There are two types of heat transfer operation: sensible heat and change of phase. Sensible heat operations involve heating or cooling of a fluid in which the heat transfer results only in a temperature change of the fluid. Changeof-phase heat transfer results in a liquid being changed into a vapor or a vapor being changed into a liquid. Boiling or vaporization is the convection process involving a change in phase from liquid to vapor. Condensation is the convection process involving a change in phase from vapor to liquid. Many applications involve both sensible heat and change-of-phase heat transfer.
Sensible Heat Transfer Inside Tubes
Sensible heat transfer in most applications involves forced convection inside tubes or ducts or forced convection over exterior surfaces.
The heating and cooling of fluids flowing inside conduits are among the most important heat-transfer processes in engineering. The flow of fluids inside conduits may be broken down into three flow regimes. These flow regimes are measured by a ratio called the Reynolds number which is an indication of the turbulence of the flow inside the conduit. The three regimes are:
Laminar Flow Reynolds numbers less than 2,100
Transition Flow Reynolds numbers between 2,100 and 10,000
Turbulent Flow Reynolds numbers greater than 10,000
