Specific heat capacity of peat table. Thermal properties of wood
The ability of wood to absorb heat is characterized by heat capacity. As a measure, specific heat capacity c is used, which is the amount of heat required to heat wood weighing 1 kg by 1 o C. The unit of specific heat capacity is kcal / kg x deg or in the international system of units SI j / kg x deg.
Estimates of world coal reserves vary widely. Of this recoverable coal, China had about 43%, the United States 17%, Soviet Union- 12%, South Africa - 5% and Australia - 4%. On the other hand, the dynamics in the coal industry of the United States, China, India, Colombia and Australia among other countries.
Adapting the turbo to the specific engine looking for a solution has two paths: more power and less consumption. It is about considering an adaptation, from a turbo to a specific engine, which would be primarily to find a solution to a specific problem with a very precise goal. The problem of engine developers is certainly not the same as that of the user, that is, the one who uses it, and who logically cannot perceive or evaluate all problems in the short or medium term, turbo.
Within the temperature range from 0 to 100°, the specific heat capacity of absolutely dry wood is from 0.374 to 0.440 kcal/kg x deg and is on average 0.4 kcal/kg x deg. When moistened, the heat capacity of wood increases, since the specific heat capacity of water (1.0 kcal / kg x deg) more heat capacity absolutely dry wood. At a positive temperature (above 0°C), the influence of humidity is more pronounced than at a negative temperature. For example, an increase in humidity from 10 to 120% at a temperature of + 20° leads to an increase in heat capacity by 70%; a change in humidity within the same limits, but at a temperature of -20 ° C, causes an increase in heat capacity by only 15%; this is explained by the lower heat capacity of ice (0.5 kcal/kg x deg).
In this regard, there are two ways, diametrically opposed, which would be the following. It was overfed concrete with a positive displacement compressor that started this journey. In the case of manufacturers or manufacturers of heat engines where there is an existing engine, where the turbocharger assembly allows to obtain power equivalent to that of an engine with a much larger displacement.
To achieve more significant powers, the following are available: an atmospheric or natural suction engine, taken as a basis, a positive displacement compressor and a turbocharger. A few years ago we saw that engines were not only sporty, but also produced large series using two technologies, even using compressed air cooling through a heat exchanger or intercooler. In the near future, in the short term, we will have a wider development of electronic engine and turbo control components, which will provide greater mechanical, thermodynamic and volumetric performance in general.
Example 1. Determine using the diagram in fig. 42 heat capacity of wood at t=20° and humidity 60%. The point of intersection of the vertical line corresponding to a given temperature with the horizontal line for a given humidity is on the 0.66 sloping curve. Consequently, the specific heat capacity of wood under given conditions is 0.66 kcal/kg x deg.
A turbocharger is a device which, for example in diesel cycle engines, directs pressurized intake air into the combustion chamber through a compressor driven by an exhaust gas driven turbine.
The turbo engine must logically withstand higher average pressures, while the pistons, rods and crankshaft are subjected to higher mechanical loads. With regard to the level of fuel consumption, in last years significant benefits have been obtained with the expectation of evolution in this regard and the search for new solutions.
Example 2. Determine the heat capacity of frozen wood at t = -10° and 80% humidity. We draw a vertical line through the point corresponding to -10° (to the left of zero on the temperature axis) until it intersects with a horizontal line corresponding to 80% humidity. The point of intersection is between two oblique straight lines 0.50 and 0.55. We estimate the position of the point from these lines by eye and find that the specific heat capacity of wood in the indicated state is 0.52 kcal / kg x deg.
As far as designers are concerned, it is important to consider that assembling a turbocharger in an existing engine achieves very similar performance as assembling a naturally aspirated engine with a higher displacement. Significant advantages are the avoidance of costly research and the operational speed of assembly in mass production.
Exhaust manifolds must respond to good turbine performance for good compressor performance. Regarding the choice of turbocharging, it should be taken into account that, depending on the displacement of the engine to be supercharged, it should be chosen within the range of turbochargers proposed by the manufacturers and where the characteristics are most suitable. This adaptation that exists between the compressor and the turbine returns to the level of the engine-turbocharger assembly.
thermal conductivity of wood
Thermal conductivity determines the ability of wood to conduct heat and is characterized by the coefficient of thermal conductivity λ, which is the amount of heat passing for 1 hour through a flat wall with an area of 1 m 2 and a thickness of 1 m at a temperature difference on opposite sides of the wall of 1 ° C. The dimension of thermal conductivity is kcal / m h x deg) or, in the SI system, W / m. x deg. Due to the porous structure of wood, thermal conductivity is low. With increasing density, the thermal conductivity of wood increases. Since the thermal conductivity of water at the same temperature is 23 times less than the thermal conductivity of air, the thermal conductivity of wood is highly dependent on humidity, increasing with its increase. With increasing temperature, the thermal conductivity of wood increases, and this increase is more pronounced in wet wood. The thermal conductivity of wood along the fibers is much greater than across the fibers.
The aim is first of all to match the exhaust gas flow rate to the good performance of the turbine so that the compressor can operate in a good performance area. Priority must be set in the compressor pressure area so that the turbine works with its bypass system.
Car terminals, like hardware factories, have kits that adapt to commercial engines and without which the turbo cannot work properly. These kits can be, among others, the following: Multiple or exhaust manifold and flange connection to the compressor. Bypass valve with connecting pipe to the exhaust system. Safety valve in the intake circuit. Engine pistons with a new design.
In the plane across the fibers, the thermal conductivity also depends on the direction, and the ratio between the thermal conductivity in the radial λ R and tangential λ t directions is different for different rocks. The value of this ratio is influenced by the volume of core rays and the content of late wood. In rocks with numerous core rays (oak) λr>λ g; at conifers with a small volume of core rays, but with a high percentage of late wood (larch), λ t >λ r . In hardwoods with a uniform structure of annual layers and relatively few short medullary rays, as well as in other conifers, λr differs little from λt.
Compressor sealing ring. Central crankcase. Heat protection cover. Turbine sealing ring. Specific turbine lubrication. Other technical components include: Heat exchanger or "intercooler". Improved lubrication and engine cooling. Measurement and control or monitoring of engine parameters at different stages with the possibility of monitoring using electronic devices.
It can be seen that the turbocharger always has a new stage of application in heat engines, as an engine-turboblock assembly as such. It is logically related to sporty and competitive engines. In diesel engines, in order to burn more diesel fuel, it is necessary to provide large quantity air. 1 - Air under pressure. 2 - Exhaust gases. 3 - Air intake. 4 - Exit exit.
the value of the coefficient K p, taking into account the change in the thermal conductivity of wood from density
| Conditional density, kg 1m 3 | K r | Conditional density, kg 1m 3 | K r |
| 340 | 0,98 | 500 | 1,22 |
| 360 | 1,00 | 550 | 1,36 |
| 380 | 1,02 | 600 | 1,56 |
| 400 | 1,05 | 650 | 1,86 |
| 450 | 1,12 |
In table. the values of the coefficient taking into account the conditional density of wood are given. The coefficient K x in the tangential direction across the fibers for all breeds is taken equal to 1.0, and in the radial direction - 1.15; along the fibers for coniferous and scattered vascular species - 2.20, and for annular vascular species - 1.60.
Carbon is abundant in nature, both in free and in combination. Free carbon is present in a large number of grades that are collected under the name of natural coals; diamond and graphite - pure or almost pure carbon; used as fuel contain more or less carbon mixed with foreign matter.
In all its forms, carbon is distinguished by its durability. It only begins to volatilize at arc temperature; soluble only in certain molten metals such as platinum and cast iron. When crystallized, it occurs in two allotropic forms: diamond and graphite. Amorphous carbon is distinguished by its absorption capacity.
Example. Determine the thermal conductivity of birch along the fibers at a temperature of 50 ° C and a humidity of 70%. According to the diagram in Fig. 43 we find that the nominal value of thermal conductivity in the indicated state of wood is 0.22 kcal / m x h x deg. According to the table 19 determine the conditional density of birch p conv = 500 kg / m 3. According to the table 20 we find the value of the coefficient K P = 1.22. The value of the coefficient K x in this case is 2.20.
Although not abundant in the earth's crust, carbon is the second most abundant element in the human body. It occurs in all tissues of animals and plants, in combination with hydrogen and oxygen, as well as in its geological derivatives, petroleum and stone charcoal, where it combines mainly with hydrogen in the form of hydrocarbons. In combination with oxygen, it is also present in the atmosphere as carbon dioxide and in rocks, in the form of carbonates, limestone, for example. In the free state, it occurs in small amounts, like diamond and graphite, which are the two alotropic forms of the element.
thermal diffusivity of wood
Thermal diffusivity determines the ability of wood to equalize the temperature throughout its volume. Thermal diffusivity A characterizes the rate of temperature propagation inside the body during non-stationary thermal processes (heating, cooling). Its dimension is m 2 / h, or, in the SI system, m 2 / sec. Between the three main thermophysical characteristics there is the following relationship: a =λ/ cf.
Basic carbonaceous ores. Diamond graphite Anthracite Coal Coal or coal Lignite peat. . Diamond in its hardness, brilliance and beauty, the most precious of precious stones. For this reason, the attention of mineralogists and crystallographers since ancient times has been focused on the study of their properties. It is also of great industrial interest.
Diamond is pure carbon, sometimes with an admixture of metal oxides, which leave ash when the mineral is burned. Diamond crystallizes in the cubic system in several forms: cube, octahedron, rhombic dodecahedron, pyramidal cube, scalenohedron, tetrahedron. It often appears in geminated crystals; one of the most common groupings is two interpenetrating and angled truncated tetrahedra, giving them the appearance of an octahedron, as well as often deformed crystals with corroded edges, curved and pumped faces.
Thermal diffusivity depends mainly on the moisture content of the wood and, to a lesser extent, temperature. With increasing humidity, the thermal diffusivity of wood decreases; This is due to the fact that the thermal diffusivity of air is much greater than that of water. On the diagram in fig. 44 shows the influence of humidity on the thermal diffusivity of pine wood in three directions. In addition, the diagram shows that the thermal diffusivity along the fibers is much greater than across the fibers, and the difference between the thermal diffusivity in the radial and tangential directions is very small. As the temperature rises, the thermal diffusivity of wood increases. The higher the density of the wood, the lower the thermal diffusivity.
Inflated crystals, when small, have a spherical aspect and are well known from garimpiros. The diamond has a very strong adamantine brilliance, characteristic and unmistakable. Very high rate refraction, 2, Usually when pure transparent and colorless. However, it may have a slight blue, yellow, pink, green color that occurs in the presence of metal oxides. Sometimes it is strongly colored, even black: carbon grade or pistil.
It is a phosphorescent mineral that changes this property with crystallization. Diamond is the hardest of the minerals, with a hardness of 10 in the Mohs range. Some varieties, such as bead and carbonate, are even harder than regular diamonds. Diamond has splitting plans in his work, which makes the task easier.
thermal deformation of wood
Temperature deformations of wood are characterized by a coefficient of linear expansion a (change in unit length when heated by 1 ° C), which for wood has a small value and depends on the direction with respect to the fibers; the expansion from heat is the smallest along the fibers and the largest across the fibers in the tangential direction. The coefficients of linear expansion of wood along the fibers are 7-10 times less than across the fibers. The insignificant value of the linear expansion of wood along the fibers from heat makes it possible in practice to ignore this phenomenon (refusal of thermal joints).
Diamond is a very brittle mineral, a property that used to be confused with hardness; specific gravity 3, 6, conchoidal fracture. Heated by an oxidizing flame, it burns slowly; burns with strong heating in the presence of oxygen. It does not dissolve in acids or alkalis.
Main varieties: diamond, hyaline or variously colored, and the most popular of all gemstones; board, an amorphous or semi-crystallized variety that is in shape. Spherical, fibrillated structure; carbonate, black diamond or pestle, opaque grade, crystal structure fragments, sometimes porous and harder than ordinary diamonds.
Peat is the geologically youngest representative of the humite class, although it can only conditionally be classified as a solid fossil fuel. Insignificant condensation of aromatic nuclei, widely branched peripheral chains, including complex functional groups, are the reason for the very high heat capacity of peat compared to the heat capacity of other humites.
Diamond is found in deposits of primary origin and secondary origin. The origin is primary when it is obtained in the rock of the spewing matrix that India laughs is pegmatite. In South Africa, the region that provides the most diamonds, the parent rock is an eruptive peridotite group called kimberlite, from which diamonds are directly derived.
In Brazil, the deposits are usually of secondary origin. Diamonds are removed from the gravel and sands of the rivers or high gravel, already semi-consolidated and are called "grou-piara", as well as gravel gravel or "weevil". The study of the diamond has always been carried out by means of the most elementary processes. The gold miners descend to the diamond rivers, guided by the "satellites" or minerals that usually accompany the diamond, and scour the "cauldrons" for large holes dug in the riverbed. Recognized as the extension of the diamond, water leakage, and then exploration of the sands and gravel, dried up.
Study thermophysical properties peat has not yet received proper development. It is only known that for absolutely dry peat at room temperature it is 0.47-0.48 kcal/(kg-°C) and weakly depends on the type of peat (moor, transitional, lowland) and on the degree of decomposition.
A characteristic feature of peat is their extremely high humidity. With an increase in humidity, the heat capacity of peat increases. Since it has been established that the bulk of water in peat (more than 90%) is in an unbound or weakly bound form and its heat capacity, therefore, is close to 1 kcal / (kg - ° C), insofar as the specific heat capacity of wet peat can be calculated by the formula
In consolidated cuttings, the process is somewhat different. Stream water is supplied to soften the rock and then comes the search for the diamond. First of all, battles were used, in the form of large wooden plates or, inside which gravel was placed, mixed in running water, which makes it easier to detect a diamond by its brightness. Later "screens", "meses" and "canoes" were introduced.
The satellites, minerals that are commonly found in gravel next to diamonds, come from the same stones as him, of course. The main diamond producing countries are: South Africa, Ghana, Angola, Guyana and Brazil. In Brazil, the richest diamonds are: Parana and Mato Grosso. Of these states, the main one is Minas Gerais, where there are two large areas of diamantiferos.
Cy=0.475^1----- + kcal/(kg-°C), (V.1)
Where Wp is the total moisture content of peat, % of the total mass.
A thermographic study of peat reveals the presence of a significant endothermic effect, the maximum of which falls on a temperature of 170-190 ° C. At temperatures above 250 ° C, thermochemical transformations of peat occur with the release of heat, most noticeable in the ranges of 270-380 ° C and 540-580 ° C. A similar picture - one endothermic maximum and two or more exothermic minimums - is also observed in the process of pyrolysis of wood (see Chapter XIII ), which is fully explained by the genetic proximity of the objects.
V. BROWN COALS
Despite the fact that brown coals are a valuable energy and technological raw material, their thermophysical properties have not been systematically studied until recently.
Due to the relatively low conversion of the molecular structure, in particular, the poorly developed condensed core and the high content of heavy heteroatoms in the peripheral groups, the heat capacity of brown coals is much higher than the heat capacity of even poorly metamorphosed coals (see Table III.1).
According to the data of E. Rammler and R. Schmidt, based on the results of a study of eleven brown coals, the average specific heat capacity of brown coal in terms of dry and ash-free mass in the range of 20 ° C-T (T ^ 200 ° C) can be calculated by the formula
Cy = 0.219+28.32-10~4(7°+5.93-104G, kcal/(kg-°C), (VI.1)
Tde d° - resin yield, % on dry organic matter; T - temperature, °C.
Analysis of the effect of mineral inclusions and free moisture on the heat capacity of brown coals allowed the authors to derive a generalized dependence that is valid at temperatures up to 200 ° C:
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Where Ts7r - working moisture; Ac - ash content of coal,%.
Since E. Rammler and R. Schmidt used the mixing method to determine the heat capacity, which, as noted above, requires a significant time to stabilize the temperature of the system, naturally, their results differ somewhat from the data obtained during dynamic heating.
So, for example, from the formula (VI.!) It follows that in the range of 20-200 ° C, the average heat capacity increases linearly with increasing temperature. This conclusion contradicts the results obtained by A. A. Agroskin et al. in determining the heat capacity of a group of domestic brown coals from various deposits. The determinations were carried out according to the diathermic shell method with dry samples pre-crushed to a particle size of less than 0.25 mm in a continuous stream of purified nitrogen at a heating rate of 10°C/min. The results are related to the current mass of the sample -
The characteristics of the studied samples are given in Table.
VI. 1, and in fig. 26 shows the dependence of the effective heat capacity on temperature.
All curves in the temperature range from 20 to 1000 ° C have a similar character and differ only slightly - 96
О 100 200 300 400 500 600 700 800 900 1000
Temperature, ° С
Rice. 26. Temperature dependence of the effective heat capacity of brown coals of some deposits:
1-4 - deposits, respectively, Irsha-Borodnskoye, Berezovskoye, Gusnnoozer-
Skoye, Yovo-Dmitrovskoe
They are separated from each other according to the absolute values of the heat capacity. The maxima and minima observed on the curves correspond to the same temperatures. At 20 ° C, the effective heat capacity, which coincides with the true one, changes for various coals within 0.27-0.28 kcal / (kg - ° C), which is in good agreement with the results obtained by formulas (VI. 1) and (VI.2).
Table VI.!
The linear variation of the effective heat capacity (see Fig. 26) takes place only in the range 20-120°C. With increasing temperature, a sharper increase in the heat capacity is observed, reaching a maximum at 200°C equal to 0.47-■
0.49 kcal/(kg-°C). This first endothermic maximum is due to the removal of bound moisture and the onset of organic mass pyrolysis reactions proceeding with heat absorption. The second endothermic maximum of 0.42-0.49 kcal/(kg-°C) takes place at a temperature of about 550°C, which indicates the predominance of endothermic reactions of the destruction of the organic mass and the decomposition of part of the mineral impurities. It is characteristic that the largest in absolute value endothermic - 7 Zach. 179 97 These peaks are characteristic of coal from the Novo-Dmitrovskoe deposit, which differs from other coals in a high yield of volatile substances.
Further heating to 1000°C leads to a gradual decrease in heat capacity to 0.07-0.23 kcal/(kg-°C) due to the occurrence of exothermic reactions of the formation of a coke structure.
A comparison of the curves of change in the effective heat capacity (see Fig. 26) with the data of a thermographic study of brown coal also reveals some discrepancies. The most significant of them is the presence of a third endothermic nick on the thermograms at a temperature of 700–715°C. On the SEf(T) curves (see Fig. 26) at these temperatures, a certain relative increase in the effective heat capacity is observed, which, however, should not be considered as an endothermic effect, since the SEf in this interval remains lower than the true heat capacity. The reason for such fluctuations in the effective heat capacity, observed, by the way, even at more high temperatures lies in the complex nature of the formation of the coke structure.
The true (equilibrium) heat capacity of all the investigated coals increases monotonically with increasing temperature (Table VI.2). The lower values of the true heat capacity of the brown coal of the Novo-Dmitrovsky deposit compared to the heat capacity of other coals are explained by its high ash content.
The total thermal effect [tab. (VI.3)] pyrolysis reactions in accordance with formulas (1.13) and (1.14) is determined by the difference between the areas bounded by the effective and
Table VI.2
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True heat capacity of brown coals
Note. The numerator is kJ / "kg K, the denominator is kcal / (kg ■ ° C). Table U1.3 Total thermal effect of brown coal pyrolysis reactions in the range of 20-1000 ° C prn heating rate 10 ° C / min |
Thermal effect of pyrolysis
Field
true heat capacity. In this case, the area located under the true heat capacity curve characterizes the exothermicity, and the area above this curve characterizes the endothermicity of the pyrolysis reactions.
With an increase in the conversion of brown coals, the heat capacity of the latter decreases (Fig. 27).
VII. COALS AND ANTHRACITES
These coals are an extremely wide range of solid fossil fuels in terms of physical and technological properties, characterized by a different, but relatively high degree of conversion of the source material.
The heat capacity of coal depends on the stage of metamorphism (see Ch. II1.1), the conditions of occurrence, ash content, humidity, and a number of other factors, the influence of which will be considered in the next chapter.
This section provides reference data on the true and effective heat capacity of bituminous coals from some basins at moderate temperatures, as well as during thermal decomposition.