Shivaji University 2006 B.E Mechanical Engineering T.E.(Mech)(Sem.-V) , HEAT AND MASS TRANSFER - Question Paper
Sunday, 19 May 2013 07:40Web
HEAT AND MASS TRANSFER
Time:3 Hours
Maximum Marks:100
Instructions:
1)Attempt any 3 ques. from every part.
2)Draw neat figures wherever necessary.
1.Solve the follwing:
a)How is thermal conductivity of a material is defined? elaborate its units? Write the values of thermal conductivity for 1 metal, 1 liquid, and for 1 gas.[Marks 5]
b)A plane wall is 150 mm thick and its wall area is 4.5m2. If its conductivity is 9.35 W/moC and surface temperatures are steady at 150oC and 45oC, determine the heat flow across the plane wall and temperature gradiet in the direction of flow of heat.[Marks 5]
c)Discuss the spectrum of electromagnetic radiations.[Marks 4]
d)Discuss the kinds and applications of fins.[Marks 4]
2.A 240mm steam main, 210mm long is covered with 50 mm of high temperature insulation(K=0.092 W/m.C) and 40mm of low temperature insulation(K=0.062 W/m.C). The inner and outer surface temperatures as measured are 390 C and 40 C respectively. compute
i)The total heat loss per hour.
ii)The heat loss per m2 of pipe surface per hour.
iii)The heat loss per m2 of outer surface per hour.
iv)The temperature ranging from 2 layers of insulation. [Marks 16]
3.a)Derive the expression for heat transfer and temperature distribution for a fin with insulated tip. [Marks 8]
b)A long hollow cylinder has inner and outer radii as 5cm and 15cm respectively. It generates the heat at the rate of 1KW/m3. The thermal conductivity of cylinder material is 0.5 W/m.C. If the maximum temperature occurs at radius 10 cm and temperature of outer surface is 50 C findi)The temperature at inner surface, and ii)The maximum temperature. [Marks 8]
4.a)Find the expression for heat exchange ranging from 2 infinite parallel gray plates. [Marks 8]
b)Determine the rate of heat loss by radiation from a steel tube of outside diameter 70mm and 3m long at atemperature of 227C. If the tube is located within a square brick conduit of 0.3m side and at 27C. Take emissivity for steel=0.79, Brick=0.93.[Marks 8]
5.a)Distinguish ranging from natural and forced convection heat transfer. [Marks 4]
b)How does radiation play an important role in boiling heat transfer? [Marks 5]
c)Explain the concept of mean film temperature. [Marks 4]
d)Enumerate applications of mass transfer. [Marks 5]
6.a)Using dimensional analysis , find the general form of formula for natural convection heat transfer. [Marks 8]
b)A surface condenser consists of 200 thin walled circular tubes(each tube is 22.5mm in diameter and 5m long) organizes in parallel , through which water flows.
If the mass flow rate of water through the tube bank is 160Kg/s and it's inlet and outlet temperatures are known to be 21C and 29C respectively, compute the avg. heat transfer coefficient associated with water flow.
Take the thermo physical properties of water at 25C.
You may use correlation
Nu=0.023((Re)^0.8)((Pr)^0.4) [Marks 8]
7.a)Explain the concept of velocity and thermal boundary layer. [Marks 4]
b)Distinguish ranging from laminar and turbulent flow. [Marks 4]
c)A vertical cylinder 1.5m high and 180mm in diameter is maintained at 100C in an atm. environment of 20C. compute heat loss by free covection from the surface of the cylinder.
presume properties of air at mean temperature.
You may use a correlation
Nu=0.10((Gr.Pr)^0.333). [Marks 8]
8.a)Derive expression for effectiveness by NTD method in case of parallel flow heat exchanger. [Marks 8]
b)In counter flow double pipe heat exchanger, water is heated from 20C to 60C by an oil with a specific heat of 1.45KJ/Kg.K and mass flow rate of 0.9Kg/s.The oil is cooled from 230C to 160C. If the overall heat transfer coefficint is 420 W/m2K, compute the following:i)The rate of heat transfer ii)The mass flow rate of water iii)The surface area of heat exchanger. [Marks 8]
| Earning: Approval pending. |
