Thermal Conductivity of Carbon Steel Pipe

Carbon steel pipe: 1.0% carbon is 29, 0.5% carbon is 31, the unit is the national standard unit W/(m.℃). The carbon content in the carbon steel pipe will affect the thermal conductivity of the carbon steel pipe. The higher the carbon content, the lower the thermal conductivity.

The thermal conductivity of carbon steel pipe depends on the purity, and the heat transfer value of carbon is very low, which will cause the heat transfer rate to a certain extent. And the higher the carbon content is, the corrosion and impact resistance are affected. In actual use, we are all galvanized as a whole and surface treated, which can improve the corrosion resistance and service life.

Different substances have different thermal conductivity; the thermal conductivity of the same substance is related to its structure, density, humidity, temperature, pressure and other factors. When the water content of the same substance is low and the temperature is low, the thermal conductivity is small. Generally speaking, the thermal conductivity of solids is greater than that of liquids, which in turn is greater than that of gases. This difference is largely due to the difference in molecular spacing between the two states. The coefficient values used in engineering calculations are all determined by special tests.

With the increase of temperature or moisture content, the thermal conductivity of the five typical building materials measured showed an increasing trend. This will be analyzed from the microscopic mechanism below. For porous materials, when they are damp, liquid water will replace the original air in the pores; and at normal temperature and pressure, the thermal conductivity of liquid water (about 0.59W/(m·K)) is much greater than that of air. The thermal conductivity (about 0.026W/(m·K)), therefore, the thermal conductivity of the wet material will be greater than that of the dry material, and the higher the moisture content, the greater the thermal conductivity. If water condenses into ice at low temperature, the thermal conductivity of the material as a whole will also increase because the thermal conductivity of ice is as high as 2.2W/(m·K)).

Different from the influence of moisture, the increase of temperature will cause the acceleration of molecular thermal motion, and promote the thermal conduction of the solid skeleton and the convective heat transfer of the fluid in the pores. In addition, the radiative heat transfer between the hole walls is also enhanced due to the increase in temperature. If the material is wet, the temperature gradient can also have important effects: the temperature gradient will form a vapor pressure gradient, allowing the water vapor to migrate from the high temperature side to the low temperature side; under certain conditions, the water vapor may condense on the low temperature side, forming a liquid state The water will in turn migrate from the low temperature side to the high temperature side driven by capillary pressure. This cycle is repeated, similar to the enhanced heat exchange effect of a heat pipe, so that the thermal conductivity of the material increases significantly.