CHE Team Challenge 1
Conclusion and Recommendations
The purpose of the double pipe heat exchanger is to regulate running hot and cold water to attain a range of temperature by opening and closing valves. This is achieved by figuring out the LEGO NXT program for the NXT Brick. Team members worked together to examine the program and all of its properties. Each team was given a basic structure of the program; however the program had to have minor adjustments for the team to solve. Once adjustments were fixed, the team tested the software to assure the program was conclusive. The motor managed to spin to be able to open and close the valves to manage the set temperature range. The team was successful at operating the program to be able to execute the actual experiment.
Explanation of Results
With the inlet and outlet temperatures, there seemed to be a negative correlation between the two. This was due to the exchanger bringing the hot and cold water to equilibrium. The LEGO NXT program recorded temperature every five seconds and would make its adjustments to the valve at twenty degree rotations. The program opened and closed the cold water valve to regulate the temperature between a five degree range. As the experiment went on, the two outlet temperatures became closer to the same temperature. The inlet temperature decreased while the outlet temperature increased bringing the temperatures to equilibrium. This result was expected due to the flow of the hot and cold water through the exchanger.
Knowing the values of the inlet and outlet temperatures of duration of a minute, the heat transfer (q) from the hot water to the cold water was found. Each trial began with different starting temperatures for inlet and outlet. That being said, for each trial the heat transfer was calculated. This was done by multiplying mass times specific heat (which is assumed constant) times the change in temperature. The mass flow rate was calculated by multiplying the density and the flow rate of the water. The heat transfer value seemed to be different values depending on the starting temperatures of the inlet and outlet. This effect had a positive correlation. If the temperatures first started higher, then the heat transferred was higher. This is logical considering that the higher the starting hot water temperature means more heat having to be transfers to the cold water to equalize.
Once heat transferred was found for each trial, the heat transferred coefficient (U) was calculated. Although each trial had different starting outlet and inlet temperatures meaning different heat transfers, the heat transfer coefficient calculated to be the same value for each trial. This is was to be expected if the data and heat transfer was calculated correctly.
Sources of Error within the Experiment...