# AE2024 Heat Transfer Anna University question bank, previous year question paper and important 2marks and 16 marks questions

**Department of Aeronautical Engineering**

**AE 2024: Heat Transfer - Question Bank**

__PART A - (2 marks____)__

- State and explain the Fourier's law of heat conduction.
- Define the efficiency and effectiveness of a fin.
- Distinguish the heat transfer by conduction and convection.
- What is the role of extended surfaces in heat transfer applications?
- What do you understand by Log Mean Area? State its significance.
- What is lumped heat analysis?
- Write about transient heat conduction.
- Write expression for variation of thermal conductivity with temperature.
- What is an error function?
- What is the difference between the free convection and forced convection?
- Define heat flux and thermal diffusivity.
- Distinguish between Grashoff number and Nussetl's number.
- What are the types of fins? Which one is more effective'?
- A thin plate 1 meter long and 1 meter wide is placed in an air stream moving with velocity of 0.25 m/s. Determine the type of flow over the plate.
- Distinguish between natural and forced convection.
- Give the physical significance of Nusselt number and Prandtl number.
- Define the Nusselt number and Prandtl number.
- Illustrate the hydrodynamic boundary layer thickness for the flow over the flat plate in the forced convection.
- “A turbulent flow over a solid surface facilitates more heat transfer when compared to a laminar flow.” Comment on the statement.
- Give at least two practical examples for free convective heat transfer.
- Explain Reynolds Analogy for laminar flow.
- Define intensity of radiation.
- Define radiation intensity and radiation shape factor.
- Define irradiation and radiosity.
- Define the terms absorptivity and transmittivity of radiation.
- State the reciprocity theorem of the radiation shape factors.
- Define radiation shape factor.
- Define black body in radiative heat transfer.
- What is Fouling factor'?
- Define effectiveness as a function of NTU of heat exchanger for counter flow type.
- Define overall heat transfer coefficient.
- Define "LMTD".
- Define the effectiveness of the heat exchanger.
- What is ablative heat transfer?
- Draw the temperature profile across a cooled rocket combustion chamber wall.
- Why does an aerospace vehicle flying at high supersonic Mach number experience aerodynamic heating in atmosphere?
- What is meant by recuperator?
- What is shape resistance .How it influences on over all heat transfer coefficient?
- How is ablation used for high speed cooling?
- Define Transpiration Cooling?

__PART B - (16marks)__- A steel pipe (K = 45.0 W/m.K) having a 0.05 m O.D is covered with a 0.042 m thick layer of magnesia (K = 0.07 W/m.K) which in turn covered with a 0.024 m layer of fiberglass insulation (K = 0.048 W/m.K). The pipe wall outside temperature is 370 K and the outside surface temperature of the fiberglass is 305 K. What is the interfacial temperature between the magnesia and fiberglass? Also calculate the steady state heat transfer.
- i) One end of a long rod, 35 mm in diameter, is inserted into a furnace with the other end projecting in the outside air. After the steady state is reached the temperature of the rod is measured at two points 180 mm apart and found to be 180° C and 145°C. The atmospheric air temperature is 25°C. If the heat transfer coefficient is 65 W/m
^{2}C, calculate the thermal conductivity of the rod. (Assume the end of the fin is insulated).^{0}

**K) sphere to cool from 500 °C to 100 °C if exposed to a cooling air flow at 25°C resulting in the convective coefficient 110 W/m**

^{O}^{2}K.

- i) Explain the following terms of the forced convection:

^{2}is proposed. The mass flow rate is to be such that Re

_{D}= 2000, and consequently the flow must remain laminar. The tube inside diameter is 25 mm. The flow is fully developed (Velocity profile). Determine the length of the tube required.

- i) In a certain glass making process, a square plate of glass 1 m
^{2}area and 3 mm thick heated uniformly to 90°C is cooled by air at 20°C flowing over both sides parallel to the plate at 2 m/s. Calculate the heat transfer rate from the plate. Neglect the temperature gradient in the glass plate and consider only forced convection.

- i) Assuming the sun to be a black body emitting radiation with maximum intensity at Î». = 0.49 Âµm, calculate the surface temperature of the sun and also heat flux at the surface of the sun.

- i) Derive the expression for the heat exchange between two black surfaces by radiation.

- i) Derive an expression for logarithmic mean temperature difference of the parallel flow heat exchanger.

^{2}

**K find the heat transfer area, if the oil enters at 105°C and leaves at 70°C.**

^{O}- i) Draw the temperature distribution curve of the fluids in the single pass parallel flow heat exchanger and single pass counter flow heat exchanger.

^{2}and overall heat transfer coefficient is 60 W/m

^{2}

^{0}C. Find out the rate of heat transfer. Assume both fluids are unmixed.

- i) Describe the working principle of the Gas turbine combustion chamber.

- i) Explain how the high speed flow heat transfer differs from normal heat transfer.

- i) Explain the concept 'internal thermal resistance' in heat transfer.

- i) Carry out the dimensional analysis for the forced convection obtain the following relationship through a long tube and Nu = f(NRe, Pr).

^{O}C) at 0°C and burned until steady state is reached. Find the temperature 30 cm away if the lamp produces 60 J/s.

- i) A hollow cone of metal with thermal conductivity 0.15 J/cm
^{o}C and thickness 1 mm connects a pipe of 6 cm diameter with exterior metal sheath of an insulated vessel. The base of the cone is 20, cm in diameter and its length measured along the cone is 24 cm. If the pipe is at 200°C and the base of the cone at 0°C, calculate the rate of heat loss through the cone.

- i) A flat plate heated to 80
^{0}c is cooled by an air stream at 20°C flowing at 10 m/s. Calculate the value of local heat transfer coefficient at X = 30 cm. Assume that the boundary layer on the plate is laminar.

- i) A fluid flows through a 10 cm ID pipe. Assume that the velocity is uniform over the cross section of the pipe but the temperature varies linearly from 100°C at the pipe wall to 0°C at the centre line. Calculate the heat transfer co-efficient based on the mean fluid temperature if the heat flow rate from the pipe wall is 117600 w/m
^{2}K

^{2}/m.

^{0}C .The diameter of the sun is 1.39 * 10

^{6 }km and its distance from the earth is 1.5 * 10

^{8}km.

^{2}K on the outside of the tube. The water velocity is 50 cm/s. Calculate the overall heat transfer coefficient based on the outer- area of the pipe.

_{0}= 30800 w/ m2 K on the outside of the tube. The water velocity is 50 cm/s. Calculate the overall heat transfer coefficient based on the outer area of the pipe.

**C) in 3 mm thick. It is protected from corrosion by 2 mm thick layer of stainless steel (K = 17 w/m.**

^{0}**C) on both sides. The temperatures of the two outer surface of steel are 400°C and 100°C. What is the temperature of the two interfaces?**

^{0}^{o}C , Kinematic viscosity = 0.124 * 10

^{-6}m

^{2}/s, Local Nusselt number,

*Nux*= 0.332 (NRex)

^{0.5}

^{0}c and the other at 500

^{0}c. The emissivities of the plates are 0.2 and 0.5, respectively. The plates are located in a very large room, the walls of which are maintained at 27°c. The plates exchange heat with each other and with the room, but only the plate surfaces racing each other are to be considered in the analysis. Find the net transfer to each plate and to the room.

^{2}DC. Specific heat for both the water is 4.18 KJ/Kg

^{o}C. Determine the number of tubes and required length of the tubes for 1--1 shell and tube heat exchanger. Given: Density of water at 50°C = 988 kg /m

^{3}, Surface area/unit length = 0.0798 m

^{2}/m per tube, Cross sectional area = 0.0003098 m

^{2}per tube.

thanks a lot

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