Free and forced convection pdf
FREE AND FORCED CONVECTION EXPERIMENTAn experimental apparatus to examine free and forced convection from a flat plate, a plate with fins and a plate with rods. The bench-mounting equipment includes a vertical duct that holds the chosen heat transfer surface and all instruments needed. Each surface has its own built-in variable-power electric heater. Students choose which surface they need to test and fit it to the duct using simple fixings. For free convection tests, the heated air rises from the surface and up the duct. For forced convection tests, a variable-speed fan draws air up through the duct and across the surface.
The influence of free convection on forced convection heat transfer becomes important in laminar flows. Numerical methods have been applied for a study of mixed convection in vertical tubes for the following conditions: temperature-dependent fluid density, constant wall temperature and parabolic profile of axial velocity at the tube entrance. Both cases: heating and cooling have been considered. Unable to display preview. Download preview PDF. Skip to main content.
Heat energy transferred between a surface and a moving fluid with different temperatures - is known as convection. In reality this is a combination of diffusion and bulk motion of molecules. Near the surface the fluid velocity is low, and diffusion dominates. At distance from the surface, bulk motion increases the influence and dominates. Forced convection occurs when a fluid flow is induced by an external force, such as a pump, fan or a mixer. Natural convection is caused by buoyancy forces due to dens ity differences caused by temperature variations in the fluid. At heating the density change in the boundary layer will cause the fluid to rise and be replaced by cooler fluid that also will heat and rise.
Problem 07 (2016) HD. Internal forced convection. Heat Transfer by Prof Josua Meyer
Forced convection is a mechanism , or type of transport in which fluid motion is generated by an external source like a pump, fan, suction device, etc. Alongside natural convection , thermal radiation and thermal conduction it is one of the methods of heat transfer and allows significant amounts of heat energy to be transported very efficiently. This mechanism is found very commonly in everyday life, including central heating , air conditioning , steam turbines and in many other machines. Forced convection is often encountered by engineers designing or analyzing heat exchangers , pipe flow, and flow over a plate at a different temperature than the stream the case of a shuttle wing during re-entry, for example. In any forced convection situation, some amount of natural convection is always present whenever there is gravitational forces present i.