Scientific Concepts Experiment: Heat Conduction in Metals

Metals are critical because they influence life and processes at different levels. For this reason, engineers are often asked to investigate thermal conductivity of metals including methods of measuring such conductivity. The phenomenon has important applications at theoretical and practical levels ranging from fields of building insulations to electronics. Conductivity refers to the process of heat transfer where thermal energy is transitioned from a heated item to a cooler item. In metals, it can refer to the transition of such energy from a heated end of the metal to a cooler end. Thermal conductivity of a material refers to the measure of its ability to conduct heat. The significance of heat conductivity in metals stems from the fact that different metals have different thermal conductivity properties. This means that not all metals can be used for certain roles that need specific conductivity properties. The objective of this report is to present the findings of an experiment comparing the heat conductivity rates of different metals.

Literature Review 

The wide application of thermal conductivity of metals has seen numerous improvised experiments conducted to establish the effectiveness of conductivity under different variables. The variables such as oscillating motion, magnetic field, and open tubes among others all have an influence on thermal conductivity coefficients of different metals. Wongkasem, Rittidech, and Bubphachot (2010) employed a mathematical model to predict the oscillating motion and heat transfer in a close-loop oscillating heat pipe in the presence of a magnetic field in different types of fluids. The researchers concluded that the magnetic field increases the oscillating motion while raising heat transfer rate, improving the efficiency of the pipe by 8%. In the same vain , Xu and Zhang (2010) experimentally investigated the applied performance of typically enhanced tubes in relation to parameters of flow pressure drop, anti-fouling performance, and friction factor in addition to enhanced heat transfer. The findings indicated that while the arc line tube has the greatest friction factor, the corrugated showed the highest energy efficiency and best anti-fouling performance. The experiments illustrate different strains and pressures that impact the efficiency of thermal conductivity in metals. The fact that different metals vary in their conductivity coefficients implies that they must be studied under uniform conditions to ascertain their effectiveness in relation to the specific function in question.

Experimental Design 

In this experiment, a non-steady-state technique was employed to measure the variable heat flux and a time-variant temperature gradient. The purpose of the experiment was to determine which metal was the best conductor of heat. Three metal wires used in the experiment: copper, brass, and steel, of equal length and thickness. Each wire was folded twice to form bridges and initially placed in a container of ice. Four pairs of cups of cold and hot water were used with three bridges of the same wire in each pair and the fourth with no bridges, acting as the control. Equal volumes of hot water were poured into four cups and the same process repeated with cold water in the other four cups. Bridges of wires were placed into pairs of cups after recording the initial temperatures of the cold waters.

The choice of the experimental design was informed by its simplicity as it required the use of readily available material. The experiment can be conducted in any setting. The experimental design is not affected by external variables hence projected to provide a clear answer to the research question about the best conducting metal.

Data collection initially began after cold water was poured into the cups. The temperature of each cup was taken. Thereafter, the temperature of each cold water cup was recorded every 5 minutes for 30 minutes for all the three metal wires used. The temperature was recorded in degrees Celsius using instant digital thermometers. A digital clock was used to monitor time, which was recorded in minutes. Data were tabulated in a notebook.

Variables 

In the experiment, the independent variable was time because it was influenced by any other variable being studied. The temperature of the cold water cup and conductivity were the dependent variables. The temperature of the cold water was determined by the thermal conductivity of the metal, which in turn depended on the type of the metal and the prevailing conditions.

Threat to Internal Validity 

The threat to internal validity was controlled through folding of the wires to form bridges, hence raising heat transfer rates of the metals. The cups with the control had a metal without folded bridges. Volumes of water were ensured to be equal in all hot water cups and similar in cold water cups.

Hypothesis 

“The temperature in the cold water cup varied differently with time for all the types of metals used.” The hypothesis was conceptualized based on the findings in the literature review showing that external factors influenced thermal conductivity of different metals. It was formulated in congruence with the objective of the study to establish which metal has the best thermal conductivity.

Process of Data Collection 

Data collection was quantitative, implying that only numerical data was captured. After the initial temperatures of the cold water cups were recorded. Subsequent measurements of temperature reflected the effectiveness of heat transfer for different metals. Only temperature changes and time intervals were captured as they represented the variables being studied.

The use of instant digital thermometers ensured that real-time temperature was captured without errors that come with reading, for instance of the calibrated tube thermometer. Measurement of temperature changes after 5-minute intervals ensured that a true reflection of each metal’s thermal conductivity was captured.

Results 

The findings of the experiments illustrate that metals have different thermal conductivities as demonstrated by the differences in heat transfer rates, captured as temperature changes in the line graphs below. Metals are known to be conductors of electricity, and the presence of free electrons in their conduction bands that are more mobile than the atoms themselves, facilitate the transfer of heat energy. The rigidity of the metal and availability of vibration bands in the crystal structure also helps in thermal conductivity. Therefore, the results show that the three metals differed in terms of their presence of free electrons, rigidity, and vibration bands, hence the differences in thermal conductivity.

Figure 1: Graphical representation of temperature changes with time for cold water cups for the three metals

The findings in the experiment illustrated that copper is the best thermal conductor, followed by brass, and lastly steel. The results confirm the hypothesis that changes in temperature in the cold water cups was dependent on the thermal conductivity of the respective metals used. The use of a non-steady state technique experimental design was instrumental determining the variables of the study as it captures the changes in temperature against time interval, thereby facilitating comparison of values for different metals. The experiment can be replicated using one of the metals and replaced the other with two different metals and comparing the outcomes. This way, the findings can be corroborated through a series of experiments, thus ensuring validity and credibility from repetitiveness.

References

Wongkasem, K., Rittidech, S., & Bubphachot, B. (2010). Motion and Heat-Transfer Analysis of a Closed-Loop Oscillating Heat Pipe with a Magnetic Field.  Journal of Enhanced Heat Transfer ,  17 (4), 369-380.

Xu, Z. M., & Zhang, Z. B. (2010). Experimental investigation of the applied performance of several typical enhanced tubes.  Journal of Enhanced Heat Transfer ,  17 (4), 331-341.