Misplaced Pages

#337662

54-415: The diatomic character of the N 2 molecule is retained after liquefaction . The weak van der Waals interaction between the N 2 molecules results in little interatomic attraction. This is the cause of nitrogen's unusually low boiling point . The temperature of liquid nitrogen can readily be reduced to its freezing point −210 °C (−346 °F; 63 K) by placing it in a vacuum chamber pumped by

108-490: A d < h c o n v {\displaystyle {{h}_{rad}}<{{h}_{conv}}} , h = h c o n v + 3 4 h r a d {\displaystyle h={{h}_{conv}}+{\frac {3}{4}}{{h}_{rad}}} The effective radiation coefficient, h r a d {\displaystyle {{h}_{rad}}} can be expressed as, h r

162-451: A d = ε σ ( T s 4 − T s a t 4 ) ( T s − T s a t ) {\displaystyle {{h}_{rad}}={\frac {\varepsilon \sigma \left(T_{s}^{4}-T_{sat}^{4}\right)}{\left({{T}_{s}}-{{T}_{sat}}\right)}}} where ε {\displaystyle \varepsilon }

216-779: A t ) ) μ v f ( T s − T s a t ) σ / g ( ρ L − ρ v ) ] 1 ╱ 4 {\displaystyle h=0.425{{\left[{\frac {k_{vf}^{3}{{\rho }_{vf}}g\left({{\rho }_{L}}-{{\rho }_{v}}\right)\left({{h}_{fg}}+0.4{{c}_{pv}}\left({{T}_{s}}-{{T}_{sat}}\right)\right)}{{{\mu }_{vf}}\left({{T}_{s}}-{{T}_{sat}}\right){\sqrt {\sigma /g\left({{\rho }_{L}}-{{\rho }_{v}}\right)}}}}\right]}^{{}^{1}\!\!\diagup \!\!{}_{4}\;}}} For vertical tubes, Hsu and Westwater have correlated

270-628: A t ) ) D o μ v ( T s − T s a t ) ] 1 ╱ 4 {\displaystyle h=C{{\left[{\frac {k_{v}^{3}{{\rho }_{v}}g\left({{\rho }_{L}}-{{\rho }_{v}}\right)\left({{h}_{fg}}+0.4{{c}_{pv}}\left({{T}_{s}}-{{T}_{sat}}\right)\right)}{{{D}_{o}}{{\mu }_{v}}\left({{T}_{s}}-{{T}_{sat}}\right)}}\right]}^{{}^{1}\!\!\diagup \!\!{}_{4}\;}}} where D o {\displaystyle {{D}_{o}}}

324-415: A liquid from a solid or a gas or that generates a non-liquid phase which behaves in accordance with fluid dynamics . It occurs both naturally and artificially . As an example of the latter, a "major commercial application of liquefaction is the liquefaction of air to allow separation of the constituents, such as oxygen, nitrogen, and the noble gases." Another is the conversion of solid coal into

378-478: A vacuum pump . Liquid nitrogen's efficiency as a coolant is limited by the fact that it boils immediately on contact with a warmer object, enveloping the object in an insulating layer of nitrogen gas bubbles. This effect, known as the Leidenfrost effect , occurs when any liquid comes in contact with a surface which is significantly hotter than its boiling point. Faster cooling may be obtained by plunging an object into

432-471: A byproduct of manufacture of liquid oxygen used for industrial processes such as steelmaking . Liquid-air plants producing on the order of tons per day of product started to be built in the 1930s but became very common after the Second World War; a large modern plant may produce 3000 tons/day of liquid air products. Liquefaction In materials science , liquefaction is a process that generates

486-410: A dangerous shift in the load. In physics and chemistry , the phase transitions from solid and gas to liquid ( melting and condensation , respectively) may be referred to as liquefaction. The melting point (sometimes called liquefaction point) is the temperature and pressure at which a solid becomes a liquid. In commercial and industrial situations, the process of condensing a gas to liquid

540-399: A few hours to a few weeks. The development of pressurised super-insulated vacuum vessels has enabled liquid nitrogen to be stored and transported over longer time periods with losses reduced to 2 percent per day or less. Liquid nitrogen is a compact and readily transported source of dry nitrogen gas, as it does not require pressurization. Further, its ability to maintain temperatures far below

594-444: A hot iron surface to water, such as within a boiler. In a pair of lectures on boiler design, he cited the work of Pierre Hippolyte Boutigny (1798–1884) and Professor Bowman of King's College, London , in studying this. A drop of water that was vaporized almost immediately at 168 °C (334 °F) persisted for 152 seconds at 202 °C (396 °F). Lower temperatures in a boiler firebox might evaporate water more quickly as

SECTION 10

#1732851933338

648-485: A liquid form usable as a substitute for liquid fuels. In geology , soil liquefaction refers to the process by which water-saturated, unconsolidated sediments are transformed into a substance that acts like a liquid, often in an earthquake. Soil liquefaction was blamed for building collapses in the city of Palu, Indonesia in October 2018. In a related phenomenon, liquefaction of bulk materials in cargo ships may cause

702-514: A liquid, for example in food preparation or laboratory use. This may be done with a blender, or liquidiser in British English. Liquefaction of silica and silicate glasses occurs on electron beam irradiation of nanosized samples in the column of transmission electron microscope. In biology , liquefaction often involves organic tissue turning into a more liquid-like state. For example, liquefactive necrosis in pathology , or liquefaction as

756-422: A means to promote chemical change of various organic liquids through their conversion by thermal decomposition into various products. Examples include decomposition of ethanol, diethyl carbonate, and glycerol. In Jules Verne 's 1876 book Michael Strogoff , the protagonist is saved from being blinded with a hot blade by evaporating tears. In the 2009 season 7 finale of MythBusters , " Mini Myth Mayhem ",

810-468: A much higher temperature causes any further drops of water to evaporate too quickly to cause this effect. The effect happens because, at temperatures at or above the Leidenfrost point, the bottom part of the water droplet vaporizes immediately on contact with the hot pan. The resulting gas suspends the rest of the water droplet just above it, preventing any further direct contact between the liquid water and

864-455: A parabolic velocity profile are assumed within the vapor phase . The heat transfer within the vapor phase is assumed to be through conduction . With these approximations, the Navier–Stokes equations can be solved to get the pressure field. The Leidenfrost temperature is the property of a given set of solid–liquid pair. The temperature of the solid surface beyond which the liquid undergoes

918-446: A parameter in semen analysis . Leidenfrost effect The Leidenfrost effect is a physical phenomenon in which a liquid, close to a solid surface of another body that is significantly hotter than the liquid's boiling point , produces an insulating vapor layer that keeps the liquid from boiling rapidly. Because of this repulsive force, a droplet hovers over the surface, rather than making physical contact with it. The effect

972-422: A result; compare Mpemba effect . An alternative approach was to increase the temperature beyond the Leidenfrost point. Fairbairn considered this, too, and may have been contemplating the flash steam boiler , but considered the technical aspects insurmountable for the time. The Leidenfrost point may also be taken to be the temperature for which the hovering droplet lasts longest. It has been demonstrated that it

1026-405: A slush of liquid and solid nitrogen rather than liquid nitrogen alone. As a cryogenic fluid that rapidly freezes living tissue, its handling and storage require thermal insulation . It can be stored and transported in vacuum flasks , the temperature being held constant at 77 K by slow boiling of the liquid. Depending on the size and design, the holding time of vacuum flasks ranges from

1080-448: A small splash or even pouring down skin will not burn immediately because of the Leidenfrost effect , the evaporating gas thermally insulates to some extent, like touching a hot element very briefly with a wet finger. If the liquid nitrogen manages to pool anywhere, it will burn severely. As liquid nitrogen evaporates it reduces the oxygen concentration in the air and can act as an asphyxiant , especially in confined spaces . Nitrogen

1134-458: Is 257 °C (495 °F). The Leidenfrost temperatures for glycerol and common alcohols are significantly smaller because of their lower surface tension values (density and viscosity differences are also contributing factors.) Non-volatile materials were discovered in 2015 to also exhibit a 'reactive Leidenfrost effect', whereby solid particles were observed to float above hot surfaces and skitter around erratically. Detailed characterization of

SECTION 20

#1732851933338

1188-485: Is named after the German doctor Johann Gottlob Leidenfrost , who described it in A Tract About Some Qualities of Common Water . This is most commonly seen when cooking , when drops of water are sprinkled onto a hot pan. If the pan's temperature is at or above the Leidenfrost point, which is approximately 193 °C (379 °F) for water, the water skitters across the pan and takes longer to evaporate than it would take if

1242-447: Is odorless, colorless, and tasteless and may produce asphyxia without any sensation or prior warning. Oxygen sensors are sometimes used as a safety precaution when working with liquid nitrogen to alert workers of gas spills into a confined space. Vessels containing liquid nitrogen can condense oxygen from air. The liquid in such a vessel becomes increasingly enriched in oxygen (boiling point 90 K; −183 °C; −298 °F) as

1296-485: Is possible to stabilize the Leidenfrost vapor layer of water by exploiting superhydrophobic surfaces. In this case, once the vapor layer is established, cooling never collapses the layer, and no nucleate boiling occurs; the layer instead slowly relaxes until the surface is cooled. Droplets of different liquids with different boiling temperatures will also exhibit a Leidenfrost effect with respect to each other and repel each other. The Leidenfrost effect has been used for

1350-434: Is sometimes referred to as liquefaction of gases . Coal liquefaction is the production of liquid fuels from coal using a variety of industrial processes. Liquefaction is also used in commercial and industrial settings to refer to mechanical dissolution of a solid by mixing , grinding or blending with a liquid. In kitchen or laboratory settings, solids may be chopped into smaller parts sometimes in combination with

1404-478: Is the emissivity of the solid and σ {\displaystyle \sigma } is the Stefan–Boltzmann constant. The equation for the pressure field in the vapor region between the droplet and the solid surface can be solved for using the standard momentum and continuity equations using a Boundary layer model . In this model for the sake of simplicity in solving, a linear temperature profile and

1458-415: Is the mass flow rate in l b m / h r {\displaystyle l{{b}_{m}}/hr} at the upper end of the tube. At excess temperatures above that at the minimum heat flux, the contribution of radiation becomes appreciable, and it becomes dominant at high excess temperatures. The total heat transfer coefficient is thus a combination of the two. Bromley has suggested

1512-670: Is the outside diameter of the tube. The correlation constant C is 0.62 for horizontal cylinders and vertical plates, and 0.67 for spheres. Vapor properties are evaluated at film temperature. For stable film boiling on a horizontal surface, Berenson has modified Bromley's equation to yield, h = 0.425 [ k v f 3 ρ v f g ( ρ L − ρ v ) ( h f g + 0.4 c p v ( T s − T s

1566-503: Is used to compress filtered air to high pressure; the high-pressure gas is cooled back to ambient temperature, and allowed to expand to a low pressure. The expanding air cools greatly (the Joule–Thomson effect ), and oxygen, nitrogen, and argon are separated by further stages of expansion and distillation. Small-scale production of liquid nitrogen is easily achieved using this principle. Liquid nitrogen may be produced for direct sale, or as

1620-402: The freezing point of water, specific heat of 1040 J ⋅kg ⋅K and heat of vaporization of 200 kJ⋅kg makes it extremely useful in a wide range of applications, primarily as an open-cycle refrigerant , including: The culinary use of liquid nitrogen is mentioned in an 1890 recipe book titled Fancy Ices authored by Agnes Marshall , but has been employed in more recent times by restaurants in

1674-412: The Leidenfrost phenomenon is termed the Leidenfrost temperature. Calculation of the Leidenfrost temperature involves the calculation of the minimum film boiling temperature of a fluid. Berenson obtained a relation for the minimum film boiling temperature from minimum heat flux arguments. While the equation for the minimum film boiling temperature, which can be found in the reference above, is quite complex,

Liquid nitrogen - Misplaced Pages Continue

1728-466: The Leidenfrost point may be quite different, with a complicated dependence on the properties of the surface, as well as any impurities in the liquid. Some research has been conducted into a theoretical model of the system, but it is quite complicated. The effect was also described by the Victorian steam boiler designer, William Fairbairn , in reference to its effect on massively reducing heat transfer from

1782-416: The advantage of extremely low friction. The effect also applies when the surface is at room temperature but the liquid is cryogenic , allowing liquid nitrogen droplets to harmlessly roll off exposed skin. Conversely, the inverse Leidenfrost effect lets drops of relatively warm liquid levitate on a bath of liquid nitrogen. The Leidenfrost point signifies the onset of stable film boiling. It represents

1836-400: The cellulose droplet (depicted at the right) was observed to occur above about 750 °C (1,380 °F), associated with a dramatic reduction in heat transfer. High speed photography of the reactive Leidenfrost effect of cellulose on porous surfaces (macroporous alumina ) was also shown to suppress the reactive Leidenfrost effect and enhance overall heat transfer rates to the particle from

1890-432: The development of high sensitivity ambient mass spectrometry. Under the influence of the Leidenfrost condition, the levitating droplet does not release molecules, and the molecules are enriched inside the droplet. At the last moment of droplet evaporation, all the enriched molecules release in a short time period and thereby increase the sensitivity. A heat engine based on the Leidenfrost effect has been prototyped; it has

1944-589: The explosion was sufficient to propel the tank through the ceiling immediately above it, shatter a reinforced concrete beam immediately below it, and blow the walls of the laboratory 0.1–0.2 m off their foundations. In January 2021, a line carrying liquid nitrogen ruptured at a poultry processing plant in the U.S. state of Georgia, killing six people and injuring 11 others. Because of its extremely low temperature, careless handling of liquid nitrogen and any objects cooled by it may result in cold burns . In that case, special gloves should be used while handling. However,

1998-404: The features of it can be understood from a physical perspective. One critical parameter to consider is the surface tension . The proportional relationship between the minimum film boiling temperature and surface tension is to be expected, since fluids with higher surface tension need higher quantities of heat flux for the onset of nucleate boiling . Since film boiling occurs after nucleate boiling,

2052-738: The following equation, h [ μ v 2 g ρ v ( ρ L − ρ v ) k v 3 ] 1 ╱ 3 = 0.0020 [ 4 m π D v μ v ] 0.6 {\displaystyle h{{\left[{\frac {\mu _{v}^{2}}{g{{\rho }_{v}}\left({{\rho }_{L}}-{{\rho }_{v}}\right)k_{v}^{3}}}\right]}^{{}^{1}\!\!\diagup \!\!{}_{3}\;}}=0.0020{{\left[{\frac {4m}{\pi {{D}_{v}}{{\mu }_{v}}}}\right]}^{0.6}}} where m

2106-601: The following equations for film boiling from the outer surface of horizontal tubes: h 4 ╱ 3 = h c o n v 4 ╱ 3 + h r a d h 1 ╱ 3 {\displaystyle {{h}^{{}^{4}\!\!\diagup \!\!{}_{3}\;}}={{h}_{conv}}^{{}^{4}\!\!\diagup \!\!{}_{3}\;}+{{h}_{rad}}{{h}^{{}^{1}\!\!\diagup \!\!{}_{3}\;}}} If h r

2160-402: The hot pan. As steam has much poorer thermal conductivity than the metal pan, further heat transfer between the pan and the droplet is slowed down dramatically. This also results in the drop being able to skid around the pan on the layer of gas just under it. The temperature at which the Leidenfrost effect appears is difficult to predict. Even if the volume of the drop of liquid stays the same,

2214-440: The liquid-to-gas expansion ratio of nitrogen is 1:694 at 20 °C (68 °F), a tremendous amount of force can be generated if liquid nitrogen is vaporized in an enclosed space. In an incident on January 12, 2006 at Texas A&M University , the pressure-relief devices of a tank of liquid nitrogen were malfunctioning and later sealed. As a result of the subsequent pressure buildup, the tank failed catastrophically. The force of

Liquid nitrogen - Misplaced Pages Continue

2268-414: The minimum temperature for film boiling should have a proportional dependence on the surface tension. Henry developed a model for Leidenfrost phenomenon which includes transient wetting and microlayer evaporation. Since the Leidenfrost phenomenon is a special case of film boiling, the Leidenfrost temperature is related to the minimum film boiling temperature via a relation which factors in the properties of

2322-414: The nitrogen evaporates, and can cause violent oxidation of organic material. Ingestion of liquid nitrogen can cause severe internal damage, due to freezing of the tissues which come in contact with it and to the volume of gaseous nitrogen evolved as the liquid is warmed by body heat. In 1997, a physics student demonstrating the Leidenfrost effect by holding liquid nitrogen in his mouth accidentally swallowed

2376-406: The pan rises above 100 °C (212 °F), the water droplets hiss when touching the pan, and these droplets evaporate quickly. When the temperature exceeds the Leidenfrost point, the Leidenfrost effect appears. On contact with the pan, the water droplets bunch up into small balls of water and skitter around, lasting much longer than when the temperature of the pan was lower. This effect works until

2430-419: The point on the boiling curve where the heat flux is at the minimum and the surface is completely covered by a vapor blanket. Heat transfer from the surface to the liquid occurs by conduction and radiation through the vapour. In 1756, Leidenfrost observed that water droplets supported by the vapor film slowly evaporate as they move about on the hot surface. As the surface temperature is increased, radiation through

2484-521: The preparation of cocktails because it can be used to quickly chill glasses or freeze ingredients. It is also added to drinks to create a smoky effect, which occurs as tiny droplets of the liquid nitrogen come into contact with the surrounding air, condensing the vapour that is naturally present. Nitrogen was first liquefied at the Jagiellonian University on 15 April 1883 by Polish physicists Zygmunt Wróblewski and Karol Olszewski . Because

2538-483: The preparation of frozen desserts, such as ice cream, which can be created within moments at the table because of the speed at which it cools food. The rapidity of chilling also leads to the formation of smaller ice crystals, which provides the dessert with a smoother texture. The technique is employed by chef Heston Blumenthal who has used it at his restaurant, The Fat Duck , to create frozen dishes such as egg and bacon ice cream. Liquid nitrogen has also become popular in

2592-620: The properties are evaluated at saturation temperature. Zuber's constant, C {\displaystyle C} , is approximately 0.09 for most fluids at moderate pressures. The heat transfer coefficient may be approximated using Bromley's equation, h = C [ k v 3 ρ v g ( ρ L − ρ v ) ( h f g + 0.4 c p v ( T s − T s

2646-497: The reactive Leidenfrost effect was completed for small particles of cellulose (~0.5 mm) on high temperature polished surfaces by high speed photography. Cellulose was shown to decompose to short-chain oligomers which melt and wet smooth surfaces with increasing heat transfer associated with increasing surface temperature. Above 675 °C (1,247 °F), cellulose was observed to exhibit transition boiling with violent bubbling and associated reduction in heat transfer. Liftoff of

2700-403: The solid being used. While the Leidenfrost temperature is not directly related to the surface tension of the fluid, it is indirectly dependent on it through the film boiling temperature. For fluids with similar thermophysical properties, the one with higher surface tension usually has a higher Leidenfrost temperature. For example, for a saturated water–copper interface, the Leidenfrost temperature

2754-507: The substance, resulting in near-fatal injuries. This was apparently the first case in medical literature of liquid nitrogen ingestion. In 2012, a young woman in England had her stomach removed after ingesting a cocktail made with liquid nitrogen. Liquid nitrogen is produced commercially from the cryogenic distillation of liquified air or from the liquefaction of pure nitrogen derived from air using pressure swing adsorption . An air compressor

SECTION 50

#1732851933338

2808-606: The surface. The new phenomenon of a 'reactive Leidenfrost (RL) effect' was characterized by a dimensionless quantity, (φ RL = τ conv /τ rxn ), which relates the time constant of solid particle heat transfer to the time constant of particle reaction, with the reactive Leidenfrost effect occurring for 10 < φ RL < 10 . The reactive Leidenfrost effect with cellulose will occur in numerous high temperature applications with carbohydrate polymers, including biomass conversion to biofuels , preparation and cooking of food, and tobacco use. The Leidenfrost effect has also been used as

2862-892: The vapor film becomes more significant and the heat flux increases with increasing excess temperature. The minimum heat flux for a large horizontal plate can be derived from Zuber's equation, q A m i n = C h f g ρ v [ σ g ( ρ L − ρ v ) ( ρ L + ρ v ) 2 ] 1 ╱ 4 {\displaystyle {{\frac {q}{A}}_{min}}=C{{h}_{fg}}{{\rho }_{v}}{{\left[{\frac {\sigma g\left({{\rho }_{L}}-{{\rho }_{v}}\right)}{{\left({{\rho }_{L}}+{{\rho }_{v}}\right)}^{2}}}\right]}^{{}^{1}\!\!\diagup \!\!{}_{4}\;}}} where

2916-405: The water droplets had been sprinkled onto a cooler pan. The effect can be seen as drops of water are sprinkled onto a pan at various times as it heats up. Initially, as the temperature of the pan is just below 100 °C (212 °F), the water flattens out and slowly evaporates, or if the temperature of the pan is well below 100 °C (212 °F), the water stays liquid. As the temperature of

#337662