Wan Ahmad Najmi Wan Mohamed

Heat transfer simulation of a single channel air-cooled Polymer Electrolyte Membrane fuel cell stack with extended cooling surface

A Polymer Electrolyte Membrane (PEM) fuel cell is an electrical power generator utilizing a hydrogen-based fuel reactant and oxygen in a reversed electrolysis reaction, with byproducts of water and heat. The application is sensitive to temperature; more power is generated at elevated operating temperatures, but excessive cell temperature causes dehydration to the membrane electrolyte and subsequent power decline as well as cell deterioration. The power-to-weight ratio and reduced parasitic load, which are the main advantages of an air-cooled system, pushes the research tendency to replace water cooling with air cooling. This work analyzes the heat transfer characteristics, using analytical and Computational Fluid Dynamics (CFD) tools, of a 3 kW PEM fuel cell stack which is equipped with a single cooling channel on each bipolar plate. The base stack design consisting of 73 bipolar plates refers to an industrial water-cooled PEM fuel cell stack available at the Faculty of Mechanical Engineering, University of Technology MARA. From the results of the coolant flow over the base stack design, extended surfaces (fins) was added at an optimized geometry to enhance the heat transfer. Both designs were subjected to a heat flux magnitude of 1.6 times greater than theoretically required, and showed excellent simulated cooling capability of 100% cooling effectiveness when subjected to flows at Reynolds number of 800 and above. Addition of extended cooling surfaces further improves the thermal gradient reduction within the plate by 30%. Though still requires practical evidence, the simulation analysis has provided the groundwork of air cooling applicability in replacing water cooling for a 3 kW PEM fuel cell stack.

An Overview of Hydrogen Production from Renewable Energy Source for Remote Area Application

Hydrogen production through solar energy technology plays a very important role in the development of sustainable energy systems. Traditionally, a wide variety of methods are available for hydrogen production from conventional sources such as natural gas, coal and oil. Their application, however, contributes to emission of ozone depleting gases such as CO2. This paper reviews the recent developments of hydrogen production methods related to solar-hydrogen production for remote area application. The methods discussed are thermochemical, photoelectrochemical and electrochemical where water is the basic raw material. From this review, the low overall efficiency of photoelectrochemical and thermochemical processes make them non-attractive for remote areas application. This paper concludes that the most suitable method for hydrogen production for remote area application is electrochemical process where electrolyzer represents the most important process to obtain hydrogen without any emission of air pollutants or greenhouse gases. This paper will be useful for manufacturers, academicians and researchers who are involved and interested in solar hydrogen system.

Steady - State potential energy recovery modeling of an open cathode PEM fuel cell vehicle

Waste heat recovery in automotive engineering is part of the sustainable energy effort to optimize energy utilization. For vehicles running on hydrogen fuel cells, the potential of heat recovery is perceived to be limited due to the low quality energy generated from the fuel cell stack. It has been established in fuel cell operation that increasing the inlet hydrogen temperature improves the conversion efficiency through higher kinetic reaction rates. A fuel cell power plant for a mini vehicle that will be competing in Shell Eco Marathon Asia 2014 was studied to identify the potential energy recovery limits for an improved power plant design with regenerative hydrogen pre-heater. Using modeling approach for fuel cell power generation and efficiency relationships, the first-order waste energy potential was identified based on test bench studies on the electrical and thermal power relationship of the fuel cell stack performance. The corresponding result is then mapped to a driving cycle to investigate the thermal power generated during the race in both aggressive and passive driving cycle. The energy recovery potential for 4 laps course under aggressive and passive driving cycle are 529 kJ and 501.8 kJ consecutively. The mean thermal powers are 485 W and 410 W respectively which is the reference energy for extended heat exchanger design purposes.

Thermal performance of Al2O3 in water - Ethylene glycol nanofluid mixture as cooling medium in mini channel

Continuous need for an optimum conversion efficiency of a Proton Exchange Membrane Fuel Cell (PEMFC) operation has triggered varieties of advancements namely on the thermal management engineering scope. Nanofluids as an innovative heat transfer fluid solution are expected to be a promising candidate for alternative coolant in mini channel cooling plate of PEMFC. In this work, heat transfer performance of low concentration of 0.1, 0.3 and 0.5 % Al2O3 in water: Ethylene glycol (EG) mixtures of 100:0 and 50:50 nanofluids have been studied and compared against its base fluids at Re number ranging from 10 to 100. A steady, laminar and incompressible flow with constant heat flux is assumed in the channel of 140mm × 200mm. It was found that nanofluids have performed better than the base fluid but the demerit is on the pumping power due to the higher pressure drop across mini channel geometry as expected.

Thermal and electrical experimental characterization of Ethylene Glycol and water mixture nanofluids for a 400w Proton Exchange Membrane Fuel Cell

Nanofluid is an emerging technology in heat transfer study. The effect of nanofluids as a cooling medium in liquid cooled Proton Exchange Membrane Fuel Cell (PEMFC) is studied. Nanofluids with 0.1% and 0.5% volume concentration of Al2O3 are dispersed in base fluid of 50:50 mixture of Ethylene Glycol and water were analyzed experimentally. A rated power of 400 W liquid cooled PEMFC was used to verify the findings. The result showed that insignificant improvement in performance of PEMFC with nanofluids through polarization curve findings, perhaps due to the lower wattage of PEMFC used. The advantage of nanofluids utilization in PEMFC might be visible in higher wattage of PEMFC due to higher working fluid temperature. Higher thermal conductivity of nanofluid at higher temperature is expected to give advantage in terms of polarization curve of a PEMFC. However, the thermal performance is improved through the heat transfer rate increment of 68.5 % and 46 % for both 0.5 % of Al2O3 nanofluid and 0.1 % of Al2O3 nanofluid respectively.

Thermal Analysis of Heat Recovery Unit to Recover Exhaust Energy for Using in Organic Rankine Cycle

Heat engines convert only approximately 20% to 50% of the supplied energy into mechanical work whereas the remaining energy is lost as rejected heat. Although some of the energy lost is intrinsic to the nature of an engine and cannot be fully overcome (such as energy lost due to friction of moving parts), a large amount of energy can potentially be recovered. This paper presents a heat transfer analysis of a WHE for recovering wasted exhaust energy whilst transferring energy to different organic working fluid used in the OrganicRankine Cycle. The types of considered fluids are R-134a, Propane and Ammonia. The results show that the Ammonia has the highesteffectiveness of 0.25. The maximum heat transferrate of 48.5 kW was recovered using the Ammonia at the exhaust gas temperature of 700°C.

Stack Cooling Profile of an Air-Cooled 3-Cell Polymer Electrolyte Membrane Fuel Cell Stack

A locally designed, 3-cell closed cathode PEM fuel cell stack was developed as a platform for thermal engineering studies. Stack polarization behavior is combined with thermal behavior analysis to identify the cooling profiles of an air-cooled fuel cell stack under variable load and cooling settings. The objective of the study is to identify the bulk thermal effects of the stack under cooling for further consideration in fuel cell system control development. The stack is designed with 40 cooling channels and tests were conducted with airflows in the range between 200 and 400 Reynolds number. Different fan settings are applied to analyze the response of the design to negative and positive pressure airflows. The temperature measurements are translated into an averaged stack temperature and a subsequent second order thermal analysis showed that an exponential cooling trend is obtained. Analytical evaluation on the dynamic cooling rates relative to response time and cooling trend is also performed and reported.

Analytical approach to predict hydrogen consumption of a lightweight PEM fuel cell vehicle

This paper reports the methodology to predict the hydrogen consumption for fuel cell vehicle (FCV). Preliminary studies has been conducted to predict fuel consumption of fuel cell vehicle for Shell Eco Marathon competition. In the design process, the starting point is to evaluate the actual performance of the fuel cell stack before applied to the model of vehicle power demand. Both experimental and numerical method has been conducted. Predictions are based on two inputs which is vehicle speed and hill slope. The relationship between power demand and hydrogen consumption are presented and discussed. Finally, driving simulation was performed under aggressive and passive driving conditions and the mileage for every kWh of fuel energy was evaluated. Under average speed of 35 km/h speed and zero slope, the specific range was calculated at 958.2 km/kWh.

Novel Design of Impact Attenuator for an 'Eco Challenge' Car

Thin-walled metallic tubular structures are generally used as impact energy absorber in automotive structures due to their ease of fabrication and installation, high energy absorption capacity and long stroke. However, unlike a normal passenger car where the impact energy can be distributed throughout the whole structure, the impact energy absorbing system of an Eco-Challenge car is confined within a limited space on the front bulkhead. The challenge is to develop an impact attenuator system that can effectively absorb the impact energy within the given space and fulfil the specified rate of deceleration. This new design utilized the standard Aluminium 6063 circular tubes, cut and welded into specific configurations i.e. stacked toroidal tubes with central axial tube sandwiched between two flat plates. Two configurations were investigated; circular and square toroids. Explicit non-linear FEA software was used to determine the impact response i.e. energy absorption, impact force and rate of deceleration. Both configurations showed promising results but the configuration that can be readily fabricated was chosen as the final design.

Computational model analysis on a bipolar plate flow field design of a PEM fuel cell

A computational fluid dynamics (CFD) analysis using commercial software Fluent have been applied to simulate and predict the complex behavior of a Proton Exchange Membrane fuel cell (PEMFC) flow field design. The numerical models are applicable for a single cell fuel cell with flow field channel and membrane electrode assembly (MEA) to simultaneously compute two-phase fluid flow, electrical current flow, species transport, pressures and temperature variations of the fuel cell. The results were compared against a published reference with good agreement. A nearly similar polarization curve was obtained at higher voltages however the Fluent model predicted that the mass concentration region were initiated earlier and reached equilibrium rapidly thus showing larger differences at lower voltage range. On the other hand the Fluent model was able to predict the liquid water activity inside the fuel cell and similar water activity were obtained at the channel exit. It was also shown that at high current density, water in liquid phase was formed over the entire operating voltages. The pressure drop was determined as well and discovered that pressure drop increases as current density increases.