Question

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Q3 - Choose the correct answer from a, b, c ord (2 marks for each branch) 1 - The value of Biot number is very small (less than 0.01) when - The convective resistance of the fluid is negligible b- The conductive resistance of the solid is negligible C. The conductive resistance of the fluid is negligible d. None of these 2 - Generally speaking, in natural convection, the heat transfer coefficients are a. More than those of forced convection b- Less than those of forced convection c- Equal to those of forced convection d- None of these do 3- Solution of the ordinary differential equation r + Q = 0 is. a- Q = C.e b. Q = C.Inr C- Q = C/Inr d-Q = C/r 4- A value of Nu=1 implies what? - No heat transfer c- Heat transfer possible by convection only b-The maximium heat transfer d-Heat transfer possible by conduction only 5:- In evaluating the Nusselt number, for the flow of air over a steel body, the value of thermal conductivity used is 4- 0.02 W/mK (ie, air) 1-30 W/mK (ie, steel) b- The average value of air and steel d-It could be the fluid value at the film temperaure

Answer 1

Q:1 Biot Number Y/KA ha "/A K. LAKA I/ha ko solid hoof fluida of YKA & Conductire resistance /A Convective resis fone mean YkA is When Biot Biot no. is less negligake wirt /A So, we şay . Conductive resistance of the şolich is negligble. can is correct option (6) D.2 Natural Convection is slow as compared to forced Convection Heat Transfer Coefficient is how fast heat Benefrates through the system.

are Less Heat transfer Coefficient are than of forced Connection. those option (6) is Correct r dd dr + 8 This equation can be written as & dd do & dr = 0 dr =1 / dr dr d (98) O dre d (ov) av de study ya dr Intergration both side. dr=0 % option (1) is Correct Q

how Nusselt No . is the fast the conduction is doiven by the fluid flow (aldvection) Nesself Number equals to I Conduction is not driven by aduechion elence, heat transfer takes places purely by conduction Nu= he means that K option (P) year frons for is possible by Conduction only sis In The enaluation of Nusself Number for flow of air over a sfeed body, the value of themal Conductivity used is ! of air (fluid) i e o 0.02 h (ie air) mk option (a) .002W is correct mk Auswege
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