Hydrogen gas: A silo of energy

Hydrogen gas is a silo of energy while by itself in its natural state, it exists in its most expanded form with no ability to further expand and do thermodynamic work. Compressed H2 is an energy carrier.

The chemical element hydrogen has the symbol H and the atomic number 1. The lightest element is hydrogen. Under normal conditions, hydrogen is a gas composed of diatomic molecules with the formula H2. It has no color, no odor, no taste, is non-toxic, and is highly combustible. Hydrogen is the most abundant chemical element in the universe, accounting for approximately 75% of all normal matter. The Sun and other stars are mostly made up of hydrogen in the plasma state. The majority of hydrogen on Earth exists in molecular forms like water and organic compounds. Each atom of hydrogen's most common isotope (symbol 1H) has one proton, one electron, and no neutrons.

Hydrogen is nonmetallic (except at extremely high pressures), and it easily forms a single covalent bond with most nonmetallic elements, resulting in compounds such as water and nearly all organic compounds. Because acid-base reactions typically involve the exchange of protons between soluble molecules, hydrogen plays a particularly important role. In ionic compounds, hydrogen can have a negative charge (i.e., anion) and is known as a hydride, or it can have a positive charge (i.e., cation) and is denoted by the symbol H+. The H+ cation is nothing more than a proton (symbol p).

Thermophysical properties of H2 gas

Thermophysical properties comparison between Air, Hydrogen, and Helium

?We chose H2 gas and air, two diatomic gases, to compare four basic thermophysical properties, thermal conductivity, viscosity, specific heat, and density, as well as their implications in energy transport and cost.

If you look at a hydrogen molecule and try to interpret all of its good and bad properties, you will notice that its small size is at the root of all of them.

Hydrogen gas is not a form of energy. Hydrogen gas has no ability to perform work on its own. The compressibility of hydrogen gas, Z, is greater than one at all temperatures. Because of the repulsion of two protons in close proximity, hydrogen gas exists in its most expanded form. It cannot do any PV thermodynamic work at any temperature.

Let us examine four fundamental thermodynamic properties of hydrogen in terms of energy transport and cost implications.

Thermal conductivity

H2 vs Air

Thermal conductivity is defined as the ability of a material to conduct heat from its one side to the other. It is represented by the thermal conductivity coefficient λ. H2 has much higher thermal conductivity than air. The system of Unit (SI unit) of thermal conductivity is measured in Watts per meter-kelvin (W/(m?K). We know that, 1 watt= 1 Joule per second =J.s-1

Thermal conductivity and energy transport

Energy is carried by molecules in a substance. At any temperature, thermal conductivity is determined by the speed of molecules. Examine the thermal conductivity unit. One watt of power is defined as the ability of a body to perform one joule of work in one second. [Joule/sec] / m-k is the thermal conductivity unit. For every kelvin temperature change, it is the energy transport/sec through a one-meter length. The speed of molecules determines how much energy can be transported over a given distance. At any temperature and with a constant kinetic energy of 12 mV2, H2 has the fastest molecule speed. As a result, H2 can carry energy faster than any other gas.

Is it positive or negative?

It is advantageous in terms of energy transport. It is a safety concern because it causes H2 molecules to conduct heat very quickly within molecules and break into highly reactive atoms. H2 has a very low activation energy of 32 kj/mol. So, while molecular H2 is not reactive, it can be broken into atoms with a single electron with little external energy addition to become very reactive and even explode when it comes into contact with electron-rich oxygen.

The viscosity of H2 gas and energy transport

Hydrogen has a smaller viscosity than air.?Viscosity is a measure of a fluid's resistance to flow. It describes the internal friction of a moving fluid. A fluid with large viscosity resists motion because its molecular makeup gives it a lot of internal friction. The low viscosity of H2 signifies its much superior energy transport

Specific heat of H2 gas

Hydrogen has the largest specific heat among gases. It is about 14.5 times more than air.

The heat is required to raise the temperature of the unit mass of a given substance by a given amount (usually one degree). Molecules store heat in the motion of atoms. It is an advantage for compressed H2 compared to air, the reason is 1 gram of hydrogen gas has about 29/2 = 14.5 times the molecules in the same mass of air.

Density

The low density or high volume caused by molecule repulsion only negates the majority of the energy advantage. It is the most negative property of H2 from both an energy and storage and transport standpoint. The cost of compressing H2 gas is very high due to very high molecule-molecule repulsion. For the same reason, H2 has a unique storage and transportation issue.

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