This paper investigates the thermoelectric characteristics of cross-flow planar type solid oxide fuel cell (SOFC) with natural gas as fuel by using a three-dimensional numerical model. The results reveal that temperature and reactant concentration increase gradually along the direction of fuel gas flow, and the reactant concentration increases in the first and subsequently decreases. In addition, the lower the temperature, the higher ideal electromotive force is as well as the less actual output electromotive force. The hydrogen concentration is positively correlated with the current density and the ideal electromotive force. However, increasing the mass flow continuously beyond the reasonable range can decrease the current and electrochemical reaction intensity. Variation in wall thickness was also simulated and found that increasing the thickness would result in higher intensity of electrochemical reaction and increased current density but at the cost of low efficiency in SOFC. Thus an optimal design can make a balance between fuel utilization and output power of SOFC.

This paper presents an application of MRI to measure flow distribution in fuel cell channels. Solid Oxide Fuel Cells (SOFC) are able to efficiently produce electricity directly from the oxidation of the natural gas by electrochemical conversion. The distribution of fuel gas between the high numbers of parallel flow paths within the fuel cell assembly is critically important to ensure high efficiency and uniform conditions within the fuel cell assembly. Practical approaches in conjunction with numerical models are needed to understand and control the physical processes taking place within fuel cells in order to design them to be efficient and reliable. The paper outlines a non-invasive experiment using magnetic resonance imaging (MRI) to measure the distribution of flow within an SOFC subassembly. The method quantifies the flow distribution by modelling the gas using water at Reynolds similar conditions. Water has a magnetic moment that can be imaged using an MRI scanner. Two-dimensional cross-section scans were taken perpendicular to the direction of flow in the fuel cell channel to measure area and velocity. The study evaluated a range of image resolutions and outlined how the data was processed to provide mass flow rates in each channel using the known fluid properties. At the highest image resolution the total mass flow rate was within 1% of the independent measurement from the experimental rig. The distribution of flow between the channels showed a similar trend to the computational model. The initial results demonstrate the feasibility for the method to measure flow in the SOFC channels.

The use of pure biodiesel for compression ignition engines during the winter poses a challenge due to gelling and plugging of engine filters and fuel lines. The most common method to prevent this issue is blending with petroleum diesel and many engine manufacturers limit the biodiesel in blends to 20% or less for warrantee purposes; as low as 5% may be set for winter months. In a previous work, the authors proposed a novel fuel tank design that could potentially solve this problem and presented a numerical validation of the concept of using phase change materials (PCM) to enable cold weather operability of 100% biodiesel by maintaining its temperature above a cloud point of 5 degrees Celsius for over 3 days at an ambient temperature of −25 degrees Celsius and initial temperature of 20 degrees Celsius. In this research, an experimental analysis is performed using a scaled model of the fuel tank with canola oil as a test fluid in the tank. The tank is subjected to an ambient temperature of −20 degrees Celsius in an icing tunnel facility with air velocity at 10 m/s. The results show that the time above cloud point was increased from 18.6 hours to 22.5 and 33 hours respectively when 4 and 12 PCM tubes were inserted in the tank containing 33 litres of canola oil. A simple numerical model was formulated to predict the transient temperature of the oil and comparison with experimental results showed excellent agreement.

This paper proposes a new combined vibration suppressing device, which can be used to suppress the swaying vibration of off-shore floating wind generator under waves. The floating wind power station tower was modeled, the wave force and the torsion force of the tower were analyzed and the FSI numerical simulation was carried out. The calculation results demonstrate that the amplitudes of the tower torsion angle have been attenuated by 8%, 11% and 17% with different vibration suppression devices which are TMD, TLD and new combined device. In this case the new combined device has the best vibration suppression performance. It is validated that compared to the other two single vibration suppression devices, the new combined device has better vibration suppression capacity and a new way is provided to design the vibration suppression device for off shore floating wind power station.

Novel particle release patterns have been proposed as a means to increase the thermal efficiency of high-temperature falling particle receivers. Innovative release patterns offer the ability to utilize light-trapping and volumetric heating effects as a means to increase particle temperatures over a conventional straight-line particle release pattern. The particle release patterns explored in this work include wave-like patterns and a series of parallel curtains normal to the incident irradiation that have shown favorable results in previous numerical studies at lower particle temperatures. A numerical model has recently been developed of an existing falling particle receiver at the National Solar Thermal Test Facility at Sandia National Laboratories to evaluate these patterns at elevated temperatures necessary to evaluate radiative and convective losses. This model has demonstrated that thermal efficiency gains of 2.5–4.6% could be realized using these patterns compared to the conventional planar release depending on the particle mass flow rate. Increasing the number of parallel curtains, increasing the spacing between curtains, and shifting the particle mass flow rate deeper in the receiver cavity was also found to increase the thermal efficiency. These effects became less significant as the particle mass flow rate increased.

The use of pumps as turbines (PAT) has gained importance in the recent years as a possible alternative to specifically developed turbine for mini/micro hydropower plants. The use of production pump for hydropower generation reduces the capital cost of the plant but the energy conversion efficiency can be remarkably lower. The paper analyses the performance of a production centrifugal pump running both in direct and reverse mode. The analysis calculates theoretically the behavior of the PAT under the best efficiency point and extends the investigation to other operating points using both a combined theoretical approach and CFD simulation under dynamic conditions. The effects of possible modifications to the initial design of the pump are investigated when running in turbine mode and their influence on the standard pump operation is also determined. Numerical simulation demonstrates that the impeller trimming leads to improvement in the PAT efficiency in some operating conditions. Conversely, the rotational speeds close to the values typical for the electric generator reduce the PAT performance. Finally, the modification of the impeller geometry at the turbine inlet increases the PAT efficiency but lowers the performance of the machine when running in pump mode.

Combined Cooling Heat and Power (CCHP) attained significant attention among energy professionals and academicians recently due to its superior thermal, economic and environmental benefit in comparison with conventional energy producing systems (internal combustion engine (ICE), micro-turbine, etc). Despite the abundance of literature on CCHP, only a few studies emphasized on the selection of appropriate prime mover for an economically sustainable CCHP system. Furthermore, the effect of part load efficiencies is commonly neglected during CCHP analysis. We had introduced these two new concepts of economic sustainability of specific prime mover and part load effects on efficiency to CCHP system in our previous paper. An algorithm based on hybrid load following method was utilized to determine the optimum prime mover for a particular location and weather type. No studies explored the effects of efficiency parameters and the selection strategies of prime mover in different building types for any particular location using this newly developed algorithm. Since building types dominates the electric, heating and cooling demand extensively, it is imperative to extend the prime mover selection analysis for building types for efficient CCHP operation. Economic, energy, and emission performance criteria have been utilized for the prime mover selection systems in different building types. Computer simulations were conducted for five different building categories (primary school, restaurant, small hotel, outpatient clinic and small office buildings) for each of three different types of prime movers (reciprocating internal combustion engine (ICE), micro-turbine and phosphoric acid fuel cell) in a cold climate zone (Minneapolis, MN). The simulation results of different prime movers were compared with the outcomes of a reference case (for each building in the same climate zone) that has a typical separate heating and power system. The cold climate zone (Minneapolis, MN) helped to explore the heating load effects on economic, energy, and emission performance of the buildings in comparison to other energy demands (i.e. electric and cooling demand). A hybrid load following method was executed, using improvements shown in our previous article. Performance parameters and other outcomes of this study showed that economic savings were observed for the ICE in all building types, and the micro-turbine in some building types. Internal rate of returns of ICE are 22.4%, 14.7%, 20.5%, 14.6% and 6.5% for primary school, restaurant, small hotel, outpatient clinic and small office respectively. ICE also shows highest energy savings among all three prime movers with an energy savings of 20%, 17.2%, 25.7%, 23.8% and 9.7% for primary school, restaurant, small hotel, outpatient clinic and small office respectively. For all types of prime mover based CCHP systems, lower CO 2 emission was observed for all building types. However, unlike ICE, which is preferable in terms of economic and energy savings, emission analysis shows that micro-turbine poses better emission characteristics compared to other types of prime movers. CO 2 emission for micro-turbine savings are 67.1%, 62.2%, 82%, 43.2% and 81.4% for primary school, restaurant, small hotel, outpatient clinic and small office respectively. The relationship between the power and thermal demand of the different buildings was determined to be a significant factor in CCHP system performance. A sensitivity analysis determining the effects of heat exchanger and heating coil efficiencies on the performance of CCHP systems shows that the economic performance was most sensitive to the heat exchanger efficiency, while energy consumption and emissions was most sensitive to the heating coil and boiler efficiency.

In this paper, a numerical simulation of tether undersea kites (TUSK) used for power generation is undertaken. The effect of varying key design parameters in these systems is studied. TUSK systems consist of a rigid-winged kite, or glider, moving in an ocean current. One proposed TUSK concept uses a tethered kite which is connected by a flexible tether to a support structure with a generator on a surface buoy. The numerical simulation models the flow field in a three-dimensional domain near the rigid undersea kite wing by solving the full Navier-Stokes equations. A moving computational domain method is used to reduce the computational run times. A second-order corrector-predictor method, along with Open Multi-Processing (OpenMP), is employed to solve the flow equations. In order to track the rigid kite, which is a rectangular planform wing with a NACA 0021 airfoil, an immersed boundary method is used. The tension force in the elastic tether is modeled by a simple Hooke’s law, and the effect of tether damping is added. PID control methods are used to adjust the kite pitch, roll and yaw angles during power (tether reel-out) and retraction (reel-in) phases to obtain the desired kite trajectories. During the reel-out phase the kite moves in successive cross-current motions in a figure-8 pattern, the tether length increases and power is generated. During reel-in the kite motion is along the tether, and kite hydrodynamic forces are reduced so that net positive power is produced. The effects of different key design parameters in TUSK systems, such as the ratio of tether to current velocity, and tether retraction velocity, are then further studied. System power output, kite trajectories, and vorticity flow fields for the kite are also determined.

Particle-based concentrating solar power (CSP) plants have been proposed to increase operating temperature for integration with higher efficiency power cycles using supercritical carbon dioxide (sCO 2 ). The majority of research to date has focused on the development of high-efficiency and high-temperature particle solar thermal receivers. However, system realization will require the design of a particle/sCO 2 heat exchanger as well for delivering thermal energy to the power-cycle working fluid. Recent work has identified moving packed-bed heat exchangers as low-cost alternatives to fluidized-bed heat exchangers, which require additional pumps to fluidize the particles and recuperators to capture the lost heat. However, the reduced heat transfer between the particles and the walls of moving packed-bed heat exchangers, compared to fluidized beds, causes concern with adequately sizing components to meet the thermal duty. Models of moving packed-bed heat exchangers are not currently capable of exploring the design trade-offs in particle size, operating temperature, and residence time. The present work provides a predictive numerical model based on literature correlations capable of designing moving packed-bed heat exchangers as well as investigating the effects of particle size, operating temperature, and particle velocity (residence time). Furthermore, the development of a reliable design tool for moving packed-bed heat exchangers must be validated by predicting experimental results in the operating regime of interest. An experimental system is designed to provide the data necessary for model validation and/or to identify where deficiencies or new constitutive relations are needed.

The paper investigates the performance of a combined heat and power system by means of a fully dynamic numerical approach. An ad-hoc library for the simulation of energy conversion systems is developed under the OpenModelica open source platform; the library includes the main components that usually equip a Combined Heat and Power (CHP) system and they can be connected as they are logically connected in the real plant. Each component is modelled by means of equations and correlations that calculate their performance on a time dependent basis. Therefore, many configurations can be evaluated not only in terms of cumulative annual results or average performance, but the instantaneous behavior can be investigated. The numerical library is constructed using the lumped and distributed parameter approach and it is validated by comparing the numerical results with the measured values over a one-year time period. The prediction capabilities of the proposed numerical approach are evaluated by simulating a case study of a health spa. This case study is selected since it is characterized by significant requirements of both thermal and electric energy. The comparison demonstrated that the calculated results are in good agreement with the measurements in terms of both annual values and distribution over the reference period. Furthermore, an optimization algorithm is adopted and linked to the developed library in order to estimate the best size of different components of the CHP system according to a number of constraints. This feature is particularly important when addressing the energy efficiency of a complete system that is depending on a number of interdependent variables. Therefore, the case study is investigated by accounting also for additional technologies that can be further enhance the performance of the system both in terms of energy consumption and economic investment. In particular, the numerical model is used to optimized the CHP energy efficiency by estimating the best trade-off between the reduction of the energy purchased and the overall cost of the system. The application of PV panels and electric energy accumulators is also investigated and the simulation demonstrates that the size of the cogeneration unit equal to 48 kW, the number of PV panels of 299 and the battery capacity of 45 kWh provide the lowest amount of energy purchased, while the best return of investment is obtained by the CHP unit of 40 kW along with 109 PV panels and a battery of 40 kWh.

Supercritical carbon dioxide (sCO 2 ) Brayton cycle is an emerging technology to be used as a power block with concentrated solar power (CSP) systems, tower type, sCO 2 Brayton cycle has the potential to be competitive with traditional Rankine steam cycle. Most of the studies have been focused on the steady state analysis of this technology. This research has developed numerical models for five configurations of sCO 2 Brayton cycles operating under quasi steady state conditions. The studied cycles are connected directly to the solar central receiver tower, which is used to provide heat input to the cycles; consequently, the heat addition is changing over time as a function of solar radiation. During the off load operation, the mass flow rate of the cycle is changing with the goal of keeping the turbine inlet temperature at 700°C. The compressor and turbine use a partial load model to adjust velocities according to the new mass flow rate. Also, the heat exchangers effectiveness are adjusted as they present off-design operation. In the recompression cycle, the model permits to explore the relationship between recompression fraction and the ambient temperature. It is demonstrated that the power generated by the cycle may be improved more than 6 % if the recompression fraction is continuously changed and controlled as a function of the ambient temperature.

This paper presents a dynamic model of a single-stage LiBr-H 2 O absorption chiller. A numerical model has been developed based on mass and energy balance equations and heat transfer equations. The model is developed using MATLAB program and the system of non-linear ordinary differential equation is solved using the 4 th -order Runge-Kutta method. The model is validated with experimental results from pertained literature. The results show that the maximum relative error is found when comparing the dynamic model predicted chilled water outlet temperature to experimental data, which is around 9%. The effect of the inlet hot water temperature on the hot, cooling and chilled water outlet temperatures, cooling capacity and coefficient of performance (COP) are also studied. The results show that as the hot water outlet temperature increases, the outlet temperatures of cooling and chilled water slightly change. Moreover, the cooling capacity increases and the COP slight decreases as the hot water temperature increases.

The performance of Savonius wind turbine can be improved by increasing the effective wind velocity. One of the methods of improving the effective wind velocity is using directional augmentation technique, which actually affects the Omnidirectional capability of the Savonius rotor. This paper works on this method by using convergent nozzle at the outlet of the rotor. The whole work is based on Metamodeling based optimization and numerical simulation. Reynolds averaged Navier-stokes equation (RANS) based turbulence model has been used for simulations, such as static simulation and dynamic simulation. The CFD simulations are validated against previously published experimental data. The optimization procedure is performed by integrating the Design of Experiment (DOE), Computational Fluid Dynamics (CFD), Response Surface Model (RSM) and analysis of variance (ANOVA). The meta-model is able to identify significant design variable and the interactions. The proposed optimal nozzle is shown to improve the coefficient of the moment from 0.3 to 0.44.

Intermittency of sustainable energy or waste heat availability calls for energy storage systems such as thermal batteries. Thermo-chemical batteries are particularly appealing for energy storage applications due to their high energy densities and ability to store thermal energy as chemical energy for long periods of time without any energy loss. Thermo-chemical batteries based on a reversible solid-gas (MgCl 2 - NH 3 ) reactions and NH 3 liquid-gas phase change are of specific interest since the kinetics of absorption are fast and the heat transfer rates for liquid — vapor phase change are high. Thus, a thermo-chemical battery based on reversible reaction between magnesium chloride and ammonia was studied. Experimental studies were conducted on a reactor in which temperature profiles within the solid matrix and pressure and flow rates of gas were obtained during charging processes. A numerical model based on heat and mass transfer within the salt and salt-gas reactions was developed to simulate the absorption processes within the solid matrix and the results were compared with experimental data. The studies were used to determine dominant heat and mass transfer processes within the salt. It is shown that for high permeability materials, heat transfer is the dominant factor in determining reaction rates. However increasing thermal conductivity might decrease permeability and reduce reaction rates. The effect of constraining mass flow rate on the temperature and reaction propagation is also studied. These results show that optimized heat and mass transfer within the solid-gas reactor will lead to improved performance for heating and air conditioning applications.

An ammonia thermochemical energy storage system consists of an endothermic reaction that disassociates ammonia into hydrogen using the solar energy, which can be stored for future use. The reverse reaction is carried out in the energy recovery process; the ammonia synthesis reaction is used to heat supercritical steam to temperatures on the order of 650 degrees Celsius as required for a supercritical steam Rankine cycle. The goal of this paper is to investigate the transient response in a synthesis reactor-heat-exchanger. It is desired to predict the time the system takes to reach steady state and the effect a perturbation has on the temperature response of the system. A numerical model has been developed to investigate the transient behavior of an ammonia synthesis reactor-heat exchanger. The model consists of a transient one dimensional concentric tube counter-flow reactor-heat exchanger. The effect of gas mass flow rate and initial gas temperature was investigated. Results show that as gas mass flow rate increases, the time for the outlet steam temperature to reach steady state decreases. For low gas mass flow rates, the required outlet steam temperature is not achieved.

On the way to a de-carbonized economy by 2050 new technologies have to be developed and deployed into the market. In solar driven thermochemical processes concentrated solar radiation is used as a renewable high temperature heat source to drive a chemical reaction. These processes are promising pathways for the production of gaseous and liquid fuels and therefore they can provide sustainable chemical energy carriers with inherent long-term storage capabilities. Amongst these processes, redox cycles for the production of syngas from water and carbon dioxide received considerable interest due to their high theoretical process efficiencies. In these processes a redox material is reduced using high temperature heat which is provided by concentrated solar radiation. In a second reaction, at considerably lower temperatures, the redox material is oxidized while splitting water or carbon dioxide. One requirement for the design of efficient redox processes is a high recovery rate of the sensible heat of the solid redox material. In recent redox process concepts the use of inert heat transfer particles in combination with a particulate redox material has been proposed. Amongst other benefits this methodology allows to recover heat from the redox material. A corresponding solid-solid heat recovery system is under development. In a single stage the heat recovery unit acts as a co-current heat exchanger. By combining several units and by using a proper flow path a quasi-counter-current heat exchanger can be obtained. Such a heat recovery system requires that particles are lifted at temperatures well above 1100°C. These high temperatures require a simple design, decent thermal insulation and the thermal shielding of all moving parts and engine. The present work is dealing with the development of a respective conveying system which can be operated at the targeted temperatures, while heat losses are prevented as far as possible. A lab scale version of the conveyer is constructed and tested. A numerical model of the conveyer is developed and validated using results of an experimental campaign with particles at 1150°C. The next step in the assessment of the conveyer system is the analysis of the performance of a scale up version. A generic process analysis will be conducted to obtain operational and design requirements of the scale up conveyer. A detailed scale up version is developed accordingly and the validated numerical model is applied to this design to predict the heat losses during the particle lifting and to discuss their impact on the total process performance.

The ability to efficiently and cost-effectively incorporate thermal energy storage (TES) systems is an important advantage of concentrating solar power (CSP) in comparison to other intermittent forms of renewable energy, such as wind or photovoltaics. As such, TES allows CSP plants to continue to provide electricity to the grid even at times when the resource (the sun) is not available, such as cloud transients or at night. Advanced power cycle systems with supercritical carbon dioxide (sCO2) as the working fluid provide high power conversion efficiency because of high temperatures attained, and less compression work and are being explored for integration with concentrating solar power plants. Currently, there is no cost-effective way to store energy at high temperatures (>565 degree Celsius). The present work analyzes the thermal performance of a novel, cost-effective thermal storage system based on elemental sulfur as the storage media. The analysis is based on a detailed system-level computational modeling of the complex conjugate heat transfer and fluid flow phenomena at multiple scales to provide a scientific basis for engineering, designing and optimizing the novel thermal storage system for transient operation. The validation of the computational model based on data from experiments and full-scale plant operation is also reported. Our studies have shown sulfur-based TES to be a promising candidate for high temperature CSP.

Efficient and cost-effective thermal energy storage system plays an important role in energy conservation. Elemental sulfur, the thirteenth most abundant element on earth, is actively being researched as a potential thermal storage medium due to its high energy storage density and low cost. The present work investigates the heat transfer behavior of elemental sulfur at temperatures between 50 degree Celsius and 250 degree Celsius. A shell and tube heat exchanger configuration with sulfur stored inside the tubes and heat transfer fluid flowing over the tubes through the shell is considered. A detailed computational model solving for the conjugate heat transfer and solid-liquid phase change dynamics of the sulfur based thermal energy storage system is developed to elucidate the complex interplay between the governing heat transfer and fluid flow phenomena during charge and discharge operations. The developed numerical model is compared with experimental results and a systematic parametric analysis of the effects of various design parameters on the performance of the thermal storage system is reported.

There is rich solar energy in Taiwan, it also has a great developing potential for solar applications. Solar hot water is able to supply the domestic hot water, the heating load, and the driving energy for absorption cooing. In this paper, a computer simulation program for a multi-purpose solar hot water system providing hot water, winter heating and summer air-conditioning is established by TRNSYS program. Simulation study is done with varying parameters including collector area, storage capacity and type of collector (flat plate and evacuated tube). In order to study the system performance in Taiwan, system simulations are made under the climate data of three representative cities (Taipei in north, Taichung in central, and Kaohsiung in southern) of Taiwan. The results of the present study can provide important reference for the development of the multi-purpose solar hot water system.

Falling particle receivers are being evaluated as an alternative to conventional fluid-based solar receivers to enable higher temperatures and higher efficiency power cycles with direct storage for concentrating solar power applications. This paper presents studies of the particle mass flow rate, velocity, particle-curtain opacity and density, and other characteristics of free-falling ceramic particles as a function of different discharge slot apertures. The methods to characterize the particle flow are described, and results are compared to theoretical and numerical models for unheated conditions.