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Oxyhydrogen
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Oxyhydrogen
Oxyhydrogen is a mixture of hydrogen (H2) and oxygen (O2) gases. This gaseous mixture is used for torches to process refractory materials and was the first gaseous mixture used for welding. Theoretically, a ratio of 2:1 hydrogen:oxygen is enough to achieve maximum efficiency; in practice a ratio 4:1 or 5:1 is needed to avoid an oxidizing flame.
This mixture may also be referred to as Knallgas (Scandinavian and German Knallgas; lit. 'bang-gas'), although some authors define knallgas to be a generic term for the mixture of fuel with the precise amount of oxygen required for complete combustion, thus 2:1 oxyhydrogen would be called "hydrogen-knallgas".
"Brown's gas" and HHO are terms for oxyhydrogen originating in pseudoscience, although x H2 + y O2 is preferred due to HHO meaning H2O.
Oxyhydrogen will combust when brought to its autoignition temperature. For the stoichiometric mixture in air, at normal atmospheric pressure, autoignition occurs at about 570 °C (1065 °F). The minimum energy required to ignite such a mixture, at lower temperatures, with a spark is about 20 microjoules. At standard temperature and pressure, oxyhydrogen can burn when it is between about 4% and 95% hydrogen by volume.
When ignited, the gas mixture converts to water vapor and releases energy, which sustains the reaction: 241.8 kJ of energy (LHV) for every mole of H2 burned. The amount of heat energy released is independent of the mode of combustion, but the temperature of the flame varies. The maximum temperature of about 2,800 °C (5,100 °F) is achieved with an exact stoichiometric mixture, about 700 °C (1,300 °F) hotter than a hydrogen flame in air. When either of the gases are mixed in excess of this ratio, or when mixed with an inert gas like nitrogen, the heat must spread throughout a greater quantity of matter, reducing flame temperature.
Oxyhydrogen is explosive and can detonate when ignited, releasing a large amount of energy. This is often demonstrated in classroom environments in which teachers fill a balloon with the gas, due to the easy access of hydrogen and oxygen.
A precisely stoichiometric mixture may be obtained by water electrolysis, which uses an electric current to dissociate the water molecules:
William Nicholson was the first to decompose water in this manner in 1800. In theory, the input energy of a closed system always equals the output energy, as the first law of thermodynamics states. However, in practice no systems are perfectly closed, and the energy required to generate the oxyhydrogen always exceeds the energy released by combusting it, even at maximum practical efficiency, as the second law of thermodynamics implies (see Electrolysis of water#Efficiency).
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Oxyhydrogen
Oxyhydrogen is a mixture of hydrogen (H2) and oxygen (O2) gases. This gaseous mixture is used for torches to process refractory materials and was the first gaseous mixture used for welding. Theoretically, a ratio of 2:1 hydrogen:oxygen is enough to achieve maximum efficiency; in practice a ratio 4:1 or 5:1 is needed to avoid an oxidizing flame.
This mixture may also be referred to as Knallgas (Scandinavian and German Knallgas; lit. 'bang-gas'), although some authors define knallgas to be a generic term for the mixture of fuel with the precise amount of oxygen required for complete combustion, thus 2:1 oxyhydrogen would be called "hydrogen-knallgas".
"Brown's gas" and HHO are terms for oxyhydrogen originating in pseudoscience, although x H2 + y O2 is preferred due to HHO meaning H2O.
Oxyhydrogen will combust when brought to its autoignition temperature. For the stoichiometric mixture in air, at normal atmospheric pressure, autoignition occurs at about 570 °C (1065 °F). The minimum energy required to ignite such a mixture, at lower temperatures, with a spark is about 20 microjoules. At standard temperature and pressure, oxyhydrogen can burn when it is between about 4% and 95% hydrogen by volume.
When ignited, the gas mixture converts to water vapor and releases energy, which sustains the reaction: 241.8 kJ of energy (LHV) for every mole of H2 burned. The amount of heat energy released is independent of the mode of combustion, but the temperature of the flame varies. The maximum temperature of about 2,800 °C (5,100 °F) is achieved with an exact stoichiometric mixture, about 700 °C (1,300 °F) hotter than a hydrogen flame in air. When either of the gases are mixed in excess of this ratio, or when mixed with an inert gas like nitrogen, the heat must spread throughout a greater quantity of matter, reducing flame temperature.
Oxyhydrogen is explosive and can detonate when ignited, releasing a large amount of energy. This is often demonstrated in classroom environments in which teachers fill a balloon with the gas, due to the easy access of hydrogen and oxygen.
A precisely stoichiometric mixture may be obtained by water electrolysis, which uses an electric current to dissociate the water molecules:
William Nicholson was the first to decompose water in this manner in 1800. In theory, the input energy of a closed system always equals the output energy, as the first law of thermodynamics states. However, in practice no systems are perfectly closed, and the energy required to generate the oxyhydrogen always exceeds the energy released by combusting it, even at maximum practical efficiency, as the second law of thermodynamics implies (see Electrolysis of water#Efficiency).
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