M.Tech III (Third) Semester Examination 2012-13
Course Code: MME303 Paper ID: 0973203
Heat Exchangers
Time: 3 Hours Max. Marks: 70 Max Marks: 75
Note: Attempt six questions in all. Q. No. 1 is compulsory.
1. Answer any five of the following (limit your answer in 50 words). (4x5=20)
a) Define the term (i) Gray Body (ii) Black Body (iii) Emissive Power.
b) Write short notes on Fouling factor.
c) Explain the pressure drop in heat exchangers.
d) Define the Temperature Pinch.
e) What is the meaning of simulation with an example?
f) Explain about Boiler Feedwater Heaters.
g) Discuss the efficiency of fin. Why it is used in I.C. Engine?
h) Discuss Log Mean Area of cylinder used in heat transfer.
2. Carbon dioxide (CO2) for a gas cooled reactor is used to generator steam. A flow rate of 90000 kg/h of CO2 at 4 bar enters the tubes of a shell and tube type steam generator at 500°C.The CO2 leaves the generator at 330°C and steam saturation temperature is 250°C. Assume that the steam formed is dry and saturated. Using 25 mm inner diameter copper tubes, 2mm wall thickness and designed for CO2 mass flow rate of 350000 kg/m2h. Calculate the length and number of tubes to be used neglecting steam side thermal resistance. Take the following properties of CO2:
Cp=1.172kJ/kg°C, µ=0.0000298Ns/m2, k= 0.043W/m°C, =3.26kg/m3. (10)
3. Briefly discuss about the influence of boundary layer on heat transfer. (10)
4. Derive an expression for calculating the effectiveness of a counter-current flow heat exchanger. (10)
5. Derive the equation for total heat transfer rate through a hollow cylinder having inner and outer radii r1 and r2 respectively. Its inner and outer surface temperatures are T1 and T2 respectively. There is no heat generation and its conductivity is constant. (10)
6. What are the common operational problems in heat exchanger? (10)
7. How to use computer for designing and simulation of heat exchangers? (10)
8. Calculate for the following cases, the surface area required for a heat exchanger which is required to cool 3200 kg/h of benzene (cp=1.74kJ/kg°C) from 72°C to 42°C. The cooling water (cp=4.18kJ/kg°C) at 15°C has flow rate of 2200kg/h.
a) Single passes counter-flow
b) Cross flow single pass with water mixed and benzene unmixed.
For each configuration, the overall heat transfer coefficient may be taken as 0.28kW/m2°C. (10)