Chapter 5, Problem 5.90P

A fuel cell is an electrochemical device that reacts hydrogen with oxygen from the air to produce water and DC electricity. A proposed application is replacement of the gasoline-fueled internal combustion engine in an automobile with a 100 kW fuel cell.

You are on a summer internship with a gas supplier planning to transport hydrogen to service stations for use in cars powered by fuel cells. The hydrogen is to be transported in tube trailers, each of which has 10 tubes of length 10.5 m and diameter 0.56 m. Hydrogen in the tubes at 2600 psig and an average temperature of 298 K is discharged at service stations to a ?nal pressure of 55 psig. Refueling each fuel-cell-powered automobile is estimated to require 4.0 kg of hydrogen.

(a) You and your of?ce-mate—an intern from a different university—have been asked to estimate the number of automobiles that can be refueled by one tube-trailer load of hydrogen. He does a very quick calculation and comes up with a value of 95 cars. Speculate how he did it and provide support for your speculation. What was his mistake?

(b) Do the calculation using the SRK equation of state. Instead of using Eqs. 5.3−11 and 5.3-13 for the parameter a, use the following correlation developed speci?cally for hydrogens:23 $a=1.202\exp \left(-0.3228T_r\right)$.

(c) Do the calculation using the law of corresponding states.

(d) In which of the three estimates would you have the greatest con?dence, and why?