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• Using a single-loop, unidirectional slug flow oscillating (pulsating) heat pipe model with the heat transfer controlled by conduction through the slug-deposited liquid film and a simple evaporation rate model relating the slug velocity and heat flux, the overall thermal resistance/conductance is predicted with an analytic expression. • The results are also compared and validated with a more complete, statistical 1-D heat, mass, momentum transport simulation results. • The prediction offers an upper bound on conductance for the available experiments with R134a, butane, acetone, and water. A simple analytic model for the thermal resistance of the oscillating (pulsating) heat pipe (OHP or PHP) is proposed and verified. It is based on the Taylor liquid film formed by moving liquid slugs, film heat conduction, and interfacial evaporation/condensation. It uses a unidirectional flow (characteristic of use of check valves) in a horizontal (no gravity effect) single-loop OHP to derive a relationship between the slug velocity and heat flux. The model predictions are verified with experiments. In addition, the CFD results for the slug-deposited liquid film thickness δ l support that the transition from laminar flow (at Reynolds number, Re D = 2000, D is the diameter) tends toward a constant film thickness regime, previously observed (experimentally) and correlated. Prior direct 1-D simulations also show that at yet higher Re D (3700), a constant slug velocity regime is reached. The evaporator specific thermal resistance, A e R e = A e /G e = δ l /k l , (k l is liquid thermal conductivity) and the total OHP thermal resistance R, is predicted and compared with the current and available related experimental results (for R134a and butane) with good agreement. The suggested ideal high heat flux (constant film thickness δ l , c limit for Re D > 2000) dimensional total ideal resistance is R = 1 G = δ l , c k l (1 A e + 1 A c ) , with δ l , c = 120 D La − 2 / 3 , providing a lower limit on R (upper limit on G). The filling ratio, flooding, and local dryout effects causing deviation from the ideal conductance are addressed. This analytical model can be extended to non-circular channels by using the hydraulic diameter. [Display omitted] [ABSTRACT FROM AUTHOR]

The delivery and distribution of fluid have wide applications in biomedicine, the fine chemical industry, pharmaceutical research, and other fields. However, existing fluid delivery and distribution systems often suffer from issues such as large size, excessive noise generation, and high-power consumption, rendering them unsuitable for convenient applications. Here, a wheel-shaped valve piezoelectric micropump with a size of only 10 mm*10 mm*1 mm is proposed and a prototype is prepared. The vibration mode, operating principle, and the liquid flow of the micropump are analyzed by finite element method. The output liquid (distilled water) flowrate of the pump is approximately 15 mL/min, and the maximum pump distilled water pressure can reach 100 KPa. The results indicate that the performance of the micropump is consistent with the analysis results, which shows its potential application in the field of portable devices and medical. [Display omitted] • A micro piezoelectric pump with simple structure, size of only 10 mm*10 mm *1 mm was designed. • The vibration mode, operating principle, and the liquid flow of the micropump are analyzed by finite element method. • Provide a new idea or a new method for piezoelectric micro pumps to achieve high flow and pressure. [ABSTRACT FROM AUTHOR]

Heat pipes are widely used in thermal management due to their high heat transfer coefficient. However, traditional heat pipes conduct heat bidirectionally, depending on the temperature at both ends of the pipe. This can lead to the transfer of external heat back into the system at high ambient temperatures, reducing system performance and potentially damaging devices. To overcome this drawback, a thermal diode with thermal rectification in the horizontal direction based on a novel check valve and modified wick is proposed, and its thermal performances are experimentally investigated. Results show that the thermal diodes with filling ratio of working fluid less than 40% can achieve thermal rectification. The best thermal rectification coefficients of filling ratio of 10%, 20%, 30%, 40% and 50% are 3.422, 4.528, 4.238, 2.601 and 1.336, respectively. The thermal diode with filling ratio of 20% can reach the maximum thermal rectification ratio (4.528) under the heating power of 20W. [ABSTRACT FROM AUTHOR]

The free-piston Stirling generator (FPSG) holds great promise as a thermal-to-electrical conversion device for space applications. However, heat transfer remains a critical factor obstructing its scalability to high power levels. In this study, we propose a high-power FPSG with a gas-compressing self-circulating heat exchanger (GSHX) that utilizes high-pressure helium as the heat transfer fluid, enhancing the reliability of the heat exchanger. By incorporating a built-in gas-compressing device and check valves, the performance degradation caused by significant pressure fluctuations in the resonant self-circulating heat exchanger is effectively addressed. Through detailed simulations, we demonstrate the principle feasibility of the GSHX with a 4 m heat transfer loop, achieving an output electric power of 11 kW and a thermal-to-electric efficiency of 20.4%. Furthermore, the GSHX exhibits similar operating characteristics to traditional FPSGs, as we analyze the systems' stability under various operating conditions. Importantly, our findings reveal that the acoustic characteristics of the loop play a pivotal role in system performance, with operating parameters exhibiting periodic variations related to helium wavelength. By carefully optimizing system parameters, GSHX with a long loop length of 29 m can achieve comparable performance to systems with shorter loops. This study provides valuable insights into the operational characteristics and performance optimization of the GSHX, offering a comprehensive heat transfer solution for long-distance, high-efficiency, and highly reliable applications of high-power FPSGs in the space domain. • Novel FPSG with gas-compressing self-circulating heat exchangers proposed. • System achieves 11 kW output power, 20.4% thermal-to-electric efficiency. • Acoustic characteristics of loop decisively impact system performance. • Optimization enables comparable performance for extended loop lengths. [ABSTRACT FROM AUTHOR]

A slit structure consisted of two bending graphene membranes is built as a nano check valve theoretically. Molecular dynamics simulations are used to investigate the opening and closing of this check valve. The backflow through the valve are also studied. The results show that the check valve can maintain the unidirectional flow of fluid and prevent backflow within the appropriate pressure range. Specifically, the opening and closing pressure of the valve are 148.2 and 24.6 MPa, respectively. The maximum working pressure of the check valve should be lower than 197.6 MPa. Moreover, the water passing rate is larger at a higher pressure due to the larger slit width and water flux. This check valve is expected to have many potential applications in the nanofluidic field. Image 1 [ABSTRACT FROM AUTHOR]

An Oscillating Water Column (OWC) device can output energy through reciprocating or unidirectional airflow. The unidirectional airflow is helpful to utilize a simple and high-efficiency unidirectional air turbine. The pentagonal BBDB proposed by us based on OWC principle can be regarded as a floating Oscillating Body and its Power Take-Off (PTO) consists of a chamber, a water column, a turbine and a generator. The Capture Width Ratio (CWR) of the pentagonal BBDB model with the reciprocating and unidirectional airflow was studied in this paper. The wave flume test results indicate the mean CWR of the pentagonal BBDB model with reciprocating airflow can reach up to 121.91% and the mean CWR of the model with unidirectional airflow could reach 100.94% during the whole wave cycle in regular waves. For irregular waves, the mean CWR of the model with the unidirectional airflow is as high as 62.83% during the whole wave cycle. Hopefully, the combination of the pentagonal BBDB with the check valve to output power during the air exhalation and conventional high-efficiency unidirectional turbine will improve the total efficiency of the BBDB. [ABSTRACT FROM AUTHOR]

A method in which the number of inlet valves is increased to raise the pump chamber pressure is proposed to suppress the generation of cavitation in micropumps during the absorbing phase, thereby improving the working performance of the pump. • A method is proposed to suppress the generation of cavitation in micropumps. • Adopt the method of increasing the number of inlet valves. • Simulation shows that the pressure in the pump chamber rise during the suction phase. • When the pump pressure above the saturated vapor pressure, the flow rate increases significantly. Cavitation is a serious constraint on micropumps. A method in which the number of inlet valves is increased to raise the pump chamber pressure is proposed to suppress the generation of cavitation in micropumps. The simulation shows that as the number of inlet valves in the pump increases, the pressure in the pump chamber rises during the absorbing phase. When the pump is designed with 6 inlet and 2 outlet valves, the pressure in the pump chamber can increase above the saturated vapor pressure, thereby the generation of cavitation can be suppressed. Experimental data show that the flow rate of the pump using 6 inlet and 2 outlet valves can reach four times that of the pump using 4 inlet and 4 outlet valves. Experiments and simulations results show that increasing the number of inlet valves can effectively suppress the generation of cavitation and improve the efficiency of micropumps. [ABSTRACT FROM AUTHOR]

Highlights • A new type of PDMS check valve is presented in a supporting piezoelectric pump. • The flow rate of improved check valve is significantly increased. • Solves a series of problems that exist with regular PDMS bridge check valve design. • The modular pump design that allows the adjustment of the pump performance. Abstract A technique of check valve improvement for high frequency and high flow rate piezoelectric pumps is presented. By adding in a blocking edge over polydimethylsiloxane (PDMS) film check valve to modify their deformation pattern, 40%–300% flow rate enhancement and 5–6 kPa output pressure increment were achieved on a bench top testing platform. Experimental results show that the new valve is benefits to design a high efficiency and high outflow piezoelectric pump. [ABSTRACT FROM AUTHOR]

Standard swing disk check valves are typically operated by pressure difference. Alternatively though, the valves might be operated by an active driving force when they cannot be operated by the pressure difference. If this simple concept is realized, the reliability of the check valve could be improved since a great portion of abnormalities currently leading to failure can be corrected. With this intention, this paper proposes a power-operated check valve and describes important factors to be considered. Through an effectiveness analysis, it was verified that the proposed concept significantly improved reliability in an example safety system. [ABSTRACT FROM AUTHOR]

To ensure the reliability of oil-gas multiphase pumps, it is necessary to model the relationship between the transient opening height of the check valve and multiphase transportation conditions. However, the choice of a suitable turbulence model is not straightforward for the widely used computational fluid dynamics (CFD) method. Additionally, the CFD models are still not easy to be validated experimentally because the transient opening motion is difficult to be accurately measured for its quick and nonlinear characteristics. In this work, an integrated probabilistic modeling (IPM) method is proposed to predict the transient opening height of the check valve in oil-gas multiphase pumps. First, candidate CFD transient models with different turbulence models are adopted to provide initial training data for several Gaussian process regression (GPR) models. Then, a probabilistic index of the trained GPR models is formulated to assess their reliability. Consequently, without knowing the actual values, a suitable GPR model is chosen from the candidates for online prediction of a new condition. Moreover, instead of the time-consuming CFD design process, a better CFD turbulence model can be selected efficiently. The superiority of IPM is demonstrated using simulation and experiments. [ABSTRACT FROM AUTHOR]

An accurate, efficient and robust numerical scheme is presented for the simulation of the interaction between flexibly-supported rigid bodies and incompressible fluid flow with topology changes and solid–solid contact. The solution of the incompressible Navier–Stokes equations is approximated by employing a stabilised formulation on Cartesian grids discretised with hierarchical b-splines. The solid is modelled as a rigid body and represented by linear segments along its boundary. Kinematic conditions along the fluid–rigid body interface are enforced weakly using Nitsche’s method, while ghost penalty operators are employed to avoid excessive ill-conditioning of the system matrix arising from small cut cells. A staggered scheme is used for resolving the coupled fluid–rigid body interaction. The contact between moving or moving and fixed solid bodies is modelled with Lagrange multipliers. The excellent performance and wide range of applicability of the proposed scheme are demonstrated in a number of benchmark tests as well as industrially relevant model problems. The examples cover the galloping phenomena, particulate flow, hydraulic check valves and a model turbine. [ABSTRACT FROM AUTHOR]

The structures and working principles of a piezoelectric pump with dual vibrators are described in this paper. The output performance of the pump was analyses under different working modes. The experimental results demonstrate that changing the driving strategy can vary the performance. When the driving voltage is 60 V at 160 Hz, the maximum output pressure of the pump in the asynchronous mode is 2.18 kPa. The performance of the upper actuator working alone is better than the lower actuator working alone, and the maximum output pressure in this case is 1.3 kPa. Taking the piezoelectric pump with a single vibrator as a typical example, an optimal design method has been applied on the check valves. The performance of the pump with wheel valves is better than that with cantilever valves; the optimum thickness of the check valves is 0.188 mm. [ABSTRACT FROM AUTHOR]

• The leakage rate of metal-to-metal contact check valve is measured. • Poiseuille flow is insufficient to account for the leakage flow. • The leakage rate is analyzed with a transition flow model. • The leakage rate at 20 K can be predicted adopting the transition flow model. A check valve which is a critical component for cryogenic sorption compressor, has been developed previously by several researches. Its leakage rate was phenomenologically explained by the model of Poiseuille flow with the effect of pressure difference or temperature. This paper specifically investigates the leakage rate of the metal-to-metal check valve at 20 K, 77 K and 294 K in the situation of the back pressure from 150 kPa to 1,450 kPa. The leakage flow phenomenon is analyzed in more detail at various temperature, pressure difference and flow regime. Since Poiseuille flow which was adopted by previous researches cannot comprehensively reflect the effect of temperature and the pressure difference, the transition flow model has been subsequently employed to predict the leakage rate at 20 K. The leakage rate at 20 K is well predicted by using the 77 K and 294 K results with maximum and minimum approximation error of 22 % and 3.5 %, respectively. Uncertainty analysis is conducted to ensure the reliability of the prediction results. Furthermore, the allowable leakage rate of the check valve according to the ratio of the actual and ideal mass flow rates of the sorption compressor are derived. [ABSTRACT FROM AUTHOR]

Acute myocardial infarction (AMI) is a serious disease with high mortality that afflicts many people around the world. The main cause of death from AMI was the inaccurate early diagnosis, which resulted from the medical treatment might be a delay. Therefore, it is crucial to achieve the rapid detection of AMI. The cardiac troponin I (cTnI) level in human serum may significantly increase as the myocardial membrane ruptured, and the creatine kinase-MB (CK-MB) was also associated with the AMI recurrence and the infarct size of myocardial infarction. Both of them are regarded as important cardiac biomarkers for the early diagnosis of AMI. Therefore, we chose these two cardiac biomarkers as indicators for simultaneous detection. We proposed a single-track finger-pump microfluidic chip for simultaneous surface-enhanced Raman scattering (SERS) detection of cTnI and CK-MB. The entire detection process takes only 5 min without the cumbersome syringe pump. Meanwhile, it enables multiple reagent additions and removals of the unbonded reactants. This microfluidic sensor employed "sandwich" immunoassays based on SERS nanoprobes, AMI biomarkers, and magnetic beads. It is possible to detect two cardiac biomarkers simultaneously in a single measurement, greatly simplifying the detection process and reducing the detection time. Magnetic beads with SERS nanoprobes were separated and captured in the microchamber by a round magnet integrated into the chip. Our results showed that the detection limits of cTnI and CK-MB could reach to 0.01 ng mL−1, respectively. The limit of detections (LODs) match with the clinical threshold values for AMI biomarkers. It is believed that the proposed single-track finger-pump microfluidic chip can be used as an effective tool for determining early AMI. [Display omitted] • A SERS-based finger-pump microfluidic chip is demonstrated to achieve the detection of dual AMI biomarkers. • The integration of two check microvalves can ensure single-track flow for multiple reagent additions on chip. • The simultaneous detections were conducted in single measurement by identifying dual SERS nanoprobes. • The cTnI and CK-MB biomarkers were detected by SERS and the detection limit could reach to 0.01 ng mL−1. [ABSTRACT FROM AUTHOR]

This study describes the development and experimental verification of a modified harvest system to enhance Factor VIII (FVIII) yield in an alternating tangential flow (ATF) perfusion culture. The main innovation of the modified harvest system is the use of check and pinch valves, eliminating the need of a peristaltic pump for harvest. The system was applied to perfusion cultures of Chinese hamster ovary cells, which co-express both recombinant human FVIII (rhFVIII) and von Willebrand factor (vWF). The modified harvest system showed comparable cell growth with the conventional harvest system using a peristaltic pump. The perfusion rate was successfully controlled using the system. In addition, the modified harvest system achieved an approximately 13.6-fold increase in the final concentration yield of FVIII activity and a 1.47-fold increase in the production yield of FVIII activity compared with a peristaltic pump. Enhancement of the yield of FVIII activity resulted from the reduction of FVIII antigen (FVIII:Ag) retention. As a result of transmembrane pressure (TMP) measurement, the reduction of the retained FVIII:Ag was due to the increased TMP, which was caused by the characteristic function of a check valve, compared with a peristaltic harvest system. The modified harvest system developed in this study could be useful to enhance the production yield of other recombinant proteins in ATF perfusion culture. [ABSTRACT FROM AUTHOR]

We present an implantable micropump with a miniature form factor and completely wireless operation that enables chronic drug administration intended for evaluation and development of cancer therapies in freely moving small research animals such as rodents. The low power electrolysis actuator avoids the need for heavy implantable batteries. The infusion system features a class E inductive powering system that provides on-demand activation of the pump as well as remote adjustment of the delivery regimen without animal handling. Micropump performance was demonstrated using a model anti-cancer application in which daily doses of 30 μL were supplied for several weeks with less than 6% variation in flow rate within a single pump and less than 8% variation across different pumps. Pumping under different back pressure, viscosity, and temperature conditions were investigated; parameters were chosen so as to mimic in vivo conditions. In benchtop tests under simulated in vivo conditions, micropumps provided consistent and reliable performance over a period of 30 days with less than 4% flow rate variation. The demonstrated prototype has potential to provide a practical solution for remote chronic administration of drugs to ambulatory small animals for research as well as drug discovery and development applications. [ABSTRACT FROM AUTHOR]

Zero flows in closed pipes in pressurised water supply networks require additional computational boundary constraints, which can result from two different operational states for pipe appurtenances. Static closed pipes are produced by turning off the isolation valves to undertake inspections/repairs of related pipe segments or to separate adjacent pressure zones. In addition, closed pipes can occur dynamically due to shutdowns of check valves and pressure/flow regulating facilities equipped with non-return valves. In this study, a generalised solution approach is developed to solve the nonlinear loop equations of the network flow problem involving closed pipes, which is integrated directly into hydraulic simulations of water distribution systems. The iterative approach uses the Newton–Raphson method based on the energy equations. The head loss across closed pipes is estimated using a novel computational technique called the unknown hydraulic function to avoid the singularity of the Jacobian matrix. The flow corrections of the related loops are performed locally using the Hardy-Cross technique, which allows small amounts of the flow rates to vary within lower ( ε min ) and upper ( ε max ) bounds during the iteration process. As an additional convergence criterion, the upper limit ( ε max ≤ 0.020 l/s) is allowed to vary in both flow directions for static closed pipes, whereas this is permitted only under reverse flow conditions for closed pipes of unidirectional control devices. The reliability and efficiency of the proposed algorithm are demonstrated using some example network applications. The results obtained after many computer runs demonstrated that the iteration process is robust and efficient, thereby ensuring consistent convergence in a rapid manner. The flow correction magnitude was reduced to negligible small values for the related loops after executing a Hardy-Cross step, which significantly helped to stabilise the direction of the solution matrix. [ABSTRACT FROM AUTHOR]

The check valve is an indispensable local component in pipe network systems, but its active components are worn during use, increasing the energy consumption of the system and endangering the safety of the fan. The traditional Tesla valve structure poorly matches the pipeline in engineering practice. This paper proposes a check valve for airducts with a nonmobile guide vane that makes the pressure drops generated when the fluid flows through the valve from the forward and reverse directions significantly different. In this study, the diodicity mechanism was analysed, the valve shape was optimized by means of machine learning, numerical simulation and full-scale test verification, and the resistance coefficient ratio (ζ) was proposed to evaluate the check effect. A comparison was made with the diodicity of the Tesla valve. The results show that the check performance of the novel check valve proposed in this study is significantly better than that of the traditional Tesla valve, and its diodicity is 255% higher. When the fluid reaches full development, the resistance coefficient ratio reaches 4.93. The novel check valve is more suitable than the existing valve designs for the pipelines in engineering practice and provides theoretical support and necessary equipment for flow control in ventilation and air conditioning systems. • A check valve with a nonmobile guide vane is investigated by machine learning and numerical simulation. • The check effect is verified by the full-scale experiments. • The resistance coefficient ratio is proposed. • Compared with the traditional Tesla valve, the diodicity of the novel check valve increased by 255%. [ABSTRACT FROM AUTHOR]

Abstract: A heaving-buoy wave energy converter equipped with hydraulic power take-off is studied in this paper. This wave energy converter system is divided into five subsystems: a heaving buoy, hydraulic pump, pipelines, non-return check valves and a hydraulic motor combined with an electric generator. A dynamic model was developed by considering the interactions between the subsystems in a state space form. The transient pressures caused by starting/stopping the buoy or closing/opening the check valves were predicted numerically using the established model. The simulation results show that transmission line dynamics play a dominant role in the studied wave energy converter system. The length of the pipeline will not only affect the amplitude of the transient pressures but also affect the converted power. The variation of the time-averaged converted electric power with the pipeline length is estimated using the simulation method for the buoy exposed to one irregular sea state. Finally, it is suggested how reduced power efficiency due to the pipelines may be ameliorated. [Copyright &y& Elsevier]

Abstract: Tesla-type check valves were integrated into a flat-plate oscillating heat pipe (FP-OHP) in order to promote and sustain a desired circulatory flow to increase overall thermal performance. Using neutron radiography, gray-scale images capturing the internal flow behavior within two bottom-heated copper FP-OHPs – one with Tesla-type valves (TV FP-OHP) and one without – both charged with water at a filling ratio of 70% – were collected. With the Tesla-type valves installed in the adiabatic section of the TV FP-OHP, it was found that circulation in the desired direction was promoted and that this promotion increased with heat input. The TV FP-OHP consistently possessed a lower thermal resistance than its counterpart without check valves. The percent-reduction in thermal resistance was on-the-order of 15–25% depending on the power input. Implementation of Tesla-type check valves is a promising means for circulatory flow rectification within an OHP, but future research is needed to further optimize valve design, quantity, and alignment. [Copyright &y& Elsevier]

Abstract: This paper introduced the structure and working principle of a new designed check valve, Contra-push check valve (CPCV), which can release water hammer and valve slam in accidents and special working status of nuclear power systems. The steady and transient characteristics of CPCV are simulated by CFD codes. Based on the experimental data, it is shown that the result is highly dependent on the turbulence model. The renormalization group theory (RNG) k–ε model is proved to be more accurate to describe the flow inside the valve. Steady hydraulic characteristics computed with RNG k–ε model agreed well with the experimental data at different positions of the plug. The Sensitivity analysis of structure parameters of CPCV were carried out in this study and two key factors were revealed. [Copyright &y& Elsevier]

Abstract: This paper describes the performance of a circular glass tube solar collector with a set of closed-loop oscillating heat-pipes with check valves (CLOHP/CV). The assembly was divided into three sections, i.e. circular glass tube, adiabatic gap and condenser water tank. A circular 10-set glass tube solar collector of 0.058m diameter and 1.50m length was housed on a collecting plate. The inside circular glass tube consisted of a CLOHP/CV and collecting plate. The adiabatic gap was 0.05m. The condenser water tank was made from a 0.03×0.05m2 zinc sheet. The CLOHP/CV consisted of the collecting plate cover with inner diameter of 0.003m and 26.40m total length per set, and it contained two check valves with evaporator 1.50m long, adiabatic gap 0.05m and condenser 0.30m long. R-134a was used as the working fluid with filling ratio of 50%. The CLOHP/CV arrangement was aligned at an inclination angle of 18 degrees from the horizontal plane, with 6 turns per set. A 0.001m thick aluminum sheet was used to make a collecting plate with 0.10×1.50m2 test area. Efficiency evaluations were conducted during daylight hours over a 2-month period and included extensive monitoring and recording of temperatures with type-K thermocouples placed at key locations throughout the system. The results confirmed the anticipated fluctuation in collector efficiency dependent on the time of day, solar energy irradiation, ambient temperature and circular tube surface mean temperature. An efficiency of approximately 76% was achieved, which correlates with the efficiency of the more expensive heat-pipe system. The CLOHP/CV system offers the additional benefits of corrosion-free operation and absence of freezing during winter months. [Copyright &y& Elsevier]

Abstract: In this work, we present alternative methods for the formation of a simple a check valve for microfluidic applications. In two different approaches we exploited the characteristic features of the proton beam micromachining (PBM) technique and the selective formation and dissolution of porous Si around the implantation damaged areas. In the first case, we implanted 10μm thick cantilever-type membrane of the valve normally to the crystal surface and at 30–60° to the sidewalls of the flow channel, which were also implanted at the same irradiation. During the porous Si formation we developed the sample 6–8μm deeper than the implanting ion range damaged the crystal. Due to the isotropic nature of the porous Si etching, the thick sidewall blocks are still connected to the crystal while the thin membranes detached from the bottom, and they are only connected to one of the sidewalls. The other construction utilized the goniometer facility mounted on the microbeam chamber. We implanted the samples at 43° tilt, and developed the samples not as deep as the ion range. This way both the sidewalls and the membranes are attached to the bottom of the sample. [Copyright &y& Elsevier]

Tools in injection moulding units, especially the check valves, can suffer dry hard metal - hard metal contact under severe conditions, thus experiencing increased wear. For the present study, various hard metal pairings were investigated using dry pin-on-disc tests to simulate the tribosystem of the check valve. Hard metal discs with W x C particle sizes between ~0.9 and 3 μm and binder contents between 9 and 17.5 wt. %, were tested against similar pins with smaller W x C particles. Results show that the cracking of carbides is the major wear mechanisms and that decreased W x C particles sizes together with decreased binder contents lead to lower wear rates. The combination of the hard metal with the smallest W x C particles and the lowest hardness differences between pin and disc leads in this case to a beneficial material transfer and tribolayer formation, resulting in increased wear resistance of both sliding counterparts, promising a lifetime enhancement of the check valves. • Dry hard metal – hard metal contact was simulated in a pin-on-disc setup. • Tribolayer formation offered an effective in-situ evolution of wear protection. • The tribolayer consists of binder, small W x C grains/fragments and oxides. • Similar W x C particle sizes in the counterbodies support optimal tribolayer coverage. • Smallest W x C particle sizes entailed lowest wear rates. [ABSTRACT FROM AUTHOR]

• Four different dynamic mesh methods are simulated. • Strategies to describe the full closure of the valve has been proposed. • The prediction of inflowing fluid velocity at the closure are compared and discussed. The present study provides recommendations for choosing the appropriate moving mesh techniques of CFD to describe the dynamic behavior of a check valve and to evaluate a pressure build-up in response to the valve's closing behavior. Four different moving mesh techniques of CFD were modeled and compared, and the compressibility of the fluid was involved in simulating the pressure build-up by valve closing. The results showed that the swing check valve's dynamic behavior during the valve closure could be well described by the moving mesh techniques presented in this study because the velocity profiles at the outlet of each method were similar until the valve was almost closed. However, even though the moving mesh techniques described the check valve's closing behavior well, the predictions of the inflowing fluid velocity at the moment when the valve was fully closed were different from one another. [ABSTRACT FROM AUTHOR]

For building ventilation, it is often necessary to create airflow in a particular direction and prevent the backflow of pollutants and unnecessary expenditure of energy. At present, most check devices can only be used in small areas, such as pipelines, which cannot fully meet the needs of building ventilation systems. Based on the principle of a Tesla structure, this paper proposes a new type of fluid diode plate (FDP) without moving parts, which can be infinitely extended in terms of area and is suitable for various ventilation environments. A series of experiments and numerical simulations were performed to test the check effect of this FDP under different influencing factors. Two evaluation indices, the pressure loss ratio (F FDP) and minor loss coefficient (ζ), were used to evaluate the flow pressure losses in both forward and reverse directions for the FDP. The results showed that the flow pressure loss in both directions for the FDP were very different. For the fluid diode plate with 4 flow loops, the pressure loss of reverse flow could be more than 6 times that of a forward flow. The pressure loss of a forward flow showed a little increase compared with an orifice plate with the same porosity. Moreover, the check effect of the FDP increased with the inflow velocity and reached a stable value when the flow in the FDP channel became fully turbulent. In future research, the check effect of the FDP will be further improved by further optimizing the structure. • A novel fluid diode plate (FDP) based on Tesla structure was proposed to prevent backflow in building ventilation system. • Inflow velocity, number of flow loop, channel ratio, and porosity, were evaluated by using pressure loss ratio and minor loss coefficient. • The variation trend of pressure loss ratio with the increase of inflow velocity was obtained. [ABSTRACT FROM AUTHOR]

• A new type of check valve is used in the experimental circuit of nuclear power plant to solve the water hammer problem when switching between two pumps. • Through the dynamic grid technique, transient flow field in different conditions of valve closing are calculated, and dynamic properties of valve head closing process is analyzed. • The inhibitation ability of water hammer in typical six conditions is analyzed. • Simulation and experiment show that the valve has good noise reduction effect. In this paper, the close process of contra-motion check valve in countercurrent pressure difference is studied in nuclear power plant experimental circuit. The transient mathematical model is established. Through the dynamic grid technique, transient flow field in different conditions of valve closing are calculated, and dynamic properties of valve head closing process is analyzed. Through the CFD transient analysis, inherent damping principle and inhibition of water hammer principle are revealed. By writing water hammer analysis, the inhibitation ability of water hammer in typical six conditions is analyzed. At last the performance verification experiments show that contra-motion check valve can effectively inhibit water hammer in the process of parallel double pump switching transition. [ABSTRACT FROM AUTHOR]

• A simple planar micro check valve using in situ fabricated hydrogel is proposed. • The valve performs better than most existing planar check valves. • A normally-closed check valve with controllable cracking pressure is further proposed. • A simple finger-actuated micro-mixer is developed based on the valve. • An earthworm-actuated micro-pump is developed based on the valve. Micro check valves play a pivotal role in many microfluidic systems. However, there is still an unmet need for low-cost check valves with good performance and easy integration. In this work, we present a planar micro check valve using a hydrogel valve core fabricated in situ in a microchannel. This valve is characterized by a simple fabrication process and easy integration with other microfluidic devices. Experimental results proved that the check valve performs better than most existing in-plane micro check valves, especially in low-pressure operations, with nearly zero forward cracking pressure and reverse leakage, adjustable forward fluidic resistance, and good repeatability. We further proposed a normally-closed check valve with controllable cracking pressure to meet different requirements of microfluidic devices. Precise cracking pressures could be achieved by regulating the valve spring width. To demonstrate the valve usefulness, we employed these valves to make a finger-actuated micro-mixer and a bio-actuated micro-pump. This study makes the flow control more simplified in integrated microfluidic systems. [ABSTRACT FROM AUTHOR]

• An innovative hybrid connected multiple-chamber piezoelectric pump with umbrella-shaped valves was proposed. • Two groups of double-chamber connected in parallel are connected in serial to form a hybrid configuration with peristalsis actuate principle for massive fluid transport application. Each chamber is installed with an umbrella-shaped check valve, serving as the sub-inlet for the chamber. • The static performance of four check valves like umbrella-shaped silicon valve, plate valve, cantilever valve and ball valve has been assessed in the same circumstance, and the results shown that the umbrella-shaped silicon valve has a lower open pressure and easier to open or close, and it has the advantages of good sealing capability, long fatigue life, easy to fix, compactable, easy to mass manufacturing and etc., it is the best choice for building the proposed pump. • A prototype of the proposed pump with umbrella-shaped valve was manufactured. With the sine wave voltage of 210 V at the frequency of 120 Hz, the maximum flow rate up to 1845 ml/min, which is one of the highest flow rates in literature at present. Moreover, the output pressure can reach 32.47 K Pa, which is also important for various applications. The pump is designed to have self-filling capability, the self-sucking pressure up to 15.4 K Pa. • The self-suck capability is important for micro-pump application without filling the pump first. The proposed pump can be applied in hemodialysis machine, agricultural dosing system, water cooling system for chip and other fields. Compact pumping system of large flow rate and high output pressure with self-filling are highly desired in many fields. In this study, a multi-chamber piezoelectric pump, built with unique umbrella-shaped check valves made of silica gel, is designed and manufactured. The chambers are installed into two groups connected in series, and each group consists of two chambers parallel connected, sharing the same inlet and outlet. These four chambers have the same structure, each of which is configured with a piezoelectric actuator clamped by two seal rings, and a check valve severing as sub-inlet of each chamber. The fluid comes into the inlet of the first group and flows out through the outlet of the second group. A prototype of this kind piezoelectric pump is manufactured and assessed. The high flow rate up to 1845 ml/min and the output pressure of 32.47 KPa are achieved with the sine wave voltage of 210 V at the actuate frequency of 120 Hz, with the valve coefficient at 0.85, and the self-sucking pressure of 15.4 KPa. [ABSTRACT FROM AUTHOR]