Incorporating Aluminum Honeycomb to Increase Efficiency of U-tube Removable Heat Exchanger

This report contains the results of attempting to improve on the results of Scott R. Sawyer and Alan M. L’Esperance research paper “Investigation of Paraffin Wax as an Energy Storage Medium Within a Shell-and-Tube Heat Exchanger.” The overall goal of the paper mentioned was to investigate the usefulness of wax as an energy storage medium. Scott R. Sawyer and Alan M. L’Esperance determined that “the amount of energy that can be released by the paraffin wax back to the airflow reaches a plateau, despite an increase in heating times.” They suggested that by surrounding the airflow tubes of a heat exchanger with metal foam that heat conduction would occur throughout the wax via the metal foam and increase the energy output from the wax. Unfortunately there was not enough money in the budget to implement metal foam to the heat exchanger and instead an aluminum honeycomb sheet was used. A difference to point out from Scott R. Sawyer and Alan M. L’Esperance experiment is this experiment uses a removable heat exchanger instead of a fixed tube heat exchanger and aluminum honeycomb was wrapped around the inflow tubes. The heat exchanger was filled with three pounds of paraffin wax. A heater heated the inflow air temperature that passed through the heat exchanger, which could be turned on or off. Thermocouples were used to measure the inflow air temperature and the outflow air temperature. A flow meter was used to measure and a valve controlled the volumetric flow rate. The experiment consisted of two tests. The first test consisted of heating the airflow into the heat exchanger for three hours and a heater off phase that lasted three hours. The second experiment was the same except that aluminum honeycomb was used to surround the inflow tubes. The findings of the experiment were similar to Scott and Alan’s, despite surrounding the inflow tubes with aluminum honeycomb there was no increase in efficiency. For both runs the amount of energy extracted from the hot wax to the cold air was only 34%. A likely reason for this is the presence of solid and liquid wax within the heat exchanger. Originally it was believed that the deposits of wax in the honeycomb would increase heat conduction, but the wax deposits in the honeycomb closest to the cold airflow tubes solidified and thus did not allow energy transfer from the hot wax to cold air because the wax deposits closest to the tube acted as an insulator.