Heat and Mass Transfer (ME-701) - Important Questions

Explain the three modes/mechanisms of heat transfer - conduction, convection and radiation - including the governing laws and distinguishing features.

The inner and outer surfaces of a 30 cm thick 5 m x 6 m brick wall (k = 0.69 W/m-C) are maintained at 20 degC and 5 degC respectively. Determine the steady one-dimensional rate of heat transfer through the wall using Fourier's law.

What is the critical thickness / critical radius of insulation and what is its significance / application for pipes and cylinders?

What is the meaning of extended surfaces (fins) and where are they used? For a longitudinal fin of uniform cross-section, derive the governing differential equation for one-dimensional heat transfer, including the infinitely long fin case.

Differentiate between fin effectiveness and fin efficiency.

A steel ball (k = 40 W/m-C) 5 cm in diameter initially at 200 degC is suddenly exposed to convection environment at 30 degC with h = 50 W/m2-C. Check validity of lumped system analysis via Biot number and using lumped capacitance method calculate the time required to cool to 80 degC. Take rho = 7800 kg/m3, cp = 460 J/kg-C.

Explain laminar vs turbulent flow regimes in convection heat transfer and compare their heat transfer coefficients, with the help of neat diagram.

Explain the application of dimensional analysis to free and forced convection heat transfer. Discuss the relevant dimensionless numbers obtained.

Air at 1 bar and 30 degC flows across a 4.0 cm diameter cylinder at a velocity of 40 m/s. The cylinder surface is maintained at 150 degC. Using appropriate empirical correlation for laminar and turbulent flow over tubular geometry, calculate the heat loss per unit length of the cylinder.

Explain the classification / types of heat exchangers with neat diagrams and characteristics of each type.

Derive the expression for logarithmic mean temperature difference (LMTD) for a counter-flow heat exchanger. Discuss how LMTD is used to determine heat exchanger size.

Explain the NTU-effectiveness method for heat exchanger analysis. Discuss its advantages over the LMTD method when outlet temperatures are unknown.

Discuss the radiant heat exchange between two black bodies separated by a non-absorbing medium and hence derive the general expression for radiation shape factor and the reciprocity theorem A1F12 = A2F21.

Explain what a radiation shield is and why it is used. Show the reduction in heat transfer obtained by inserting one shield between two parallel plates.

Write short notes on any two of the following: (i) Radiation heat exchange between black and gray surfaces, (ii) Filmwise and dropwise condensation, (iii) Fouling factors in heat exchangers.