Cross-sectional Flow Research Articles

Investigation of erosion-corrosion failure of API X52 carbon steel pipeline

A failure analysis of API X52 steel pipeline was conducted. The investigation included complete material characterizations using tensile and hardness testing, optical microscope, SEM, and EDS. The main failure occurred in the downstream pipe located near the welded joint at the elbow outlet instead of elbow which was interesting. The main mechanism of failure was found to be erosion-corrosion mechanism that caused breakdown of the protective FeCO3 film, thinning of the downstream pipe, and finally failure. It is believed that the erosion-corrosion was induced by sand impingement due to turbulent flow that was promoted by sudden change in the flow cross section between the elbow inlet and upstream pipe and poor welding quality of joint at the elbow outlet.

Slip boundary condition near the wall-interface contact line in axial stratified two-phase flow

The behavior of the velocity and shear stresses in two-phase laminar stratified flow near a triple point (TP), formed in the flow cross-section by the intersection of the interface with the conduit wall, is reconsidered. Differently from the no-slip boundary condition that showed a possibility of diverging shear stresses upon approaching the TP, we allow a slip of the fluids at the wall that can be prominent in the TP region. The Navier's boundary condition is used, which considers a linear relationship between the slip velocity and the strain rate component perpendicular to the surface. The solution for the velocity field in the TP region is obtained in terms of a power series of the distance from the TP having a discrete set of powers. Similarly to the solution obtained with no-slip B.C., a so-called ‘characteristic equation’ is obtained. Its solution yields a discrete set of non-integer powers that are dependent on the dynamic viscosity ratio and the contact angle. However, contrary to the no-slip solution, with Navier's B.C, each of these powers introduces a tower of terms resulting from the relation between the slip velocity and the velocity derivative at the wall. In addition, the solution also includes a tower of integer powers. The solution yields the velocity and the shear stress fields, as well as the flux of the force per length that acts on an arbitrary surface in the flow field. The latter is obtained by considering an equivalent 2D representation of the stress tensor. These are examined in comparison to the corresponding results obtained when no-slip at the wall is imposed. The relaxation of the wall shear stresses in cases where the no-slip condition predicts diverging wall shear stresses at the TP is demonstrated. It is shown that if the local velocity in the TP region is a limit of a global no-slip solution, the scaled velocity field in the TP region is independent of the details of the global flow field.

Investigation on the compressibility characteristics of laminar flow in rotating channel

In high-speed rotating channels, significant compressive effects are observed, resulting in distinct flow characteristics compared to incompressible flows. This study employs a finite volume method, based on the implicit formulation, to solve for low-speed compressible laminar flow in rotating channels using an orthogonal uniform grid. The governing equations include the full Navier–Stokes equations and the energy equation. The alterations in flow within rotating channel are primarily influenced by the compressive effects of centrifugal force and the compressibility of fluid within the flow's normal section. The first effect involves a reduction in the velocity due to centrifugal force, leading to an increasing influence of the Coriolis force compared to inertial forces. This trend change aligns closely with the increase in rotation speed. The second effect arises from the increase in the rotating Mach number and the Coriolis compression, resulting in slight density differences within the cross section. Strong centrifugal forces generate significant centrifugal additional force (buoyancy force). Consequently, under the same local rotation number, the velocity profiles of the mainstream experience considerable changes. Additionally, a higher rotating Mach number significantly impacts wall shear stress, with the leading side being notably affected. For instance, at cross-sectional Ro = 0.6 and MaΩ = 2.1, the dimensionless shear stress on the leading side decreased by 13%. Furthermore, while an increase in the rotating Mach number has minimal impact on the cross-sectional secondary flow structure, changes in mainstream velocity profiles influence secondary flow intensity, resulting in an enhanced velocity peak and a shift toward the trailing side.

A Kinematic Modeling Study of the Reorganization of Snowfall between Cloud-Top Generating Cells and Low-Level Snowbands in Midlatitude Winter Storms

Abstract This paper explores whether particles within uniformly spaced generating cells falling at terminal velocity within observed 2D wind fields and idealized deformation flow beneath cloud top can be reorganized consistent with the presence of single and multibanded structures present on WSR-88D radars. In the first experiment, two-dimensional wind fields, calculated along cross sections normal to the long axis of snowbands observed during three northeast U.S. winter storms, were taken from the initialization of the High-Resolution Rapid Refresh model. This experiment demonstrated that the greater the residence time of the particles in each of the three storms, the greater particle reorganization occurred. For experiments with longer residence times, increases in particle concentrations were nearly or directly collocated with reflectivity bands. For experiments with shorter residence times, particle reorganization still conformed to the band features but with less concentration enhancement. This experiment demonstrates that the combination of long particle residence time and net convergent cross-sectional flow through the cloud depth is sufficient to reorganize particles into locations consistent with precipitation bands. Increased concentrations of ice particles can then contribute, along with any dynamic forcing, to the low-level reflectivity bands seen on WSR-88D radars. In a second experiment, the impact of flow deformation on the reorganization of falling ice particles was investigated using an idealized kinematic model with stretching deformation flow of different depths and magnitudes. These experiments showed that deformation flow provides for little particle reorganization given typical deformation layer depths and magnitudes within the comma head of such storms. Significance Statement Past research with vertically pointing and scanning radars presents two different perspectives regarding snowfall organization in winter storms. Vertically pointing radars often observe cloud-top generating cells with precipitation fallstreaks descending into a broad stratiform echo at lower altitudes. In contrast, scanning radars often observe snowfall organized in quasi-linear bands. This work attempts to provide a connection between these two perspectives by examining how two-dimensional convergent and deformation flow occurring in winter storms can contribute to the reorganization of snowfall between cloud top and the ground.

Modeling of the flow and heat exchange in pipes with turbulators of viscous heat carriers in the laminar region, as well as in the transition to turbulent flow

Objective. Mathematical modeling of heat transfer in pipes with turbulators for viscous heat carriers at Reynolds numbers characteristic of laminar and transient flow regimes is carried out by the calculation method. The solution of the heat exchange problem for semicircular cross-section flow turbulators based on multiblock computing technologies based on the solution of the Reynolds equations (closed for the transient mode using the Menter shear stress transfer model) and the energy equation (on multi-scale intersecting structured grids) by the factorized finite-volume method (FCOM) was considered.Method. The calculation was carried out on the basis of a theoretical method based on the solution of the Reynolds equations, closed for transient modes using the Menter shear stress transfer model, and the energy equation on multiscale intersecting structured grids (FCOM), by a factorized finite-volume method.Result. Both local and averaged characteristics of the flow and heat exchange in pipes with turbulators for a viscous coolant for laminar and transient flow modes of the coolant were obtained using the FCOM method in the work, which made it possible to determine for these modes the levels of heat exchange intensification that satisfactorily correlate with the existing experiment.Conclusion. The calculated relative hydraulic resistance for low turbulators increases quite slightly, and for medium-altitude turbulators reaches 2÷2.5 to the critical Reynolds number, and subsequently it increases up to 3 times; for high turbulators, the relative hydraulic resistance increases up to 4 times even before the transition flow regime is reached, after which it increases up to 4.5 times. The calculated relative isothermal intensified heat exchange under the laminar flow regime of a viscous coolant for relatively high turbulators increases almost 2 times; for relatively medium heights of turbulators — almost one and a half, and for low relative heights, the intensification of heat exchange is insignificant.

Novel approach of combined planar and cross-sectional defect analysis of stressed normally-on HEMT devices with leaky Schottky gates

The clear correlation of defect localization by Electroluminescence to nanometer sized defects at Schottky gate contacts of GaN HEMTs are always challenging and limiting the root cause analysis of the stress related electrical degradation of the devices. In this paper a novel approach combining large area planar TEM defect screening followed by cross sectional preparation at identified defect sites is demonstrated to get access to relevant structural damages at the gate. The analysis flow is applied for normally-on GaN HEMT devices with an increased leakage at the Schottky gates observed after electrical stressing. To initiate electrical active degradation these devices were stressed up to significant changes in the electrical performance and then Electroluminescence spots were detected identifying possible defect positions. Metal intrusions into the AlGaN/ GaN stack underneath the Schottky gate contacts of only 20 nm size could be found by the newly combined planar/ cross-sectional analysis flow in good correlation to the EL spot positions. Analytical TEM investigations of the defects reveal Pt and Au inside the semiconductor reaching the 2DEG at a threading dislocation of the HEMT. These intrusions contribute to the gate leakage current and are causing the increased leakage current after electrical testing.

Design and Flow Analysis of Special-Shaped Cross-Section Flow Channel Based on Selective Laser Melting

Selective laser melting has the potential to be applied into hydraulic pipelines manufacturing because it can realize the forming of flow channels with arbitrary direction and curvature. Due to the stacking of layers, selective laser melting still has many limitations while processing complex flow channels. In particular, the manufacturing of overhanging structures with circular cross sections needs to use internal supports to prevent surface collapse, which is challenging to be removed. Therefore, it is necessary to optimize the flow channel with a self-supporting ability, then systematically discussing its forming quality with the influence on fluid dynamics to compromise. In this paper, a simplified multi-channel structure with 1 inlet and 4 outlets is extracted from a hydraulic valve block of an aero-engine system, and the cross-section of its branch channel is re-designed to guarantee its self-supporting ability based on additive manufacturing optimization strategy. Numerical simulation was used to analyze the influence of different shape sections on the pressure loss and mass flow rate of multi-channel structure. The results show that the pressure loss and outlet flow of the 45° rhombus + ellipse section are the closest to the circular area. According to the maximum internal deformation of the three outlets, the 65° rhombus section has the better forming quality and the non-circular section is not the worst.

Numerical Study on the Influence of Variable Section-Enhanced Mass Transfer Flow Field Design on PEMFC Performance Based on Underrib Convection Flow

The optimal design of variable section is a flow field optimization method that changes the pressure of the reacting gas in the flow channel by setting up a contraction surface in the flow channel, which is effective in improving many aspects of the proton exchange membrane fuel cell (PEMFC) performance. However, there are also problems such as uneven oxygen distribution in some of the flow channels, and the current density and net output power are not significantly improved. To find a balance among gas transfer efficiency, drainage capacity, uniformity of current density distribution, and output performance, this paper investigates the design of a variable cross-section-enhanced mass transfer flow field for PEMFC flow channel contraction by establishing a three-dimensional numerical model, starting from the sidewall width direction and the bottom height direction of the flow channel cross-section dimensions, in order to assess the effects of variable cross-section contraction at the bottom and sidewalls of the flow channel on the cell performance. The polarization curves, mass transfer capacity, current density distribution, and net output power of the variable cross-section contraction flow field are analyzed and compared with the straight flow field. On this basis, the optimum size parameters and operating parameter combinations are determined. Variable cross-sectional contraction flow field improves PEMFC output performance. The contraction of the variable cross-section contraction flow field at the sidewalls effectively improves reactive gas transfer efficiency and drainage capacity, improves current density distribution, and increases the net output power of the PEMFC. In particular, the sidewall contraction flow field has a 9.0% increase in power density, a 6.45% increase in the effective mass transfer coefficient (EMTC), a 6.52% increase in uniformity of current density distribution, and a 6.05% net power increment compared to the straight flow field, respectively. The best output performance, the highest oxygen concentration, and the lowest water concentration are achieved with a combination of parameters: number of sidewall contractions N = 6 , length L f = 6 mm , and width W f = 1.2 mm . And a wide range of air stoichiometry ratios are applied when the contraction of the variable cross-section contraction flow field is located at the sidewalls. Increasing the cathode stoichiometry ratio from 10 to 50 increased the cell power density by 25.5% and from 50 to 90 increased the cell power density by 9.5%. The simulation results can provide theoretical basis for the application of variable section flow field design for practical PEMFC.

Human immune phenotyping reveals accelerated aging in type 1 diabetes.

The proportions and phenotypes of immune cell subsets in peripheral blood undergo continual and dramatic remodeling throughout the human life span, which complicates efforts to identify disease-associated immune signatures in type 1 diabetes (T1D). We conducted cross-sectional flow cytometric immune profiling on peripheral blood from 826 individuals (stage 3 T1D, their first-degree relatives, those with ≥2 islet autoantibodies, and autoantibody-negative unaffected controls). We constructed an immune age predictive model in unaffected participants and observed accelerated immune aging in T1D. We used generalized additive models for location, shape, and scale to obtain age-corrected data for flow cytometry and complete blood count readouts, which can be visualized in our interactive portal (ImmScape); 46 parameters were significantly associated with age only, 25 with T1D only, and 23 with both age and T1D. Phenotypes associated with accelerated immunological aging in T1D included increased CXCR3+ and programmed cell death 1-positive (PD-1+) frequencies in naive and memory T cell subsets, despite reduced PD-1 expression levels on memory T cells. Phenotypes associated with T1D after age correction were predictive of T1D status. Our findings demonstrate advanced immune aging in T1D and highlight disease-associated phenotypes for biomarker monitoring and therapeutic interventions.

Assessment of morphological changes of river bank erosion using landsat satellite time-series images

River morphology is one of the most important fields of river engineering and the study of the changes in the flow direction and cross-sections of a river. Over the past years, using the unique properties of remote sensing (RS) and satellite images, many studies have been conducted on rivers' morphological changes. In this study, the morphological changes of the river boundary displacement and the changes in river width resulting from deposition and erosion during 30 years period (1985 to 2015) in the Bazoft River, one of the North sub-basins of the Karun River basin in Iran, using 26 satellite images of TM, ETM+, and OLI Landsat in the ENVI 5.3 and ArcGIS 10.3 software have been assessed. The results indicated that the greatest change in the river bank takes place in the distance between 62 and 84 km from Karun-4 Dam to the upstream. Besides, analyzing long-term periods indicated that in the time intervals of 1985–1994, 1994–2005, and 2005–2015 the sediment had deposited along river banks. For 30 years, the river's average deposition and erosion levels areas are estimated to be 69.4 and 42.4 ha, respectively, meaning that ground with 27.1 ha is formed by virtue of deposition. According to the assessments, it was indicated that there is no significant difference between average deposition and erosion on the left bank in short periods, and the deposition bank is approximately 2% greater than bank erosion. However, on the right bank, the deposition level is approximately 8% greater than erosion, which is significant at a confidence level of 95%. The results of this study perfectly indicated the ability of sub-pixels and the use of water indicators in revealing the river form changes using Satellite Images Time Series (SITS).

Penetration characteristics of water in calcium silicate hydrate nanoslit and temperature effect

ABSTRACT This study investigates the penetration characteristics of water and temperature effect, aiming to understand the mechanism of water intrusion and provide a basis for studying the transport of aggressive ions in concrete. Molecular dynamics simulations were employed to simulate the capillary motion of water in hydrated calcium silicate (C–S-H) slit. The effects of temperature on water density, chemical bond of atomic pairs, flow velocity distribution, and slip length during the flow process were analysed, and the flow equations were modified. It was found that the density of water in the region of 0.55 nm from the interior wall of the C–S-H slit manifests significant inhomogeneity. The stronger the chemical bond of atomic pairs, the less the residence time is influenced by temperature. Increasing the temperature from 280 K to 360 K results in a significant increase in the cross-sectional flow velocity within the nanoslit, while the changes in the size of the inhomogeneous region and the slip length are insignificant. The modified Bosanquet equation is suitable for describing the second stage of nanocapillary flow, while the Lucas-Washburn equation is suitable for describing the third stage.

Study on Hydrodynamics of Fish-Friendly Open-Channel Flow

To elucidate the hydrodynamic characteristics of a fish-friendly open channel, a three-dimensional numerical hydrodynamic model is constructed in this study employing the Large-eddy Simulation (LES) technique. The reliability of this numerical model is thoroughly validated by incorporating periodic boundaries in the flow direction, allowing for the recurrent development of water flow within the computational domain and utilizing experimental data from a flume. The results demonstrate that the fish-friendly channel is partitioned into a high-velocity mainstream zone and a low-velocity habitat zone. The time-averaged flow velocity in the mainstream zone is approximately 2.0 times the cross-sectional average flow velocity. In the low-velocity habitat zone, the average hourly flow velocity and turbulence are at a relatively low level, rendering the zone suitable for fish habitation and the incubation of adhesive fish eggs. A significant vortex structure is present in the mixing layer at the junction of the main flow area and the habitat area, which not only markedly increases the turbulence intensity but also serves as the primary driver of momentum exchange within the open channel.

Quantifying the relationship between spreading depolarization and perivascular cerebrospinal fluid flow

Recent studies have linked spreading depolarization (SD, an electro-chemical wave in the brain following stroke, migraine, traumatic brain injury, and more) with increase in cerebrospinal fluid (CSF) flow through the perivascular spaces (PVSs, annular channels lining the brain vasculature). We develop a novel computational model that couples SD and CSF flow. We first use high order numerical simulations to solve a system of physiologically realistic reaction–diffusion equations which govern the spatiotemporal dynamics of ions in the extracellular and intracellular spaces of the brain cortex during SD. We then couple the SD wave with a 1D CSF flow model that captures the change in cross-sectional area, pressure, and volume flow rate through the PVSs. The coupling is modelled using an empirical relationship between the excess potassium ion concentration in the extracellular space following SD and the vessel radius. We find that the CSF volumetric flow rate depends intricately on the length and width of the PVS, as well as the vessel radius and the angle of incidence of the SD wave. We derive analytical expressions for pressure and volumetric flow rates of CSF through the PVS for a given SD wave and quantify CSF flow variations when two SD waves collide. Our numerical approach is very general and could be extended in the future to obtain novel, quantitative insights into how CSF flow in the brain couples with slow waves, functional hyperemia, seizures, or externally applied neural stimulations.

Confinement width and inflow-to-sediment discharge ratio control the morphology and braiding intensity of submarine channels: insights from physical experiments and reduced-complexity models

Abstract. Submarine channels conveying sediment gravity flows are often topographically confined, but the effect of confinement width on channel morphodynamics is incompletely understood. We use physical experiments and a reduced-complexity model to investigate the effects of confinement width (B) and the inflow-to-sediment discharge ratio (Qin/Qs) on the evolution of submarine braided channels. The results show that a larger confinement width results in increased active braiding intensity (BIA) and that BIA takes longer to stabilize (i.e., a longer critical time; tc). At a fixed confinement width, a higher Qin/Qs slightly decreases the BIA. Digital elevation models of difference (DoD) of the experiments allow measurement of the morphological active width (Wa) of the submarine channels and the bulk morphological change (Vbulk) within an experiment, defined as the sum of total erosion and deposition. We find that Wa and Vbulk are proportional to B. We further confirm that BIA is proportional to both dimensionless sediment–stream power (ω**) and dimensionless stream power (ω*). These trends are consistent for submarine braided channels both with and without confinement width effects. Furthermore, we built a reduced-complexity model (RCM) that can simulate flow bifurcation and confluence of submarine braided channels. The simulated flow distribution provides reliable predictions of flow depth and sediment transport rate in the experiments. Using kernel density estimation (KDE) to forecast the probability and trends of cross-sectional flow distribution and corresponding BIA under extreme events, we find that skewness of the flow distribution decreases as discharge increases. The development of braided submarine channels, shown here to extend to conditions of topographic confinement, suggests that factors not modeled here (e.g., fine sediment) may be necessary to explain the abundance of single-thread submarine channels in nature.

Experimental investigation of the crossflow of water in a 7-pin wire-wrapped rod bundle

In this study, the crossflow of water in a 7-pin wire-wrapped rod bundle was investigated experimentally using particle image velocimetry and the technique of matching index of refraction. Three Reynolds numbers, 3000, 6000, and 9000, were used to examine the effect of the Reynolds number on crossflow. A large-dimension rod bundle was utilized to provide sufficient space for high-resolution measurements. The cross-sectional flow distribution in the wire-wrapped rod bundle was obtained. Both global circulation flow in the bundle outer region and local reverse flow in the bundle interior were identified. In general, crossflow distribution is complex and is characterized by vortices of various scales. Previously, a large-scale vortex has been observed near the rod, which is related to the wall-fluid interaction. However, small vortexes are likely to appear on the lead side of the wire, which is attributed to the blockage effect of the wire. The distributions of the dimensionless velocity and turbulent kinetic energy in three typical subchannels were studied. The features of streamwise flow were also examined briefly. The flow blockage and redistribution caused by the wrapped wires were observed. The experimental data can be applied to validate CFD codes, turbulence models, and subchannel crossflow models.

Dry reforming of methane using a novel microreactor fabricated from stacking of stainless steel wire-mesh support catalysts

We fabricated a novel microreactor with stainless steel wire-mesh supports coated with Ni-based hydrotalcite catalysts for dry reforming of methane (DRM) reaction. Catalytic performance and long-term stability of microreactor was tested by stacking the stainless steel wire-mesh support catalysts to allow parallel and cross-sectional flow to stacking configurations. Conversion rates of CH4 and CO2 were measured and found to be 92% and 95% respectively, and syngas ratio of 0.92 was obtained. Only a small decrease of about 3–4% in conversion rates was observed after 100 h of reaction which could be due to whisker like carbon formation as carbon nanofibers (CNFs). Investigation of spent catalysts revealed that surfaces of support catalysts were not fully covered with CNFs, leaving active sites for reactant gases with little effect on long-term stability. In addition to CNFs, in situ formation of γ-Al2O3 flakes were obtained during long-term DRM reaction from the parent FeAl powder that was used for annealing of stainless steel wire-mesh supports to increase the adhesion of hydrotalcite-derived spinel catalysts. Effect of γ-Al2O3 flakes on microreactor's performance turned out to be very useful because sites of γ-Al2O3 flakes further prevented the deposition of carbon on surface and acted as active sites for reactant gases. Moreover, stacking of stainless steel wire-mesh support catalysts for parallel and cross-sectional flow configurations caused the better mixing of reactant gases due to the tortuosity of the narrow porous microstructure of the support. The excellent throughput was verified by numerical calculations using CFD simulations.

Clinical application of optical coherence tomography angiography in diabetic macular edema.

Diabetic macular edema (DME) is characterized by a retinal thickening or hard exudation deposition in the fundus microvasculature, capillary leakage, increased vascular permeability, extracellular fluid accumulation in the fovea of a foveal disc. Optical coherence tomography angiography (OCTA) is a new item of fundus structure examination. OCTA is to reconstruct the retinal choroidal vascular structure from the continuous same cross-sectional views and blood flow signals obtained by optical scanning, thereby obtaining an image. It is very significant to evaluate, diagnose, treat and manage the disease.

EXPERIMENTAL EVALUATION OF THE HOMOGENEITY OF THE OUTPUT STREAMS OF OPTICAL RADIATION OF A RECTANGULAR SHAPE FOR VARIOUS VERSIONS OF THE OUTPUT SECTIONS OF THE LIGHT GUIDE NOZZLES FOR MEDICAL LASER EQUIPMENT

The article presents the results of a study of the homogeneity of rectangular optical radiation fluxes for different versions of the initial sections of the light guide nozzles. When conducting a significant part of laser exposure in medicine, pathological areas of biological tissue or their projections located on the surface of the body are covered with light spots with contours, as a rule, in the form of flat geometric shapes.
 The variability of the implementation of light spots in shape (circle, square, rectangle, triangle, rhombus, etc.) and linear dimensions of the cross section allows you to select the shape and size of the light spot, covering a specific pathological surface with minimal capture of intact tissues. At the same time, regardless of the shape and linear dimensions, the light spots should be as uniform as possible. To date, of particular interest is the provision of optical uniformity of rectangular light spots.
 Firstly, similar forms of spots are widely used under the influence of laser medicine. Secondly, in the original optical stages of laser equipment and the light guides connected to them, first of all, optical fibers of a cylindrical shape with a rounded cross section of the optical flow at the output are used. The purpose of this work is to optimize the parameters of light guide nozzles of medical laser equipment with rectangular output optical radiation fluxes by evaluating the uniformity of the power density distribution for various options for the output sections of the nozzles. In the work, optical flows at the output of three versions of the distal sections of light guides were studied. The light guides were formed by optical fibers, including the use of microlenses at the output ends, and were apertured by channel optical waveguides in the form of rectangular parallelepipeds.
 The experimental results obtained at the stage of physical modeling show the promise of using spherical micro-optical elements at the initial ends of optical fibers in combination with rectangular apertures in the form of channel optical waves to obtain rectangular light spots with a high level of optical homogeneity.

Experimental study on the performance of different photovoltaic thermal collectors with nano-technology

ABSTRACT The process of cooling the photovoltaic cell effectively leads to improving the electrical efficiency of the cell. Herein, the current experimental study employed three different nanofluids (CuO, ZnO, and TiO2) to cool the PV panel to produce a hybrid collector, also known as a photovoltaic thermal solar collector (PVT). The nanoparticle volume fraction was 0.1, 0.2, and 0.3 vol%. The process of cooling the PV panel was carried out using a copper tube on the back of the PV, which was placed to cover the largest possible area on the back of the PV. Three different flow cross sections – rectangular, square, and circular – were used to compare them. This experimental study was carried out under solar radiation conditions ranging from 450 W/m2 to 750 W/m2, and the flow rates of the nanofluid were 0.5, 1, 1.5, and 2 L/min. The results show the electrical and thermal efficiency of the PVT system at different conditions. The electrical efficiency increased as a result of adding nanofluid compared to normal water, where the cell with CuO/nanofluids gave the highest value of electrical efficiency at 450 W/m2, equaling 11.8%, while it was equal to 11.6%, 11.5%, and 10.8% for ZnO/nanofluids, TiO2/nanofluids, and water, respectively. An increase in mass flow rate leads to increased thermal, electrical, and combined PVT efficiencies. As well. The high mass flow rate increases the heat transfer coefficients between the tube wall and flowing fluid, which in turn decreases the PV module’s temperature. Finally, the rectangular section and the CuO/nanofluids gave the best value for the electrical power, which reached 83.17 W, and the highest electrical efficiency, which reached 11.5%.

Uniform temperature field in panel radiators using modified spacer rings

This article describes the development of the best possible prototype panel radiator spacer ring using mathematical modelling. It is shown for the first time in the literature that this smallest part of the radiators has a very important function of distributing water in the upper distribution chamber of the radiator. This research brings new knowledge to the field of water flow in the radiator, which is fundamentally affected by the holes located radially in the spacer ring. On the basis of the experiment, the CFD model of the most commonly used spacer ring was validated. Various structural modifications of the spacer ring were investigated in order to achieve the most uniform distribution of the surface temperature along the length of the radiator plate. It was found that a wedge-shaped design solution most closely resembles this state. This patented solution represents the best possible way to ensure the most even distribution of the water in the radiator without changing the flow cross-section of the distribution chamber.