Heat Transfer By Convection

Engr. Aki EspaldonDepartment of Chemical EngineeringRuano Drive, Faculty of EngineeringUniversity of Santo Tomas

Heat Transfer via ConvectionEnergy transfer by random molecular motion (as in conduction) plus bulk (macroscopic) motion of the fluid.

Convection: transport by random motion of molecules and by bulk motion of fluid.Advection: transport due solely to bulk fluid motion.

Forced convection: Caused by external means, (fans and blowers)

Natural (free) convection: flow induced by buoyancy forces, arising from density differences arising from temperature variations in the fluid

The above cases involve sensible heat (internal energy) of the fluid

Latent heat exchange is associated with phase changes boiling and condensation.

Dimensionless numbers in Heat TransferReynolds NumberNusselt Number

Dimensionless numbers in Heat TransferPrandtlNumber

Dimensionless numbers in Heat TransferGrashofNumber

Dimensionless numbers in Heat TransferRayleigh Number

Natural Convection

Natural Convection

Forced Convection, Heat Transfer Inside Pipes

Forced Convection, Heat Transfer Inside Pipes

Forced Convection, Heat Transfer Inside Pipes

Forced Convection, Heat Transfer Inside Pipes

Double-Pipe Heat Exchanger

Log-Mean Temperature DifferenceUtility Fluid (i.e.cooling water or steam)- AnnulusProcess fluid(i.e. Steam or product such as milk)The temperature difference between the bulk fluid and the surface of the steel pipe or insulation varies

Double Pipe Heat Exchanger

Log-Mean Temperature Difference

References Transport Phenomena, Bird, Lightfoot, StewartTransport Processes and Separation Processes Principles, Christie GeankoplisUnit Operations in Chemical Engineering, McCabe, Smith, HarriotSome slides from Prof. Morrison, Michigan Tech UniversitySome compiled slides/ notes from Engr. Andrew Tengkiat Some compiled slides/ notes from Engr. AndrewAlberto Laurito