Evaporation
Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. The surrounding gas must not be saturated with the evaporating substance; when the molecules of the liquid collide, they transfer energy to each other based on how they collide with each other. When a molecule near the surface absorbs enough energy to overcome the vapor pressure, it will escape and enter the surrounding air as a gas; when evaporation occurs, the energy removed from the vaporized liquid will reduce the temperature of the liquid, resulting in evaporative cooling. On average, only a fraction of the molecules in a liquid have enough heat energy to escape from the liquid; the evaporation will continue until an equilibrium is reached when the evaporation of the liquid is equal to its condensation. In an enclosed environment, a liquid will evaporate. Evaporation is an essential part of the water cycle; the sun drives evaporation of water from oceans, moisture in the soil, other sources of water.
In hydrology and transpiration are collectively termed evapotranspiration. Evaporation of water occurs when the surface of the liquid is exposed, allowing molecules to escape and form water vapor. With sufficient energy, the liquid will turn into vapor. For molecules of a liquid to evaporate, they must be located near the surface, they have to be moving in the proper direction, have sufficient kinetic energy to overcome liquid-phase intermolecular forces; when only a small proportion of the molecules meet these criteria, the rate of evaporation is low. Since the kinetic energy of a molecule is proportional to its temperature, evaporation proceeds more at higher temperatures; as the faster-moving molecules escape, the remaining molecules have lower average kinetic energy, the temperature of the liquid decreases. This phenomenon is called evaporative cooling; this is. Evaporation tends to proceed more with higher flow rates between the gaseous and liquid phase and in liquids with higher vapor pressure.
For example, laundry on a clothes line will dry more on a windy day than on a still day. Three key parts to evaporation are heat, atmospheric pressure, air movement. On a molecular level, there is no strict boundary between the vapor state. Instead, there is a Knudsen layer; because this layer is only a few molecules thick, at a macroscopic scale a clear phase transition interface cannot be seen. Liquids that do not evaporate visibly at a given temperature in a given gas have molecules that do not tend to transfer energy to each other in a pattern sufficient to give a molecule the heat energy necessary to turn into vapor. However, these liquids are evaporating, it is just that the process is much slower and thus less visible. If evaporation takes place in an enclosed area, the escaping molecules accumulate as a vapor above the liquid. Many of the molecules return to the liquid, with returning molecules becoming more frequent as the density and pressure of the vapor increases; when the process of escape and return reaches an equilibrium, the vapor is said to be "saturated", no further change in either vapor pressure and density or liquid temperature will occur.
For a system consisting of vapor and liquid of a pure substance, this equilibrium state is directly related to the vapor pressure of the substance, as given by the Clausius–Clapeyron relation: ln = − Δ H v a p R where P1, P2 are the vapor pressures at temperatures T1, T2 ΔHvap is the enthalpy of vaporization, R is the universal gas constant. The rate of evaporation in an open system is related to the vapor pressure found in a closed system. If a liquid is heated, when the vapor pressure reaches the ambient pressure the liquid will boil; the ability for a molecule of a liquid to evaporate is based on the amount of kinetic energy an individual particle may possess. At lower temperatures, individual molecules of a liquid can evaporate if they have more than the minimum amount of kinetic energy required for vaporization. Note: Air used here is a common example. Concentration of the substance evaporating in the air If the air has a high concentration of the substance evaporating the given substance will evaporate more slowly.
Concentration of other substances in the air If the air is saturated with other substances, it can have a lower capacity for the substance evaporating. Flow rate of air This is in part related to the concentration points above. If "fresh" air is moving over the substance all the time the concentration of the substance in the air is less to go up with time, thus encouraging faster evaporation; this is the result of the boundary layer at the evaporation surface decreasing with flow velocity, decreasing the diffusion distance in the stagnant layer. The amount of minerals
Inversion (meteorology)
In meteorology, an inversion known as a temperature inversion, is a deviation from the normal change of an atmospheric property with altitude. It always refers to an inversion of the thermal lapse rate. Air temperature decreases with an increase in altitude. During an inversion, warmer air is held above cooler air. An inversion traps air pollution, such as smog, close to the ground. An inversion can suppress convection by acting as a "cap". If this cap is broken for any of several reasons, convection of any moisture present can erupt into violent thunderstorms. Temperature inversion can notoriously result in freezing rain in cold climates. Within the lower atmosphere the air near the surface of the Earth is warmer than the air above it because the atmosphere is heated from below as solar radiation warms the Earth's surface, which in turn warms the layer of the atmosphere directly above it, e.g. by thermals. Given the right conditions, the normal vertical temperature gradient is inverted such that the air is colder near the surface of the Earth.
This can occur when, for example, a warmer, less-dense air mass moves over a cooler, denser air mass. This type of inversion occurs in the vicinity of warm fronts, in areas of oceanic upwelling such as along the California coast in the United States. With sufficient humidity in the cooler layer, fog is present below the inversion cap. An inversion is produced whenever radiation from the surface of the earth exceeds the amount of radiation received from the sun, which occurs at night, or during the winter when the angle of the sun is low in the sky; this effect is confined to land regions as the ocean retains heat far longer. In the polar regions during winter, inversions are nearly always present over land. A warmer air mass moving over a cooler one can "shut off" any convection which may be present in the cooler air mass; this is known as a capping inversion. However, if this cap is broken, either by extreme convection overcoming the cap, or by the lifting effect of a front or a mountain range, the sudden release of bottled-up convective energy – like the bursting of a balloon – can result in severe thunderstorms.
Such capping inversions precede the development of tornadoes in the Midwestern United States. In this instance, the "cooler" layer is quite warm, but is still denser and cooler than the lower part of the inversion layer capping it. An inversion can develop aloft as a result of air sinking over a wide area and being warmed by adiabatic compression associated with subtropical high-pressure areas. A stable marine layer may develop over the ocean as a result; as this layer moves over progressively warmer waters, turbulence within the marine layer can lift the inversion layer to higher altitudes, even pierce it, producing thunderstorms, under the right circumstances, tropical cyclones. The accumulated smog and dust under the inversion taints the sky reddish seen on sunny days. Temperature inversion stops atmospheric convection from happening in the affected area and can lead to the air becoming stiller and murky from the collection of dust and pollutants that are no longer able to be lifted from the surface.
This can become a problem in cities. Inversion effects occur in big cities such as: but in smaller cities such as: These cities are surrounded by hills and mountains, or on plains which are surrounded by mountain chains, which makes an inversion trap the air in the city. During a severe inversion, trapped air pollutants form a brownish haze that can cause respiratory problems; the Great Smog of 1952 in London, England, is one of the most serious examples of such an inversion. It was blamed for an estimated 11,000 to 12,000 deaths. Sometimes the inversion layer is at a high enough altitude that cumulus clouds can condense but can only spread out under the inversion layer; this prevents new thermals from forming. As the clouds disperse, sunny weather replaces cloudiness in a cycle that can occur more than once a day; as the temperature of air increases, the index of refraction of air decreases, a side effect of hotter air being less dense. This results in distant objects being shortened vertically, an effect, easy to see at sunset where the sun is visible as an oval.
In an inversion, the normal pattern is reversed, distant objects are instead stretched out or appear to be above the horizon, leading to the phenomenon known as a Fata Morgana or mirage. Inversions can magnify the so-called "green flash"—a phenomenon occurring at sunrise or sunset visible for a few seconds, in which the sun's green light is isolated due to dispersion; the shorter wavelength is refracted most, so it is the first or last light from the upper rim of the solar disc to be seen. High frequency radio waves can be refracted by inversions, making it possible to hear FM radio or watch VHF low-band television broadcasts from long distances on foggy nights; the signal, which would be refracted up and away from the ground-based antenna, is instead refracted down towards the earth by the temperature-inversion boundary layer. This phenomenon is called tropospheric ducting. Along coast lines during Autumn and Spring, due to multiple stations being present because of reduced propagation losses, many FM radio stations are plagued by severe signal degradation causing them to sound scrambled.
When an inversion layer is present, if a sound or explosion occurs at ground level
Oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table, a reactive nonmetal, an oxidizing agent that forms oxides with most elements as well as with other compounds. By mass, oxygen is the third-most abundant element in the universe, after helium. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. Diatomic oxygen gas constitutes 20.8% of the Earth's atmosphere. As compounds including oxides, the element makes up half of the Earth's crust. Dioxygen is used in cellular respiration and many major classes of organic molecules in living organisms contain oxygen, such as proteins, nucleic acids and fats, as do the major constituent inorganic compounds of animal shells and bone. Most of the mass of living organisms is oxygen as a component of water, the major constituent of lifeforms. Oxygen is continuously replenished in Earth's atmosphere by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide.
Oxygen is too chemically reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone absorbs ultraviolet UVB radiation and the high-altitude ozone layer helps protect the biosphere from ultraviolet radiation. However, ozone present at the surface is a byproduct of thus a pollutant. Oxygen was isolated by Michael Sendivogius before 1604, but it is believed that the element was discovered independently by Carl Wilhelm Scheele, in Uppsala, in 1773 or earlier, Joseph Priestley in Wiltshire, in 1774. Priority is given for Priestley because his work was published first. Priestley, called oxygen "dephlogisticated air", did not recognize it as a chemical element; the name oxygen was coined in 1777 by Antoine Lavoisier, who first recognized oxygen as a chemical element and characterized the role it plays in combustion. Common uses of oxygen include production of steel and textiles, brazing and cutting of steels and other metals, rocket propellant, oxygen therapy, life support systems in aircraft, submarines and diving.
One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle and surrounding the vessel's neck with water resulted in some water rising into the neck. Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries Leonardo da Vinci built on Philo's work by observing that a portion of air is consumed during combustion and respiration. In the late 17th century, Robert Boyle proved. English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. In one experiment, he found that placing either a mouse or a lit candle in a closed container over water caused the water to rise and replace one-fourteenth of the air's volume before extinguishing the subjects.
From this he surmised that nitroaereus is consumed in both combustion. Mayow observed that antimony increased in weight when heated, inferred that the nitroaereus must have combined with it, he thought that the lungs separate nitroaereus from air and pass it into the blood and that animal heat and muscle movement result from the reaction of nitroaereus with certain substances in the body. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract "De respiratione". Robert Hooke, Ole Borch, Mikhail Lomonosov, Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element; this may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, modified by the chemist Georg Ernst Stahl by 1731, phlogiston theory stated that all combustible materials were made of two parts.
One part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. Combustible materials that leave little residue, such as wood or coal, were thought to be made of phlogiston. Air did not play a role in phlogiston theory, nor were any initial quantitative experiments conducted to test the idea. Polish alchemist and physician Michael Sendivogius in his work De Lapide Philosophorum Tractatus duodecim e naturae fonte et manuali experientia depromti described a substance contained in air, referring to it as'cibus vitae', this substance is identical with oxygen. Sendivogius, during his experiments performed between 1598 and 1604, properly recognized that the substance is equivalent to the gaseous byproduct released by the thermal decomposition of potassium nitrate. In Bugaj’s view, the isolation of oxygen and the proper association of the substance to that part of air, required for life, lends sufficient weight to the discovery of oxygen by Sendivogius.
This discover
Isentropic process
In thermodynamics, an isentropic process is an idealized thermodynamic process, both adiabatic and reversible. The work transfers of the system are frictionless, there is no transfer of heat or matter; such an idealized process is useful in engineering as a model of and basis of comparison for real processes. The word "isentropic" is though not customarily, interpreted in another way, reading it as if its meaning were deducible from its etymology; this customarily used definition. In this occasional reading, it means a process. For example, this could occur in a system where the work done on the system includes friction internal to the system, heat is withdrawn from the system in just the right amount to compensate for the internal friction, so as to leave the entropy unchanged; the second law of thermodynamics states that T s u r r d S ≥ δ Q, where δ Q is the amount of energy the system gains by heating, T s u r r is the temperature of the surroundings, d S is the change in entropy. The equal sign refers to a reversible process, an imagined idealized theoretical limit, never occurring in physical reality, with equal temperatures of system and surroundings.
For an isentropic process, which by definition is reversible, there is no transfer of energy as heat because the process is adiabatic, δQ = 0. In an irreversible process of transfer of energy as work, entropy is produced within the system. For reversible processes, an isentropic transformation is carried out by thermally "insulating" the system from its surroundings. Temperature is the thermodynamic conjugate variable to entropy, thus the conjugate process would be an isothermal process, in which the system is thermally "connected" to a constant-temperature heat bath; the entropy of a given mass does not change during a process, internally reversible and adiabatic. A process during which the entropy remains constant is called an isentropic process, written Δ s = 0 or s 1 = s 2; some examples of theoretically isentropic thermodynamic devices are pumps, gas compressors, turbines and diffusers. Most steady-flow devices operate under adiabatic conditions, the ideal process for these devices is the isentropic process.
The parameter that describes how efficiently a device approximates a corresponding isentropic device is called isentropic or adiabatic efficiency. Isentropic efficiency of turbines: η t = actual turbine work isentropic turbine work = W a W s ≅ h 1 − h 2 a h 1 − h 2 s. Isentropic efficiency of compressors: η c = isentropic compressor work actual compressor work = W s W a ≅ h 2 s − h 1 h 2 a − h 1. Isentropic efficiency of nozzles: η n = actual KE at nozzle exit isentropic KE at nozzle exit = V 2 a 2 V 2 s 2 ≅ h 1 − h 2 a h 1 − h 2 s. For all the above equations: h 1 is the specific enthalpy at the entrance state, h 2 a is the specific enthalpy at the exit state for the actual process, h 2 s is the specific enthalpy at the exit state for the isentropic process. Note: The isentropic assumptions are only applicable with ideal cycles. Real cycles have inherent losses due to compressor and turbine inefficiencies and the second law of thermodynamics. Real systems are not isentropic, but isentropic behavior is an adequate approximation for many calculation purposes.
In fluid dynamics, an isentropic flow is a fluid flow, both adiabatic and reversible. That is, no he
Sphere
A sphere is a round geometrical object in three-dimensional space, the surface of a round ball. Like a circle in a two-dimensional space, a sphere is defined mathematically as the set of points that are all at the same distance r from a given point, but in a three-dimensional space; this distance r is the radius of the ball, made up from all points with a distance less than r from the given point, the center of the mathematical ball. These are referred to as the radius and center of the sphere, respectively; the longest straight line segment through the ball, connecting two points of the sphere, passes through the center and its length is thus twice the radius. While outside mathematics the terms "sphere" and "ball" are sometimes used interchangeably, in mathematics the above distinction is made between a sphere, a two-dimensional closed surface, embedded in a three-dimensional Euclidean space, a ball, a three-dimensional shape that includes the sphere and everything inside the sphere, or, more just the points inside, but not on the sphere.
The distinction between ball and sphere has not always been maintained and older mathematical references talk about a sphere as a solid. This is analogous to the situation in the plane, where the terms "circle" and "disk" can be confounded. In analytic geometry, a sphere with center and radius r is the locus of all points such that 2 + 2 + 2 = r 2. Let a, b, c, d, e be real numbers with a ≠ 0 and put x 0 = − b a, y 0 = − c a, z 0 = − d a, ρ = b 2 + c 2 + d 2 − a e a 2; the equation f = a + 2 + e = 0 has no real points as solutions if ρ < 0 and is called the equation of an imaginary sphere. If ρ = 0 the only solution of f = 0 is the point P 0 = and the equation is said to be the equation of a point sphere. In the case ρ > 0, f = 0 is an equation of a sphere whose center is P 0 and whose radius is ρ. If a in the above equation is zero f = 0 is the equation of a plane. Thus, a plane may be thought of as a sphere of infinite radius; the points on the sphere with radius r > 0 and center can be parameterized via x = x 0 + r sin θ cos φ y = y 0 + r sin θ sin φ z = z 0 + r cos θ The parameter θ {
Lapse rate
The lapse rate is the rate at which an atmospheric variable temperature in Earth's atmosphere, changes with altitude. Lapse rate arises in the sense of a gradual change, it corresponds to the vertical component of the spatial gradient of temperature. Although this concept is most applied to the Earth's troposphere, it can be extended to any gravitationally supported parcel of gas. A formal definition from the Glossary of Meteorology is: The decrease of an atmospheric variable with height, the variable being temperature unless otherwise specified. In general, a lapse rate is the negative of the rate of temperature change with altitude change, thus: Γ = − d T d z where Γ is the lapse rate given in units of temperature divided by units of altitude, T is temperature, z is altitude; the temperature profile of the atmosphere is a result of an interaction between radiation and convection. Sunlight heats it; the ground heats the air at the surface. If radiation were the only way to transfer heat from the ground to space, the greenhouse effect of gases in the atmosphere would keep the ground at 333 K, the temperature would decay exponentially with height.
However, when air is hot, it tends to expand. Thus, hot air tends to transfer heat upward; this is the process of convection. Convection comes to equilibrium when a parcel of air at a given altitude has the same density as the other air at the same elevation; when a parcel of air expands, it pushes on the air around it. Since the parcel does work but gains no heat, it loses internal energy so that its temperature decreases; the process of expanding and contracting without exchanging heat is an adiabatic process. The term adiabatic means that no heat transfer occurs out of the parcel. Air has low thermal conductivity, the bodies of air involved are large, so transfer of heat by conduction is negligibly small; the adiabatic process for air has a characteristic temperature-pressure curve, so the process determines the lapse rate. When the air contains little water, this lapse rate is known as the dry adiabatic lapse rate: the rate of temperature decrease is 9.8 °C/km. The reverse occurs for a sinking parcel of air.
Only the troposphere in the Earth's atmosphere undergoes convection: the stratosphere does not convect. However, some exceptionally energetic convection processes—notably volcanic eruption columns and overshooting tops associated with severe supercell thunderstorms—may locally and temporarily inject convection through the tropopause and into the stratosphere; these calculation use a simple model of an atmosphere, either dry or moist, within a still vertical column at equilibrium. Thermodynamics defines an adiabatic process as: P d V = − V d P γ the first law of thermodynamics can be written as m c v d T − V d P γ = 0 Also, since α = V / m and γ = c p / c v, we can show that: c p d T − α d P = 0 where c p is the specific heat at constant pressure and α is the specific volume. Assuming an atmosphere in hydrostatic equilibrium: d P = − ρ g d z where g is the standard gravity and ρ is the density. Combining these two equations to eliminate the pressure, one arrives at the result for the dry adiabatic lapse rate, Γ d = − d T d z = g c p = 9.8 ∘ C / km The presence of water within the atmosphere complicates the process of convection.
Water vapor contains latent heat of vaporization. As a parcel of air rises and cools, it becomes saturated. With further decrease in temperature the water vapor in excess of the equilibrium amount condenses, forming cloud, releasing heat. Before saturation, the rising air follows the dry adiabatic lapse rate. After saturation, the rising air follows the moist adiabatic lapse rate; the release of latent heat is an important source of energy in the development of thunderstorms. While the dry adiabatic lap
Work (thermodynamics)
In thermodynamics, work performed by a system is energy transferred by the system to its surroundings, due to macroscopic forces exerted by the system on its surroundings, where those forces, their external effects, can be measured. Such work is the only kind; the externally measured forces and external effects may be electromagnetic, gravitational, or pressure/volume or other macroscopically mechanical variables. Thermodynamic work is defined to be measurable from knowledge of such external macroscopic factors. For thermodynamic work, these external factors are matched by values of or contributions to changes in macroscopic internal state variables of the system, which always occur in conjugate pairs, for example pressure and volume or magnetic flux density and magnetization. In the SI system of measurement, work is measured in joules; the rate at which work is performed is power. In the surroundings of a thermodynamic system, external to it, all the various mechanical and non-mechanical macroscopic forms of work can be converted into each other with no limitation in principle due to the laws of thermodynamics, so that the energy conversion efficiency can approach 100% in some cases.
Work sometimes is said to be done on a system of interest by an external system that lies in the surroundings, not a thermodynamic system as defined by the usual thermodynamic state variables. The paddle stirring experiments of Joule provide an example, illustrating the concept of isochoric mechanical work; such work is not adiabatic, because it occurs through friction on the system of interest. Though the external system does macroscopic mechanical work, described by its own macroscopic mechanical variables, the thermodynamic work, as defined here, such as pressure–volume work, done by the system of interest, is zero; the external system generates friction on and in the system of interest. Another form of isochoric work is Joule heating, not adiabatic, because it occurs through friction as the electric current passes through the system of interest; because no thermodynamic work is done by the system of interest, no matter is transferred, such an energy transfer is regarded as a heat transfer into the system of interest.
A system of interest cannot raise a weight by such work. It is a consequence of the second law of thermodynamics that a thermodynamic system in its own state of internal thermodynamic equilibrium cannot do isochoric mechanical work on an external system. Thermodynamic work is a version of the concept of work in physics. Work, i.e. "weight lifted through a height", was defined in 1824 by Sadi Carnot in his famous paper Reflections on the Motive Power of Fire, where he used the term motive power for work. According to Carnot: We use here motive power to express the useful effect that a motor is capable of producing; this effect can always be likened to the elevation of a weight to a certain height. It has, as we know, as a measure, the product of the weight multiplied by the height to which it is raised. In 1845, the English physicist James Joule wrote a paper On the mechanical equivalent of heat for the British Association meeting in Cambridge. In this paper, he reported his best-known experiment, in which the mechanical power released through the action of a "weight falling through a height" was used to turn a paddle-wheel in an insulated barrel of water.
In this experiment, the friction and agitation of the paddle-wheel on the body of water caused heat to be generated which, in turn, increased the temperature of water. Both the temperature change ∆T of the water and the height of the fall ∆h of the weight mg were recorded. Using these values, Joule was able to determine the mechanical equivalent of heat. Joule estimated a mechanical equivalent of heat to be 819 ft•lbf/Btu; the modern day definitions of heat, work and energy all have connection to this experiment. In this arrangement of apparatus, it never happens that the process runs in reverse, with the water driving the paddles so as to raise the weight, not slightly; the doing of such isochoric mechanical work by the device, which lies external to the water, while the energy supplied by the fall of the weight becomes heat passing into the water, is irreversible. A pre-supposed guiding principle of thermodynamics is the conservation of energy; the total energy of a system is the sum of its internal energy, of its potential energy as a whole system in an external force field, such as gravity, of its kinetic energy as a whole system in motion.
Thermodynamics is concerned with transfers of energy. Transfer of energy by work has been given logical priority in thermodynamics since the end of the nineteenth century. Besides transfer of energy by work, thermodynamics admits transfer of energy as heat. For a process in a closed thermodynamic system, the first law of thermodynamics relates changes in the internal energy of the system to those two forms of energy transfer, by work, as heat. Adiabatic work is done without heat transfer. In principle, in thermodynamics, for a process in a closed system, quantity of heat transferred is defined by the amount of adiabatic work that would be needed to effect the change in the system, occasioned by the heat transfer. In experimental practice, heat transfer is estimated calorimetrically, through change of temperature of a known quantity of calorimetric material substance. In the surroundings
