In the figure, the direction of the temperature gradient is indicated by a number. Vertical temperature gradient
TEMPERATURE GRADIENT
TEMPERATURE GRADIENT
vertical or vertical thermal gradient (Vertical thermal gradient) - drop in air temperature for every 100 m in the vertical direction. In dry air the temperature gradient is about 1°, in air saturated with water vapor it is about 0.5°.
Samoilov K. I. Marine Dictionary. - M.-L.: State Naval Publishing House of the NKVMF of the USSR, 1941
See what "TEMPERATURE GRADIENT" is in other dictionaries:
temperature gradient- A vector directed normal to the isothermal surface in the direction of increasing temperature, numerically equal to the partial derivative of the temperature in this direction. [GOST 25314 82] Topics of non-destructive thermal control... Technical Translator's Guide
Vertical, a vector reflecting the change (difference) in temperature in the atmosphere with altitude (in degrees per 100 m). Ecological encyclopedic Dictionary. Chisinau: Main editorial office of the Moldavian Soviet Encyclopedia. I.I. Dedu. 1989 ... Ecological dictionary
Temperature gradient- 4. Temperature gradient A vector directed normal to the isothermal surface in the direction of increasing temperature, numerically equal to the partial derivative of the temperature in this direction Source: GOST 25314 82: Non-destructive testing... ... Dictionary-reference book of terms of normative and technical documentation
temperature gradient- temperatūros gradientas statusas T sritis fizika atitikmenys: engl. temperature gradient vok. Temperaturgradient, m rus. temperature gradient, m; temperature gradient, m pranc. gradient de temperature, m; gradient thermique, m … Fizikos terminų žodynas
temperature gradient- A vector directed normal to the isothermal surface in the direction of increasing temperature and numerically equal to the partial derivative of the temperature in this direction... Polytechnic terminological explanatory dictionary
Change in air temperature for every 100 m vertically in the troposphere. The temperature gradient value ranges from 0.6 to 1°C. EdwART. Smart Military maritime Dictionary, 2010 ... Marine Dictionary
Soil temperature gradient- positive or negative temperature difference at two points, per unit distance between them. Gradients measured in the vertical direction usually reach the greatest values. If there are uneven surfaces... ... Explanatory dictionary of soil science
The rate of temperature decrease with increasing altitude. In some environments (in the stratosphere), the temperature rises as it rises, and then a reverse, or inversion, vertical gradient is formed, which is assigned a minus sign. Ecological... ... Ecological dictionary
vertical temperature gradient- A value characterizing the decrease in air temperature with increasing altitude, on average equal to 0.6 ° C per 100 m of altitude. Syn.: temperature gradient… Dictionary of Geography
adiabatic temperature gradient- The rate of change of temperature in a mass of air during its adiabatic movement vertically as a reaction to the expansion or compression of this air mass... Dictionary of Geography
Books
- Dynamics of the Earth's lithosphere, B. I. Birger. Large-scale thermal convection in the Earth's mantle forms an upper cold boundary layer in each convective cell, which moves as a whole along the Earth's surface and almost ...
The temperature gradient of the atmosphere can vary widely. On average, it is 0.6°/100 m. But in a tropical desert near the surface of the earth it can reach 20°/100 m. With temperature inversion, the temperature increases with height and the temperature gradient becomes negative, i.e. it can be equal to, for example , -0.6°/100 m. If the air temperature is the same at all altitudes, then the temperature gradient is zero. In this case, the atmosphere is said to be isothermal.[...]
When the ambient air temperature gradient is approximately equal to the dry adiabatic vertical gradient (Fig. 3.8, b), the stability of the atmosphere is called indifferent. Any volume of air that moves rapidly up or down for any reason will have the same temperature as the surrounding air at the new altitude. Consequently, there is no incentive for any further vertical movement due to temperature differences, and the volume of air in question will remain in the same place. If the temperature gradient of the surrounding air is less than the dry adiabatic vertical gradient, then the atmosphere is called adiabatic. Using arguments similar to the superadiabatic case, it can be shown that the subadiabatic atmosphere is stable. This means that any small volume of air unexpectedly displaced in a vertical direction will tend to return to its original position. For example, the volume of air moved from position L to B in Fig. 3.8,6, will have a higher density than the surrounding air at point B. Consequently, it tends to return to its original height.[...]
VERTICAL TEMPERATURE GRADIENT. See vertical temperature gradient.[...]
Normal, or standard, temperature gradient based on international agreement, thus equal to 0.66 °C/100 m, or 3.6 T/100 ft. The temperature profile for the standard atmosphere in comparison with the dry adiabatic temperature profile is shown in Fig. 3.7.[...]
Enrichment within this temperature gradient along the length of the substance flow inside the enrichment device would seem to be the best solution to the problem, since the compounds to be enriched can accumulate on the stationary phase, which is the best enriched phase, and will not cause difficulties in terms of subsequent separation conditions. On the other hand, enriched compounds can accumulate in separate areas within a given temperature gradient, and each compound will occupy the thermodynamically most favorable location, i.e. a focusing effect occurs, making enrichment even more effective.[...]
A typical daily cycle of changes in the temperature gradient over an open area on a cloudless day begins with the formation of an unstable rate of temperature drop, intensifying during the day due to the intense thermal radiation of the sun, which leads to the emergence strong turbulence. Just before or shortly after sunset, the surface layer of air quickly cools and a steady rate of temperature drop occurs (temperature increases with height). During the night, the intensity and depth of this inversion increase, reaching a maximum between midnight and the time of day when the earth's surface has minimum temperature. During this period, atmospheric pollution is effectively trapped within or below the inversion layer due to little or no vertical dispersion of pollution. It should be noted, that, in conditions stagnation, pollutants discharged near the surface of the earth do not spread into the upper layers of the air and, conversely, emissions from tall chimneys under these conditions generally do not penetrate into the layers of air closest to the ground (Church, 1949). As the day progresses, the earth begins to warm up and the inversion gradually disappears. This can lead to “fumigation” (Hewso n a. Gill, 1944) due to the fact that contaminants that enter the upper layers of air during the night begin to quickly mix and rush down. Therefore, high concentrations often occur in the early afternoon hours prior to the full development of turbulence that ends the daily cycle and provides powerful mixing. atmospheric pollution. This cycle can be disrupted or altered by the presence of clouds or precipitation, which prevent strong convection during the daytime hours, but can also prevent the occurrence of strong inversions at night.[...]
A fan-shaped jet (Fig. 3.2, c, d) is formed during temperature inversion or at a temperature gradient close to isothermal, which characterizes very weak vertical mixing. The formation of a fan-shaped jet is favored by weak winds, clear skies and snow cover. This jet is most often observed at night.[...]
Thus, if the theory of electrification due to the temperature gradient is able to quantitatively explain the results of experiments with cloud-sized droplets, then it cannot explain the results of experiments with the explosion of large droplets. Therefore, it is necessary to give preference to the theories of Kachurin and Bekryaev, Imyanitov and others, based on the idea of charge separation during phase transitions of water.[...]
Formula (136) allows us to determine how many times the temperature gradient against the top of the ellipse (i.e., the gradient along the X axis) exceeds the smallest gradient (along the Y axis) near the coast.[...]
The temperature gradient of the oceans can also be used to generate electricity, which is indirect method energy conversion solar radiation. Absorption of thermal radiation from the sun by water occurs predominantly in the surface layer, the temperature of which is higher than the underlying layers. At relatively shallow depths, the temperature drops to about 4°C. In this case, it is possible to use a temperature gradient to generate electricity in a closed thermodynamic cycle, in which the working fluid is a liquid with a low boiling point, for example, ammonia, propane, ethane, etc. Small temperature difference between the “hot” (top layer) and the “cold” (lower layer) of sources determines the low efficiency of the cycle, amounting to only 3-4% when the working fluid is heated by 10-12°C. But the lack of fuel costs, even with high specific capital investments in ocean solar thermal power plants (OSTES), forces scientists and engineers to pay attention to this method of generating electricity. The working fluid in the steam generator is heated and turns into a vapor state by the heat of water from the surface layer of the ocean. The steam thus obtained does work in the turbine and after the turbine is condensed in a condenser cooled by cold deep water.[ ...]
With small pipe diameters and the absence of a significant temperature gradient across the pipe cross-section, the concentration of solid particles in the boundary sublayer will be close to their concentration in the volume. This allows us to assume that the amount of deposits will be directly proportional to the concentration of dispersed particles in a given section. With an increase in the cooling intensity through the wall, this proportionality may be violated towards an increase in the amount of deposits as a result of an increase in the temperature gradient near the pipe wall. It was shown that the temperature difference at the wall-liquid interface in wells does not exceed 0.5 °C.[...]
The most interesting is the upper layer, already in the stratosphere. The temperature gradient there turned out to be negative all year round] all year round the stratosphere above the ocean is colder than the stratosphere above the mainland (at the heights studied - up to 20 km above sea level).[...]
In the surface layer of the atmosphere above the underlying surface heated during the daytime, the values of temperature gradients (in terms of 100 m) can be many times greater than those obtained in (1.46), which gives impetus for the development of upward movements.[ ...]
If in a massif the pollutant is contained in a pore solution or in a vapor-gas phase, then in the presence of a temperature gradient in different parts array, it will move along with the thermoosmotic flow of liquid or gas from an area with a higher temperature to an area with a lower temperature. With thermoosmosis in soils that are not completely saturated with water, the movement of water or a pollutant in the pores can occur in both the liquid and gas phases. [...]
When pollutants are released through high pipes (A = 100-120 m), maximum concentrations will occur at a normal temperature gradient at a distance of 2-3 km from the release sites, and with inversion gradients even further (i.e., in most cases, beyond the rupture zones ). But this does not mean that at high emissions the role of mandatory (according to sanitary standards) rupture zones is reduced. In all cases, it should be borne in mind that the rupture zone is primarily the territory where dispersal of unorganized inflows of gases and dust occurs.[...]
It is impossible to quantitatively determine the specific contribution of each of the probable reactions under conditions of constantly changing concentration and temperature gradients. Any instantaneous value of temperature and concentrations of compounds coexisting in the gas phase corresponds to a state of instantaneous dynamic equilibrium specified by a combination of these parameters.[...]
The thermal conductivity of soil is understood as the ability to absorb and conduct heat from layer to layer in the direction opposite to the thermal gradient, i.e. from hot to cold. The amount of thermal energy transferred through the soil layer is proportional to the temperature gradient and thermal conductivity coefficient. The thermal conductivity coefficient (K) is equal to the amount of heat in J transmitted per second through soil with a cross section of 1 cm2 (10 4 m2) with a layer thickness of 1 cm (10 2 m) and a temperature gradient at the ends of the layer of 1 ° C. The dimension of the coefficient % in the SI system is J/(m s °C). The magnitude of the thermal conductivity of the soil depends on the thermal conductivity of its main components (solid and liquid phase).[...]
Since air temperatures decrease with height, heating of the underlying surface usually causes large temperature gradients in the surface layer of air at high altitudes, although the soil-air temperature difference depends on weather conditions. Aulicki processed detailed measurement data at the forest edge (2072 m) near Obergurgl (Austria) and showed that there is a linear relationship between the average and extreme values of soil and air temperature when the soil is not frozen (Fig. 2.26). IN transitional seasons soil temperature is lower than air temperature due to radiation cooling of the surface in autumn and delayed snow removal in spring. In the Alps, the soil tends to have its coldest temperatures in the fall when frozen, while winter snow cover protects the soil from freezing.[...]
However, these climate models also have a number of serious shortcomings. The vertical structure of the models is based on the assumption that the vertical temperature gradient is equal to the equilibrium one. Their simplicity does not allow us to correctly describe very important atmospheric processes, in particular the formation of clouds and convective energy transfer, which by their nature are three-dimensional fields. Therefore, these models do not take into account the reverse impact of changes in the climate system caused by changes, for example, in cloud cover, on the characteristics of the latter, and the modeling results can only be considered as initial trends in the evolution of the real climate system with changes in the properties of the atmosphere and underlying surface.[... ]
Strong offshore winds at Cape Dennison come and go, usually suddenly, and Ball explains this as a stationary jump phenomenon. The strong temperature gradient between Cape Dennison on the coast and Charcot Station (69° S, 2400 m a.s.l.) enhances the main gravitational flow of cold air from the Polar Plateau. At 2400 m the difference between the average annual temperatures at these two stations is 17 °C, this difference leads (assuming that this temperature gradient is isobaric) to a density difference of about 7%. The thermal wind component associated with the surface temperature inversion is also likely to be of some importance, since winds typically span a layer of several hundred meters. The jump is usually observed over the sea near the coast, but if it moves inland, then the regime of strong winds (gusty flow) upstream of the jump is replaced by almost calm conditions in a layer of cold air that increases in thickness (cf. Fig. 3.7 6). Ball showed that typical conditions in this region correspond to the presence of a jump, since the Froude number is significantly greater than one. Near Davis Station (68°S, 78°E), standing jumps are usually noted as a wall of drifting snow 30-100 m high. Between May 30 and November 14, 1961, 31 such jumps were observed or heard (by the roar of the wind) at Davis Station. Lead notes that they usually appear a few hours after the development of the katabatic regime.[...]
The change in temperature of a certain volume of dry air moving vertically is constant and equal to 1°/100 m. Meteorologists call this value the adiabatic temperature gradient of dry air. The adjective “adiabatic” means that there is no heat exchange between a given volume of air and the environment, and “dry” means that the process occurs without condensation or vaporization. If condensation or vaporization occurs in a moving volume of air, then the corresponding temperature gradient is called an adiabatic temperature gradient for humid air. This value is less than 1°/100 m, and it varies depending on temperature and altitude. However, in most studies on air pollution we can limit ourselves to the case of dry air.[...]
The ability of an air mass to diffuse strongly depends on the vertical temperature distribution. The change in temperature in the atmosphere for every 100 m of altitude is called a temperature gradient. At a constant temperature at all altitudes, the vertical temperature gradient is called isothermal.[...]
Field observations also show that the flow entering the pond warm water applies mainly to relatively few greater depth, while having an insignificant vertical temperature gradient; Below this layer, the water temperature drops sharply. By installing special deep water intakes in the pond, the flow of warm water spreads to a greater depth and, thus, more is taken from the pond. cold water.[ ...]
This phenomenon plays a significant role in the capture of particles from hot gases when they pass through cold nozzles. In narrow channels with a temperature difference of 50 °C, a temperature gradient of 1000 K/cm can be obtained. Calculations show that this should lead to the deposition of 98.8% of particles with a size of 0.1 μm in a packing layer 230 mm deep at 500 °C. [...]
In Fig. U-10 presents two hypothetical cases that can be analyzed. The earth's crust 30 km thick was studied, consisting of granite to a depth of 10 km, and basalt (the remaining 20 km); the heat flux through the surface was 5.02 J/(cm2-s). Curve A - dependence of the temperature gradient on depth for the case when the entire heat flow arises from a source located under earth's crust, and curve B is for the case when three quarters heat flow originates within the cortex; these cases appear to be extreme.[...]
Ocean energy is environmentally friendly. It can be used in tidal power plants (TPP), wave power plants (WWPP) and power plants sea currents(ESMT), where the mechanical form of ocean energy is converted into electrical energy. There are installations that use the presence of a temperature gradient between the upper and lower layers The world's oceans - the so-called hydrothermal power plants (HPP). We have already covered this before.[...]
IN northern regions In the basin, the thickness of permafrost reaches several hundred meters. Fresh waters they are turned into ice, and interpermafrost brines are supercooled (“cryopegs”). Low temperature in this zone and below it contributes to the transition of hydrocarbon gases to the gas hydrate state.[...]
In sections of the river with a strong current, Cladophora glome rat and Kutz. predominates; in the coastal areas and backwaters, zygnema and edogonia algae dominate, in some places with standing water only ulothrix are noted. Spirogyra species are the most resistant to temperature gradients, displacing Oedogonium and Mougeotia in colder areas. The largest proportion of conjugating zygnema filaments was noted in some coastal areas (up to 100%), puddles and shallow pools. Conjugating threads occur up to a depth of 20 cm, which is associated with the light regime. Species of the genus Spirogyra are most often conjugated, and Mougeotia is less common. Observations were carried out for a month - during this time, no significant changes in the algal flora were observed, it is noted sharp increase shares of conjugating filaments of zygnema.[...]
Based on the results of numerical modeling of a five-stage extraction of arenes from a model mixture - TDF 270-360 °C with watered 1,4-dioxane using the studied technological methods, the mode for obtaining a raffinate containing 12.4% arenes was determined: extractant/raw material ratio = 4:1 vol. , water content in the extractant = 8.0% vol., extraction temperature gradient = 10 aC, temperature in the extractor cube = 40 °C; share of raffinate recycle to raw materials = 0.5 wt. With these process parameters, the raffinate yield is 69.4% of the feedstock, the loss of paraffin-naphthenic components with the extract is 11.9%.[...]
The most important element climate mountainous areas, undoubtedly, is temperature. In the majority mountain areas there are detailed temperature observations around the world and there are many statistical research temperature changes with altitude. This change represents complex problem when compiling climate atlases due to sharp temperature gradients over short distances and their seasonal variability. Some recent studies of temperatures in mountains, such as in and , have used regression analysis to relate temperatures to altitude and to separate the effects of inversions from those due to slope steepness. Pielke and Mehring, trying to clarify spatial distribution temperatures for one area in northwestern Virginia, used linear regression analysis of average monthly temperatures as a function of elevation. They showed that the correlations are maximum (r=-0.95) in the summer, as is usually the case at mid-altitudes. In winter, inversions on low levels will introduce a lot of variability, and by choosing appropriate polynomial functions or using potential temperatures, better estimates can be obtained. For the purpose of producing topoclimatic maps for the Western Carpathians, a series of regression equations were similarly developed. For this, as described in paragraph 2B4, separate regression equations are used for different slope profiles. Note that there are few attempts to describe changes in mountain temperature) at. using some more general statistical model.[...]
Direct and indirect losses to the natural environment are associated with (and therefore can be expressed by) state asymmetry artificial object. In the case of a gradual, non-jump-like development of losses, there is a general asymmetry that characterizes natural trends in changes in the state of the object (design position, stress-strain potential, temperature gradient, etc.) at any time interval.[...]
Thus, all of the above allows us to assume that the initial accumulation of the solid phase on the sediment surface occurs in the general case due to the fixation of the most dispersed part of the solid phase from the volume of oil, while the formation of crystals directly on the surface is of a subordinate nature and can only be observed as a special case in the presence sharp temperature gradient on the pipe wall.[...]
Depending on the conditions, two types of evaporation are distinguished - static and dynamic. The evaporation of fuel from a surface stationary relative to the environment is called static. If a liquid and a gaseous medium move relative to each other, evaporation is called dynamic. During evaporation, convective flows are always formed due to the difference in molecular masses and the temperature gradient in the boundary layer near the evaporation surface. [...]
Some semblance of systematic deviations is outlined on the curve calculated for a horizon of 0.25 m. But it is easy to see that if we had specified not the thermal conductivity coefficient 5 10 3, which we assumed to be constant throughout the entire thickness of the ice, but the coefficient 1.7-10 3, which was found by Malmgren in a long - indirect - way for the surface layer, then the deviations would be disproportionately large: the temperature gradient in the upper layers would be much greater (3 times), and therefore the amplitude of the calculated curve would be even much smaller.[...]
Revelle concluded that the North Atlantic is the most northwestern part Pacific Ocean- and the Weddell Sea - are the main areas in which the release of deep ocean waters and the release of CO2 into the atmosphere will occur. He quantitatively characterized climate change under the influence of increasing CO2 concentrations. Since this effect will occur mainly in cold areas, the temperature gradient between high and high temperatures will decrease. low latitudes. This conclusion is discussed in more detail in the article by Manabe and Weatherald.[...]
As already mentioned, the necessary meteorological data for the area of interest to us is not always available, or they can only be used for a separate point in this area. Thus, it is required at least qualitative determination of spatial vibrations of the corresponding meteorological factors. It is often possible to determine the degree of deviation of the wind flow (in direction and speed) and changes in the temperature gradient during the transition to another territory and, thus, apply the available data to characterize another area of interest to us. More difficult is the question of the relationship between the duration of meteorological measurements and the duration of sampling to determine the concentration of atmospheric pollution. The various working formulas for calculating diffusion measurements usually rely on short-term sampling to determine the concentration of contaminants in the air. As the duration of this period increases to hours, days or even months, the diffusion coefficients no longer correspond to reality, which requires appropriate corrections (Smith, 1955). On the other hand, for these long periods simple average figures for wind and stability may be sufficient, if only fluctuations in wind directions and daily changes in the studied parameters are taken into account.[...]
The turbulent diffusion coefficient Ktf varies widely depending on stability conditions. Largest values it has in an unstable atmosphere, and the formation of inversions that prevent the development of turbulent flows leads to its decrease. The influence of thermal conditions on turbulent transport can be traced by the Küf value in the troposphere and stratosphere: if in the entire thickness of the troposphere with a negative temperature gradient (-6.5 K/km) it is approximately 105 cm2/s, then in the middle layers of the stratosphere with a positive gradient it decreases by 20 times.[...]
Moving on to the microwave range of radio emissions, it should be noted that among the bioeffects in this case, the thermal effect of microwaves, associated with an increase in the temperature of the irradiated tissue, is well known. Due to the thermal effect, decimeter and centimeter waves of medium and high intensity are widely used in physiotherapy for the treatment of many diseases, including cancer and cardiovascular diseases. The idea of treatment is to create temperature gradients in various organs of the body, changing the functioning conditions of the affected organ.[...]
The value of the period T of the natural oscillations of the system, found by Osmolovskaya, allows us to estimate the order of magnitude of m], which appeared in the theoretical formula (236). Let us substitute into it a fairly plausible value 0 = 3-4°, as well as the values p = 2.5 108 cm (as indicated above), P = 1.6 103 and T = 8 days (of course, breaking them down into seconds). Then it turns out that approximately r x 0.1, i.e., approximately only 1/10 of the amount of heat additionally brought air currents, goes to change the temperature gradient in the monsoon layer and the associated change in pressures and velocities in the oscillatory system. Of course, for now this value r should be considered only approximate, indicating only the order of the “utilization coefficient” of energy brought by flows in the field of thermobaric seiches: any accurate solution will be possible only after finding the integral of the complete equation (223), taking into account the effect of the Coriolis force on basis (227).[...]
Now the concentration or flow rate of the trace component can be increased significantly, from 10 to several hundred times, provided that the size of the system and its operating conditions can be optimized. The required dimensions for trace analysis are the minimum possible dimensions; As for connections in terms of separation and consumption of the mobile phase, it is necessary to achieve the best conditions for enrichment rather than optimization of separation conditions. Elution within an optimized temperature gradient results in focused sites for substances and prevents dilution by diffusion.[...]
Next, the effect of water content in the extractant was studied at extractant/raw material ratios from 3:1 to 4:1 vol. on the results of a five-stage extraction of arenes from the TDF feedstock model 270-360 °C of West Siberian oil. It has been established that the production of raffinate with a total arenes content of 10% is ensured at a ratio of extrageate/raw material = 4:1 vol. and the water content in the extractant is 8.0% vol. In this case, the yield of raffinate is % of the original raw material, the loss of papafinonaphthenic components by the extract is 19.6%. It is possible to increase the yield of raffinate while maintaining AO quality and reduce the loss of target components with the extract by using special technological methods: creating a temperature gradient of extraction (the difference in the temperatures of the top and bottom of the extractor), recirculating part of the extract or raffinate. A study of the influence of a temperature gradient on the extraction results showed that in order to create internal recycling in the extractor, it is necessary to maintain the extraction temperature gradient at a level not exceeding 10 ° C, since its increase, although it leads to a decrease in the content of arenes in the raffinate, simultaneously reduces the yield of the raffinate.[ ...]
The duration of the oxidation process into bitumen is one of the production bottlenecks. The following are proposed as catalysts for the oxidation of tar into bitumen: a spent catalyst for the polymerization of olefin-containing petroleum gases- phosphorus on kieselguhr, orthophosphoric acid. The oxidation process of tars can be intensified: by changing the dissolving power of the dispersed medium; by changing the depth of selection of distillate fractions during the preparation of raw materials; thermal compaction of raw materials; recycling of products in the reaction device; adding effective complexing agents to raw materials; temperature regulation. In addition, intensification of the process can be carried out by creating local temperature gradients in the reaction volume due to the supply of cooled or superheated product streams, the placement of cooled (or heated to higher temperatures) surfaces in the reactor, or the presence of adsorption surfaces (metals or metal oxides) in the reactor.[ ...]
Yoshino identified four synoptic types of pressure distribution that cause bora. In winter it is mostly associated with a cyclone over Mediterranean Sea or an anticyclone over Europe. In summer, cyclonic systems occur less frequently and the anticyclone may be located further to the west. In any system, the gradient wind should be from the east to the northeast. For the development and preservation of bora, a suitable pressure gradient, stagnation of cold air east of the mountains and its flow through the mountains, converting potential energy into kinetic energy, are simultaneously required. Bora develops best where the Dinaric Mountains are narrow and close to the coast, such as in Split. This increases the temperature gradient between the coastal and internal parts country and enhances the downwind effect. The Dinaric Mountains have an altitude of over 1000 m, and low passes, such as that of Xin, also favor local intensification of bora. On days when there is bora, the inversion layer is usually located between 1500-2000 m on the windward side of the mountains and at the same or lower level on the leeward side.[...]
The dispersion of atmospheric pollutants is associated, generally speaking, with two main characteristics of atmospheric circulation: average speed wind and atmospheric turbulence. Atmospheric turbulence has not yet been sufficiently studied. Turbulence in the atmosphere usually includes wind fluctuations that have a frequency of more than 2 cycles/hour. More important fluctuations have frequencies from 1 to 0.01 cycles/s. Atmospheric turbulence is the result of two processes: a) heating of the atmosphere, which results in the formation of natural convective currents (dp/dz), and b) “mechanical” turbulence, which is the result of wind shear du/dz). Although both effects typically occur under any given atmospheric conditions, mechanical or thermal (convective) turbulence typically predominates. Thermal vortices occur more often in sunny days when the wind speed is low and the temperature gradient is significantly negative. The period of such cyclic fluctuations will be on the order of minutes. On the other hand, mechanical vortices predominate during periods of indifferent stability on windy nights, and wind fluctuations in this case are on the order of seconds. Mechanical turbulence is formed as a result of air movement over earth's surface, and is influenced by the placement of buildings and the relative roughness of the terrain.
Temperature gradient
Parameter name | Meaning |
Article topic: | Temperature gradient |
Rubric (thematic category) | Mathematics |
Temperature field
BASIC LAW OF THERMAL CONDUCTIVITY
1. Name elementary methods heat transfer.
2. What is the heat transfer process?
4. What is convective heat transfer?
5. How to determine the amount of heat during heat transfer using Newton’s formula?
6. Describe the process of conduction (heat conduction).
7. What factors influence the intensity of heat transfer processes?
At different temperatures in different parts of the body, a spontaneous process of heat transfer occurs from areas with a higher temperature to areas with a lower temperature. The occurrence of the process is caused by a property commonly called thermal conductivity. Energy transfer occurs due to energetic interactions between molecules, atoms, and electrons. The process of thermal conductivity is associated with the temperature distribution inside the body and in this regard it is extremely important to establish the concepts of temperature field and temperature gradient.
Temperature characterizes the thermal state of the body, determining the degree of its heating. And if the process of thermal conductivity occurs in a body, then the temperature of its different parts is different. The set of temperature values for all points of the body in this moment time is usually called the temperature field. The temperature field equation has the form:
t = f(x,y,z,t), (12.1)
where t is the body temperature at a point;
x, y, z - point coordinates;
If the temperature changes over time, such a temperature field is usually called non-stationary; it corresponds to an unsteady, non-stationary heat conduction process, and if the temperature does not change over time, the temperature field is stationary and the heat conduction process is stationary (steady).
Temperature must be a function of one, two or three coordinates. Accordingly, the temperature field is usually called one-, two-, or three-dimensional. A one-dimensional field has the simplest form of the equation t = f(x). For example, during a stationary process of heat conduction through a flat wall.
For any temperature field, there are points in the body with same temperature. The geometric location of points with the same temperature forms an isothermal surface. At one point in space there should not be two different temperatures, and therefore the isothermal surfaces do not touch or intersect. They either end at the boundaries of the body, or form a closed contour (as, for example, in a cylindrical body). Temperature changes in the body are observed only in directions intersecting isothermal surfaces. In this case, the most dramatic change in temperature is observed in the direction normal to the isothermal surfaces. Limit of temperature change ratio (Dt) to minimum distance between these isotherms (Dn), provided that this distance tends to zero, is usually called the temperature gradient.
The main tasks of heat transfer theory include establishing an analytical connection between heat flow and temperature distribution in media. The set of instantaneous values of any quantity at all points of a given medium (body) is called the field of this quantity. Accordingly, the set of temperature values at a given time for all points of the medium under consideration is called the temperature field.
In the most general case, the temperature at a given point depends on the coordinates of the point in space and changes over time:
This dependence is the equation of an unsteady temperature field.
For a steady temperature field
In practice, in addition to a three-dimensional stationary temperature field, two-dimensional and one-dimensional temperature fields are quite often encountered, which are a function of two and one coordinates, respectively.
The geometric location of points having the same temperature is called an isothermal surface. Temperatures vary from one isothermal surface to another, with the greatest temperature change occurring normal to the isothermal surfaces.
The limit of the ratio of temperature change to the normal distance between isothermal surfaces is called the temperature gradient:
The temperature gradient is a vector quantity. The positive direction of the temperature gradient is considered to be the direction towards increasing temperatures.
HEAT FLOW is a vector directed in the direction opposite to the temperature gradient and equal in abs. the amount of heat passing through the isothermal. surface per unit time. Measured in watts or kcal/h (1 kcal/h=1.163 W)
Thermal conductivity is the process of transferring thermal energy from more heated areas of the body to less heated ones as a result of thermal movement and interaction of microparticles. As a result of thermal conductivity, body temperature is equalized.
1. The basic law of thermal conductivity, established by Fourier (1768--1830) and named after him, states that the amount of heat dQ transferred by thermal conductivity is proportional to the gradient of temperature, time and cross-sectional area dF perpendicular to the direction of heat flow:
where: - coefficient of thermal conductivity of the medium, W/(m*K)
The thermal conductivity coefficient of substances depends on their nature and state of aggregation, temperature and pressure. The thermal conductivity coefficient of gases increases with increasing temperature and is almost independent of pressure. For liquids, with the exception of water and glycerin, on the contrary, it decreases with increasing temperature. For most solids increases with increasing temperature.
The differential equation of thermal conductivity, also called the Fourier equation, describes the process of heat propagation in a medium. It is derived based on the law of conservation of energy and written in the following form:
where: =a - thermal diffusivity coefficient, m 2 / h or m 2 / s; With - specific heat material, kJ/(m*K); - material density, kg/m 3
The thermal conductivity equation makes it possible to solve issues related to the propagation of heat by thermal conductivity under conditions of both steady-state and unsteady processes.
When solving specific problems, the heat conduction equation must be supplemented with corresponding equations describing the initial and boundary conditions.
As an example, consider the steady process of heat transfer by thermal conduction through a flat wall from a hot coolant to a cold one. Let the wall temperature on the hot coolant side be t st1, and on the cold side - t st2; thermal conductivity of the wall material; wall thickness. As can be seen from Fig. 9.1, the temperature field is one-dimensional and temperatures change only in the direction of the x axis. The equation describing the thermal conductivity of a flat wall at steady state has the form
where: - thermal conductivity of the wall.
The reciprocal of the thermal conductivity of the wall () is called the thermal resistance of the wall. In the case of a two-layer wall, for example enameled, or multilayer, one can similarly obtain
where n is the number of wall layers.
The main kinetic characteristics of the heat transfer process are the average temperature difference, the heat transfer coefficient, and the amount of heat transferred (the size of the heat exchange equipment depends on this value).
The driving force of heat exchange processes is the difference in coolant temperatures. Under the influence of this difference, heat is transferred from the hot coolant to the cold one.
The amount of heat Q transferred per unit time from a hot coolant to a cold one over the entire heat exchange surface F of the heat exchanger is determined from the heat balance equation:
The driving force during heat transfer between two coolants does not retain its constant value, but changes along the heat exchange surface.
For example, with direct flow at the entrance of coolants into the heat exchanger, the local driving force is maximum: = t 1 "-t 2 ", and at the exit from the apparatus it is minimal: = t 1 "" -t 2 "" The same picture is observed with counterflow. Therefore, when calculating heat transfer processes, they use the average driving force process. Obtain a relationship for calculating the average driving force of the heat transfer process
At different temperatures in different parts of the body, a spontaneous process of heat transfer occurs from areas with a higher temperature to areas with a lower temperature. The occurrence of the process is caused by a property called thermal conductivity. Energy transfer occurs due to energetic interactions between molecules, atoms, and electrons. The process of thermal conductivity is associated with the temperature distribution inside the body and therefore it is necessary to establish the concepts of temperature field and temperature gradient.
Temperature characterizes the thermal state of the body, determining the degree of its heating. And if the process of thermal conductivity occurs in the body, then the temperature of its different parts is different. The set of temperature values for all points of the body at a given time is called the temperature field.
The temperature field equation has the form:
t = f (x, y, z, t), (12.1)
where t is the body temperature at a point;
x, y, z — coordinates of the point;
t — time.
If the temperature changes with time, such a temperature field is called non-stationary, it corresponds to an unsteady, non-stationary process of heat conduction, and if the temperature does not change with time, the temperature field is stationary and the heat conduction process is stationary (steady).
Temperature can be a function of one, two or three coordinates. Accordingly, the temperature field is called one-, two-, or three-dimensional. A one-dimensional field has the simplest form of the equation t = f(x). For example, during a stationary process of heat conduction through a flat wall.
For any temperature field, there are points in the body with the same temperature. The geometric location of points with the same temperature forms an isothermal surface. There cannot be two different temperatures at one point in space, and therefore isothermal surfaces do not touch or intersect. They either end at the boundaries of the body or form a closed contour (as, for example, in a cylindrical body).
Temperature changes in the body are observed only in directions intersecting isothermal surfaces. In this case, the most dramatic change in temperature is observed in the direction normal to the isothermal surfaces. The limit of the ratio of temperature change (Dt) to the minimum distance between these isotherms (Dn), provided that this distance tends to zero, is called the temperature gradient.
Deg/m, (12.2)
The temperature gradient shows the intensity of temperature change; it is a vector directed towards increasing temperature.