This article presents heat transfer and fluid flow characteristics in a solar air heater (SAH) channel with multi V-type perforated baffles. The flow passage has an aspect ratio of 10. The relative baffle height, relative pitch, relative baffle hole position, flow attack angle, and baffle open area ratio are 0.6, 8.0, 0.42, 60°, and 12%, respectively. The Reynolds numbers considered in the study was in the range of 3000⁻10,000. The re-normalization group (RNG) k-ε turbulence model has been used for numerical analysis, and the optimum relative baffle width has been investigated considering relative baffle widths of 1.0⁻7.0.The numerical results are in good agreement with the experimental data for the range considered in the study. Multi V-type perforated baffles are shown to have better thermal performance as compared to other baffle shapes in a rectangular passage. The overall thermal hydraulic performance shows the maximum value at the relative baffle width of 5.0.

In order to determine the most cost effective alternative among hardening options of power systems, the direct monetary benefits should be evaluated above all other things. Therefore, this paper presents a life-cycle cost model which describes total monetary costs experienced in annual time increments during the project with consideration for the time value of money. In addition, to minimize the risks associated with estimated cost errors due to uncertainties of input data, the stochastic input data are considered. Using the Monte Carlo method, the probabilities and cost ranges in the case studies can be predicted, in turn resulting in better decisions in the selection of hardening options which are cost effective.

A novel converter that can directly transform electrical, wind, hydraulic and other types of mechanical energy into thermal energy is presented in this study. First, the thermal energy of the converter is classified and then calculated by a finite element method. The eddy current distribution in the stator of the converter is also discussed. Second, the temperature field of the converter is calculated using a boundary element method. Subsequently, a thermal power⁻temperature coupled calculation method is presented to calculate the actual thermal power and temperature of the converter. The characteristic curves of the actual thermal power and the increase in water flow temperature are then presented based on the calculation results. Lastly, an experimental system is built, the thermal power and temperature of the converter are measured and the experimental results and the analytical calculations are compared.

The exhaust gas in an internal combustion engine provides favorable conditions for a waste-heat recovery (WHR) system. The highest potential is achieved by the Rankine cycle as a heat recovery technology. There are only few experimental studies that investigate full-scale systems using water-based working fluids and their effects on the performance and operation of a Rankine cycle heat recovery system. This paper discusses experimental results and practical challenges with a WHR system when utilizing heat from the exhaust gas recirculation system of a truck engine. The results showed that the boiler’s pinch point necessitated trade-offs between maintaining adequate boiling pressure while achieving acceptable cooling of the EGR and superheating of the water. The expander used in the system had a geometric compression ratio of 21 together with a steam outlet timing that caused high re-compression. Inlet pressures of up to 30 bar were therefore required for a stable expander power output.... [more]

This paper presents numerical and experimental analyses aimed at evaluating the technical and economic feasibility of photovoltaic/thermal (PVT) collectors. An experimental setup was purposely designed and constructed in order to compare the electrical performance of a PVT solar field with the one achieved by an identical solar field consisting of conventional photovoltaic (PV) panels. The experimental analysis also aims at evaluating the potential advantages of PVT vs. PV in terms of enhancement of electrical efficiency and thermal energy production. The installed experimental set-up includes four flat polycrystalline silicon PV panels and four flat unglazed polycrystalline silicon PVT collectors. The total electrical power and area of the solar field are 2 kWe and 13 m², respectively. The experimental set-up is currently installed at the company AV Project Ltd., located in Avellino (Italy). This study also analyzes the system from a numerical point of view, including a thermo-economi... [more]

The Up-THERM heat converter is an unsteady, two-phase thermofluidic oscillator that employs an organic working fluid, which is currently being considered as a prime-mover in small- to medium-scale combined heat and power (CHP) applications. In this paper, the Up-THERM heat converter is compared to a basic (sub-critical, non-regenerative) organic Rankine cycle (ORC) heat engine with respect to their power outputs, thermal efficiencies and exergy efficiencies, as well as their capital and specific costs. The study focuses on a pre-specified Up-THERM design in a selected application, a heat-source temperature range from 210 °C to 500 °C and five different working fluids (three n-alkanes and two refrigerants). A modeling methodology is developed that allows the above thermo-economic performance indicators to be estimated for the two power-generation systems. For the chosen applications, the power output of the ORC engine is generally higher than that of the Up-THERM heat converter. However... [more]

The potential of organic Rankine cycle (ORC) systems is acknowledged by both considerable research and development efforts and an increasing number of applications. Most research aims at improving ORC systems through technical performance optimization of various cycle architectures and working fluids. The assessment and optimization of technical feasibility is at the core of ORC development. Nonetheless, economic feasibility is often decisive when it comes down to considering practical instalments, and therefore an increasing number of publications include an estimate of the costs of the designed ORC system. Various methods are used to estimate ORC costs but the resulting values are rarely discussed with respect to accuracy and validity. The aim of this paper is to provide insight into the methods used to estimate these costs and open the discussion about the interpretation of these results. A review of cost engineering practices shows there has been a long tradition of industrial cost... [more]

This work reports the performance of an energy converter characterized by an emitting parallelepiped element with inside two, three, or five swirling connected combustion chambers. In particular, the idea is to adopt the heat released by H₂/air combustion, occurring in the connected swirling chambers, to heat up the emitting surfaces of the thermally-conductive emitting parallelepiped brick. The final goal consists in obtaining the highest emitting surface temperature and the highest power delivered to the ambient environment, with the simultaneous fulfillment of four design constraints: dimension of the emitting surface fixed to 30 × 30 mm², solar mode thermal efficiency greater than 20%, emitting surface peak temperature T > 1000 K, and its relative ∆T < 100 K in the combustion mode operation. The connected swirling meso-combustion chambers, inside the converter, differ only in their diameters. Combustion simulations are carried out adopting 500 W of injected chemical power, stoichio... [more]

NMOS-based Integrated Modular Bypass for Use in Solar systems (NIMBUS) is designed as a replacement for the traditional bypass diode, used in common solar panels. Because of the series connection between the individual solar cells, the power output of a photovoltaic (PV) panel will drop disproportionally under partial shading. Currently, this is solved by dividing the PV panel into substrings, each with a diode bypass placed in parallel. This allows an alternative current path. However, the diodes still have a significant voltage drop (about 350 mV), and due to the fairly large currents in a panel, the diodes are dissipating power that we would rather see at the output of the panel. The NIMBUS chip, being a low-voltage-drop switch, aims to replace these diodes and, thus, reduce that power loss. NIMBUS is a smart bypass: a completely stand-alone system that detects the failing of one or more cells and activates when necessary. It is designed for a 100-mV voltage drop under a 5-A load cu... [more]

In the present paper, we consider the employment of working-fluid mixtures in organic Rankine cycle (ORC) systems with respect to thermodynamic and heat-transfer performance, component sizing and capital costs. The selected working-fluid mixtures promise reduced exergy losses due to their non-isothermal phase-change behaviour, and thus improved cycle efficiencies and power outputs over their respective pure-fluid components. A multi-objective cost-power optimization of a specific low-temperature ORC system (operating with geothermal water at 98 °C) reveals that the use of working-fluid-mixtures does indeed show a thermodynamic improvement over the pure-fluids. At the same time, heat transfer and cost analyses, however, suggest that it also requires larger evaporators, condensers and expanders; thus, the resulting ORC systems are also associated with higher costs. In particular, 50% n-pentane + 50% n-hexane and 60% R-245fa + 40% R-227ea mixtures lead to the thermodynamically optimal cyc... [more]

Metal hydride alloys are considered as a promising alternative to conventional hydrogen storage cylinders and mechanical hydrogen compressors. Compared to storing in a classic gas tank, metal hydride alloys can store hydrogen at nearly room pressure and use less volume to store the same amount of hydrogen. However, this hydrogen storage method necessitates an effective way to reject the heat released from the exothermic hydriding reaction. In this paper, a finned conductive insert is adopted to improve the heat transfer in the cylindrical reactor. The fins collect the heat that is volumetrically generated in LaNi₅ metal hydride alloys and deliver it to the channel located in the center, through which a refrigerant flows. A multiple-physics modeling is performed to analyze the transient heat and mass transfer during the hydrogen absorption process. Fin design is made to identify the optimum shape of the finned insert for the best heat rejection. For the shape optimization, use of a pred... [more]

The clearances in the slide guide system of a hydraulic press are one of the significant factors affecting its accuracy. These clearances also affect the energy consumption of the press. An energy loss model that considers the oil leaks and friction associated with these clearances was proposed, and the size of clearances was optimized based on the model. The maximum allowable eccentric load and the energy loss on the wedge clearance condition were calculated to ensure the slide and guide pillars function properly. The stiffness of pillars and wear of guide rails were checked under an eccentric load condition. A case for rapid sheet metal forming with a 20 MN hydraulic press was examined. For this case, the optimum fit clearances were found to be approximately 0.4 mm. The energy loss under an eccentric load condition was increased by approximately 83% compared to a non-eccentric load condition. The pillars were optimized by reducing excessive stiffness, which served to decrease the pi... [more]

Worldwide interest in low grade heat valorization using organic Rankine cycle (ORC) technologies has increased significantly. A new small-scale ORC with a net capacity of 3 kW was efficiently integrated with a concentrated solar power technology for electricity generation. The excess heat source from Photovoltaic (PV) collectors with a maximum temperature of 100 °C was utilized through a supercritical heat exchanger that uses R-404A as working medium. By ensuring supercritical heat transfer leads to a better thermal match in the heat exchanger and improved overall cycle efficiency. A helical coil heat exchanger was designed by using heat transfer correlations from the literature. These heat transfer correlations were derived for different conditions than ORCs and their estimated uncertainty is ~20%. In order to account for the heat transfer correlation uncertainties this component was oversized by 20%. Next, a prototype was built and installed in an integrated concentrated photovoltaic... [more]

Organic Rankine cycle (ORC) power systems have recently emerged as promising solutions for waste heat recovery in low- and medium-size power plants. Their performance and economic feasibility strongly depend on the expander. The design process and efficiency estimation are particularly challenging due to the peculiar physical properties of the working fluid and the gas-dynamic phenomena occurring in the machine. Unlike steam Rankine and Brayton engines, organic Rankine cycle expanders combine small enthalpy drops with large expansion ratios. These features yield turbine designs with few highly-loaded stages in supersonic flow regimes. Part A of this two-part paper has presented the implementation and validation of the simulation tool TURAX, which provides the optimal preliminary design of single-stage axial-flow turbines. The authors have also presented a sensitivity analysis on the decision variables affecting the turbine design. Part B of this two-part paper presents the first applic... [more]

Despite the increasing interest in organic Rankine cycle (ORC) systems and the large number of cycle models proposed in the literature, charge-based ORC models are still almost absent. In this paper, a detailed overall ORC simulation model is presented based on two solution strategies: condenser subcooling and total working fluid charge of the system. The latter allows the subcooling level to be predicted rather than specified as an input. The overall cycle model is composed of independent models for pump, expander, line sets, liquid receiver and heat exchangers. Empirical and semi-empirical models are adopted for the pump and expander, respectively. A generalized steady-state moving boundary method is used to model the heat exchangers. The line sets and liquid receiver are used to better estimate the total charge of the system and pressure drops. Finally, the individual components are connected to form a cycle model in an object-oriented fashion. The solution algorithm includes a prec... [more]

Because of their low cost, photovoltaic (PV) cells made from upgraded metallurgical grade silicon (UMG-Si) are a promising alternative to conventional solar grade silicon-based PV cells. This study investigates the outdoor performance of a 1.26 kW grid-connected UMG-Si PV system over five years, reporting the energy yields and performance ratio and estimating the long-term performance degradation rate. To make this investigation more meaningful, the performance of a mono-Si PV system installed at the same place and studied during the same period of time is presented for reference. Furthermore, this study systematizes and rationalizes the necessity of a data selection and filtering process to improve the accuracy of degradation rate estimation. The impact of plane-of-array irradiation threshold for data filtering on performance ratio and degradation rate is also studied. The UMG-Si PV system’s monthly performance ratio after data filtering ranged from 84% to 93% over the observation per... [more]

The concept of the Misselhorn cycle is introduced as a power cycle that aims for efficient waste heat recovery of temperature sources below 100 °C. The basic idea shows advantages over a standard Organic Rankine Cycle (ORC) in overall efficiency and utilization of the heat source. The main characteristic of this cycle is the use of at least three parallel batch evaporators instead of continuous heat exchangers. The operational phases of the evaporators are shifted so that there is always one vaporizer in discharge mode. A transient MATLAB® model (The MathWorks: Natick, MA, USA) is used to simulate the achievable performance of the Misselhorn cycle. The calculations of the thermodynamic states of the system are based on the heat flux, the equations for energy conservation and the equations of state found in the NIST Standard Reference Database 23 (Reference Fluid Thermodynamic and Transport Properties - REFPROP, National Institute of Standards and Technology: Gaithersburg, MD, USA). In... [more]

This paper describes a study of the relative influences of different system design decisions upon the performance of an organic Rankine cycle (ORC) used to generate electricity from foundry waste heat. The design choices included concern the working fluid, whether to use a regenerator and the type of condenser. The novelty of the research lies in its inclusion of the influence of both the ORC location and the auxiliary electricity used by the pumps and fans in the ORC power system. Working fluids suitable for high temperature applications are compared, including three cyclic siloxanes, four linear siloxanes and three aromatic fluids. The ORC is modelled from first principles and simulation runs carried out using weather data for 106 European locations and a heat input profile that was derived from empirical data. The impact of design decisions upon ORC nominal efficiency is reported followed by the impact upon annual system efficiency in which variations in heat input and the condition... [more]

Advanced biomass-based motor fuels and chemicals are becoming increasingly important to replace fossil energy sources within the coming decades. It is likely that the new biorefineries will evolve mainly from existing forest industry sites, as they already have the required biomass handling infrastructure in place. The main objective of this work is to assess the potential for increasing the profit margin from sawmill byproducts by integrating innovative downstream processes. The focus is on the techno-economic evaluation of an integrated site for biomass-based synthetic natural gas (bio-SNG) production. The option of using the syngas in a biomass-integrated gasification combined cycle (b-IGCC) for the production of electricity (instead of SNG) is also considered for comparison. The process flowsheets that are used to analyze the energy and material balances are modelled in MATLAB and Simulink. A mathematical process integration model of a typical Nordic sawmill is used to analyze the... [more]

Wind generation systems require mechanisms that allow optimal adaptation of the generator to varying wind speed and to extract maximum energy from the wind. Robust and affordable high-performance methods are also needed for isolated sites. This paper takes this approach, in which an AC switched reluctance generator is used as a generator with a variable rotor speed. Although the voltage obtained is of insufficient quality to connect the generator directly to the power grid, this kind of generator can be used in isolated sites to charge a battery bank with a simple bridge rectifier. Due to the nonlinear behavior of the machine with the position and current, along with the alternating nature of the current that circulates through its phases, the machine experiences cyclical energy transformations of a mechanical, electrical and magnetic nature. This paper analyzes these transformations for the purpose of providing guidelines for machine design and optimization as a wind turbine in isolat... [more]

For zeotropic mixtures, the temperature varies during phase change, which is opposed to the isothermal phase change of pure fluids. The use of such mixtures as working fluids in organic Rankine cycle power plants enables a minimization of the mean temperature difference of the heat exchangers, which is beneficial for cycle performance. On the other hand, larger heat transfer surface areas are typically required for evaporation and condensation when zeotropic mixtures are used as working fluids. In order to assess the feasibility of using zeotropic mixtures, it is, therefore, important to consider the additional costs of the heat exchangers. In this study, we aim at evaluating the economic feasibility of zeotropic mixtures compared to pure fluids. We carry out a multi-objective optimization of the net power output and the component costs for organic Rankine cycle power plants using low-temperature heat at 90 ∘ C to produce electrical power at around 500 kW. The primary outcomes... [more]

Axial-flow turbines represent a well-established technology for a wide variety of power generation systems. Compactness, flexibility, reliability and high efficiency have been key factors for the extensive use of axial turbines in conventional power plants and, in the last decades, in organic Rankine cycle power systems. In this two-part paper, an overall cycle model and a model of an axial turbine were combined in order to provide a comprehensive preliminary design of the organic Rankine cycle unit, taking into account both cycle and turbine optimal designs. Part A presents the preliminary turbine design model, the details of the validation and a sensitivity analysis on the main parameters, in order to minimize the number of decision variables in the subsequent turbine design optimization. Part B analyzes the application of the combined turbine and cycle designs on a selected case study, which was performed in order to show the advantages of the adopted methodology. Part A presents a... [more]

This paper explores the layout of an optimum process for supplying heat to Russian municipal heating systems operating in a market environment. We analyze and compare the standard cogeneration unit design with two-stage reheating of service water coming from controlled extraction locations and layouts that employ three in-line reheaters with heat the supply controlled by a rotary diaphragm and qualitative/quantitative methods (so-called “uncontrolled extraction”). Cogeneration unit designs are benchmarked in terms of their thermal efficiency expressed as a fuel consumption rate. The specific fuel consumption rate on electricity production is viewed as a key parameter of thermal efficiency.

In this study, two systems are brought forward to recover the waste heat of a proton exchange membrane fuel cell (PEMFC), which are named the organic Rankine cycle (ORC), and heat pump (HP) combined organic Rankine cycle (HPORC). The performances of both systems are simulated on the platform of MATLAB with R123, R245fa, R134a, water, and ethanol being selected as the working fluid, respectively. The results show that, for PEMFC where operating temperature is constantly kept at 60 °C, there exists an optimum working temperature for each fluid in ORC and HPORC. In ORC, the maximal net power can be achieved with R245fa being selected as the working fluid. The corresponding thermal efficiency of the recovery system is 4.03%. In HPORC, the maximal net power can be achieved with water being selected in HP and R123 in ORC. The thermal efficiency of the recovery system increases to 4.73%. Moreover, the possibility of using ORC as the cooling system of PEMFC is also studied. The heat released f... [more]

In power conversion of photovoltaic (PV) energy, a hard-switching buck converter always generates some disadvantages. For example, serious electromagnetic interference (EMI), high switching losses, and stresses on an active switch (metal-oxide-semiconductor-field-effect-transistor, MOSFET), and high reverse-recovery losses of a freewheeling diode result in low conversion efficiency. To release these disadvantages, a buck converter with soft-switching cells for PV panel applications is proposed. To create zero-voltage-switching (ZVS) features of the active switches, a simple active soft-switching cell with an inductor, a capacitor, and a MOSFET is incorporated into the proposed buck converter. Therefore, the switching losses and stresses of the active switches and EMI can be reduced significantly. To reduce reverse-recovery losses of a freewheeling diode, a simple passive soft-switching cell with a capacitor and two diodes is implemented. To verify the performance and the feasibility of... [more]