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Temperature, voltage and fuel flow distribution all contribute considerably to fuel cell performance. Conventional methods cannot accurately determine parameter changes inside a fuel cell. This investigation developed flexible and multi-functional micro sensors on a 40 μm-thick stainless steel foil substrate by using micro-electro-mechanical system...
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One of the key components of a chemical gas sensor is a MEMS micro-heater. Micro-heaters are used in both semiconductor gas sensors and NDIR gas sensors; however they each require different heat dissipation characteristics. For the semiconductor gas sensors, a uniform temperature is required over a wide area of the heater. On the other hand, for th...
Micro reformers still face obstacles in minimizing their size, decreasing the concentration of CO, conversion efficiency and the feasibility of integrated fabrication with fuel cells. By using a micro temperature sensor fabricated on a stainless steel-based micro reformer, this work attempts to measure the inner temperature and increase the convers...
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Heat is one of the main causes of performance degradation and failure of proton exchange membrane fuel cells (PEMFCs). The ‘hot spot’ and uneven temperature distribution formed when fuel cells operate can result in the severe degradation of membrane and catalyst layers. To better understand these phenomena, this review presents a systematic and comprehensive summary and discussion on the heat transfer within a PEMFC. Notably, (i) the overall introduction of the basic concept and thermal effect; (ii) the analysis of heat transfer mechanisms, including heat generation and energy transport, as well as the effects of multi-scale; (iii) the summary and discussion of the thermal conductivity and contact resistance of porous media; and (iv) the latest developments in numerical calculation and temperature measurement are crucial. In addition, several outlooks are proposed for further advanced research. We consider that this paper will aid readers in deepening their understanding of this field.
Methanol can be used as the hydrogen source for the operation of fuel cells, given its features of safe storage and transportation management, as well as low reforming temperature (250̃300°C). The micro reformer can convert methanol into hydrogen for portable fuel cells, resulting in many advantages. This study integrated micro temperature, flow andpressure sensors using the micro-electro-mechanical systems (MEMS) technology, and embedded integrated multifunction micro sensor in the micro reformer, so as to measure the distributions of temperature, flow and pressure simultaneously for real-time diagnosis. This study also discussed the internal reaction mechanism of micro reformer, and identified the internal reaction of micro reformer correctly for real-time monitoring and adjustment. This study was consisted of two parts: 1) integration of micro sensor: the polyimide (PI)film is used as substrate to develop the micro temperature, flow and pressure sensors; 2)real-time monitoring of micro reformer: the integrated multifunction micro sensor is embedded in the micro reformer for real-time microscopic monitoring of the changes in temperature, flow and pressure.
In recent years, the development of fuel cells has proceeded rapidly, and so the reformation of methanol to produce hydrogen has become a serious problem. Supplying hydrogen from a methanol microreformer to fuel cells is an important topic. The structure of a microflow channel must support the transfer of external heat to the reform reaction, facilitating the diffusion of methanol vapor into the catalyst layer, thereby increasing the rate of transfer of hydrogen. In this investigation, the micro-electromechanical systems (MEMS) technique is utilized to fabricate pressure, temperature, and flow microsensors. Polyimide film (PI) exhibits high temperature resistance and stress corrosion resistance, and is adopted herein as a flexible substrate. Multifunctional microsensors are inserted into methanol microreformers to measure the internal pressure, temperature, and flow in situ, and the signals thus obtained are used to improve their efficiency.
Thermometry plays an extremely important role in engineering and basic sciences. Accurate measurements of temperature are vital for: (a) improving our understanding of various physical phenomena; (b) process control and optimization; (c) determination of material properties; and (d) energy conservation. This review highlights some of the developments that have occurred in thermometry during the period 1984 to 2011. The ensuing discussions focus on the physical principles that have been exploited for the purpose of thermometry. The developments mentioned in this review offer a peek into the past 27 years of thermometry research that has produced several innovations based upon optical refraction, luminescence, fluorescence, thermo-reflectance, color change, radiation, ferro-electricity, acoustic resonance, Raman Effect, and magnetic resonance principles, to name a few. In tune with the emergent interest in micro/nano-scale interdisciplinary technologies, automated high-speed manufacturing processes, and advances in medical engineering, many of the patents reviewed here relate to thermometry for specialized applications. A sizeable majority of these novel arrangements are non-intrusive and non-contact in nature, suitable for remote measurements. Developments on contact-type temperature sensors, that may require invasive techniques and arrangements, are also presented.
Requirement and difficulties of intra-stack measurement are analyzed. The state of the art in intra-stack temperature and humidity measurement is presented. Methodologies in temperature (field) measurement are micro-thermocouple (array), resistive temperature detector (array), infrared image, fiber-bragg gratings and phosphor thermometry; while chromatography, tunable laser absorption spectrum, micro-electronic humidity sensor and fiber-bragg gratings are applied in humidity measurement. Comparison of the measurement technologies shows that micro sensors have good spatial and signal resolution with low cost, while optic fiber bragg gratings benefits in chemical inertness, immunity to electromagnetic interference and multiplexing capability, which has the most brilliant future.
The operating temperature and internal water accumulation influence the fuel cell performance significantly, and various regions inside the fuel cell still have non-uniformity. At present, only external, invasive, theoretical and simulation methods are available. The real information inside the fuel cell cannot be known instantly.
This study used micro-electro-mechanical systems (MEMS) technology to develop a temperature, pressure and flow 3-in-1 micro sensor. First, the PI foil (Polyimide foil, 50 μm thick) was used to develop a 3-in-1 micro sensor, and then the 3-in-1 micro sensor was embedded in the low-temperature fuel cell for real-time microscopic monitoring of internal temperature, pressure and flow of fuel cell.
In terms of temperature inside the fuel cell, as the upstream and midstream formed heat can be carried away by sufficient gas at the inlet, and the downstream reaction is violent, the downstream temperature is higher than upstream and midstream temperatures. In terms of pressure, in long-term observation, the internal pressure fluctuates, the pressure increases momently and reverts at some time points. This is possibly due to the removal of accumulated water from the flow channel. In terms of flow, the flow supplied by flow controller is higher than the upstream and downstream micro flow sensors, and the difference matches the gas leakage value.
A novel test scheme for in situ measurement of temperature within a single polymer electrolyte membrane fuel cell (PEMFC) is proposed, which possesses the following attractive features: measuring interference with the internal environment of the fuel cell is likely reduced to minimum; simultaneous measurements for local temperatures of both sides of the fuel cell are conducted with enough numbers of measurement locations; and the cell temperatures are controlled in relatively careful and stringent strategies. Thermal and electrical behaviors of the cell tested are investigated, including the local and averaged temperatures at the back sides of cathode and anode flow field plates (FFPs), the outlet currents, and their variations with the test time. It is found that both temperatures and outlet currents exhibit complex dynamic behaviors; and the rise of temperature and the non-uniformity of temperature distribution of the back sides of the two FFPs are not negligible.
Temperature, flow and pressure are critical parameters that influence the performance of fuel cells, in terms of potential, current and power density, for example. Hence, the monitoring of non-uniform temperature/flow rate/pressure within a proton exchange membrane fuel cell (PEMFC) is crucial. To prevent degradation of the performance of a PEMFC, the size of sensors is reduced herein to a µm scale using micro-electro-mechanical systems (MEMS). Integrated flexible micro sensors were fabricated and embedded in a PEMFC to measure local pressure, temperature, and flow rate. The temperatures upstream and downstream of the PEMFC were respectively 64.8°C and 64.7°C at RH50% and 0.1 A/cm2, and 62.7°C and 64.3°C at RH100% and 0.1 A/cm2.
