Heat Transfer Analysis Of New Hollow Insulation Pipe

Energy-saving and environment protection is a key factor to achive the sustainable development of national economy. Insulation is called the fifth energy. It is effective to improve the pipe insulation for energy-saving and increasing economic efficiency. Hollow insulation structure has the unique advantages in improving the insulations, reducing the corrosion and keeping the thermal characters of the teat mediums compared with the conventional coated insulation structure. However, to the best of the author’s knowledge, no data have been reported in the open literatures on the thermal properties and the heat transfer mechanism for the hollow insulation pipeline which are used at atmospheric pressure, and the structure parameter determination of supporting ribs number and thickness, air layer thickness and the external protecting tube thickness are lacks of theoretical basis to new type of hollow insulation structure. The reason why the heat-loss in hollow insulation structure in higher than the limits of national standard. Therefore, research on the thermal insulation property of hollow insulation pipeline is very important in the theory and application.Firstly, according to the references home and abroad of the hollow insulation structure research, based on the heat transfer theory and the thermal calculating method of thermal pipeline, the finite element analysis short tube model of analyzing heat loss is established by neglect the axial heat loss of the pipeline and the influence of support plate heat transfer. The heat loss of the hollow insulation pipeline and the traditional insulation structure coated by glass wool and rock wool was analyzed and calculated. The results show that, under the same thickness of insulating layer, hollow insulating pipe surface temperature and heat loss were lower than those of the conventional pipe with coated glass wool and rock wool. The hollow insulation pipe possessed good thermal insulating property compared with the conventional pipe with coated glass wool and rock wool, and the novel type of thermal insulation structure can be used for heat preservation of conduit.Secondly,in order to make the heat transfer more close to the reality, there is need to consider the temperature changes of the axial direction and the influence of the supporting ribs structure and the thickness of external protecting on the heat-loss of tube. On these basis,a finite elements analysis model of heat loss in the long tube of hollow insulation structure was established. And the simulated calculation has been used to analyses the heat loss of the pipeline by using Fluent software. The results show that, heat loss for thermal insulation increase with increase of the numbers and the thickness of the ribs, on the premise of meeting the structural strength, the number of ribs in hollow insulation structure as low as possible; With the increase of air layer thickness, heat loss shows the tendency of increase with decrease of the first, when the thickness of air layer was about 20mm, it reached to the minimal value. The excessive large thickness in hollow insulation structure is not conductive to the thermal insulation. When the heat-loss is lower than national standard value 163W/m2, the air layer thickness should be selected in the range of 16-25mm; With the increase of outer sheath thickness, the heat loss decrease first and then increase, on the premise of meeting the structural strength and economical requirement, the thickness of outer sheath should be selected in the range of 1-2.5mm.Finally, the structural parameters of hollow insulation pipeline were optimized by using orthogonal design method, and the results of experiment were analyzed by using maximum difference method. It concludes the prominent factor of the structure parameters that affect the heat-loss of hollow insulation pipeline. The greatest factor is the numbers of supporting ribs. The thickness of supporting ribs is the second. The thickness of air-layer is the third. And the last is the thickness of external protecting tube. Under the condition of heating season working, the heat-loss of optimal parameter array structure is 126.81 W/m2, which is better than the national standard.