A B C D E F G H
HABIT, CRYSTAL SHAPE HAGEN-POISEUILLE EQUATION HALL COEFFICIENT HALL CURRENT HALL DISCHARGE HALL EFFECTS ON PERISTALTIC TRANSPORT HALL-TAYLOR EQUATION FOR ELECTRICAL CONDUCTIVITY HALOGENATED FLUOROALKANES HALOGENS HAMAKER CONSTANT HAMILTON-TYPE EQUATIONS HAMPSON COIL HANKEL FUNCTION HARDENING HARMONIC ANALYSIS Hartman number Hartman number Headers and Manifolds, Flow Distribution in HEADS HEAT HEAT ACTUATED HEAT CAPACITY, OF AIR HEAT CONDUCTION HEAT EXCHANGER NETWORKS HEAT EXCHANGER STANDARDS, TEMA HEAT EXCHANGERS HEAT EXCHANGERS, MULTI-STREAM HEAT EXCHANGERS, PLATE FIN HEAT FLUX HEAT FLUX MEASUREMENT HEAT FLUX METERS HEAT ISLAND HEAT OF ADSORPTION HEAT OF MELTING HEAT OF VAPORIZATION HEAT PIPES HEAT PROPAGATION HEAT PROTECTION HEAT PUMPS HEAT RECOVERY BOILERS HEAT RECOVERY NETWORK DESIGN HEAT STORAGE, SENSIBLE AND LATENT HEAT TRANSFER HEAT TRANSFER AND FLUID FLOW SERVICE HEAT TRANSFER AND NON-EQUILIBRIUM PHASE CHANGE OF LAMELLAE HEAT TRANSFER COEFFICIENT HEAT TRANSFER COEFFICIENT, IN COILED TUBES HEAT TRANSFER COEFFICIENT, IN POROUS MEDIA HEAT TRANSFER COEFFICIENT, TYPICAL VALUES HEAT TRANSFER COMPLEX HEAT TRANSFER CORRELATIONS HEAT TRANSFER ENHANCEMENT HEAT TRANSFER ENHANCEMENT DEVICES HEAT TRANSFER FLUIDS Heat transfer in aerospace applications HEAT TRANSFER IN AGITATED VESSELS HEAT TRANSFER IN BOILING MIXTURES HEAT TRANSFER IN BUBBLY FLOW Heat transfer in buildings Heat transfer in combustion systems HEAT TRANSFER IN FLUIDIZED BEDS Heat transfer in material processing HEAT TRANSFER IN PLUG FLOW HEAT TRANSFER IN POROUS MEDIA Heat transfer in solar engineering HEAT TRANSFER MEDIA HEAT TRANSFER MODELING HEAT TRANSFER OF AIR HEAT TRANSFER PROBE HEAT TRANSFER TO PIPELINES HEAT TREATMENT OF STEELS HEAT WAVES HEAT WHEELS Heat-shielding properties of quartz fibrous materials HEATING DEGREE DAYS HEATING OF BUILDINGS HEATING, VENTILATION & AIR CONDITIONING, HVAC HEAVY WATER HEAVY WATER REACTORS HEDH HEDSTROM NUMBER Hele-Shaw Flows HELICAL COIL BOILERS HELICAL COIL HEAT EXCHANGERS HELIUM HELIUM-NEON LASERS HELMHOLTZ FREE ENERGY HELMHOLTZ-TAYLOR INSTABILITY HEMISPHERICAL EMISSIVITY Hemispherical transmittance and reflectance at normal incidence HENRY'S LAW HEPTANE HERMITIAN, CONJUGATE, LINEAR OPERATORS HERRINGBONE CORRUGATIONS HERSCHEL-BULKLEY FLUIDS HETEROGENEOUS CATALYSIS HETEROGENEOUS FLOW REGIME HETEROGENEOUS REACTIONS HETEROGENEOUS SPRAY COMBUSTION HETEROSPHERE HEXANE HIEMENZ FLOW HIGH DEFLECTION OF INLET FLOW VELOCITY HIGH ENTHALPY PLASMA JETS HIGH FREQUENCY HEATING HIGH LEVEL LANGUAGE HIGH SPEED PHOTOGRAPHY HIGH TEMPERATURE GAS REACTORS HIGH TEMPERATURE PLASMA HIGH TEMPERATURE REACTOR, HTR HIGH VOLTAGE CIRCUIT BREAKER HIGH-ENERGY PULSATIONS IN HEAT AND MASS TRANSFER Highly porous cellular foams Highly porous isotropic and anisotropic fibrous materials HINDERED DRYING HINDERED SETTLING HOLDUP HOLDUP WAVES HOLES AND CONDUCTION ELECTRONS HOLLOW SCRUBBER HOLOGRAMS HOLOGRAPHIC INTERFEROMETRY HOLOGRAPHIC METHODS, FOR PARTICLE SIZING HOLOGRAPHY HOMEOSTASIS HOMOGENEOUS CATALYSIS HOMOGENEOUS DENSITY HOMOGENEOUS FLOW HOMOGENEOUS FLOW, CONSERVATION EQUATIONS HOMOGENEOUS MODEL HOMOGENEOUS SPRAY COMBUSTION HOMOGENISATION HOMOGENISER HOMOSPHERE HOMOTOPY-PERTURBATION METHOD HOOKE'S LAW HOOKEAN SOLID HOPPERS, GRANULAR FLOW FROM HORIZONTAL THERMOSYPHON REBOILER HORIZONTAL TUBE SHELL SIDE EVAPORATOR HORIZONTAL TUBES HOT DRY ROCK, HDR, GEOTHERMAL HEAT HOT FILM ANEMOMETERS HOT WATER BOILER HOT WIRE METHOD HOT-WIRE AND HOT-FILM ANEMOMETERS HOTTEL-WHILLIER-BLISS EQUATION HTFS HUGONIOT ADIABAT HUMAN EYE HUMAN LUNGS HUMAN THERMOREGULATORY SYSTEM HUMID HEAT HUMID VOLUME HUMIDITY HUMIDITY CHART HUMIDITY MEASUREMENT HUMIDITY, OF EARTH'S ATMOSPHERE HVAC, HEATING, VENTILATION & AIR CONDITIONING Hybrid method HYBRID NAVIER-STOKES METHOD HYBRID SIMULATION HYDRATE FORMATION Hydraulic Diameter HYDRAULIC GRADIENT LINE HYDRAULIC JUMP HYDRAULIC PROPERTIES OF HETEROGENEOUS ROCKS HYDRAULIC RADIUS HYDRAULIC REACTION TURBINE Hydraulic Resistance HYDRAULIC TURBINES Hydraulics HYDRAZINE COMBUSTION HYDRO POWER HYDROCARBONS HYDROCHLORIC ACID HYDROCHLOROFLUORCARBON-22 HYDROCHLOROFLUOROCARBON, HCFC HYDROCRACKER HYDROCYCLONES HYDRODYNAMIC ENTRANCE LENGTH, IN TUBES HYDRODYNAMIC INSTABILITY HYDRODYNAMIC RAM EVENT HYDRODYNAMIC THEORY OF BOILING HYDRODYNAMICS HYDROELASTIC WAVES HYDROENTANGLEMENT PROCESS HYDROFLUORIC ACID HYDROFLUOROCARBON, HFC HYDROGEN HYDROGEN AS ENERGY SOURCE HYDROGEN BOMBS HYDROGEN CHLORIDE HYDROGEN COMBUSTION HYDROGEN ENERGY HYDROGEN FLUORIDE HYDROGEN IODIDE HYDROGEN PEROXIDE HYDROGEN/FLUORINE COMBUSTION HYDROKINEMATICS HYDROMAGNETIC FREE CONVECTION HYDROMAGNETIC INSTABILITY HYDROMETALLURGY HYDROPHILE-LYOPHILE BALANCE, HLB HYDROPHILLIC/HYDROPHOBIC SURFACES HYDROSTATIC FORCES HYDROSTATIC LIFT FORCE Hydrostatics HYGROMETER HYGROSCOPICITY HYPERBOLIC DIFFERENTIAL EQUATIONS HYPERBOLIC EQUATIONS HYPERSONIC FLOW HYSTERESIS OF CONTACT ANGLE
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HYDROGEN

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Hydrogen–(Gr. hydro, water, and genes, forming), H; atomic weight (natural) 1.0079; atomic weight (H1) 1.007822; atomic number 1; melting point –259.14°C; boiling point –252.87°C; density 0.08988 g/1; density (liquid) 70.8 g/1 (–253°C); density (solid) 70.6 g/1 (–262°C); valence 1.

Hydrogen was prepared many years before it was recognized as a distinct substance by Cavendish in 1766. It was named by Lavoisier. Hydrogen is the most abundant of all elements in the universe, and it is thought that the heavier elements were, and still are, being built from hydrogen and helium.

It has been estimated that hydrogen makes up more than 90% of all the atoms or three quarters of the mass of the universe. It is found in the sun and most stars, and plays an important part in the proton-proton reaction and carbon-nitrogen cycle, which accounts for the energy of the sun and stars. It is thought that hydrogen is a major component of the planet Jupiter and that at some depth in the planet's interior the pressure is so great that solid molecular hydrogen is converted into solid metallic hydrogen. In 1973, it was reported that a group of Russian experimenters may have produced metallic hydrogen at a pressure of 2.8 Mbar. At the transition the density changed from 1.08 to 1.3 g/cm3. Earlier, in 1972, a Livermore (California) group also reported on a similar experiment in which they observed a pressure-volume point centered at 2 Mbar. It has been predicted that metallic hydrogen may be metastable; others have predicted it would be a superconductor at room temperature.

On earth, hydrogen occurs chiefly in combination with oxygen in water, but it is also present in organic matter such as living plants, petroleum, coal, etc. It is present as the free element in the atmosphere, but only to the extent of less than 1 ppm, by volume. It is the lightest of all gases, and combines with other elements, sometimes explosively, to form compounds. Great quantities of hydrogen are required commercially for the fixation of nitrogen from the air in the Haber ammonia process and for the hydrogenation of fats and oils. It is also used in large quantities in methanol production, in hydrodealkylation, hydrocracking, and hydrodesulfurization. It is also used as a rocket fuel, for welding, for production of hydrochloric acid, for the reduction of metallic ores, and for filling balloons. The lifting power of 1 ft3 of hydrogen gas is about 0.076 1b at 0°C, 760 mm pressure.

Production of hydrogen in the U.S. alone several amounts to several billion cubic feet per year. It is prepared by the action of steam on heated carbon, by decomposition of certain hydrocarbons with heat, by the electrolysis of water, or by the displacement from acids by certain metals. It is also produced by the action of sodium or potassium hydroxide on aluminum.

Liquid hydrogen is important in cryogenics and in the study of superconductivity as its melting point is only a few degrees above absolute zero. The ordinary isotope of hydrogen, 1H1, is known as protium. In 1932, Urey announced the preparation of a stable isotope, deuterium1H2 or D) with an atomic weight of 2. Two years later an unstable isotope, tritium1H3), with an atomic weight of 3 was discovered. Tritium has a half-life of about 12.5 years. One atom of deuterium is found mixed in with about 6000 ordinary hydrogen atoms. Tritium atoms are also present but in much smaller proportion. Tritium is readily produced in nuclear reactors and is used in the production of the hydrogen bomb. It is also used as a radioactive agent in making luminous paints, and as a tracer.

Quite apart from isotopes, it has been shown that hydrogen gas under ordinary conditions is a mixture of two kinds of molecules, known as ortho- and para-hydrogen, which differ from one another by the spins of their electrons and nuclei. Normal hydrogen at room temperature contains 25% of the para form and 75% of the ortho form. The ortho form cannot be prepared in the pure state. Since the two forms differ in energy, the physical properties also differ. The melting and boiling points of para-hydrogen are about 0.1°C lower than those of normal hydrogen. (See also Cryogenic Fluids.)

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