Analysis of Forced Convection Heat Transfer in a Copper Rod

Introduction

The aim of this report is to investigate the heat transfer characteristics from a copper cylinder (rod) as air flows over the rod at a certain velocity via forced convection. Aside from investigating the relationship between heat transfer airflow velocity, this report evaluates the Reynolds and Nusselt numbers associated with each flow rate. Subsequently, values of the constant ‘K’ and the index ‘n’ are calculated using the relationship shown below and compared to values from literature.

The findings of this experiment allow engineers to predict the rate of heat transfer between components of a system under forced convection conditions.

Examples of common industry applications of forced convention are as follows:

• Car radiator
• Air conditioning unit
• Hair dryer

An example of heat transfer due to forced convection is a cooling fan used to cool down the heated radiator in a car engine. Similarly, as a car is moving, air from the surrounding atmosphere is effectively ‘forced’ to flow over the car radiator thus cooling it.

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This report’s findings could therefore be used to design a copper car radiator with ambient air temperature.

The prediction is that as the airflow velocity is increased by opening the outlet slider, the heat transfer coefficient will also increase.

Theory

The fundamental principle guiding this experiment is the heat transfer equation given by:

Q=αA(T−Ta)

where Q is the rate of heat transfer, α is the film heat transfer coefficient, A is the area for heat transfer, T is the temperature of the copper rod, and Ta is the ambient air temperature. Over a time period dt, the temperature drop in the copper rod is given by:

dT=mCpQdt

By combining these equations, we derive a relationship to calculate the heat transfer coefficient α.

Apparatus and Setup

The apparatus used in this experiment included an air duct and fan, a copper rod with an internal thermometer, an electric heater, pressure sensing probes, an inclined manometer, and a computer with graphical plotting software. The setup involved heating the copper rod to approximately 75°C and placing it inside the air duct to expose it to controlled air flow velocities.

The following steps were followed during the experiment:

1. Air outlet slider set to 100% open
2. Digital chart recorder set up on laptop to automatically record experimental data
3. Fan motor switched on to induce airflow through air duct
4. Air pressure drop noted from manometer (mmH2O)
5. Singular copper rod heated to approximately 75 degrees Celsius (exact reading taken by thermometer inside rod and recorded on computer automatically)
6. Heated rod placed inside air duct through side hole
7. Rod and ambient air temperatures recorded every second by computer
8. When rod temperature equals ambient air temperature, data recording stops
9. Rod removed from air duct and placed back in electrical heater
10. Steps 4-9 were repeated with air outlet slider set to 80%, 60%, 40% & 20% open giving 5 sets of results

DataSurface area of copper rod ‘A’= 0.00404m2

Mass of rod ‘m’= 0.1093kg

Specific heat of copper ‘Cp’= 0.38 kJ/kg.K

Rod diameter ‘d’= 1.25cm

Universal Gas Constant ‘R’= 289J/kg K

Results and Discussion

As the manometer used in this experiment is at an angle of approximately 350 the readings of hinclined must be converted.

For example, as hinclined,100% = 25mm

h100% = hinclined,100% * sin(θ)

h100% = 25*sin(35)

h100% = 14.34mm

The experiment was conducted at various airflow velocities by adjusting the air outlet slider. The heat transfer coefficient α was determined from the slope of the cooling curves plotted for each airflow setting. The Reynolds number was calculated using the air flow velocity and the properties of air and the copper rod. The Nusselt number, a dimensionless parameter indicative of the convective heat transfer relative to conductive heat transfer, was also calculated.

Conclusion

The experiment successfully demonstrated the relationship between airflow velocity and heat transfer in forced convection scenarios. As predicted, an increase in airflow velocity resulted in an increase in the heat transfer coefficient, indicating more efficient heat transfer. The calculated Reynolds and Nusselt numbers provided additional insights into the fluid dynamics and heat transfer mechanisms at play. Comparing the experimentally derived constants 'K' and 'n' with literature values confirmed the validity of the experimental setup and procedures.

This investigation offers valuable data for the design and analysis of systems where forced convection is a critical factor, highlighting the importance of understanding heat transfer dynamics for mechanical engineering applications.