The results of researches of condensation processes in the vapour channel similar to the Laval nozzle of short linear heat pipes are presented. Capacitive sensors are additionally installed in cooled top covers of the...The results of researches of condensation processes in the vapour channel similar to the Laval nozzle of short linear heat pipes are presented. Capacitive sensors are additionally installed in cooled top covers of the heat pipes, and electromagnetic pulses were supplied to them from the external generator. At heating the heat pipe evaporator, starting from a certain thermal power threshold value, electromagnetic pulses became modulated. It is related with the formations of the boiling process in the capillary-porous evaporator and large amount of vapour over it. Boiling process results in rapid increase of the pressure under which the average temperature of the evaporator occurs to be less than the boiling temperature of the working fluid under increased pressure. Considering condensation of excess vapour, this leads to repeated initiation and extinction of the boiling process in the evaporator, which reflects in pressure pulsations in the vapour channel. Pressure pulsations cause modulating effect on electromagnetic impulses. Pulsations frequencies are measured as well as their dependence from overheating of the evaporator. Using the capacitive sensors and a special electronic equipment we measured the local thickness of the working fluid at the condensing surface inside the heat pipes. Time-averaged values of the condensate film thickness are measured, depending on the heat load on the capillary-porous evaporator. The measurement error does not exceed 2 × 10–3 mm. It is demonstrated that the condensate film thickness lessens sharply with the increase of the heat load on the evaporator of a Laval-like low-temperature heat pipe, while the heat resistance of the film on the condensing surface reaches 60% of the total heat resistance of heat pipe with the capillary-porous evaporator.展开更多
In the framework of finite deformation theory, the burst failure analysis of end-opened defect-free pipes with plastic anisotropy under internal pressure is carried out. The analytical solutions of burst pressure and ...In the framework of finite deformation theory, the burst failure analysis of end-opened defect-free pipes with plastic anisotropy under internal pressure is carried out. The analytical solutions of burst pressure and the corresponding equivalent stress and strain are obtained for thin-walled pipes, which can take into account the effects of material plastic anisotropy and strain hardening exponent. The influences of plastic anisotropy on the burst pressure and the corresponding equivalent stress and strain are discussed. It is shown that the burst pressure and the corresponding equivalent stress and strain are dependent upon the plastic anisotropy of material, and the degree of dependence is related to the strain hardening exponent of material. In addition, the effects of the strain hardening exponent on burst failure are investigated.展开更多
Crack opening displacement(COD) was applied to characterize the fracture initiation of the tough high density polyethylene. Normal single side notched three point bend specimens and silica rubber replica techniques ...Crack opening displacement(COD) was applied to characterize the fracture initiation of the tough high density polyethylene. Normal single side notched three point bend specimens and silica rubber replica techniques were used to study the characteristic COD of high density polyethylene pipe and its butt fusion joints including the weld fusion zone and heat affected zone at different temperature from -78 ℃ to 20 ℃ . Testing results show that the characteristic COD appears to depend on the structural features that are determined by welding process and the testing temperature. As the temperature is lowered, the characteristic COD of all zones studied decreases. Because the welding process significantly changes some structural feature of the material, characteristic COD of the weld fusion zone is the smallest one among those of the three zones. The results can be used for the engineering design and failure analysis of HDPE pipe.展开更多
文摘The results of researches of condensation processes in the vapour channel similar to the Laval nozzle of short linear heat pipes are presented. Capacitive sensors are additionally installed in cooled top covers of the heat pipes, and electromagnetic pulses were supplied to them from the external generator. At heating the heat pipe evaporator, starting from a certain thermal power threshold value, electromagnetic pulses became modulated. It is related with the formations of the boiling process in the capillary-porous evaporator and large amount of vapour over it. Boiling process results in rapid increase of the pressure under which the average temperature of the evaporator occurs to be less than the boiling temperature of the working fluid under increased pressure. Considering condensation of excess vapour, this leads to repeated initiation and extinction of the boiling process in the evaporator, which reflects in pressure pulsations in the vapour channel. Pressure pulsations cause modulating effect on electromagnetic impulses. Pulsations frequencies are measured as well as their dependence from overheating of the evaporator. Using the capacitive sensors and a special electronic equipment we measured the local thickness of the working fluid at the condensing surface inside the heat pipes. Time-averaged values of the condensate film thickness are measured, depending on the heat load on the capillary-porous evaporator. The measurement error does not exceed 2 × 10–3 mm. It is demonstrated that the condensate film thickness lessens sharply with the increase of the heat load on the evaporator of a Laval-like low-temperature heat pipe, while the heat resistance of the film on the condensing surface reaches 60% of the total heat resistance of heat pipe with the capillary-porous evaporator.
文摘In the framework of finite deformation theory, the burst failure analysis of end-opened defect-free pipes with plastic anisotropy under internal pressure is carried out. The analytical solutions of burst pressure and the corresponding equivalent stress and strain are obtained for thin-walled pipes, which can take into account the effects of material plastic anisotropy and strain hardening exponent. The influences of plastic anisotropy on the burst pressure and the corresponding equivalent stress and strain are discussed. It is shown that the burst pressure and the corresponding equivalent stress and strain are dependent upon the plastic anisotropy of material, and the degree of dependence is related to the strain hardening exponent of material. In addition, the effects of the strain hardening exponent on burst failure are investigated.
文摘Crack opening displacement(COD) was applied to characterize the fracture initiation of the tough high density polyethylene. Normal single side notched three point bend specimens and silica rubber replica techniques were used to study the characteristic COD of high density polyethylene pipe and its butt fusion joints including the weld fusion zone and heat affected zone at different temperature from -78 ℃ to 20 ℃ . Testing results show that the characteristic COD appears to depend on the structural features that are determined by welding process and the testing temperature. As the temperature is lowered, the characteristic COD of all zones studied decreases. Because the welding process significantly changes some structural feature of the material, characteristic COD of the weld fusion zone is the smallest one among those of the three zones. The results can be used for the engineering design and failure analysis of HDPE pipe.
