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Proton Exchange Membrane (PEM) fuel cell systems have been studied as the alternatives of the internal combustion engine systems. However, these systems are not appearing in daily life yet, due to the high cost, shortage of infrastructure, technical issues, etc. Concerning technical issues, water/thermal management is a critical one to keep high proton conductivity in the electrolyte membrane for the design of PEM fuel cell systems. Therefore, the heat and mass balances in the PEM fuel cell system have been studied for a long time. However, the influence of stack design on the power and heat generation have not been deeply discussed yet. In this study, influence of the pressure drop and maldistribution in a PEM fuel cell stack on the heat and mass balance in the 100 kW systems was studied. It has been found the heat load in the radiator is reduced by the consideration of the pressure drop in the stack. This is because of the reduction of the water condensation in the stack. The amount of heat, which is reduced in the radiator, is mostly shifted to the condenser for the water recovery. As a conclusion, it can be argued that, by involving the influence of pressure drop in the stack, the amount of heat load in the radiator is reduced about 5%. This is mostly due to less water condensation in the stack. This reduced heat is shifted to the condenser. It corresponds to about 10% increase in the heat load in the condenser. The design of the radiator and condenser must consider this shift in heat load due to the pressure drop in the stack.

The Proton Exchange Membrane (PEM) fuel cell has been investigated for a long time because it has a high power density, low emission, wide choice of fuel sources, etc. However, the performance of a stack of PEM cells degrades with respect to that of a single cell. This is mainly due to the introduction of the manifold in which supplies the reactants to individual cells. The manifold can induce an additional pressure drop and a flow maldistribution. Therefore, it is critical to consider the interaction between the design of the manifold and the flow maldistribution. In this study, the sensitivity of the friction factor in the individual cells to the flow maldistribution and the interaction between the flow maldistribution and water condensation are discussed. As a result, it is found that the friction factors in the individual cells strongly influences the flow maldistribution especially when the flow in the unit cell is changed from laminar flow to turbulent. Large flow maldistributions induce the large pressure drops. As a result, water condensation can be little. However, it also induces a degradation in stack performance. A bipolar plate with a low number of flow channels can improve the flow maldistribution and water condensation in the unit cell although at the expense of a large pressure drop.

Several serious problems such as material durability and fouling in the High Temperature Heat Exchanger (HTEH) for Externally Fired Micro Gas Turbines (EFMGT) cause the low thermal efficiency. In this study for increasing the thermal efficiency, a duct around a cylindrical fixed bed combustor which burns wood pellets is proposed and two different designs, empty and porous material filled, are investigated. A heat transfer model, based on coupling between radiative and convective modes at the combustor and duct sides is developed to evaluate the important geometrical parameters in the different designs. The predicted results for the empty duct show that although an increase of the combustion length increases the temperature of air at the duct outlet, an increase of the combustor diameter is more effective. In addition, an increase of the duct cross section is the most effective way and according to the predictions, the pressure drop in this case is still acceptable. The porous duct design shows a significant increase in the air temperature at the duct outlet. However, the pressure drop is high. The investigation shows the possibility of reduction of the pressure drop with the same amount of heat transfer by selecting suitable particle size and porosity. Copyright © 2007 by ASME.

Proton exchange membrane fuel cell (PEMFC) systems have been investigated as alternative power sources for the stationary and automotive applications. However, they do not appear on the market yet. One of the main reasons is the difficulty of the water/thermal management in the system. Several water recovery schemes have been proposed to overcome this difficulty and to simplify the system configuration. In this paper, the influence of the water recovery schemes on the water/thermal balances in the PEMFC system is investigated. One is a scheme without water phase change at the condenser and the humidifier. The other is a scheme with water phase change. As a result, at low operating pressure, the scheme with water phase change has a large heat dissipation from the system. This is because large water recovery is required in the condenser. With increasing operating pressure, the influence of the difference in the water recovery scheme is diminished from the thermal balance point of view. This is because the requirement of the water recovery becomes small. In the favorable operating range for the stack, the water/thermal balances in the system with water phase change is quite difficult because the heat loads in the intercooler and condenser are very large. However, the water recovery scheme without phase change can solve this difficulty. This scheme makes the component design simpler in this operating range. Copyright (Less)

In this paper, heat and mass balances of the intercooler in a 100 kW Proton Exchange Membrane Fuel Cell (PEMFC) system are analyzed by employing a commercial software IPSEpro. The compressor, ambient temperature, the humidification method and the PEMFCs cathode operating temperature were considered as the parameters influencing the heat and mass balances in the intercooler. Parametric studies of the heat and mass balances in the intercooler are carried out with various values of the parameters, such as operating pressure, air mass flow rate, compressor efficiency, ambient air temperature, cathode operating temperature and H2O injection temperature for the humidification, etc. As indicated in the paper, in the system with either high ambient temperature, high operating pressure, low cathode operating temperature or internal humidification, the required heat transfer rate in the intercooler is large. However, evaporation of H2O for the humidification contributes to reduction of the required heat transfer rate. Copyright (Less)

In Proton Exchange Membrane Fuel Cell (PEMFC) systems, an intercooler contributes to proper thermal management of the reactant air into the cathode. However, the structure/performance of it is not clear yet. In this paper, two case studies concerning an intercooler in a 100 kW PEMFC system are carried out. Plate-fin and tube-fin heat exchangers are analyzed as the intercooler, in terms of volume, pressure drop and weight, The e-NTU method is used. As general characteristics of the intercooler, the volume is increased with system operating pressure, while the pressure drop is decreased due to the volume expansion. The plate-fin intercooler contributes to the weight reduction of the system because aluminum is used. However, at the high operating pressure, space consumption is large. The tube-fin intercooler contributes to the volume reduction because the coolant is a liquid. However, the usage of stainless steel contributes to weight increase. The tube-fin intercooler in aluminum may contribute to space and weight reduction. However, a liquid coolant, which is proper for the PEMFC stack cooling without corrosion of aluminum, is needed. Copyright © 2005 by ASME. (Less)

Heat exchangers are used in proton exchange membrane fuel cell systems (PEMFCs) for stack cooling, intercooling, water condensation and fuel reforming. Especially, the heat exchanger for the intercooling before the humidifier is investigated in this paper. It is found that, at high pressure or high mass flow rate, the need to cool the air (oxidant) is large. The heat exchanger uses coolant water from the stack cooling system or ambient air as the cold stream. With water-cooling, the volume of the heat exchanger will be small. However, difficulties exist because the small available temperature difference. Air-cooling can be used over a wide operating range but the heat exchanger volume will be large.