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The blade angle has a great effect on hydraulic performance and internal flow field for axial-flow pumps. This research investigated the effect of the blade angle on hydraulic performance and tip leakage vortex (TLV) of a slanted axial-flow pump. The hydraulic performance and the TLV are compared with different setting angles. The dimensionless turbulence kinetic energy (TKE) is used to investigate the TLV. A novel variable fv is utilized to analyze the relation among the TLV, strain tensor and vorticity tensor. The proper orthogonal decomposition (POD) method is used to analyze TLV structure. The results show that with the increase of the blade angle, the pump head is getting larger, the flow rate of the best efficiency moves to be larger, and both the primary TLV (P-TLV) and the secondary TLV (S-TLV) are getting stronger. The P-TLV often exists in the outer edge of TKE distribution and S-TLVs often exist in the largest value area of TKE. This phenomenon is more evident with blade angle increasing. Through POD method, it shows that the first six modes contain more than 90% of TKE. The reason why the TKE value near the region of S-TLV is high is that the tip leakage flow is a kind of jet-like flow with high kinetic energy. The main structure of the P-TLV is shown in modes 4−6, resulting in a reflux zone but not with the highest TKE.

In this paper, a three-dimensional non-isothermal computational model for predicting indoor SVOC distribution is proposed, considering the effects of turbulence diffusion and suspended particles. The realizable k-e model is introduced for turbulent flow simulation in a room. The Euler-Euler method is adopted to deal with the gas-particle two-phase flow coupled problem. Inertia slip velocity and irreversible first-order absorption boundary are employed for more accurate prediction of particle motion. The simulated curve of outlet gas-phase di-2-ethylhexyl phthalate (DEHP) concentration with emission time is verified by available experimental data. The emission process of DEHP in a 15 m2 room in Beijing during 100 days with or without air cleaner is simulated by the developed model considering air leak through window and door gaps. It is found that if the air cleaner keeps on all the time during 100 days the gas-phase DEHP concentration in the room will tend to be uniform, while the emission process is far from equilibrium without an air cleaner even the emission lasts 100 days. Results also suggest that floor heating, decrease of particle concentration, weaken of heat transfer, enhancement of mass transfer, and air infiltration in window gap contribute to decrease DEHP concentration.

Exploring the origins of local transport resistance and characterizing the oxygen transport resistances in the catalyst layer (RCL) are critical for cost reduction. In this paper, a comprehensive mesoscopic model for simulating coupled transport processes of oxygen and water vapor for different structural parameters under different operating conditions in reconstructed microstructures is proposed. The local transport resistance is calculated after achieving the limiting current density and the effective diffusivity of oxygen. The results demonstrate that RCL increases greatly with decreasing platinum loading (LPt) and the transport resistances in other components of the cell dominate for high-loadings. Both the reduced oxygen permeation coefficient in the ionomer thin-film and the adsorption resistance account for the origins of local transport resistance. The local transport resistance increases with the bare carbon ratio for a constant LPt and Pt/C ratio due to the decreased effective ionomer surface, and increases with the I/C ratio due to the increased ionomer thickness and decreased Knudsen diffusivity. Due to the presence of liquid water, a slight decrease followed by an increase of the local transport resistance versus relative humidity is obtained. The contribution of ionomer thin-films to RCL is more sensitive to liquid saturation compared with that of pores. This journal is

Favourable effects of oxygen vacancies in TiO2-x synthesized via a calcination method on the electrochemical performance of dual Mg/Li-ion batteries are investigated. The dual-ion cell shows excellent rate capabilities up to 40 C and outstanding cyclability up to 2500 cycles.

In this paper, the groove effect on the tip leakage vortex cavitating flow characteristics of a simplified NACA0009 hydrofoil with tip gap is studied. Considering local rotation characteristics and curvature effects of the tip leakage vortex flow, the rotation-curvature corrected shear-stress-transport turbulence model is applied to simulate the time-averaged turbulent flow. The Zwart–Gerber–Belamri cavitation model is used to simulate the cavitating flow. The results show that the groove could affect the tip leakage vortex cavitating flow. The groove enhances the interaction between the tip leakage flow and main flow, and then it affects the cavitation of the tip leakage vortex. Compared with the non-groove case, for groove cases of αgre ≤75°, the tip leakage vortex cavitating flow is suppressed, the flow pattern in the gap is improved, and the mean leakage velocity Vlk gre≥90°, neither the tip leakage vortex cavitating flow nor flow pattern in the tip gap is ameliorated, the mean leakage velocity Vlk lies the range from 0.90 to 0.96. The region of high leakage velocity still exists and even the tip leakage vortex cavitation area is increased. Based on three-dimensional streamlines and vorticity transport equation, the interaction between the tip leakage flow and main flow leads to the variation of the tip leakage vortex cavitating flow. This paper aims for a useful reference to mitigate the tip leakage vortex cavitation and control the influence of the tip leakage vortex cavitating flow for the hydraulic machinery.

Proton exchange membrane fuel cell (PEMFC) has been recognized as the most promising energy conversion device due to its outstanding merits, such as high energy efficiency, low pollution, low operating temperature and low noise. Due to the complicated process of water production and transportation in porous media, the water concentration can affect the distribution of species and ionic conductivity, thus, the water management has been regarded as one of the most critical issues for PEMFC. In this paper, a three dimensional multiphase non-isothermal model for the PEMFC performance prediction has been developed to study the effect of ionomer volume fraction on the performance of PEMFC. The numerical results show that the ionomer volume fraction of catalyst layer has an appreciable effect on the performance of PEMFC and water distribution in porous electrodes, the higher ionomer volume fraction in catalyst layer can be helpful to avoid the flooding problem in porous electrodes.

In this study, we synthesized a novel N-halamine precursor, sulfuric acid mono-[2-(4-[4-chloro-6-(2-[4,4- dimethyl-2,5-dioxo-imidazolidin-1-yl]-ethylamino)-[1,3,5]triazin-2-ylamino]-benzenesulfonyl)-ethyl] ester sodium (TB), which contains two reactive groups of monochloro triazine reactive groups and bis-sulphatoethylsolphone reactive groups. The structure of TB is similar to iso-bifunctional group reactive dyes and could be coated on cotton fabrics by covalent bonds through a reactive dyeing process. The cotton coated with TB was characterized by FTIR and SEM. After chlorination, the treated cotton fabrics showed excellent antibacterial efficacy and inactivated all inoculated S. aureus (ATCC 6538) and E. coli O157: H7 (ATCC 43895) within 1 min of contact. Over 85 % of tensile strength retained both in warp and weft directions after treatment and chlorination. Almost 80 % of active chlorine can be regained by treating with household bleach after extensive washing and long time storage.

Understanding transport resistances in a polymer-electrolyte fuel cell (PEFC) catalyst layer (CL) is essential to mitigate the unexpected voltage loss when using low loadings of precious metals. In this paper, we explore through mesoscopic modeling the quantification analyses of the transport resistances in CL as derived using hydrogen-pump limiting current. Numerical treatments on the conjugated interfacial conditions at interfaces of ionomer/pore and Pt/ionomer are proposed to describe the mesoscopic transport processes of hydrogen and proton. Characterizations of the reconstructed microstructure of CL are performed. Parameter analyses on the influences of the critical transport properties such as the permeation coefficient and the dissolution and adsorption reaction rates at the surfaces of ionomer/pore and Pt/ionomer on the local transport resistance are presented. It is found that the local transport resistance is mainly originated from the diffusion resistance of the ionomer thin-film, which is more resistive than its bulk analogue with its permeation coefficient fitted to be 5.9% of the bulk one. The interfacial transport resistances and the diffusion resistance are coupled. The local transport resistance increases with I/C ratio due to thicker ionomer coated on the particles. Higher Pt/C ratio and bare carbon fraction lead to higher local transport resistance since the ionomer loading relative to Pt roughness factor decreases. The local transport resistance decreases with the porosity. The contribution of pores to the CL resistance, which decreases with the porosity, is comparatively small at low loadings.

Shape memory polymers (SMPs) are a class of active, deformable materials that can switch between a temporary shape, which can be freely designed, and their original shape. With their large deformation, low density, various stimulation methods, good biocompatibility and other advantages, SMPs have become widely accepted as smart materials. However, SMPs have many limitations and weaknesses that are exposed in engineering applications. For this reason, the significance of SMP composites (SMPCs) has been analyzed in terms of four aspects: reinforcement, innovation and improvement of driving methods, the creation of specific deformations and the creation of multifunctional materials. We then introduce the constitutive theory of SMPs and the post-buckling analysis of SMPCs. Afterward, we introduce the extensive applications of SMPCs in the fields of aerospace, biomedical equipment, self-finishing, deformable mandrels and the 4D printing of active origami structures, demonstrating their ability to undergo active driving and deformation, their adaptiveness, their ease of transport and their rapid production capacity, which fully demonstrate the unique advantages of SMPs in solving application problems. Finally, the advantages and disadvantages of SMPCs in applications are summarized, and the prospects for new SMPCs and new SMPC structures are described.

A new kind of plain plate fin with twelve vortex generators of delta winglets around each tube in fin-and-tube heat exchanger proposed by the present authors is experimentally studied in this paper. Experiments of four heat exchanger surfaces of real size are conducted to compare the comprehensive characteristics of the proposed fin with a circular wavy fin: two wavy fin-and-tube heat exchangers with 6 rows of tubes at the fin pitch of 2.54 mm and 2.117 mm (10-wavy and 12-wavy for short) respectively; and two proposed fin-and-tube heat exchanger surfaces with five rows of tubes at the same fin pitches (10-LVG and 12-LVG) correspondingly. The inlet velocity of the air side varies from 1.5 m/s to 7.5 m/s, and the water side flow rate is fixed at a certain value at each air inlet velocity. Experimental results indicate that the heat transfer rate and pressure penalty of heat exchanger surfaces using proposed fin with five-row tubes are almost the same with the six-row tubes wavy heat exchanger surfaces. Correlation of the Nusselt number Nu and the friction factor f on the air side are achieved. Entransy analysis is conducted to reveal the heat enhancement mechanism.

This paper presents an adsorption boundary condition based on linear adsorption isotherm for Lattice Boltzmann (LB) model. An axisymmetric 2-D LB model is built for an axisymmetric device. The model is used to study the effects of surface adsorption and airflow on SVOC mass transport in the device. In terms of surface adsorption, the research is divided in two parts: pure diffusion and convection-diffusion. The results show that the simulated data based on the presented adsorption boundary agree well with experimental data. In both the pure diffusion and advection-diffusion process, surface adsorption has no impact on the steady-state concentration, but it affects the time to reach steady state. Airflow greatly reduces both the time to reach steady state and the steady-state concentration. An exponential relationship involving hm, ACH and velocity is proposed and verified experimentally. Discussion on the parameter n in the exponential relation is conducted.

Nucleate boiling heat transfer (NBHT) from enhanced structures is an effective way to dissipate high heat flux. In the present study, the cavities behaviours for nucleation on roughened surface are numerically studied on the entire ebullition cycle based on a phase-change lattice Boltzmann method without introducing any artificial disturbances. The adopted model is firstly validated with the Laplace law and the two phase coexistence curve, and then applied to investigate the effects of cavity structure on NBHT. The bubble departure diameter, departure frequency and total boiling heat flux of an ebullition cycle are also explored. It is demonstrated that the cavity widths and the cavity grooves show significant influence on the features of NBHT. Cavity with circular groove in the present research shows the best performance for NBHT in terms of the averaged heat flux and bubble release frequency. When a specific cavity is combined with other different cavities on roughened surfaces its nucleation process on different roughened surfaces may differ greatly.

The oxygen transport resistance in catalyst layer of proton-exchange-membrane fuel cells has garnered much attention because it increases dramatically with the decreasing platinum loading. In this paper, the local transport behaviors of oxygen in electrode with different liquid water saturations, and platinum distributions are explored at mesoscopic level. The two-phase flow regime in electrode is simulated via a multicomponent multiphase flow model to reconstruct the liquid water morphologies. The effective oxygen diffusivities under wet conditions, the limiting current density, and the electrode resistance are numerically obtained before determining the local transport resistance. The results demonstrate that the effective oxygen diffusivities under wet condition decrease with the contact angle of the electrode. The limiting current density decreases with the liquid water saturation due to the blockage of ionomer surface area and the decreasing pore size distribution. The contribution of ionomer and liquid water to the electrode resistance dominates for the electrode resistance at low platinum loading. The local transport resistance of hydrophilic electrodes increases dramatically if the oxygen permeation in liquid water is excluded. More platinum particles distributed near the gas diffusion layer are beneficial for the reduction of the local transport resistance.

In this paper we use the multiphase multispecies Lattice Boltzmann method to investigate the influence of non-condensable gas on condensation. Condensation on a horizontal cold wall as well as that on a vertical wall with droplet movement is investigaged. The presence of non-condensable gas obviously reduces the condensation mass rate as well as the heat flux compared to condensation from pure vapor. The waiting time before nucleation is increased with non-condensable gas, and the wetting characteristics are also changed (the contact angles are increased), which further influences the heat transfer. Correlations of the relationship between droplet diameter and condensing time for different surface wettability, or contact angles, as well as different air mass fraction are obtained. As for condensation on a surface parallel to the gravitational force, it’s demonstrated that the presence of non-condensable gas reduces the droplet departure diameter and increases the period between subsequent droplet formation and departure.

Nucleate boiling heat transfer (NBHT) from enhanced structures is an effective way to dissipate high heat flux. In the present study, a 3D multi-relaxation-time (MRT) phase-change lattice Boltzmann method in conjunction with conjugated heat transfer treatment is proposed and then applied to the study of cavities behaviours for nucleation on roughened surfaces for an entire ebullition cycle without introducing any artificial disturbance. The bubble departure diameter, departure frequency and total boiling heat transfer rate are also explored. It is demonstrated that the cavity shapes show significant influence on the features of NBHT. The total heat transfer rate increases with the cavity mouth and cavity base area while decreases with the increase in cavity bottom wall thickness. The cavity with low wetting can enhance the heat transfer and improve the bubble release frequency.

Gas purge for eliminating water from gas diffusion layer (GDL) and membrane is of great importance for polymer electrolyte membrane fuel cell (PEMFC) start-up at subfreezing temperature. A gas purge model was developed to investigate the water transport phenomenon in GDL and membrane. In simulations, hydrogen and air were used as purge streams in anode and cathode, respectively. Effects of purge conditions on gas purge were numerically studied. In addition to relative humidity, flow rate and temperature, the flow configuration of purge gases was studied for the first time. In order to improve purge performance, several purge protocols were proposed and discussed in detail with respect to purge effectiveness and energy saving.

The lifting lug is one of the most important structures of aerial bomb, which mainly bears the variable amplitude cyclic loading during the working process. In this paper, the failure analysis of several lifting lugs which failed in fatigue test was carried out. Firstly, through the mechanical analysis, fatigue cumulative damage analysis and fracture surface analysis of the lifting lug structure, it was determined that the fracture failure was not caused by the issue of structural design, but by the Al2O3 inclusion defect in the casting process. Next, the crack source defect was equivalent to the initial crack, and the fatigue full-life was predicted by the method of fatigue crack growth (FCG). The FCG process was divided into two stages: small crack growth stage and long crack growth stage for life prediction respectively. Finally, the validity of this method was verified by comparing with the experimental results, and it was suggested to adopt advanced lifting lug casting and detection technology to prevent similar faults.

The groove effect on the tip leakage vortex around a NACA0009 hydrofoil was studied by numerical method. The results show that, as the groove angle is 45°, the groove could enhance the turbulence kinetic energy around the TLV, weaken the TLV strength and improve the pressure in the TLV core, resulting in an efficient suppression effect on the TLV cavitating flow. When the groove angle is 0° and 45°, the groove could decrease the tip leakage flow rate and the TLV gets lower and moves away from the tip gap. As the groove angle is 90° and 135°, the tip leakage flow rate gets larger, and the TLV gets higher and closer to the tip gap.

In this paper, the axial position of the grooves effect on the inlet flow characteristics and hydraulic performance of an axial-flow pump is studied by numerical method. The computational results show that setting the grooves on the pump inlet pipe could significantly improve the inflow characteristics of impeller and the saddle zone would be effectively suppressed. Under the deep stall condition, the grooves could improve the axial velocity of inflow and effectively reducing its streamline bending degree, and it also can block and destroy the vortex structures and then dissipate them rapidly. Reducing the axial distance between grooves and impeller can improve the hydraulic performance and the inflow characteristics of axial-flow pump.

NiSe2/Ti3C2 hybrid prepared by the one-step hydrothermal method is used as a cathode material for Mg/Li hybrid ion battery (MLIB) for the first time. The NiSe2/Ti3C2 hybrid shows exciting electrochemical performance, with a reversible capacity of 150 mA h g−1 at a very high current density of 5 A g−1. In contrast, pure NiSe2 only has a capacity of 50 mA h g−1 at 5 A g−1. The sharp improvement can be ascribed to the enhanced conductivity and the lowered charge-transfer resistance (Rct) when Ti3C2 is introduced. Moreover, the working mechanism of NiSe2/Ti3C2 in MLIB is investigated. This work provides a novel method to design cathode materials with high rate performance by combining MXenes with metal selenides.

A comprehensive macroscopic three-dimensional multiphase non-isothermal polymer electrolyte membrane fuel cell (PEMFC) model coupled with an improved electrochemical kinetics model considering the geometric structure parameters of the cathode catalyst layer (CCL) and oxygen transport process in CCL is developed. The effects of five CCL design parameters are investigated. It is found that the Pt loading of CCL has a significant effect on the performance, a low platinum (Pt) loading is more likely to cause oxygen starvation. The increase of Pt/C ratio can promote the performance significantly at a lower Pt/C ratio. A lower I/C ratio is good for the enhancement of limiting current density, a larger I/C ratio is good for the increase of maximum power density, and the increase in I/C ratio is better for the uniformity of membrane water distribution. With the decrease of carbon particle radius, the oxygen concentration on the Pt surface of CCL increases significantly. The increase of electrochemical specific area (ECSA) of Pt particles can promote the performance. In addition, a discussion on applicability of new correlations of capillary pressure-water saturation and effective diffusivity and their effects on the predicted PEMFC performance is presented.

In this paper, a three-dimensional numerical investigation is performed for both heat transfer and pressure drop of a new kind of slit fin applied to heat exchangers in air compression industry by FLUENT. A comparison between this new slit fin and normal plain fin is made. It is found that the flow and heat transfer come into full development stage after 12 rows. The effects of seven different parameters on the fully developed heat transfer performance are examined and all the calculation results agree well with the field synergy principle.Among these parameters,reducing spanwise fin pitch has the largest performance improvement. The optimum values are found for the height of slit and the length of rear slit. The correlations for j and f factors are proposed, which take four and five dimensionless geometric parameters into consideration, respectively.

Characterizing the emission performance of formaldehyde is critical for control strategies. Most previous emission models assume that formaldehyde concentrations are well-mixed. In this study, a computational fluid dynamics-based model is developed for simulating the mass transfer and adsorption/desorption processes of formaldehyde from particleboards in a chamber with a mixing fan. Numerical investigations on the impacts of the mixing fan, adsorption/desorption rate constants, and key transport parameters influencing the emission behaviors are conducted for the first time. The results show that the complete mixing assumption is not appropriate in the early emission period. Incomplete mixing becomes more significant with a decreasing rotation speed, leading to a time-dependent equivalent mass transfer coefficient. The deviation in the maximum concentration between the simulated curves with and without the adsorption/desorption effect is approximately 8.5%. A coefficient of mixing of 0.0283 is suitable for evaluating complete mixing in the chamber. With an increase in the rotation speed, the degree of mixing improves, and the mass transfer coefficient increases sub-linearly. Secondary reemission becomes more significant and begins earlier for materials with lower partition coefficients and higher diffusivity.

A 2D lattice Boltzmann model combining the enthalpy-based method (EBM) is established to investigate the ice melting process in the gas diffusion layer (GDL). The effects of GDL melting position, porosity, Rayleigh number and Stefan number on the melting rate, ending time of melting, temperature distribution and solid-liquid interface distribution are investigated. It is found that the GDL melting positions have a significant effect on the melting process, the melting rate in the In-plane position increases fastest. When the porosity is large, the effect of the carbon fiber layer number on the melting process is more significant than that of the carbon fiber length. In the In-plane position, the increase of natural convection intensity has a promoting effect on the ice melting process. The increasing of Stefan number can promote the melting process significantly when the Stefan number is not high. And reducing the GDL porosity can effectively promote the melting process.

A general interfacial treatment for the transport process in multicomponent systems governed by the convection-diffusion equation, together with conjugated interfaces where continuity or discontinuity interfacial conditions with regard to the physical scalar and its flux exist, is developed using the lattice Boltzmann method (LBM) with a multiple-relaxation-time collision operator. Factors accounting for interfacial jumps at conjugated interfaces typically include the difference in solubility, porosity, and transport properties, and the interfacial transport resistance. Difficulties in satisfying the discontinuity conditions, where continuity conditions are inherent in the conventional LBM, are overcome based on a second-order accurate treatment for both Dirichlet and Neumann boundary conditions. As a result, the unknown populations at the interface are obtained with a combination of the existing postcollision populations and the defined interfacial jumps without finite-difference approximations, thereby enabling the interfacial requirements precisely. Since the present treatment considers local intersected link fractions of the interface, it can be applied for curved interfaces naturally. As for straight interfaces located at the midpoints of the nodes, the present treatment can be significantly simplified with only two current nodes required. Validation work on the present treatment are performed with four specific problems, including the steady and unsteady convection diffusion in a fluid-fluid channel, steady convection diffusion in a fluid-solid system, steady and unsteady pure conduction in a composite slab, and steady pure conduction in an annulus. Such an interfacial scheme is finally applied to the conjugated mass transfer in a heterogonous medium, highlighting its practicability in complex systems with complicated interfacial conditions. In addition, detailed error analysis on interior nodes, interfacial values, and interfacial fluxes shows that our model is second-order accurate in space for straight interfaces regardless of various interfacial conditions, indicating no artificial disturbance is introduced to the model. While for curved interface, only superlinear and first-order accuracies are obtained for the interior nodes and the interfacial values or fluxes, respectively. Discussions on the degradation of the accuracy are presented. Note that the present interfacial treatment is mainly focused on two-dimensional problems, extensions of the model to be three-dimensional are straightforward.

Shape memory polymers (SMPs) are excellent active moving smart materials that switch between a variable temporary shape and the original shape, which can deform or provide a driving force. From the end of the last century, this kind of material research has been great development. In this chapter, the basic concepts of SMPs are expatiated first. Then, the milestones in the development process of SMPs and four kinds of excellent SMPs (styrene, epoxy, cyanate, and polyimide) are reviewed. Subsequently, from the mesoscopic to macroscopic, reinforced and functional SMP composites, the microstructure of SMPs and their applications in a wide range from biomedicine to aerospace were introduced.

A coupled numerical model is employed to investigate the emission process of volatile organic compounds (VOCs) in the building material and chamber. In this model, for the first time the Langmuir-isotherm sink model is introduced by taking into account of the adsorption/desorption process between the absorbed VOCs on the material surfaces and the gas phase VOCs in pores. The porous material adopted in the model is reconstructed with a random generation-growth algorithm for 3D microstructures fibers. This model is numerically implemented by a multiscale strategy with the lattice Boltzmann method (LBM) being used to simulate pore-scale diffusion and finite volume method (FVM) for macroscopic transport. Information transferring from the macro scalar obtained from FVM zone to the distribution functions in LBM zone is executed with a reconstruction operator. The model is validated with the well-mixed diffusion model, and then applied to predict the VOCs emission process. A comprehensively investigation of the effects of sorption parameters, including adsorption/desorption rate constants, partition coefficient, Schmidt number and Reynolds number on the VOCs adsorption/desorption process in building material and emission process in chamber is conducted. The simulation results reveal that the equilibrium VOCs concentration in the building material pores could be numerically estimated with our proposed model; the equilibrium concentration of VOCs in a closed chamber depends on the initial emitted VOCs concentration and partition coefficient; Reynolds number can promote the emission process in a ventilated chamber.

In this paper, a 3-D, nonisothermal numerical model with anisotropic property of gas diffusion layer (GDL) is applied to investigate the effect of thermal contact resistance (TCR) between rib and GDL, channel and rib width, and different heat transfer coefficients on the temperature distribution and performance of a single PEM fuel cell. A proper thermal contact resistance in this model is determined by comparing the predicted temperature variation between plate and cathode electrode to the available experimental results. The numerical results proved that to improve the prediction accuracy of temperature distribution and cell performance, the effect of TCR cannot be neglected. An underestimate of 1.5 K is found when cell output voltage to be 0.6 V of the case without TCR. And it is found that the rib and channel width and the ratio between them have an obvious effect on heat and mass transfer processes occurred in the electrode. The relatively optimum rib to channel width ratio is found to be 1.0 mm/0.8 mm, and the narrower the channel and rib widths the better the performance when their widths equal to each other. By comparing the temperature distribution between different heat transfer coefficients, it is found that when natural air convection is applied to cooling down the PEM fuel cell, the generated heat cannot be removed completely, however, when liquid water is used as the cooling fluid, the heat removed ability greatly exceeds the real demands of single PEM fuel cell, and the temperature of water must be heated to a proper value (larger than 333 K for the cases studied) to prevent over cooling of fuel cell.

Temperature uniformity in a water-cooled mini-channel heat sink with different flow field configurations under high heating flux was numerically studied. A thermal resistance network model was established and the concept of variable-height channels was proposed to improve the temperature uniformity on the heating surface. The influence of flow field configurations on the flow distribution uniformity is firstly studied, and a circular turning constructal distributor was selected due to its best flow distribution uniformity and cooling performance. And then the effects of fluid velocity, heating area, substrate thickness and three novel channels on the temperature uniformity and thermal resistance were investigated. Result shows that for the heat sink with the circular turning distributor and variable-height channels, the temperature non-uniformity achieved on a 3 × 3 cm heating surface can be reduced to less than 1 K with the heat flux as high as 2 MW m−2.

Dielectric elastomer is a kind of typical soft active material. It can deform obviously when subjected to an external voltage. When a dielectric elastomer with randomly oriented dipoles is subject to an electric field, the dipoles will rotate to and align with the electric field. The polarization of the dielectric elastomer may be saturated when the voltage is high enough. When subjected to a mechanical force, the end-to-end distance of each polymer chain, which has a finite contour length, will approach the finite value, reaching a limiting stretch. On approaching the limiting stretch, the elastomer stiffens steeply. Here, we develop a thermodynamic constitutive model of dielectric elastomers undergoing polarization saturation and strain-stiffening, and then investigate the stability (electromechanical stability, snap-through stability) and voltage induced deformation of dielectric elastomers. Analytical solution has been obtained and it reveals the marked influence of the extension limit and polarization saturation limit on its instability. The developed thermodynamic constitutive model and simulation results would be helpful in future to the research of dielectric elastomer based high-performance transducers.