Cross-flow Configuration Research Articles

The effect of methane addition on reacting hydrogen jets in crossflow

The combustion characteristics in a jet in crossflow configuration are numerically investigated using Large Eddy Simulation (LES) with subgrid scale modelling for partially premixed combustion. The time-averaged statistics are compared with the experimental measurements. Both the temperature and velocity comparisons show good agreement with measurements. The distribution of reaction regions of nitrogen-diluted hydrogen fuel jet is then examined in both physical and mixture fraction space. The results demonstrate that the fuel consumption in potential core, near-field and far-field regions occurs at various mixture fraction ranges. In the potential core region, reactions predominantly occur between the lean and stoichiometric mixture fraction range. This range broadens to include fuel-rich conditions in the near-field region and narrows again to fuel-lean combustion in the far-field region. With these changes in the mixture fraction range, the fractional contribution from different combustion modes also changes. A closer study of these changes reveals that the fractional contribution from the non-premixed mode is highest at the end of the potential core region. The dependency of these combustion modes on the fuel composition is studied by increasing the volume fraction of methane in the jet. This resulted in altered chemical kinetics and thereby increased the fractional contribution of the non-premixed mode, particularly in the potential core region.

Catalytic Ozonation of Pharmaceuticals Using CeO2-CeTiOx-Doped Crossflow Ultrafiltration Ceramic Membranes.

The removal of persistent organic micropollutants (OMPs) from secondary effluent in wastewater treatment plants is critical for meeting water reuse standards. Traditional treatment methods often fail to adequately degrade these contaminants. This study explored the efficacy of a hybrid ozonation membrane filtration (HOMF) process using CeO2 and CeTiOx-doped ceramic crossflow ultrafiltration ceramic membranes for the degradation of OMPs. Hollow ceramic membranes (CM) with a 300 kDa molecular weight cut-off (MWCO) were modified to serve as substrates for catalytic nanosized metal oxides in a crossflow and inside-out operational configuration. Three types of depositions were tested: a single layer of CeO2, a single layer of CeTiOx, and a combined layer of CeO2 + CeTiOx. These catalytic nanoparticles were distributed uniformly using a solution-based method supported by vacuum infiltration to ensure high-throughput deposition. The results demonstrated successful infiltration of the metal oxides, although the yield permeability and transmembrane flow varied, following this order: pristine > CeTiOx > CeO2 > CeO2 + CeTiOx. Four OMPs were examined: two easily degraded by ozone (carbamazepine and diclofenac) and two recalcitrant (ibuprofen and pCBA). The highest OMP degradation was observed in demineralized water, particularly with the CeO2 + CeTiOx modification, suggesting O3 decomposition to hydroxyl radicals. The increased resistance in the modified membranes contributed to the adsorption phenomena. The degradation efficiency decreased in secondary effluent due to competition with the organic and inorganic load, highlighting the challenges in complex water matrices.

Effect of using a ZnO-TiO2/water hybrid nanofluid on heat transfer performance and pressure drop in a flat tube with louvered finned heat exchanger

This study used an experimental setup consisting of a flat tube with a louvered finned crossflow configuration to examine the effects of utilizing a ZnO-TiO2-water hybrid nanofluid on heat transfer rate, heat transfer coefficient, Nusselt number, and pressure drop. The studies were carried out under laminar flow conditions (200 < Re < 800), at four different temperatures (50, 60, 70, 80 °C), four different volume concentrations of nanoparticles (0.025, 0.05, 0.1, 0.2%), and three different volume flow rates (4, 6, 8 LPM). The findings were compared with pure water (0%). The results indicate that using hybrid nanofluid improves the heat transfer performance and increases pressure loss in comparison with pure water. When comparing hybrid nanofluid to pure water, the largest increases in heat transfer rate, heat transfer coefficient, Nusselt number, and pressure drop were 87.8%, 21.7%, 26.4%, and 10%, respectively. In addition, it was found that, up to a specific value (0.05%), increasing the nanoparticle volume concentration enhanced the heat transfer rate, heat transfer coefficient and Nusselt number, but which began to decrease on increasing the concentration past this value. Therefore, it was concluded that nanoparticle volume concentrations greater than 0.05% negatively affect heat transfer under the current operating conditions. The maximum heat transfer rate, heat transfer coefficient, and Nusselt number were obtained under the conditions of an 8 LPM volume flow rate, 80 °C inlet temperature, and 0.05% volume concentration.

Investigations on adsorption – Evaporation characteristics and cycle time effects of integrated desiccant coated M-cycle cooler

This paper looks into the possibility of undertaking simultaneous dehumidification and evaporative cooling in a single heat exchanger, through the conceptualisation of a desiccant-coated M-cycle cooler. The cooler utilises waste heat as a low-grade thermal energy input to regenerate the silica gel desiccant. The interplay between the adsorption and evaporation phenomena has been studied for the crossflow and counterflow configurations of the cooler. Partial differential equations have been formulated for both heat and mass transfer across each of the control volumes. Results obtained from the transient analysis reveal three distinctive temperature regimes of the counterflow configuration and two regimes for the crossflow configuration. It is also observed that the evaporative cooling effects are more predominant in the counterflow setup. Cycle time analysis reveals that the counterflow configuration has greater operational times and lower downtimes as compared to the crossflow configuration. At 82.5 °C, the operational time of counterflow configuration is observed to be double the downtime, thereby doubling its cooling capacity. Thus, the study showcases the potential of utilising low-grade waste heat to develop an integrated adsorption-evaporation cooler for air-conditioning applications.

Experimental and numerical investigation of jet impingement cooling onto a rib roughened concave internal passage for leading edge cooling of a gas turbine blade

Considered is thermal protection of the concave surface within an internal passage, which models the leading edge cavity of vanes or blades of stationary or aero engine gas turbines. Included along the internal surface are different arrangements of V-shaped ribs to further augment surface cooling heat transfer rates. Impingement jets are employed for the cooling, which are configured so that associated cooling air exits the cavity through a crossflow outlet and an array of staggered film cooling holes. The curved part of the asymmetric, concave target plate features a constant radius and connects to straight lines on the pressure and suction sides. Addressed are H/Djet values of 2.7 and 4.0, and Reynolds number Re values of 18,000, 24,000, and 30,000. A maximum crossflow configuration is utilized wherein the coolant flow exits the cooling passage through the film cooling holes and from one end of the passage, as the opposite end is blocked. Different surface configurations are investigated, including 4 V-ribs in four different positions, 8 V-ribs in one position, and a smooth surface of the leading edge cavity. Each V-rib geometry consists of a regular V-rib pointing upstream. A transient thermochromic liquid crystal (TLC) technique is employed to obtain spatially-resolved surface heat transfer data on the internal wall of the leading edge cavity. Resulting experimental heat transfer data are used to validate and verify CFD simulations. Employed for this purpose are steady-state 3D RANS simulations obtained using the OpenFOAM Version 7 numerical code with a kω-shear-stress-transport (SST) turbulence model. Experimentally-measured surface Nusselt number results indicate significant local enhancements adjacent to rib wakes, provided local crossflow velocity values are substantial. Local surface Nusselt number enhancements thus depend upon rib position, but local surface heat transfer increases are most strongly tied to magnitudes of local crossflow velocity. In contrast to these experimental results, CFD simulation results do not show significant variations as rib position is altered. The best thermal performance is associated with 4 V-rib arrangements in two positions, and 8 V-ribs in one position.

Intensification of atmospheric freeze drying for thin food slices with impinging jet

Atmospheric freeze drying obviates the complexities and costs of maintaining a high vacuum for freeze drying. One of the main drawbacks of atmospheric freeze drying is the low sublimation rate, which is restricted by drying temperatures possible at ambient pressure to prevent food products from softening during dehydration. There is a strong need to intensify the process to reduce the total drying time. This study evaluated the feasibility of using impinging jets to enhance the mass transfer characteristics of the atmospheric freeze drying process. Atmospheric freeze drying experiments on thin lamb slices between −3 to −7 °C showed that the impinging jet configuration has a significant effect in improving the rate of mass transfer flux compared to the conventional cross-flow configuration. This was consistent across different thicknesses of the lamb slices, which would have presented different degrees of internal resistance to mass transfer. Given the amount of non-frozen water in the lamb slices at the drying temperature range evaluated, a scheduled switch from cold air atmospheric freeze drying to a mild hot air drying condition was explored. This strategy enhanced the removal of the remaining water content in the lamb slices, mainly the non-frozen water.

Numerical study of the influence of amplitudes on heat transfer in a tube bundle

The objective of this study is to investigate the impact of different surface roughness levels on a staggered arrangement of tubes in a cross-flow configuration, with water as the fluid being used. The focus lies in comparing the data obtained from the rough surface configuration with that of a smooth cylinder reference point. To assist this comparison, a comprehensive two-dimensional computational fluid dynamics (CFD) model is created, which accurately represents the distinctive characteristics of each surface shape. This study also included modifying the Remax within a range of 10 000–16 000 and analyzing the outcomes of using four different tube types, each with different supernatant thicknesses labeled as [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] accordingly. Surprisingly, the tube with a 0.4 wave surface had significantly higher average Nusselt numbers (Nu) compared to the other tubes, indicating superior performance. The ideal tube design was found based on three main metrics: The performance evaluation criterion (PEC), the global performance criterion (GPC) and the average Nu. The performance metrics encompassed the PEC, GPC and the Colburn factor [Formula: see text]. The average Nu of the wavy_0.4 tube was higher than that of the SM by 31.66–32.54%, higher than that of the wavy_0.2 tube by 19.76–20.74%, and higher than that of the wavy_0.1 tube by 9.38–16.58%. According to the statistics, a heat exchanger that cools and has a wave with an amplitude of 0 is the most efficient choice for offshore energy systems. The smooth bundle tube (SBT) demonstrated the most significant increase in GPC, with values of 9.3–12.7% and 20.3–28.3% higher than those of wavy tubes with amplitudes of 0.1 and 0.2, respectively. In addition, correlations for the Nu are given, with results verified using empirical data from Balabani et al.

The impact of wettability on the performance of a two row wavy fin and tube liquid desiccant system for dehumidification and regeneration

This study investigates the challenge of enhancing wettability in falling film type dehumidifiers/regenerators, a crucial factor in optimizing the performance of building air conditioning systems. The emergence of Severe Acute Respiratory Syndrome (SARS) has underscored the need for improved indoor air quality (IAQ) and energy efficiency. This research specifically addresses the suboptimal wettability issue in fin and tube liquid desiccant systems, which is essential for efficient dehumidification and regeneration processes. The experimental setup employed a cross-flow configuration within the heat exchanger elements, where the flow of ionic liquid intersected with horizontal airflow through cooling and heating coils. By systematically adjusting the wettability on the heat exchanger surfaces, the study examined its impact on relative humidity and dry bulb temperature at the system's inlet and outlet. The results indicate that the wetting fraction on fin and tube surfaces significantly influences the delta humidity ratio of air. In the dehumidification phase, for instance, the delta air humidity ratios varied between 9.4 and 9.7 g/kg with corresponding wetting ratio values ranging from 0.47 to 0.5. Similarly, during regeneration, delta air humidity ratios fluctuated from 9.08 g/kg to 9.6 g/kg, with wetting fractions between 0.47 and 0.5. In conclusion, this study offers in-depth insights into the impact of wettability on the efficiency of fin and tube liquid desiccant systems. These findings have implications for enhancing IAQ and energy efficiency in building air conditioning, particularly in tropical regions like Indonesia.

On the stabilization mechanisms of a diffusion edge flame in a cross-flow configuration

This work focuses on the stabilization and combustion efficiency of a gaseous diffusion flame at the lip of a hole where pure methane is injected into a crossflow of air. This configuration mimics the flame base of many flares, used to burn excess gas in the oil and gas industry. In a flare, the flame base, near the lips of the fuel jet duct, is a critical zone where the flame attaches or not. When the cross flow air speed is too high or the torch lips too cold, the flame cannot attach to the lips so that methane can leak below the lifted flame front near the injector lip and avoid combustion totally. This cannot be accepted for climate change since unburnt fuel like methane has a radiation forcing larger than 20 times the value reached for CO2. Combustion efficiencies close to unity are expected for the flares of the future. Two main parameters control the anchoring of the diffusion flame on a thin lip: the air cross-flow velocity uair and the temperature of the lip or equivalently its cooling, measured here by a thermal resistance Rth. Dimensional analysis is used to construct two reduced parameters controlling stabilization and simulations are performed to populate this diagram. The resulting diagram shows how uair and Rth control flame anchoring. Large values of Rth (adiabatic lips) lead to high lips temperatures and to flames which can resist high air cross-flow velocities. For low values of Rth (cold lips), the flame lifts off for smaller values of uair. The simulations also reveal that triple flames are the flame elements controlling the flame anchoring and how these triple flames interact with the lips forming a flame topology called RS (Rim Stabilized) edge flame.

Direct Numerical Simulation of a Reacting Turbulent Hydrogen/Ammonia/Nitrogen Jet in an Air Crossflow at 5 Bar

The article aims to analyze the fluid dynamics and combustion characteristics of a non-premixed flame burning a fuel mixture derived from ammonia partial decomposition injected in an air crossflow. Nominal pressure (5 bar) and inlet air temperature (750 K) conditions are typical of micro-gas turbines. The effects of strain on the maximum flame temperature and NO generation in laminar non-premixed counter-flow flames are initially explored. Then, the whole three-dimensional fluid dynamic problem is investigated by setting up a numerical experiment: it consists of a Direct Numerical Simulation, based on accurate transport, chemical, and numerical models. The flow topology of the specific reacting jet in crossflow configuration is described in terms of its main turbulent structures, like shear layers, ring, and horse-shoe vortices, as well as of its leeward recirculation region anchoring the flame. The reacting region is characterized by providing instantaneous spatial distributions of temperature, heat release, and some transported chemical species, including NO, and calculating the Flame Index to identify non-premixed and premixed combustion local conditions. The latter is quantified by looking at the distribution of the volume fraction associated with a certain Flame Index versus the Flame Index and at the distribution of the average values of both the Heat Release Rate and NO versus the Flame Index and the mixture fraction.

State switching in the wake of a transverse circular cylinder in the transonic regime

The flow past a circular cylinder in a cross-flow configuration was investigated using a wind tunnel experiment across a range of Mach numbers M∞ from 0.30 to 0.85 and corresponding Reynolds numbers, based on diameter, ranging from 2×105 to 5×105. The boundary layer at the cylinder surface is either free or fixed turbulent using artificial tripping at azimuth 12.5°, 25°, and 50°. Measurements combine temporal recordings of the wall pressure and schlieren high-speed visualizations of the flow past and downstream of the cylinder. First, by attaching the tripping strips to the cylinder at the different azimuthal positions, the effect of the boundary layer state on the cylinder wake is found to be strong at subsonic speeds but much smaller in the transonic regime. Multiple flow states are observed depending on the value of M∞. Of particular interest was the narrow region between M∞=0.80 and =0.85, which yields three different states, namely the vortex shedding state, the parallel shear layer state, and the crossed shear layer state. By precisely managing back and forth travels in Mach number with the wind tunnel, it is found that the transitions between these states have a hysteresis behavior. This sub-critical behavior could explain the surprisingly variable threshold values between these different states reported in the literature.

Comparative investigation on direct contact crossflow and direct contact counterflow packed beds condensers: Experimental and modeling analyses

Humidification and dehumidification systems are based on relatively low-cost designs that operate using low grade heat. An important component in these systems is the condenser. The current work focuses on estimating the performance of a crossflow direct contact condenser in which the fluids flow perpendicularly from one another while being in direct contact. Packed beds are employed to enhance the surface area between the fluids. A steady-state two-dimensional mathematical model is presented for crossflow direct contact condensers incorporating packed beds. The balances of mass and energy are solved numerically for the liquid, air/vapor, and packed bed phases. Simulations results are presented on crossflow condensers with varying inlet conditions for the liquid and air/vapor phases. A laboratory scale experimental setup is developed and compared with simulation results. The measured liquid temperature exhibits a deviation of approximately 10 percent from the predicted value, whereas the air temperature deviates by roughly 6 percent from the predicted value. In addition, a comparative study between cross flow and counter flow direct contact packed beds condensers is provided. It has been discovered that both cross flow and counter flow direct condenser have almost similar freshwater production for most of the considered conditions. A cross flow configuration can thus also be used effectively instead of a counter flow direct contact packed beds condenser and can accommodate a variety of spaces and configurations.

Numerical study on thermal stress of solid oxide electrolyzer cell with various flow configurations

Development of solid oxide electrolyzer cell (SOEC) is of great significance for hydrogen energy utilization. In order to have a better understanding of the multiphysics field processes in SOEC, numerical simulation is a necessary means to be adopted. In this study, a complete three-dimensional model of a planar SOEC short stack with three flow configurations (co-flow, cross-flow, counter-flow) was built. Multiple physical fields, including electron(ion), momentum, mass, and heat transfer, and thermal stress as well, were considered. The accuracy of the model was verified by comparing with the experimental results, with the maximum relative error less than 5%. The performances of SOEC with variant flow configurations were compared in detail. Due to the difference of flow configurations, the distribution of temperature, current density, hydrogen mole fraction, and stress present different characteristics. The effects of the operating voltage and the inlet gas temperature on hydrogen production and stress concentration in SOEC were also studied. The results show that compared with co-flow and counter-flow, the hydrogen production rate of cross-flow increases by about 15%, while the stress concentration decreasing by about 70%. All results show the better performance of cross-flow configuration, which provides guidance for design and application of SOEC.

An investigation of water gas shift reaction in a Pd-alloy membrane reactor with an optimized crossflow configuration

In this study, the performance of a high-temperature water gas shift reaction (WGSR) using a Fe-Cr catalyst along with a Pd alloy membrane was simulated by computational fluid dynamics (CFD). The influences of using Pd membranes, catalytic layer thickness ratio (R/R0), Reynolds number, and steam-to-CO ratio (S/C) on the reaction were investigated by comparing CO conversion and hydrogen recovery (HR). In the CFD simulation, one-tube and four-tube systems were simulated at 500 °C. This study also compared the performance between tandem and optimized configurations. The results show that the CO conversion can be improved up to 22.9% when the WGSR reactor system uses a Pd membrane compared to the system without a Pd membrane. The system has the best hydrogen recovery performance at S/C = 4 and R/R0 larger than 1.5. At Re=5, the optimized configuration for CO conversion has better performance when R/R0 is larger than 1.75. Compared to the tandem configuration, the optimized configuration also shows better performance for HR at every R/R0. The results indicate that a Pd membrane and optimized configuration can significantly improve CO conversion and that R/R0 and S/C optimization is very important for effective reactor performance.

Flow-induced reconfiguration and cross-flow vibrations of an elastic plate and implications to energy harvesting

We numerically study flow-induced vibrations (FIV) of an elastic cantilevered plate in a cross-flow configuration. The plate is kept upright in an open domain with a fixed bottom end. Such a configuration eliminates energy losses in the wall boundary. Due to allowed vortex shedding from its bottom end, the resulting novel dynamics of the fluid-structure interaction (FSI) system is explored. An in-house sharp-interface immersed boundary method-based flow solver, coupled with a Saint-Venant Kirchhoff material model-based open-source finite element solver, is employed. Two sets of simulations were carried out in two-dimensional Cartesian coordinates at Reynolds number of 100 for a wide range of reduced velocity (UR), by performing a parametric sweep of dimensionless Young’s modulus (E) and mass ratio (M). In general, FIV characteristics of the plate are similar to the transverse vortex-induced vibration of an elastically-mounted cylinder. The plate deforms to a curved mean position depending on E and M and exhibits angular oscillations. In particular, the following FIV regimes are obtained with increasing UR: initial excitation, lock-in with the first mode, desynchronization after the first lock-in, lock-in with the second mode, and desynchronization after the second lock-in. During lock-in, the plate oscillation and vortex shedding frequency are closer to the first or second mode natural frequency of plate. A larger angular amplitude and increased energy exchange between the structure and fluid characterize the lock-in. We quantify the modal contributions of Euler-Bernoulli modes in the plate’s vibration response with a curved mean position. The spatiotemporal variation of energy exchange between the fluid and plate is analyzed to understand the observed plate dynamics. The flow physics of the wake is discussed using wake patterns, vortex formation length, and vortex strength. Drag over the plate reduces due to flow-induced reconfiguration and strongly correlates with these parameters. Lastly, based on the spatial distribution of strain energy density over the plate, we present a potential design for an ambient fluid energy harvester to harness the plate’s vibration energy with optimized piezoelectric patching. The optimum location and height of a piezoelectric patch on the plate for different cases are reported.

Design and performance optimization of a direct ammonia planar solid oxide fuel cell for high electrical efficiency

Achieving higher efficiency of direct ammonia solid oxide fuel cells (DA-SOFC) requires high compatibility between cell design and temperature distribution during NH3 decomposition. Therefore, this work aims to provide a comprehensive study of the DA-SOFC different design configurations and parameter optimization. Three main flow configurations are co-flow, counter-flow, and cross-flow. In addition, a detailed parametric study of the cross-flow configuration is performed to optimize cell performance by minimizing thermal stress, considering thermal management, efficiency, and manufacturing advantages. The model is experimentally validated, and the mean relative error and root mean square error is found to be less than 2%. The co-flow configuration has shown lower power output at higher current densities than the counter and cross-flow configurations. At the same time, co-flow possesses minimum thermal stress across the cell cross-section. In cross-flow design, the maximum electrical efficiency of 51.4% with 152 K cell temperature difference is established at 60% fuel utilization, 3% air utilization, fuel intake temperature, and air inlet temperature at 923 K. This study is expected to help optimize the design and operating parameters to maximize DA-SOFC stacking performance and durability and minimize cost.

Thermal performance investigation of metal foam heat exchanger for micro-gas turbine

This study presents the experimental monitoring of heat transfer performance of metal foams in transient state. Micro gas turbines require a compact recuperator with high effectiveness to achieve higher thermal efficiency. Porous media such as metal and ceramic foams are characterised by high surface-to-volume ratio. They are known to increase heat transfer and potentially can be incorporated in recuperators. Their structure is ideal for thermal management of compact and lightweight applications. The idea is to combine excellent thermal properties of metal foams with turbine gases heat fluxes exploitation, in order to elevate the temperature of a different working fluid such as water or compressed air before it enters the combustor. A novel facility was designed and developed for monitoring heat transfer mechanisms that occur in metal foams. A copper cylinder is filled with metal foam which is heated in transient state by a sudden switch from cold to hot water flow whereas a cold stream cools the device in a crossflow configuration. The study demonstrates a method based on computerisation of true-colour analysis of digital images for surface temperature visualisation using thermochromic liquid crystals (TLC). Results of temperature as well as local and mean heat transfer coefficient were obtained showing that the hot flow inside the foam was more dominant in heat transfer than the cold flow in the empty channel. The method is promising for the evaluation of transient phenomena in a tube that is filled with porous media.

Intensified biodiesel production from waste cooking oil and flow pattern evolution in small-scale reactors

In this paper, the transesterification reaction of waste cooking oil (WCO) with methanol using KOH as catalyst to produce biodiesel was performed in a micro-reactor (1 mm ID) using a cross-flow inlet configuration. The effects of different variables such as, methanol-to-oil molar ratio, temperature, catalyst concentration, and residence time on biodiesel yield, as well as the associated flow patterns during the transesterification reaction were investigated and the relationship between flow characteristics and mass transfer performance of the system was examined. The work reveals important aspects and the links between the hydrodynamic behaviour and the mass transfer performance of the intensified reactors. It was found that high yield (&amp;gt;90%) of biodiesel can be achieved in one-stage reaction using cross-flow micro-reactors for a wide range of conditions, i.e., methanol-to-oil molar ratio: 8–14, catalyst concentration: 1.4%–1.8% w/w, temperature: 55°C–60°C, and residence times: 55–75 s.

Environmental and thermoecological comparative assessment of improved humid air waste heat recovery configurations

This paper provides a comprehensive assessment of the humid air turbine-based waste heat recovery system with respect to different flow configurations in the air saturator. The novelty of this work is to provide a holistic approach to the environmental and thermoecological assessment of Maistosenko cycle-based waste heat recovery units by considering three configurations of air saturator namely, counter-flow, cross-flow, and mixed-flow configuration. In other words, the assessment is carried out to evaluate the performance improvements while comparing the environmental as well as thermoecological perspectives. This provides a broader and wholesome perspective allowing a wider application of these configurations, especially in different climatic conditions experiencing varying ambient temperatures. The ambient temperature is particularly important when air is used as working fluid and routed in three different configurations within the heat recovery unit i.e., air saturator. The addition of humidity in the air saturator tends to improve the performance of bottoming cycle depending on the air direction within the saturator which has a counter, cross and mixed flow configurations. Moreover, ambient or dead state temperature is considered one of the influencing parameters on the performance of considered heat recovery configurations. With the rising ambient temperatures up to 50 °C, owing to intensive heat waves and sustained droughts; the performance indicators of power generation units indicate as much as 25% reduction in the sustainability index along with 10% lowering of energy and exergy efficiencies. In this regard, the flow configuration and efficiency of air saturators become critically important especially as a heat recovery unit while working in intense operating conditions. The results have suggested that counter configuration can offer the highest among of net-work marking 51.9 MW whereas the cross-flow configuration can mark only 49.78 MW. Thermoecological assessment has suggested that the ambient temperature of this type of powerplant can be less than 40 °C. It is concluded that the optimal configuration is counter-flow configuration for the waste heat recovery in gas turbines based upon second law and thermoecological assessment.

Thrust scaling for a large-amplitude heaving and pitching foil with application to cycloidal propulsion

A numerical solution procedure using the mesh-superposition approach, known as the Chimera method, together with the OpenFOAM toolbox environment is used to compute the forces generated by large amplitude heaving and pitching foil. The possibility of fitting thrust prediction laws, based on classical potential flow theories, with the numerically computed forces is explored, for a Reynolds number of 5104. It is shown, first for a pure heaving motion and subsequently by adding a harmonic pitching motion, that theoretical scaling may be fitted to numerical time-averaged thrust data, even in the case of large amplitude motions. The thrust-prediction law is shown to still apply to pitching-rotating motions, such as those of blades in cycloidal propulsion devices, the mean pressure correction due to the additional surging motion being small. The synchronized rotation-pitching of three foils typical of a cross-flow propeller configuration is addressed as well. The numerical global thrust results are shown to be in general agreement with the theoretical prediction, but also with blade-embedded load cell measurements for an experimental device developed by the French Naval Academy Research Institute.