Lifting helium

Modern airships, sometimes called blimps for their oblong shape, use an unreactive gas like helium for lift. Helium is twice as dense as hydrogen, but still lighter than air. 

Upon the United States entry into World War 1 in 1917, helium became a war material of first priority. Helium was sought to replace hydrogen as the lifting gas in lighter-than-air craft for military use. As a war material, helium became a government monopoly, was given a code name, and was shrouded in secrecy. By the war s end, quantities of helium had been produced, but none had reached combat. 

C05-0149. A balloon filled with helium gas at 1.0 atm and 25 °C is to lift a 350-kg payload. What is the minimum volume required for the balloon Assume that dry air at the same pressure and temperature makes up... 

Gas lasers, 14 681-696 carbon dioxide, 14 693-696 excimer lasers, 14 691-693 helium-neon, 14 681-683 ion lasers, 14 683-688 molecular nitrogen, 14 688-691 Gas lift electrolyte circulation, 9 621 Gas-liquid base stocks, 15 217 Gas-liquid chromatography (glc), 6 374 analysis of sugars via, 23 476 silylation for, 22 692, 697 Gas-liquid contactor, reciprocating jet,... 

The resist has been used as a mask in wet etching and in lift-off processes, and more recently in etching chromium films in a chlorine-oxygen-helium plasma. In the latter, the etch rates have ranged from 4 to 5.5nm/min at lOOW power in a barrel type reactor. Chromium etches at about 6.5nm/min under these conditions. The etch rate of the resist appears to be independent of the degree to which it has been cured before exposure, so the sensitive form described here is just as effective a mask as the highly cross-linked resists described earlier, at least in the chromium etching process. 

A rubber balloon weighing 10 g is 15 inches in diameter when inflated with helium at 735 torr and 75°F How much weight will the balloon lift in addition to its own weight"7 (Assume the density of alr to be 1 20 g/hter under these... 

Then the valve is actuated. The flow (volume) of helium being usually too small to lift the valve by itself, the valve to be tested must be previously fitted with a lift lever which will be used to actuate the valve. After an agreed number of actuations, the leak rate is measured once again at 90% of the set pressure. The valve is considered acceptable if the leak rate is below a certain level (e.g. according to API 527). 

Fig. 7.60 Using the inside-out technique, the piece in question is filled with helium and then placed in a covering of some type that can be evacuated. Any helium that is released within this covering will be detected by the helium leak detector. Note that the tested piece can have either end lifted up so that all surfaces are exposed to the vacuum. From Introduction to Helium Mass Spectrometer Leak Detection, Figs. 3.3 and 3.4, by Varian Associates, Inc. 1980, reproduced with permission.

You have a helium balloon at 1.00 atm and 25°C. You want to make a hot-air balloon with the same volume and same lift as the helium balloon. Assume air is 79% nitrogen, 21% oxygen by volume. The lift of a balloon is given by the difference between the mass of air displaced by the balloon and the mass of gas inside the balloon. 

It seems impossible that a light fabric bag can lift such a weight. It does so because the air inside the fabric bag or balloon is hotter than the outside air iuid the density of the heated air is much lower. Children s helium balloons float attached to their strings because the density of helium at room temperature and pressure is less than that of air. Release them from their strings and they will float off high into the sky - causing great distress to the children ... 

Helium is also used to inflate balloons and other lighter-than-air craft, such as dirigibles (blimps). Helium does not have the lifting power of hydrogen. However, hydrogen is flammable and helium is not. 

Modern airships use helium to provide lift. The Hindenburg used hydrogen gas, which provides about twice the lift of helium but is no longer used because it is extremely flammable. The hehum is contained in bags made of a space-age, leakproof fabric called Tedlar, a type of plastic. The bags are loosely inflated so that the helium pressure is about the same as atmospheric pressure. The quantity of helium determines the lifting ability of the ship. 

Some natural gas wells also produce helium, which can occur in commercial quantities nitrogen and carbon dioxide are also found in some natural gases. Gas is usually separated at as high a pressure as possible, reducing compression costs when the gas is to be used for gas lift or de-... 

If both white dwarfs were helium white dwarfs [62], the helium-burning layer will have unprocessed helium beneath. Heating from the nuclear reactions will lift the degeneracy of the top layers of the helium core and allow the helium-burning shell to burn into the center in a series of mild pulses. At this point the star should resemble an extreme horizontal branch star. Although the surface layers will be predominantly composed of helium from the disrupted white dwarf, there should be sufficient hydrogen to diffuse to the surface (helium will sink) to form the helium-poor atmosphere usually observed in sdB stars. Of course, this channel will always lead to the formation of a single EHB star. 

The large difference in gas densities of helium and nitrogen (which makes up about 80% of the air) accounts for the lifting power of helium. A balloon filled with helium will rise through a predominantly nitrogen atmosphere because its gas density is less than 15% of the density of the surrounding atmosphere ... 

Helium is used for air-ships, blimps, etc, its non-inflammability rendering it particularly suitable for these purposes although its lifting power is only hair that of pure hydrogen. To a limited extent helium is employed in thermometry and in lamps for yielding the A line in optical work. When inhaled with oxygen, helium is used as a cure for asthma and other ailments, such as croup and diphtheria, in which the windpipe is obstructed. 

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