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Exploring effective strategies for fabricating electrocatalysts toward oxygen reduction reaction (ORR) is of great importance for the fuel cells application. Herein, a facile strategy was developed to combine structurally ordered intermetallics with N-doped carbon confinement. Taking N-doped carbon encapsulated Pt-Fe ordered intermetallic nanoparticles (O-Pt-Fe@NC/C) as example, the in situ formed N-doped carbon shell not only benefits the nanoparticles distribute homogeneously on carbon support but also prevents the nanoparticles from agglomeration or detachment. As a result, the O-Pt-Fe@NC/C exhibits excellent ORR performance and stability as well as enhanced anti-poisoning capability towards CO, SOx and POx. When assembled as cathode materials for high temperature polymer electrolyte membrane fuel cells, a peak power density of 384 mW cm−2 is obtained for O-Pt-Fe@NC/C electrode at 160 °C. The demonstrated strategy provides a new insight into the preparation of highly durable and active carbon encapsulated Pt-based nanocatalysts for fuel cells.

Fuel cell vehicle (FCV) is regarded as a worldwide promising technology due to its high efficiency and zero emission. Heat management is very important during the operation of FCV, especially under high power output and environment temperature. As a consequence, development of a high heat dissipation ability radiator is necessary for the state-of-the-art FCV. In this paper, heat exchange characteristics of four different radiators are investigated in detail. A special air flow deflection phenomenon in the Windward bend structure is found to be beneficial for heat dissipation. A novel structure of Windward-Louvered fin (WLF) is proposed to be used in the radiator. The result shows that its Nusselt number is 1.2-1.3 times higher than that in Windward bend structure. In addition, field synergy theory is used for the evaluation of the heat transfer ability among the four structures. The synergy angles between velocity vector and temperature gradient are 82.1°, 82.5°, 87.0°, 81.8° at the air flow rate of 12 m•s−1, respectively. The WLF structure has the smallest synergy angle, thus the heat exchange amount is over 1.25 times higher than that of Windward bend structure.

Flow field plays an important role in the design and application of proton exchange membrane fuel cell (PEMFC). The superiority of flow field is commonly evaluated by comparing the performance improvement of PEMFC. However, it’s necessary to decrease the flow resistance to reduce the parasitic power and to obtain more uniform water and gas distributions during operation. As a consequence, the combined effect of performance and resistance should be considered during the optimal design of flow channel in PEMFC. A new criterion of efficiency evaluation criterion (EEC) using Sherwood number and Euler number has been proposed to evaluate the relationship between the mass transfer and the pressure drop in this study. The performances of PEMFCs with parallel, single-serpentine, and pressured parallel flow fields are investigated in detail. The results show that PEMFC with single-serpentine flow field has a better performance under normal atmospheric pressure, while the pressure drop in cathode is much larger than that in the parallel flow field. The pressured parallel flow field presents better performance and uniform gas distribution and it is thus proposed as the flow channel in the application of PEMFC.

Water management is one of the key issues for efficient and stable operation of proton exchange membrane fuel cells (PEMFCs). Water flooding easily occurs at the elevated operation current density, especially at the downstreaming of the flow channel where the generated water should flow out. Proper water management should meet the needs of adequate membrane hydration and the avoidance of flooding in the catalyst and gas diffusion layers. Flooding will not only lead to performance losses due to the hindered reactant supply, but also the safety issue because of the cell reversal. A partial flooding model is proposed to investigate the effect of the porosity on the performance of a PEMFC. The results show that high temperature is conducive to the suppression of flooding at low relative humidity, and flooding would lead to the deterioration of mass transfer due to the porosity decrease of gas diffusion layer, especially at high current densities. Partial flooding won’t significantly affect the power generation capacity of the fuel cell, but will cause uneven distribution of current density, resulting in an adverse influence on long-term operation. Moreover, the performance would suffer serious degradation with completely flooding. Once the area inside the PEMFC is seriously flooded, the current density in non-flooded area is up to 4.7 times higher than that in the flooded area, and the performance is difficult to recover even if increasing the stoichiometry of reactants. The study illustrates the importance of the water management at the downstreaming of the fuel cell.

Flow field plays a vital role in the design and application of a proton exchange membrane fuel cell (PEMFC). Combined with the enhancement of the abilities of mass transfer and water removal in the flow channel, a new optimized three-dimensional (3D) flow field is proposed to investigate the water transport and cell operating characteristics. The 3D flow field is composed of several straight flow units arranged in a staggered manner with an inclination at the end, and the transition areas and subchannels between the flow units are subjected to hydrophilic treatment. The result indicates that the new type of flow field can effectively separate liquid water from the reactant flow and water can be partially removed through the subchannel. Compared with the conventional flow field, the 3D flow field could enhance the mass transfer ability and improve the PEMFC performance, especially at high current densities. Based on the field synergy principle, we prove that the synergic degree between the velocity vector and concentration gradient agrees with the performance changes under the turbulence of the staggered flow units and the effective mass transfer coefficient (EMTC) in the direction of electrochemical reaction of the 3D flow field is also enhanced.

PEMFC (Proton exchange membrane fuel cell) operated under dead-ended anode mode is an effective and simple device for high hydrogen utilization. Herein, the operation characteristics of PEMFC with dead-ended anode are systematically investigated under various operating temperature, anode inlet pressure, and cathode stoichiometry. In each operating parameter, the solenoid valve located at the anode outlet is closed all the time and the hydrogen utilization reaches 100%. It has been found that fuel cell with dead-ended anode can operate continuously for 26 h with slight decrease in output voltage under 600 mA cm−2 at 65 °C, 80% of RH (relative humidity) with hydrogen inlet pressure of 0.4 bar gauge and oxygen stoichiometry of 4.0. After accumulated 150 h operation under dead-ended anode mode, the degradation of according MEA (membrane electrode assembly) has been analyzed using CV (cyclic voltammetry) and cross-sectional morphology. The results show that the accumulation of water induced corrosion of catalyst layer is responsible for the decrease in ECSA (electrochemical surface area) of catalyst layer and the according degradation of cell performance. Moreover, the degradation of catalyst layer became much more serious at the vicinity of cathode outlet than the other regions.

Although Nafion is regarded as the most preferred electrolyte membrane and often used as a benchmark for comparative evaluation of other electrolyte membranes, its wide spread for commercial PEM fuel cells is limited by the poor electrochemical properties at elevated temperatures and low relative humidity conditions. Herein, sol–gel synthesized mesoporous silica functionalized with a protogenic molecule (imidazole) is introduced into the Nafion matrix via a colloid mediated process. The formation of a stable colloid enables homogeneous dispersion of the silica-imidazole nanoparticles without aggregation. Under non-humidified conditions, the amphoteric and self-dissociative character of the tethered imidazole within the matrix functions as a transporting medium to facilitate proton conductivity. The structural and chemical phases are characterized, and qualitatively evaluated by XRD, TEM, FT-IR, TGA, and DMA. The results show that the average proton conductivity of the composite membrane with the optimal amount of functionalized nanoparticles increases progressively to 1.06 × 10 −2 S cm −1 at 130 °C, corresponding to an activation energy of 6.95 kJ mol −1 under non-humidified conditions. The mechanism governing the dynamics of proton conductivity and structural limitations as a function of temperature is discussed.

Humidification is one of the most important factors for the state-of-the-art Proton Exchange Membrane Fuel Cell (PEMFC) to maintain high water content in the electrolyte and to ensure reasonable ionic conductivity. However, liquid water may generate when the partial pressure of the water vapor reaches to its saturated point during operation, which can cause water flooding to the electrode and lead to poor performance of the PEMFC, especially at high current density. Moisture dehumidification is introduced to help remove the excessive water inside a 3 kW PEMFC stack in this paper. A radiator is set at the outlet of the stack to cool the moisture of the cathode. Thus, liquid water is condensed from the moisture due to the variation of the saturated pressure of water vapor, which can accelerate the evaporating of the liquid water inside the stack and mitigate the probability of flooding in the membrane electrode assembly (MEA). The stack with a radiator at the outlet of the cathode is fabricated to systematically investigate the effects of the stack temperature, air relative humidity, and operating pressure on the stack performance. The results show that with the help of moisture condensation, water removal ability is improved inside the stack. With the introduction of moisture dehumidification, 13% of increase in stack performance at 1.0 A cm −2 is observed compared with the stack performance without moisture dehumidification.

Proton exchange membrane fuel cells operated in the dead-ended anode mode can improve the utilization of hydrogen and simplify the fuel cell system. Gas purging was an effective way to remove the excess water to avoid water flooding and performance degradation in PEMFC. Effective back diffusion of water from the cathode to the anode was critical for performance recovery after gas purging. The purging operation was the process of water rebalancing in the electrode. The water back diffusion rate across the membrane was mainly related to temperature, pressure and current density. The performance degradation and recovery characteristics during the purging process in a proton exchange membrane fuel cell with a dead-ended anode were investigated under various operating conditions in this paper. Performance decreased rapidly during the duration of purging, after which it increased immediately at first and then gradually reached its original level a few seconds after gas purging. Nevertheless, performance would eventually stabilize before the next purging operation was begun.

Summary Thermal management has been considered as one of the most important issues for the operation of proton exchange membrane fuel cells (PEMFCs). Phase change affects the performance and even the heat balance of the stack during operation. A 46 single cell PEM stack with anode and cathode humidification is developed to investigate, both theoretically and experimentally, the effect of phase change on the heat generation and removal characteristics of the stack. The results show that the heat removed by the coolant water is greater than that generated by the electrochemistry reaction, and heat released due to the phase change of water vapor cannot be neglected. Heat generated in the stack can be removed completely by the coolant water, which need to be forced cooling for recycling use when the current density reaches 1000 mA·cm−2. The arithmetic product of the specific heat capacity and mass of the stack can be used as a novel criterion to evaluate the validity of the heat balance in the system. The exothermic reaction is very fast in the stack, which consequently requires bipolar plates with high heat conductivity coefficient to improve the temperature uniformity at the elevated operational current density. Copyright © 2014 John Wiley & Sons, Ltd.

Durability is one of the remaining challenges for practical application of proton exchange membrane fuel cells. Seals or gaskets around perimeters of each cell in a fuel cell stack are important to prevent leakage of reactant gases, avoiding the decay in utilization of gases and in overall cell performance. In this study, degradation of silicone rubbers, often used as sealing material in fuel cells, with different hardness in various aqueous solutions is investigated. Although the weight loss increases with the increase in hardness, the durability seems enhanced with the increase in hardness, as revealed by the variation of surface morphology and mechanical properties of silicone rubbers before and after exposure to acidic aqueous solutions. It also turns out that the degradation of silicone rubbers can be catalyzed by protons, leading to severe corrosion of materials in strong acidic environment. The results described in this study may provide guidance to evaluation or selection of silicone rubbers as seals for PEMFC applications.

A 3-D numerical study is carried out to investigate the laminar flow and heat transfer performance of the rectangular mini-channel where the discrete double-inclined ribs are worked as the longitudinal vortex generators. The effects of the Reynolds number, the height of the ribs and the number of double-inclined ribs along the mainstream on the heat transfer and flow performance of the mini-channel are examined and analyzed from the field synergy perspective and the entropy generation. The results show that the heat transfer performance is enhanced effectively by the double-inclined ribs which cause the generation of the longitudinal vortexes in the mini-channel. The heat transfer performance increase with the increasing height or number of the double-inclined ribs, but the flow resistance will increase at the same time. In order to obtain the best overall performance of the mini-channel, the height of the ribs should be reduced with the increase of the Reynolds, and the overall performance would be improved with the increase of the ribs number in the mini-channel. The heat transfer performance has a direct relation to the field synergy characteristic of the mini-channel. The entropy generation rate dues to heat transfer irreversibility and fluid frictional irreversibility can be used for the evaluation of the heat transfer and the flow performance of the mini-channel well respectively, while the total entropy generation rate cannot be used as a criterion for the overall performance.

A miniature loop heat pipe (LHP) with a flat evaporator is a promising solution for dealing with cooling requirements for high-power electronic devices. The present paper discusses the operating performance and heat transfer characteristics of a miniature LHP with a flat disk-shaped evaporator. It had a heated disk diameter of 40 mm and height of 19 mm, and was designed with brass as the evaporator material with braze welding, 630 mesh stainless steel wire mesh as the wick and methanol as the working fluid. In this investigation, both start-up and variable heat load tests were conducted. Three start-up modes were experimentally observed in this investigation: (1) zigzag start-up, (2) overshoot start-up, and (3) stable start-up. When the evaporator’s heated wall temperature was lower than 85 °C, with a variable heat load ranging from 20 W to 240 W corresponding to the heat flux of 1.6–19.1 W/cm2, the LHP ran stably and showed good self-adjusting ability. Moreover, comparison of the impacts of sealing method for evaporator on operating performance of miniature LHP with flat-disk type evaporator was conducted. With the same structural parameters and operating conditions, the LHP with an O-ring sealing evaporator could only work stably with heat loads ranging from 30 W to 140 W, corresponding to the heat flux of 2.38–11.1 W/cm2. This work was able to verify the importance of the sealing method in improving the performance of the miniature flat type LHPs.

In situ measurement of temperature distribution in a Proton Exchange Membrane Fuel Cell (PEMFC) stack is conducted by embed 36 T-type thermocouples on the MEA surface in four representative cells. Temperature increasing rate can get to 2.5 °C min−1 at 1000 mA cm−2. The largest temperature difference is observed in the middle of the stack, and the temperature difference can reach 17 °C at the bottom of the stack. The non-uniformity of temperature distribution is found to be improved by increasing the operation pressure, and the largest temperature difference decreases by 2.5 °C when the absolute operation pressure is increasing from 100 kPa to 150 kPa.

Air-cooled proton exchange membrane fuel cells (PEMFC) simplify the traditional cooling and air supply system. Three air-cooled stacks are assembled with different cells to investigate the effect of the polytetrafluoroethylene (PTFE) content in the gas diffusion layer (GDL), air flow rate, as well as the stack temperature on the stack performance. The results show that GDL with appropriate thickness and PTFE content can optimize the stack operation performance. The effect of the cell order on its performance can be neglected. A thermal equilibrium resulting from the heat generation and loss in the stack is achieved near the ambient temperature at low current density of 150 mA cm−2. The output power increases with the increase of air flow rate. However, when the air flow rate exceed 44.7 L min−1 or the stack temperature is higher than 65 °C, the stack performance decreases.

SUMMARY Hydrogen permeation across the membrane is unavoidable in proton exchange membrane fuel cells, especially for super-thin membranes, which lowers the open-circuit voltage and could even be a safety concern. In this paper, hydrogen permeation across two membranes (25-um-thick Nafion® 211 and 18-um-thick reinforced composite membrane) are evaluated at various temperatures, relative humidity (RH), and gas pressure differences between the anode and cathode. The results indicate that the hydrogen permeation rate in both membranes increases almost exponentially with temperature and linearly with pressure differences. Compared with RH, the effects of temperature and pressure differences are more crucial to hydrogen permeability. However, the effect of RH on the hydrogen permeation is quite complicated. The permeability exhibits a minimum value at intermediate RH (approximately 40% RH) for both applied membranes. The permeability of Nafion® 211 appears more sensitive to RH than that of reinforced composite membrane at elevated temperature. Copyright © 2013 John Wiley & Sons, Ltd.

A membrane electrode assembly (MEA) is one of the core components of proton exchange membrane fuel cells (PEMFCs) comprising a catalyst coated membrane, gas diffusion electrodes, frames, and seals. By employing a 2D finite element model the mechanical stresses in membrane caused during the cell assembly procedure are analyzed for different MEA frame materials, frame structures and contact behaviors. The stress distributions in the membrane are presented and quantified. A zone with strong nonuniform stresses in the membrane under the end edge of frame/membrane is observed. The stepped frames assembly (SFA) and the bonded contact behaviors have more uniform stress distributions than the aligned frames assembly (AFA) does. The frame materials are not the main factors affecting the stress concentration in membrane for the SFA, while for the AFA the mechanical properties of frame materials should be close to those of the membrane. The results are expected to be helpful for people to select the frame materials and to design frame structures, and can be applied to guide the assembly of PEMFCs.

Distribution expressions of total gas pressure and partial water vapor pressure along the channel direction were established based on lumped model by analyzing pressure loss in the channel and gas diffusion in the layer. The mechanism of droplet formation in the flow channel was also analyzed. Effects of the relative humidity, working temperature and stoichiometry on liquid water formation were discussed in detail. Moreover, the force equilibrium equation of the droplet in the flow channel was deduced, and the critical flow velocity for the water droplet removal was also addressed. The experimental results show that the threshold position of the liquid droplet is far from the inlet with the increase of temperature, and it decreases with the increase of the inlet total pressure. The critical flow velocity decreases with the increase of the radius and the working pressure.

Temperature mapping is measured by micro-thermocouples embedded into the cathode plate of the model cell. The effects of different operation conditions on temperature distribution are investigated in detail. The results show that the temperature of the stack turns on “Parabola” distribution, and the temperature increases along the flow field from the inlet to the outlet under various conditions. Temperature difference of the single cell in the stack increases with the increased operation current density, and decreases with the increased air flow rate. The effect of the inlet air temperature on the temperature difference can be neglected in the stack, and the temperature uniformity can be improved by increasing the mass flow rate of the coolant water.

Composite membranes containing ePTFE matrix and short side chain perfluoronated sulfonated ionomers are introduced as electrolytes for proton exchange membrane fuel cell applications. The output voltage at 800 mA cm−2 for single cell using composite membrane as electrolyte reaches 0.61 V at 95 °C under 40% relative humidity whereas it is only 0.41 V for cell assembled from pristine short side chain perfluoronated sulfonated membrane at the same condition. The performance of fuel cell stack using composite membrane as electrolyte in kilowatts ranges has been experimentally investigated at 95 °C under ambient pressure. With the increase in the inlet gas temperature, the performance of the stack is enhanced. The non-monotonic behavior in instantaneous average voltage of single cells in the stack has been observed and the peak value is appeared at the stack temperature of 90 °C. The observed water accumulation phenomena suggest that the decrease in stack performance above 90 °C is attributed to the lack of water in the system. The results observed in this study demonstrate that the composite membrane has the potential operating at 95 °C under reduced relative humidity to 40%, which is a suitable operating condition for fuel cell vehicle applications.

Amine-tailored titanate nanotube is introduced to polymer electrolyte membranes for improving the interfacial compatibility between polymeric resin and inorganic materials and enhancing the proton conductivity of the membrane at low relative humidity. Amine-tailored titanate nanotubes are formed through the coupling reaction of surface hydroxyl groups with 3-aminopropyltrimethoxysilane in anhydrous toluene. The grafting density of surface-tailored amino groups reaches 5.19×10−3 mol g−1. Vibrational spectroscopy and X-ray photoelectron spectroscopy confirm that both hydrogen-bonded and free amino groups exist on surface functionalized titanate nanotubes. Polymer electrolyte composite membranes containing the surface functionalized titanate nanotubes and Nafion polymers are characterized for the interfacial compatibility and proton conductivity. The surface grafted amino-groups exhibit positive effect on the interfacial compatibility of polymeric materials and inorganic materials, resulting in increased yield strength of composite membranes. At 100° C and 50% relative humidity, the proton conductivity of the formed composite membrane impregnated with functionalized titanate nanotubes reaches 0.045 Scm−1 that is about 4–5 times higher than that of pristine Nafion membrane and 3 times higher than that of composite membrane impregnated with unmodified titanate nanotubes.

Humidification is one of the most important factors for the operation of proton exchange membrane fuel cell (PEMFC). To maintain the membrane at hydrated state, plenty of water is needed for the state-of-the-art of PEMFC technology, especially in large power applications or long time operation. A condenser is introduced to separate liquid water from the air outlet for air self-sufficient in water of the stack in this study. The condensed temperature at the outlet of the condenser and water recovered amount for air self-sufficient in water are investigated theoretically and experimentally. It is shown that the condensed temperature for air self-sufficient in water is irrelevant with the working current of the stack. When the condenser outlet temperature was above the theoretical line, recovery water was not sufficient for the air humidification. On the contrary, it is sufficient while the temperature was below the theoretical line. It is also shown that when the moisture is sufficiently cooled, large amount water can be separated from the outlet gas, and it increased almost linearly with the time. With the introduction of the condenser, the recovered amount of water can easily satisfy the air self-sufficient in water by condensing the outlet gas to a proper temperature.

A novel miniature porous heat sink system was presented for dissipating high heat fluxes of electronic device, and its operational principle and characteristics were analyzed. The flow and heat transfer of miniature porous heat sink was experimentally investigated at high heat fluxes. It was observed that the heat load of up to 280 W (heat flux of 140 W/cm2) was removed by the heat sink with the coolant pressure drop of about 34 kPa across the heat sink system and the heater junction temperature of 62.9 °C at the coolant flow rate of 6.2 cm3/s. Nu number of heat sink increased with the increase of Re number, and maximum value of 323 for Nu was achieved at highest Re of 518. The overall heat transfer coefficient of heat sink increased with the increase of coolant flow rate and heat load, and the maximal heat transfer coefficient was 36.8 kW(m2 °C)−1 in the experiment. The minimum value of 0.16 °C/W for the whole thermal resistance of heat sink was achieved at flow rate of 6.2 cm3/s, and increasing coolant flow rate and heat fluxes could lead to the decrease in thermal resistance. The micro heat sink has good performance for electronics cooling at high heat fluxes, and it can improve the reliability and lifetime of electronic device.

In this paper, the effect of shutoff sequences of hydrogen and air on the degradation behaviours of proton exchange membrane fuel cells (PEMFCs) is investigated with two different shutdown procedures. After one of the gases is shut off, the dummy load is applied to consume the residual gas in the flow field. Theoretical analysis and experimental tests indicate that different gas shutoff sequences have great effect on the oxygen permeation rate across the membrane during introducing the dummy load, resulting in producing the H2/O2 interface at the anode in the next startup process. Electrochemical techniques, including the measurement of polarization curves, cyclic voltammetry, and cross-sectional scanning electron microscopy (SEM) of membrane electrode assemblies (MEAs) and transmission electron microscopy (TEM) of Pt/C catalyst are employed to evaluate the performance decay of PEMFCs after 1500 startup and shutdown cycles. The results show that the case if air is shut off firstly would significantly alleviate both the performance decay and the decrease in the electrochemically active surface area, resulting in an improvement in the durability of PEMFCs.

A mathematical model based on the Lucas–Washburn equation has been developed to address the relations of the capillary height, capillary radius and the heat flux in a capillary column and the equation is extended to a capillary loop for investigating the stability of the condensing interface with phase change by some simplifications in the paper. The stability of the condensing interface is studied by introducing a small disturbance into capillary height. The dynamics performances of the condensing interface under three different operating conditions are discussed in this paper. The results show that the condensing interface presents high instability under non-gravitational condition, while the stability can be enhanced in gravitational condition with a certain gravitational height, moreover, regular vibration can be formed on the condensing interface due to the periodic oscillation of the pressure in the system.

One of the technical barriers for high temperature proton exchange membrane fuel cell is the membrane that should have reasonable proton conductivity at reduced relative humidity. In this paper, membranes containing Nafion and 2-substituted imidazole derivatives have been formed through casting process. Imidazole moieties are immobilizied inside the formed membrane though grafting of hydrophobic hydrocarbon chains at 2-position of imidazole. The proton conductivity of the so-formed membranes reaches 6.8×10-3 S cm-1 at 160 °C under anhydrous conditions. Compared to pristine Nafion membrane, the thermal stability of the formed membranes is enhanced. The inter-connected ionic clusters formation has been observed through electrostatic force microscopy. Based on activation energy for proton transportation, the mechanism of proton transportation below and above 120 °C is proposed.

As catalyst support materials, the oxidation of carbon materials is considered one of the major factors for performance decay during the startup and shutdown process of proton exchange membrane fuel cells, which must be mitigated to achieve acceptable durability. In this paper, the effect of cathode exhaust conditions on the degradation behaviors of fuel cells is investigated using two single cells named the open-ended and closed cells. The cathode inlet pressure during the introduction of the dummy load is an important factor in analyzing the performance decay of membrane electrode assemblies under different conditions. Electrochemical techniques, including the measurement of polarization curves, cyclic and linear sweep voltammetry, and cross-sectional scanning electron microscopy of tested membrane electrode assemblies, are employed to evaluate the performance decay of fuel cells. The results show that a closed cathode exhaust valve during the introduction of the dummy load would significantly alleviate both the performance decay and the decrease in the electrochemically active surface area, resulting in an improvement in fuel cell durability. No significant deterioration of the membranes is observed for both the open-ended and the closed cells during frequent startup and shutdown processes.

Two-dimensional mathematical model of the miniature flat plate capillary pumped loop (CPL) evaporator is presented to simulate heat and mass transfer in the capillary porous structure and heat transfer in the vapor grooves and metallic wall. The overall evaporator is solved with SIMPLE algorithm as a conjugate problem. The shape and location of vapor–liquid interface inside the wick are calculated and the influences of applied heat fluxes, liquid subcooling and metallic wall materials on the evaporator performances are discussed in detail. The effect of heat conduction of side metallic wall on the performance of miniature flat plate CPL evaporator is also analyzed, and side wall effect heat transfer limit is introduced to estimate the heat transport capability of capillary evaporator. The conjugate model offers a numerical investigation in the explanation of the robustness of the flat plate CPL operation.

According to heat pipe theory, capillary force is the only driving force for the circle of working fluid in heat pipe with porous wick. By developing a simulating circuit of liquid and vapor flow in heat pipe with porous wick, this paper presents a new driving mechanism which is from phase change of fluid. Furthermore, by analyzing transport process of working fluid between evaporation and condensation interfaces, a mathematical model is developed to describe this driving mechanism. Besides, calculating examples are given for heat pipe with water as working fluid to predict its driving force and flow resistance. By applying the model presented in the paper, thermal design and calculation for heat pipe with porous wick, especially for miniature heat pipe, can be made correctly, and phase change driving mechanism of working fluid can be explained, which thereby leads to a better understanding of heat transfer limitation of heat pipe with porous wick.

The start-up characteristics of a flat miniature loop heat pipe (LHP) with different heat loads were experimentally investigated in this article. Reasons for the difficulties in its start-up were analysed. An overall two-dimensional numerical model was developed to address the heat and mass transfer characteristics in the evaporator of the miniature LHP. The numerical results showed that the performance of the flat miniature LHP could be enhanced by improving the geometrical structure in a limited working space. Effects of thickness of the side wall, height of the compensation chamber, and the wick on system performance were discussed in detail.

Two-dimensional numerical model for the global evaporator of miniature flat plate capillary pumped loop (CPL) is developed to describe heat and mass transfer with phase change in the porous wick, liquid flow and heat transfer in the compensation cavity and heat transfer in the vapor grooves and metallic wall. The governing equations for different zones are solved as a conjugate problem. The side wall effect heat transfer limit is introduced to estimate the heat transport capability of evaporator. The influences of liquid subcooling, wick material, metallic wall material and non-uniform heat flux on the evaporator performance are discussed in detail.

Recently, we have developed a semidirect breath figure (sDBF) method for direct fabrication of large-area and ordered honeycomb structures on commercial polystyrene (PS) Petri dishes without the use of an external polymer solution. In this work, we showed that both the pore size and the pore uniformity of the breath figure patterns were controllable by solvent amount. The cross-sectional image shows that only one layer of pores was formed on the BF figure patterns. By combing the sDBF method and Pickering emulsion and using the modular building blocks, we endowed the honeycomb-structured Petri dish with molecular recognition capability via the decoration of molecularly imprinted polymer (MIP) nanoparticles into the honeycomb pores. The radioligand binding experiments show that the MIP nanoparticles on the resultant honeycomb structures maintained high molecular binding selectivity. The reusability study indicates that MIP-BF patterns had excellent mechanical stability during the radioligand binding process. We believe that the modular approach demonstrated in this work will open up further opportunities for honeycomb structure-based chemical sensors for drug analysis, substrates for catalysts, and scaffold for cell growth.

Anhydrous proton conducting materials based on surface attachment of protonated 1,2,4-triazole moieties on titanate nanotubes are prepared through self-assembly technique. H-1 MAS NMR spectra have revealed that the triazole moieties located at the outer surface of nanotubes. The distance between two ionic groups at the surface is observed to be shorter than 1 nm, which may facilitate the formation of continuous proton conducting domains, leading to easy proton transport through segmental motion and structural re-organization in the absence of water. The maximum proton conductivity of the synthesized materials reaches about 2.4 x 10(-3) S cm(-1) at 160 degrees C under anhydrous conditions. (C) 2014 Elsevier Inc. All rights reserved.

Proton conducting materials having reasonable proton conductivity at low humidification conditions are critical for decrease in system complexity and improvement of power density for polymer electrolyte membrane fuel cells. This study shows that polyelectrolyte brushes on titanate nanotubes formed through surface-initiated free radical polymerization exhibit less humidity-dependent proton conduction because of the high grafting density of polymer electrolyte chains and well-distribution of ionic groups. The results described in this study provide an idea for design of new proton conductors with effective ion transport served at relatively low humidification levels.

Efficient membrane proton conductivity at elevated temperatures (>100 degrees C) and reduced humidification conditions is a critical issue hindering fuel cell commercialization. Herein, proton conducting materials consisting of high surface area acid catalyzed mesoporous silica functionalized with sulfonated dimethylphenethylchlorosilane was investigated under anhydrous conditions. The organic moiety covalently bonded to the silica substrate via active hydroxyl groups on the silica pore surface. The structure and dynamic phases of the attached organic molecule were characterized and qualitatively determined by XRD, TEM, FT-IR, and solid state NMR The amount of grafted organic molecules was estimated to be 2.45 mu mol m(-2) by carbon elemental analysis. The so-formed composite materials showed adequate thermal stability up to 300 degrees C as determined by TGA. Under anhydrous conditions, ionic conductivity of the composite material upon ionic liquid impregnation reaches a peak value of 1.14 x 10(-2) S cm(-1) at 160 degrees C associated with the activation energy of 9.24 kJ mol(-1) for proton transport.

To realize selective mineralization of low-level chlorophenols (CPs) in the presence of high-level ordinary pollutants, molecularly imprinted polymers (MIPs) coated photocatalyst was prepared using substrate analog as template. The pseudo-template imprinted photocatalysts showed rapid decomposition ability toward a group of CPs. Based on the complete dechlorination and spectrophotometry, a new method was proposed to detect the total organochlorine on CPs in water samples. The method showed good linearity when the concentrations of the total organochlorine on CPs is in the range of 12.0-200.0μmolL(-1). The detection limit is 1μmolL(-1) for this method. When this method was applied to measure the total organochlorine of the CPs in both tap water and river water samples, an average recovery ranged from 96.3% to 105.1% was obtained with RSD values less than 5%. In this green and simple method, the common inorganic ions in water showed no interference for the detection. The determination of the total organochlorine on the CPs might be used for estimation of the toxicity and the persistence of the water samples.

A novel porous micro heat sink system is presented for dissipating high heat flux of electronic devices. Numerical model for the micro heat sink is proposed to describe heat transfer in the metallic wall and liquid flow and heat transfer in the porous wick structure, and it is solved with SIMPLE algorithm as a conjugate problem. The numerical results showed that the heated surface temperature of porous micro heat sink is low at high heat fluxes. Increasing inlet fluid velocity can greatly decrease the temperatures of the heated surface temperature and bottom surface. The temperature of the heated surface can maintain good isothermal characteristic when inlet located in the bottom of micro heat sink.

A capillary pumped loop (CPL) for the cooling of electronic apparatus was presented, and its operation principle and characteristics were analysed. This paper has pointed out the driving mechanism of the interface which is from phase change of fluid in Capillary Pumped Loop (CPL) and Loop Heat Pipe (LHP). A mathematical model has been developed to describe the driving mechanism. According to the theoretical analysis, there will be an effect on the Yang-Laplace equation and the phase change of the interface because of the heat added to the system. The formulas reflecting relations of the real operating capillary radius with the evaporating temperature and the heat density have been developed to quantitatively evaluate the system characteristic. The model will be a newly driving mechanism for all the capillary wick or micro-groovy channel.

Imidazole functionalized polyhedral oligomeric silsesquioxane (ImPOSS) is synthesized and introduced into a polymer electrolyte membrane for elevated temperature applications. Aggregates of ImPOSS containing 30–40 blocks of POSS cages are observed. The synthesized ImPOSS are well distributed in the hybrid membrane without further aggregation during the membrane formation process. The resulting hybrid membrane exhibits strong Coulombic interaction between sulfonic acid groups on Nafion and imidazole moieties on ImPOSS, leading to increased glass transition temperature and improved thermal stability of the membranes. Under anhydrous conditions, Vogel–Tamman–Fulcher type temperature-dependent proton conductivity is observed, suggesting that structural reorganization of incorporated imidazole moieties dominates the long-range proton transfer in the hybrid membrane. The anhydrous proton conductivity of hybrid membranes containing 35 wt% of ImPOSS reaches 0.0256 S cm−1 at 140 °C. The output voltage of a single cell assembled from the hybrid membrane is observed to be 0.41 V at 600 mA cm−2 under 120 °C and 25% relative humidity using hydrogen and oxygen as reaction gases. The results show the potential applicability of ImPOSS-Nafion hybrid membranes for elevated polymer electrolyte membrane fuel cells.