I.E.S-(Conv.)-2000
(a) A four cylinder single acting ammonia compressor with cylinder dimensions dimensions as 7.5 x 10 cm operates at 600 r.p.m. Condenser and evaporator pressures are 12 and 2 bar respectively. The vapour from the evaporator to suction of compressor is dry and saturated and there is no under-cooling in the condenser. Compression takes place according to law PV 1.2 = constant. If clearance is 2% of the t he stroke, calculate: (i) Refrigerating capacity in tons of refrigeration (ii) Power required to drive the compressor in KW. (iii) Heat rejected to cylinder jacket water in kJ/min. (iv) Heat rejected to the condenser in KJ/min. Take value of gama for NH3 as 1.31 (20) (b) 100 m3 per minute minute outdoor air air at 43.3° C d.b.t. and 37% relative relative humidity humidity is mixed with 200 m3 per minute minute of air at 38.2° C d.b.t. and and 24.5° C wet bulb bulb temperature. The mixed mixed air is dehumidified first by a cooling coil having by-pass factor of 0.32 and apparatus dew point of 15° C and then by a chemical dehumidifier. Air leaves the chemical dehumidifier at 30° C dry bulb temperature. Air is then passed over a cooling coil whose surface temperature is 15° C and by-pass factor 0.26. Calculate (i) Capacity of two cooling coils in tons of refrigeration (ii) Capacity of coil dehumidifier in Kg / mm. (iii) Capacity of chemical dehumidifier dehumidifier in Kg / mm. (iv) Total humidifying capacity of the system in Kg / mm. (20)
I.E.S-(Conv.)-1999
(a) An air conditioning system is designed under the following conditions: Outdoor conditions – 30°C 30°C dbt, 75% R.H. Required indoor conditions – 22°C 22°C dbt, 70% R.H. Amount of free air circulated – 3.33 3.33 m3/s Coil dew point temperature – 14° 14° C The required condition is achieved first by cooling and dehumidification, and then by heating. Estimate (i) the capacity of the cooling coil in tonnes, (ii) the capacity of the heating coil in KW, and (iii) the amount of water vapour removed in kg/s. (20) (b) What are the differences between heat pump and refrigeration cycle? What is the relation between (C.O.P) Heat pump and (C.O.P) Refrigerator? What are the differences between Kelvin Planck and Clausius Statements Statements of 2nd Law? (20)
I.E.S-(Conv.)-1998
a) The following date refers to design of an air conditioning system of a theatre: Total seating capacity 600 persons Sensible heat per person 200 kJ/hr Latent heat per person 130 kJ/hr Solar heat gain through glass, doors and walls 2,50,000 kJ/hr Outside design condition 40° C DBT, 27° C WBT Inside design condition 24° C DBT, 50% RH Apparatus dew point temperature of cooling oil 4° C 50% of return air is recirculated and it is mixed with fresh a ir before entering the cooling coil. Calculate (i) the bypass factor of the cooling coil. (ii) the mass flow rate of supply air to the theatre, and. (iii) the refrigeration capacity of the coil in tons of refrigeration. (b) A 20 ton vapour compression refrigeration system using Freon 12 operates between evaporator pressure of 1 .004 bar and condenser pressure of 13.663 bar. The s ystem uses a sub-cooling superheating heat exchanger with 10° of superheat added. Determine (i) the mass flow rate, (ii) the COP, (iii) the degree of sub-cooling and (iv) the power required. The refrigerant leaving the condenser is dry saturated liquid and leaving the evaporator is dry saturated vapour. The compression in compressor is isentropic (20)
I.E.S-(Conv.)-1997
(a) A food storage locker requires a refr igeration capacity of 50 kW. It works between a condenser temperature of 35° C and an evaporator temperature of – 10°C. The refrigerant is ammonia. It is subcooled by 5° C before entering the expansion valve by the dry saturated vapour leaving the evaporator. Assuming a single cylinder, single-acting compressor operating at 1000 rpm with stroke equal to 1.2 times the bore, determine (a) the power required, and (b) the cylinder dimensions. (20)
(b) 300 m3/mm of air at 10° c dry bulb temperature and 90% relative humidity is to be heated and humidified to 35°C dry bulb temperature and 22.5°C wet bulb temperature. The required conditions are achieved by heating, humidifying and then again by heating. The relative humidity of the air coming out of the humidifier is 90%. Find (20) (i) the heating capacity of the first heater and the by-pass factor if the surface temperature of the coil is 40°C (ii) the capacity of the humidifier in kg/hour (iii) the heating capacity of the second heater and the coil surface temperature if the bypass factor is 0.5, and (iv) the humidifying efficiency of air washer ( humidifier). I.E.S-(Conv.)-1996
(a) What is effective temperature ? Sketch a comfort chart and explain its s ignificance. (b) The properties of air in a room are temperature 35°C and relative humidity 70 per cent. Determine (i) the partial pressure of air, (ii) the humidity ratio, (iii) the saturation ratio, (iv) dew point temperature, (v) density of the air-vapour mixture, (vi) the enthalpy of mixture per kg of dry air. Assume room pressure to be 1.0132 bar and the specific heat for the superheated vapour as 1.863 kJ/kg K. Solve the problem with the help of steam tables. (c) A Freon -12 refrigerator producing a cooling effect of 20 kJ/s operates on a simple cycle with pressure limits of 1.509 bar and 9.607 bar. The vapour leaves the evaporator dry saturated and there is no under cooling. Deter V mine the power required by the machine. If the compressor operates at 3000 rpm and has a clearance volume of 3% of stroke volume determine the piston displacement of the compressor. For compressor assume that the expansion follows the law pv1.13 = constant.
I.E.S-(Conv.)-1995
(a) Atmospheric air at 40°C dry bulb temperature and 55% relative humidity is passed over a cooling coil at the rate of 600 m 3/min. At exit from the coil the air is saturated and its temperature is 8°C. The condensate also leaves at 8 °C. Determine the amount of condensate leaving the coil per minute and the refrigeration required in kW. The specific heat of superheated steam may be assumed to be 1.88 kJ/kg. K. Solve the problem without the use of Psychometric chart. (b) A vapor compression heat pump is driven by a power cycle having a thermal efficiency of 25%. For the heat pump, refrigerant 12 is compressed from saturated vapor at 2.0 bars to t he condenser pressure of 12 bars. The isentropic efficiency of the compressor is 80%. Saturated liquid enters the expansion valve at 12 bars. For the power cycle, 80% of the heat rejected by it is transferred to the heated space which has a total heating requirement of 500 kJ/min. Determine the power input to the heat pump compressor. The following data for refrigerant 12 may be used. Vapor specific heat at constant pressure = 0.7 kJ/kg. K
I.E.S-(Conv.)-1994
A cascade refrigeration system of 100 tons (350 kW) capacity uses ammonia and carbon dioxide the evaporating and condensing temperatures of CO 2 are -40°C and 5°C, respectively. The evaporating temperature of NH 3 is -7°C. The power supplied to the ammonia compressor is 96.5 kW. In the CO 2 circuit, the liquid leaving the condenser is saturated, the vapor leaving the evaporator is dry and saturated, and compression is isentropic. Calculate the mass flow rate of CO 3 and the C.O.P. of the system. The following darn for CO2 may be used: Specific heat of superheated vapor C p = 0.85 kJ/kg K.
I.E.S-(Conv.)-1993
(a) A vapour compassion refrigeration system using refrigerant 12 is employed to produce 8640 kg of ice per day. The condensing and evaporating temperatures of the refrigerant are 48°C and .200 C, respectively. Saturated liquid leaves the condenser and saturated vapour leaves the evaporator. Compression is isentropic. Water at 35°C is used t o from ice. The temperature of ice should be -8°C. Heat flows into the brine tank from the surroundings may be taken to be 10 percent of the total heat removed from water to form ice at the specified temperature. Determine the power required to drive the compressor, in kW. Take specific heat of ice = 2.26 kJ/kg. K, latent heat of ice = 334.72 kJ/kg and specific heat of water = 4.187 kJ/kg K. The following data for refrigerant 12 may be used: Specific heat of vapour = 0.82 kJ/kg. K
(b) Outside air at 35°C, 60% RH is passed over a cooling coil having an apparatus dew point of 10°C and 0.06 bypass factors. The cooled air is then supplied to a room which is to be maintained at 22°C dbt and 60% R.H. The supply air rate 4500 kg/hr. Estimate the sensible and latent heat loads of the room and the heat removed in the cooling coil, in kW. I.E.S-(Conv.)-1992
A refrigeration machine is required to produce ice at 0°C from water at 20°C. The mach ine has a condenser temperature of 28 K while the evaporator temperature is 268K. The relative efficiency of the machine is 50° and 6 kg of Freon -12 refrigerants is circulated through the system per minute. The refrigerant enters the compressor with a dryness fraction of 0.6. Specific heat of water is 4. 187 kJ/kg K and the latend heat of ice is 335 KJ/Kg. Calculate the amount of ice produced in 24 hours. The table of properties of Freon-12 is given below
b) A small auditorium is required to be maintained at 22°C dry bulb temperature and 70% relative humidity. The ambient conditions are at 30°C dry bulb temperature and 75% relative humidity. The amount of free air circulated is 200 m 3/min. The required conditions are achieved by first cooling and dehumidifying through a cooling coil having apparatus dew point of 14°C and then by heating. With the help of psychrometric chart find. (i) The cooling capacity of cooling coil in tons of refrigeration and its bypass factor. (ii) The amount of water vapour removed by the cooling coil in kg/h. (iii) Assuming tile b pass factor as 0.2 determine the capacity of the heating coil in kW and its surface temperature.
I.E.S-(Conv.)-1991
(a) Air at 0 C and 95% R.H. has to be heated and humidified to 25 C and 40% R.H. by preheating, adiabatic saturation in a recalculated-water air-washer and then reheating to final state. Calculate heating required in two heaters, make-up water required in washer and temperature of air wasber.
