Cross-flow Configuration Research Articles

Investigation of Heat Transfer and Pressure Drop of Non-Newtonian Nanofluid Performance Through Micro Channels Heat Exchanger (MCHE) in Cross-Flow Configuration

Investigation of Heat Transfer and Pressure Drop of Non-Newtonian Nanofluid Performance Through Micro Channels Heat Exchanger (MCHE) in Cross-Flow Configuration

Supersonic driven detonation dynamics for rotating detonation engines

In this paper we present the first exploration of detonation wave propagation dynamics in premixed supersonic flows using a novel rotating detonation engine (RDE) configuration. An RDE with a coupled linear extension, referred to as ρDE, is used to divide detonations traveling radially in the RDE into linearly propagating waves. A tangential propagating wave is directed down a modular tangential linearized extension to the engine for ease of optical diagnostics and hardware configuration investigations. A premixed Mach 2 supersonic linear extension is coupled to the ρDE to investigate the effects of varying crossflow configurations for detonation propagation, particularly the interaction between detonations and supersonic reactive mixtures. Detonation waves are generated at the steady operating frequency of the RDE and visualized using high speed schlieren and broadband OH* chemiluminescence imaging. The stagnation pressure was varied from over- to ideally-expanded supersonic regimes. Experimental analysis of detonation interaction with the supersonic regimes show that the detonation propagates freely in the ideally-expanded regime. Deflagration-to-detonation transition (DDT) occurs in the over-expanded regime. Based on the data collected, the DDT process favors supersonic flow with higher source pressures.

Counter cross-flow evaporator geometries for supercritical organic Rankine cycles

With recent advancements in advanced manufacturing techniques, it is now possible to fabricate complex geometries that take advantage of well known principles of heat transfer. Therefore, unconventional configurations to enhance effectiveness beyond conventional designs can now be considered for practical application. Thermal performance and overall cost of a new design of heat exchangers in counter cross-flow configurations are studied using a simplified but accurate computational method. The new heat exchanger design was introduced and studied previously for a cross-flow configuration by Sabau et al. (2016, 2018). This new design concept uses multi-scale configurations with successive plenums for the working fluid. At the smallest scale the tubes are sized to be equal to the hydraulic entrance length of the inside fluid, in accord with constructal design. Results indicate that compared to the earlier cross-flow configuration, the counter cross-flow arrangement improves the thermal performance of the heat exchanger by as much as 17% and lowers the total cost by as much as 14%.

Hydrodynamic coefficients of yawed cylinders in open-channel flow

The hydrodynamic response of a cylinder in an open-channel flow is experimentally investigated by considering the effects of horizontal orientation and submergence, the latter ranging from fully submerged to half-submerged cases. Drag and side coefficients are measured with a specific hydrodynamic balance which allows the planar rotation and the variation of submergence of the sample. The instrument design and characteristics are discussed, also estimating the uncertainties of force and hydrodynamic coefficients measurement. The tests are carried out under four submergence ratios (SR, submerged height to water depth), showing that for lower SR the drag and side coefficients increase with respect to tests performed on a fully submerged cylinder, which correspond to the highest SR. The tests performed for a half-submerged cylinder show instead a reduction of the side and drag coefficients, mainly due to the reduced submerged section. The effect of orientation on the two coefficients is different, yet it leads to similar submergence-independent trends. The drag coefficient is maximum for the 90° crossflow configuration, where maximum flow deviation occurs, while the side coefficient is maximum for the 45° orientation, which shows the most asymmetrical flow pattern. Measurements for deep submergence are validated against available literature results, confirming the reliability of the obtained values.

Comparative Study of CO2 Capture Using Counter and Cross Flow Configurations in a Rotating Packed Bed Absorber Using Mono Ethanol Amine (MEA)

Comparative Study of CO2 Capture Using Counter and Cross Flow Configurations in a Rotating Packed Bed Absorber Using Mono Ethanol Amine (MEA)

Application of the counter- and cross-flow indirect evaporative cooler for heat recovery under different climate conditions

This paper investigates the potential of applying an indirect evaporative cooler for heat recovery in air-conditioning system under various climate conditions. The counter- and cross-flow configurations of the indirect evaporative exchanger are addressed in this study in terms of their performance and applicability for different climate zones. Presented analyses are carried out with original ε-NTU model considering condensation from the product airflow and validated against experimental data. It was stated that both configurations of the indirect evaporative exchanger have a high application potential to be employed as a heat recovery device under most climatic parameters. Additionally for each climate zone considered in this paper, the air-conditioning system that consists of either the indirect evaporative exchanger and vapor-compression cooler or indirect evaporative exchanger and direct evaporative cooler is proposed.

Design and operating considerations for a shell-and-plate, moving packed-bed, particle-to-sCO2 heat exchanger

An efficient modeling methodology for simulating moving packed-bed heat exchangers for the application of particle-to-sCO2 heat transfer in next-generation concentrating solar power (CSP) plants is presented. Moving packed-bed heat exchangers have application to power-cycle heat addition for particle-based CSP plants and indirect energy storage for direct sCO2 CSP receivers. Further development of moving packed-bed heat exchangers for application to commercial CSP systems requires numerical simulation tools for the design and evaluation of particle-to-sCO2 heat transfer. In this paper, a steady-state reduced-order model of a shell-and-plate moving packed-bed heat exchanger is presented and used to investigate design considerations and performance limitations. The model appropriately captures the flow configuration of a multi-bank shell-and-plate design where the local cross-flow and global counter-flow configurations are addressed. This allows for the design tradeoffs in heat exchanger geometry and particle properties to be explored on the heat exchanger conductance and sCO2 pressure drop. Overall heat transfer coefficients for the particle-to-sCO2 heat exchanger at CSP operating temperature (500–800 °C) can approach 400 W m−2 K−1 using particle channel dimensions of 4 mm with particle diameters of 200 µm. The sensitivity of particle thermophysical properties was also explored to identify important parameters for improving the overall heat transfer coefficient that can be leveraged in the development of alternative particles. Packed bed void fraction and solid thermal conductivity were identified to be areas for potential improvement of sintered bauxite particles, which could increase the overall heat transfer coefficient by up to 60 W m−2 K−1. To achieve DOE cost targets (<$150 kWt−1) for sCO2 power cycle heat addition, diffusion bonded plates containing sCO2 microchannels must be produced at less than $2400 m−2 for the moving packed-bed heat exchanger to become commercially viable.

Numerical analysis of flow configurations and electrical contact positions in SOFC single cells and their impact on local effects

Predictable long-term operation is key to the industrial roll-out of SOFC technologies; as one of the primary factors hindering steady and reliable operation, performance degradation is one of the main challenges facing SOFC development. A homogeneous temperature profile is essential to the steady long-term operation of SOFC cells. In order to investigate and improve the temperature distribution across the cells, a ceramic housing was developed for an industrial scale (100×100mm2) SOFC single cell with the aid of a spatially resolved numerical model. This study investigated the influence of co-, counter-, and cross-flow configurations, as well as various electrical contact positions in order to analyse the current density distribution and temperature evolution within the cell. The chemical and electrochemical performance of the model were validated with in-house experimental data gained from operating the cell within the developed cell housing under three hydrogen/nitrogen mixtures of varying levels of humidification. The simulations revealed that the outermost parts of the cathode are subject to diffusion limitations, which can lead to local air starvation effects. Moreover, they showed that the position of the cell's electrical contacts has a distinct impact on the current density distribution, in addition to affecting the temperature profile of the cell. This study found that the counter-flow configuration, in combination with placing the electrical contacts on the inlet side of the cathode led to the most homogeneous current density and temperature distribution across the cell. Most importantly, the position of the electrical contacts was identified as having a major influence on the cell's current density profile, and these position changes were able to homogenize the temperature distribution across the electrolyte. This configuration is thus proposed as a viable method of both ensuring the steady long-term operation of SOFCs and prolonging their lifetimes.

Steady three-dimensional flows past hollow fiber membrane arrays – cross flow arrangement

Hollow fiber membrane (HFM) modules are among the most common separation devices employed in membrane separation applications. Three-dimensional steady-state computational fluid dynamics (CFD) simulations are carried out to study flow past hollow fiber membrane banks (HFMB). The current study investigates the effects of flow behavior on membrane performance during binary mixture separations. Carbon dioxide (CO2) removal from methane (CH4) is examined for various arrangements of HFMs in staggered and inline configurations. The common HFM module arrangement is the axial flow configuration. However, this work focuses on the radial cross-flow configuration. The HFM surface is a functional boundary where the suction rate and concentration of each species are coupled and are functions of the local partial pressures, the permeability, and the selectivity of the HFM. CFD simulations employed the turbulent k–ω shear stress transport (SST) model to study HFM performance for Reynolds numbers, 200 ≤ Re ≤ 1000. The efficiency of the inline and staggered arrangements in the separation module is evaluated by the coefficient of performance and the rate of mass flow per unit area of CO2 passing across the membrane surface. This work demonstrates that the module with staggered arrangement outperforms the module with the inline arrangement.

Crossflow electrochemical filtration for elimination of ibuprofen and bisphenol a from pure and competing electrolytic solution conditions.

For the first time, a crossflow electrochemical filtration system containing multiwalled carbon nanotubes (MWNTs) blended with buckypaper as a flat sheet dual membrane electrode was investigated for the removal of two contaminants of emerging concern, Ibuprofen and Bisphenol A. Breakthrough experiments revealed that a crossflow configuration could be highly efficient in eliminating both contaminants at applied DC potentials of 2 and 3 V over an extended period, from pure salt electrolyte as well as from synthetic secondary wastewater effluent. The shear flow provided consistent surface coverage resulting in excellent sorption performance. The long residence time of the two contaminants within the membrane (18.3 s) was sufficient enough to allow for almost complete degradation of phenolic aromatic products and quinoid rings and the resulting formation of aliphatic carboxylic acids, which was more evident at a higher applied potential (3 V). The formation of the non-toxic aliphatic carboxylic acids is a clear indication of the superior electrochemical performance of the crossflow mode over the dead-end flow-through system. Moreover, this study provides an in-depth understanding of different factors such as filter surface area and residence time that can greatly affect the removal of the contaminants considered.

Performance comparison between counter- and cross-flow indirect evaporative coolers for heat recovery in air conditioning systems in the presence of condensation in the product air channels

Following paper presents a comparative study of the indirect evaporative exchangers operating as heat recovery units, arranged in the counter- and cross-flow configuration. Presented analyses are carried out with particular emphasis on the condensation process that occurs in the product air channels of the exchangers. Several aspects related to the water vapor condensation are address. Those aspects include the identification of factors that influence the condensation process and analyzing those factors impact on different IEC exchanger configuration. Another issue is a performance comparison of the counter- and cross-flow exchanger for various inlet parameters and operating conditions. Performed analyses are based on the numerical simulations conducted with mathematical ε–NTU model of the heat and mass transfer. Presented model is validated against experimental data and the measurements taken at the test station. Achieved results showed that the counter-flow configuration has higher sensible and latent cooling potential than the cross-flow unit. Nonetheless, due to the technical limitation of the counter-flow configuration, the cross-flow exchanger achieved higher Energy Efficiency Ratio and is characterized by lower investment cost.

Evolutionary computation for maximizing CO2 and H2 separation in multiple-tube palladium-membrane systems

Membrane separation is a promising method to separate CO2 and H2 from hydrogen-rich gases. This simultaneously achieves H2 recovery and CO2 enrichment. The latter is conducive to subsequent carbon capture and storage, and thereby the development of negative emission technologies. In this study, single-, double-, triple-, and quadruple-tube systems with palladium (Pd) membranes and cross-flow configuration are considered, while the Reynolds number (Re) is in the range of 1–50. To maximize H2 recovery and CO2 enrichment in the systems, the systems are designed using a two-stage optimization in which the parametric sweep technology followed by the evolutionary computation of the Nelder-Mead simplex method is applied to find the best configuration and the exit H2 concentration is chosen as the objective function. On account of the scavenging waves stemming from the upstream tubes, the goals of the optimization is to diminish the concentration polarization effect of the upstream tubes upon the downstream ones. The predictions indicate that an increase in the number of tubes raises the optimization efficiency. Compared to the tubes in tandem, the optimized configuration at Re = 10 can improve the hydrogen recovery up to 12.2%, while the CO2 enrichment can be intensified by up to 7%.

Submerged Osmotic Processes: Design and Operation to Mitigate Mass Transfer Limitations.

Submerged forward osmosis (FO) is of high interest for bioreactors, such as osmotic membrane bioreactor, microalgae photobioreactor, food or bioproduct concentration where pumping through pressurized modules is a limitation due to viscosity or breakage of fragile components. However, so far, most FO efforts have been put towards cross flow configurations. This study provides, for the first time, insights on mass transfer limitations in the operation of submerged osmotic systems and offer recommendations for optimized design and operation. It is demonstrated that operation of the submerged plate and frame FO module requires draw circulation in the vacuum mode (vacuum assisted osmosis) that is in favor of the permeation flux. However, high pressure drops and dead zones occurring in classical U-shape FO draw channel strongly disadvantage this design; straight channel design proves to be more effective. External concentration polarization (ECP) is also a crucial element in the submerged FO process since mixing of the feed solution is not as optimized as in the cross flow module unless applying intense stirring. Among the mitigation techniques tested, air scouring proves to be more efficient than feed solution circulation. However, ECP mitigation methodology has to be adapted to application specificities with regards to combined/synergetic effects with fouling mitigation.

Quasi-three-dimensional numerical simulation of a solid oxide fuel cell short stack: Effects of flow configurations including air-flow alternation

The effects of flow configuration in solid oxide fuel cell (SOFC) stacks are investigated using a quasi-three-dimensional numerical model. Flow configurations with alternated air flows in parallel and perpendicular to the fuel flows are considered in addition to the conventional co-, counter-, and cross-flow configurations. The stacks have eight cells with unity aspect ratio and an active area of 4900 mm2 and are compared at fuel utilization of 0.193, 0.386, 0.579, and 0.772. The numerical model is capable of analyzing both the streamwise and spanwise directions of the cells. Although the counter-flow stack achieves the highest voltage efficiency among the stacks with the conventional flow configurations, it has the highest dispersion of the current density distribution on the cells. Air-flow alternation is effective to achieve uniform and high cell temperature and hence low dispersion of the current density. Alternate air flows parallel to the fuel flows achieve the highest voltage efficiency of 0.797 at a fuel utilization of 0.772, while alternate air flows perpendicular to the fuel flows reduce the risk of local fuel depletion as compared with the cross-flow stacks. Appropriate selection of the air-flow configuration within stacks allows operation at higher efficiency without fuel depletion.

Design and experimental testing of a Mini Channel Heat Exchanger made in Additive Manufacturing

In order to achieve a polytropic expansion through a reciprocating machine, an extremely compact heat exchanger is designed. It is a Mini Channel Heat Exchanger (MCHE), cross-flow configuration, aluminium made. The exchanger was expected to work with air on one side and water or diathermic oil on the other. The exchanger was also expected to bear high pressure on the air side (up to 12 bar). These pressures are too high for exchangers made up by glue collected plates. So, the additive manufacturing DMLS technique was used to make the exchanger. This technique gave also the chance to produce the needed collectors together with the exchanger, so there is no need of welding process. Then, the exchanger was tested in stationary conditions to characterize it. First, the geometrical constrains and the exchanger requirements are presented. Then a simplified design calculation is used to roughly predict its performance. Finally, the experimental test rig and the experimental data are shown.

Numerical study of the ignition behavior of a post-discharge kernel in a turbulent stratified crossflow

Ensuring robust ignition is critical for the operability of aeronautical gas-turbine combustors. For ignition to be successful, an important aspect is the ability of the hot gas generated by the spark discharge to initiate combustion reactions, leading to the formation of a self-sustained ignition kernel. This study focuses on this phenomena by performing simulations of kernel ignition in a crossflow configuration that was characterized experimentally. First, inert simulations are performed to identify numerical parameters correctly reproducing the kernel ejection from the ignition cavity, which is here modeled as a pulsed jet. In particular, the kernel diameter and the transit time of the kernel to the reacting mixture are matched with measurements. Considering stochastic perturbations of the ejection velocity of the ignition kernel, the variability of the kernel transit time is also reproduced by the simulations. Subsequently, simulations of a series of ignition sequences are performed with varying equivalence ratio of the fuel-air mixture in the crossflow. The numerical results are shown to reproduce the ignition failure that occurs for the leanest equivalence ratio (ϕ=0.6). For higher equivalence ratios, the simulations are shown to capture the sensitivity of the ignition to the equivalence ratio, and the kernel successfully transitions into a propagating flame. Significant stochastic dispersion of the ignition strength is observed, which relates to the variability of the transit time of the kernel to the reactive mixture. An analysis of the structure of the ignition kernel also highlights the transition towards a self-propagating flame for successful ignition conditions.

Membrane Processing in the Sustainable Production of Low-Sugar Apple-Cranberry Cloudy Juice

Ultrafiltration and diafiltration were proposed for the production of cloudy apple-cranberry juice of reduced sugar content. Ceramic membrane of 15 kDa MWCO was used in a cross-flow configuration, the retentate was treated as a final product. The juice before and after membrane treatments were characterized for total soluble solids content, glucose and fructose content, density, acidity, total phenolic content, antiradical activity, color parameters and FTIR spectra. The transmission of sugars after ultrafiltration was 24% and after diafiltration it reached 36%, with the simultaneous rejection of colloids, high molecular weight compounds and fine particles. The percentage of the reference intake of sugars connected with the consumption of 250 mL portion of obtained products was reduced from 27.0 to 20.7 and 15.7%, after ultrafiltration and diafiltration, respectively.

Effects of different block designs on the performance of inline cross-flow turbines in urban water mains

Cross-flow turbines offer a promising, cost-effective solution to harvest hydropower from water mains to supply power to water monitoring systems. However, the design and performance of cross-flow turbines in water mains have not been fully investigated. In this paper, an inline cross-flow turbine configuration with two blocks is proposed and a block design method is presented. Specifically, numerical investigations are carried out to verify the proposed method and study the effect of different block designs on turbine performance. Flow velocity analysis shows that the proposed block can improve the flow attack angle at the runner inlet and significantly increase the flow velocity through the runner. In addition, the pressure distribution indicates that the blocks can increase the pressure difference through the runner and thus improve turbine performance. A comparison of three models with different guide block orientation angles reveals that the model with the largest conversion block orientation angle performs best, because the blocks from this model not only function better in terms of flow separation and negative torque reduction at the first stage, but also convert more water head into kinetic energy. Numerical results show that the inline turbine can achieve its maximum efficiency of 42.4% with a power output of about 1500 W and that the water head reduction is limited within an acceptable range.

Separation of oil-in-water emulsions stabilized by different types of surfactants using electrospun fiber membranes

The compositions of oil-in-water emulsions encountered in industrial processes or in the environment vary widely in the nature of surfactants that stabilize them. This variety creates challenges for applications of membrane separation. Electrospun fiber membranes have shown high permeability and improved robustness against fouling in emulsion separation, but the interaction between emulsions and the membrane, and the fouling mechanism, remains unclear. In this paper, electrospun polyamide membranes were challenged by model emulsions of dodecane stabilized by anionic, cationic, non-ionic and zwitterionic surfactants in both dead-end and cross-flow filtration configurations under constant pressure of 2 psi. The membrane was shown to have high oil rejection (92.7 ± 1.5%), sufficient to meet EPA's regulatory limit, when separating emulsions stabilized by anionic surfactant in cross-flow filtration, while maintaining a steady flux of 44.3 ± 2.6 LMH. Analysis of permeate flux and oil rejection revealed that the types of surfactants influenced the membrane fouling in both dead-end and cross-flow systems, but in different ways. Fouling in dead-end filtration was found to be a function of the electrostatic interactions between the oil droplets and the membrane, while fouling in cross-flow filtration was mainly determined by the hydrophilic/hydrophobic interactions due to the adsorption of surfactants at the interfaces. Blocking filtration models are used to corroborate these findings and illustrate the transition between modes of fouling in dead-end filtration. A de-fouling process was found when separating emulsions stabilized by cationic surfactant in dead-end filtration, which was attributed to coalescence of oil droplets at the membrane surface, based on a kinetic model and direct observation. These results indicate that not only membrane-foulant but foulant-foulant interactions can influence the membrane fouling.

Transient analysis of a solid oxide fuel cell stack with crossflow configuration

This study investigates the transient response of the cell temperature and current density of a solid oxide fuel cell having 6 stacks with crossflow configuration. A commercial software repeatedly solves the governing equations of each stack, and get the convergent results of the whole SOFC stack. The preliminary results indicate that the average current density of each stack is similar to others, so the power output between different stacks are uniform. Moreover, the average cell temperature among stacks is different, and the central stacks have higher temperature due to its harder heat dissipation. For the operating control, the cell temperature difference among stacks is worth to concern because the temperature difference will be over 10 °C in the analysis case. The increasing of the inlet flow rate of the fuel and air will short the transient state, increase the average current density, and drop the cell temperature difference among the stacks. Therefore, the inlet flow rate is an important factor for transient performance of a SOFC stack.