Free & Forced Convection Heat Transfer

Sultan Qaboos University
College of Engineering
Department of Mechanical & Industrial Engineering

Heat Transfer
Lab report

Free & Forced Convection Heat Transfer

Mahmood Mohsin AL-Khusaibi 85135
Amur Sultan Al-Habsi 86260
Rashid Nasser Al Shabibi 85362

Aim: The objective of this experiment to investigate the use of extended surface to improve heat transfer through surfaces. In addition, another target is to demonstrate the effect of the fluid speed on the heat transfer by convection.

Introduction: Heat transfer by convection is one of three heat transfer methods which are conduction, radiation and convection. Convection is form of energy transfer between a solid surface and the adjacent fluid. It engrosses the mixed effect of the fluid velocity and conduction. The fluid velocity and the surface area effect are both proportional with the rate of heat transfer.

Theory: Heat transfer due to convection is expressed by Newton’s law of cooling as:

Qconv = hAs(Ts-Tinf)…………..(1)

Where h is the convection heat transfer coefficient and As is the effected surface area. Heat transfer can be improved by using a larger surface area however, in practice this not always applicable. In similar situation, the surface area can be increased by adding fins or pins. This effect can be demonstrated by comparing different types of extended surface area with a flat plate.

Apparatus: The apparatus used in this are the duct that work like a wind tunnel different types of plates for heat transfer (flat, pined, finned), heat generator and a stopwatch for time measurement.

Procedure: First of all, Apparatus for this experiment was prepared. Then, the flat plate heat exchanger was fitted into the duct. Heat power control was set to 75w till the temperature reaches steady state. After that, heat power control was set to 20 w till the temperature reaches steady state once again. Once that happened the temperature was recorded. Next, the temperature was recorded for different fan speeds 0.5, 0.8 and1m\s. the same procedure was repeated for the finned plate and the pinned plate.

Results: velocity | flat plate | pinned plate | finned plate | (m/s) | TS (C°) | TS-T∞ (C°) | TS (C°) | TS-T∞ (C°) | TS (C°) | TS-T∞ (C°) | 0 | 89.1 | 68.1 | 54.4 | 33.4 | 49.3 | 28.3 | 0.5 | 88.6 | 67.6 | 51 | 30 | 45.5 | 24.5 | 0.8 | 87.4 | 66.4 | 45.4 | 24.4 | 41 | 20 | 1 | 85.6 | 64.6 | 39.7 | 18.7 | 36.5 | 15.5 | | | | | | | |
Table [ 1 ] recorded temperature of different types of plates

Figure [ 1 ] velocity aganist temperature difference

Discussion of Results: Table 1 shows the recorded temperature for different types of plates (flat, pinned and finned). The recorded temperature indicates that while using the extended area “finned plate” temperature difference is at its minimum. In other word the heat transfer using the finned area as expected is greater than other types of plates, that’s why fins are used on the cylinder and head of air cooled petrol engine. Errors may have occurred due to human errors in taking the temperature difference. Also, using a stopwatch for measuring the time periods is not very precise. Moreover, at the time of the experiment the fan in the duct had some issues that prevent it from reaching its maximum speed.

Conclusion: The use of extended surface to improve heat transfer through surfaces was successfully demonstrated. Furthermore, the relation of the effect of the fluid speed on the heat transfer by convection was established. Heat transfer using the finned area as expected is greater than other types of plates. Errors may have occurred due to human errors and may also occur due a malfunction in the duct fan.