ME HT

 

1	Derive general heat conduction equation in rectangular coordinate system
2	Derive general heat conduction equation in cylindrical coordinate system
3	Explain thermal Contact resistance. How contact pressure effects thermal contact resistance?
4	For cylinder, prove that critical radius of insulation, r critical = k/h, where k=thermal conductivity of insulation and h=convective heat transfer coefficient. Explain effect of thickness of insulation on heat transfer.
5	Define : (1) Emissivity (2) Monochromatic emissive power (3) Opaque body (4) Radiosity (5) Radiation intensity (6) Solid angle
6	For natural convection heat transfer, prove that Nu=φ(Pr)(Gr), where Nu=Nusselt number, Pr=Prandlt number and Gr=Grashoff number.
7	Derive an equation for heat transfer from very thin and long enough fin so that the heat loss from the fin tip may be assumed negligible.
8	What is physical significance of dimensionless parameters? Explain in brief
9	Derive equation of NTU for parallel flow heat exchanger
10	Derive equation of LMTD for parallel flow heat exchanger.
11	Derive equation of logarithmic mean temperature difference for parallel flow Heat-exchanger.
12	Prove that intensity of normal radiation is 1/π times the emissive power. 0
13	Write general heat conduction equation for non-homogeneous material, self heat generating and unsteady three-dimensional heat flow in cylindrical coordinates. Name and state the unit of each variable. Step 1. Reduces above equation to one dimensional Step 2. Reduces step 1 equation for steady and without heat generation Step 3. Reduces step 2 equation for homogeneous and isotropic material Step 4. Reduces step 3 equation to r(dt/dr) = constant.
14	By dimensional analysis show that for natural convection heat transfer the Nusselt number can be expressed as a function of Grashof number and Prandtl number.
15	Derive the relation for temperature variation with respect to time, instantaneous heat transfer rate and total heat transfer using lumped parameter analysis.
16	Derive general heat conduction equation in cylindrical coordinate system.
17	Derive an expression for heat transfer for an adequately long of Rectangular fin with insulated tip.
18	Explain term Boiling also explain various regimes of boiling
19	State the relationship between Nusselt, Grashoff and Prandtl number in case of heat transfer by nature convection from a vertical plate
20	In a counter flow heat double pipe heat exchanger ,water is heated from 250C to 650C by oil with specific heat of 1.45 kJ/kg K and mass flow rate of 0.9 kf/s. The oil is cooled from 2300C to 1600C. If overall Heat transfer coefficient is 420 W/m2 0C. calculate following (i) The rate of heat transfer (ii) The mass flow rate of water , and (iii) The surface area of heat exchanger
21	A solid sphere of 1 cm made up of steel is at initially at 3000Ctemperature. Properties of steel : k =60 WmK Density = 7800 kg/m 3 , sp. Heat =434J/kg K Calculate the time required for cooling it up to 500Cin the following two cases (i) cooling medium is air at 250Cwith h = 20 W/m2 K (ii) cooling medium is water at 250C with h =100 W/m2K
22	A pipe carrying the liquid at -20o C is 10mm in outer diameter and is exposed to ambient at 25o C with convective heat transfer coefficient of 50W/m2 K. It is proposed to apply the insulation of material having thermal conductivity of 0.5W/mK. Determine the thickness of insulation beyond which the heat gain will be reduced. Also calculate the heat loss for 2.5mm, 7.5mm and 15mm thickness of insulation over 1m length. Which one is more effective thickness of insulation?
23	Two rods A and B of equal diameter and equal length, but of different materials are used as fins. The both rods are attached to a plain wall maintained at 160o C, while they are exposed to air at 30o C. The end temperature of rod A is 100o C and that of the rod B is 80o C. If the thermal conductivity of rod A is 380 W/mK, calculate the thermal conductivity of rod B. This fin can be assumed as short with end insulated.
24	A steel tube of 5 cm inner diameter and 8 cm outer diameter (k = 16 W/mK), is covered with an insulation of 3 cm thickness (k = 0.3 W/mK). A hot gas at 350o C h = 400 W/m2 K flows. Calculate the heat loss from the tube for 20 meter length. Also calculate the temperature at the interface of insulation and steel.