INTRODUCTION1.0 Objective1. To demonstrate the use of fin (extended surface) in order to improve the heat transfer in forced convection.2. To perform calculation to find the heat transfer coefficient for each finned and pinned surfaces.

2.0 BackgroundConvection is heat energy transfers between a solid and a fluid when there is a temperature difference between the fluid and the solid. Generally, convection heat transfer cannot be ignored when there is a significant fluid motion around the solid. On the other hand, convection is said to be the flow of heat through a bulk, macroscopic movement of matter from a hot region to a cool region, as opposed to the microscopic transfer of heat between atoms involved with conduction. In order to make it clearer, consider heating up a local region of air. As this air heats, the molecules spread out, causing this region to become less dense than the surrounding, unheated air. Being less dense than the surrounding cooler air, the hot air will subsequently rise due to buoyant forces. This movement of hot air into a cooler region is then said to transfer heat by convection.There are two types of convection. The first one is natural convection. Theoretically, natural convection happens when the temperature of the solid due to an external field such as fluid buoyancy can induce a fluid motion. It is a strong function of the temperature difference between the solid and the fluid. Besides that, when the blowing air over the solid by using external devices such as fans and pumps can also generate a fluid motion. This is known as forced convection. This report is going to discuss about forced convection only. In forced convection, the fluid has a nonzero streaming motion in the far field away from the body surface, caused perhaps by a pump or fan or other driving force independent of the presence of the body.

Two major examples are duct flows and bodies immersed in a uniform stream. Since fluid velocities are forced and may be large, heat transfer via forced convection will usually be significantly larger than that in natural convection. Heating a pot of water on a stove is a good example of the transfer of heat by convection. When the stove is first turned on heat is transferred first by conduction between the elements through the bottom of the pot to the water. However, eventually the water starts bubbling - these bubbles are actually local regions of hot water rising to the surface, thereby transferring heat from the hot water at the bottom to the cooler water at the top by convection. At the same time, the cooler, more dense water at the top will sink to the bottom, where it is subsequently heated.

Figure 1 The movement of heat by gas molecules.

3.0 Theory

Heat transfer from an object can be improved by increasing the surface area in contact with the coolant i.e air by adding fins or pins normal to the surface. From the Newtons Law of Cooling, the convection heat transfer rate is:

Figure 2 The illustration of experimental equipment.Where;= Power inputh = convection heat transfer coefficientAs = area of plateTs = heater temperatureT = air temperatureFor this experiment, we use finned plate and pinned plate to compare the effect of heat transfer by each plates under the same conditions of power and flow. To calculate the area for finned plate and pinned plate used, we use the equation shown below:

APPARATUS AND EQUIPMENTThe surfaces are shown in the figure below. The finned surface consists of 9 fins that are each of 0.1 m high and 0.068 m wide. The pinned surface consists of 17 pins that each have a diameter of 0.013 m and are 0.068 m long.

Figure 3 Dimensions of finned and pinned surfaces. Figure 4 Finned surfaces. Figure 5 Pinned surfaces.

Figure 6 Full experimental apparatus.