Quick Start-up Research Articles

Improving the Durability of Perfluorosulfonic Acid Membrane in Pemfcs Using Cerium-Based Radical Scavengers Including Organic Ligand Group

Polymer electrolyte membrane fuel cells (PEMFCs) are promising alternative power sources for stationary and automotive applications due to their low exhaust emissions and quick start-up and load response. However, the widespread commercialization of PEMFCs is still challenging to meet the cost and durability. Therefore, enhancing the durability of the PEMFC stack is the most important aspect of recent studies through improving the electrochemical and mechanical stability of major components such as polymer electrolyte membranes (PEM). The main factors contributing to the durability deterioration of PEM are chemical and mechanical degradation caused by the inescapable generation of hydroxyl and hydroperoxyl radical species through gas crossover during PEMFC operation.1 Several studies have proven using the cerium ions as radical scavengers effectively mitigates the chemical degradation of PEMs to solve these problems. Although cerium is an effective radical scavenger, it can be combined with sulfonic acid groups to lower the proton conductivity during cell operation.2 In this study, we aimed to mitigate the polymer electrolyte membrane chemical degradation and minimize proton conductivity deterioration by introducing an organic ligand group to cerium-based radical scavengers. The cerium-based radical scavengers were incorporated into the catalyst ink at different concentrations, and membrane electrode assemblies (MEAs) were subsequently fabricated by spray-coating onto perfluorosulfonic acid membranes using the prepared catalyst inks. The chemical stability of the MEAs including radical scavengers was evaluated by open circuit voltage (OCV) decay and electrochemical gas crossover at high temperatures and with low relative humidity (RH) reactant gases. The fuel cell performance was also conducted using the polarization curve, impedance, cyclic voltammetry, and linear sweep voltammetry at 80 °C and 100% RH conditions. The Cerium-based radical scavenger incorporated PFSA membrane showed significantly extended lifetimes during the steady-state OCV test as compared with a non-stabilized PFSA membrane. The MEA performance tests confirmed that the cerium-based radical scavenger dramatically mitigates degradation effects, which improves MEA chemical durability and minimizes performance losses.

Comparison of denitrifying nitrite accumulation performance when sludge fermentation liquid progressively replaced acetate

Sludge fermentation liquid (SFL), rich in volatile fatty acids, is supposed to be the promising organic carbon source to substitute acetate for driving partial denitrification (PD). However, it did not guarantee a comparable nitrate-to-nitrite transformation rate (NTR) when compared with using acetate due to its complicated composition. This study compared the PD performance of SFL and acetate in two parallel reactors (R1 and R2, respectively) and used progressive replacement to enhance the robustness of SFL. At first, PD was rapidly established in R1 and R2 within 21 days by using acetate and setting the carbon-to-nitrate ratio at 5. Then, after SFL progressively and completely replaced acetate in R1, the NTR of 64.7 ± 8.5 % and nitrate reduction rate of ∼39.7 mg/(L∙h) was obtained, which was comparable to those in R2 (58.7 ± 6.2 % and 50.9 mg/(L∙h)). Furthermore, the adopted long famine time caused extra nitrite soaking duration, leading to the system's quick startup but low biomass yield. According to high-throughput sequencing analyses of 16S rRNA, Thauera, a speculative PD contributor, was dominant in both reactors, and its relative abundance was ∼4.6 %.

A novel advanced hybrid fuzzy MPPT controllers for renewable energy systems

At present, the availability of nonrenewable sources and their usage for electric vehicle technology is reducing gradually because of their disadvantages are more environmental pollution, direct effect on human health, less reliability, and taking more time to start functioning. So, in this article, the proton exchange membrane fuel cell (PEMFC) is considered for the automotive application because of its advantages quick startup, more power density, more safety to handle, high efficiency, and capability of operating at very low operational temperature conditions. However, the drawback of PEMFC is very difficult to identify the accurate MPP position of the fuel system. Here, the improved variable step genetic algorithm is added with the adaptive neuro-fuzzy inference system for tracking the operational point of the proposed system with high efficiency. These hybrid MPPT controller features are easy to understand, more accurate, have a better dynamic response, and have low design complexity. The evaluated proposed MPPT controller operational efficiency, and settling time of the converter voltage at different fuel stack temperature conditions are 98.7402%, and 0.01607 s respectively. Finally, the boost converter is used in this work to enhance the voltage supply capability of the entire system. The proposed system is investigated by applying the MATLAB tool.

Full-speed domain position sensorless control strategy for PMSM based on a novel phase-locked loop

This paper proposes a full-speed-domain position-sensor-less control strategy for precise control under forward and reverse rotation conditions to address the weak convex polarity of surface-mounted permanent magnet synchronous motor (SPMSM). The strategy comprises several key stages: pre-positioning of the rotor, constant current variable frequency (I/F) start-up, construct the Luenberger State Observer, and utilization of an improved phase-locked loop (PLL) for position estimation. In the pre-positioning stage, a constant amplitude current is applied to drag the rotor to a predetermined position. Subsequently, the I/F start-up stage accelerates the motor to a predetermined speed before transitioning to the Luenberger observer for closed-loop speed control, which is based on an extended back electromotive force (back-EMF) a two-phase rotating coordinate system. The improved PLL for position and speed estimation features three components: a phase discriminator (PD), a voltage-controlled oscillator (VCO), and loop filter (LF). Experimental results demonstrate the efficacy of the proposed strategy, showing quick start-up response, speed estimation error below 2 RPM, rotor position estimation error under 0.6 degrees post-loop closure, stable tracking during rapid speed changes, and consistent accuracy and stability even under reverse rotation conditions, thereby meeting the control strategy’s objectives.

Effect of Membrane Thickness and Operating Conditions on PEMFC Limiting Current Analysis

Hydrogen powered proton exchange membrane fuel cells (PEMFC) have great potentials to replace the traditional internal combustion engines due to its inherent advantages of zero greenhouse gas emissions, better fuel efficiency, quick startup, silent operation, less required maintenance, etc. In a PEMFC, oxygen transport is a critical performance limiting factor because of the sluggish oxygen reduction reaction kinetics. Limiting current method is a well-established in-situ diagnostic tool to measure the oxygen transport resistance in a PEMFC. To obtain accurate oxygen transport resistances, a few key assumptions need to be made including: (1) the effect of temperature gradient in the diffusion media is negligible, (2) no convective flow in the porous media, (3) oxygen is diluted in a gas mixture of nitrogen and water vapor, (4) the total oxygen transport resistance combines gas diffusion layer, microporous layer, and catalyst layer, (5) the effect of membrane thickness has negligible effect, and (6) the anode side does not affect the measurement results due to fast hydrogen oxidation reaction. In this study, we perform a systematic study of the effect of membrane thickness and operating conditions on obtaining robust and reliable limiting current measurement. Standard Nafion membranes of three different thicknesses (25, 50, and 85 µm) are tested with Toray 060 and Freudenberg H23C8 diffusion media. In addition, we further study the interaction between membrane thickness and asymmetric pressure and relative humidity and their effects on limiting current results. Our results show that membrane thickness and relative humidity are critical factors in obtaining reliable oxygen transport resistance due to their effect on overall water balance in the cell. Lastly, the experimental data are compared with the simulation results to establish fundamental understanding. Detailed experimental and analytical results will be presented at the conference.

Establishing mainstream partial nitrification in the membrane aerated biofilm reactor by limiting the oxygen concentration in the biofilm

The proliferation of nitrite oxidizing bacteria (NOB) still remains as a major challenge for nitrogen removal in mainstream wastewater treatment process based on partial nitrification (PN). This study investigated different operational conditions to establish mainstream PN for the fast start-up of membrane aerated biofilm reactor (MABR) systems. Different oxygen controlling strategies were adopted by employing different influent NH4+-N loads and oxygen supply strategies to inhibit NOB. We indicated the essential for NOB suppression was to reduce the oxygen concentration of the inner biofilm and the thickness of aerobic biofilm. A higher NH4+-N load (7.4 g-N/(m2·d)) induced higher oxygen utilization rate (14.4 g-O2/(m2·d)) and steeper gradient of oxygen concentration, which reduced the thickness of aerobic biofilm. Employing closed-end oxygen supply mode exhibited the minimum concentration of oxygen to realize PN, which was over 46% reduction of the normal open-end oxygen mode. Under the conditions of high NH4+-N load and closed-end oxygen supply mode, the microbial community exhibited a comparative advantage of ammonium oxidizing bacteria over NOB in the aerobic biofilm, with a relative abundance of Nitrosomonas of 30–40% and no detection of Nitrospira. The optimal fast start-up strategy was proposed with open-end aeration mode in the first 10 days and closed-end mode subsequently under high NH4+-N load. The results revealed the mechanism of NOB inhibition on the biofilm and provided strategies for a quick start-up and stable mainstream PN simultaneously, which poses great significance for the future application of MABR.

Advanced Nafion/nanofiller composite proton exchange membranes for fuel cell applications

Proton exchange membrane fuel cells (PEMFCs) exhibit increasing potential in a variety of applications, from automotive to stationary power generation, due to their superior advantages such as high efficiency, quick start-up and low emissions. The cell performance and operation life of PEMFCs are directly affected by the proton exchange membranes (PEMs). Nafion, a well-known perfluorosulfonic acid polymer, represents the state of the art of PEMs. To further improve the performance of Nafion, various nanofillers are incorporated into Nafion matrices, leading to the formation of composite PEMs with enhanced proton conductivity, mechanical strength and chemical stability. This review summarizes the recent advancements in Nafion composite PEMs based on four typical kinds of nanofillers: framework nanomaterials, carbon nanomaterials, polyoxometalate nanoclusters, and inorganic oxide nanoparticles. The preparation strategy, structure-property relationship and fuel cell applications of these membranes are discussed comprehensively, particularly focusing on the synergistic effect between Nafion and nanofillers. This review can provide an instructive insight for designing high-performance PEMs towards emerging energy technologies.

Implementation of high step-up power converter for fuel cell application with hybrid MPPT controller

As of now, there are multiple types of renewable energy sources available in nature which are hydro, wind, tidal, and solar. Among all of that the solar energy source is used in many applications because of its features are low maitainence cost, less human power for handling, a clean source, more availability in nature, and reduced carbon emissions. However, the disadvantages of solar networks are continuously depending on the weather conditions, high complexity of the solar energy storage, and lots of installation place is required. So, in this work, the Proton Exchange Membrane Fuel Stack (PEMFS) is utilized for supplying the power to the local consumers. The merits of this fuel stack are high power density, ability to work at very less temperature values, efficient heat maintenance, and water management. Also, this fuel stack gives a quick startup response. The only demerit of PEMFS is excessive current production, plus very less output voltage. To optimize the current supply of the fuel stack, a Wide Input Operation Single Switch Boost Converter (WIOSSBC) circuit is placed across the fuel stack output to improve the load voltage profile. The advantages of the WIOSSBC are less current ripples, uniform voltage supply, plus good voltage conversion ratio. Another issue of the fuel stack is nonlinear power production. To linearize the issue of fuel stack, the Grey Wolf Algorithm Dependent Fuzzy Logic Methodology (GWADFLM) is introduced in this article for maintaining the operating point of the fuel cell near to Maximum Power Point (MPP) place. The entire system is investigated by utilizing the MATLAB software.

A Recent Comprehensive Review of Fuel Cells: History, Types, and Applications

This review discusses the history, fundamentals, and applications of different fuel cell technologies, including proton exchange membrane fuel cells (PEMFCs), direct methanol fuel cells, solid oxide fuel cells (SOFCs), phosphoric acid fuel cells (PAFCs), alkaline fuel cells (AFCs), and molten carbonate fuel cells (MCFCs). Recent advances in fuel cell technologies have led to potential applications in aerospace, transportation, and portable and stationary power generation due to high efficiency and low emissions. Fuel cell types are also compared based on efficiency, operating temperature, lifetime, energy/power density, and cost. It was noticed that PEMFCs have the highest mass power density, reaching 1,000 W/kg compared to less than 100 W/kg for SOFCs, which makes them suitable for portable applications such as aircraft. PEMFCs and AFCs are suitable for low‐temperature applications and are highly efficient. SOFCs and MCFCs are better for high‐temperature operations. SOFCs are robust and suitable for high‐power demands, while MCFCs are advantageous for high‐power output. Hydrogen fuel cells promise to decarbonize transportation and aviation sectors with the advantages of lower weight, compactness, and quick startup times. However, challenges remain around renewable hydrogen production/infrastructure and aircraft integration, besides hydrogen storage, water management inside fuel cells, and operational robustness under varying pressures. Generally, for all fuel cell types, more focus should be given to enhancing the stability and efficiency of fuel cell materials and reducing their cost.

Plasma Electrolytically Surface-Engineered SS316L Bipolar Plates for PEM Fuel Cells

The proton exchange membrane fuel cell (PEMFC) technology is one of the clean energy technologies with advantages like, quick start-up, low working temperature (60-90 oC), high specific energy and specific power, and high reliability. Stainless steel bipolar plates for PEMFC offer many advantages over conventional graphite and graphite composites. Some of them have superior mechanical properties over graphite, the possibility to fabricate in thin cross sections, and easy formation of flow fields by stamping, which is more economical when compared with the grooving of the graphite counterparts. Despite these advantages, metallic bipolar plates are prone to corrosion in fuel cell working conditions which is often overcome by oxide layer formation on the surface. But the interfacial ohmic loss between the metallic bipolar plate and membrane electrode assembly due to oxide formation decreases the overall performance of PEMFC. For combating these problems, there are different surface engineering techniques like chemical vapor deposition, physical vapor deposition, sputtering, thermal nitridation, etc. Among all methods, plasma electrolytic processing has advantages like less processing time, use of environmentally friendly electrolytes, economical process, easy scale-up for mass production and etc.The 316L stainless steel was surface-engineered using the cathodic plasma electrolytic process in two different aqueous electrolytes containing urea and acetic acid, which acted as a nitrogen and carbon source, respectively. The processed samples were characterized using a scanning electron microscope to study surface morphology and for qualitative chemical analysis. It revealed the diffusion of nitrogen and carbon into the surface in respective electrolytes. The electrochemical performance of as-received/bare 316L and surface-engineered samples were evaluated in a simulated fuel cell environment (half-cell conditions). The electrolyte comprised 0.5 M H2SO4 with 2 ppm HF at 80 oC, and it was purged with N2 or air to simulate anodic and cathodic conditions, respectively. The potentiodynamic polarization studies revealed similar active-passive behavior for bare 316L and surface-engineered samples. Different electrochemical parameters like corrosion current density (icorr), corrosion potential (Ecorr), and passive current density (ipassive) were deduced. The corrosion potentials for the bare sample were observed to have -0.306 V and -0.316 V in cathodic and anodic conditions, respectively. After surface modification, corrosion potentials shifted to more noble values, i.e., -0.234 V, -0.250 V for samples processed in urea solution and -0.219 V, -0.198 V for samples processed in the acetic acid solution for anodic and cathodic conditions, respectively. But the surface-modified samples showed higher passive current densities for both anodic and cathodic conditions than the bare sample, suggesting inferior passivation ability.Also, long-term potentiostatic studies for 8 hours were conducted to understand the samples' behavior. The current densities at the end of the test were -28.7 µA cm-2 (anodic condition) and 7.5 µA cm-2 (cathodic condition) for bare samples. While the samples processed in urea solution showed 27.4 and 9.0 µA cm-2, and the samples processed in acetic acid solution had -115.5 and 89.8 µA cm-2 of current densities in anodic and cathodic conditions, respectively. At different loads, the interfacial contact resistance measurements between the samples and the gas diffusion layer for all samples were determined. At a load of 140 N cm-2, the bare SS316L and samples processed in urea and acetic acid solution showed values of 118.82, 26.78, and 10.97 mΩ cm2, respectively. These studies suggest plasma electrolytically processed SS316L in acetic acid solution offers the least interfacial contact resistance of 10.97 mΩ cm2 and almost satisfies the Department of Energy target of 10 mΩ cm2 for metallic bipolar plates. A scale-up of coating in a 4×4 cm area and its performance in a single-cell setup will be highlighted.

Corrosion-Resistant and Electrically Conductive Oxide Coatings for Metal Bipolar Plates for PEM Electrolyzers

The PEM electrolyzers are considered a promising alternative to alkaline water electrolyzers, as the advantages of PEM technology are high efficiency, high power density, a wide range of power inputs, low operating temperatures, relatively quick start-up, and easy scale-up. The ability of PEM electrolyzers to function dynamically makes them particularly appealing in energy capture and storage systems where electrical energy is derived from renewable sources such as solar and wind power. The bipolar plates (BPPs) are essential components of the PEM electrolyzer stacks and account for the main fraction of the total weight and cost. The BPPs must be electrically conductive, highly corrosion-resistant, and maintain a low interface contact electrical resistance (ICR). The root causes of the BPPs corrosion issues are non-conductive oxides formation increasing electrical resistance, and metal ions out-diffusion poisoning the catalyst and electrolyte membrane. The US Department of Energy has set targets for bipolar plates in fuel cells, including corrosion current densities < 1 µA/cm2 and ICR < 10 mΩ·cm2. Even though these targets do not apply to BPPs in PEM electrolyzers, they provide an indication of acceptable values. The problems outlined above are being overcome or minimized by applying corrosion-resistant and simultaneously electrically conductive coatings.This work, therefore, investigates various corrosion-resistant and electrically conductive oxide coatings prepared by reactive high-power impulse magnetron sputtering (HiPIMS) on SS316L substrates. Reactive HiPIMS is an advanced and progressive magnetron sputter deposition technique suitable for preparing high-quality oxide coatings. The main advantage of HiPIMS is a high degree of ionization of sputtered particles in the discharge plasma and the associated high ion-to-atom ratio in particle flux toward the substrate. This allows one to achieve coating densification and crystallinity at low substrate temperature and without applying a substrate bias voltage. In our case, the native oxide on the SS316L substrate surface was removed by employing plasma etching prior to the coating deposition utilizing HiPIMS-generated ions accelerated towards the substrate by an applied bias voltage. The oxide coatings were deposited using an unbalanced magnetron with a directly water-cooled planar target with a diameter of 100 mm in argon-oxygen gas mixtures at the argon pressure of 1 Pa in an ultra-high vacuum chamber. The oxygen partial pressure was controlled by a PID regulator at a given power density in a pulse. This allowed the deposition of the coatings with different stoichiometries and, thus, different electrical conductivity and corrosion resistance.The electrical resistivity of oxide coatings was measured by a four-point probe system on a non-conductive glass substrate. The compaction pressure dependence of ICR between the test plate and a gas diffusion layer (GDL) was measured in a range from 0.3 to 2.0 MPa on a custom-designed device using gold-coated cylindrical copper electrodes. All electrochemical measurements were performed in an H2SO4 electrolyte solution with an acidity of pH 5.5, fluorine ions concentration of 5 ppm, and a temperature of 60 ℃ to simulate the PEM electrolyzer environment. Accelerated corrosion tests were carried out in extreme anodic conditions of the PEM electrolyzer via potentiostatic polarization at a potential of 2 V vs SHE. Open circuit potential, corrosion current, Tafel slopes, and polarization resistance were determined from potentiodynamic polarization curves measured from 0 to 2 V vs SHE recorded at a scan rate of 1 mV/s, this range should cover most of the potentials experienced inside a PEM electrolyzer. Potentiodynamic polarization and ICR versus compaction pressure were measured before and after the accelerated corrosion test.

A Hybrid Direct Ammonia Fuel Cell

Ammonia has emerged as a highly promising energy carrier [1], primarily because it offers a noticeable economic benefit over hydrogen in terms of source-to-tank expenses, owing to reduced transmission, distribution, and dispensation costs [2]. Direct ammonia fuel cells (DAFCs) are capable of directly converting the chemical energy stored in ammonia into electrical energy. With its quick start-up advantage, this fuel cell technology holds great potential in the field of zero-emission transportation [3]. Although promising, this fuel cell performance needs to be much improved before the widespread commercialization becomes possible. The limiting factors include the sluggish kinetics of ammonia oxidation and the poor conductivity of anion exchange membranes. In addition, another important factor that limits the cell performance is that thermodynamically, its theoretical voltage is low (1.17 V). In this work, a hybrid direct ammonia fuel cell is developed, which consists of an alkaline anode, a cation exchange membrane, and an acid cathode. This hybrid fuel cell offers a theoretical voltage of as high as 2.55 V. The experimental results have shown that it exbibits an open-circuit voltage of 1.35 V and a peak power density of 437.1 mW cm−2 at 90 °C. Acknowledgement This work was fully supported by a grant from the National Natural Science Foundation of China (Project No. 52022003).

Anhydrous Proton Conduction Through a Chemically Robust Electrolyte Enabling a High-Temperature Non-Precious Metal Catalyzed Fuel Cell.

Fuel cells offer great promise for portable electricity generation, but their use is currently limited by their low durability, excessive operating temperatures, and expensive precious metal electrodes. It is therefore essential to develop fuel cell systems that can perform effectively using more robust electrolyte materials, at reasonable temperatures, with lower-cost electrodes. Recently, proton exchange membrane fuel cells have attracted attention due to their generally favorable chemical stability and quick start-up times. However, in most membrane materials, water is required for proton conduction, severely limiting operational temperatures. Here, for the first time it is demonstrated that when acidified, PAF-1 can conduct protons at high temperatures, via a unique framework diffusion mechanism. It shows that this acidified PAF-1 material can be pressed into pellets with high proton conduction properties even at high temperatures and pellet thickness, highlighting the processibility, and ease of use of this material. Furthermore, a fuel cell is shown with high power density output is possible using a non-precious metal copper electrode. Acid-doped PAF-1 therefore represents a significant step forward in the potential for a broad-purpose fuel cell due to it being cheap, robust, efficient, and easily processible.

A Quick Startup Low-Power Hybrid Crystal Oscillator for IoT Applications

In this paper, we propose a hybrid crystal oscillator which achieves both quick startup and low steady-state power consumption. At startup, a large negative resistance is realized by configuring a Pierce oscillating circuit with a multi-stage inverter amplifier, resulting in high-speed startup. During steady-state oscillation, the oscillator is reconfigured as a class-C complementary Colpitts circuit for low power consumption and low phase noise. Prototype chips were fabricated in 65nm CMOS process technology. With Pierce-type configuration, the measured startup time and startup energy of the oscillator are reduced to 1/11 and 1/5, respectively, compared with the one without Pierce-type configuration. The power consumption during steady oscillation is 30 μW.

Design of permanent magnet synchronous motor control system for electric vehicle air conditioning compressor

The permanent magnet synchronous motor (PMSM) is extensively utilized in electric vehicle air conditioning compressor control systems due to its numerous advantages, including high efficiency, lightweight design, compact size, excellent reliability, and low maintenance costs. In order to achieve PMSM without position sensor full speed range operation, this paper designs an optimized control strategy for full speed range operation. At low and zero speed, the I/F control mode is employed to achieve quick motor startup with minimized repetition rate, avoiding the overcurrent problem that is easy to occur by traditional V/F control, and the control is switched to the Phase-locked Loop (PLL) adaptive sliding mode observer (SMO) for position estimation at medium and high speed, avoiding the problems of high-frequency jitter and low position accuracy of traditional SMO. The feasibility of this strategy is confirmed by the simulation results of Simulink.

Experimental Study on the Feasibility of Quick Startup of Instant Heat Pump Water Heaters Based on Active Control of Heat Sink Flow Step

The influence of flow step ratio (FSR) on the startup characteristics of instant heat pump water heaters (IHPWHs) with natural mixture M (R744/R290 (12/88)) under nominal conditions was studied experimentally to verify the feasibility of a new quick startup method. The results show that the FSR had a marked effect on the startup time of system performance parameters. Under the optimal FSR of 0.6, the shortest system startup time and available hot water supply time were 700 s and 250 s, respectively, which were markedly shorter than those in the conventional startup. Therefore, rapid startup of the system and rapid production of usable domestic hot water can be realized by controlling the flow step. The influence of flow step on the variation trend of system performance parameters was obviously different, and there was no slow warming section for the heat sink outlet temperature (HSOT) under three FSRs. The HSOT, heating capacity, and high pressure side pressures had the maximum values in the quick startup, and the maximum values were obviously affected by the FSR. The FSR had no marked effect on the minimum suction pressure. The refrigerant pressures and refrigerant temperatures fluctuated markedly in both rapid and conventional starts.

Experimental study on the characteristics of loop heat pipe with modified carbon fiber felt wick

In order to achieve accurate and effective thermal management of high-performance electronic components, the performance of a small flat loop heat pipe was investigated. A flexible composite capillary wick material has been applied in a flat loop heat pipe. Surface modification of carbon fiber felt was carried out using arc spraying technology to make it a more suitable material for producing capillary wicks. The physical properties of the modified carbon fiber felts were determined by measuring their wettability, porosity, capillary force, and thermal conductivity. A small flat loop heat pipe assembled with carbon fiber felt wick was designed and fabricated, and experimental testing was conducted. The experimental data indicated that the performance of methanol was better than that of acetone and water. The loop heat pipe with a 60% filling ratio maintained the heat source temperature at 84.47 °C under a load of 120 W (30 W/cm2). Conditions where the heat source starts before the cooling system are more favorable for the quick and stable startup of the loop heat pipe. The experimental results demonstrated that the loop heat pipe with a modified carbon fiber felt wick exhibited excellent operational and heat transfer performance.

Ice Formation during PEM Fuel Cell Cold Start: Acceptable or Not?

Proton exchange membrane (PEM) fuel cell faces the inevitable challenge of the cold start at a sub-freezing temperature. Understanding the underlying degradation mechanisms in the cold start and developing a better starting strategy to achieve a quick startup with no degradation are essential for the wide application of PEM fuel cells. In this study, the comprehensive in situ non-accelerated segmented techniques are developed to analyze the icing processes and obtain the degradation mechanisms under the conditions of freeze-thaw cycle, voltage reversal, and ice formation in different components of PEM fuel cells for different freezing time. A detailed degradation mechanism map in the cold start of PEM fuel cells is proposed to demonstrate how much degradation occurs under different conditions, whether the ice formation is acceptable under the actual operating conditions, and how to suppress the ice formation. Moreover, an ideal starting strategy is developed to achieve the cold start of PEM fuel cells without degradation. This map is highly valuable and useful for researchers to understand the underlying degradation mechanisms and develop the cold start strategy, thereby promoting the commercialization of PEM fuel cells.

Numerical and experimental investigation of a Mg/N2O powdered fuel rocket engine

Powdered metal fuel rocket engines, utilizing high energy density metal powder as fuel, have great potential in the development of propulsion systems for upper-stage rockets, and thrusters for attitude or trajectory control. The main challenges of this rocket engine technology currently lie in the realization of stable powder fuel supply, quick engine start-up, and high combustion efficiency. In this paper, we present a computational analysis of the reactive flow in a Mg/N2O powdered metal fuel rocket engine. Consideration in this work includes effects of a flame holder, mass flow rate ratio and entry angle of N2O on combustion efficiency. Based on the numerical simulation results, an experimental Mg/N2O powdered metal fuel rocket engine was designed, and working processes of the engine were investigated through hot fire tests with Mg powder as fuel and N2O as oxidant. A ground test system, consisting of a high-precision test bench, a fuel feed unit, an oxidant feed unit, and a measurement and control unit, was established. The test results show that the combustion of Mg powder and N2O can be sustained.

Improving anammox activity and reactor start-up speed by using CO2/NaHCO3 buffer

Anammox bacteria grow slowly and can be affected by large pH fluctuations. Using suitable buffers could make the start-up of anammox reactors easy and rapid. In this study, the effects of three kinds of buffers on the nitrogen removal and growth characteristics of anammox sludge were investigated. Reactors with CO2/NaHCO3 buffer solution (CCBS) performed the best in nitrogen removal, while 4-(2-hydroxyerhyl)piperazine-1-ethanesulfonic acid (HEPES) and phosphate buffer solution (PBS) inhibited the anammox activity. Reactors with 50 mmol/L CCBS could start up in 20 days, showing the specific anammox activity and anammox activity of 1.01±0.10 gN/(gVSS·day) and 0.83±0.06 kgN/(m3·day), respectively. Candidatus Kuenenia was the dominant anammox bacteria, with a relative abundance of 71.8%. Notably, anammox reactors could also start quickly by using 50 mmol/L CCBS under non-strict anaerobic conditions. These findings are meaningful for the quick start-up of engineered anammox reactors and prompt enrichment of anammox bacteria.