Science and Technology and Engineering Research on the Influence of Water Content on the Heat Transfer of Low Temperature Pipe Cooling Structure Dai Yong Li Zhenqin Zhu Shifeng Zhuang Xuewu And light hydrocarbon production. Therefore, analyzing the influence of water content on the heat transfer of the low-temperature pipeline cooling structure can provide a scientific basis for the future transformation of low-temperature devices and pipeline cooling. By establishing the heat transfer model of the water-cooling low-temperature pipeline insulation structure, the influence of water content on the heat transfer of the low-temperature pipeline insulation structure under different insulation thicknesses and different pipeline medium temperatures is analyzed. The research results show that: (1) At the same pipe diameter and medium temperature, with the increase of water content in the cold storage structure, the heat flux density becomes larger and the cold loss becomes larger; similarly, when the water content is the same, with the increase of the thickness of the cold storage , The heat flux density is reduced and the cold loss is reduced. (2) With the same pipe diameter, insulation thickness and medium temperature, as the water content of the insulation structure increases, the heat flux density becomes larger and the cooling loss becomes larger; similarly, when the water content is the same, with the medium in the pipeline As the temperature decreases, the heat flux density becomes larger and the cold loss becomes larger.
Affecting the classification number TE832.34 of the Chinese Library Classification; the code A China is facing a long-term energy problem, and the task of energy saving and consumption reduction is very critical. Due to the large temperature difference between the low temperature unit of the natural gas processing device and the external environment, there is a 120 ° C heat transfer temperature difference between the natural gas and the outside air in the equipment and pipelines, and the heat transfer power is large. The cooling effect of low-temperature equipment and pipelines directly affects the energy consumption of the device and the output of light hydrocarbons. Through on-site investigation, it was found that the freezing surface of the 15 sets of low-temperature equipment and pipelines of the natural gas processing equipment of the branch company existed to varying degrees. It can be seen that the ambient air has a heat absorbing effect on it and the system has a certain amount of cooling loss.
Sun Fenghai1 started from the selection principles of the performance and economy of cold insulation materials, focusing on the advantages of using foam glass and rigid polyurethane composite cold insulation structures below -30 C, and combined with practical experience, discussed common cold insulation failures in construction The main reason. Professor Wu Guozhong of Northeast Petroleum University25 conducted a series of studies based on the problems existing in the pipeline heat loss test process, and proposed the thermocouple calibration principle, infrared imager error correction principle, and pipeline heat transfer evaluation model during the measurement process. In this paper, by establishing the heat transfer model of the cooling structure of the water-containing cryogenic pipeline, the analysis of the water-containing cryogenic tube received on January 12, 2012. First received: Dai Yong (1975―), male, senior engineer, research direction: natural gas com. The influence of heat will provide a scientific basis for the related transformation of low-temperature equipment and pipeline cooling in the future.
1 Heat transfer model of water-containing low-temperature pipeline insulation structure 1.1 Physical model The pipeline of water-containing insulation structure is the analysis object, and the heat transfer process of the structure is convection heat transfer between the fluid and the inner wall of the pipe from the outside to the inside. Heat conduction process and convection and radiation heat transfer process with the atmospheric environment. For ease of calculation, the model is simplified to the heat conduction process from the inner wall to the outer wall of the cold insulation material and the convection heat transfer process between the outer wall and the atmospheric environment.
Physical model of the cooling structure of water-containing cryogenic pipeline 1.2 Mathematical model The boundary conditions are: external ambient temperature, ° C is the convection heat transfer coefficient, WKmK); blackness; black body radiation constant, the value is 5.67x10-8W / (m2 K4) ; A is the thermal conductivity of the water-containing cold insulation layer material at the use temperature, WmK); A1 is the thermal conductivity of the cold insulation layer material at the use temperature, WmK); A2 is the thermal conductivity of water at the use temperature, WKmK); X1 , 2 are the ratio of the quality of the cold insulation material and water to the total mass of the cold insulation structure containing water; r., R1 are the radius of the pipe, the cylindrical equipment and the radius of the cold insulation layer, m. 2 numerical simulation 2.1 The simulation conditions of the effect of heat transfer of the cold insulation structure of the low temperature pipeline: the diameter of the low temperature pipeline is DN200mm, the cold insulation structure is a single layer, and the nitrile rubber polymer is used. The thermal conductivity of the pipeline is 43Wmk), the density is 7790kg / m3, the specific heat capacity is 470 / (kg.K), the medium temperature is -60 ° C; the thermal conductivity of the pipeline protective layer is 81.1WmK), the density is 7 870kg / m3, and the specific heat capacity 455 / (kgK); the thermal conductivity of the thermal insulation structure is the weighted average of the thermal conductivity of the thermal insulation material and the thermal conductivity of water or ice, and the cold insulation thickness is 25mm, 75mm, 100mm, 150mm, and the low temperature of water content is 0, 0.1, 0.5, 0.8 The pipeline carries out the numerical simulation calculation of heat transfer of the heat preservation structure.
It can be seen that with the same pipe diameter and medium temperature, as the water content of the cold storage structure increases, the heat flux density becomes larger and the cold loss becomes larger. Similarly, when the water content is the same, as the thickness of the cold storage increases, the heat flux density decreases Small, the cold loss is reduced. The international standard standard cold loss is 32W / m263. Therefore, when the medium temperature is -60 ° C, the cold insulation thickness is 150mm, 100mm, 75mm, the moisture content is 0.1 and the cold insulation thickness is 150mm, and the moisture content is 0.5, the cold insulation structure is temporarily Not invalidated.
Change chart of heat flux density at different insulation thicknesses Heat transfer density diagram at different medium temperatures With the decrease of insulation thickness and the increase of water content, the insulation structure gradually begins to fail.
2.2 The effect of water content at different medium temperatures on the heat transfer of the low-temperature pipeline cooling structure simulation conditions: the basic conditions are the same as 2.1. The low-temperature pipeline insulation thickness is 100mm, and the pipeline medium temperature is -20 ° C, -60 ° C, -100 ° C, -200 ° C, the numerical simulation calculation is carried out when the moisture content of the cold storage structure is 0, 0.1, 0.5 and 0.8, and the change of heat flux density is as shown.
It can be seen that with the same pipe diameter, insulation thickness and medium temperature, as the water content of the insulation structure increases, the heat flux density becomes larger and the cooling loss becomes larger. Similarly, when the water content is the same, with the medium in the pipeline As the temperature decreases, the heat flux density becomes larger and the cold loss becomes larger. When the temperature of the pipeline medium is -20 ° C, -60 ° C, -100C, and the moisture content is 0.1, and the temperature of the pipeline medium is -20C, and the moisture content is 0.5, the cooling structure has not failed temporarily. With the decrease of temperature and the increase of water content, the cooling structure gradually began to fail.
3 Conclusion (1) With the same pipe diameter and medium temperature, with the increase of water content in the cold storage structure, the heat flux density becomes larger and the cold loss becomes larger. Similarly, when the water content is the same, with the increase of the thickness of the cold storage, the heat flow The density is reduced and the cold loss is reduced.
(2) With the same pipe diameter, insulation thickness and medium temperature, as the water content of the insulation structure increases, the heat flux density becomes larger and the cooling loss becomes larger; similarly, when the water content is the same, with the medium in the pipeline As the temperature decreases, the heat flux density becomes larger and the cold loss becomes larger.
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