Page 1 of 10
PAPER - I
Time Allowed: 3 hours Maximum Marks: 200
INSTRUCTIONS
Candidates should attempt any FIVE questions.
Notations used are standard and will have their usual meanings. Assume suitable data, if found necessary,
and indicate them clearly.
For air R = 0.287 KJ/kg-K, Cp = 1.005 kJ/kg-K
= 14, M = 28966 kg/ kg-mole
1. (a) If u = f (T,v) and h = f(T,p) prove that
du = Cv dT + T p dv k
dh = Cp dT + v(1–T) dp
(15)
(b) A house is to he maintained at 25° C in summer as well as in winter. For this purpose, it is
proposed to use a reversible device as a refrigerator in summer and as a heat pump in winter.
The ambient temperature is 40°C in summer and 3 °C in winter. The energy loss as heat from
the roof and the walls is estimated at 5 kW per degree Celsius temperature difference
between the room and the ambient conditions. Calculate the power required to operate the
device in summer and in winter.
(10)
(e) A cylindrical water tank of 50 cm diameter and 120 cm height is initially filled with water
The top of the tank is open to the atmosphere. A discharge plug is fitted at the bottom of the
tank. When the plug near the bottom of the tank is pulled out, water jet streams out of the
tank with a jet diameter of 1 cm. The mean velocity of the jet is given by v = 2gh where h
is the height of the water in the tank measured from the centre of the hole. Determine how
long it will take for the water level in the tank to drop to 60 cm level from the bottom.
Neglect the distance between the bottom of the tank and the centre of the hole compared to
the total water height.
(15)
2. (a) What are the advantages and disadvantages of using hydrogen as an IC. Engine fuel ? Explain
one method by which hydrogen can be used in C.I. Engine.
(10)
(b) Mention three problems related to environment that are created by exhaust emissions from
the I.C. Engine. What are the major exhaust emissions ?
(6)
(c) What is delay period ? Mention the various factors affecting the delay period. Discuss any
four of them.
I.E.S-(Conv.)-2006
MECHANICAL ENGINEERING
www.estudentzone.com
For more Study Material Visit : http://me-engg-education.blogspot.com
Page 2 of 10
(10)
(d) Discuss the advantages and disadvantages of using LPG in S.I. Engine.
(6)
(e) Air at 25 kPa and 230 K enters a turbojet engine with a velocity of 250 m/sec. The pressure
ratio across the compressor is 12. The turbine inlet temperature is 1400 K and the pressure at
the nozzle exit is 25 kPa. The diffuser, compressor, turbine and nozzle processes are
isentropic and there is no pressure drop for flow through the combustor. Under steady state
operating conditions, determine (i) the velocity at the nozzle exit, and (ii) the pressures &
temperatures at each state. State the assumptions made. Draw the line diagram indicating all
the components & show the processes on a T–s diagram.
(8)
3. (a) Heat losses from the windows are to be reduced by covering them from inside with a
polystyrene insulation (kins = 0027 W/m-K). Consider application of 25 mm-thick windows
(kw = 14 W/m-K). The contact resistance between the glass and the insulation may be
approximated as (R”t, c = 0002 m2
-K/W), while the convection coefficient at the outside
surface of the window is nominally losing heat (h0 = 20 W/m2
-K).
With the insulation, the convection coefficient at the inner surface is hi = 2 W/m2
-K; without
the insulation it is hi = 5 W/m2
-K.
(i) What is the percentage reduction in heat loss associated with the use of insulation ?
(ii) If the total surface area of the windows is As = 12 m2
, what are the heat losses
associated with insulated and uninsulated windows for interior and exterior
temperatures of T, i = 20°C and T, 0 = – 12°C ?
(iii) If the home is heated by a gas furnace operating at an efficiency of f = 080 and the
natural gas is priced at Cg = Re. 1 per MJ, what is the daily saving associated with
covering windows for 12 hours ?
(15)
(b) Water at 20° C flows normal to the axis of a circular tube with a velocity of 15 m/sec. The
diameter of the tube is 25 mm. Calculate the average heat transfer coefficient if the tube
surface is maintained at a uniform temperature of 80°C. Also estimate the heat transfer rate
per unit length of the tube. Properties of water at 20 80 50
2
o T C f
are
Specific heat, Cp = 41813 kJ/kg-K
Kinematic viscosity, = 0568 10–6 m2
/sec
Thermal conductivity, k = 06395 W/m-K
Prandtl number, Pr = 368
Density, = 990 kg/mm3
Dynamic viscosity of water (w) at 80°C = 35456 x 10–4 kg/m-sec
at 20°C = 1006 x kg/m-sec.
Use the relation
1/4
0.5 2/3 0.4 Nu 0.4 Re 0.06 Re Pr
w
(10)
www.estudentzone.com
For more Study Material Visit : http://me-engg-education.blogspot.com
Page 3 of 10
(c) An electrically heated sphere of 15 cm diameter is cooled in a quiescent medium of air at
315 K. In order to maintain the surface temperature of the sphere at 385 K, estimate the
amount of heat to be supplied by the electrical heater.
D = 15 x 10–2 m T = 273 + 20 = 293 K
The properties of air at 315 385 350
2
k are
Kinematic viscosity, v = 2076 x 10–5 m
2
/sec
Prandtl number, Pr = 0697
Thermal conductivity, k = 003 W/m-K
Coefficient of thermal expansion, = l/Tf = 286 x 10–3 K–1
Use the relationship 1/4 Nu 2 0.43 Ra D
(5)
(d) The configuration of a furnace can be approximated as an equilateral triangular duct which is
sufficiently long that the end effects are negligible. The hot wall is maintained at T1 = 1000 K
and has an emissivity 1 = 08. The cold wall is at T2 = 500 K and has an emissivity 2 = 08.
The third wall is reradiating zone for which Q3 = 0. Calculate the net radiation flux leaving
the hot wall.
(10)
4. (a) How can the solar energy be used to obtain refrigeration effect ? Explain with a neat and
clean sketch.
A geothermal well at 130° C supplies heat at a rate of 100,500 kJ/h to an absorption
refrigeration system. The environment is at 30o
C and the refrigerated space is maintained at
–22° C. Determine the maximum possible heat removal from the refrigerated space.
(15)
(c) Obtain an expression for the capacity of a refrigeration system (tonnage) in terms of the rate
of upper and lower pressure limits, expansion index (n), vc/vs, (vc = clearance volume and vs
= swept volume), N (rpm), vc, v1 (specific volume at the inlet to compressor) and the
refrigeration effect (h1 – h4).
If the pressure ratio is 65, n = 11, vc/vs = 0025, N = 900, vs = 600 cc, v1 = 0078 m3
/kg and
refrigeration effect = 150 kJ/kg, calculate the capacity of the system.
(15)
(c) (i) List the various refrigeration arid air-conditioning controls and their functions.
(4)
(ii) Explain adiabatic saturation and thermodynamic wet- bulb temperature. When are the
adiabatic saturation and wet-bulb temperatures equivalent for atmospheric air?
(3)
(iii) What is metabolism ? What is the range of metabolic rate for an average man ? Why
are we interested in the metabolic rate of the occupants of a building when we deal
with heating and air-conditioning ? (3)
5. (a) Show that for a flow governed only by gravity, inertia and pressure forces, the ratio of rates
of flow in two dynamically similar systems equals to the 5/2 power of the length ratio.
(8)
www.estudentzone.com
For more Study Material Visit : http://me-engg-education.blogspot.com