This study aims to reveal the mechanism of variable fan speed control in Open cathode PEM fuel cell (OC-PEMFC) by the experiments, which analyze the effects of variable fan speed on the operating ...parameters under different fuel cell loads. The operating parameters are cell temperature, stack voltage, voltage uniformity, and parasitic power. The results reveal that the fan speed has strong effects on the operating parameters: (1) it affects the temperature distribution and overheats the middle cells of fuel cell stack, especially, when it operates at high power; (2) it affects the variation trend of the voltage under different loads; (3) it affects the voltage uniformity, which can be improved via forced convection; (4) it affects the system efficiency due to the parasitic load consumed by the fan. Considering the varying effects of these operating parameters on performance, durability and system efficiency under different fuel cell loads, the variable fan speed control should adapt the variation of fuel cell loads and weigh multiple operating parameters.
•Effect of fan speed on operating parameters is experimentally investigated.•The influence on the performance, durability and efficiency are discussed.•The fan speed control should consider varying demand under different loads.•An adaptive multi-objective optimization problem is introduced.
•The opposed-piston FPEG test platform is built.•The continuous and stable operation of the prototype is realized.•The appropriate ignition and injection timing and scavenge pressure are ...determined.•The stable operation mechanism and synchronization error of the system are analyzed.
As a novel energy conversion device, opposed-piston free piston engine generator (FPEG) has high energy conversion efficiency, high power density, low heat transfer loss and excellent NVH performance. The opposed-piston FPEG test platform is built, and the continuous and stable operation of the prototype is realized. The influence laws of key parameters such as fuel injection timing, ignition timing, fuel injection quantity, scavenging pressure and rebound cylinder initial pressure on the performance of the system are systematically analyzed, the suitable value for the opposed-piston FPEG is determined, and the stable operation mechanism and synchronization error of the system are analyzed. It is found that there is a matching relationship between injection timing and ignition timing. The injection position should be set at 37 mm-39 mm, the ignition position should be 25–27 mm, and the injection and ignition interval should be controlled at about 12 mm. The peak in-cylinder pressure increases with the increase of fuel injection quantity, and the fuller the P-V diagram is. When the scavenging pressure is 1.5 bar and the ignition position is 25 mm-27 mm, the basic indexes have extreme points. When the ignition position is 27 mm, the peak in-cylinder pressure is the largest and the engine indicated thermal efficiency is the highest. When the initial pressure of rebound cylinder is 1.7 bar, the indicated thermal efficiency is the highest. Under the trajectory tracking control strategy, the system realizes continuous and stable operation and can deal with large cylinder pressure fluctuation. The synchronization error changes periodically and is relatively large in the middle of the expansion stroke and near the outer dead center.
Magnetorheological (MR) valves attracted the interest of researchers across diverse fields, owing to the controllable nature of MR fluid. The use of MR fluid in valves enables fast response, energy ...efficiency, and robustness, while several studies designed MR valves that can sustain high-pressure. However, although these studies present efficient solutions, they are still unable to exist in miniaturized form while maintaining high-pressure-sustaining capabilities. This paper presents the analytical, numerical, and experimental analysis of a novel miniaturized cylindrical magnetorheological (MR) valve with high performance in terms of the maximum fluid pressure it is able to sustain. The study considers the flux fringing phenomenon that enhances the value of sustained pressure. The fabricated valve is validated experimentally in closed and open states, as well as during state switching. Finally, comparisons between the analytical, numerical, and experimental results are reported. The novel MR valve demonstrates a capacity to withstand at least 1 MPa of pressure with a volume of 353 mm3 and 3.2 g weight, unlike previous studies that report these values of pressure with valves of larger size and higher structure complexity. These results hold promise for applications demanding high pressure control in constrained spaces, such as medical ones or soft robotics.
The focus of this study is to explore the thermodynamic characteristics of an intermediate heat-exchange cycle (IHEC) system in aero engines, employing experimental analysis. Using air, fuel, and ...intermediate working fluid (IWF) as working mediums, an IHEC system experimental platform incorporated two heat exchangers (HEX) was established. A theoretical analysis model for characteristics of the IHEC system was developed using the heat current method and a novel method for estimating the overall heat transfer coefficient (K). Deviations between experimental and simulation results for system equilibrium heat transfer rates and temperatures at each node of the IHEC system are within ±10%, and the maximum average relative deviation of the proposed method for estimating K is −7.93%. Detailed analyses have been conducted regarding the effects of fuel mass flow rate, IWF mass flow rate, air mass flow rate, and air inlet temperature on the system. Raising the fuel mass flow rate leads to reduced temperatures at each system node, while the system's equilibrium heat transfer rate initially increases and then stabilizes. Variations in IWF mass flow rate have complex impacts on the IHEC system, influenced by HEX design margins and heat transfer capacities. Tailored analyses are necessary based on specific circumstances.
•A theoretical analysis model for system-level characteristics of the IHEC system was developed.•A two-stage heat exchanger combined IHEC system experimental platform was established.•Different parameter's effects on systematic thermodynamic performance have been conducted.•The accuracy of the mathematical model was verified by experiments.
•We show how to collect and classify variants of Simulated Annealing (SA) algorithms.•We use automatic configuration to improve existing Simulated Annealing algorithms.•We show how to automatically ...design new state-of-the-art SA algorithms.•We study the components needed to design good SA algorithms on different scenarios.
Simulated Annealing (SA) is one of the oldest metaheuristics and has been adapted to solve many combinatorial optimization problems. Over the years, many authors have proposed both general and problem-specific improvements and variants of SA. We propose to accumulate this knowledge into automatically configurable, algorithmic frameworks so that for new applications that wealth of alternative algorithmic components is directly available for the algorithm designer without further manual intervention. Here, we describe SA as an ensemble of algorithmic components, and describe SA variants from the literature within these components. We show the advantages of our proposal by (i) implementing existing algorithmic components of variants of SA, (ii) studying SA algorithms proposed in the literature, (iii) improving SA performance by automatically designing new state-of-the-art SA implementations and (iv) studying the role and impact of the algorithmic components based on experimental data. Our experiments consider three common combinatorial optimization problems, the quadratic assignment problem and two variants of the permutation flow shop problem.
The AIAS group studying Energetic Methods for Experimental Analysis, MEAS, is performing round robin experimental tests for the rapid determination of fatigue limit on steels by different ...thermographic techniques. This work is part of the project and describes the experimental activity performed at Politecnico di Milano, based on stepwise cyclic tests. Thermograms are processed in terms of: 1) amplitude of the first order harmonic, in-phase with respect to the loading signal; 2) amplitude of the second harmonic, out-of-phase; 3) slope of the thermal signal with respect to the number of cycles. These values typically show bilinear trends, allowing to define a breakup point and a corresponding stress which is the thermographic estimation of the fatigue limit. The paper presents and discusses the results of tests with different stress ratios, i.e. fully reversed cycling with R=-1 and tensile-tensile cycling with R=0.1.
Hydrogen refueling stations (HRSs) are key infrastructures rapidly spreading out to support the deployment of fuel cell electric vehicles for several mobility purposes. The research interest in these ...energy systems is increasing, focusing on different research branches: research on innovation on equipment and technology, proposal and development of station layout, and research aiming to provide experimental data sets for performance investigation. The present manuscript aims to present an overview of the most recent literature on hydrogen stations, by presenting the technological status of the system at the global level, and their research enhancement on the involved components and processes. After the review of the mentioned aspects, this paper will present the already existing layouts and the potential configurations of such infrastructures, considering several options of the delivery routes, the end-user destination, and hydrogen storage thermodynamic status, whether liquid or gaseous.
•Overview of the most recent literature on HRS operation and experimental activities•Discussion on already existing layouts of hydrogen refueling stations•Hydrogen storage thermodynamic status, liquid or gaseous, and related HRS layout•Research enhancement on the involved components and processes
Ship motion is an important influencing factor in passenger ship evacuation that affects the entire evacuation process by reducing an individual’s walking speed. This study aims to quantify such ...effects in ship berthing and sailing operations by collecting experimental data to support passenger ship evacuation decisions. The study utilized Dalian Maritime University’s training ship to conduct human walking experiments to study the influence of ship motion on passengers’ normal and fast walking speeds. It was found that during the berthing period, an individual’s normal walking speed was 1.28–1.68 m/s, and the fast walking speed was 1.50–2.14 m/s. During the sailing, the ship’s rolling motion reduced the normal walking speed by 3.8%–10.3% and the fast walking speed by 3.7%–14.0%. Due to the influence of ship rolling, the higher the deck and the farther away the rolling centre is, the smaller the athwartship and fore-aft walking speeds. Athwartship walking was slightly faster than fore-aft walking. Similarly, in the normal walking mode, the athwartship walking speed was 1.6%–3.7% faster than fore-aft walking, while in the fast walking mode, the athwartship walking speed was 0.8%–4.9% faster than fore-aft walking. Furthermore, during the berthing period, the average walking speed of the younger group was 24.1% higher than that of the older group. Finally, during the sailing, the speed reduction ratio of an individual’s walking speed was 86.0%–96.2%, and the value decreased as the deck height increased.
•The impact of ship motion on human walking speed was experimentally investigated.•The ship’s rolling motion reduced the normal walking speed by 3.8%–10.3%.•The farther away the rolling centre is, the smaller the human walking speed.•The athwartship fast walking speed was 0.8%–4.9% faster than fore-aft fast walking.•During voyage, the reduction ratio of the human walking speed was 86.0%–96.2%.
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