Answer:
a) fuel cell weight and volume: 50 kg, 33.3 L
b) fuel tank weight and volume: 321 kg, 643 L
Explanation:
<u>Fuel Cell</u>
Delivery of 50 kW from a source with a power density of 1.5 kW/L requires a source that has a volume of ...
(50 kW)/(1.5 kW/L) = 33.3 L
The weight of the power source is 1 kW/kg, so will be ...
(50 kW)/(1 kW/kg) = 50 kg
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<u>Fuel Tank</u>
400 miles at 70 mph will take (400/70) h ≈ 5.71429 h. In that time, the energy used by the vehicle power plant is ...
(50 kW)(5.71429 h)(3600 s/h) = 1028.57 MJ
Since the power plant is 40% efficient, it must be supplied with 2.5 times that amount of energy, or 2571.43 MJ.
The tank volume and mass will then be ...
volume = 2571.43 MJ/(4 MJ/L) = 642.9 L
mass = 2571.43 MJ/(8 MJ/L) = 321.4 kg
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<em>Comment on fuel tank volume</em>
It appears the fuel tank would need to be equivalent in size to a sphere about 1.1 m in diameter.
