Heat and mass transfer of convection heat transfer.ppt

HMT

1. MAHAMMEDJUNED
Convection OF HEAT TRANSFER

2. CONTENT:
Basic Definitions
Natural And Force Convection
Factor Affecting convective Heat Transfer Coefficient
Nusselt Number And Prandlt Number
Dimensional Relationship of Natural Convection With
Gr and Pr

3. BASICS DEFINIONS
1.Heat Transfer:
HeatTransferDefineAsTheTransmissionofEnergyFromOneRegiontoanotherRegionas
aresultofTemperatureGradient.
Conduction:
ConductionTransferHeatviaDirectMolecularCollision.AreaofGreaterkineticenergywill
TransferThermalenergytoanareawithlowerkineticenergy.
Convection:
WhenaFluid,suchasairorLiquid,isheatedandthentravelsaway
fromthesource,itcarriesthethermalenergyalong.ThistypeofHeat
Transferiscalledconvection.
Radiation:
ThermalRadiationGeneratesfromtheemissionofelectromagnetic
waves.Thesewavescarrytheenergyawayfromtheemittingobject.

4. Natural And Force Convection
Natural Convectionis a type of heat transfer, in which the fluid motion is not generated by
any external source (like a pump, fan, suction pump etc.) but only by density differences in the
fluid occurring due to temperature gradients.
The Example of free convection is a heated plate when kept in an atmosphere, it gets cooled by air.
Here the circulation of air take place due to density difference, which is caused by temperature
difference between solid plate and air.
Natural convection is the process of heat transfer which occurs due to movement of the fluid
particles by density change associated with temperature differential in a fluid.
Some Example are given below:
1.The cooling of electrical transformers and
rectifiers.
2. The heat transfer from hot pipes by cooled air .

5. Forced convectionis a type of transfer in which fluid motion is generated by an external source
(like a pump, fan, suction device, etc.)
It is mostly used in all heat transfer application because the convection due to it, will be much higher
as compared to free convection.
If a heated plate is kept under a fan for cooling, it is called as forced convection.

6. Factor Affecting convective Heat Transfer
Coefficient
1. Temperature Difference (T)
T the greater the heat transfer rate.
2. Fluid flow rate
Increasing flow rate increasing heat transfer rate.
3. Surface area
the larger the surface area of conducting interfaces, the greater the heat
transfer rate.

7. Nusselt Number And Prandlt Number


8. 

9. Dimensional Relationship of Natural
Convection With Gr and Pr


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