5HE - October 1999
Use of Steam Tables is permitted
Part A (20 x 2 = 40 Marks)
- What are the three modes of heat transfer? Mention about the mechanism in each mode
- Write briefly about the effect of temperature on thermal conductivity of materials/substances
- Write the one-dimensional steady state heat conduction for a hollow cylinder
- Determine the heat flux across 15.2 cm thick slab when one face is kept at 500 K and the other face at 280 K. The thermal conductivity of the slab material varies linearly with temperature in accordance with the equation k = ko(1 + BT) where ko = 0.0346 W/m.K and B = 3.6 x 10-3 oK-1.
- Write the two dimensional steady state heat transfer conduction equation
- What is transient heat conduction?
- Write a short note on heat transfer in packed beds
- Write the equation giving the individual heat transfer coefficients as a function of relevant variables in the case of natural convection
- Is a counter flow heat exchanger more efficient than a parallel heat exchanger? If so, why?
- Draw a neat sketch of 1-2 counterflow heat exchanger
- List out the various types of heat exchangers
- Explain the significance of NTU in heat exchangers
- How does a scale deposit affect the heat transfer rate?
- Explain the concept of log mean temperature difference
- Explain the mechanism of thermal radiation
- Write a note on radiation between surfaces
- What are the applications of tubular furnaces?
- Define 'evaporation'
- Give the statement of Duhring's rule
- Is multiple effect operation more economical than single effect operation, in evaporation? Why?
Part B (5 x 12 = 60 Marks)
- (a) Discuss briefly about heat conduction through a series of resistances (6)
(b) The two faces of a slab at x = 0 and x = L are kept at t1 and t2 oC respectively. The 'k' of the material is given by as a temperature dependent value by k = ko(t2 - to2) where to and ko are constants. Deduce the expression for (i) heat flow/unit area and (ii) kav for this material (6)
- (a) A long hollow cylinder has its inner and outer surfaces maintained at temperatures Tb and Ta respectively. The inner and outer radii are b and a respectively. Calculate the temperature profile in the solid section of the cylinder and determine the flux at both surfaces. Assume steady state condition (8)
(b) Write a short note on conduction through liquids (4)
- (a) Heat is generated within a sphere at 2.07 x 108 W/m3. The sphere is 8 cm in diameter. The surface temperature is 370 K. (i) Calculate the temperature at the center of the sphere (ii) Calculate the temperature at a radial distance of 2 cm. (8)
(b) Briefly explain the concept of heat transfer by convection (4)
- (a) Determine the rate of heat transfer between two fluids separated by a copper tube 2 mm thick, 2 cm OD and 1.5 m long, if the inner fluid (water) temperature is 30oC and the outer fluid (steam) temperature is 100oC. The water side film coefficient is 2000 W/m2.K and the steam side heat transfer coefficient is 15000 W/m2.K. The thermal conductivity of copper is 400 W/m.K (8)
(b) Write a note on drop-wise condensation and film-type condensation (4)
- (a) Derive the expression for log mean temperature difference in heat exchangers (8)
(b) Explain the terms capacity ratio and effectiveness (4)
- Discuss briefly about the design of furnaces and design of tubular reactors
- (a) Explain the concept of thermal radiation (6)
(b) Explain the significance of Stefan-Boltzmann's law (6)
- Write a short note on: (3 x 4 = 12)
(a) Radiation error in temperature measurement
(b) Clouds of particles and luminous flames
(c) Tubular furnaces
- (a) Discuss about the capacity and economy of multiple effect evaporators (8)
(b) State Duhring's rule and explain its significance in evaporation (4)
- Write short notes on: (3 x 4 = 12)
(a) Single and multiple effect evaporation
(b) Boiling point elevation
(c) Types of evaporators