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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HELIUM

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Helium – (Gr. helios, the sun), He; atomic weight 4.00260; atomic number 2; melting point below – 272.2°C (26atm); boiling point – 268.934°C; density 0.1785 g/1 (0°C, 1 atm); liquid density 7.62 lb/ft3 at boiling point; valence usually 0.

Evidence of the existence of helium was first obtained by Janssen during the solar eclipse of 1868 when he detected a new line in the solar spectrum; Lockyer and Frankland suggested the name helium for the new element; in 1895, Ramsay discovered helium in the uranium mineral clevite, and it was independently discovered in clevite by the Swedish chemists Cleve and Langlet about the same time. Rutherford and Royds in 1907 demonstrated that the particles are helium nuclei.

Except for hydrogen, helium is the most abundant element found throughout the universe. It has been detected spectroscopically in great abundance, especially in the hotter stars, and it is an important component in both the proton-proton reaction and the carbon cycle, which account for the energy of the sun and stars. The fusion of hydrogen into helium provides the energy of the hydrogen bomb.

The helium content of the atmosphere is about 1 part in 200,000. While it is present in various radioactive minerals as a decay product, the bulk of the world's supply is obtained from wells, for example, in Texas, Oklahoma, Kansas and Swift River, Saskatchewan.

Helium has the lowest melting point of any element and has found wide use in cryogenic research, as its boiling point is close to absolute zero. Its use in the study of superconductivity is vital. Using liquid helium, Kurti and co-workers, and others, have succeeded in obtaining temperatures of the few microdegrees K by the adiabatic demagnetization of copper nuclei, starting from about 0.01 K.

Five isotopes of helium are known. Liquid helium (He4) exists in two forms: He4 I and He4 II, with a sharp transition point at 2.174 K (3.83 cm Hg). He4 I (above this temperature) is a normal liquid, but He4 II (below it) is unlike any other known substance. It expands on cooling; its conductivity for heat is enormous; and neither its heat conduction nor viscosity obeys normal rules. It has other peculiar properties. Helium is the only liquid that cannot be solidified by lowering the temperature. It remains liquid down to absolute zero at ordinary pressures, but it can readily be solidified by increasing the pressure. Solid He3 and He4 are unusual in that both can readily be changed in volume by more than 30% by application of pressure. The specific heat of helium gas is unusually high. The density of helium vapor at the normal boiling point is also very high, with the vapor expanding greatly when heated to room temperature. Containers filled with helium gas at 5 to 10° K should be treated as though they contained liquid helium due to the large increase in pressure resulting from warming the gas to room temperature.

While helium normally has a 0 valence, it seems to have a weak tendency to combine with certain other elements. Means of preparing helium difluoride have been studied, and species such as HeNe and the molecular ions He+ and He++ have been investigated. Helium is widely used as an inert gas shield for arc welding; as a protective gas in growing silicon and germanium crystals, and in titanium and zirconium production; as a cooling medium for nuclear reactors, and as a gas for supersonic wind tunnels. A mixture of 80% helium and 20% oxygen is used as an artificial atmosphere for divers and others working under pressure. Helium is extensively used for filling balloons as it is a much safer gas than hydrogen. While its density is almost twice that of hydrogen, it has about 98% of the lifting power of hydrogen. At sea level, 1000 ft3 of helium lifts 68.5 lb.

One of the recent largest uses for helium has been for pressuring liquid fuel rockets. A Saturn booster such as used on the Apollo lunar missions requires about 13 million cubic feet of helium for a firing, plus more for checkouts.

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