Thermo Fluid 2010

B.E Civil Engineering MODEL QUESTION PAPER – 2010,

RGPV, Bhopal, Thermo fluid for Civil Engg.

NOTE:-1 DO ALL QUESTIONS.

2 WRITE WITH PEN ONLY AND NOT WITH PENCIL

Q 1 – An air conditioning unit heats and humidifies air at 10 kPa, 200C and 50 percent relative humidity to 350C and 60 percent relative humidity.

(i) Find the change in wet bulb temperature of air

(ii) Find the change in dew point temperature of air

(iii) Find the change in specific volume of air

(iv) Find the change in specific humidity of air

(v) Find the change in specific enthalpy of air

(vi) If the flow rate through the air conditioner is 75 kg/min, find the heat added.

(vii) If the C.O.P of the air conditioner is 4.5, find the power required fot this process

(viii) Show the process on psychometric chart.
Q 2 A store house 10m x 10m x 5m has the roof and the floor made of such material that the heat transfer through these is negligible. Its four wall are made of concrete { } of thickness 150 mm. The wall is insulated from outside as well as inside. The outside insulation is a plaster { } of thickness 30 mm whereas the inner side insulation is a fiber glass board { }of thickness 5 mm. The outside temperature is 350C and the inside temperature is 50C. The outside and inside heat transfer coefficients are and .

• Find the total thermal resistance of the walls.

• Find the rate of heat transfer to the store room.

• Find the interface temperatures at all layers of a wall.

• An air conditioner is used to maintain the inside temperature as 50C, and the C.O.P of the air conditioner is 4.5, find the power consumed.

Question #1

A house has a composite wall of wood, fiberglass insulation, and plaster board, as indicated in Fig. 1. On a cold winter day the convection heat transfer coefficients are ho = 60 W/m oC, and hi = 30 W/m2 oC. The total wall surface area is 350 m2. The thermal conductivity of the wall are kP = 0.22 W/m oC, kb = 0.038 W/m oC, and ks = 0.12 W/ m oC as shown in the figure(1). Assuming heat transfer through the wall to be one dimensional and steady and neglect the radiation heat transfer, determine:

i- the total thermal resistance of the wall, including inside and outside convection effects for the prescribed conditions.

ii- the rate of heat transfer through the wall

iii- the temperature at the interface between the plaster board and the glass fiber blanket and also between the glass fiber blanket and

the plywood siding (assume perfect contact),

iv- draw the electrical analogy circuit of the wall,

v- draw the temperature profile through the wall.