Heat transfer: Dimensionless numbers PHYSICAL SIGNIFICANCE OF PRANDTL NUMBER 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 =δth If Pr <1 then δ < δth If Pr […]
Mcq ON RADIATION EXCHANGE 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 and size of […]
Heat transfer: quantity,Symbols & formula-2 DIFFERENCE BETWEEN THERMODYNAMICS AND HEAT TRANSFER 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 =2898 […]
Heat transfer: quantity,Symbols & formula-1 HEAT TRANSFER 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 heat transfer ii. Change in final state (properties) of the system Tells […]
mcq: Radiation 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 law is for […]
mcq: Heat transfer-1 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 (a) Black […]
mcq: Heat transfer-2 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 (a) Large wavelengths (b) Short wavelengths (c) Large as […]
Heat transfer-PTU paper solution 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 which […]
Heat transfer-PTU paper solution-A1 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) […]
Question bank-Radiation RADIATION 2 MARK OBJECTIVE QUESTIONS According to Kirchoff’s law, Radiated heat is proportional to the fourth power of absolute temperature Emissivity is equal to absorbtivity Emissive power depends on absolute temperature None Ans: (b) All the radiations from a black body are Reflected Transmitted Partly absorbed and partly reflected None Ans: (d) According […]