The critical purpose of the cooling subsystem is to prevent overheating of the water and oil. Excessive temperatures of either fluid can lead to vehicle malfunction and even internal engine damage. The goals of the cooling subsystem in 2017 were to keep water temperatures below 220 degrees F and the oil temperatures below 250 degrees F. In the past, the water temperature had reached a peak of 270 degrees F after extended periods of hard driving and that raised some concerns for the cooling efficiency of the radiator.
For the 2018 vehicle, I decided to investigate causes of our high water temperatures and how to decrease our operating water and oil temperatures to be an acceptable maximum. For the water temperature, a goal of 220 degrees F is acceptable as it would be 50 degrees less than the maximum seen previously and is a reasonable achievement for a properly designed cooling system. For the oil temperature, a goal of 250 degrees F is acceptable because it is 10 degrees away from the breakdown temperature of the selected motor oil.
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A local company, Mezzo Technologies, Inc., was willing to sponsor us with a specially designed micro tube radiator used on shifter karts. The micro tube radiator was able to pass an equal amount of water flow while keeping the water volume low, making the Mezzo radiator a desirable lightweight radiator (three pounds less than previous radiators).
The first step to designing the cooling system was to estimate how much heat transfer was necessary to cool the water passing through the radiator. To do this, I used three different methods of calculating output energy from the engine: combustion thermodynamics, power output, and fuel consumption. Combustion thermodynamics was to be solved using the NTU method, but it was unable to reach an accurate estimation due to the complexities. Power output calculations assumed that the peak horsepower created a certain percentage of energy into heat dissipated to the cooling system, however too many assumptions were made to make this method work. Finally, the fuel consumption method was considered the better method of the three as it was derived from the amount of fuel consumed and the time in which it was consumed, giving a rate of consumption and thus a rate of energy generation. This method used less assumptions and the results made sense, which allowed me to move toward properly sizing the radiator. A simple long fin heat transfer equation was used to find the core volume of the radiator.
The first step to designing the cooling system was to estimate how much heat transfer was necessary to cool the water passing through the radiator. To do this, I used three different methods of calculating output energy from the engine: combustion thermodynamics, power output, and fuel consumption. Combustion thermodynamics was to be solved using the NTU method, but it was unable to reach an accurate estimation due to the complexities. Power output calculations assumed that the peak horsepower created a certain percentage of energy into heat dissipated to the cooling system, however too many assumptions were made to make this method work. Finally, the fuel consumption method was considered the better method of the three as it was derived from the amount of fuel consumed and the time in which it was consumed, giving a rate of consumption and thus a rate of energy generation. This method used less assumptions and the results made sense, which allowed me to move toward properly sizing the radiator. A simple long fin heat transfer equation was used to find the core volume of the radiator.
The next component to spec was the fan. Using the heat transfer rate found by the previous energy calculations, the airflow required to cool the water sufficiently was calculated. The fan fan selected was a SPAL fan similar in performance to previous years, but smaller and consumed less amperage from the battery.
Finally, the last main component to the cooling system is the radiator shroud. The shroud functions in creating a nozzle of airflow and thereby increasing the flow through the radiator. The fan is mounted on the end of this shroud to pull air from the radiator when speeds are low or if the car is stationary. A simple nozzle fluids equation was used to calculate the mass flow, given both inlet and outlet areas (radiator and fan areas) were known. If you would like to learn more about this project, please read the full design report below. |