Water has a high heat capacity. The large heat capacity of water plays a significant role in the process of cooling and heating of water bodies, as well as in the formation climatic conditions annexing areas. Water slowly cools and heats up both during the day and during the change of seasons. Max Swing temperatures in the oceans do not exceed 40°C, while in the air these fluctuations can reach 100-120°C. The thermal conductivity (or transfer of thermal energy) of water is negligible. Therefore, water, snow and ice do not conduct heat well. In water bodies, heat transfer to depths is very slow.
Viscosity of water. Surface tension
As salinity increases, the viscosity of water increases slightly. Viscosity or internal friction- the property of fluid (liquid or gaseous) substances to resist own course. The viscosity of liquids depends on temperature and pressure. It decreases both with increasing temperature and with increasing pressure. The surface tension of water determines the strength of adhesion between molecules, as well as the shape of the surface of the liquid. Of all liquids other than mercury, water has the highest surface tension. As the temperature rises, it decreases.
Laminar and turbulent, steady and unsteady, uniform and non-uniform movement of water
laminar motion- parallel jet flow, at a constant water flow, the speed of each point of the flow does not change in time either in magnitude or in direction. Turbulent - a form of flow in which the elements of the flow make disorderly movements along complex trajectories. At uniform motion the surface is parallel to the leveled bottom surface. at uneven movement the slope of the flow velocity of the living section is constant in the length of the section, but varies along the length of the flow. Unsteady motion is characterized by the fact that all hydraulic elements of the flow in the considered section change in length and in time. Established - on the contrary.
The water cycle, its continental and oceanic links, the intracontinental cycle
Three links are distinguished in the cycle - oceanic, atmospheric and continental. Continental includes lithogenic, soil, river, lake, glacial, biological and economic links. The atmospheric link is characterized by the transfer of moisture in the air circulation and the formation of precipitation. The oceanic link is characterized by the evaporation of water, during which the content of water vapor in the atmosphere is continuously restored. Intracontinental circulation is typical for areas of internal runoff.
The water balance of the world's oceans, the globe, sushi
The Earth's global moisture cycle finds its expression in the Earth's water balance, which is mathematically expressed by the equation water balance(for the globe as a whole and for its separate parts). All components (components) of the water balance can be divided into 2 parts: incoming and outgoing. Balance is quantitative characteristic water cycle. The method of calculating the water balance is used to study the incoming and outgoing elements large parts the globe - land, the Ocean and the Earth as a whole, individual continents, large and small river basins and lakes, and finally, large areas of fields and forests. This method allows hydrologists to solve many theoretical and practical tasks. The study of the water balance is based on a comparison of its incoming and outgoing parts. For example, for land, precipitation is the incoming part of the balance, and evaporation is the outgoing part. The ocean is replenished with water through runoff. river waters from land, and consumption - due to evaporation.
Related information:
- How can you buy the sky or the warmth of the earth? This idea is incomprehensible to us. If we don't own fresh air and splashes of water, how can you buy them from us?
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The thermal conductivity of water is about 5 times higher than that of oil. It increases with increasing pressure, but at pressures that occur in hydrodynamic transmissions, it can be taken constant.
The thermal conductivity of water is approximately 28 times higher than that of air. In accordance with this, the rate of heat loss increases when the body is immersed in water or in contact with it, and this largely determines the heat sensation of a person in air and in water. So, for example, at - (- 33, the air seems warm to us, and the same water temperature seems indifferent. The air temperature 23 seems to us indifferent, and the water of the same temperature seems cool. At - (- 12, the air seems cool, and the water seems cold .
The thermal conductivity of water and water vapor is undoubtedly the best studied of all other substances.
| Dynamic viscosity (x (Pa-s of some aqueous solutions. | Change in the mass heat capacity of aqueous solutions of some salts depending on the concentration of the solution. | Thermal conductivity of some solutions depending on the concentration at 20 C. |
The thermal conductivity of water has a positive temperature course, therefore, at low concentrations, the thermal conductivity aqueous solutions many salts, acids and alkalis increases with increasing temperature.
The thermal conductivity of water is much greater than that of other liquids (except metals) and also changes anomalously: it increases up to 150 C and only then begins to decrease. The electrical conductivity of water is very small, but increases markedly with an increase in both temperature and pressure. The critical temperature of water is 374 C, the critical pressure is 218 atm.
The thermal conductivity of water is much greater than that of other liquids (except metals), and it also changes anomalously: it increases up to 150 C and only then begins to decrease. The electrical conductivity of water is very small, but increases markedly with an increase in both temperature and pressure. The critical temperature of water is 374 C, the critical pressure is 218 atm.
| Dynamic viscosity q (Pa-s of some aqueous solutions. | Change in the mass heat capacity of aqueous solutions of some salts depending on the concentration of the solution. | Thermal conductivity of some solutions depending on the concentration at 20 C. |
The thermal conductivity of water has a positive temperature course, therefore, at low concentrations, the thermal conductivity of aqueous solutions of many salts, acids and alkalis increases with increasing temperature.
The thermal conductivity of water, aqueous solutions of salts, alcohol-water solutions and some other liquids (for example, glycols) increases with increasing temperature.
The thermal conductivity of water is very small compared to the thermal conductivity of other substances; so, the thermal conductivity of the cork is 0 1; asbestos - 0 3 - 0 6; concrete - 2 - 3; tree - 0 3 - 1 0; brick-1 5 - 2 0; ice - 5 5 cal / cm sec deg.
The thermal conductivity of water X at 24 is 0 511, its heat capacity with 1 kcal kg C.
The thermal conductivity of water prn 25 is 1 43 - 10 - 3 cal / cm-sec.
Since the thermal conductivity of water (R 0 5 kcal / m - h - deg) is approximately 25 times greater than that of still air, the displacement of air by water increases the thermal conductivity of the porous material. With rapid freezing and formation in the pores building materials no longer ice, but snow (R 0 3 - 0 4), as our observations have shown, the thermal conductivity of the material, on the contrary, decreases somewhat. Correct accounting for the moisture content of materials is of great importance for thermal engineering calculations of structures, both aboveground and underground, for example, water and sewage.
The thermal conductivity of water is a property that we all, without suspecting it, very often use in everyday life.
Briefly about this property, we already wrote in our article. CHEMICAL AND PHYSICAL PROPERTIES OF WATER IN THE LIQUID STATE →, in this material we will give a more detailed definition.
First, consider the meaning of the term thermal conductivity in general.
Thermal conductivity is...
Technical Translator's Handbook
Thermal conductivity - heat transfer, in which the transfer of heat in an unevenly heated medium has an atomic-molecular character
[Terminological dictionary for construction in 12 languages (VNIIIS Gosstroy of the USSR)]
Thermal conductivity - the ability of a material to transmit heat flow
[ST SEV 5063-85]
Technical Translator's Handbook
Explanatory Dictionary of Ushakov
Thermal conductivity, thermal conductivity, pl. no, female (physical) - the property of bodies to distribute heat from more heated parts to less heated ones.
Explanatory Dictionary of Ushakov. D.N. Ushakov. 1935-1940
Big Encyclopedic Dictionary
Thermal conductivity is the transfer of energy from hotter areas of the body to less heated areas as a result thermal motion and the interactions of its constituent particles. It leads to equalization of body temperature. Usually the amount of energy transferred, defined as the density heat flow, proportional to the temperature gradient (Fourier's law). The coefficient of proportionality is called the coefficient of thermal conductivity.
Big Encyclopedic Dictionary. 2000
Thermal conductivity of water
For a more voluminous understanding of the overall picture, we note a few facts:
- The thermal conductivity of air is approximately 28 times less thermal conductivity water;
- The thermal conductivity of oil is approximately 5 times less than that of water;
- As the pressure increases, the thermal conductivity increases;
- In most cases, with increasing temperature, thermal conductivity is weak concentrated solutions salts, alkalis and acids also grows.
As an example, we present the dynamics of changes in the values of thermal conductivity of water depending on temperature, at a pressure of 1 bar:
0°С - 0.569 W/(m deg);
10°С - 0.588 W/(m deg);
20°С - 0.603 W/(m deg);
30°C - 0.617 W/(m deg);
40°C - 0.630 W/(m deg);
50°С - 0.643 W/(m deg);
60°С - 0.653 W/(m deg);
70°С - 0.662 W/(m deg);
80°С - 0.669 W/(m deg);
90°С - 0.675 W/(m deg);
100°С – 0.0245 W/(m deg);
110°С – 0.0252 W/(m deg);
120°С - 0.026 W/(m deg);
130°С - 0.0269 W/(m deg);
140°С - 0.0277 W/(m deg);
150°С - 0.0286 W/(m deg);
160°С - 0.0295 W/(m deg);
170°С - 0.0304 W/(m deg);
180°С - 0.0313 W/(m deg).
Thermal conductivity, however, like all the others, is a very important property of water for all of us. For example, we very often, without knowing it, use it in everyday life - we use water to quickly cool heated objects, and a heating pad to accumulate heat and store it.
Under thermal conductivity refers to the ability various bodies conduct heat in all directions from the point of application of a heated object. Thermal conductivity increases as the density of a substance increases, because thermal vibrations are more easily transmitted to more dense matter where individual particles are located closer to one another. Liquids also obey this law.
Thermal conductivity is determined by the number of calories passing in 1 second. through an area of 1 cm2 with a temperature drop of 1 ° over a 1 cm path. In terms of thermal conductivity, water occupies a place between glass and ebonite and is almost 28 times superior to air.
Heat capacity of water. Under specific heat is understood as the amount of heat that can heat 1 g of the mass of a substance by 1 °. This amount of heat is measured in calories. The unit of heat is the gram-calorie. Water perceives at 14-15° large quantity heat than other substances; for example, the amount of heat required to heat 1 kg of water by 1° can heat 8 kg of iron or 33 kg of mercury by 1°.
Mechanical action of water
Most strong mechanical action differs shower, the weakest - full baths. Let's compare the mechanical effect, for example, of Charcot's shower and full baths.
Additional pressure water on the skin in a bath where the water column does not exceed 0.5 m is about 0.005, or 1.20 atmospheric pressure, and the impact force of a water jet in the Charcot shower, directed at the body from a distance of 15-20 m, is 1.5-2 atmospheres.
Regardless temperature of the applied water, under the influence of the shower, an energetic expansion of the skin vessels occurs immediately after the water jet falls on the body. At the same time, the exciting action of the soul is manifested.
For research mechanical action of sea and river: bathing, the formula F = mv2/2 is applicable, where the force F is equal to half the product of the mass m and the square of the speed v2. mechanical action maritime and river waves depends not so much on the mass of water advancing on the body, but on the speed with which this movement takes place.
Water as a chemical solvent. Water has the ability to dissolve various mineral salts, liquids and gases, from this the irritating effect of water is enhanced. Great importance attached ion exchange occurring between water and a human body immersed in a mineralized bath.
Under normal pressure(i.e. when zero temperature) one volume of water absorbs 1.7 volumes of carbon dioxide; with increasing pressure, the solubility of carbon dioxide in water increases significantly; at two atmospheres of pressure at a temperature of 10°C, three volumes of carbon dioxide are dissolved instead of 1.2 volumes at normal pressure.
Thermal conductivity of carbon dioxide half the thermal conductivity of air and thirty times less than the thermal conductivity of water. This property of water is used to arrange various gas baths, sometimes replacing mineral springs.
In the downward direction, they begin to be detected when the thickness of the water layer is between spherical (with a radius of curvature of about 1 m) and flat
As a result of the heat exchange between the vapor and the liquid, only the upper layer of the liquid will take on the saturation temperature corresponding to the average drain pressure. The temperature of the bulk of the liquid will remain below the saturation temperature. Heating of the liquid proceeds slowly due to the low value of the thermal diffusivity of liquid propane or butane. For example, liquid propane on the saturation line at a temperature ts - 20 ° C a = 0.00025 m - / h, while for water, which is one of the most thermally inert substances, the value of the thermal diffusivity at the same temperature will be a = 0.00052 m/h
The thermal conductivity and thermal diffusivity of wood depend on its density, since, unlike heat capacity, these properties are affected by the presence of air-filled cell cavities distributed over the volume of wood. The thermal conductivity coefficient of absolutely dry wood increases with increasing density, while the thermal diffusivity decreases. When the cell cavities are filled with water, the thermal conductivity of wood increases, and the thermal diffusivity decreases. The thermal conductivity of wood along the fibers is greater than across.
WHAT depends on the sharply different values of these coefficients for the substances of coal, air and water. Thus, the specific heat capacity of water is three times, and the coefficient of thermal conductivity is 25 times greater than that of air, therefore, the coefficients of heat and thermal diffusivity increase with increasing moisture in coals (Fig. 13).
The device shown in fig. 16 on the left, serves to measure the heat and thermal diffusivity of bulk materials. In this case, the test material is placed in the space formed by the inner surface of the cylinder 6 and the cylindrical heater 9, placed along the axis of the device. To reduce axial flows, the measuring unit is equipped with covers 7, 8 made of heat-insulating material. In the jacket formed by the inner and outer cylinders, water of constant temperature circulates. As in the previous case, the temperature difference is measured by a differential thermocouple, one junction of which 1 is fixed near the cylindrical heater, and the other 2 - on the inner surface of the cylinder with the test material.
We come to a similar formula if we consider the time required for the evaporation of a single drop of liquid. The thermal diffusivity Xv of liquids such as water is usually low. In this regard, the heating of the drop occurs relatively slowly during the time t o/Xv. This allows us to assume that the evaporation of the liquid occurs only from the surface of the drop without significant heating.
In shallow waters, water is heated not only from above due to heat exchange processes with the atmosphere, but also from below, from the side of the bottom, which quickly warms up due to low thermal diffusivity and relatively low heat capacity. At night, the bottom transfers the heat accumulated during the day to the layer of water located above it, and a kind of greenhouse effect occurs.
In these expressions, Yad and H (in cal mol) are the heats of absorption and reaction (positive when the reaction is exothermic), and the remaining designations are indicated above. The thermal diffusivity for water is about 1.5-10"cm 1sec. Functions and
The thermal conductivity and thermal diffusivity of drilling fluids are much less studied. In thermal calculations, their thermal conductivity, according to V. N. Dakhnov and D. I. Dyakonov, as well as B. I. Esman and others, is taken the same as water - 0.5 kcal / m-h-deg. According to reference data, the coefficient of thermal conductivity of drilling fluids is 1.29 kcal/m-h-deg. S. M. Kuliev et al. proposed the equation for calculating the thermal conductivity coefficient
For approximate calculations of the processes of water evaporation into air and water condensation from moist air, the Lewis ratio can be used, since the ratio of the thermal diffusivity to the diffusion coefficient at 20 ° C is 0.835, which is not very different from unity. In section D5-2, the processes occurring in humid air were studied using a plot of specific moisture content versus enthalpy. Therefore, it would be useful to transform equation (16-36) in such a way that in its right side instead of partial
In equations (VII.3) and (VII.4) and boundary conditions (VII.5), the following designations are adopted Ti and T - respectively, the temperatures of the hardened and unhardened layers - the temperature of the medium T p - cryoscopic temperature a and U2 - respectively, the thermal diffusivity of these layers a \u003d kil ifi), mV A.1 - thermal conductivity coefficient for frozen meat, W / (m-K) A.2 - the same for chilled meat, W / (m-K) q and cg - specific heat capacities of frozen and chilled meat, J / (kg-K) Pi ip2 - density of frozen and chilled meat p1 \u003d pj \u003d 1020 kg / m - thickness of the frozen layer, counted from
