Heating pipe with insulator pipe armored low-temperature fused salt as resistance heating body

Abstract

A heating tube with an insulator tube armored with low-temperature fused salt as a resistance heating body is characterized in that a low-temperature fused salt tube is arranged in the insulator tube with a certain length and a certain section geometric dimension, so that the fused salt in the insulator tube has a certain resistance value, and metal electrodes are inserted into two ends of the insulator tube to be in contact with the low-temperature fused salt; one end of the metal electrode is in contact with the low-temperature fused salt, and the other end extends out of the insulator tube to be sealed and packaged to form a heating tube with the insulator tube armored low-temperature fused salt as a resistance heating body; after the metal electrode is electrified, the solid-state low-temperature fused salt is used as a resistor body to be heated to be molten, solid-liquid phase change heat storage is performed, and the temperature of the low-temperature fused salt is always at the melting point temperature of the low-temperature fused salt through temperature control; the heating mode of the heating pipe taking the insulator pipe armored low-temperature fused salt as the resistance heating body to a heated object is a combined mode of a non-contact infrared radiation heating mode, a direct contact heat conduction mode and an infrared radiation heating mode. The infrared radiation heating mode is that the tube wall of the composite material insulator tube mixed with the high infrared radiation composite oxide powder performs infrared heating on a heated object, and the low-temperature fused salt is doped with the high infrared radiation composite oxide particles to perform infrared heating on the heated object.

Description

Technical Field

[0001] A heating tube with an insulating tube armor and a low-temperature molten salt as a resistance heating element is disclosed, relating to the field of thermal heating technology. Background Technology

[0002] The heating element in a typical low-temperature heating tube is a resistance wire, and the armored tube is made of stainless steel or quartz glass. Because the surface area of ​​the resistance wire in the heating tube is very small, that is, the area used for heating and heat exchange is very small, and the heating power per unit area needs to be very high, that is, the surface power density of the resistance wire is very high, the temperature of the resistance wire can only be increased. The resistance wire needs to be heated to above 500°C before it can radiate and convect through the stainless steel tube and quartz glass tube to heat the object being heated. In other words, the surface temperature of the stainless steel tube and quartz glass tube is high, so they cannot be used for direct contact heating at temperatures below 300°C. At the same time, due to the small heat capacity of the heating tube, smooth temperature control cannot be achieved.

[0003] This invention discloses a heating tube with an insulated tube armored low-temperature molten salt as the resistive heating element, which effectively avoids the drawbacks of general low-temperature heating tubes. A low-temperature molten salt tube is inserted into an insulated tube of a certain length and diameter, giving the molten salt a certain resistance value. Metal electrodes are inserted into both ends of the insulated tube to contact the low-temperature molten salt. The insulated tube is sealed with one end of the metal electrode in contact with the low-temperature molten salt and the other end extending out of the insulated tube, forming an insulated tube armored low-temperature molten salt heating tube as the resistive heating element. When the metal electrodes are energized, the solid low-temperature molten salt acts as a resistive element and is heated to melting, undergoing a solid-liquid phase change to store heat. Temperature control keeps the temperature of the low-temperature molten salt at its melting point, allowing for direct contact heating of the object being heated. Multiple such insulated tube armored low-temperature molten salt heating tubes can be connected in series, parallel, or a combination of series and parallel to form a large-area heater. Summary of the Invention

[0004] A heating tube using insulated tube armored low-temperature molten salt as a resistive heating element is disclosed. The low-temperature molten salt tube is inserted into an insulated tube of a certain length and cross-sectional geometry, giving the molten salt a specific resistance value. Metal electrodes are inserted into both ends of the insulated tube to contact the low-temperature molten salt. The insulated tube is sealed with one end of the metal electrodes in contact with the low-temperature molten salt and the other end extending out of the insulated tube, forming an insulated tube armored low-temperature molten salt heating tube as a resistive heating element. When the metal electrodes are energized, the solid low-temperature molten salt, acting as a resistive element, is heated to melting, undergoing a solid-liquid phase change for heat storage. Temperature control maintains the temperature of the low-temperature molten salt at its melting point, allowing for direct heating. The heating element is heated by contact or non-contact heating; multiple heating tubes with insulating tube armor and low-temperature molten salt as resistance heating elements are connected in series, in parallel, or in a combination of series and parallel to form a large-area heater; the heating tubes with insulating tube armor and low-temperature molten salt as resistance heating elements are used in a combination of non-contact infrared radiation heating, direct contact heat conduction, and infrared radiation heating. The infrared radiation heating method is infrared heating of the heated object by the wall of the composite material insulating tube mixed with high infrared radiation composite oxide powder, and infrared heating of the heated object by radiation by high infrared radiation composite oxide particles doped into the low-temperature molten salt.

[0005] The insulating tube is made of polytetrafluoroethylene (PTFE), silicone, or glass. The maximum operating temperature of the PTFE tube is below 270°C, the maximum operating temperature of the silicone tube is 280°C, and the maximum operating temperature of the glass tube is 300°C. The insulating tube has a circular or rectangular cross-sectional shape.

[0006] The aforementioned insulator tube is formed by mixing 5% to 25% by volume of composite oxide powders containing ferric oxide, manganese dioxide, copper oxide, chromium oxide, and cobalt oxide with high infrared emissivity and an average particle size of less than 2 micrometers during the insulator tube molding process. This forms polytetrafluoroethylene (PTFE) composite material and silicone composite material, which are then extruded to form PTFE composite tubes and silicone composite tubes with high infrared emissivity. This improves the infrared radiation heating efficiency of the heating tube with insulator tube armored low-temperature molten salt as the resistance heating element. The weight fraction of the composite oxide powder is: 10% to 30% ferric oxide, 50% to 70% manganese dioxide, 7.5% to 12.5% ​​copper oxide, 2.5% to 5% chromium oxide, and 7.5% to 12.5% ​​cobalt oxide.

[0007] The composite oxide powder used for mixing polytetrafluoroethylene composite materials and silicone composite materials is a mixture of oxides with the following weight fractions: 10%~30% ferric oxide, 50%~70% manganese dioxide, 7.5%~12.5% ​​copper oxide, 2.5%~5% chromium trioxide, and 7.5%~12.5% ​​cobalt oxide. The oxides are ground to an average particle size of less than 2 micrometers, then calcined at 1000℃~1200℃, crushed, ground again to an average particle size of less than 2 micrometers, and dried before being used for mixing polytetrafluoroethylene composite materials and silicone composite materials.

[0008] The aforementioned low-temperature molten salt is composed of two or three of sodium nitrite, sodium nitrate, and potassium nitrate, with a melting point of 137℃~300℃. The composition of the low-temperature molten salt is determined according to the isothermal heating temperature of the heated object, based on the binary or ternary phase diagram of sodium nitrite, sodium nitrate, and potassium nitrate. The composition of the low-temperature molten salt has a melting point that corresponds to the isothermal temperature required by the heated object, i.e., the controlled temperature of the heating tube using the insulated tube armored low-temperature molten salt as a resistive heating element. Typical melting points of low-temperature molten salts include: 55% potassium nitrate and 45% sodium nitrite: melting point 137℃; 55% sodium nitrate and 45% sodium nitrite: melting point 220℃; 55% sodium nitrate and 45% potassium nitrate: melting point 218℃; and 100% sodium nitrate: melting point 317℃.

[0009] The aforementioned low-temperature molten salt is a doped low-temperature molten salt that does not change the melting point of the low-temperature molten salt. The doped low-temperature molten salt is a composite oxide particle with high infrared emissivity and a particle size of 0.2mm to 1mm, consisting of ferric oxide, manganese dioxide, copper oxide, chromium oxide, and cobalt oxide, accounting for 5% to 60% of the volume fraction of the inner volume of the insulator tube. After melting, the low-temperature molten salt fills the gaps between the composite oxide particles. The non-conductivity and volume fraction of the composite oxide are used to adjust and control the resistance value of the low-temperature molten salt in the insulator tube armored heating tube, i.e., the heating power under constant voltage, and to improve the infrared radiation heating efficiency and thermal conductivity of the insulator tube heater. The weight fraction of the composite oxide particles is: ferric oxide 10% to 30%, manganese dioxide 50% to 70%, copper oxide 7.5% to 12.5%, chromium oxide 2.5% to 5%, and cobalt oxide 7.5% to 12.5%.

[0010] The composite oxide particles used for doping low-temperature molten salt are a mixture of oxides with a weight fraction of 10%~30% ferric oxide, 50%~70% manganese dioxide, 7.5%~12.5% ​​copper oxide, 2.5%~5% chromium trioxide, and 7.5%~12.5% ​​cobalt oxide. The oxides are ground to an average particle size of less than 2 micrometers, then calcined at 1000℃~1200℃, crushed and pulverized to a particle size of 0.2mm~1mm, and dried before being used for doping low-temperature molten salt.

[0011] The aforementioned low-temperature molten salt or uniformly mixed doped low-temperature molten salt is heated until the crystal water is completely removed and then placed into a press mold to press it into a circular or rectangular cylinder with a geometric dimension smaller than the internal geometric dimension of the insulating tube and a length 1 to 2 times its geometric dimension. The circular or rectangular cylinders are then inserted one by one into the insulating tube to the designed length. After vacuuming, the electrodes are sealed and placed in a heating furnace to be heated until the low-temperature molten salt is completely melted and in contact with the metal electrodes. The insulating tube armored heating tube, in which the low-temperature molten salt in the insulating tube armored heating tube is completely melted, is placed into a mold and cooled to form a heating tube with an insulating tube armored low-temperature molten salt as a resistance heating element, which facilitates installation.

Claims

1. A heating tube using insulated tube armored low-temperature molten salt as a resistive heating element, characterized in that: a low-temperature molten salt tube is inserted into an insulated tube of a certain length and diameter, so that the molten salt in the insulated tube has a certain resistance value and a certain heating power under a certain voltage; metal electrodes are inserted into both ends of the insulated tube to contact the low-temperature molten salt; one end of the metal electrode contacts the low-temperature molten salt, and the other end extends out of the insulated tube and is sealed to form an insulated tube armored low-temperature molten salt heating tube using resistive heating element; when the metal electrodes are energized, the solid low-temperature molten salt is heated to melt as a resistive element, and heat is stored through a solid-liquid phase change; the temperature of the low-temperature molten salt is kept at the melting point of the low-temperature molten salt by temperature control. The heating element is used for direct or non-contact heating of the object being heated; multiple heating tubes with insulating tube armor and low-temperature molten salt as resistance heating elements are connected in series, in parallel, or in a combination of series and parallel to form a large-area, high-power heater; the heating method of the heating tubes with insulating tube armor and low-temperature molten salt as resistance heating elements is a combination of non-contact infrared radiation heating, direct contact heat conduction, and infrared radiation heating; the infrared radiation heating method is infrared heating of the object being heated by the composite material insulating tube wall mixed with high infrared radiation composite oxide powder, and infrared heating of the object being heated by the high infrared radiation composite oxide particles doped in the low-temperature molten salt.

2. According to claim 1, the insulating tube is: a polytetrafluoroethylene tube, a silicone tube, or a glass tube; the insulating tube is a circular tube or a rectangular tube.

3. According to claim 1, the insulator tube is formed by mixing 5% to 25% by volume of composite oxide powders of ferric oxide, manganese dioxide, copper oxide, chromium trioxide, and cobalt oxide with high infrared radiation coefficients and an average particle size of less than 2 micrometers during the molding process of the insulator tube to form polytetrafluoroethylene composite material and silicone composite material, which are then extruded to form polytetrafluoroethylene composite material tubes and silicone composite material tubes with high infrared radiation coefficients, so as to improve the infrared radiation heating efficiency and thermal conductivity of the heating tube with insulator tube armored low-temperature molten salt as the resistance heating element; the weight fraction of the composite oxide powder is: ferric oxide 10% to 30%, manganese dioxide 50% to 70%, copper oxide 7.5% to 12.5%, chromium trioxide 2.5% to 5%, and cobalt oxide 7.5% to 12.5%.

4. According to claim 1, the composite oxide powder is a mixture of oxides with the following weight fractions: 10%~30% ferric oxide, 50%~70% manganese dioxide, 7.5%~12.5% ​​copper oxide, 2.5%~5% chromium trioxide, and 7.5%~12.5% ​​cobalt oxide. The mixture is ground to an average particle size of less than 2 micrometers, then calcined at 1000℃~1200℃, crushed, ground again to an average particle size of less than 2 micrometers, and dried before being used in the mixing of the polytetrafluoroethylene composite material and the silicone composite material.

5. According to claim 1, the low-temperature molten salt is a low-temperature molten salt composed of two or three of sodium nitrite, sodium nitrate, and potassium nitrate, with a melting point of 137°C to 300°C. The composition of the low-temperature molten salt is determined according to the constant temperature heating temperature of the heated object based on the binary or ternary phase diagram of sodium nitrite, sodium nitrate, and potassium nitrate. The composition of the low-temperature molten salt has a melting point at the constant temperature required for the heated object, that is, the controlled temperature of the heating tube with the insulating tube armored low-temperature molten salt as the resistive heating element.

6. According to claim 1, the low-temperature molten salt is a doped low-temperature molten salt that does not change the melting point of the low-temperature molten salt. The doped low-temperature molten salt is a composite oxide particle with high infrared emissivity and a particle size of 0.2mm to 1mm, consisting of ferric oxide, manganese dioxide, copper oxide, chromium trioxide, and cobalt oxide, accounting for 40% to 65% of the volume fraction of the inner volume of the insulator tube. After the molten salt melts, it fills the gaps between the composite oxide particles. The non-conductivity and volume fraction of the composite oxide particles are used to adjust and control the resistance value of the low-temperature molten salt in the insulator tube armored heating tube, i.e., the heating power under constant voltage and to improve the infrared radiation heating efficiency of the insulator tube heater.

7. According to claim 1, the composite oxide particles are a mixture of oxides with a weight fraction of 10%~30% ferric oxide, 50%~70% manganese dioxide, 7.5%~12.5% ​​copper oxide, 2.5%~5% chromium trioxide, and 7.5%~12.5% ​​cobalt oxide, which are ground to an average particle size of less than 2 micrometers, calcined at 1000℃~1200℃, crushed and pulverized to a particle size of 0.2mm~1mm, and dried before being used in the doped low-temperature molten salt.

8. According to claim 1, the low-temperature molten salt or uniformly mixed doped low-temperature molten salt is heated until the crystal water is completely removed and then placed into a press mold to press it into a circular or rectangular cylinder with a geometric dimension smaller than the internal geometric dimension of the insulating tube and a length 1 to 2 times its geometric dimension. The circular or rectangular cylinders are then inserted one by one into the insulating tube to the designed length. After vacuuming, the electrodes are sealed and placed in a heating furnace to heat until the low-temperature molten salt is completely melted and in contact with the metal electrodes. The insulating tube armored heating tube, in which the low-temperature molten salt is completely melted, is placed into a mold and cooled to form a heating tube with an insulating tube armored low-temperature molten salt as a resistance heating element, which facilitates installation.