Important RGPV Question
ME-701, Heat and Mass Transfer
VII Sem, ME
Unit -1 Basic Concepts
Q.1 Consider a 0.8 m high and 1.5 m wide double-pane window consisting of two 4 mm thick layers of glass (k = 0.78W / (m O C) separated by a 10 mm wide stagnant air space (k = 0.026W / (m O C) , Determine the steady rate of heat transfer through this double-pane window and the temperature of its inner surface for a day during which the room is maintained at 20 O C while the temperature of the outdoors is -10°C. Take the convection heat transfer coefficients on the inner and outer surfaces of the window to h_{1} = 10W / (m ^ 20) O C and h_{2} = 40W / (m ^ 20) O C, which includes the effects of radiation? (RGPV June 2023)
Q.2 A stainless steel tube (k_{s} = 19W / m 0 K) of 2 cm ID and 5 cm OD is insulated with 3 cm thick asbestos (k_{a} = 0.2W / m 0 K) . If the temperature difference between the innermost and outermost surfaces is 600 O C Find the heat transfer rate per unit length? (RGPV June 2023)
Q.3 Derive expression for temperature distribution, under one dimensional steady state heat conduction for a cylinder. (RGPV June 2023)
Q.4 Two slabs are placed in contact, but due to roughness, only 40% of area is in contact and the gap in the remaining area is 0.02 mm thick and is filled with air. The slabs are 10 cm thick each and their conductivities are 15.5 W/mk and 200 W/mK. The temperature of the face of the hot surface is at 250°C and the outside surface of the other slab is at 35°C, Determine the heat flow and the contact resistance. The conductivity of air is 0.0321 W/mK. (RGPV Nov 2022)
Q.5 A surface at 260°C converts heat at steady state to Air at 60°C with a convection coefficient of 30 W/mK. If this heat has to be conducted through wall with thermal conductivity of 9.5 W/mk, determine the temperature gradient in the solid. (RGPV Nov 2022)
Q.5 A hollow cylindrical insulation has an internal diameter of 16 cm thickness of 8 cm. The inner surface is at-10°C while the outer surface is at 35°C Determine the radius at which the temperature is 0°C. (RGPV Nov 2022)
Q.7 What do you mean by contact resistance ? (RGPV Dec 2020)
Q.8 Explain the modes of heat transfer. (RGPV Dec 2020)
Q.9 Give the conduction, statement of Fourier’s law of heat. (RGPV Dec 2020) (RGPV June 2020)
Q.10 Define the critical thickness of insulation? Derive equation for sphere with suitable sketch. (RGPV Dec 2020)
Q.11 Derive the general heat conduction equation for spherical co-ordinates. (RGPV Dec 2020)
Q.12 Define thermal resistance and conductance. (RGPV June 2020)
Q.13 A Furnace wall comprises three layers: 13.5cm thick inside layer of fire brick, 7.5cm thick middle layer of insulating brick and 11.5cm thick outside layer of red brick. The furnace operates at 870 °C and it is anticipated that the outside of this composite wall can be maintained at 40 °C by the circulation of air. Assuming close bonding of layers at their interfaces, find the rate of heat loss from the furnace. The wall measures 5m x 2m and thermal conductivities are as follows:
Fire Brick, k, = 1.2 W/m-deg
Insulating Brick, k, = 0.14 W/m-deg
Red Brick, k,=0.85 W/m-deg. (RGPV June 2020)
Q.14 What are different modes of heat transfer? Explain with examples. (RGPV June 2020)
Q.15 Establish analogy between flow of heat and electricity. (RGPV June 2020)
Q.16 Write short note on critical thickness of insulation. (RGPV June 2020)
Q.17 What do you mean by critical thickness of insulation? Derive the formula to find it for cylinder. (RGPV May 2018)
Q.18 Beginning with a general conduction equation make suitable assumptions to show that temperature distribution through a plane wall is linear. (RGPV May 2018)
Q.19 Compare conduction, convection and radiation modes of heat transfer with examples (RGPV May 2018)
Q.20 What is overall heat transfer coefficient? Write the expression for the same. (RGPV May 2018)
Unit -2 Extended Surface(Fins)
Q.1 A long rod 12 mm square section made of low carbon steel protrudes into air at 35°C from a furnace wall at 200°C. The convective heat transfer co-efficient is estimated at 22 W/m²K. The conductivity of the material is 51.9 W/mK. Determine the location from the wall at which the temperature will be 60°C. Also calculate the temperature at 80 mm from base. Attempt the question with derivative approach. (RGPV June 2023), (RGPV Nov 2022)
Q.2 Air at 20°C flows through a tube 8 cm dia with a velocity of 9 m/s. The tube wall is at 80°C. Determine for a tube length of 5 m, the exit temperature of air. (RGPV June 2023)
Q.3 A copper wire of radius 0.5 mm is insulated with a sheathing of thickness 1 mm having a thermal conductivity of 0.5W / m – K . The outside surface convective heat transfer coefficient is 10W / m2 – K . If the thickness of insulation sheathing is raised by 10 mm, then comment on the electrical current-carrying capacity of the wire. (RGPV June 2023)
Q.4 Define “semi-infinite solid” as used in transient conduction analysis. Write the differential equation for the problem. (RGPV Nov 2022)
Q.5 A thermocouple is formed by soldering end-to-end wires [of 0.5 mm dia. The thermal diffusivity of the material is 5.3 x 10 m/s. The conductivity of the material is 19.1 W/mK. The probe initially at 30°C is placed in a fluid at 600°C to measure the temperature of the fluid. If the convective heat transfer coefficient between the wire and the fluid is 85 W/mK, determine the time constant for the probe and the time taken for it to read 598°C. (RGPV Nov 2022)
Q.6 A steel rod (k-30 W/m-deg) Icm in diameter and Sem long protrudes from a wall which is maintained at 100°C The rod is insulated at its tip and is exposed to an environment with h 50 W/m-deg and t-30°C. Calculate the fin efficiency and temperature at the tip of fin. (RGPV June 2020)
Q.7 Derive the expression for temperature distribution and heat dissipation in an infinite long fin of rectangular profile. (RGPV Nov 2022)
Q.8 Derive the general equation for infinite long fin with neat sketch. (RGPV Dec 2020)
Q.9 Differentiate between fin effectiveness and fin efficiency. (RGPV Dec 2020) (RGPV June 2020)
Q.10 What is meant by lumped capacity? What are the physical dimensions necessary for a lumped unsteady state analysis to apply? (RGPV May 2018)
Q.11 Derive relation for heat dissipation from an infinitely long fin. Also write design considerations for fins. (RGPV May 2018)
Q.12 Define the following numbers with significance: (RGPV May 2018)
a) Reynold’s number
b) Prandtl number
c) Nusselt number
Q.13 Air flow through a long rectangular (400×60 cm) air conditioning duct maintains the outer duct surface temperature at 15°C. If the duct is uninsulated and exposed to the air at 27°C. Calculate the heat gained by the duct per meter length, assuming it to be horizontal. (RGPV May 2018)
Q.14 What is time constant for thermocouples? Write the expression for the same. (RGPV May 2018)
Unit- 3 Convection
Q.1 Explain the Significance of Dimensionless numbers. Write down the advantages and limitations of dimensional analysis. (RGPV June 2023)
Q.2 Derive the momentum equation for hydrodynamic boundary layer over a flat plate. (RGPV June 2023)
Q.3 The properties of mercury at 300 K are density-13529 kg/m², specific heat at constant pressure 0.1393 kl/kg-K.. dynamic viscosity 0.1523 x 10N.s/m² and thermal conductivity = 8.540 W/mk. Find the Prandti number of the mercury at 300 K ? (RGPV Nov 2022)
Q.4 A low speed wind tunnel is to be designed for tests up to Re = 5×105 with air at 0.8 atm and 20°C. The model length is restricted to 0.3 m. If the test section is 0.45 m square, determine the mass flow required. Check whether the boundary layer on the wall will affect the test. The tunnel length is 1.5 m. (RGPV Nov 2022)
Q.5 Explain about Buckingham’s л theorem. (RGPV Nov 2022, RGPV June 2020)
Q.6 Derive an expression for energy equation of thermal boundary layer over a flat plate. (RGPV Dec 2020)
Q.7 Write down the significance of Reynolds and Nusselt number. (RGPV Dec 2020)
Q.8 State principle and applications of dimensional analysis. (RGPV June 2020)
Q.9 A horizontal heated plate at 200°C and facing upwards has been placed in still air at 20°C. If the plate measures 1.25m Im. Calculate the heat loss by natural convection. The convective film coefficient for free convection is given by the following empirical relation: h-0.32 (θ)W/m-k. Where θ is mean film temperature in degree kelvin. (RGPV June 2020)
Q.10 Write short notes on Free and Forced convection. (RGPV June 2020)
Unit-4 Heat Exchanger & Mass Transfer
Q.1 Explain the need of NTU method over the LMTD method? State the merits and demerits of NTU method over LMTD method. (RGPV June 2023)
Q.2 Define about diffusion and explain Fick’s law of diffusion. Explain the term mass diffusivity. (RGPV June 2023), (RGPV June 2020)
Q.3 Explain the condition under which the slope of the hot and cold fluid temperature lines will be equal. Indicate the effect of such condition in the case of counter flow exchangers. (RGPV June 2023)
Q.4 In a cross-flow heat exchanger, air is heated by water. Air enters the exchanger at 150°C and a mass flow rate of 2 kg/s while water enters at 900°C and a mass flow rate of 0.25 kg/s. The overall heat transfer coefficient is 250 W/m².K. If the heat exchanger has a heat transfer area of 8.4m ^ 2 find the exit temperatures of both the fluids (RGPV June 2023)
Q.5 What is Fouling? What are its effects on heat exchanger performance? (RGPV June 2023)
Q.6 In a counter flow heat exchanger, hot fluid enters at 60°C and cold fluid leaves at 30°C. Mass flow rate of the hot fluid is 1 kg/s and that of the cold fluid is 2 kg/s. Specific heat of the hot fluid is 10 kJ/kgK and that of the cold fluid is 5 kJ/kgK. Find the Log Mean Temperature Difference (LMTD) for the heat exchanger in °C. (RGPV NOV 2022)
Q.7 Define Schmidt and Lewis numbers. Discuss the significances of each. 60mm thick plate with a circular hole of 30mm diameter along the thickness is maintained at uniform temperature of 277°C. Find the loss of energy to the surroundings at 20°C, assuming that the two ends of the hole to be as parallel discs and the metallic surfaces and surroundings have black body characteristics. RGPV NOV 2022
Q.8 What do you mean by fouling in heat exchanger? (RGPV Dec 2020)
Q.9 The exhaust gases (Cp=1.12 kJ/kg-K) flowing through a tubular heat exchanger at the rate of 1200 kg/hr are cooled from 400°C to 120°C. The cooling is affected by water. (Cp=4.18 kJ/kg-K) that enters the system at 10°C at the rate of 1500 kg/hr. If the overall heat transfer coefficient is 500 kJ/m² -hr-K. What heat exchanger area is required to handle the load for
i) Parallel flow
ii) Counter flow arrangement (RGPV Dec 2020)
Q.10 Explain the equation for the LMTD method for the parallel flow arrangement. (RGPV Dec 2020)
Q.11 Establish the expression for log mean temperature difference for a counter flow heat exchanger.
Or
Derive an expression for LMTD of a counter flow heat exchanger. (RGPV June 2020) (RGPV May 2018)
Q.12 Explain steady state diffusion through stationary medium. (RGPV June 2020)
Q.13 Explain Planck’s distribution law. (RGPV June 2020)
Q.14 What is meant by Fouling? Define Fouling factor. (RGPV May 2018)
Unit-5 Thermal Radiation, Boiling & Condensation
Q.1 Explain the boiling heat transfer phenomenon and regimes of boiling with neat sketch. (RGPV June 2023)
Q.2 Explain the significance of Shape factor. Determine the shape factor from the base of a cylinder to the curved surface. Also find the shape factor from curved surface to base and the curved surface to itself. (RGPV June 2023) (RGPV June 2020)
Q.3 Define Radiosity and irradiation. (RGPV June 2023) (RGPV Nov 2022)
Q.4 Imp State Lambert’s cosine law and its significance. (RGPV June 2023) (RGPV Nov 2022)
Q.5 Write the short note on “Wien’s displacement law”. Draw the neat sketch to represent it. (RGPV Nov 2022)
Q.6 Explain the boiling heat transfer phenomenon and regimes of boiling with neat sketch. (RGPV Nov 2022)
Q.7 A 60mm thick plate with a circular hole of 30mm diameter along the thickness is maintained at uniform temperature of 277°C. Find the loss of energy to the surroundings at 20°C, assuming that the two ends of the hole to be as parallel discs and the metallic surfaces and surroundings have black body characteristics. (RGPV Nov 2022)
Q.8 Explain the term ‘Boiling”? (RGPV Dec 2020)
Q.9 What do you mean by radiation? Derive the general equation for n shields. (RGPV Dec 2020)
Q.10 Differentiate between Forced and Natural convection and also explain the phenomenon of Film wise and Drop wise condensation. (RGPV Dec 2020) (RGPV June 2020)
Q.11 State Stefan Boltzmann Law. (RGPV June 2020)
Q.12 Define emissive power, gray surface and black surface. (RGPV June 2020)
Q.13 Write short note Radiation shields. (RGPV June 2020)
Q.14 What is Shape factor? State its applicability. (RGPV May 2018)
Q.15 Discuss types of condensation. (RGPV May 2018)
— Best of Luck for Exam —
