PRESSURE DROP CHARACTERISTICS OF R410A-OIL MIXTURE FLOW BOILING IN SMALL SMOOTH TUBES

Gao, Yifeng,Deng, Bin,Ding, Guoliang,Hu, Haitao,Huang, Xiangchao The Society of Air-Conditioning and Refrigerating 2010 International Journal Of Air-Conditioning and Refr Vol.18 No.2

This study presents experimental frictional pressure drop for R410A/oil mixture flow boiling in small horizontal smooth tubes with inside diameters of 4.18mm and 2.0 mm. Experimental conditions cover nominal oil concentrations from 0 to 5%. The test results show that the presence of oil enhances two-phase frictional pressure drop about 0-120% and 0-90% at present tee conditions for 4.18mm I.D. smooth tube and 2.0mm I.D. smooth tube, respectively, and the enhanced effect is more evident at higher vapor qualities where the local oil concentrations are higher. A new correlation to predict the local frictional pressure drop of R410A/oil mixture flow boiling inside conventional size and small smooth tubes is developed based on local properties of refrigerant-oil mixture, and the experimental data of 4.18mm I.D. and 2.0mm I.D. smooth tubes and that of 6.34mm I.D. smooth tube (Hu et al., 2008) are well-correlated with the new correlation.

Strength Prediction of a Single Tooth Bound to Composite Pre-tightened Tooth Connection (PTTC) Joints based on Different Failure Criteria

Yifeng Gao,Fei Li,Qilin Zhao,Jiangang Gao,Yubo Hu 대한토목학회 2019 KSCE Journal of Civil Engineering Vol.23 No.8

A method capable to predict the strength of single tooth bound to composite pre-tightened tooth connection (PTTC) joints is presented. The proposed method uses four representative failure criteria: max-stress, Tsai-Hill, Tsai-Wu and Hashin. The characteristic length method is also used to obtain prediction strengths. Three types of experiments of single PTTC joints were conducted using the following variations: 1) tooth depth, 2) tooth length, and 3) pre-tightened force. The experimental results were compared with the two-dimensional failure envelope diagram calculated using the four representative failure criteria. The physical nature and the strength predictive ability of each criterion were investigated. The obtained results show that the shear failure mode of single PTTC joint was accurately predicted by all four failure criteria. However, the Tsai-Wu criterion when compared to Maximum Stress, Tsai-Hill and Hashin criteria, exhibits better accuracy regarding the prediction strength of single PTTC joints, this is due to the fact that the Tsai-Wu criterion reflects more accurately the increase in the interlaminar shear strength caused by the transverse compressive stress.

Study on load distribution ratio of composite pre-tightened tooth joint by shear nonlinearity

Yifeng Gao,Fei Li,Qilin Zhao,Jiangang Gao,Lin Shi,Zhiqin Zhao 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.40 No.5

Load distribution has a great influence on the mechanical properties of composite pre-tightened multi-tooth connection. To obtain the load distribution mechanism of composite pre-tightened multi-tooth joints, the multi-tooth joints were studied by experimental and theoretical methods. First, an experimental study was conducted on three-tooth specimens with different tooth depths and tooth lengths, and the failure mode, bearing capacity and load distribution mechanism of the specimens were obtained. Then, based on the nonlinear constitutive of interlaminar shear, an analytical model for load distribution of composite pre-tightened multi-tooth joint was proposed to research the multi-tooth load distribution mechanism. Finally, the theoretical and experimental results were compared. The research showed: (1) The theoretical results of the multi-tooth load distribution ratio were in good agreement with that of the experimental results, the maximum error between the theoretical value and the experimental value of the three-tooth joint was 17.44%, and the minimum error was only 2.35%; (2) The load distribution ratio of composite pre-tightened multi-tooth was uneven, for three-tooth joints, the values of load distribution ratio from large to small were: the first tooth, the third tooth and the second tooth.; (3) Multi-tooth load distribution ratio changed with the change of external load. The change of load distribution ratio was obvious in the early stage of loading, and tended to be gentle in the later stage of loading.

PRESSURE DROP CHARACTERISTICS OF R410A-OIL MIXTURE FLOW BOILING IN SMALL SMOOTH TUBES

YIFENG GAO,BIN DENG,GUOLIANG DING,HAITAO HU,XIANGCHAO HUANG 대한설비공학회 2010 International Journal of Air-Conditioning and Refr Vol.18 No.2

This study presents experimental frictional pressure drop for R410A/oil mixture flow boiling in small horizontal smooth tubes with inside diameters of 4.18 mm and 2.0 mm. Experimental conditions cover nominal oil concentrations from 0 to 5%. The test results show that the presence of oil enhances two-phase frictional pressure drop about 0–120% and 0–90% at present test conditions for 4.18 mm I.D. smooth tube and 2.0 mm I.D. smooth tube, respectively, and the enhanced effect is more evident at higher vapor qualities where the local oil concentrations are higher. A new correlation to predict the local frictional pressure drop of R410A/oil mixture flow boiling inside conventional size and small smooth tubes is developed based on local properties of refrigerant–oil mixture, and the experimental data of 4.18 mm I.D. and 2.0 mm I.D. smooth tubes and that of 6.34 mm I.D. smooth tube (Hu et al., 2008) are well-correlated with the new correlation.

SIMULATION-BASED DESIGN METHOD FOR ROOM AIR CONDITIONER WITH SMALLER DIAMETER COPPER TUBES

Guoliang Ding,TAO REN,YONGXIN ZHENG,YIFENG GAO,JI SONG 대한설비공학회 2012 International Journal Of Air-Conditioning and Refr Vol.20 No.3

Promoting the use of smaller diameter tube in room air conditioner is bene¯cial to reduce copper consumption and refrigerant charge, but may cause reduction of air conditioner performance, so a design method is needed. This paper presents a simulation-based design method for air conditioner with smaller diameter tube. The new method combines heat exchanger simulator and knowledge-based evolution method optimizer for designing air conditioner heat exchanger with smaller diameter tube. The simulation-based design method is illustrated in detail by an air conditioner of replacing 7mm tube indoor unit heat exchanger and 9.52mm tube outdoor unit heat exchanger with 5mm tube. Case study shows that the cost of the designed air conditioner with 5mm copper tube is 17.3% lower than that of the original one while the performance deviation between these two air conditioners is less than 0.7%.

Static performance of a new GFRP–metal string truss bridge subjected to unsymmetrical loads

Dongdong Zhang,Jiaxin Yuan,Qilin Zhao,Feng Li,Yifeng Gao,Ruijie Zhu,Zhiqin Zhao 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.35 No.5

A unique lightweight string truss deployable bridge assembled by thin-walled fiber reinforced polymer (FRP) and metal profiles was designed for emergency applications. As a new structure, investigations into the static structural performance under the serviceability limit state are desired for examining the structural integrity of the developed bridge when subjected to unsymmetrical loadings characterized by combined torsion and bending. In this study, a full-scale experimental inspection was conducted on a fabricated bridge, and the combined flexural–torsional behavior was examined in terms of displacement and strains. The experimental structure showed favorable strength and rigidity performances to function as deployable bridge under unsymmetrical loading conditions and should be designed in accordance with the stiffness criterion, the same as that under symmetrical loads. In addition, a finite element model (FEM) with a simple modeling process, which considered the multi segments of the FRP members and realistic nodal stiffness of the complex unique hybrid nodal joints, was constructed and compared against experiments, demonstrating good agreement. A FEM-based numerical analysis was thereafter performed to explore the effect of the change in elastic modulus of different FRP elements on the static deformation of the bridge. The results confirmed that the change in elastic modulus of different types of FRP element members caused remarkable differences on the bending and torsional stiffness of the hybrid bridge. The global stiffness of such a unique bridge can be significantly enhanced by redesigning the critical lower string pull bars using designable FRP profiles with high elastic modulus.

Study on grinding mechanism and machining technology of Si3N4 ceramic spindle

Songhua Li,Chuang Li,Minghe Liu,Yonghua Wang,Chuang Zuo,Hao Zhang,Yifeng Gao 한양대학교 청정에너지연구소 2023 Journal of Ceramic Processing Research Vol.24 No.6

In order to improve the machining accuracy of the cylindrical surface of silicon nitride ceramic spindle, the machining technologyof the cylindrical surface of ceramic spindle was studied by high-speed universal cylindrical grinder in this experiment. Firstly, the primary and secondary order of the influence of various factors on the surface roughness of ceramic spindleis determined by orthogonal experiment, then the influence law of single grinding parameter on the surface roughness ofceramic spindle is explored by single factor experiment, and the prediction model of the grinding surface roughness value ofceramic spindle is calculated by numerical analysis software, and finally the optimal processing parameters of the cylindricalsurface of ceramic spindle are obtained. The experimental results show that the grinding surface roughness of silicon nitrideceramic spindle first decreases and then increases with the increase of grinding wheel linear speed and workpiece linearspeed, and then increases with the increase of transverse feed speed and axial feed speed. The relative error between the predictedvalue of the prediction model and the actual measured value is less than 5%, which shows that the prediction modelhas a good prediction effect and provides a theoretical basis for actual machining