Despite its widespread use, there are no universally established guidelines for determining when the local thermal equilibrium (LTE) assumption is applicable, leading to inconsistencies in porous media heat transfer modeling. To address this gap, this study conducted a comprehensive numerical analysis using critical parameters such as the flow rate, permeability, and thermal diffusivity ratio of hydrodynamic and thermal characteristics. Using the Darcy-Forchheimer-Brinkman model, simulations were conducted for a wide range of Reynolds numbers (1 to 1000), Darcy numbers (10-6 to 100), and thermal diffusivity ratios (10-3 to 103) to assess thermal behavior with both the LTNE and LTE approaches. The results indicated that, at low Reynolds numbers (Re <= 10), significant temperature differences existed between the solid and fluid phases, implying a dominant LTNE regime. However, as the Reynolds number increased beyond Re approximate to 100, enhanced convective effects facilitated better thermal coupling, validating the LTE assumption. The Darcy number significantly influenced thermal dispersion, with low Da (<= 10-6) enhancing mixing and promoting LTE while high Da (>= 100) restricted thermal interaction due to boundary layer formation. The impact of the thermal diffusivity ratio was most pronounced at low Re, where a high value (>= 103) led to significant thermal disequilibrium due to the solid's high conduction capability relative to the fluid. However, at high Re (>= 1000), convection dominated, making LTE applicable across a wide range of TDR values. By systematically mapping the LTE-LTNE transition across a broad parametric space, this study provides a novel framework for assessing the applicability of the LTE assumption.

The present work employs pore-scale simulations by constructing true porous shape in order to reduce the uncertainties associated with porous transport models. For a fixed value of porosity, the rib height is varied, while the flow rate is maintained at the lower Reynolds number range (Re = 1 and 10). For various rib heights and flow rates, pressure drop and heat transfer coefficient are determined. It has been showed that as height rises (blockage fraction increases), the resistance to flow created by the porous ribs increases continuously, leading to a greater pressure decrease across the channel. In addition, as the rib height increases, the magnitude of the effective heat transfer coefficient (shown by Nusselt number) increases. Since the Thermal Performance Factor (TPF) can reach to 20.2 and 10.5, respectively, at Re = 1 and 10, the channel with ribs is observed to be improving the overall thermo-hydraulic performance as compared to the empty channel. As a result, inserting the porous rib into the channel may have the intended outcomes of enhancing thermo-hydraulic performance, reducing the maximum temperature of the heated zone and promoting temperature uniformity.

One of the high-temperature materials, ferritic stainless steel (FSS), was joined using laser beam welding (LBW), which reduced intermetallic phases and grain growth. The CO2 laser was effectively applied to join AISI 409 FSS tubes of wall thickness 4 mm. The power of the laser beam, which influences mechanical and metallurgical properties, varied from 2.6 kW to 3.4 kW. No defects were observed at the weld zone (WZ). However, the lowest laser power produced an undercut at the bottom of WZ. Coarsening of grains was not observed in the microstructure at HAZ. The dendritic microstructure was found in the WZ, which consists of both axial and columnar grains. A coarse dendritic structure was formed with high laser power. The delta ferrite phase was partially transformed into martensite phase at the WZ. The dislocation fields along with substructure formation were seen in TEM micrographs. The WZ was strengthened due to the phase transformation. The tensile strength of all the joints was close to the base metal (BM). More than 20% elongation was observed except for the joint at 2.6 kW. The fracture mode was observed to be ductile in all the joints.

The heat pipes or similar systems involve multi-physics and multi-scale flow and thermal phenomena which need the more detailed investigations to control the design and performance parameters. The present study attempts to investigate the phase change phenomena inside the system (analogous to the heat pipe) containing the porous media by using the pore-scale numerical simulation. The porous medium is uniquely constructed by the Triply Periodic Minimal Surface (TPMS) based Fisher Koch S lattice with a uniform porosity of 50 % having the pore size variation of 0.2-0.8 mm. The evaporator and condenser are heated and cooled, respectively, by constant heat flux of 105 W/m2. The performance of the system is evaluated for four different orientations with respect to the gravity, i.e., (a) Normal gravity, (b) Gravity opposed evaporator, (c) Gravity supported evaporator, and (d) Zero gravity. The results shows that the vapor mass is the lowest in the gravity supported system and achieved the maximum overall wall temperature for gravity opposed system. The system gets stabilized (steady state) quickly for all the cases except gravity supported evaporator wherein it achieves the oscillatory state with constant mean value after sufficient duration of operation. The complex vapor circulation is evident which has significantly affected the liquid film shape and the system performance. The gravity opposed evaporator shows the inferior performance compared to the others. The flow resistance is minimum in gravity supported evaporator, even though the thermal resistance is almost similar to the normal and zero gravity scenario.

The coupled pore-scale and Darcy-scale numerical simulations are used in this work toinvestigate heat transport and hydrodynamic characteristics within a porous channel con-structed by using a primitive lattice based on triply-periodic-minimal-surface. The pore-scale simulation is used in void subdomain, whereas the microporous-solid subdomain issimulated by Darcy-scale simulation for a range of mass transfer rates 4x10(-7)to2x10(-3)kg/s (corresponding Reynolds numbers 0.1= 10-11m(2)(active regime). The Darcy numberand effective Nusselt number are found to be increasing, while the inertial drag coefficientand deviation from LTE are found to be decreasing with the permeability in the activeregime only.[DOI: 10.1115/1.4065189]

In this study, a Primitive lattice based on Triply Periodic Minimal Surfaces (TPMS) is used to build a porous structure for performing a combination of pore-scale numerical simulation along with the porous media flow simulation. On the three-dimensional lattice, numerical analysis is performed for single-phase fluid subjected to uniform heating at the walls. The void subdomain of the lattice is designated as the fluid zone, to perform the pore-scale numerical simulations; whereas, the solid subdomain of the lattice is designated as the microporous zone to perform porous transport simulations. The parametric studies for overall pressure drop and heat transfer coefficient are performed for a range of permeability of microporous zone. It is shown that when the micro-permeability is increased in the range 10^ - 10 < Da_μ < 10^ - 5 , there is no significant change in pressure drop as well as the heat transfer coefficients. On the other hand, increase of micro-permeability in the range of 10^ - 5 < Da_μ < 10^ - 1 causes a sharp drop in the pressure drop and a marginal drop in the effective heat transfer coefficient. Therefore, replacing the solid zone with porous zone for the solid subdomain of the lattice provides an improved thermo-mechanical performance for the mini-channel even in the low flow rate regime ( Re = 10 ).

When a porous media is introduced into a flow path, it significantly alters the flow path's hydrodynamic and thermal characteristics. Due to the complex structure of the solid matrix in the flow route, the fluid particles encounter a significant amount of resistance in the form of viscous and inertial momentum loss, resulting in a proportionally considerable pressure drop along the channel. This results in a higher input power required to pump the fluid through the channel, although flow through porous media has been demonstrated to improve heat transfer performance. In electronic cooling applications, the lack of available space lowers the size of channels, making pumping more difficult. While partially porous channels have been found to meet this requirement, their pressure drop is many orders of magnitude more than that of non-porous channels under similar conditions (Hadim in Forced convection in a porous channel with localized heat sources, 1994; Hadim and Bethancourt in Numerical study of forced convection in a partially porous channel with discrete heat sources, 1995; Ahmed et al. in Int Commun Heat Mass Transf 108:104336, 2019; Perng et al. in Int J Therm Sci 50(10):2006–2015, 2011; Zimbeck et al., Loop heat pipe technology for cooling computer servers, pp 19–25, 2008). As a result, it is critical to seek out strategies for optimizing the pressure drop in these channels while maintaining their thermal performance. This parametric analysis considers a partially porous channel with alternate combinations of porous and non-porous zones separated uniformly along the flow direction. The 2D planer and 3D channel are investigated numerically for laminar, steady, incompressible, forced flow subjected to asymmetrical bottom wall heating utilizing discrete heat sources. Additionally, these heat sources are positioned beneath the porous zones. Forchheimer-tenure Brinkman's was extended The Darcy equations are solved for momentum conservation, taking into consideration viscous and inertial losses, as well as the boundary impact. Due to the assumption of local thermal equilibrium between the solid matrix and saturated fluid, an energy conservation single equation model is solved (Carbonell and Whitaker in Fundamentals of transport phenomena in porous media. Springer, pp 121–198, 1984; Straughan in Convection in porous media 165, 2008). The overall pressure drop and heat transfer coefficient are investigated parametrically in two distinctive conditions in a mini-scale channel. In the first scenario, a two-dimensional numerical analysis was conducted to investigate the effect of substituting oblique porous plugs for normal porous plugs with the intent of enhancing the thermomechanical performance of the plug. The obliqueness of the porous plug was changed in both forward and reverse directions for this study. It was observed that forward oblique porous plugs degraded overall performance by reducing heat transfer and increasing the pressure drop in the channel, whereas backward oblique porous plugs augmented the overall performance of the channel by significantly reducing the pressure drop at higher angles of obliquity without impacting the heat transfer coefficient. In the second scenario, a three-dimensional analysis was conducted to determine the effect of introducing solid and porous ribs on the pressure distribution and heat transfer coefficient of flow through a mini-channel subjected to a constant heat flux boundary condition at the bottom wall. The solid block and porous blocks with varying permeabilities were compared to the channel without any blocks under identical flow and heating conditions. It was discovered that solid and porous blocks functioned almost identically at lower permeability values, with the overall effect of increasing the pressure drop in the channel while maintaining the heat transfer coefficient. However, using porous blocks with a higher permeability resulted in a massive improvement in heat transfer performance without affecting the pressure drop.

Background Linezolid (LNZ) is extremely prone to resistance. The development of resistance to LNZ should be taken into consideration when selecting this drug as a therapeutic option. It is well established that reactive oxygen species (ROS) generated by iron oxide nanoparticles (MNPs) could kill the infecting bacteria. So, we hypothesized the synergistic antibacterial effect of iron oxide nanoparticles and LNZ. Objective To study the release and antibacterial effects of LNZ-loaded superparamagnetic iron oxide nanoparticles (SPIONs) on Staphylococcus aureus and Streptococcus pneumoniae. Method Ferrofluid containing SPIONs was synthesized via chemical co-precipitation method and stabilized by sodium lauryl sulphate (SLS). SPIONs were then loaded with LNZ and characterized for particle size, FT-IR, XRD, and entrapment efficiency. Further antibacterial activity of SPIONs and LNZ-loaded SPIONs was investigated. For the in vitro release findings, HPLC analytical method development and validation were performed. Results Isolation of LNZ was accomplished on a C-18 column with methanol-TBHS (tetra butyl ammonium hydrogen sulphate, 50:50, v/v). The eluate was monitored at 247 nm with a retention time of 4.175 min. The MNP's DLS measurement revealed monodispersed particles with an average size of 16.81 & PLUSMN; 1.07 nm and PDI 0.176 & PLUSMN; 0.012. In optimized formulation, 25 & PLUSMN; 1.75% (w/w) of the drug was found to be entrapped. XRD revealed uniform coating of oleic acid covering the entire magnetic particles' surface with no change in its crystallinity. An effective antimicrobial activity was observed at the lowered dose of drug. Conclusions A robust HPLC method was developed to quantify the LNZ in MNPs, and outcomes showed that the reduced dose of LNZ incorporated in SPIONs was able to show similar activity as the marketed product.

Complex physical phenomena take place while dealing with the convective heat transfer in porous medium. Due to involved complexities, most of the earlier numerical studies are performed using various porous models compromising the detailed phenomena. Therefore, a pore-scale simulation has been performed for convective heat transfer in triply-periodic-minimal-surface lattices, with identical void fraction and unit-cell size, but different geometrical shapes (tortuosity), namely Diamond, Inverted Weaire–Phelan, Primitive, and Gyroid. Further, each lattice derived into three different types of porous structures by designing second subdomain as solid (in Type 1), fluid (in Type 2), and microporous zones (in Type 3). The convective heat transfer in a square mini-channel filled with the porous structures is investigated for the range of flow Reynolds number 0.01 10. For the range of Re considered here, the Primitive lattice shows the maximum deviation from LTE assumption.

In this paper, the effectiveness of ferrofluid as a working fluid for solar flat plate collectors (FPCs) is studied. A mini‐ferrofluid‐based solar FPC is designed and tested under laboratory conditions. The thermal performance of the designed solar FPC is evaluated under different conditions and it is observed that it provides higher efficiency for the case of ferrofluid in the presence of a magnetic field. The thermal efficiency is observed to increase by 54% for ferrofluid in presence of a magnetic field as compared to no magnetic field. The thermal efficiency is observed to increase further with the increase in the magnetic field. The increase in thermal efficiency is attributed to the combined effects of higher thermal conductivity and magnetohydrodynamics of ferrofluid, which result in higher convective heat transfer from the riser tube walls into ferrofluid. The higher heat transfer for ferrofluid with a magnetic field is established by calculating the Nusselt number numerically using COMSOL. Simulation results show an increase in Nusselt number for ferrofluid with magnetic field and hence higher thermal efficiency for the solar FPC. The designed FPC provides simple modifications to conventional FPCs to use ferrofluid with magnetic field for higher thermal efficiencies.

The modeling of flow and heat transfer in porous media systems has always been a challenge, and the extended Darcy transport models are used for macro-level analysis. However, these models are subjected to the limitations depending upon the porous geometry such as pore size, pore type, effective porosity, tortuosity, permeability, and the flow characteristics. The forced convective flow of an incompressible viscous fluid through a channel filled with four different types of porous geometries constructed using the Triply Periodic Minimal Surface (or TPMS) model is presented in this study. Four TPMS lattice shapes, namely Diamond, I-WP, Primitive, and Gyroid, are created with same volume fraction of solid subdomain as 0.68 (or void fraction as 0.32). Using different configurations for the solid subdomain by treating it as (a) solid, (b) fluid, and (c) porous zone, three different classes of porous structures are further generated for each TPMS lattice. The present study is executed with the objective to investigate the effect of shape–morphology, tortuosity, microporosity, and effective porosity on permeability and inertial drag factor. A pore-scale direct numerical simulation approach is performed for the first two types of porous media by solving the Navier–Stokes equations. The specific microporosity is quantitatively induced in the solid subdomain where Darcy–Forchheimer equation is solved, whereas the Navier–Stokes equations are solved for the void subdomain in the third type of porous media. The results reveal that Darcy flow regime exists up to the mean velocity value of U < 0.0025 m/s (Re < 10) for all the cases discussed here, and it deviates at the higher mean velocity. The conductance to the flow shown by Darcy number has the maximum and minimum values for the Primitive Type 2 and I-WP Type 1 cases. The inertial drag coefficient is minimum in Diamond lattice and maximum in Primitive lattice at lower porosity (0.32), while Primitive lattice has minimum and I-WP lattice has maximum value of inertial drag coefficient for higher porosity (~ 1).

The present paper reports actuation of sessile ferrofluid droplets over a hydrophobic substrate in the presence of a time-dependent magnetic field generated by an electromagnet. The internal hydrodynamics of the ferrofluid droplet in the presence of magnetic field are measured using both bright field visualization and micro-particle image velocimetry (μ-PIV) techniques. During ON cycle of the magnetic field, bright field visualizations show the migration of nanoparticles towards the contact line near the vicinity of the electromagnet resulting in aggregation of nanoparticles inside the droplet. Similarly, aggregated nanoparticles at the contact line from the ON cycle are observed to disperse from the cluster of nanoparticles during the OFF cycle of the magnetic field. Both migration and dispersion of nanoparticles result in bulk motion inside the ferrofluid droplet during the ON and OFF cycle of the magnetic field. Velocity measurements from μ-PIV technique successfully validate the qualitative measurements of flow field from bright field visualization technique. A critical frequency is observed for the applied magnetic field above which negligible dispersion of nanoparticles resulted inside the ferrofluid droplet during the OFF cycle of the magnetic field.

The present work reports the dynamics of an isolated ferrofluid slug of predefined length driven by air inside a dry capillary under the influence of constant as well as time dependent magnetic fields. It is shown that the pressure characteristic (pressure drop across the slug versus time) of slug, due to the supportive (slug at upstream of magnet) and resistive nature (slug at downstream of magnet) of the magnetic force field, exhibits a drop and rise pattern. We also noted that the peak pressure becomes constant beyond a threshold slug length $$\left( {L/D = 10} \right)$$ for a given strength of applied field. Also, we observed that the pressure characteristics of the slug are qualitatively similar for both types of magnetic perturbation, though, differ quantitatively due to the development of complex force field in the magnetically influenced zone. Substantial draining of liquid film has been observed from the receding meniscus of the slug, under constant magnetic field at two different regions viz., as the slug enters into the “Magnetically Assisted (MA)” zone and when it leaves from the “Magnetically Opposed (MO)” zone (From here onwards, we will be using “MA” and “MO” zones unambiguously.). Finally, the effect of the alternating magnetic field modulated by the frequencies $$\left( f \right)$$ gives rise to an impulsive force on the slug in the magnetically influenced zone, which in turn leads to accelerated–decelerated motion of the slug. This accelerated–decelerated motion yields substantial amount of film deposition on the wall for $$f = 3$$ Hz. A theoretical model is developed and subsequently compared with the experimental results, for estimation of the maximum pressure drop exhibited by the ferrofluid slug in presence of magnetic field. The inferences drawn from the study may have far reaching consequences in designing microscale thermal management systems/devices.

In this paper, a ferrofluid-based cooling technique is proposed for solar photovoltaic (PV) systems, where ferrofluid flow can be easily altered by the application of an external magnetic field leading to enhanced heat transfer from the hot surface of PV systems. The effect of both constant and alternating magnetic field on ferrofluid flow through a minichannel is explored numerically in the present work. A detailed parametric study is performed to investigate the effect of actuation frequencies of alternating magnetic field (0.5–20 Hz) and Reynolds numbers (Re = 24, 60, and 100) on heat transfer characteristics of ferrofluid. An overall enhancement of 17.41% is observed for heat transfer of ferrofluid in the presence of magnetic field compared to the base case of no magnetic field. For the case of alternating magnetic field, a critical actuation frequency is observed for each Reynolds number above which heat transfer is observed to decrease. The enhancement or decrease in heat transfer of ferrofluid is found to depend on several factors such as actuation frequency of alternating magnetic field, Reynolds numbers of ferrofluid flow, and formation/dispersion of stagnant layers of ferrofluid at the magnet location. Preliminary visualization of ferrofluid flow is also carried out to provide a qualitative insight to the nature of transportation of ferrofluid in the presence of an alternating magnetic field.

At present, parabolic trough technology is considered as the most low‐cost and powerful large‐scale technology to utilize solar energy for electricity generation and produce steam for different industrial usages. This article recommends the generation of electricity by using a parabolic trough solar concentrator in the central area of the Kingdom of Saudi Arabia (KSA) at Dawadmi city. Pressurized water is used as the heat‐transfer working fluid. A computer algorithm was built using the Matlab program to simulate the performance parameters of the Euro Trough collector (ETC). The input data included the properties of the working fluid (pressurized water) and the designing parameters of ETC. The output data were the outlet water temperature, the coefficient of heat transfer, the heat loss, and the thermal, solar, and global efficiencies. The obtained results indicated the ability of this type of parabolic trough in KSA to generate electric power due to the high‐performance parameters achieved. Also, the validity of using the simulation technique was measured and it showed good conformity.