Summary - Complete - Heat Transfer all Important Equations PDF

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Heat transfer all important equations...

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Equation Sheet for Heat Transfer These are the main equations you should know. You will not be given this sheet for class tests or examination. This is meant as a guide to aid your revision and the list is by no means exhaustive.

General

H  mc P TB  TA   mc P T

(for mass)

H  Q  mC cPC TC1  TC 2 

(for mass flow)

And heat/energy balances

Conduction Q  kA

Q

T1  T2 

(single slab)

x

T T   x  RT    kA 

(slabs in series)

Know how to determine resistances in parallel

T  T2 Q  k 2L 1 r  ln  2   r1 

Q

2 L(T1  T3 ) r r ln( 2 ) / ka  ln( 3 ) / k b r2 r1

(single cylinder)

(cylinders in series)

Convection Nu = f(Gr, Pr) Natural Convection Nu = f(Re, Pr) Forced Convection

Nu 

hL k

Nusselt number

cp

Pr 

Prandtl number

k

Re 

Lu

Reynolds number



Know how to use the exact and MacAdams (approximate formulas) see pages 3 – 5 Convection notes Know how to use Sieder and Tate and Dittus-Boelter equations

d 2  d1

de =

equivalent hydraulic diameter for non circular channels

-

Q  h A T

Newtons Law of heating/cooling

1  do 1      U o  hi d i ho 

Overall heat transfer coefficient for thin walled pipes

Q  U o Ao TLM

Overall Heat transfer rate across an object

LMTD   TLM 

Ao = πdoL,

T 2  T1  T  ln  2   T1 

Long mean temperature difference

Surface area of a pipe

Know difference between co-current and countercurrent flow Velocity profiles in laminar and turbulent flow

Radiation

max  T  C3

Weins displacement Law - Third radiation constant C3

Eb    T 4

Stefan-Boltzmann Law for black body

Qr A

 Eb1  Eb 2   (T1 4  T 24 ) or qb = T14 - T24

Radiative heat exchange (flux) between 2 black body plates

 

E and a  E Eb Eb

so a  

E    E b      T4

q1 2 

1 1  1

1

if

A1  A2

 2 1

then

Kirchoff’s Law

Stefan-Boltzmann for Grey (real) bodies

   ( T14  T24 )

Radiative heat flux between 2 grey plates

q1 2  1    ( T14  T24 )

Know where view factors (F) and Hottel coefficients ( 1 2 ) are included in Stefan-Boltzmann equations for black and grey bodies

Eg  g  As   Tg4

Radiation of gases

Gs ,0  Sc  f  cos 

Extraterrestrial radiation...