Introduction to Heat Transfer — Winter 2019

State Fourier’s law of heat conduction? Mention the significance of negative sign in heat conduction equation.

Differentiate Critical thickness of Insulation and Optimum thickness of Insulation

Describe the different kind of Boundary conditions used in heat transfer studies

An electrically heated plate dissipates heat by convection at a rate of q = 8000 W/m2 into ambient air at T = 25 °C. If the surface of hot plate is at T = 125 f W °C. Calculate heat transfer coefficient for convection between plate and air.

What is lumped System analysis? Mention the importance of Biot number in lumped system analysis.

Develop expression for one dimensional steady state temperature distribution T(r) in a sphere where inner surface at r = a and outer surface of r = b of hollow sphere are maintained at temperatures of Tand Trespectively.12 Consider that thermal conductivity (k) of sphere is constant

Atmospheric air at T = 400 Kwith a velocity u = 1.5 m/s flows over a flat   plate L = 2 m long maintained at uniform temperature of T = 300K. W Calculate average value of heat transfer coefficient and average heat transfer rate from airstream to plate over entire length of L = 2m.

Write the significance of following dimensionless numbers used in heat transfer studies (i) Reynolds number (ii) Prandtl number (iii) Nusselt number

Differentiate velocity boundary layer and thermal boundary layer

Estimate the total heat loss by convection and radiation from an unlagged steam pipe, 50 mm o.d. at 415 Kto air at 290K (17 °C). Emissivity e = 0.90 Film coefficient for calculation of heat loss by natural convection is given by h = 1.18 (T/D )0.25 W/m2K C O

Mention the factors governing the rate of heat transfer in forced and natural convection.

Define Absorptivity, Reflectivity and Transmissivity

Calculate heat transfer area of 1 – 2 heat exchanger from the following data. Inlet and outlet temperatures of cold fluid are 303 Kand 318 Krespectively. Overall heat transfer coefficient = 4100 W/m2 K. Heat loss = 407 kW. LMTD correction factor = 0.84.1

What is drop wise condensation? Explain why heat transfer coefficient is lesser for film wise condensation than drop wise condensation?

With neat diagrams explain classification of heat exchangers according to flow arrangement.

Aheat exchanger is required to cool 20 kg/s of water from 360K to 340K by means of 25kg/s of water entering at 300K. If the overall heat transfer coefficient is 2000 W/m2K. calculate the surface area required in

Acounter current concentric heat exchanger

Aco-current flow concentric tube heat exchanger. (Take Cof water P = 4.187 kJ/kg K)

Discuss the phenomena of hysteresis in a boiling curve.

Why saturated steam is used as heating medium in industries?

What is understood by boiling point elevation in evaporators

What is Vapor recompression? Mention different methods in which vapor recompression can be done.

With help of boiling curve mention different regimes in a pool boiling.

Define the terms of Capacity & Economy in Evaporators

Explain the different methods of feeding of multiple effect evaporators.

An evaporator operating at atmospheric pressure is designed to concentrate 5% solute to 20 % solute by weight at a rate of 5000 kg/h. Dry saturated steam at a pressure corresponding to saturation temperature of 399K is used. The feed is at 298 Kand boiling point rise is 5 K. Overall heat transfer coefficient is 2350 W/m2 K. Calculate economy of evaporator and area of heat transfer to be provided assuming that there is no boiling point elevation for the solvent. Data: Latent heat of Condensation of steam = 2185 kJ/kg Latent heat of vaporization of water at 101.325 kPa and 373 K = 2257 kJ/kg Specific heat of feed = 4.187 kJ/ kg K