Convection is the movement of molecules within fluids and is one of the major modes of heat and mass transfer. Forced convection occurs when an external source, like a fan or pump, generates fluid motion. This allows for very efficient heat transport and is commonly used in heating, cooling, and machinery. Extended surfaces like fins and pins can be added normal to a surface to increase the surface area and improve heat transfer between the surface and surrounding fluid according to Newton's Law of Cooling. Comparing finned and unfinned surfaces under the same conditions demonstrates the effect of extended surfaces.

1. INTRODUCTION
Convection is the movement of molecules within fluids (i.e. liquids, gases). It cannot take place in
solids, since either bulk current flows or significant diffusion can take place in solids. Convection is
one of the major modes of heat transfer and mass transfer.
Forced convection is a mechanism, or type of heat transport in which fluid motion is
generated by an external source (like a pump, fan, suction device, etc.). It should be considered as
one of the main methods of useful heat transfer as significant amounts of heat energy can be
transported very efficiently and 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). However, in any forced convection situation, some amount of natural convection
is always present whenever there are g-forces present (i.e., unless the system is in free fall). When
the natural convection is not negligible, such flows are typically referred to as mixed convection.
The removal of excessive heat from system components is essential to avoid damaging
effects of burning or overheating. Therefore, the enhancement of heat transfer is an important
subject of thermal engineering. Extended surfaces (fins) are frequently use in heat exchanging
devices for the purpose of improve the heat transfer between a primary surface and the surrounding
fluid.

2. THEORY
Heat transfer from an object can be improve by increasing the surface area in contact with the air by
adding fins or pins normal to the surface. This can be seen in Newton’s Law of Cooling that states
that the rate of heat loss of a body is proportional to the difference in temperatures between the body
and its surroundings, which defines the convection heat transfer rate.
The constant of proportionality h is termed the convection heat-transfer coefficient. The heat
transfer coefficient h is a function of the fluid flow, so, it is influenced by the surface geometry, the
fluid motion in the boundary layer and the fluid properties as well. The effect of the surfaces can be
demonstrated by comparing finned and unfinned surfaces with a flat plate under the same conditions
of power and flow.
A heated surface dissipates heat to the surrounding fluid primarily through a process called
convection. Heat is also dissipated by conduction and radiation, however these effects are not
considered in this experiment. Air in contact with the hot surface is heated by the surface and rises
due to reduction in density. The heated air is replaced by cooler air, which is in turn heated by the
surface, and rises. This process is called free convection.
Convection heat transfer from an object can be improved by increasing the surface area in
contact with the air. In practical it may be difficult to increase the size of the body to suit. In these
circumstances the surface area in contact with the air may be increased by adding fins or pins
normal to the surface. These features are called extended surfaces. A typical example is the use of
fins on the cylinder and head on an air-cooled petrol engine. The effect of extended surfaces can be
demonstrated by comparing finned and pinned surfaces with a flat under the same conditions of
power input and airflow.