Vorlesung Teil 2

• Physical state variable

• Unit: [Joule, kWh]

• different Forms: mechanical, thermal, electrical and chemical Energy

• Amount of energy transferred or converted per unit time

• unit [Watt, Joule/seconds]

• 350-700 bar

• room temperature

• composite cylinder

• 1-5 bar

• 20K

• dewar vessel

• <= 350 bar

• 20K - room temperature

• high pressure dewar vessel

• liquid organic hydrogen carriers

• <= 50 bar

• 150-320 °C

• convential liquid tank

• metal organic frameworks

• <= 100 bar

• cryogenic conditions

• cryogenic tank

• metal hydrides

• 10-150 bar

• -40 - 400°C

• (low) pressure vessel

absorption: Absorption of a substance into a condensed phase or a porous material

adsorption: Adsorption is an accumulation of substances on the surface of solids

• titration (sieverts-type apparatus)

• x-ray diffraction

• scanning electron microscopy

• differential scanning calorimetry

• mass spectrometer

• transient plane source method

• pycnometer

• BET analysis

• Particle size distribution analysis

• Hydrogen tank testing facilities

• neutron imaging

• very focused electron beam

• deflected in a defined manner and can thus scan the sample

• interactions of primary electrons with the sample material

• -> resultung in backscatter and secondary electrons and characteristic x-rays emerge of the sample surface

• used for elemental analysis

• sample must be must be electrically conductive to avoid charging

• energy can be converted, but it can neither produced nor destroyed

• total energy in the universe is constant

• a spontaneous change of state increases the entropy

• the entropy of the universe tends toward a maximum

ΔG = ΔH – T*ΔS

if ΔG < 0, the reaction is carried out spontaneous

if ΔG = 0, the system is in equilibrium.

if ΔG > 0, the reaction is not carried out spontaneous

• Reaction kinetics is the study of the rates of chemical reactions

• The law of speed for the first-order reaction of reactant A is: r(A)=k*c(A)

  or dc(A)/c(A)=-k*dt

• -> c(A) = c0 (A) · e^(-k·t)

• Kinetic energy can be converted into potential energy according to the theory of transition state

• This is necessary to provide sufficient energy in case of a collision for binding

• This necessary additional energy is called activation energy Ea

• -> Arrhenius: k = A · e^(-Ea/R*T)

• A catalyst is a substance whose presence increases the speed of a reaction without being consumed

• The catalyst opens a new path for the reaction where the total activation energy can be lowered

• homogenous catalyst: same phase as reactants

• heterogenous catalyst: reactants and catalyst are present in different phases

• The hydrogenation reaction is favored at low temperatures where ΔH is large

• Dehydrogenation reaction becomes thermodynamically favored At high temperatures though, -TΔS is larger in magnitude than ΔH

• gibbs free energy: ΔG = ΔH – T · ΔS

real plateau:

• high enthalpy of formation -> high stability -> high temperature of operation

Destabilization through alloying

• Elements which form stable phases with Mg, but do not form a stable hydride

• -> Strengthening the bond between metal and Mg

• -> Weaken the bond between Mg and H

• -> e.g.: Mg2Ni = - 14 kJ/g-atom

-> consider equilibrium conditions and resulting hydrogenation/dehydrogenation conditions

• stationary application

• mobile application

• applications could be cars, trucks, trains, ships etc.

• pressure and temperature ranges

• H2 capacity, stability and speed

• cost

• ease of handling in air before activation

• availibility at large-scale

• powder form

• pellet form

• thermal conductivity increases similar to the apparent density strong in the beginning

• increase of the thermal conductivity is different according to the direction

• thermodynamic parameters

• kinetic parameters

• heat exchange parameters

• densities

• particle size

• compatible with the code (AD2000)

• proper TüV pressure certification

• the shell should stand the internal pressure generated by the loading

• materials for the tank shell: stainless steel

• material design and properties

• reservoir shell

• heat exchange

• -> FEM simulation

• -> FEM for simple analysis by discretization of a cpmplex object

1. hydrogen pressure

2. concentration

3. temperature

• using the resulting heat of absorption and fuel cells for the heat demand

• One proton and one electron

• 14-times lighter than air

• Highest diffusivity of all gases

• Hydrogen atoms are very reactive

• Pure hydrogen in molecule state (enthalpy of formation: 436.22 kJ / mol)

• GWP: 4.3