HEAT TRANSFER BY FINS

SUBMITTED BY:

SATYAM SINGHSANJAY SHARMASUSHIL KUMARSUSHIL KUMAR SINGH

1. What is fin…??2. Types of fin3. Application of fin4. Material of fin5. Fin performance6. Heat dissipation from an infinitely long fin7. Heat dissipation from a fin insulated at tip8. Heat dissipation from a fin losing heat at tip

CONTENTS

A fin is a surface that extends from an object to increase the rate of heat transfer to or from the environment by increasing convection.

The amount of conduction, convection, or radiation of an object determines the amount of heat it transfers.

Adding a fin to an object, increases the surface area resulting in an effective heat transfer.

What is fin…??

Types of fins

a) Rectangular/ plate finsb) Tapered finc) Radial plate finsd) Disk/ annular finse) Pin fins

APPLICATION OF FIN

Economizers for steam power plants.

Convectors for steam power plants.

Air cooled cylinders of aircraft engines, I.C. engines and air compressors.

Electrical transformers and motors.

Cooling coils and condenser coils in refrigerators and air conditioners.

Electronic equipment etc..

Economizers for steam power plants

Application of economizers in steam power-plants is to capture the waste heat from flue gas and transfer it to the boiler feed water.

This raises the temperature of the boiler feed water, lowering the needed energy input.

The most common heat sink materials are aluminium alloy has one of the higher thermal conductivity values at 229 W/mK  but is mechanically soft.

Copper has around twice the thermal conductivity of aluminium and faster, more efficient heat absorption. But it is more expensive than aluminium Applications : In industrial facilities, power plants, solar thermal water systems, gas water heaters, forced air heating and cooling systems, and electronic systems etc.

Materials of fins

Diamond is another heat sink material, and its thermal conductivity is about 2000 W/mK .

Lattice vibrations are responsible for diamond's very high thermal conductivity.

Nowadays synthetic diamond is used as sub mounts for high-power integrated circuits and laser diodes.

Composite materials, example  copper tungsten, silicon carbideDymalloy (diamond in copper-silver alloy matrix), and E-material (beryllium oxide in beryllium oxide in  matrix) are also used.

It is considered that fin protruding from a wall surface is straight.its length is “ l ”constant cross-sectional area “ Ac ”and the circumferential parameter “ P ”

For rectangular fin

Ac = bt ; P = 2(b+t)

For circular fin (spine)

Ac = (π/4) × d2 ; P = πd

Steady flow of heat along a rod

Heat from the heated wall is conducted through the fin and it is convected from the sides of the fin to the surroundings.

So, heat conducted into the fin at plane “ l = x ” ,

Qx = -k A ( dT/ x)

where k = thermal conductivity of fin dT = change in temp. of fin at l = x and temp. at base Tc

A = p l

Fin performance

The utility of a fin in dissipating a given quantity of heat is generally assessed on the basis of the following parameters :

Efficiency of fin

Effectiveness of fin

Efficiency of fin

Fin efficiency is defined as the ratio of actual heat transfer rate to the maximum possible heat transfer rate from the same fin.

(i.e. it would dissipate heat at maximum rate if the entire fin surface area is maintained at the base temperature).

=

Effectiveness of fin

It is the ratio of the fin heat transfer rate to the heat transfer that would exist without a fin.

=

Heat dissipation from an infinitely long fin

Qfin = c

where, P = circumferential parameter, m h = convective heat transfer coefficient, W/m²K k = thermal conductivity, W/mK Ac = cross-sectional area, m² To = temp. at the base of fin, K Ta = surrounding temp. , K

(To – Ta)

Heat dissipation from a fin insulated at tip

Qfin = c (To – Ta) tanh ml

Heat dissipation from a fin losing heat at tip

Qfin = c (To – Ta) [tanh ml + h/km] / [1+h/mk tanh ml]

Thank you all for your kind attention