Our results prove that further testing is necessary for better understanding of the combustion and heat exchanger system. There were some discrepancies that were found in our results and from those we were able to identify ways to solve these issues and improve experimental run analyses.
5.2.1 Determine the Heat Content of Fuel by a Calorimetry
Analyzing the heat content of fuels in a calorimeter would provide more accurate information regarding the efficiency of the Espar heater. The team used heat content information sourced from the Department of Energy’s Alternative Fuels Data Center and noted that different sources reported variations in the heat content of both diesel and biodiesel. Experimentally derived heat contents would allow for the heat contents of a particular sample of fuel to be determined.
5.2.2 Changes and Additions to Process Equipment
a. Installation of a Thermocouple in the Heater’s Exhaust Pipe
During testing, the team determined that the heat transfer in the heat exchanger trended negatively with increasing water flow for all fuel types. The team believes that the
heater’s controller is responsible for this negative trend. The controller lowers the coolant flow rate to achieve its temperature differential goals. This drop in coolant flow causes less heat to be transferred into coolant. Conservation of energy indicates that most of the energy not transferred from the combustion gases exits the system in heater exhaust. The group suggests that a thermocouple be installed in the engines exhaust line. If there is a positive correlation between the temperature of the exhaust and the cooling water flow rate, then it will be clear that the engine controller is responsible for the negative trend in heat duty with increasing water flow rate.
b. Installation of Continuous Digital Log of Coolant Flow
In addition to the installation of a thermocouple in the heater’s exhaust pipe, a continuous digital log of the coolant flow can help determine the controller’s influence on the flow rate of the coolant. The apparatus currently has a glass rotameter for measuring the
coolant flow with an accuracy of 2% of the rotameter’s max flow. The team observed that the float in the rotameter moved around constantly within a 2% range at high cooling water flow rates and did not possess this oscillatory pattern when the system operated at a lower water flow rate. The magnitude of the drop in the rotameter with increasing water flow was also small. At the lower water rate, the rotameter read a continuous 60% of the max flow. At the high water flow rate; it oscillated between 56% and 58.5%. The team suggests adding a digital flowmeter that is setup to output data at least once a second to a data logger. Doing so would allow for a more accurate characterization of the coolant flow rate’s dependence on the cooling water flow rate and thus provide further insight into the behavior of the heater controller. It would help solidify the team’s hypothesis that the controller is responsible for the negative trend in heat transfer rate through the heat exchanger.
36 c. Installation of a Second Type of Heat Exchanger
The current apparatus is fully capable of supporting a full-scale Unit Operations
Laboratory for future students. With further additions, it could support two full labs – one that focuses on identifying differences between biofuels and petrol fuels and another that focuses on heat exchanger design. A second heat exchanger could be added to the current system in parallel to the existing plate heat exchanger. Valves could be placed to allow students to isolate coolant flow to one exchanger or the other. Making the second exchanger a shell and tube pattern exchanger would provide a strong illustration to students about the differences between the two most common types of heat exchangers that they will encounter in their careers. The new heat exchanger would have to be of comparable size to the current plate exchanger in order for a valid comparison to be conducted. The team recommends that the new exchanger matches the current one in surface area. The addition of the new exchanger would open up the possibility of a new lab focused exclusively on heat exchangers and would have a structure similar to that of the fluid circuit lab, where students study the flow of water through pipes of different sizes, configuration, and compare the flow through an orifice and venturi meter.
d. Installation of Emission Sensors
The current experimental apparatus succeeds at quantifying the differences in thermal properties between diesel and biodiesel fuels. An improvement that would drastically expand the capability of the apparatus is the addition of emission testing sensors.
Quantifying the level of CO emissions would show differences in the extent of complete combustion of a fuel. Sensors that identify sulfur and nitrogen compounds would provide significant information on the potential environmental and health impacts of using one fuel over another. The apparatus burns fuel at a constant volumetric flow rate and thus comparisons could easily be drawn between fuels.
e. Eliminating Air from Coolant Line
The testing performed by the team in the validation of the apparatus was done with a coolant loop filled only once. There was clearly a pocket of air present in the loop in an unknown, but constant amount. While in operation, the air became uniformly dispersed in the liquid coolant as small bubbles. This system of small air bubbles dispersed in an ethylene glycol and water solution has no known empirical estimation of specific heat capacity. The lack of a known heat capacity caused difficulty in accurately calculating the heat duty of the plate heat exchanger using the data collected from the coolant stream. The team advises that the coolant loop be drained and refilled before further testing is conducted. The coolant was not refilled during this project because of the desire to maintain a constant coolant composition between all trials.
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