HEAT TRANSFER: PHYSICAL SIGNIFICANCE OF PRANDTL NUMBER, GRASHOFF’S NUMBER, NUSSELT NUMBER AND REYNOLDS NUMBER PHYSICAL SIGNIFICANCE OF PRANDTL NUMBER The Prandtl number (Pr) is a dimensionless number. Pr = momentum diffusivity/Thermal diffusivity =μ Cp/kf Value of Prandtl number signifies the thickness of thermal boundary layer as compared to the thickness of hydro boundary layer. If Pr =1, δ […]
MCQ ON RADIATION EXCHANGE BETWEEN SURFACES Shape factor F12 between two bodies depends on the (a) Shape and size of the two bodies (b) Shape and size of the bigger body (c) Shape, size and orientation of the bigger body (d) None ANS:(d) Shape factor F12 between two bodies depends on the (a) Shape […]
HEAT TRANSFER FOR READY REFERENCE FOR AN UNIVERSITY EXAMINATION—–SHEET 3 25 Stefan’s Boltzmann Law Gives TOTAL emissive power of a black body. Etotal T4 . T is absolute temp Etotal Etotal =σ T4 W/m2 26 WIEN’S DISPLACEMENT LAW The wavelength for maximum emissive power decreases with increase in absolute temperature λmaxT =2898 λmaxT […]
HEAT TRANSFER FOR READY REFERENCE FOR AN UNIVERSITY EXAMINATION—SHEET 2 11. FREE OR NATURAL CONVECTION When bulk motion of the fluid is caused by the density difference or Buoyancy force, it is called Free or Natural convection. It is governed by the product of Grashoff’s number and Prandtl number. All the convection processes […]
HEAT TRANSFER FOR READY REFERENCE FOR UNIVERSITY EXAMINATION—–SHEET 1 HEAT TRANSFER BRIEF NOTES FOR THE FINAL EXAMINATION DIFFERENCE BETWEEN THERMODYNAMICS AND HEAT TRANSFER Sr. No. Thermodynamics HEAT TRANSFER i. How much is the heat supplied and how much is the work done Tells rate of heat transfer and Tells the mode of […]
MCQ ON RADIATION HEAT TRANSFER Plank’s law gives the radiation flux for a (a) A single wavelength (b) Two wavelengths ( c) Three wavelengths (d) None ANS: (a) Plank’s law gives the radiation flux for a (a) A Black body (b) A Grey body ( c) All types of bodies (d) None ANS: (a) Stefan’s Boltzmann […]
HEAT TRANSFER MCQ-RADIATION, CONVECTION, BOILING— Law for the monochromatic radiation emissive power is (a) Stephen’s Boltzmann Law (b) Planck’s Law (c) Wien’s displacement Law (d)None ANS: (b) Radiosity is defined as (a) Total reflected radiations (b) Total emitted radiations (c) Difference of emitted and reflected radiations (d) None ANS: (b) Absorbtivity is zero for an opaque […]
HEAT TRANSFER—M C Q on Radiation, Convection and Boiling Which Law gives the monochromatic emissive power? (a) Stefan’s Boltzmann Law (b) Kirchoff’s Law (c) Wien’s Displacement Law (d) None ANS: (d) All types of radiations are emitted from a body at (a) Room temperature (b) Boiling temperature of water (c) Melting temperature of steel (d) None ANS: (d) Radiations are more harmful with […]
HEAT TRANSFER PTU PAPER SOLUTION—–SECTION–B SECTION-B Q2. Explain different phases of flow boiling. ANS: Flow boiling is much more complex than nucleate boiling. Here it will be a two phase heat transfer. Consider a vertical tube as shown in figure. Sub-cooled liquid is entering from below. As it moves upwards, getting heat from the tube […]
DECEMBER 2015 SECTION-A Q1. Write briefly : a) Define Thermal conductivity. How it is different from apparent thermal conductivity? b) What is meant by critical thickness of insulation? How it is calculated in case of a cylinder? c) Define Stefan Boltzmann’s law. d) Why thin fins are preferred over a thick fin? e) What is […]