In-plane Temperature Distribution Research Articles

Operando analysis of in-plane heterogeneity for the PEM electrolyzer cell: Mappings of temperature and current density

The internal multi-physical fields of a proton exchange membrane electrolyzer cell (PEMEC) are affected by various factors, exhibiting an intricate coupling state. During electrolysis process, the complexity manifests as heterogeneous distribution of in-plane temperature and current density, potentially leading to local hot spots and performance degradation. Such challenges pose threats to the lifespan and operational safety of PEMEC. This study developed temperature measurement endplates and segmented printed circuit board (PCB), enabling operando measurement of in-plane temperature and current density distribution inside a 25 cm2 lab-scale PEMEC. The mappings of temperature and current density were plotted, and the in-plane heterogeneity was assessed by the introduced indexes. The results indicate that variations in operational parameters affect the balance among cell heat production, heat dissipation, and heat input in the flow area, leading to temperature distribution heterogeneity. The migration mechanism of high-temperature zone is elucidated. Factors such as water-gas flow and local conduction contribute to the heterogeneity in current density distribution. Additionally, specific operating conditions including cold and warm start-up, and water starvation are taken as cases, and a detailed analysis is conducted on the dynamic behaviors of current and temperature distribution and the heterogeneity evolution. This work not only provides experimental evidence for the electrical-thermal characteristics inside the PEMEC but also offers insights for local performance evaluation and operation fault diagnosis in practical applications.

Electrochemical performance analysis of a commercial-scale planar solid oxide fuel cell stack and its sensitivity to operating parameters

Solid oxide fuel cell (SOFC) is a promising energy conversion technology for stationary applications due to its high efficiency, originating from the high operating temperature. It acts as a stable power supply with high space utilization when densely stacked, producing electrical output up to 1∼5 kW. Despite these advantages, it still faces the challenge of resolving thermal imbalance and nonuniform distribution of reaction zones within the stack. This study aims to elucidate the commercial-scale stack’s electrochemical response to the key operating conditions including fuel utilization and operating current density, mainly focusing on the changes in the cell voltage trend, the current density distribution, and the temperature profile. Key indexes affecting the stack performance are defined, and their sensitivities are analyzed. A commercial-scale three-dimensional hydrogen-fueled SOFC stack is used as the physical model. The results show that, at high fuel utilization, the voltage loss occurs as heat generation increases, which is caused by reactant depletion. In-plane temperature and current density distribution also deteriorate. Increasing the operating current density has a relatively minor impact on the planar current density distribution while still increasing the in-plane temperature deviation. Integrating the abovementioned insights, effective methods to adjust the operating conditions are suggested.

Elucidating the sensitivity to key operating parameters of a commercial-scale solid oxide fuel cell stack with open cathode manifolds

Solid oxide fuel cell (SOFC) is considered a promising eco-friendly energy conversion technology due to its high efficiency and fuel flexibility resulting from its high-temperature operation and ceramic structure. However, nonuniformities in thermal and electrochemical distribution within the SOFC stack can lead to performance degradation and hinder its market competitiveness. This study aims to identify optimal operating conditions to minimize these nonuniformities by investigating the effects of key operating conditions on the internal phenomena and local thermodynamic states of a commercial-scale stack. A highly reliable hydrocarbon-fueled SOFC model is developed and used to investigate the response of a 1-kW commercial-scale stack with open cathode manifolds to changes in key operating conditions. A parametric study is conducted on the air inlet temperature, air utilization, external reforming rate, and operating current density. Results show that increasing the air inlet temperature improves the uniformity of in-plane temperature distribution but deteriorates the uniformity of current density distribution. Air utilization and air inlet temperature have an identical mechanism to alter the internal distribution, thus showing a similar effect on local thermodynamic states. However, when altering the air utilization, the rate of decrease in uniformity of vertical temperature and current density is 5.39 times and 2.47 times larger than the change in the air inlet temperature. Increasing the external reforming rate exacerbates the overall distribution of local thermodynamic states. Among the selected operating parameters, the operating current density has the greatest influence on the in-plane temperature and current density distribution. This study provides guidance on the desired internal conditions inside the stack by quantitatively analyzing the effects of key operating conditions on the internal phenomena and local thermodynamic states of the stack through performance parameters and sensitivity analysis.

Impacts of Separator Thickness on Temperature Distribution and Power Generation Characteristics of a Single PEMFC Operated at Higher Temperature of 363 and 373 K

The aim of this study is to investigate the effects of the separator thickness on not only the heat and mass transfer characteristics, but also the power generation characteristics of a polymer electrolyte membrane fuel cell (PEMFC) with a thin polymer electrolyte membrane (PEM) and thin gas diffusion layer (GDL) operated at higher temperatures of 363 and 373 K. The in-plane temperature distributions on the back of the separator at the anode and cathode, which are the opposite sides to the GDL, are measured using a thermograph at various initial cell temperatures (Tinit), relative humidity (RH) levels, and supply gas flow rates. The total voltage corresponding to the load current is measured in order to evaluate the performance of the PEMFC. As a result, it is revealed that the effect of the RH on the power generation characteristics is more significant when the separator thickness decreases. It is revealed that the power generation performance obtained at high current densities decreases with the increase in Tinit with thinner separator thicknesses. According to the investigation of the in-plane temperature distribution, it is clarified that the temperature decreases at corner positions in the separator with the separator thickness of 2.0 mm, while the temperature gradually increases along with the gas flow with separator thicknesses of 1.5 mm and 1.0 mm.

A novel interconnect design for thermal management of a commercial-scale planar solid oxide fuel cell stack

Solid oxide fuel cell (SOFC) is a promising technology for stable power supply with high efficiency and high quality heat utilization, but it still faces the technical challenge of low long-term durability caused by thermal imbalance of its stack. An effective, novel thermal management method is urgently required for its market deployment. This study proposes a novel interconnect design for effective thermal management and elucidates the influence of its design variables on internal thermal conditions and heat transfer characteristics of a 1-kW planar SOFC stack. Three-dimensional thermo-fluid simulations are performed on the new stack design employing the novel interconnect and the conventional stack design for comparison. The new design is developed for the purpose of uniform in-plane (horizontal) temperature distribution by modifying the displacement of gas manifolds. At the repeating-unit scale, due to the reduced thermal resistance for horizontal heat transfer of the new stack, its in-plane temperature deviation decreases by 35–60 °C. At the stack scale with 30 unit-cells stacked vertically, the average temperature increases by 30 °C, and the vertical temperature difference decreases by 50 °C. Such thermal fields are the combined results of reduced gaseous convection and enhanced vertical solid-phase conduction through each repeating unit. In the new stack, the amount of heat transferred to the gas within each repeating unit is generally decreased, but is recuperated by increasing solid conduction through metallic interconnects. The relatively weakened gaseous heat transfer of the new design provides more thermal load at the lowest unit of the stack than the reference design, which promotes gas pre-heating prior to reaching the unit-cells and hence results in the elevated stack temperature. Such gas pre-heating also reduces the temperature difference in the vertical direction of the new design. The lower temperature differences both in horizontal and vertical directions enable the new stack to reduce its thermal imbalance and potentially to improve long-term durability.

Thermoelastic stability of thin CNT-reinforced composite cylindrical panels with elastically restrained edges under nonuniform in-plane temperature distribution

In order to fill the evident lack of investigations on nonlinear response of nanocomposite curved panels under nonuniform temperature, this paper aims to analyze the nonlinear thermoelastic stability of cylindrical panels made of carbon nanotube (CNT) reinforced composite, rested on elastic foundations and subjected to sinusoidal-type in-plane temperature distribution. Reinforcement is carried out through functional rules of CNT volume fraction. An extended rule of mixture is adopted to estimate the effective properties of CNT-reinforced composite. Governing equations are derived based on classical shell theory accounting for von Kármán–Donnell nonlinearity, initial imperfection, interactive pressure from elastic foundation, and preexisting lateral pressure. In addition, the elasticity of in-plane constraints of boundary edges is included. Approximate analytical solutions are assumed to satisfy simply supported boundary conditions and Galerkin procedure is adopted to derive nonlinear closed-form relation between thermal load and deflection. Parametric studies are carried out and interesting remarks are obtained. The present study finds that, unlike case of uniform temperature rise, thermal instability of cylindrical panels under sinusoidal temperature distribution still occurs even though all edges are movable and load carrying capacity is the weakest for an intermediate value of CNT volume fraction. Under sinusoidal temperature distribution, the cylindrical panel may be deflected at the onset of loading and, for the most part, has no longer bifurcation-type buckling response. Furthermore, small values of preexisting external pressure have beneficial influences on the stability of nanocomposite cylindrical panels under nonuniform thermal loads.

Buoyant-flow downward flame spread over carbon fiber reinforced plastic in variable oxygen atmospheres

This study explored the downward flame spread over carbon fiber reinforced plastic (CFRP) sheets under buoyant flow in variable oxygen concentrations. Tested CFRP sheets were fabricated by laminating two unidirectional carbon fiber (CF) sheets impregnated with epoxy resins and curing them in a high-temperature furnace. The fabricated CFRP sheets were combusted in a glovebox which allowed oxygen concentration to vary. Epoxy resin sheets were also tested to investigate the effect of CFs. SEM images of burned and unburned CFRP sheets showed that the flame spread over the CFRP sheets was driven via the pyrolysis of the impregnated epoxy resins. The limiting oxygen concentration (LOC) of the CFRP sheets was 31%, while that of the epoxy resin sheets was 19%. The difference in flammability would be produced by the different thermal inertia. Contrary to the order of flammability, the flame spread rate of the CFRP sheets was higher than that of the epoxy resin sheets in more than 31% O2. In-plane temperature distributions visualized via an IR camera suggested that the CFs conductively transferred heat from flame forward, thereby accelerating the flame spread. In other words, the CFs acted as heat conductors, such as metal cores in electrical wire fires. To predict the flame spread behaviors of the CFRP sheets, this work developed a novel simplified flame spread model that involves solid-phase heat transfer. According to the model with a simulated surface temperature profile, the analytical solution of flame spread rate was derived by formulating energy balance in each zone. When the calculated flame spread rates were compared with the measured ones, a quantitative agreement was recognized. This model would be applicable to other thermally thin high-thermal-conductivity materials as well as the CFRP sheets and therefore contribute to the fire risk assessment of such materials.

Inkjet deposition of lines onto thin moving porous media - experiments and simulations

We have studied the deposition of lines of water onto a thin porous medium by means of a droplet-on-demand, single-nozzle inkjet system. We systematically varied the substrate speed and the droplet frequency. Optical transmission imaging was used to measure the dynamic moisture distribution in the substrate in conjunction with infrared thermography to determine the in-plane temperature distribution of the paper. The temperature of the paper becomes non-uniform due to evaporative cooling. Furthermore, we have developed a two-dimensional model coupling the Richards equation for moisture transport in unsaturated porous media with evaporative mass loss and heat transfer. The results of the numerical simulations agree qualitatively well with the measured data.

Impact of Microporous Layer on Heat and Mass Transfer in a Single Cell of Polymer Electrolyte Fuel Cell Using a Thin Polymer Electrolyte Membrane and a Thin Gas Diffusion Layer Operated at a High-Temperature Range.

The impact of microporous layer (MPL) on the heat- and mass-transfer characteristics and power generation performance of a polymer electrolyte fuel cell using a thin polymer electrolyte membrane (PEM) and a thin gas diffusion layer (GDL) is investigated in this paper. The power generation is investigated at the operational temperatures of 90 and 100 °C which are the target temperatures from year 2020 to 2025 according to the New Energy and Industrial Technology Development Organization’s road map in Japan. The in-plane temperature distributions on the separator back at the anode and the cathode are also measured by a thermograph. As a result, it is found that the voltage drop with the MPL at a high current density is larger compared to that without the MPL irrespective of the initial temperature of the cell and relative humidity conditions. The study also revealed from the anode side observation that the in-plane temperature distribution with the MPL is wider compared to that without the MPL, especially at the initial temperature of 90 °C of the cell . Similarly, from the cathode side observation, the in-plane temperature distributions with the MPL were found to be wider compared to that without the MPL. This study has concluded that the MPL is not effective in obtaining a high performance and even an in-plane temperature distribution for a polymer electrolyte fuel cell with the thin PEM and the thin GDL at a high operational temperature range.

A comprehensive two-phase proton exchange membrane fuel cell model coupled with anisotropic properties and mechanical deformation of the gas diffusion layer

Adequate mechanical compression applied to a proton exchange membrane fuel cell is essential for enhancing performance and durability. The compression not only improves the intimate contact between each layer component, but also causes significant deformation of the gas diffusion layer (GDL). As a result, the level of compression results in changes of electrical and thermal contact resistances, and anisotropic distribution of porosity and tortuosity in the GDL. To improve the fundamental understanding of the compression effect, a comprehensive two-phase model coupling solid mechanics, heat and mass transfer, and electrochemical reactions is developed. First, the model results are validated and show good agreement with the experimental data at baseline operating conditions of 80 °C, 200 kPa, 80% relative humidity, and 20% compression strain ratio with hydrogen and air. Then, oxygen, temperature and liquid saturation distribution at low, intermediate and high current densities are studied at the baseline compression level (20% strain). Finally, five compression strain ratios ranging from 5%, 10%, 15%, 20% and 25% are investigated to study the effect on stress distribution, transport properties, and fuel cell performance. Our results indicate that significant GDL deformation and channel intrusion are caused by land and rib distribution. As a combined effect from heat and mass transport, the liquid water condensation tends to initiate near the rib/GDL interface and can reach near 30% saturation at high current density. In addition, significant difference of in-plane temperature, oxygen, current, and load distributions can be observed due to the geometric aspect ratio and anisotropic GDL properties. A compression strain ratio of 20% is found to have an optimal performance balancing between high contact resistance caused by low compression and high transport resistance due to high compression. The findings of this study provide a new insight to the understanding the complicated coupling effect between mechanical, thermal, mass transport, and electrochemical multiphysics.

Thermal management of open-cathode proton exchange membrane fuel cell stack with thin vapor chambers

Proton exchange membrane fuel cell (PEMFC) is one of the most promising electricity-generating devices with zero pollution. However, a large amount of waste heat will be generated during the operation. The waste heat must be dissipated in time to prevent performance deterioration and irreversible damage. In this paper, a novel cooling strategy is proposed and implemented. Five thin vapor chambers (VCs) are integrated into a 10-cell open-cathode PEMFC stack to enhance its heat dissipation effect. PEMFC stack with VCs has been successfully fabricated and tested experimentally. Results show that VCs can effectively reduce the operating temperature of PEMFC and the minimum in-plane temperature difference can be reduced to 0.5 °C, which provides a reliable and stable thermal environment for safe operation. The effects of VCs on the through-plane and in-plane temperature distribution is studied and analyzed in detail. In addition, when the cathode air flow is small, the thermal management of the stack is significantly affected by the inclination angle. This study has fully demonstrated the feasibility of integrating VCs in PEMFC stack to improve thermal management, and provides guidance for designing and developing a better cooling system of PEMFC stack.

Thermally induced postbuckling of thin CNT-reinforced composite plates under nonuniform in-plane temperature distributions

This paper presents an analytical investigation on postbuckling behavior of thin plates reinforced by carbon nanotubes (CNTs) and subjected to nonuniform thermal loads. Unlike many previous works considered ideal case of thermal load is that uniform temperature rise, the present study considers more practical situations of thermal load are that sinusoidal and linear in-plane temperature distributions. CNTs are reinforced into matrix through functionally graded distributions and effective properties of nanocomposite are estimated according to extended rule of mixture. Basic equations are based on classical plate theory taking into account Von Karman nonlinearity, initial geometrical imperfection, interactive pressure from elastic foundations and elasticity of tangential constraints of simply supported boundary edges. Basic equations are solved by using analytical solutions and Galerkin method. From the obtained closed-form relations, thermal buckling and postbuckling behavior of nanocomposite plates are analyzed through numerical examples.

Measurement of the in-plane temperature field on the build plate during polymer extrusion additive manufacturing using infrared thermometry

The process of filament-to-filament adhesion during polymer extrusion additive manufacturing (AM) is critically influenced by temperature distribution around the filament. Direct measurement of temperature distribution around the filament being deposited is, therefore, important for fully understanding this critical process. While past papers have reported side-view (x-z) temperature measurement using infrared (IR) thermography, this paper presents measurement of the in-plane (x-y) temperature field on the build plate during printing of the first layer by infrared thermography. This measurement is carried out from under the build plate. A small part of the build plate is replaced by an infrared-transparent window. In conjunction with an infrared right-angle prism mirror positioned underneath, direct measurement of in-plane temperature distribution is carried out with an infrared camera. With a thin graphite coating on the build plate, in-plane temperature field on the build plate is obtained, whereas experiments without the graphite coating result in direct measurement of the filament temperature distribution. Bottom-view measurements are shown to agree well with side-view measurements. Temperature fields on the build plate are measured as functions of time for single-line and multi-line printing. A few key features revealed by measurements include symmetrical and asymmetrical temperature distributions for single and multi-line printing, respectively, and the thermal influence between lines being limited only to the adjacent line. The in-plane temperature measurement approach complements past side-view measurements, and improves upon our understanding of thermal phenomena during polymer AM.

Opposed-flow flame spread over carbon fiber reinforced plastic under variable flow velocity and oxygen concentration: The effect of in-plane thermal isotropy and anisotropy

This work explores opposed-flow flame spread over carbon fiber reinforced plastics (CFRPs) with an emphasis on the in-plane thermal isotropy and anisotropy depending on carbon fiber (CF) orientation. CFRP sheets with different CF orientations were fabricated by laminating unidirectional prepregs in different directions and combusted via a chimney where flow velocity and oxygen concentration were variable. The limiting oxygen concentration (LOC) under buoyant flow significantly increased with CF orientation angle. At more than 45°, a flame did not spread at all but was extinguished immediately after ignition even at 60% O2. The flammability of CFRPs with CF orientation angles of 0°, 15°, and 30° was further investigated with varying opposed-flow velocities and oxygen concentrations. The LOC of CFRP was higher than that of polymethyl methacrylate (PMMA) over all tested opposed-flow velocities regardless of CF orientation. The response of LOC to opposed-flow velocity varied with CF orientation angle. At 0°, the LOC was not overly sensitive to opposed-flow velocity but almost constant at 31% O2. Meanwhile, the LOCs at 15° and 30° linearly decreased with increased opposed-flow velocity. Flame spread for CFRP was much faster than that for PMMA because of the high thermal conductivity of carbon fibers. The flame spread rate of CFRPs was affected by CF orientation and that at 0° was highest among the three tested CFRP sheets. IR images used to visualize the in-plane temperature distribution during flame spread showed that the preheat region was significantly varied according to CF orientation. Varying CF orientation, therefore, causes the in-plane thermal anisotropy, resulting in the differences in the LOC and flame spread rate. The findings from this work help us evaluate the fire risk and hazard of CFRP and serve to discuss flame spread behaviors of other anisotropic materials.

Measurement of temperature difference on catalyst layer surface under rib and channel in PEFC using micro sensors

Understanding the temperature distribution inside the polymer electrolyte fuel cell (PEFC) during power generation is essential for improving its performance. An originally developed thin-film temperature sensor was used and the measurements of the local temperature in the catalyst layer (CL) and micro porous layer (MPL) interface under the rib and channel were performed for the first time. Results showed that the dry and wet environment inside the cell had a significant effect on the in-plane temperature distribution. The temperature under the rib was lower than the temperature under the channel while supplying 80% relative humidity (RH) gas. Meanwhile, the temperature under the channel was lower than the temperature under the rib in the low current density region when dry gas was supplied. The results of this study could be used to design the components and flow field and optimize the operating conditions such as gas flow rate and humidification.

Research on the in-plane temperature distribution in a PEMFC stack integrated with flat-plate heat pipe under different startup strategies and inclination angles

Thermal behavior plays an important role in the application of a proton exchange membrane fuel cell (PEMFC) stack. Flat-plate heat pipe (FPHP) is proposed as an alternative cooling device in this study. Compared with conventional liquid-cooled PEMFC stack, PEMFC-FPHP stack needs less parasitic power for auxiliary system and provides a uniform temperature field. A PEMFC-FPHP stack was fabricated, assembled and tested. The experimental result shows that FPHP successfully delivers heat from the stack to surroundings. A more even in-plane temperature uniformity of cell unit is observed as load increases. The transient and stable in-plane temperature field of cell unit are influenced by startup strategy and gravity. In addition, direction of improvement for future work is given.

Impact of MPL on Temperature Distribution in Single Polymer Electrolyte Fuel Cell with Various Thicknesses of Polymer Electrolyte Membrane

The impact of micro porous layer (MPL) with various thicknesses of polymer electrolyte membrane (PEM) on heat and mass transfer characteristics, as well as power generation performance of Polymer Electrolyte Fuel Cell (PEFC), is investigated. The in-plane temperature distribution on cathode separator back is also measured by thermocamera. It has been found that the power generation performance is improved by the addition of MPL, especially at higher current density condition irrespective of initial temperature of cell (Tini) and relative humidity condition. However, the improvement is not obvious when the thin PEM (Nafion NRE-211; thickness of 25 μm) is used. The increase in temperature from inlet to outlet without MPL is large compared to that with MPL when using thick PEM, while the difference between without MPL and with MPL is small when using thin PEM. It has been confirmed that the addition of MPL is effective for the improvement of power generation performance of single PEFC operated at higher temperatures than normal. However, the in-plane temperature distribution with MPL is not even.

Thermal Buckling Analysis of Laminated Composite plates with General Elastic Boundary Supports

In this study, the modified Rayleigh-Ritz method and Fourier series are used to determine the thermal buckling behavior of laminated composite thin plates with a general elastic boundary condition applied to in-plane uniform temperature distribution depending upon classical laminated plate theory(CLPT). A generalized procedure solution is developed for the Rayleigh-Ritz method combined with the synthetic spring technique. The transverse displacement of the orthotropic rectangular plates is not a different term as a new shape expansion of trigonometric series. In this solution approach, the plate transverse deflection and rotation due to bending are developed into principle Fourier series with a sufficient smoothness auxiliary polynomial function, the variable of boundary condition can be easily done by only change the boundary spring stiffness of at the all boundaries of laminated composite plate without achieving any replacement to the solution. The accuracy of the current outcome is verified by comparing with the result obtained from other analytical methods in addition to the finite element method (FEM), so the excellent of this technique is proving during numerical examples.

Heat and mass transfer analysis in single cell of PEFC using different PEM and GDL at higher temperature

According to the H2 and fuel cell road map in Japan, the target operating temperature of polymer electrolyte fuel cell (PEFC) should be 90 °C from 2020 to 2025. In this study, the impact of polymer electrolyte membrane (PEM) and gas diffusion layer (GDL)'s thickness on heat and mass transfer characteristics as well as power generation performance of PEFC is investigated at operating temperature of 90 °C. The in-plane temperature distributions on anode and cathode separator are also measured using thermograph. As a result, it is observed that the increase in power from 1 W to 5 W at the current density of 0.80 A/cm2 as well as even temperature distribution within 1 °C can be obtained at operating temperature of 90 °C by decrease in GDL's thickness from 190 μm to 110 μm. In addition, the power is increased from 3 W to 4 W at the current density of 0.80 A/cm2 operated at 90 °C by decrease in the PEM's thickness from 127 μm to 25 μm.

Static behavior of thermally loaded multilayered Magneto-Electro-Elastic beam

The present article examines the static response of multilayered magneto-electro-elastic (MEE) beam in thermal environment through finite element (FE) methods. On the basis of the minimum total potential energy principle and the coupled constitutive equations of MEE material, the FE equilibrium equations of cantilever MEE beam is derived. Maxwell\'s equations are considered to establish the relation between electric field and electric potential; magnetic field and magnetic potential. A simple condensation approach is employed to solve the global FE equilibrium equations. Further, numerical evaluations are made to examine the influence of different in-plane and through-thickness temperature distributions on the multiphysics response of MEE beam. A parametric study is performed to evaluate the effect of stacking sequence and different temperature profiles on the direct and derived quantities of MEE beam. It is believed that the results presented in this article serve as a benchmark for accurate design and analysis of the MEE smart structures in thermal applications.