1.0 Introduction
The transfer of heat normally involves the change in temperature of an object with high temperature to another object with lower temperature. According to the First Law of Thermodynamics, heat transfer changes the internal energy of both systems involved.
As such, the three modes of heat transfer are; Conduction, Convection and Radiation. According to C.R. Nave (Hyper Physics, 2010), conduction is heat transfer by means of molecular agitation within a material without any motion of the material as a whole, convection is heat transfer by mass motion of a fluid such as air or water when the heated fluid is caused to move away from the source of heat, carrying energy with it and radiation is heat transfer by the emission of electromagnetic waves which carry energy away from the emitting object.
The aim of this laboratory exercise focus on conducting practical exercises to identify the variety of different heat transfer concepts involved and develops an understanding of their applications and functions.
As such, this laboratory report comes in 4 parts where the first 2 parts, will touch on practical exercise on heat transfer by radiation of a copper rod with blackened surface and heat transfer by natural convection of the same material respectively. The last 2 parts will touch on practical exercise on heat exchanger performance and heat losses in pipes respectively.
1.2 Equipment

* Copper rod with internal electric heating element * DC power supply * Pressure valve and vaccum pump * Thermocouple on surface of heated rod * Thermocouple on inside surface of pressure vessel wall * Digital pressure gauge (for low pressures < 10000 Pa absolute) * Digital pressure gauge (for vacuum gauge pressures up to atmospheric, in Bar) * Barometer * Heated Copper rod (L = .1 m, D = .018 m)

1.3 Procedure

1. Vacuum pump was run to remove as much air as was possible within the pressure vessel. a. This would result in absolute pressure <10 Pa but would be ideally closer to 5 Pa. 2. Electric heating element was activated and set to 9 Watts of input power, which was equivalent to 56% setting. 3. Thermal equilibrium was established after waiting a short duration. b. Surface temperature of the rod stopped changing. 4. Electric heat input the rod was recorded as the electric power supplied. 5. 5% was subtracted from the power due to power dissipation within the cables. 6. Other measurements were recorded; pressure in the vessel, temperature of the heated rod (T1) and also the temperature of the surrounding pressure vessel wall (T2). 7. A small amount of air was allowed to enter the pressure vessel through the inlet valve (WHY??) 8. Steps 3 to 7 were repeated for another 6 different pressures that could be as close as possible too 5, 100, 500, 1600, 3900 and 8100 Pa. Heat Transfer by Radiation | Input Power setting = 56% (% maximum power) | Input power = 9 (Watts) | Reading No. | Air Pressure (Absolute) (kPa) | Air Pressure Raised to Power of 0.25 (kPa) | Copper Rod Temperature T1 (°C) | Surroundings Temperature T2 (°C) | 1 | 5 | 1.495348 | 179 | 25.6 | 2 | 101 | 3.170153 | 173.2 | 25.9 | 3 | 455.5 | 4.619788 | 170.3 | 26.1 | 4 | 1530 | 6.254215 | 168.3 | 26.3 | 5 | 3770 | 7.835835 | 166.7 | 26.4 | 6 | 7700 | 9.367477 | 164.4 | 26.5 |

Graph 1 below shows the linear relationship between temperatures of both the heated copper rod and the surrounding vessel wall versus the air pressure raised to the power of 0.25 together with extrapolated values of the temperature.

1.1. Assumptions

* Steady state operating conditions exist at the time of readings taken. * The copper rod is completely surrounded by the walls of the pressure vessel. * Heat transfer by convection is not considered. * Heat transfer by conduction through the copper rod’s suspending medium is negligible.
Calculations

The