1. FREE CONVECTION – FIXED POWER TD1005

2. Objectives
To compare the maximum temperature each surface reached for a given input power when free convection.

3. Introduction
Heat can be transferred from one point to another by three common methods:
Conduction (vibration and free electron).
convection (heat transfers by a fluid flow ).
Radiation (heat transfers through electromagnetic radiation).
Convective heat transfer, often referred to simply as convection, is the transfer of heat from one place to another by the movement of fluids. Convection is usually the dominant form of heat transfer in liquids and gases.

4. Free convection :This when the heat transfers from the object under the influence of fluid (air) density changes.
Forced convection :This is when an external force moves air around or across the surface.

5. 1- Flat Plate
2-Pinned Surface
3-Finned

6. The flat surface has little or no effect on airflow and sits flush with the duct wall. The main body of the airflow does not pass the surface.

7. The pinned surface
sits directly in the main body of airflow.
It causes turbulent airflow and varied velocities in the around its pins.
This surface creates an air pressure difference (drop) between upstream and downstream airflows.
The airflow at its inlet may be uniform, but the airflow immediately downstream is turbulent. It causes a greater obstruction to airflow and pressure drop than the flat or finned surfaces.

8. The finned surface sits directly in the main body or airflow
The finned surface sits directly in the main body or airflow. It has a less pronounced effect on airflow and pressure drop than the pinned surface, with a relatively uniform airflow into and out of the fins.

9. Equipment's
Free and Forced Convection TD1005

10. Procedure Remove the fan from the top of the duct.
Fit your chosen heat transfer surface.
Create a blank results table.
T1(Inlet ambient)
T2(Surface)
Delta(T)
Flat plate
Pinned
Finned

11. Switch on the heater and set it to 15 watts power.
Wait for temperature to stabilize - this may take 30 to 40 minutes.
Record the maximum temperature surface reaches and inlet (ambient temperature).
Switch off the heater and allow the surface to cool down to near ambient temperature.
Repeat the experiment for the other heat transfer surface.