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Maxx Planck Institute

Subject: Heat and Mass Transfer

Max. Marks: 100 Duration: 3 Hrs

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PART A (10 x 2 = marks)

1. State Fourier's law of eat conduction.

!. "at is eat #eneration in solids$ %i&e exa(les.

3. "at is lu(ed s)ste anal)sis$ "en is it used$

*. +n wic ode of eat transfer is te con&ection eat transfer coefficient usuall) i#er,

natural or forced con&ection$ ")$

-. Define bulk te(erature.

. /ist te &arious (rooters used for aintainin# dro(wise condensation.

. Define /MTD of a eat excan#er.

. "at do )ou understand b) teral radiation$

2. "at does te &iew factor re(resent$ "en te &iew factor fro a surface to itself is ero$

10. "at is te ()sical eanin# of Scidt nuber$

PART B (5 x 16 = 80 marks)

11. 4a5 4i5 Define teral conducti&it). How does it &ar) wit te(erature for #ases$ 4*5

4ii5 Deri&e te #eneral 36diensional eat conduction e7uation in c)lindrical coordinates.

8ssue te aterial as oo#eneous isotro(ic continues. 41!5

9r

4b5 8 cold stora#e roo as walls ade of !3 c of brick on te outside, c of (lastic foa

and finall) 1.- c of wood on te inside. Te outside and inside air te(eratures are !! ; and

6! ; res(ecti&el). Te inside and outside eat transfer coefficients are res(ecti&el) !2 and 1!

"

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res(ecti&el). +f te total wall area is 20 !, deterine te rate of eat reo&al b) refri#eration

and te te(erature of te inside of te suruface of te brick.

1!. 4a5 4i5 Define te &elocit) boundar) la)er and teral boundar) la)er ticknesses for flowo&er a flat (late. 4*5

4ii5 8ir at *00 = and 1 bar (ressure flows at a s(eed of 1.- x(lain briefl) foulin# in eat excan#ers. 45

4ii5 Hot #ases enter a finned tube, cross flow eat excan#er wit a flow rate of 1.- k#

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9r

4b5 4i5 ;onsiderin# radiation in #ases, deri&e te ex(onential6deca) forula. 45

4ii5 Two lar#e (arallel (lanes wit eissi&ities 0.3- and 0.- excan#e eat b) radiation. Te

(lanes are res(ecti&el) 103 = and 3 =. 8 radiation sield a&in# te eissi&it) of 0.0* is(laced between te. Find te (ercenta#e reduction in radiation eat excan#e and te(erature

of te sield. 4105

1-. 4a5 4i5 "it neat sketces, ex(lain te different t)(es of fins. 4*5

4ii5 8ir at 1.01 bar and 30 ; flows (ast a tra) full of water wit a &elocit) of !