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• Boiling heat transfer of ammonia in a vertical rectangular microchannel at high pressure of 354–615 kPa was investigated. • The wake at lower end of the primary bubbles increases the local flow rate significantly. • Influence of saturation temperature on bubble growth and heat transfer performance was analyzed. Ammonia boilers are commonly used as expendable radiators during the return phase of spacecraft. The aim of this study is to investigate the bubble behavior and heat transfer characteristics within a vertical rectangular microchannel of a plate-fin ammonia boiler under gravity at an absolute pressure of 354–615 kPa. In order to achieve this, a single rectangular microchannel unit was intercepted from the ammonia boiler structure to construct a simulation model, and the high-pressure boiling process of ammonia in the rectangular microchannel was numerically investigated using the VOF model. Good agreement was obtained by comparing the numerical results with the experimental data with the error within 8 %. The results show that the wake flow at the lower end of the primary bubbles has an enhanced effect on the heat transfer, which is about 50–60 %. The maximum horizontal dimension of primary bubbles increases with increasing superheat, and significant bubble coalescence occurs when 45 % of the rectangular microchannel spacing is exceeded. In addition, the effect of different saturation temperatures on the heat transfer performance on the hot high temperature wall was investigated. Significant heat transfer deterioration was found to occur at saturation temperatures below 4 °C (superheat above 15 °C). The reason found in this study was that bubble coalescence significantly increases the percentage of gas-phase contact area on the high-temperature wall (from 25 % to 54 %) and weakens the wake enhancement effect. [ABSTRACT FROM AUTHOR]

• The total magnetic field in the gap of full-compensated nested Halbach cylinders (NHC) dependence on the rotation angle of inner array is described by the cosine modulus function. • High operating frequency, a large amount of working space, ease of use, and a small number of moving parts make NHC effectiveness in realizing the AMR cycle. • Phase shift angles between the rotation of the inner cylinder of NHC and the piston displacement processes in the range of 70 - 90° to ocure a maximum thermal span. • The volume of pumped heat transfer fluid through the regenerator must be 20–30 % of its voids volume. In this study, a numerical model of the Active Magnetic Regenerator (AMR) cycle, implemented in the reciprocal demonstrator, was developed using COMSOL Multiphysics. A nested Halbach cylinder (NHC) array served as the magnetic field source. Additional simulation of an operation of the NHC array was carried out. To eliminate the discrepancies between the heat exchange duration of the heat transfer medium (HTM) and the hot and cold ends of the regenerator, an adequate time dependence of the inner cylinder rotation angle was calculated. The latter provides the symmetrical sinusoidal form of time dependence of the magnetic flux density in the gap of NHC array, which is important for enhancing the performance of a magnetic refrigerator. It was established that in order to achieve a maximal temperature span, it is necessary to shift the phases of the magnetic field insertion/removal and heat transfer fluid pumping processes by nearly half of the operating cycle period. The latter brings the simulated cycle closer to the ideal AMR cycle. [ABSTRACT FROM AUTHOR]

• A transient numerical model of scroll compressor for electric vehicle is established. • Errors are within 9.5 % between the simulation and experimental results. • The effects of discharge port size and shape on compressor performance are studied. • Power consumption reduces by 5.82 % as discharge port diameter rises from 5.2 to 9 mm. • Composite-shaped discharge port displays the best performance compared with others. Scroll compressor with short scroll profile length shows great potential in electric vehicles for its compact structure and better reliability, while shorter scroll profile results in less compression time and under-compression in most cases. To investigate the influence of discharge port structure on compressor performance, a three-dimensional transient model of scroll compressor for electric vehicle is established. The theoretical and experimental results exhibit good consistency within a deviation of 9.5 %. With this validated model, the effects of discharge port size and shape on compressor performance are studied respectively. When the circular discharge port diameter increases from 5.2 mm to 9.0 mm, the power consumption and discharge temperature can be reduced respectively by 5.82 % and 5.29 %. The discharge mass flow rate can be promoted by 1.09 %. The discharge pressure fluctuation and imbalance between the upside and downside chambers enhanced obviously. To further improve the discharge flow characteristics, different discharge port shapes were employed including waist-shaped, arc-shaped and composite-shaped port. Compared with 5.2 mm circular port, the power consumption with composite-shaped port reduces by 5.81 % and mass flow grows by 1.26 %. Results indicated changes in discharge port structure parameters have greater influence on power consumption rather than mass flow rate. [ABSTRACT FROM AUTHOR]

Mass transfer resistance within the adsorbent felt, governed by pore diffusion, limits adsorption efficiency. Current gas and solid side resistance models, which cover both micro- and macro-pore diffusion, are complex due to their numerous parameters. Sometimes, adsorbate transfer in the felt is predominantly controlled by macro-pore diffusion. This paper uses two key assumptions to introduce a simplified macro-pore diffusion model, distilled from a detailed macro–micro pore diffusion model. The model's accuracy was confirmed by simulating two desiccant wheels, demonstrating its effectiveness in streamlining adsorbent felt analysis and predicting mass transfer dynamics. • Concluded the preconditions for simplifying the micropore–macropore diffusion model. • Streamlined the mass transfer analysis of adsorbent felt with bimodal pore size distribution. • Confirmed the simplified model's prediction accuracy by simulating two desiccant wheels' performance. [ABSTRACT FROM AUTHOR]

• Proposed a cooling unit with an anisotropic encapsulation structure for a phase change cooling garment. • The optimal cooling performance is achieved with a phase change material thickness of 8 mm, a slow-release heat absorption layer of 3 mm, and a spacing of 5 cm between the cooling units. • The novel phase change cooling garment is capable of supporting electricians in high-temperature environments (38 °C) for up to 2 h. • It can improve thermal comfort and safety for electricians in extreme heat conditions through advanced garment design. • Potential applications extend to various industries requiring heat-stress mitigation for workers. To mitigate the effects of heat stress on electricians during outdoor activities such as inspection, circuit repair, and daily maintenance in high-temperature environments, a novel design for a portable, efficient, and ergonomic phase change cooling garment is presented. First, the optimal phase change material is selected considering economic and environmental factors. Then, based on the heat balance equation of the human body and Fourier's law, the required phase change material mass and the optimal thickness of the retarded heat-absorbing layer are obtained and verified by numerical simulations and experiments. The results indicate that in a high-temperature environment of 38 °C for 2 h, electricians require 2.39 kg of phase change material. To meet the protective duration requirements of electricians' daily tasks, the optimal thickness of the phase change material is 8 mm, and the optimal thickness of the slow-release heat absorption layer is 3 mm. The results of this study have significant implications for the safety and protection of electricians in high-temperature environments. It aims to provide theoretical guidance for the design and innovation of personal cooling garments for electricians. [ABSTRACT FROM AUTHOR]

• A numerical simulation was conducted to analyze the susceptibility to crosswinds during the spraying of the air cooler. • The flow field temperature within the skid-mounted CNG air cooler when subjected to crosswind conditions was analyzed. • The installation of baffles enhances the air intake of the cooler, which effectively eliminates the adverse effects of ambient wind. Air cooler is a critical heat dissipation equipment applied in the field of oil and gas storage, which is mainly used to control the temperature during oil and gas storage and ensure the safety of oil and gas storage. After the installation of the spray cooling system on the skid-mounted compressed natural gas (CNG) air cooler Suqiao gas storage, the inlet air temperature of the air cooler decreases, resulting in reduced compressor power consumption. This effectively addresses the issue of unit shutdown due to high temperatures during the summer. However, the actual spray effect on-site reveals the impact of crosswinds, which poses a challenge. In this study, the flow field and causes of the skid-mounted CNG air cooler equipped with a spray cooling system under the influence of crosswinds are analyzed. Additionally, a solution involving the installation of a baffle is proposed. The results highlight that crosswinds have an adverse effect on outdoor spray cooling. With the installation of the baffle, the low-temperature area expands, resulting in lower temperatures. The cooling range is approximately 2 K, effectively counteracting the negative effects of crosswinds. [ABSTRACT FROM AUTHOR]

Microchannel condensers play an essential role in cryogenic two-phase heat management systems due to their efficient heat transfer characteristics. Thus, it is worth conducting an in-depth study on microscale condensation characteristics of cryogenic fluids. This paper delves into the flow condensation process of methane in microchannels. A two-dimensional transient model with high accuracy for cryogenic fluids has been developed by combining a self-defined program for the source term of the phase transition model. The model fully considers the boundary layer thickness and accurately explores the mesh accuracy. The complete condensation flow patterns are captured for various vapor quality, mass flux, and wall subcooling degrees. The injection flow is a unique flow regime for condensation in microchannels. The decrease in wall subcooling degree and increase in mass flux leads to the separation point at the neck of the injected flow moving towards the exit, while the annular flow region is expanding and the flow pattern transition is lagging. The mass flux improves the heat transfer coefficient more significantly at high vapor quality. During injection and bubble flow, the wall shear stress and local heat transfer coefficient are subject to bouncing and oscillations, which may induce fluctuations in the upstream annular flow. The prediction performance of six classical heat transfer correlations is evaluated. The results indicate that the Nie et al. correlation has the highest comprehensive prediction accuracy with MRD and MARD of -5.00 % and 15.83 %, respectively. [ABSTRACT FROM AUTHOR]

Copyright of Irrigation & Drainage is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The performance of a magnetocaloric heat pump (MCHP) consisting of active magnetocaloric regenerators (AMR) of 12 layers of MnFePSi magnetocaloric materials (MCM) with a linear distribution of Curie temperatures was investigated using a 1D numerical model. The model predicted the heating power and coefficient of performance (COP) of the AMR for a fixed temperature span of 27 K, between 281 K and 308 K, and variable flow rate and AMR cycle frequency. A maximum applied magnetic field strength of 1.4 T was used. A well-insulated house with a maximum heating power demand of 3 kW (under quasi steady state conditions) was considered. Ambient temperature in The Netherlands was taken as a reference for the estimation of the seasonal heating power demand. Without optimizing the design of the AMR, the model predicts a maximum single-AMR heating power equal to 43.5 W when the AMR operates at 3 Hz and 3 L min-1, and a maximum COP equal to 5.8 when it operates at 1.5 Hz and 1 L min-1 Considering the maximum heating power of a single AMR, approximately 69 AMRs are needed to provide the design heating power demand of the house. It was found that it is possible to achieve an AMR seasonal COP of 5.6 by continuously adjusting the flow rate and frequency of operation of the MCHP along with the ON/OFF switching of some groups of AMRs in order to adjust the heating power of the MCHP to the heating power demand of the house. • MnFePSi is used for the setup of a 12-layer active magnetocaloric regenerator (AMR). • AMR heating power and COP are mapped against flow rate and frequency using a 1D model. • A part-load operating strategy is proposed for residential magnetocaloric heat pumps. • ON/OFF switching of AMR groups is used along with flow rate and frequency modulation. • A heating AMR seasonal COP of 5.6 is obtained under Dutch climate conditions. [ABSTRACT FROM AUTHOR]

• Preliminary exploration of radial wave rotors in refrigeration applications. • Radial configuration simplifies refrigeration cycle. • Two strategies are posited to augment equipment adaptability. • The dynamics of radial heat transfer and power consumption have been investigated. • The refrigeration coefficient peaks when φ = φ i and n = 2750 rpm. Gas wave refrigeration technology is an innovative refrigeration technique that harnesses pressure waves to facilitate energy exchange. In this paper, the wave rotor undergoes a transformation from its original axial structure to a radial structure. The self-pressurization capability of radial structure is proven to facilitate autonomous gas circulation, obviating the necessity for a drive fan, according to numerical simulations. We explore two methods to regulate the cycling ability for improved adaptability: altering exhaust ports and controlling exhaust resistance. The former offers a broader range of adjustment, while the latter is suitable for fine-tuning due to associated throttling pressure loss. Additionally, the mechanism of radial heat transfer is probed, revealing its intensification correlating with rising rotational speeds. The study also delves into the power consumption dynamics unique to the radial configuration. Influenced by these two factors, the device attains its peak efficiency near the specific internal circulation state of φ = φ i. The optimal rotational speed is determined to be 2750 rpm, which offers a balance between eddy current loss and power consumption. This study demonstrates that a radial gas wave refrigerator enables the integration of the pressurization and refrigeration processes. It serves as the foundation for subsequent structural optimization and experimental research on radial configurations. [ABSTRACT FROM AUTHOR]

Liquid methane is a critical cryogenic fluid that is accelerating into widespread applications. Since the heat transfer process is continuously weakened during methane liquefaction, it is significant to conduct studies on heat transfer enhancement methods. By applying the VOF model, this study numerically simulates a designed converging minitube, investigates the mechanism of heat transfer enhancement intensively, and compares results with those of two straight minitubes with different diameters. An in-depth analysis combining several aspects of dimensionless velocity, turbulence intensity, and liquid film thickness is provided. It is found that the condensation heat transfer coefficient of the converging minitube decreases and then increases with declining vapor quality and shows a remarkable heat transfer enhancement compared to straight minitubes. The overall heat transfer efficiency of the converging tube is improved to a maximum of 94.72 % compared to the straight tube (D =1 mm, G =400 kg m−2 s−1). The turbulent intensity is mainly responsible for the heat transfer enhancement in the converging tube. For straight tubes, the combined effect of liquid film thickness and turbulent kinetic energy is required to determine the ultimate heat transfer performance, especially at low mass flux. The impact of flow directions is also discussed in the context of practical application scenarios. It is revealed that gravity could enhance heat transfer under specific conditions, enabling the horizontal arrangement to demonstrate better heat transfer performance. This research reveals the characteristics and mechanism of the condensation heat transfer enhancement of methane in the converging minitube, thus providing guidance for practical applications. [ABSTRACT FROM AUTHOR]

Copyright of Irrigation & Drainage is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• Biomimetic fins are proposed to enhance the solidification in spherical capsules. • The influences of geometrical configurations of fins are investigated quantitatively. • An optimum design of biomimetic fin is proposed. • A prediction formula of ice volume under different cooling conditions is generalized. Ice storage enhanced by biomimetic fins in spherical capsules is studied numerically based on enthalpy-porosity method. The evolution of water/ice interface, the temperature variation, and the cooling energy storage capacities are examined quantitatively to gain further insight into the solidification process in capsules. Especially, the geometrical configurations of fins, including the maximum bifurcate level and fractal dimension of length, are investigated. In addition, four evaluation criteria are employed to determine the optimum design for the biomimetic fins. The results show that the biomimetic fins are significantly effective in enhancing the heat transfer in the stage of cooling energy storage through sensible heat in ice. The performance enhancement is facilitated as the level of fins is increased that average 24% reduction in solidification time is achieved by the fin-Ⅲ series with only 1.24% loss of cooling energy storage capacity averagely. An optimum design for biomimetic fins is the fin-Ⅲ with a fractal dimension of 3, which results in a 30.01% increase in dimensionless cooling energy storage capacity per unit time and weight compared to the case without a fin. Aluminum is a favorable fin material considering both the enhancing performance and material cost of the capsule. A prediction formula of ice volume under different cooling conditions is generalized. [ABSTRACT FROM AUTHOR]

• Water and steam two-phase flow numerical simulation was carried out. • Wall-approaching film formation characteristics of the injected water were studied. • Effects of injection parameters on film formation characteristics were analyzed. • Optimal operating conditions of water injection parameters were obtained. To investigate the wall-approaching film formation (WAFF) mechanism of water injected during the compression process of single screw compressor, then to realize reasonable control of water injection parameters, a numerical simulation of water and steam two-phase flow inside the compression chamber during the compression process was carried out. The WAFF characteristics of water injected inside the compression chamber and the influence laws of the key parameters such as water injection angle (IA), injection velocity (IV), injection mass flow rate (IMFR), screw rotor rotational speed (SRRS) and injection hole spatial position (IHSP) on the WAFF characteristics were analyzed. The results show that the water injected into the chamber forms a water film by approaching the wall. With the increase of IA and IV, the effective water film average thickness (EWF-AT) and surface area (EWF-SA) show an increasing trend. In the process of IMFR growth, EWF-AT and EWF-SA exhibit maximum values. Considering the goal of minimizing the injection power consumption, the IA of 70°, IV of 30 m·s−1 and IMFR of 0.3 kg·s−1 were determined as the optimal water injection parameters. Selecting the appropriate IMFR, SRRS and IHSP will effectively increase EWF-AT and EWF-SA, then to prevent leakage. [ABSTRACT FROM AUTHOR]

Despite their potential severity, collisions against obstacles on alpine ski slopes remain poorly described and a better understanding of these accidents is required to improve the protection of users on the slopes. Therefore, this study aimed to characterize the impact conditions applied to the human body during collisions against obstacles by coupling multibody simulations while skiing with an epidemiological analysis to model representative scenarios. In France, between 2014 and 2019, 201,805 snow sports accidents led to ski patrol interventions and/or ski resort doctors' consultations. The 3393 collisions against obstacles included in these accidents were analyzed (population, injuries, accident conditions). Based on this characterization, 1080 multibody simulations of collisions against obstacles were performed. They included various skier speed and size, slope angle, obstacle type and distance at impact to better understand loading conditions applied to the human body. Victims of collisions against obstacles were frequently skiers, young people, wore a helmet and head/neck and trunk were injured in up to 46% of the accidents. The numerical simulations confirmed head protection as a priority, due to the high frequency of head impacts (68%), especially as the first impact location (47%), associated with high normal impact speeds (30 ± 15 km/h). Trunk impacts (63% of the accidents) also appeared at risk. Moreover, the initial speed and the distance to the obstacle are 2 key factors influencing impact severity and should be considered in the slopes' layout. Thus, this work provided an original epidemiological characterization of victims of collisions against obstacles and of their injuries. The large database of numerical simulations identifies the impact conditions of representative accidents. These data and impact conditions are key elements for the evaluation and design of safety mattress, for standards revision, for slopes' layout, for the reconstruction of a specific collision against obstacle and for the evaluation of the potential severity of such accidents. [ABSTRACT FROM AUTHOR]

● The Gd/Cu bimetal composites are fabricated and interfacial layers are observed. ● Interfacial thermal resistance (ITR) is calculated based on thermal resistance test. ● Equivalent thermal conductivity is proposed to evaluate heat transfer capability. ● Reducing the ITR can significantly improve solid-state magnetic cooling performance. ● Combination of a topology-optimized structure and a reduced ITR is more beneficial. The low heat transfer efficiency caused by a magnetocaloric material (MCM) with low thermal conductivity is the bottleneck that limits the performance of magnetic refrigeration (MR). Previous studies have shown that a bimetal composite of a high thermal conductivity material and an MCM is effective in improving the heat transfer rate. However, the bimetal composite structure causes extra interfacial thermal resistance (ITR). Therefore, this study investigates the processing of gadolinium/copper bimetal composites by fusion casting and experimentally determines the ITR. To evaluate the structural heat transfer capability, the equivalent thermal conductivity (k eq) is proposed, which is calculated based on the ITR result and simulation. The influence of the ITR and k eq on the cooling performance of a fully solid-state MR is carefully investigated using a validated simulation model. The results show that the smallest ITR of 3.74 × 10−5 m2 K W −1 is obtained with a copper pouring temperature of 1200 °C owing to the thinnest bonding interfacial layer. The topology-optimized structure, using the ITR obtained by fusion casting, has an k eq of 159.8 W m −1 K −1, with an increase of 39% compared to the structure assembled with thermal grease. As a result, the maximum specific cooling power (SCP max) range and corresponding optimal operating range are significantly expanded to 45.6–209.3 W kg−1 and 0.23–0.61 rpm, respectively, with an average SCP max increase of 35.5%. The combination of using topology optimization design to reduce the structural thermal resistance and using a suitable forming process to reduce the ITR can be more beneficial to the performance improvement of solid-state MR. [ABSTRACT FROM AUTHOR]

• A spray pre-cooled NDDCT model under crosswind conditions was developed. • The behavior of droplets under crosswind and no crosswind were compared. • Feasible nozzle arrangements were explored under different crosswinds. • Good nozzle arrangement should consider height, radius, spray angle and crosswind. Crosswind affects the airflow fields of the natural draft dry cooling towers (NDDCTs), thus the spray zones for pre-cooling the inlet air of the NDDCT might be different from no crosswind. Therefore, a 3-D model of pre-cooled NDDCT under crosswind was established by Fluent 16.2 to investigate the feasible zone of nozzle spray of a 120 m high NDDCT based on the behavior of the droplets. Six nozzle heights, nine nozzle radiuses and four spray angles were simulated for the NDDCT application within the crosswind speeds of 0∼10 m/s. The evaporation percentage of droplets higher than 99% and the maximum effective evaporation ratio are selected as the criterion for the feasible zone of nozzle arrangement. Simulation finds that: (1) the nozzle arrangement height should be set at 7 m when the crosswind speed is 0 m/s, and it should be set at 9 m when the crosswind speeds are 2 m/s, 4 m/s,6 m/s, 8 m/s and 10 m/s, respectively. (2) The feasible spray angles of nozzles are 0°and 90° at the crosswind speeds of 0∼4 m/s and 6∼10 m/s, respectively. (3) The nozzle radiuses are 0∼41.5 m at crosswind speed of 0 m/s, they are 0∼21.5 m at the crosswind speed of 2 m/s, and they are 0∼16.5 m when the crosswind speeds are 4 m/s, 6 m/s, 8 m/s and 10 m/s, respectively based on the above feasible heights and spray angles. The results will provide a guidance for nozzle design of spray pre-cooled NDDCT under crosswinds. [ABSTRACT FROM AUTHOR]

The cryogenic organic Rankine cycle (ORC) is appropriate for recovering the cold energy of liquefied natural gas (LNG) for power generation. However, pure working fluids in ORC are challenging to match the evaporation curve of LNG appropriately, which causes a large amount of exergy loss. Thus, adopting mixture working fluid is a good option due to their temperature-varying evaporation and condensation process. This study investigates the heat transfer characteristic of R134a/ethane (widely adopted in cryogenic ORC as pure working fluid) binary mixture in the horizontal micro-tube through numerical simulation. The law of boiling heat transfer characteristics with vapor quality, heat flux, mass flow, ethane mole fraction, and other factors are obtained. The simulation illustrated that the boiling heat transfer coefficient increases with the heat flux and mass flow. Furthermore, compared with R134a, ethane has higher thermal conductivity, lower vapor density, and latent heat of vaporization. Hence, the heat transfer coefficient of the R134a/ethane mixture increases with the ethane's mole fraction. The fluid disturbance mainly influences the pressure drop and the turbulence intensity significantly when the fluid is transformed into a gas–liquid flow. This study could provide insights into boiling heat transfer improvement of binary mixtures for ORC power generation applications. • The heat transfer characteristics of R134a/ethane mixture are studied by numerical simulation. • The mechanism of boiling heat transfer characteristic is explained by means of the flow pattern. • The mixture's boiling heat transfer coefficient is higher than pure ethane in high vapor quality. • The positive and negative effects of mass flow on heat transfer coefficient are analyzed. [ABSTRACT FROM AUTHOR]

In this paper, microchannel flow boiling heat transfer and critical heat flux (CHF) are numerically characterized under both static and rolling conditions. The volume of fluid (VOF) based numerical model of a rectangular microchannel with the dimension of 4 × 400 mm is established. The additional force induced by rolling motion is loaded via a user defined function (UDF). Rolling amplitude and rolling period vary in the range of 10∼20° and 1∼2 s, respectively. The results demonstrate that bubble flow, slug flow, stretch bubble flow and annular flow are observed under static conditions. However, under rolling conditions, bubbles are more difficult to agglomerate and coalesce under the influence of additional forces. Rolling motion maximumly deteriorates CHF by 81.1% and wall temperature by 18.8%, respectively. Moreover, CHF decreases with the increase of rolling period while increases with the increase of rolling amplitude. The purpose of this research is to understand the microchannel CHF triggering mechanism under rolling conditions to aid in marine heat exchanger design. [ABSTRACT FROM AUTHOR]

This paper aims at providing exact expressions for the mechanical fields induced by Laser Shock Peening and comparing them to their numerical estimations. We use a uniaxial strain field hypothesis with an elastic perfectly plastic behavior to derive the stress wave equation. An exact solution to this equation is given using the method of characteristics for a step time profile for the pressure loading, and numerically using finite differences schemes adapted for this hyperbolic equation. An additional residual stress modeling is used, providing the residual stress distribution assuming a planar infinite plate with a finite thickness. Results are presented for three loading pressures, each one corresponding to a different structure in the exact solution. The exact and numerical results present a good match, allowing either the use of the exact solution for an initial estimation of the mechanical fields, or to test the accuracy of other numerical methods. [ABSTRACT FROM AUTHOR]

Copyright of Irrigation & Drainage is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• Inclination angle improves refrigeration performance. • Loss in the oscillating tube is mainly vortex loss and shock intensity loss. • A numerical model of velocity pattern and pressure retention coefficient is built. • Inclination angle can reduce cyclic force and shaft work consumption. Gas wave refrigerator (GWR) is a new type of refrigeration machinery that uses pressure waves to transfer energy between gases. In this paper, the flow characteristics and refrigeration mechanism in the wave rotor are numerically simulated. The nozzle angle is introduced to improve the overall refrigeration performance and expand the efficient operating range of the equipment. After verifying the model and method, the potential mechanism of refrigeration loss in the oscillating tube and the effect of loss on refrigeration efficiency are discussed in detail. Then the influence of incident angle on flow loss, refrigeration temperature drop, and power consumption are discussed. The association model of velocity development pattern and the maintenance of pressure performance at the inlet position of the oscillating tube is established during the high-pressure gas incident. The obtained numerical results show that flow loss and shock intensity loss are the main energy loss factors in the wave rotor. The incident angle determines the loss of the refrigeration process. The optimal incident angle of the device at the working point is obtained. The "balance" of velocity distribution in the oscillating tube can effectively reduce vortex loss. Arranging nozzles in the same rotation direction as the wave rotor can reduce work consumption, and the variation law is approximately negative linear correlation. Furthermore, based on the current simulation results, a set of nozzle design methods are obtained. It laid the foundation for the subsequent experimental research and optimization of GWR equipped with adaptive nozzles. [ABSTRACT FROM AUTHOR]

• In run pipe, "descend-ascend" of static and total pressure happens under high F. • The local pressure drops of R1234yf, R600a and R245fa increase in turn. • An ANN predicting model of local pressure drop was established. • Sensitivity analysis of flow parameters on K 12J and K 13J was conducted. The two-phase flow behaviors in T-junction are quite complex in energy transport systems. In this paper, the two-phase flow pressure drop of refrigerants in a horizontal branching T-junction was analyzed numerically and predicted using artificial neural network. Firstly, the distribution of static and total pressure was obtained based on Eulerian method, and the parametric studies on the local pressure drop were conducted. It is observed that the vortexes in the entrance of branch pipe lead to the pressure fluctuation and irreversible pressure losses, and the "descend-ascend" of static and total pressure happens under high mass flow split ratio in run pipe. Then, the ANN predicting model of local pressure drop coefficients was established. It shows that GA-BPNN and PSO-BPNN has the best predicting ability for K 12J and K 13J respectively, and the relative errors are within 10% for most cases. Finally, the sensitivity analysis was conducted, indicating that the effect of mass flow split ratio (F) and inlet quality (x 1) is the most significant for K 12J and K 13J respectively. [ABSTRACT FROM AUTHOR]

• Simulation on constituent separation and mass transfer in T-junction is performed. • Numerical simulation with mass transfer is compared to that without mass transfer. • The influence of the quality at inlet on the constituent separation is studied. • Flow characteristic and mass transfer of base case are discussed. • A correlation of mass transfer for annular flow in T-junction is proposed. The study of constituent separation in T-junction is important to realize the operation of the constituent adjustable system. This paper presents a numerical simulation on the constituent separation and mass transfer of R134a and R600a in T-junction. The multiphase flow model of volume of fluid (VOF) is adopted, and the interphase mass transfer of R134a and R600a is achieved by adding source terms in governing equations. The quality at inlet varies from 0.51 to 0.92. The mass flow rate at inlet and flow rate weighting of branch outlet are 10 g⋅s−1 and 0.3, respectively. Results show that the error of numerical simulation with mass transfer is lower than that of numerical simulation without mass transfer. When the quality at inlet is 0.81, the error of numerical simulation with mass transfer can be reduced by 50.07% compared with the numerical simulation without mass transfer. The higher the quality at inlet, the higher the separation efficiency of R134a when the quality at inlet is less than 0.81. When the quality at inlet is 0.81, the separation efficiency of R134a in the numerical simulation with mass transfer is the largest, whose value is 1.47%. Most of the flow patterns are annular flow. The pressure and flow pattern have an important influence on the constituent separation and the interphase mass transfer rate. A correlation with 10% error band of interphase mass transfer for annular flow in T-junction is proposed. [Display omitted] [ABSTRACT FROM AUTHOR]

• The cabin heat dissipation was analyzed under two ventilation modes (air supply/air exhaust). • The Experimental devices and CFD method were introduced and the results comparison were made. • The flow fields of the two conditions were analyzed and compared. • A better heat dissipation environment of reefer container was obtained in the air supply condition. In global refrigerated transportation, marine reefers play an extremely important role. Considering the high freight cost and harsh surroundings of the decks during the voyage, reefer containers are always loaded into cabins for safe and economical purpose. However, under severe environment conditions in cabin , the refrigeration efficiency of reefer units was greatly affected, because of the weak ventilation and low heat exchange capacity. In order to find a more scientific and reasonable way to ventilate the cabin of reefer containers, two different ventilation modes, that is, air supply and air exhaust, were experimented and simulated. The temperature distribution was analyzed in a typical reefer cabin with 14.4 m (in length) × 23.2 m (in width) × 16.85 m (in height). Compared with two contrary ventilation modes, the temperature distribution in the cabin at steady state was simulated and analyzed. The results show that, the temperature of the cabin under the air exhaust condition was about 4K lower than that under the air supply condition. But with higher heat dissipation efficiency, the air exhaust condition sacrifices the uniformity of the temperature in the cabin. A relatively uniform temperature distribution and airflow field were obtained under air supply condition. Therefore, considering the heat dissipation effect of the container and the uniformity of airflow distribution, the air supply method was recommended. The two ventilation modes were compared in detail in this paper, and the results provide a reference for ventilation design of reefer container vessels. [ABSTRACT FROM AUTHOR]

This paper presents an analytical model for quantifying the uncertainty of three-dimensional fracture intensity measurements (P32), which measure fracture area per sampling volume, and for determining the geometrical representative elementary volume (REV) of fractured rock. The analytical model for estimating the variance of P32 is derived from the probability of a given number of fractures in a sample of rock. This model is validated through numerical simulations of fractured rock masses based on the discrete fracture network method. A series of parametric studies are conducted considering the dip angle, dip direction, Fisher constant, size and shape of the rock mass space, specimen volume, fracture diameter, and P32. Based on the results of the analytical model and the parametric studies, a simple model to quantify the coefficient of variation (COV) of P32 is established, which requires only the data of specimen volume, fracture diameter, and P32. Four engineering applications of the proposed analytical model are presented, including two case studies of estimating the geometrical REV at a given COV, one of assessing the variation of mechanical properties, and another of determining the variation of permeability. [ABSTRACT FROM AUTHOR]

The cylinder profile primarily determines the working performance of the sliding vane compressor. In order to increase the built-in volume ratio and compression ratio of the compressor, in this study, a novel asymmetrical cylinder profile composed of an exponential spiral was proposed, and then a novel asymmetrical sliding vane compressor was obtained. A geometric model of the proposed asymmetrical cylinder profile was established, and effects of power exponent n on the built-in volume ratio, area utilization ratio and acceleration of the cylinder profile were discussed. Furthermore, the working process of the proposed sliding vane compressor were simulated using structured dynamic grids, distributions of flow fields in the working chambers were obtained, and the gas pressure varying with the rotational angle was also analyzed. The study results show that the proposed sliding vane compressor has many remarkable advantages, small discharge volume, large built-in volume ratio and large compression ratio, compared with the traditional sliding vane compressor with the symmetrical cylinder of a circle profile under the same geometric size. The contents of this study are of great significance for promoting the development and application of sliding vane compressors. [ABSTRACT FROM AUTHOR]

• Superheated condensation is a combination of convection and phase transition. • The film is thinner at higher mass flow rates in the condensing-superheated zone. • High mass flow rate enhances heat transfer in superheated condensation zone. • This study explains the heat transfer mechanism in the condensing-superheated zone. The heat transfer process in the condenser is often divided into superheated, two-phase and subcooled zone. But the three-zone model has discontinuities of the heat transfer coefficient between single phase and two-phase regions. This study applies a computational fluid dynamics (CFD) study on the two phase flow and the heat transfer characteristics in the condensing-superheated zone. The condensation process of R410A (T sat =44.59°C) in a horizontal pipe (D i =6.1 mm) is simulated by using VOF (volume of fluid) model. The formation and the development of the condensation film are detailed analyzed. The heat transfer mechanism in the condensing-superheated zone includes both the single-phase convection and the phase transition. The heat transfer coefficient in the superheated condensation area increases from the single-phase convection to the saturated condensation. Combined with the development of liquid film morphology, this study is helpful for understanding the flow and heat transfer mechanism in the condensing-superheated zone. [ABSTRACT FROM AUTHOR]

L'objectif du présent travail est d'étudier numériquement le comportement hydrodynamique et les transferts thermiques par convection forcée de l'eau circulant dans un micro canal rectangulaire d’une hauteur allant de 100 à 1 mm. Le nombre de Reynolds est compris entre 50 et 10000. La simulation a été effectuée à l'aide du code de calcul 'Fluent' qui est basé sur la Méthode des Volumes Finis. L'étude numérique indique que l’évolution numérique du coefficient de frottement, pour des écoulements laminaires et turbulents dans des micro canaux lisses, est bien prévue par les lois classiquement utilisées aux échelles conventionnelles. Les résultats ont également confirmé que le nombre de Nusselt est en bon accord avec les valeurs théoriques, sauf pour les canaux de moins de 200 de hauteur où il a été noté une forte diminution des valeurs de Nu.

• The pressure distribution and phase separation parameters of branches are analyzed. • The phase split performance between two branches is compared. • An optimal value of branches' distance is found. • The phase separation of branches reaches best when the distance is 2.0 m. • An empirical correlation is proposed to predict the split efficiency of branch. T-junction is widely used as a phase separation component to separate two-phase flow because of its simple structure and low cost. Previous studies suggest that an increase in the number of T-junction branches is conducive to raise phase separation efficiency. In this paper, the pressure distribution and phase separation performance of two-phase flow of R134a in horizontal double T-junctions are studied. The phase separation performance between two branches is compared. The parameters including inlet quality (0.3-0.6), inlet mass flow rate (10.0 g s−1-25.0 g s−1), diameter ratio (1, 0.75) and the distance between two branches (0.3 m-2.6 m) are studied. The inlet mass flow rate has significant influence on the phase separation, and the separation performance reaches best when it is 10.0 g s−1. Results show that the change of parameters has greater influence on the phase separation performance of the second branch compared with the first branch. When the distance between branches is 2.0 m, the total phase separation capacity of the branches reaches the best. By comparing the phase separation of branches, it can be found that when the distance increases gradually, the phase separation performance of the second branch first increases and then decreases, indicating that there is a specific distance that maximizes the gas phase separation efficiency of branches. The optimal distance is also related to the mass flow ratio of the second branch. Therefore, an empirical correlation equation which can accurately predict the gas phase separation efficiency of the second branch is proposed. [Display omitted] [ABSTRACT FROM AUTHOR]

Liquid film pattern is crucial for mass transfer performance of falling film liquid desiccant dehumidifier (LDD). Rough plate may be effective on modifying the liquid film pattern and then enhance dehumidification efficiency of the LDD. Therefore, this study aims to investigate unsteady gas-liquid flow and dehumidification performance of falling film LDD for smooth and rough plates. The gas-liquid flow was predicted by the RNG k-ε turbulence model while the interface patterns were tracked by volume of fluid (VOF) model. The dehumidification performance was simulated by user-defined function (UDF) codes based on the penetration theory. The dynamic liquid film characteristics, the gas-liquid flow fields, the mass fraction fields and dehumidification enhancement mechanisms were analyzed and discussed. Moreover, the effects of inlet air velocity and inlet desiccant concentration on the mass transfer characteristics were investigated. The results showed that the ribbed plate can induce liquid film waves and significantly enhance dehumidification performance of the falling film LDD. The dehumidification enhancement can reach 30.9% by the rough plate when inlet air velocity is 0.5 m s−1 and inlet desiccant concentration is 30%, compared with the smooth plate case. The enhancement mechanisms of dehumidification by the rough plate include the liquid film waves, the flow vortex and high-value TKE near the gas-liquid interface. The outlet mass fraction of water vapor is decreased when the inlet air velocity is lower and the inlet desiccant concentration is higher. The rough plate is effective for the mass transfer enhancement for different inlet air velocity and desiccant concentration. [ABSTRACT FROM AUTHOR]

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Dans ce contexte, le travail présenté porte sur l’étude, la modélisation d’une machine hexaphasée alimentée par un onduleur héxaphasé. Cette machine asynchrone hexaphasée (MASHP) n’est pas un système simple, car de nombreux phénomènes compliqués interviennent dans son fonctionnement, comme la saturation, l’effet de peau, etc..., [1]. L’objectif de ce travail est de présenter le modèle général de la MASHP dans le repère réel (abc). Ensuite, nous présenterons les différentes étapes permettant d’aboutir au modèle diphasé de la MASHP, obtenu à partir d’une matrice de transformation appropriée [2]. Afin de simplifier l’étude, la simulation numérique de la MASHP, le système de dimension six sera décomposé en trois sous-systèmes découplés. Après l’alimentation de la MASHP par un onduleur de tension héxaphasé sera présentée. Dans ce qui suit, nous allons étudier l’influence du changement de l’angle de déphasage sur le comportement de la MASHP et nous avons montré que les meilleures performances sont obtenues pour la configuration =30°.

• A parametric convective heat transfer term is used to assess t span & cooling power. • Four major magnetocaloric materials are screened. • Optimal fluid velocity depends on the magnetic transition temperature. A 2-dimensional numerical model of a room temperature operating Active Magnetic Regenerator (AMR) that comprises of a regenerator, hot and cold heat exchangers, heat transfer fluid is developed. The regenerator is made of a magnetocaloric material (MCM) which heats up upon applying a magnetic field, H, and cools down when the field is removed; thus, making it the most essential part of an AMR. The model takes experimentally measured ∆T ad (H,T) and the C p (H,T) data as input and provides quantitative performance metrics of the magnetic cooling system, such as ∆T span and the cooling load, as output. With this model, it is possible to assess a wide range of MCMs in an AMR. 4 different MCMs were investigated using this model in terms of their ∆T span and the cooling loads—LaFe 10.96 Co 0.97 Si 1.07 , MnFeP (1-x) As (x) and AlFe 2 B 2 and Gd. During the screening of MCMs, all the important operating conditions of the device were fixed such as the fluid flow rate, ambient temperature, cycle duration, magnetic field strength. Our results indicate that Gd exhibits the maximum ∆T span with respectable cooling load, while AlFe 2 B 2 generates the lowest ∆T span. Even though LaFeCoSi compound did not perform as well as Gd, it could be the MCM choice for the realization of magnetic refrigeration on a global scale due to its much lower cost. [ABSTRACT FROM AUTHOR]

• Heat transfer between shell-side fluid and shell wall in the SWHEs is simulated. • The thermal entrance length is determined in terms of tube bundle number. • Effect of geometrical parameters on Nusselt number is investigated. • Nusselt number correlations are developed for entrance and fully developed regions. Heat transfer between heat exchangers and the surrounding environment, referred to as heat-in-leak, is a crucial phenomenon in the cryogenic applications which can substantially degrade the heat exchanger performance. Present research is organized to investigate the mechanism of heat transfer between the shell-side fluid and the shell wall of spiral wound heat exchangers (SWHEs) to determine the heat transfer coefficient used in the heat-in-leak calculations. The heat transfer characteristics are studied using computational fluid dynamics (CFD) tools. First, 20 dissimilar SWHE models with respect to the geometrical parameters are built and then numerically simulated at different Reynolds numbers. Based on numerical simulations, the thermal entrance length in which local Nusselt number varies is specified to be equal to around 80 tube bundles. Finally, the multiple regression analysis method is applied to establish the multivariate Nusselt number correlations in terms of Reynolds number and non-dimensional geometrical parameters. The average error of Nusselt number correlations in the entrance and fully developed regions are 6.2% and 5.6%, respectively. [ABSTRACT FROM AUTHOR]

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• Evaporation and concurrent evaporation and boiling of falling flow is simulated • Transition to boiling presence of R-245fa and R1233zd(E) is investigated • Tanasawa model simulates heat transfer up to (T w -T sat) of below 7 K for both fluids • Lee model predicts both evaporation and boiling of R-245fa with maximum error of 7% • Tanasawa model has to be selected carefully in falling film evaporation modeling Design of some thermal industrial equipment like Heating Ventilation and Air Conditioning falling film evaporators and desalination units requires knowing discrete portion of convective evaporation and boiling. While most models are based on sole dominant evaporation, one small variation in design parameters can increase boiling part and threaten the model. Heat transfer simulation of such equipment is dependent on mass transfer modeling. Therefore, this study uses different mass transfer models and numerically investigates two laminar falling film flows around a horizontal tube heating insomuch that leads to sole evaporation and evaporation with boiling. The multi-phase volume of fluid model is used and the performance of mass transfer models is investigated for heat transfer coefficient, film thickness, bubble generation and liquid superheating. Results show that for 240 mL*min−1 of R-245fa at saturation pressure of 123.8 kPa at wall and saturation temperature difference of below 7 K, main contribution of heat transfer is due to evaporation which is accurately modeled by Tanasawa and Lee phase change models. With increasing wall heat flux, boiling portion signifies. Accordingly, Tanasawa model is not able to simulate boiling part but Lee model predicts total heat transfer coefficient with 7% error. After validating the numerical model, the model has been used for R1233zd(E) as a low Global Warming Potential refrigerant and transition to boiling presence of the falling flow is investigated. Comparison of the results represents governing evaporation up to 7 K of wall and saturation temperature difference of R1233zd(E) at similar saturation temperature of R-245fa. [ABSTRACT FROM AUTHOR]

• A numerical model of the nitrogen condensation is developed to predict the performance at different practical operations. • The fin efficiency η of the tall fins at low temperature (<120 K) can be as high as 0.7. • An improved correlation of condensation heat transfer is proposed. • The 1 kW cooling power require only 1.5 K temperature difference at 77 K. Of importance is the study of the cryogenic condensation as it physically behaves differently owing to the interesting fluid properties of cryogens appearing at extremely low temperature. In the paper, we focus on numerically exploring the nitrogen condensation in mini channels having the high aspect ratio of 12.5 towards the application of the kW-scale cooling power. It is found that the heat transfer rate and coefficient lie in between the Nusselt condensation (NC) and extended surface condensation (ESC) solutions among the selected operational conditions. The numerical results reveal that the longitudinal conduction plays a role. Interestingly, the reversing flow happens as the inlet flow rate is insufficient to satisfy the nitrogen condensation and particularly it becomes dominant at the larger temperature difference. Most importantly, an improved correlation of the cryogenic condensation heat transfer is proposed and strongly suggests that the fin efficiency η can be as high as 0.7, which is different from the expectation that tall fins are ineffective in condensation. In terms of the 1 kW cooling power, the high-aspect-ratio fin exchanger studied just needs the temperature difference of 1.5 K and it can improve 10 times the efficiency of condensation. It is important that the studies can inform the optimization of the cryocoolers. [ABSTRACT FROM AUTHOR]

• The constituent separation in a 3D T-junction is numerically simulated. • The constituent separation efficiencies are obtained with the inlet quality 0.1–0.4. • The phenomenon of component separation with mass transfer in T-junction is discussed. T-junction, which is regarded as an effective solution to phase separation of air-water, has already been widely applied in industry sector, especially in thermodynamic cycles for improving cycle performance. However, the research on constituent separation of organic refrigerants in the T-junction is just emerging without clear understanding on mechanism, variation and application. In this paper, the constituent separation performance of organic refrigerants, R134a/R600a, in horizontal branch T-junctions is numerically investigated. The computations are conducted based on the Eulerian method with the k-ε turbulence model, which has been used to predict phase separation and an agreement is concluded. The inlet mass flux and qualities are 200 kg·m−2·s−1 and from 0.1 to 0.4, respectively. Based on the model, detailed phase and constituent distribution in T-junction are obtained and then discussed. Furthermore, the separation efficiencies of R134a are analysed based on calculation results. The results show that an agreement is observed on the separation efficiency with the inlet quality varying from 0.123 to 0.286 by comparing with the experimental results. When the inlet quality is 0.4, the inconsistency between the simulation results and the theoretical results and the experimental results may be due to two factors: changing of flow patterns and mass transfer of constituents. [ABSTRACT FROM AUTHOR]

• DC flow influence on the Vuilleumier type pulse tube cryocooler is studied. • Numerical simulation shows that a certain amount of positive DC flow rate is beneficial. • A certain amount of positive DC flow increases the expansion efficiency by mainly affecting the gas-wall heat transfer. DC flow may exist in a pulse tube cryocooler if a closed loop is formed by double inlet, etc. It has been found that, given the right amount and the right direction, DC flow may be favorable to the cooling performance of a PTC working at liquid hydrogen temperature and liquid helium temperature with Stirling type or G-M type PTC. In case of Vuilleumier type PTC, which is driven by a thermal compressor, none has been studied. In this paper, the effects of DC flow on a Vuilleumier type PTC working around 10 K have been studied through numerical analysis. In the simulation, the software SAGE is utilized to study the DC flow with a double-inlet module capable of adjusting the DC flow rate. The dependence of performance for thermal compressor on DC flow was firstly investigated. Then the influence of DC flow on the cooling performance was studied, including the cold end enthalpy, cooling capacity, expansion efficiency for pulse tube, etc. Main factors affecting the pulse tube expansion efficiency was distinguished. Finally, the operating parameters effects on cooling performance with varying DC flow rate were carried out. It is found that certain amount of DC flow is beneficial to the system performance with the optimum ratio between DC flow rate and AC flow rate amplitude lying within the approximate range from 0.05% to 0.08%. [ABSTRACT FROM AUTHOR]

• Four different heat pump systems (CVI-1S, CVI-SR, CVI-2S and CVI-3S) are analyzed. • The COP of each heat pump is maximized by optimizing the heat pump design. • The optimizations involve 167 fluids as possible refrigerants in the heat pumps. • The optimal fluids and the maximal COP are reported in charts. • The refrigerants dme, r161, r40, cf3i, r435a, r510a are among the best fluids. In this paper, numerical optimization analyses are performed for four distinct heat pump systems, namely, the CVI-1S, CVI-SR, CVI-2S and CVI-3S systems. These analyses are performed for various combinations of hot side and cold side temperature values (i.e., for hot side temperatures ranging from 25 °C to 60 °C, and for cold side temperatures ranging from -40 °C to 10 °C). A total of 167 fluids are compared in order to obtain the highest COP value, for each temperature combination investigated. A robustness analysis is also achieved so as to identify the fluids that provide a COP value larger than 95% of the maximal COP value. Results are presented as charts that allow identifying the best fluids and the most robust fluids for each heat pump system. The results show that heat pump systems involving more equipment or including separators are more efficient than the others. Moreover, the results show that the refrigerants dme, r161, r40, cf3i, r435a and r510a are among the most robust fluids for all heat pump systems investigated. [ABSTRACT FROM AUTHOR]

• The bypass cycle and injection cycle in a multi-split VRF system help increase the sub-cooling degree at inlet of EEV. • Energy efficiency ratio (EER) of the multi-split VRF system increases with application of the bypass cycle and injection cycle. • Performance of the VRF system with the injection cycle is more efficient under the same cooling capacity. In this study, the performance of a multi-split VRF system using the bypass cycle and injection cycle is evaluated using the numerical simulation as a possible sub-cooling method to prevent flash gas generation in liquid pipelines. The simulation for the multi-split VRF system is developed by considering the applications of the bypass cycle and injection cycle, and is validated with experimental data. The bypass cycle and injection cycle in the multi-split VRF system yield improvements in their cooling capacities of the order of 3.22% and 13.43%, respectively, and energy efficient ratio (EER) of the order of 1.98% and 1.72%, respectively. The input power of the injection cycle is reduced by up to 4.45% when the performance of the multi-split VRF systems with bypass cycle and injection cycle is compared under the same cooling capacity conditions. [ABSTRACT FROM AUTHOR]

• Evaporator carryover is a strong function of liquid level, mass flux, and saturation temperature. • Vapor velocity is the driving force behind the effects of mass flux and saturation temperature. • Droplet dynamics in the headspace may be numerically simulated using Lagrangian physics. The distribution of liquid droplets emerging from an evaporator tube bundle is characterized for refrigerant R-134a with a triangular tube arrangement with a pitch of 1.167. The purpose of this research was to improve understanding of the droplet ejection process to aid in design of evaporators typically used in larger chiller systems. A laser and camera system captured images of the evaporator headspace at varying conditions. Conventional shadowgraphy techniques were applied to recognize and match droplets for velocity calculations. The evaporator conditions varied with bundle mass fluxes of 20.3 and 40.7 kg s−1m−2, top-rows heat fluxes of 15.8 and 31.5 kWm−2, and outlet saturation temperatures of 4.4 and 12.8°C. Conditions ranged from flooded to dryout of the top rows. Droplet number, size distribution, velocity, and liquid volume fraction are presented in the headspace above the bundle. A method to numerically duplicate the droplet loading in the headspace using CFD with a Lagrangian discrete-phase model is also presented and verified, providing a powerful design tool. Liquid distribution in the headspace is found to be a strong function of all varied properties, particularly mass flux, liquid level, and saturation temperature. [ABSTRACT FROM AUTHOR]

• Effective force area and discharge coefficient are reported for a large range of valve operating conditions. • The Finite Volume Method implemented in OpenFOAM is used to obtain the parameters. • The lift influences significantly both parameters. • The diameter ratio influences more significantly the effective force area. • The Reynolds number influences more significantly the effective force area. Radial diffusers have been used as valve model to determine effective force area and discharge coefficient of the flow. A comprehensive data set of these parameters is lacking in the literature. Here, we present numerical results of these parameters for a wide range of incompressible flow operating conditions. The code OpenFOAM® was used to solve the problem for radial diffusers with diameter ratios ranging from 1.15 to 1.7, Reynolds numbers ranging from 3000 to 50,000, and lifts varying from 0.01 to 1.0. The influence of the diameter ratio on the effective force area is found to be high. There is a decrease of up to 80% for small lifts and an increase of 40% for large lifts, but it has a negligible effect on the discharge coefficient. The influence of the Reynolds number on the discharge coefficient is small, up to 8%, but it is large on the effective force area. [ABSTRACT FROM AUTHOR]

The Note is concerned with a feasibility study of time reversal in a non-homogeneous elastic medium, from data recorded in an acoustic medium. Our aim here is to determine the presence and some physical properties of elastic "inclusions" (unknown, not observable solid objects, characterized by their elastic properties) from partial observations of acoustic waves scattered by these inclusions. A finite element numerical method, based on a variational acousto-elastodynamics formulation, is derived and used to solve the forward, and then, the time-reversed problem. A criterion, derived from the reverse time migration framework, is introduced, to help construct images of the inclusions to be determined. Numerical illustrations on configurations that mimic the breast cancer configuration are proposed, and show that one can differentiate between two inclusions, even with different properties. [ABSTRACT FROM AUTHOR]

Copyright of Larhyss Journal is the property of Biskra University, Research Laboratory in Subterranean & Surface Hydraulics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Highlights • Numerical model was developed to predict the performance of multi-split variable refrigerant flow (VRF) systems using the vapor-injection with the geometry-based model of a scroll compressor. • The performance of multi-split VRF system was affected by the variation of the intermediate pressure due to the variation in the sub-cooling degree and the isentropic efficiency of a scroll compressor. • The temperature difference in each indoor room affected the intermediate pressure to maintain the preset degree of superheating at the exit of injection line. Abstract The performance of the variable refrigerant flow (VRF) system becomes poor at a very low ambient temperature because of the decrease in the suction mass flow rate. The vapor injection is applied to the heat pump system to enhance the performance of the systems in a cold season. In this study, the influence of the vapor injection under different intermediate pressures and outdoor ambient temperatures was investigated mathematically, and the results were validated with experimental data. In addition, the performance variation was observed with different indoor ambient temperatures in nine indoor units. The intermediate pressure affected the heating capacity, input power, coefficient of performance (COP), and isentropic efficiency of the compressor. The improvement of the COP with vapor injection was dominant at a low ambient temperature. The heating capacity at different indoor ambient temperatures was observed with different refrigerant mass flow rates in each indoor unit. [ABSTRACT FROM AUTHOR]

Highlights • Developed an energy efficient control method enabling online selection of optimum V *. • Developed the procedure to determine the map of the optimum V *. • Discovered 17.4% efficiency enhancement from the baseline control method. • Identified the transient loss caused by simultaneous control of frequency and V *. Abstract Magnetic cooling system has a significant energy saving benefit, if the part load operations can be properly leveraged. In this study, an online optimum control method is proposed that not only automatically maintains the temperature of the cold heat exchanger, but also provides additional efficiency enhancement since the optimum utilization factor is determined based on the instant operating conditions in real time. Numerical simulations are carried out to characterize the steady state performance map. The database of the optimum utilization factor is then developed based on it. When applying the optimum utilization factor to the control method, both the transient responses during the start-up process and the variable load operation are evaluated. It is found that the proposed online optimum control method introduces an additional transient loss, due to the simultaneous adjustments of frequency and utilization factor. [ABSTRACT FROM AUTHOR]