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JolleSI ,.

Code: M813812

B.Tech (Eighth sernester) Examination April-Muy zal6subject: Refrigeration & Air conditilning

Branch: Mechanical EngineeringTime: Three Hours Maximum Mark: g0

Note: Minimum pass Mark: 2g

Ill Attempt all parts of a question in continuity.qi) All questions are compulsory and cany equal marks.(ii| Assume suitable data, if necessary.(iv) Use of refrigeration and, air conditioning data book and psychrometric tables anclcharts are permitted.(v) students are here by advised tg

_ur:preferably refrigeration and psychrometric

properlies tables and chart by Mathur & Mehta published uy luin nrothers.(vi) students are also advised ti enclose the psychiometric chart or refrigerantsproperties chart that has been userlfor ioiving the problem nt prip , pluce withanswer sheet.Q.1. Solve qny one tiut of a and b.

a' A two stage vapor compression refrigeration system working on R 12 refrigerant isoperating between pressure limits of 0.r Mpa (rbar) and 1.0 Mpa (r0 bar). Therefrigerant leaves the condensel as saturated liquid and is first throttled to a flashchamber operating at 0.32 Mpa. vapor from the flash chamber is mixed to therefrigerant leaving the low pressure compressor. The mixture is than compressed tocondenser pressure by High pressure compressor. The liquid in the flash chamber isthrottled to the evaporator pressure and vaporizes in evaporator. Assuming refrigerant

leaves the evaporator as a saturated vapor and bcth compression being isentropiccalculate:

1. Mass fraction of vapor leaving the flash chamber.2. Refrigeration effect per kg of refrigerant.3. COP of the system.Draw schernatic as well as p-h diagram for solving the problem, during labeling labelsuction point of row pressure compressor as l and proceed fuither.

b' Explain explicitly the effect of followings onsimple vapor compression systemusing p-h diagrams. (diagrams must speak the effects)

1. the effect ofrise and fall in suction pressure.2. the effect of rise and fail in delivery pressure.3. the effect of superheating.

4. the effect of sub cooling of liquid.

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Q.2. Solve sny one out af $ and b.

;/ Fot a simple air cycle refrigeration system, the highest refrigeration temperature islsoc and the exit temperature of the air from the heat exchanger after cooling is 40 ocfind the rninimum pressure ratio necessary for producing refrigeration at I ata pressure.If the capacity of plant is 30000 kJ/hr and the pressure ratio is 4 than calculate:

(1) The Mass flow rate of air passing through the conditioned prace.(2) The theoretical displacernent of compressor.

16h' An air cooling system for a jet plane flying from Raipur to Delhi operates on a simplecycle' The pilot cabin and passenger area has to be maintained at l g oc. The outsicle airpressure and temperature are 0.3 bar and -15oc. The pressure ratio of the jetcompressor is 3' The flying speed of plane is 1000 kilometer per hour. The pressuredrop through the heat exchanger is 0.1 bar. Pressure in the purr rrg., space is 1.023 bar.The pressure of the air leaving the cooling turbine is 1.0g ba, and totat cooling load is50000 kJ/h' Assume that

the air is dry and behaves as a perfect gas. calculate:(a) Stagnation t6mperature of air entering the compressor(b) Mass flow rate of air circurated through the cooling space?(c) Maximum vorume rate of air flow through compressor and expander.(d) Net horse power delivered by the engine to the refrigeration system and(e) C.O.p. of the system.

t6Q.3. Solve any one out ef o and b

a' How the refrigerants are internationarly designated, explain:i. The samefor Rl 11,-R11, Rti RzZ,'nli3, R50, RI70, R290.ii. How the brorninated refrigerants *e d*noiea ;;l;;; uy ,*u*pt..iii' How the common inorfanic refrigerants are designated explain byexamples.

t6b' Discuss the replacement for Rl2, Rl l,R22and R502 in the light of phasing out cFCsbecause of depletion of ozone layer.

t6Q.4. Solve aiy one oat of a and b.

-fl'In an

air conditioning system air at aflow rate of 120 kg/min enters the cooling coil at25oc and 50% RH and leaves the cooling coil at l loc and g0% RH. The apparatus dewpoint of the cooling coil is 7 c. Find a) The required cooring cupacity of the coit, b)sensible Heat Factor for the process, and c) By-pass factar af the cooting coil.Assume the barometric pressure to be I atm. Assume the condensate water to leave thecoil at ADp (h = 29.26 kJ/kg).

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b. In the central computer center of NIT Raipur air-conditioning system the condenser iswater cooled and a cooling tower is used for cooling the condenser water of therefrigeration system. Refrigeration system is having a heat rejection rate of 100 kW. In

the cooling tower air

tower at a DBT of 26

enterso

C and

at 35 C (DBT) and 24 C (WBT) and leaves the cooling

relative humidity of 95o/o. What is the requiredflow rateJof air at the inlet to the cooling tower in m /s? What is the amount of make-up water

to be supplied? Thetemperature of make-up water is at 30oC, at which its enthalpy (h*)

may be taken as 125.4 kJ/kg. Assume the barometric pressure to be 1 atm.

l6Q.5. Solve

You have to design a air conditioning system for the restaurant of NIT Raipur. Thefollowing data is available for the seating chairs of capacity of 45 persons. The datarelated to the proposed restaurant is given below.

Inside design condition:Out Side design conditions:Minimum temperature of air supplied to roomTotal amount of fresh air suppliedTotal infiltration of airSeating chairs for diningTotal employees serving the mealsSensible heat gain per personLatent heat gain per seating personLatent heat gain per employeeSensible heat added from per meals

Latent heat added from per mealsTotal heat flow through the walls. roof and floorSolar heat gain through glassEquipment sensible heat gainEquipment latent heat gainTotal Motor power connected to fanThe fan is located before cooling coil

Draw schematic affangement for air conditioning system of the restaurant with labeling of thesame. Draw various points on the psychrometric chart corresponding to schematic arrangementdrawn and:Determine:

1. Amount of air delivered to the restaurant in m3/h2. Percentage of recirculated air.3. Refrigeration load on the coil in tones of refrigeration; and4. Dew point temperature of the cooling coil and by pass factor

ET{D

26OC DBT, 55 % RH36 OC DBT, 27 OC wBT16 OC DBT1550 m3/h390 m3/h

455

60w45W75W0.16 kw0.28 kw5,9 kW1.9 kW2.15 kw0.6s kw7.s kw

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