In order to investigate the effects of freezing and thawing on the compressibility of fine-grained soils, freezing and thawing tests and subsequent compression tests with fine-grained soils in an oedometer were carrie...In order to investigate the effects of freezing and thawing on the compressibility of fine-grained soils, freezing and thawing tests and subsequent compression tests with fine-grained soils in an oedometer were carried out. During the freezing, a part of the soils is loosened and another part is over-consolidated under the freezing pressure σE. The compression curves after the freezing and thaw consolidation are neither different from the normal consolidation curve nor from the rebound curve of an unfrozen soil, until the consolidation pressure σz = σE is arrived. Based on the experimental results, a theoretical model has been devel- oped to predict the frost heaves, the thaw-settlements and the compressive deformations of fine-grained soils after the thaw consolidation. The theoretical results are very close to the experimental results.展开更多
A new experimental device has been developed for analyzing compression load deflection of the door seal by using stereovision theory. Precision instruments of optical grating and force sensor are also integrated in th...A new experimental device has been developed for analyzing compression load deflection of the door seal by using stereovision theory. Precision instruments of optical grating and force sensor are also integrated in this device. Force-displacement response characteristics of compression at varied speed can be controlled. Solid foundations for characteristic and structure as well as optimization design of the car door seal are elucidated.展开更多
Fluid pressure variations due to process fluctuations or balance drum seal degradation can result in rotor thrust increasing that may jeopardize thrust bearing and compressor’s reliability. Also, the leakage flow thr...Fluid pressure variations due to process fluctuations or balance drum seal degradation can result in rotor thrust increasing that may jeopardize thrust bearing and compressor’s reliability. Also, the leakage flow through balance drum seal can seriously affect the efficiency of compressor. A method that can improve both the efficiency and reliability of centrifugal compressor is presented. The method focused on rotor thrust control and balance drum seal upgrading. The low leakage feature of Dry-Gas-Seal（DGS）, high reliability of labyrinth, and the feasibility of upgrading existing structure are taken into account at the same time to design a combined labyrinth-dry gas seal system on the balancing drum. Based on the combined seal system, a Fault Self-Recovering（FSR） system for the fault of rotor shaft displacement is introduced to assure the safety and reliability of centrifugal compressor. The modern Computational Fluid Dynamics（CFD） is used to validate this envision. The numerical result and relevant information indicate that the combined sealing system could improve the efficiency of the centrifugal compressor by about 4%.展开更多
A numerical model to predict the temperature field in a hermetic reciprocating compressor for household refrigeration appliances is presented in this work. The model combines a high resolution three-dimensional heat c...A numerical model to predict the temperature field in a hermetic reciprocating compressor for household refrigeration appliances is presented in this work. The model combines a high resolution three-dimensional heat conduction formulation of the compressor＇s solid parts, a three-dimensional CFD （computational fluid dynamics） approach for the gas line domain and lumped formulations of the shell gas and the lubrication oil. Heat transfer coefficients are determined by applying CFD to the gas line side and correlations from the literature on the shell gas and oil side, respectively. The valve in the gas line simulation is modelled as a parallel moving fiat plate. By means of an iterative loop the temperature field of the solid parts acts as boundary condition for the CFD calculation of the gas line which returns a cycle averaged quantity of heat to the solid parts. Using an iteration method which is based on the temperature deviation between two iteration steps, the total number of iterations and consequently the computational time can be reduced. The loop is continued until a steady-state temperature field is obtained. Calculated temperatures of the solid parts are verified by temperature measurements of a calorimeter test bench.展开更多
The suction muffler of hermetic reciprocating compressors is installed in order to attenuate the noise generated by the gas pulsation of the flow through the suction valve. However, the installation of the suction muf...The suction muffler of hermetic reciprocating compressors is installed in order to attenuate the noise generated by the gas pulsation of the flow through the suction valve. However, the installation of the suction muffler affects the operation of the compressor owing to gas pressure drop, which causes volumetric and energetic efficiency loss due to the gas specific volume augmentation. Therefore, there is a compromise between sound attenuation and pressure drop increase, which has to be taken into account by compressor designers. In this work, it presents a numerical solution to the flow through a suction muffler in order to analyze the pressure field and point out the main contributions to the overall pressure drop of the flow. A commercial CFD （computational fluid dynamics） code was used to perform the numerical simulations and the results were validated by using experimental data. After analyzing the pressure field, the geometry of the muffler was modified intending to decrease the flow pressure drop. The geometric modification produced a 28% reduction on the overall pressure drop, without influencing the sound attenuation.展开更多
To enhance the reliability and to extend service life of packing rings, tribological and sealing perfor- mances are investigated based on the experimental results. Friction force, leakage rate and power consumption of...To enhance the reliability and to extend service life of packing rings, tribological and sealing perfor- mances are investigated based on the experimental results. Friction force, leakage rate and power consumption of three materials of pressure packing seals are measured in a refitted vertical gas compressor. The rings are made of common filled polytetrafiuroethylene （Filled PTFE）, PTFE reinforced with 30% mass fraction carbon fiber （30%CF^PTFE）, and carbon-carbon composites infiltrated with PTFE （C/C＋PTFE）, respectively. It is found that packing rings will periodically vibrate with the periodic vibration of pressure packing after the travel direction of motion abruptly turns to the reverse direction. Furthermore, the amplitude of vibration slows down with the increasing crank angle. Approximate value of friction force is available by multiple-point fast Fourier transformation （FFT） employed to process the experimental results by reducing the impact of vibration to a great extent. Of three materials of rings employed in experiments, Filled PTFE presents minimal leakage rate accom- panied with maximum power consumption. And 30%CF＋PTFE exhibits minimum friction power and moderate leakage rate. As for C/C＋PTFE, its high mechanical and thermal properties are favorable factors to enhance the ability of operating under high pressure and velocity and to improve the wear resistance. Unfortunately, this also leads to a large leakage rate. Comprehensive consideration should be taken into to evaluate the availability, reliability and service life for a type of packing ring under dry running conditions.展开更多
文摘In order to investigate the effects of freezing and thawing on the compressibility of fine-grained soils, freezing and thawing tests and subsequent compression tests with fine-grained soils in an oedometer were carried out. During the freezing, a part of the soils is loosened and another part is over-consolidated under the freezing pressure σE. The compression curves after the freezing and thaw consolidation are neither different from the normal consolidation curve nor from the rebound curve of an unfrozen soil, until the consolidation pressure σz = σE is arrived. Based on the experimental results, a theoretical model has been devel- oped to predict the frost heaves, the thaw-settlements and the compressive deformations of fine-grained soils after the thaw consolidation. The theoretical results are very close to the experimental results.
基金Supported by Science and Technology Development Foundation of Shanghai Automotive Industry (1315A)
文摘A new experimental device has been developed for analyzing compression load deflection of the door seal by using stereovision theory. Precision instruments of optical grating and force sensor are also integrated in this device. Force-displacement response characteristics of compression at varied speed can be controlled. Solid foundations for characteristic and structure as well as optimization design of the car door seal are elucidated.
基金Supported by the National Natural Science Foundation of China （No. 50575016 and No. 50375014）
文摘Fluid pressure variations due to process fluctuations or balance drum seal degradation can result in rotor thrust increasing that may jeopardize thrust bearing and compressor’s reliability. Also, the leakage flow through balance drum seal can seriously affect the efficiency of compressor. A method that can improve both the efficiency and reliability of centrifugal compressor is presented. The method focused on rotor thrust control and balance drum seal upgrading. The low leakage feature of Dry-Gas-Seal（DGS）, high reliability of labyrinth, and the feasibility of upgrading existing structure are taken into account at the same time to design a combined labyrinth-dry gas seal system on the balancing drum. Based on the combined seal system, a Fault Self-Recovering（FSR） system for the fault of rotor shaft displacement is introduced to assure the safety and reliability of centrifugal compressor. The modern Computational Fluid Dynamics（CFD） is used to validate this envision. The numerical result and relevant information indicate that the combined sealing system could improve the efficiency of the centrifugal compressor by about 4%.
文摘A numerical model to predict the temperature field in a hermetic reciprocating compressor for household refrigeration appliances is presented in this work. The model combines a high resolution three-dimensional heat conduction formulation of the compressor＇s solid parts, a three-dimensional CFD （computational fluid dynamics） approach for the gas line domain and lumped formulations of the shell gas and the lubrication oil. Heat transfer coefficients are determined by applying CFD to the gas line side and correlations from the literature on the shell gas and oil side, respectively. The valve in the gas line simulation is modelled as a parallel moving fiat plate. By means of an iterative loop the temperature field of the solid parts acts as boundary condition for the CFD calculation of the gas line which returns a cycle averaged quantity of heat to the solid parts. Using an iteration method which is based on the temperature deviation between two iteration steps, the total number of iterations and consequently the computational time can be reduced. The loop is continued until a steady-state temperature field is obtained. Calculated temperatures of the solid parts are verified by temperature measurements of a calorimeter test bench.
文摘The suction muffler of hermetic reciprocating compressors is installed in order to attenuate the noise generated by the gas pulsation of the flow through the suction valve. However, the installation of the suction muffler affects the operation of the compressor owing to gas pressure drop, which causes volumetric and energetic efficiency loss due to the gas specific volume augmentation. Therefore, there is a compromise between sound attenuation and pressure drop increase, which has to be taken into account by compressor designers. In this work, it presents a numerical solution to the flow through a suction muffler in order to analyze the pressure field and point out the main contributions to the overall pressure drop of the flow. A commercial CFD （computational fluid dynamics） code was used to perform the numerical simulations and the results were validated by using experimental data. After analyzing the pressure field, the geometry of the muffler was modified intending to decrease the flow pressure drop. The geometric modification produced a 28% reduction on the overall pressure drop, without influencing the sound attenuation.
文摘To enhance the reliability and to extend service life of packing rings, tribological and sealing perfor- mances are investigated based on the experimental results. Friction force, leakage rate and power consumption of three materials of pressure packing seals are measured in a refitted vertical gas compressor. The rings are made of common filled polytetrafiuroethylene （Filled PTFE）, PTFE reinforced with 30% mass fraction carbon fiber （30%CF^PTFE）, and carbon-carbon composites infiltrated with PTFE （C/C＋PTFE）, respectively. It is found that packing rings will periodically vibrate with the periodic vibration of pressure packing after the travel direction of motion abruptly turns to the reverse direction. Furthermore, the amplitude of vibration slows down with the increasing crank angle. Approximate value of friction force is available by multiple-point fast Fourier transformation （FFT） employed to process the experimental results by reducing the impact of vibration to a great extent. Of three materials of rings employed in experiments, Filled PTFE presents minimal leakage rate accom- panied with maximum power consumption. And 30%CF＋PTFE exhibits minimum friction power and moderate leakage rate. As for C/C＋PTFE, its high mechanical and thermal properties are favorable factors to enhance the ability of operating under high pressure and velocity and to improve the wear resistance. Unfortunately, this also leads to a large leakage rate. Comprehensive consideration should be taken into to evaluate the availability, reliability and service life for a type of packing ring under dry running conditions.
