.16 Draw- (a) T-s diagram of Reversed Carnot cycle, indicate different processes. (b) P-h diagram of Vapour Compression cycle, indicate different processes. (10M-Apr./May-2011) 2
UNIT -2 Q.1 Write the limitations of reversed Carnot cycle with gas as refrigerant.(2m-apr./may-2009) Q.2 Give the necessity of cooling air craft. (2M- Nov/Dec-2009) Q.3 Draw P-V diagram of reversed Brayton cycle.(2m-apr./may2011) Q.4 A Bell-Coleman cycle works between 1 and 6 bar pressure limits. The compression and expansion is 1.225 and 1.3 respectively. Obtain COP and tonnage of the unit for an air flow rate of 0.5kg/sec. Neglect clearance volume and take temperature at the beginning of compression and expansion to be 7 C and 37 C respectively. (14M-Nov/Dec-09) Q.5 Sketch a boot strap regenerative system and obtain an expression for COP and power requirement for an ideal system in terms of main and auxiliary compression ratio and expansion ratio. (14M- Nov/Dec-2009) Q.6 Prove that in reversed Brayton cycle, COP is a function of pressure ratio only.(4m- Apr./May-2009) Q.7 What are limitation of Carnot refrigeration cycle. (2M- Nov/Dec-2010) Q.8 Draw schematic and T-s diagram of Boot -Strap air refrigeration system.(4m-2011) Q.9 Derive the COP of a Bell-Coleman air refrigeration cycle. Mention its advantage and disadvantages. (14M- Nov/Dec-2010) Q.10 The capacity of a refrigerator is 600TR when working between -5 c and 20 C. Find the mass of ice produced within 24 hrs when water is supplied at 10 c also find the minimum KW required.assume the cycle of operation is Carnot cycle. Latent heat of ice =336 KJ/Kg. (6M-Apr./May-2010) Q.11 A simple air cooled system is used for an Aeroplane to take the load of 20 tons. Atmospheric pressure and temperature condition are 0.9 bar and 23 C. The pressure of air is increased due to isentropic ramming from 0.9 bar and 1 bar. The pressure of air leaving the main compressor is 3.5 bar and its 60% heat is removed in the air cooled heat exchanger and then it is passed through an evaporator foe further cooling. The temperature of air reduced by 7 C in the evaporator. Lastly the air is passed through cooling turbine and then it is supplied to the cooling cabin where the pressure is maintained at 1.03 bar. Assuming isentropic efficiency Of the compressor and turbine are 80% and 75%. Find a) KW capacity required to take the load of cabin. (b) COP of system The temperature of the air leaving cabin should not exceed 25 C. Draw good figure of the system and cycle. (14M-Nov/Dec-2010) Q.12 For an air cycle refrigeration system, the highest refrigeration temperature is 15 C and the exit temperature of the air from the cooling coils is 40 C.find the minimum pressure ratio necessary for producing refrigeration at 1 atmosphere pressure. If the capacity of the plant is 33.5 KW and the pressure ratio is 4, calculate: (i) The mass rate of the air circulated. (ii) Theoretical displacements to the compressor and expander. (iii) The theoretical horsepower of the plant and its COP.(10M-Apr./May-2009) Q.13 A regenerative air refrigeration system is designed to take 18 tonnes of refrigeration load of an aircraft cabin. The ambient air at pressure 0.82 bar and temperature 12 C is rammed isentropically till the pressure rises to 1.2 bar. The air blend off the main compressor of 4.4. bar is cooled by the ram air in the heat exchanger whose effectiveness is 0.62.the air from the heat exchanger is further cooled to 64 C in the regenerative heat exchanger with a position of the air blend after expansion in the cooling turbine. The cabin is to be maintained at a temperature of 22 C and a pressure of 1 bar. If the isentropic efficiencies of the compressor and turbine are 88% and 82% respectively. Determine: (i) Mass of the air bled from the cooling turbine to be used for the regenerative cooling. (ii) Power required for maintaining the cabin at the required condition. (iii) COP of the system. Assume that the temp. of air coming out of regenerative heat exchanger is 100 C.(10M- Apr./May-2009) 3
Q.14 A refrigerator working on Bell- Coleman cycle operates between pressure limits of 1.05 bar and 8.5 bar. Air is drawn from the cold chamber at 10 c.air coming out of compressor is cooled to 30 c before entering the expansion cylinder. Expansion and compression follow the law pv 1.35 =C. Determine the theoretical COP of the system. (10M-Apr./May-2010) Q.15 The speed of aircraft flying at an altitude of 8000 m, where the ambient air is at 0.34 bar pressure and 263 K temperature is 900 kmph. The compression ratio of air compressor is 5. The cabin pressure is 1.013 bar and temperature is 27 c. Determine the power requirement for pressurization, additional power requirement for refrigeration and refrigerating capacity on the basis of 1 Kg/s flow of air. (10M-Apr./May-2010) Q.16 An open air cycle operated by air operated by air refrigeration system is required to produce 6 tonnes of refrigeration effect with a cooler pressure of 11 bar abs. and a refrigerated space or region at a pressure of 1.05 bar. The temperature of air leaving the cooler is 38 C and the air leaving the room is 16 C. Calculate: (i) Mass of air circulated/min (ii) Compressor displacement required/min (iii) Expander displacement required/min (iv) COP (vi) Power required per tonne of refrigeration Assume theoretical cycle is operating with isentropic compression and expansion with no compressor clearance and no losses. For air. Take y=1.41 and c p = 1.003 KJ/kg-k(10M-Apr./May-2011) Q.17 An aircraft refrigeration plant has to handle a cabin load of 25 tonnes. The atmospheric temperature is 16 C. The atmospheric air is compressed to a pressure of 0.96 bar and temperature of 29 Cdue to ram action. The air is then further compressed in a compressor to 4.8 bar, cooled in a heat exchanger to 66 C, expanded in a turbine to 1 bar pressure and supplied to the cabin.the air leaves the cabin at a temperature of 26 C.the isentropic efficiencies of both compressor and turbine are 0.9. Calculate: (i) The mass of air circulated/min (ii) COP Cp = 1.005 KJ/kg-k, γ = 1.4 (10M-Apr./May-2011) 4
UNIT -3 Q.1 How a refrigerant is designated. (2M-2009,2011) Q.2 Give two refrigerant which are used in vapour absorption system. (2M- Nov/Dec-2010) Q.3 Suggest the suitable refrigerant for the following applications with justification: (i) Cold storage for potatoes (ii) Air conditioning system for 1000 bed hospital. (2M-Apr./May-2010) Q.4 Describe electrolux refrigerator system and derive the COP of a simple vapour absorption refrigerator. (14M-Nov/Dec-2009) Q.5 Draw a schematic of Electrolux Refrigerator.state the principle and working. (4M- Apr./May-2009) Q.6 Describe classification and nomenclature of refrigerations. Give salient properties of a good refrigerant suitable for (a) Vapour compression (b) Vapour absorption system. (14M-Nov/Dec-2010) Q.7 Write a short note on any one of the following: (i) capillary tube (ii) thermetically sealed compressor evaporative condenser. (4M-Apr./May- 2010) Q.8 Why is ammonia water absorption system so popular. (2M- Nov/Dec-2009) Q.9 State the properties and uses of ammonia, carbondioxide (4M-Apr./May- 2011) Q.10 Draw a neat sketch of practial ammonia water vapour absorption system and explain the function of each element or equipments used. (14M-Nov/Dec-2009) Q.11 In an acqua-ammonia absorption refrigeration system of 9 tonnes refrigeration capacity the vapours leaving the generator are 100 % pure NH3 saturated at 40 C.the evaporator, absorber, condenser and generator temperatures are -20 C, 30 C, 40 C and 170 C resp.. at absorber exit (strong solution) the concentration of ammonia in solution is x=0.35 and enthalpy h = 22KJ/kg. at generator exit (weak solution) x = 0.1 and h = 695KJ/kg. (i) Determine the mass flow rate of ammonia in the evaporator. (ii) Carry out overall mass conservation and mass conservation of ammonia in absorber (iii) to determine mass flow rates of weak and strong solution. Determine the heat rejection in absorber and condenser, heat added in generator and COP. (10M-Apr./May-2009) Q.12 Explain the working of Electrolux three phase vapour absorption system with a neat sketch and give their merits and demerits. (14M- Nov/Dec-2009) Q.13 What are the different types of refrigerant compressors and expansion devices with suitable sketch write their working.(any 3 compressor and 2 expansion devices) (10M-Apr./May- 2009) Q.14 Draw the neat diagram of Electrolux refrigerator and explain its working principle. What is the important role of hydrogen in this refrigeration system. (10M-Apr./May-2010) Q.15 (A) Draw simple vapour absorption system and briefly explain it. (B) In an absorption type refrigerator, the heat is supplied to NH3 generator by condensing steam at 2 bar and 90% dry.the temperature in the refrigerator is to be maintained at -5 C.find the maximum COP possible. If the refrigeration load is 20 tonnes and actual COP is 70% of the max. COP. find the mass of the steam required/hour. take the temperature of air as 30 C.assume that only latent heat of steam is used for heating purpose. (10M-Apr./May-2011) Q.16 What are the various types of refrigerant compressor. A single stage reciprocating compressor is required to compress 1.5 m3/min of vapour refrigerant from 1 bar to 8 bar. find the power required to drive the compressor,if the compression of the refrigerant is -1) isothermal 2) polytropic with polytropic index as 1.12. (10M-Apr./May-2011) 5
UNIT - 4 Q.1 Define dew point temperature and wet bulb temperature. (2M-Apr./May-2009) Q.2 Define by-pass factor. (2M-Nov/Dec-2010) Q.3 Define comfort air conditioning.(2m-apr./may-2011) Q.4 100 cu.m. of air per minute at 30 C DBT and 60% R.H is cooled to 20 C DBT by passing through a cooling coil. Find the following (a) (b) Capacity of cooling coil in tons of refrigeration. Relative humidity of coming out air and its wet bulb temperature. (14M- Nov/Dec- 2010) Q.5 Draw the schematic diagram of air washer. Show the range of psychrometric processes possible with an air washer.(4m-apr./may-2009) Q.6 What are factors affecting human comfort? Explain effective temperature for human bodies. Gives comfort chart for humans and its requirements. (14M-Nov/Dec-2010) Q.7 Define (i) Specific humidity (ii) Dew point temperature (iii) Degree of saturation (iv) Wet bulb temperature(4m-apr./may-2011) Q.8 List various psychrometric properties. (2M-Nov/Dec-2009) Q.9 Without using psychometric chart, from first principle obtain specific humidity, dew point temperature,relative humidity, enthalpy and specific volume of air for the following measurements recorded for an air sample: barometer =755 mm of Hg DBT = 40 c WBT =30 c (6M-Apr./May-2010) Q.10 The values obtained from a sling psychrometer are tdb = 30 C and twb = 20 C The barometric reading is 740mm of Hg. Calculate (a) Dew point and relative humidity. (b) Degree of saturation (c) Specific humidity (d) Specific volume (e) Specific enthalpy (14M-Nov/Dec-2009) Q.11 39.6 cmm of a mixture of recirculated room air and outdoor air enter a cooling coil at 31 C DB and 18.5 C WB temperature.the effective surface temperature of the coil is 4.4 C. the surface area of coil is such as would give 12.5 KW of refrigeration with the given entering air state.deermine the wet and dry bulb temp. of the air leaving the coil and the coil bypass factor.(10m-apr./may-2009) Q.12 Write short notes on the human body reacts to change in temperature in environment. Also explain the effect of activity on heat exchange for comfort application. (7M-Nov/Dec-2009) Q.13 Saturated air at 19 C is passed through a drier so that its final relative humidity is 25 %.the drier uses silica gel adsorbent. The air is then passed through a cooler until its final temperature is 19 C DBT without change in specific humidity. determine the following: (i) (ii) (iii) (iv) (v) Temperature of air at the end of the drying process. Heat rejected during the cooling process. Relative humidity at the end of the cooling process. Dew point temperature at the end of the drying process Moisture removed during the drying process. (10M-Apr./May-2009) Q.14 What is effective temperature and factor effecting effective temperature. Sketch comfort chart and show on it the comfort zone. (7M- Nov/Dec-2009) Q.15 150 cm of air at 10 c DBT and 8 c WBT heated and adiabatic humidified upto 20 c DBT and 60% RH. Find (i) Heating capacity of the coil in KW and its surface temp.if BF of coil is 0.32. (ii) The capacity of the humidifier. (10M-Apr./May-2010) 6
Q.16 Two streams of air at 40 c DBT and 45% RH and 24 Cand 60% RH are mixed in the ratio of 3:2 respectively and passed over the coil (ADP=13 c, BF=0.3) find: (i) Condition of air entering and leaving the cooling coil. (ii) Now the air is passed over the heating coil (BF=0.3) and heated upto 24 c DBT and 60% RH, find the surface temperature of heating coil. (10M-Apr./May-2010) Q.17 An air conditioned space is maintained at 27 C DBT and 50% RH. The ambient condition are 40 C DBT and 27 C WBT. The space has a sensible heat gain of 14 KW.air is supplied to the space at 7 C saturated. calculate: (i) Mass of moist air supplied to the space in kg/h (ii) Latent heat gain of space in KW (iii) Cooling load of the air washer in KW if 30% of the air supplied to the air is fresh, the remainder being recirculated. (10M-Apr./May-2011) Q.18 Air at 12 C DBT and 85% RH is to be brought to 36 C DBT and 23.2 WBT with the help of winter air conditioner. if the humidified air comes out of the humidifier at 85% RH, draw the various processes involved on a psychrometric chart and determine: (i) Temperature to which air should be heated (ii) Efficiency of the washer. (10M-Apr./May-2011) 7
8 UNIT -5 Q.1 What is meant by effective room sensible heat (ERLH) and effective room latent heat (ERLH). (2M-Apr./May-2009) Q.2 Define sensible heat factor. How room sensible heat factor is shown in the psychrometric chart. (2M-Nov/Dec-2009) Q.3 Define RSHF,GSHF (2M-Apr/May-2011) Q.4 What do you understand by the term cooling load? Discuss briefly the different type of heat load which has to be taken into account in order to estimate the total heat load of a large resturent for summer air conditioning. Sketch the scheme on psychrometric chart and diagram. (14M-Nov/Dec-2009) Q.5 What point should be considered while making heat load calculations. (4M-Apr./May-2009) Q.6 Give schematic diagram and equipment for winter air conditioning, summer air conditioning and year round air conditioning system. Show the process on psychrometric charts for each types. (14M- Nov/Dec-2009) Q.7 Define bypass factor, list the effects of increasing bypass factor. (4M-Apr./May-2011) Q.8 What is cryogenic refrigeration. (2M-Nov/Dec-2010) Q.9 Discuss winter air conditioning system. (6M-Apr./May-2010) Q.10 Define sensible heat ratio, over all heat transfer coefficient sun load, effective sensible heat factor (ESHRF) GSHF, RSHF. Describe summer air conditioning. (14M-Nov/Dec-2010) Q.11 A conference room for seating 100 persons is to be maintained at 22 C dry bulb temperature and 60% relative humidity. The outdoor conditions are 40 C dry bulb temperature and 27 C wet bulb temperature.the various load in the auditorium are as follows: sensible and latent heat load per person. 80 W and 50 W resp.; light and fans, 15000 W; sensible heat gain through glass, wall, ceiling etc., 15000W. the air infilteration is 20 m3/min and fresh air supply is 100 m3/min. two-third of the recirculated room air and one-third of fresh air are mixed before entering the cooling coils. The bypass factor of the coil is 0.1.determine apparatus dew point, the grand total heat load and effective room sensible heat factor. (10M-Apr./May-2009) Q.12 In an industrial evaporative cooling application with outside conditions 40 C DB, 27 C WB, the inside is to be maintained at a maximum relative humidity of 55%.the room sensible heat is 581.5KW. all outdoor air must be used. Find the room dry bulb temperature and supply air quantity as a function of humidifying efficiencies of 80,85,90,95 and 100 %. (10M- Apr./May-2009) Q.13 A spray cooling coil is chosen to operate under the following conditions Air inlet condition 28 C DBT 21 C WBT. Air outlet condition 10 C DBT and 6 C WBT. Total amount of air flow 2000 m3/min.the chilled water inlet and outlet temperature area are 7 C and 12 C respectively. Find the following (a) The cooling load on the coil. (b) Water flow rate through the coil. (14M-2010, Nov-Dec) Q.14 Discuss the different factors which must be considered for evaluating cooling load?(10m- Apr./May-2010) Q.15 The following data relate to a conference room for seating 80 persons. Inside design conditions -22 C, 55%RH Outside design conditions -38 C DBT, 28 WBT Sensible and latent heat loads per person-75w & 45 W resp. Lights and fans load 12000W Sensible heat gain through glass, walls, ceilings, etc.- 12000W Fresh air supply-80m3/min Air infilteration-18m3/min By pass factor of coil-0.1 If two-third of re-circulated room air and one-third of fresh air are mixed before entering the cooling coils, determine: (i) Apparatus dew point (ii) Grand total heat load (iii) Effective room sensible heat factor (10M-Apr./May-2011)
Q.16 List the components of cooling load and heating load (10M-Apr./May-2011) Q.17 An air conditioning system is designed for restaurant when the following data is available. Total heat flow through the walls, roof and floor=21200kj/hr. Solar heat gain through glass = 6800 KJ/hr. Equipment sensible heat gain =10000 KJ/hr. Equipment latent heat gain=2400 KJ/hr. Sensible heat gain due to infiltration air = 4005 KJ/hr. Latent heat gain due to infiltration air =6230 KJ/hr. Sensible heat gain due to occupants = 22750 KJ/hr. Latent heat gain due to occupants = 10300 KJ/hr. Outdoor condition =35 c DBT and 28 c WBT. Indoor condition =27 c DBT and 55% RH. Temp of air supplied to room =17 c DBT. Fresh air mixed with re-circulated air in the ratio of 3:7. Find: (i) RSHF, (ii) DPT and BF of cooling coil, (iii) Load of cooling coil in TR. (16M-Apr./May-2010) 9