Thermodynamics of Insulated Pressure Vessels for Vehicular Hydrogen Storage

Abstract

This paper studies the application of insulated pressure vessels for hydrogen-fueled light-duty vehicles. Insulated pressure vessels can store liquid hydrogen (LHz); low-temperature (80 K) compressed hydrogen (CHZ); or ambienttemperature CHZ.In this analysis, hydrogen temperatures, pressures and venting losses are calculated for insulated pressure vessels fieled with LHz or with low-temperature CHZ, and the results are compared to those obtained in low-pressure LHz tanks. Hydrogen losses are calculated as a fhnction of daily driving distance during normal operation; as a fimction of time during long periods of vehicle inactivity; and as a function of initial vessel temperature during fbeling. The number of days before any venting losses occur is also calculated as a function of the daily driving distance.The results show that insulated pressure vessels have packaging characteristics comparable to those d conventional, low-pressure LHz tanks (low weight and volume), with greatly improved dommncy and much lower boil-off. Insulated pressure vessels used in a 17 knoll (40 mpg) car do not lose any hydrogen when the car is driven at least 15 kmhy in average. Since ahnost all cars are tilven for longer distances, most cars would never lose any hydrogen. Losses during long periods of parking are also relatively small. Due to their high-pressure capacity, these vessels would retain about a third of their full charge even after a very long dormancy, so that the owner would not risk running out of fuel. If an insulated pressure vessel reaches ambient temperature, it can be cooled down very effectively by fheling it with LHz with no losses during fbeling. The vessel has good thermal performance even when thermally insulated with inexpensive microsphere insulation. In addition, the insulated pressure vessels greatly ease fhel availability and infrastructure requirements, since it would be compatible with both compressed and cryogenic hydrogen refbeling. NOMENCLATURECp,v specific heat of the vessel enclosed within the insulation h specific enthalpy of hydrogen mass flow rate of hydrogen extracted from the vessel : total mass of hydrogen stored in the vessel M" mass of the vessel enclosed within the insulation P vessel pressure Q heat transfer rate fkom the environment into the vessel t time T temperature u specific internal energy of hydrogen P density of the hydrogen leaving the vessel INTRODUCTIONIn the search for an alternative to today's petroleum-powered vehicles, efficient hydrogen-fbeled vehicles are an attractive solution. Hydrogen vehicles can use the advanced technology of electric vehicles to improve environmental quality and energy security, while providing the range, performance and utility of today's gasoline vehicles.

Insulated Pressure Vessels for Vehicular Hydrogen Storage: Analysis and Performance Evaluation

“…Insulated pressure vessels also have much reduced evaporative losses compared to LH 2 tanks. This has been demonstrated in a previous work [10], which presents a thorough analysis of evaporative losses in cryogenic pressure vessels based on the first law of thermodynamics. Figure 1 illustrates some of the main results.…”

“…Losses from a LH 2 tank grow rapidly as the daily driving distance drops. A vehicle driven 50 km per day (the average for the USA, [10]) loses almost 1 kg (20%) of the fuel to evaporation. On the other hand, insulated pressure vessels lose hydrogen only for very short daily driving distances (less than 5 km/day).…”

Vehicular storage of hydrogen in insulated pressure vessels

“…The dormancy (period of inactivity before a vessel releases hydrogen to reduce pressure build up) can be calculated from the first law of thermodynamics [7] and the properties of H 2 [5] as a function of vessel maximum operating pressure. The results are shown in Figure 2.…”

Hydrogen binding property of Co- and Ni-based organometallic compounds

“…The US Department of Energy has set a target for the development of hydrogen storage technologies that the capacity should reach 6 wt% by weight hydrogen by the year 2010 and 9 wt% by the year 2015 [4]. During the last two decades, many groups dedicated to develop a high-efficiency hydrogen storage method both in experiments and theory, including highpressure hydrogen storage tank, liquid hydrogen, metal hydrides, complex hydrides, and microporous metalorganic frameworks [5][6][7][8][9]. However, due to various obstacles, such as slow kinetics, poor reversibility, and either too high or too low dehydrogenation temperatures [5,10], it is difficult to apply these methods to practice.…”