• Energy Research

AbstractIn this paper, a CFD study of two types of axial-flow automotive cooling fans was conducted to investigate the effects of upstream and downstream blockage on aerodynamic performance of each fan. The realizable k-e turbulence model was applied and simulations were performed to represent an automotive engine bay and quantify performance changes as a function of blockage distance. Modeling was performed for two fan designs: one optimized for a low flow rate, high-pressure operation; and a second optimized for high flow rate, low-pressure operation. The results show that the pressure loss caused by engine blockage increases at higher vehicle speed, and decreasing blockage distance. A new relation between blockage to fan proximity and fan performance was established. It is determined that the pressure change follows a quadratic type dependence, but the coefficients may vary, depending on fan type. The fan efficiency can be improved by taking advantage of larger blockage distances at higher speeds of th...

Abstract Hydrogen recirculation loop in the fuel supply system of a proton exchange membrane (PEM) fuel cell increases the fuel consumption efficiency and maintains moisture within the cell. Conventional recirculation systems utilize mechanical compressors with high power consumption or ejectors that are sensitive to any deviation from the optimum operating conditions. In this paper, an electrochemical pump is analyzed in the hydrogen recirculation loop of a PEM fuel cell and it is compared with two conventional systems, i.e. ejector and mechanical compressor, in terms of system efficiency. The results reveal that the efficiency of the integrated system with a mechanical compressor is lower than two other systems at any working current density due to higher power consumption. Moreover, the efficiency of hydrogen recirculation system with electrochemical pump is close to the system with ejector at low current density. However, at high current density, efficiency of ejector is relatively higher than electrochemical pump because PEM fuel cell has higher parasitic power that can be compensated using ejector in the anodic recirculation system.

Abstract In this paper, a finite volume numerical method is developed to investigate a high temperature polymer exchange membrane (PEM) electrolyzer cell using a three-dimensional and non-isothermal model. The results that are obtained for the single cell are generalized to a full stack of electrolyzer and an exergoeconomic analysis is performed based on the numerical data. The effects of operating temperature, the pressure of cathode, gas diffusion layer (GDL) thickness, and membrane thickness on the energy and exergy efficiencies and exergy cost of the electrolyzer are examined. This study reveals that by increasing the working temperature from 363 K to 393 K, the exergy cost of hydrogen decreases from 23.16 $/GJ to 22.39 $/GJ, and the exergy efficiency of PEM electrolyzer stack at current density of 10,000 A/m2 increases from 0.56 to 0.59. The results indicate that increase of pressure deteriorates the system performance at voltages below 1.4 V. It is concluded that operation of the electrolyzer at higher pressures results in decrease of the exergy cost of hydrogen. Increase of membrane thickness from 50 μm to 183 μm leads to increase of the exergy cost of hydrogen from 23.24 $/GJ to 35.99 $/GJ.

Abstract Absorption chiller systems are advantageous to vapor compression cooling systems due to capability of utilizing low-grade heat sources such as waste heat from industries, renewable energies, and generated heat by fuel cell. The main issue in absorption cooling system is the low cycle coefficient of performance (COP) that can be addressed by integrated ejector-absorption cooling systems. In this study, an integrated system of proton exchange membrane (PEM) fuel cell that thermally drives an ejector-absorption refrigeration cycle is proposed. The effects of generator temperature, condenser pressure, evaporator pressure, and inlet fuel mass flow rate to the fuel cell on the ejector entrainment ratio ( ϕ ) and COP are evaluated. Moreover, the performance of the integrated system is evaluated at different geometrical and operating conditions of PEM fuel cell. The results reveal that the ϕ and COP parameters increase up to 18.51% and 48% by increasing the generator temperature from 70 °C to 100 °C, respectively. At higher inlet mass flow rate of fuel to the reformer, the cooling capacity and the system COP improve. Furthermore, the maximum value of ϕ and COP are 0.39 and 0.77, respectively, at the best operating condition of the PEM fuel cell, i.e. the current density of 0.75 A/cm2. It is also concluded that the system overall energy efficiency at temperature of 80 °C and the current density of 0.5, 0.6, 0.75, and 0.85 A/cm2 are 43%, 39%, 35%, 32%, and 37%, respectively. Moreover, the COP of absorption chiller with ejector at the operating pressure of 1 bar and the temperature of 80 °C for PEM fuel cell is 6.7% higher than conventional absorption chiller.

Abstract In this paper, the performance of an integrated Rankine power cycle with parabolic trough solar system and a thermal storage system is simulated based on four different nano-fluids in the solar collector system, namely CuO, SiO 2 , TiO 2 and Al 2 O 3 . The effects of solar intensity, dead state temperature, and volume fraction of different nano-particles on the performance of the integrated cycle are studied using second law of thermodynamics. Also, the genetic algorithm is applied to optimize the net output power of the solar Rankine cycle. The solar thermal energy is stored in a two-tank system to improve the overall performance of the system when sunlight is not available. The concept of Finite Time Thermodynamics is applied for analyzing the performance of the solar collector and thermal energy storage system. This study reveals that by increasing the volume fraction of nano-particles, the exergy efficiency of the system increases. At higher dead state temperatures, the overall exergy efficiency is increased, and higher solar irradiation leads to considerable increase of the output power of the system. It is shown that among the selected nano-fluids, CuO/oil has the best performance from exergy perspective.

AbstractThe present study investigates the effects of different parameters on the performance of a cold energy storage system based on spherical capsules using two‐ and three‐dimensional (2D and 3D) numerical analyses. The effect of different arrangements of the capsules is studied using a 2D model. The impact of using nanoparticles, diameter, and material of a spherical capsule and working parameters that affect the melting and solidification process are evaluated in a 3D model. The results revealed that the hexagonal arrangement compared to the triangular and rectangular arrangements, yields a lower charging time of 10.71% and 16.67%, respectively. Utilization of a 3% volume fraction of graphene nanoparticles in the phase change material reduces the charging and discharging process time by 11.11% and 22.22%, respectively. The diameter of the capsule is an effective parameter for the charging and discharging time, so the capsule with a diameter of 20 mm in comparison with a diameter of 40 mm reduces the charging and discharging time by 71.1% and 66.67%, respectively. Also, capsules made of graphite yield lower charging process time compared to plastic and glass capsules by 17.39% and 5%, respectively.

The cryogenic carbon capture (CCC) process is a promising post-combustion CO2 removal method. This method is very novel compared with conventional and well-developed methods. However, cryogenic carbon capture is not yet commercially available despite its techno-economic benefits. Thus, a model-based design approach for this process can provide valuable information. This paper will first introduce the cryogenic carbon capture process. Then, a comprehensive literature overview that focuses on different methods for modeling the process at the component level will be given. The modelling methods which are deemed most effective are presented more in depth for each of the key system components. These methods are compared with each other in terms of complexity and accuracy and the simplest methods with an acceptable level of precision for modelling a specific component in the CCC process are recommended. Furthermore, potential research areas in modeling and simulation of the CCC process are also highlighted.

A nanofluid is used as working fluid in a solar parabolic trough collector (PTC) for solar cooling and hydrogen production. The combined system is composed of five sub-systems including PTC, Rankine cycle, thermal energy storage, triple effect absorption cooling system (TEACS), and proton exchange membrane (PEM) electrolyzer. The results of the thermodynamic model for the hybrid PTC/Rankine cycle, TEACS and PEM electrolyzer subsystem are validated. Furthermore, the effects of ambient temperature, solar irradiation and nanofluid volume fraction on the hydrogen production, COP and exergy efficiency of TEACS, and the overall energy and exergy efficiency of the hybrid system are examined. We found that the rate of hydrogen production increases at higher solar radiation intensity because the Rankine cycle delivers more power to the PEM electrolyzer. Exergy analysis reveals that the efficiency of the hybrid system increases approximately by 9% by increase of ambient temperature from 5 to 40 °C. The power generation by Rankine cycle and hydrogen production by electrolyzer increases using higher volume fraction of nanoparticles. The overall energy and exergy efficiency of the hybrid system with the nanoparticles volume fraction of 0 are 1.55 and 1.4 times more than the nanoparticles volume fraction of 0.03 at solar intensity of 600 W m −2 . © 2019 Elsevier Ltd

© 2023 Hydrogen Energy Publications LLCIn this study, energy, exergy and exergy-economic analyses of a novel system that simultaneously generates cooling effect, heat, electricity, hot water and desalinated water for a zero-energy building are presented. It is aimed to evaluate the feasibility of using a solar-geothermal system to meet the energy and water demands of a residential building using exergy-economic indexes. The multi-generation system operates based on solar and geothermal energies, and it consists of proton exchange membrane (PEM) electrolyser, PEM fuel cell, photovoltaic system, and a desalination system with a pressure exchanger. Results indicate that energy and exergy efficiencies in cooling mode are 13.27% and 32.44%, respectively, and in heating mode are 17.25% and 42.4%, respectively. The largest exergy destruction occurs in the photovoltaics and organic Rankine cycle. It is observed that the turbine and boiler have the highest portion in the exergy destruction of the organic Rankine cycle. The capital investment and operating and maintenance cost rate, and the cost of produced distilled water are 4.288 ($/h), 67.63 (c$/m3), respectively. Moreover, the unit exergy costs of power, heating and cooling effect are investigated. The exergy-economic factor and the cost of exergy destruction for the entire system are 57.38% and [Formula presented], respectively.