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"Gas expanders"
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Expanders for oil and gas operations
Filled with effective methods for recovering gas energy using expanders, this practical resource offers in-depth details on different types of expanders, addressing the background, mechanical design features, design and operating requirements, operational processes, and potential problems for each class expander.
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Experimental investigation of efficient and safe heat pump operation with model-based superheat control
Heat pumps are crucial for the electrification of heating demand and are a key component in the transition towards sustainable energy systems. To maximize their contribution to reducing CO2 emissions, heat pumps must be operated efficiently. An efficient operation of the heat pump reduces the electric consumption of the heat pump’s compressor. The use of electrically controllable components, like compressor, evaporator fan and expansion valve, allows for variable control of heat pumps. The control of suction line superheat is particularly important to ensure safe operation and maximize efficiency. The superheat is typically controlled by a PI-Controller using a superheat setpoint that ensures safe operation. Existing literature lacks experimental evaluation of model-based superheat control for heat pumps utilizing natural refrigerants. This paper introduces a model-based feed-forward control strategy for superheat regulation in a heat pump using propane (R290) as a natural refrigerant. The developed controller uses data-driven models to predict the optimal expansion valve opening degree and superheat setpoint under consideration of disturbances. The performance of the developed controller is evaluated on a self-built heat pump test bench in a realistic scenario and compared to a conventional PI-controller. The results show that the feed-forward controller achieves more stable and precise superheat control than the PI-controller, with reduced over- and undershooting during transient phases. Compared to a PI-controller, the efficiency can be improved by up to 8.2% and the IAE by up to 31.6%. In future work, the data-driven models can be improved by e.g. online-learning.
Journal Article
Simulation study on the performance of heat pump air conditioning system for pure electric vehicles
This study constructed an experimental bench for a R134a heat pump air conditioning system in a commercial electric vehicle. Based on the results from the experimental bench, the simulation model of the heat pump air conditioning system developed by AMESim was calibrated, and its reliability was verified. As the compressor and electronic expansion valve (EXV) are essential control components of the heat pump air conditioning system, simulations were conducted to investigate the impact of EXV opening on performance parameters such as refrigerating capacity, subcooling, superheat compressor power consumption, and Coefficient of Performance (COP) at different compressor speeds. The findings indicate that EXV opening significantly affects system subcooling and COP, and higher COP can be obtained by controlling the subcooling of the system through the EXV.
Journal Article
Design and Application of Downhole Drilling Mud Pulse Signal Transmission System
Time-efficient measurement of undisturbed formation through measurement while drilling technology is an effective means to improve drilling efficiency in deep formations and increase the drilling-encounter ratio of reservoirs. Based on the application and development trend of existing downhole signal transmission technology, a pulse signal transmission system of downhole mud while drilling is designed. The system pulse generation device adopts the structure of a positive pulse generator, which is through the internal driving circuit and hydraulic circuit of the device to drive the valve head to move to generate a mud pulse signal while using the design of a limit switch to optimize the expansion spacing of the valve head so that the generated pulse signal amplitude is close. The system uses combined encoding as the encoding method, while the ground part of the system is designed to monitor and process the collected signals. Finally, the transmission capability and accuracy of the system are tested through field experiments, and the field results show that the system can work smoothly in the downhole environment to transmit downhole data to the wellhead with small errors, which meets the design requirements and field requirements. The field applications are carried out in several wells, such as the Shixi 105 well. The results show that the system has good downhole pulse signal transmission functions such as borehole inclination measurement, which helps to promote the development of existing drilling measurement technology.
Journal Article
Can the pinwheeling index serve as a surrogate for accelerated leaflet degeneration in transcatheter heart valves?
Transcatheter heart valve (THV) replacement is an advancing field, with various valve designs incorporating features like flexible frames to improve valve hemodynamics, durability, and patient outcomes. Leaflet pinwheeling, a common metric, is thought to negatively impact long-term durability. This study investigates the pinwheeling index and its correlation with stress distribution across different THV designs. Three THV designs were created using an optimization framework, each with a nominal size of 26-mm and varying leaflet coaptation heights of 10-mm, 13-mm, and 16-mm. Each valve design was evaluated under two conditions: one with a rigid frame and one with a flexible frame. The valves were implanted with a 90 % area expansion ratio, and their performance was assessed by examining key mechanical parameters, including the pinwheeling index and maximum in-plane principal stress under a diastolic loading condition. At a coaptation height of 10-mm, the pinwheeling index was 0 % for both frame types. At 13-mm, the rigid frame maintained a low index of 2 %, while the flexible frame increased slightly to 4 %. At 16-mm, the index rose for both frames, with the rigid frame at 7 % and the flexible frame at 10 %. The study found that leaflet stress was unrelated to the pinwheeling index. While flexible frames may reduce stress and improve long-term durability, they increase the pinwheeling index. Therefore, the traditional pinwheeling index may not reliably predict accelerated leaflet degeneration across different valve designs in comparative analyses. A comprehensive evaluation incorporating computational modeling, digital image correlation, and experimental validation is crucial for preclinical assessments.
Journal Article
Research on transient dynamic behavior and stress of reciprocating compressor valve under air volume regulation
By establishing the motion equation of the air valve under the condition of air volume adjustment, the motion law of the air valve in the process of expansion, compression, suction and exhaust of the reciprocating compressor under different loads is calculated, and the reciprocating compressor with stepless air volume adjustment is used. The compressor unit verifies the calculation results. The maximum stress of the valve plate under different loads is analyzed, and the results show that in the ideal state where the fork pressure disappears instantaneously, the adjustment method of the partial stroke pressure opening suction valve has a greater influence on the stress concentration of the valve plate than the normal condition; in the partial stroke pressure opening suction valve adjustment method, the free retraction speed and stress of the valve plate will increase as the compressor load decreases.
Journal Article
Self-Expandable Prosthesis Valve Adaptation: Non-Uniform Expansion and Stent Frame Decoupling
The incidence of non-uniform expansion in the context of the self-expandable transcatheter heart valve (THV) is little investigated, along with stent-frame decoupling, which is a form of stent adaptation, in which the lower part of the THV stent conforms to both the ellipticity of the left ventricle outflow tract and the native annulus while maintaining the higher part of the valve more circular. We analyzed post-implant multi-detector computed tomography scans in 50 patients. Prosthesis non-uniform expansion was assessed by computing the prosthesis eccentricity on 6 prespecified levels: (1) frame inflow, (2) native annulus, (3) leaflet inflow, (4) prosthesis waist, (5) leaflet outflow, and (6) frame outflow. Stent-frame decoupling was assessed by comparing the mean eccentricity on 6 different prosthesis levels. Implantation depth, leaflet expansion and alignment, and residual anatomic sinus area ratios were also calculated. Subclinical leaflet thrombosis was defined as hypoattenuated lesion of a meniscal shape. At a 12-month follow-up, non-uniform expansion was consistently detected at each valvular level. Highest eccentricity was measured at the native annulus level (eccentricity: 0.54 ± 0.12), while the lowest index at the frame outflow level (0.23 ± 0.11). Similar results were observed in the subgroup analyses of sizes 23, 26, 29, and 34. Eccentricity significantly decreased from the annulus level to the prosthesis frame outflow (p <0.001). Notably, the incidence of mild-to-severe subclinical leaflet thrombosis was relevant (16%). In conclusion, prosthesis non-uniform expansion and stent frame decoupling frequently occur after self-expandable THV replacement. The clinical and hemodynamic implications remain uncertain.
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Journal Article
A feasibility study of leaflets configuration adaptive to annular growth in pediatric aortic valve reconstruction
Aortic valve reconstruction preserves the native aortic annulus and permits its physiological growth, offering a superior alternative to prosthetic valve replacement for pediatric patients. However, following aortic valve reconstruction, leaflet adaptation to annular growth remains poorly understood, and current clinical leaflet configurations may have some growth adaptation limitations in children.
This study utilized numerical simulations and in-vitro experiments to model annular expansion after aortic valve reconstruction. We investigated the stress distribution and hemodynamic performance of clinical leaflet configurations during annular dilation and designed a refined leaflet configuration for pediatric patients and conducted a feasibility study on it.
Results demonstrated that clinical leaflets—characterized by excessive height and reduced width—developed elevated stress concentrations within the belly region during annular growth. It led to valve incompetence, increasing the regurgitation fraction by 4.61 % (p < 0.001). The refined leaflets, featuring increased width and reduced redundant basal tissue, exhibited lower belly region stress. Following annular expansion, refined valves’ regurgitation rate increased minimally (1.03 %, p = 0.011) and there was no valvular incompetence.
In summary, leaflet configuration affects the hemodynamic performance of the reconstructed valve during aortic annular growth. Refined valves exhibited enhanced adaptive capacity to annular growth, providing an optimized direction for leaflet design in pediatric aortic valve reconstruction surgery.
Journal Article
Thermal Analysis of Cascade Refrigeration System Employing the Refrigerant Pair R23-R404A
In this study, a thermal analysis is conducted on a refrigeration cycle utilizing the refrigerant pair R23-R404A, specifically designed for ultra-low temperature applications reaching as low as -80°C. The study is motivated by the growing demand for ultra-low temperatures in applications such as automotive cold hardening and specialized electronic component testing. Our main goal is to select the appropriate refrigerant pair and carry out the detail thermal design calculations along with refrigeration component selection. The refrigerant selection approach describes the working envelopes for high stage along with low stage for efficient operation. The refrigerant selection process is a crucial focus, considering safety classifications for toxicity and flammability. R23 and R404A are chosen for their non-flammable properties and lower toxicity levels, making them suitable for ultra-low temperature industrial applications. The study outlines a systematic approach for designing, optimizing, and selecting components like compressor, condenser, expansion valve, evaporator etc. and prioritizing efficiency in achieving optimal performance. The design methodology includes detailed analyses of cooling load calculations, thermodynamic equations, and key performance parameters. The research also addresses challenges in component selection, providing insights into potential hurdles and considerations.
Journal Article
Modelling of the refrigerant distribution in a critically charged propane heat pump cycle for performance evaluation
The investigation of heat pumps employing natural refrigerants as working fluids has gained substantial momentum, driven by increasingly stringent regulations addressing the global warming potential (GWP) and ozone depletion potential (ODP) of refrigerants. Propane (R290) stands out as an attractive option due to its low GWP and zero ODP. However, a major drawback of propane lies in its flammability. When using propane as working fluid, it will therefore be necessary to limit the total refrigerant charge within the system, without compromising on the heat pump performance. This study endeavors to address this challenge by developing a model of the refrigerant charge distribution in a critically charged heat pump system consisting of an evaporator, a compressor, a condenser, and an expansion valve. In the model, the charge distribution in the two heat exchangers is modelled in detail using a suitable void fraction correlation. For the compressor and expansion valve, a simplified model is employed, in which no refrigerant charge is calculated. Using an iterative procedure, the model can then be used to determine the coefficient of performance (COP), evaporator- and condenser pressure for a heat pump with an established total charge and heat capacity. The influence of different design and operation parameters, such as the degrees of subcooling and superheat, the volume ratio of the evaporator and the condenser, etc., can be assessed.
Journal Article