ME-701 Heat and Mass Transfer - Jun 2025 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 5 Marks
   aHow are heat, internal energy, and thermal energy related to each other?
   How to answer

   • Define heat as energy in transit due to temperature difference
   • Define internal energy as sum of microscopic kinetic and potential energies
   • Define thermal energy as sensible and latent part of internal energy
   • Explain interrelation with examples
2. 5 Marks
   bHow does heat conduction differ from convection?
   How to answer

   • Define conduction as diffusion through stationary medium via Fourier law
   • Define convection as bulk fluid motion plus diffusion via Newton law of cooling
   • Contrast mechanism, medium, governing laws
   • Give examples
3. 4 Marks
   cThe inner and outer surfaces of a $0.5$ cm thick $2 \times 2\, m^2$ window glass in winter are $10^{\circ}C$ and $3^{\circ}C$, respectively. If the thermal conductivity of the glass is $0.78\, W/m.\, ^{\circ}C$, determine the amount of heat loss, in kJ, through the glass over a period of 5 hours.

   

   How to answer

   • State Fourier's law $Q = kA\Delta T/L$
   • Calculate area $A=2\times 2 =4\,m^2$ and $\Delta T=7^{\circ}C$
   • Compute steady heat rate $\dot Q$
   • Multiply by time 5 hours to get heat loss in kJ
4. 4 Marks
   aDefine the parameters by which the fins performance is measured.
   How to answer

   • Define fin effectiveness
   • Define fin efficiency
   • Define fin parameter m and related performance
   • State how each measures enhancement
5. 4 Marks
   bWhat is the reason for the widespread use of fins on surfaces?
   How to answer

   • Low heat transfer coefficient on gas side limits heat transfer
   • Fins increase effective surface area
   • Enhance heat dissipation with low cost and weight
   • Examples of applications
6. 6 Marks
   cA steel rod ($k = 30\, W/m-deg$) $1$ cm in diameter and $5$ cm long protrudes from a wall which is maintained at $100^{\circ}C$. The rod is insulated at its tip and is exposed to an environment with $h = 50\, W/m^2-deg$ and $t_a = 30^{\circ}C$. Calculate the fin efficiency and temperature at the tip of fin.
   How to answer

   • Compute fin parameter $m = \sqrt{hP/kA_c}$ for circular rod
   • Apply insulated-tip efficiency $\eta = \tanh(mL)/mL$
   • Calculate heat transfer and tip temperature $T(L)$ formula
   • Substitute $k=30$, $d=1\,cm$, $L=5\,cm$, $h=50$, $T_b=100^{\circ}C$, $T_a=30^{\circ}C$
7. 4 Marks
   aState the Buckingham pie theorem.
   How to answer

   • State number of pi terms = n-m
   • Explain repeating variables selection
   • State formation of dimensionless groups
   • Give functional relation form
8. 10 Marks
   bA domestic oven has a composite wall formed by $0.5$ cm thick chrome-nickel ($k = 19\, W/mk$) sheet supported by $1$ cm thick asbestos ($k = 0.1105\, W/mk$) sheet. In steady state operation the hot gases inside the oven are at $350^{\circ}C$ while atmospheric air in at $30^{\circ}C$. The convective heat transfer coefficient at inside and outside surface of the oven are $100\, W/m^2k$ and $15\, W/m^2k$ respectively. Determine the rate of heat losses per unit area through the oven wall.
   How to answer

   • Draw thermal resistance network: two convection + two conduction in series
   • Compute conduction resistances $L/k$ and convection $1/h$
   • Compute overall heat transfer coefficient U
   • Compute $q/A = (350-30)/\Sigma R$
9. 6 Marks
   aWhat is the difference between evaporation and boiling?
   How to answer

   • Define evaporation as surface phenomenon below boiling point
   • Define boiling as bulk phenomenon at saturation temperature
   • Contrast temperature, bubble formation, energy
   • Give examples
10. 8 Marks
    bWhat is the difference between film and dropwise condensation? Which is a more effective mechanism of heat transfer?
    How to answer

    • Describe film condensation with continuous liquid film and thermal resistance
    • Describe dropwise with discrete droplets exposing bare surface
    • Compare heat transfer coefficients
    • Conclude dropwise is more effective with reason
11. 5 Marks
    aWhat is forced convection? How does external forced convection is differing from internal forced convection?
    How to answer

    • Define forced convection with external agency
    • Define external flow over bodies vs internal flow in ducts
    • Contrast boundary layer development, entrance effects
    • Give examples
12. 5 Marks
    bHow does turbulent flow differ from laminar flow? For which flow is the heat transfer coefficient higher?
    How to answer

    • Describe laminar ordered layers vs turbulent random fluctuations
    • Contrast velocity profile, mixing, Reynolds number
    • State turbulent has higher heat transfer coefficient due to mixing
    • Give critical Re ranges
13. Marks
    cHow does the Rayleigh number differ from the Grashof number?
    How to answer

    • Define Grashof number as buoyancy/viscous ratio
    • Define Rayleigh as Gr x Pr
    • Explain role of thermal diffusivity
    • State use in natural convection correlation
14. 4 Marks
    aWhat is a radiation shield? Why is it used?
    How to answer

    • Define radiation shield as low-emissivity barrier
    • Explain reduction of radiative exchange by multiple reflections
    • Give formula with and without shield
    • State applications
15. 4 Marks
    bExplain the Planck's distribution law?
    How to answer

    • State Planck's law $E_{b\lambda}(T)$ expression
    • Explain spectral variation with wavelength and temperature
    • Mention Wien's displacement and Stefan-Boltzmann deduction
    • Sketch distribution curves
16. 6 Marks
    cConsider a person whose exposed surface area is $1.7\, m^2$, emissivity is $0.85$, and surface temperature is $30^{\circ}C$. Determine the rate of heat loss from that person by radiation in a large room whose walls are at a temperature of (i) $300\, K$ and (ii) $280\, K$.
    How to answer

    • State radiative loss $Q=\varepsilon A\sigma(T_s^4-T_{surr}^4)$
    • Convert $T_s=30^{\circ}C=303\,K$
    • Compute for $T_{surr}=300\,K$ and $280\,K$
    • Compare increase with colder surroundings
17. 7 Marks
    aClassify heat exchangers according to construction type and explain the characteristics of each type.
    How to answer

    • List types: double-pipe, shell-and-tube, plate, cross-flow, regenerative
    • Explain construction of each
    • State characteristics: compactness, pressure, fouling, application
    • Give examples
18. 7 Marks
    bEstablish the expression LMTD equation for parallel flow Heat Exchangers.
    How to answer

    • Consider differential element with energy balance
    • Integrate $d(\Delta T)/\Delta T$ along length
    • Obtain $Q = UA\Delta T_{lm}$ expression
    • Define $LMTD = (\Delta T1-\Delta T2)/\ln(\Delta T1/\Delta T2)$ for parallel flow
19. 14 Marks
    Write short notes on any four of the followings.

    1. i)Fin effectiveness
    2. ii)Gray body
    3. iii)Fick's Law
    4. iv)LMTD
    5. v)Thermocouple
    6. vi)Parallel flow heat exchanger
    How to answer

    • Select any four topics from list
    • Give definition/governing law or formula for each
    • Explain physical significance with example
    • Mention applications