Convection heat transfer from cylinders in a porous medium using the two-equation energy model

This numerical study is directed at exploring the flow characteristics and thermal response for the flow over a circular cylinder(s) embedded in a horizontal packed bed under steady or unsteady forced convection. The analysis is made for an incompressible fluid flow through a two-dimensional bed, which consists of spherical particles that are packed randomly. The subproblems that are considered in the present study are: First, forced convective steady and pulsatile cross flows over a single cylinder placed in a porous bed. Where, for steady flow, the effects of the thermal and structural properties of the porous medium on the convective and conductive heat transfer to the fluid and solid phases, are examined. While, for pulsatile flow, the flow and heat transfer is investigated subject to a sinusoidally varying inlet flow, for both a non-filled and porous material filled channels. The effects of pulsation frequency and amplitude on heat transfer are quantified. Second, forced convective steady cross flow over multiple cylinders arranged in two staggered or in-line configurations, embedded in a porous bed. The focus is directed on how the spacing parameter between the cylinders affects heat transfer from each, at different thermal conductivity ratios and Reynolds numbers for both configurations. Specifically, the generalised momentum model, i.e., the Darcy-Brinkmann-Forchheimer (DBF) model, is employed to model the flow field. This takes into consideration the non-Darcian terms, such as inertial and viscous effects. Moreover, the energy transport within the solid and fluid phases is modelled using separate energy equations for each phase. This is sometimes called the Local Thermal Non-Equilibrium (LTNE) model, in that it makes no assumptions about local thermal equilibrium between phases. The additional convective heat transfer term between the fluid and solid phases, which emerges when using the two-phase model, is formulated using a documented empirical correlation. Furthermore, the thermal dispersion phenomenon due to the complex path of local fluid elements through the solid matrix, causing mixing and recirculation in both the longitudinal and the transverse directions, is incorporated in the modelling of the fluid phase energy equation

Legitimacy of the Local Thermal Equilibrium Hypothesis in Porous Media: A Comprehensive Review

Local thermal equilibrium (LTE) is a frequently-employed hypothesis when analysing convection heat transfer in porous media. However, investigation of the non-equilibrium phenomenon exhibits that such hypothesis is typically not true for many circumstances such as rapid cooling or heating, and in industrial applications involving immediate transient thermal response, leading to a lack of local thermal equilibrium (LTE). Therefore, for the sake of appropriately conduct the technological process, it has become necessary to examine the validity of the LTE assumption before deciding which energy model should be used. Indeed, the legitimacy of the LTE hypothesis has been widely investigated in different applications and different modes of heat transfer, and many criteria have been developed. This paper summarises the studies that investigated this hypothesis in forced, free, and mixed convection, and presents the appropriate circumstances that can make the LTE hypothesis to be valid. For example, in forced convection, the literature shows that this hypothesis is valid for lower Darcy number, lower Reynolds number, lower Prandtl number, and/or lower solid phase thermal conductivity; however, it becomes invalid for higher effective fluid thermal conductivity and/or lower interstitial heat transfer coefficient

Legitimacy of the local thermal equilibrium hypothesis in porous media: A comprehensive review

Local thermal equilibrium (LTE) is a frequently-employed hypothesis when analysing convection heat transfer in porous media. However, investigation of the non-equilibrium phenomenon exhibits that such hypothesis is typically not true for many circumstances such as rapid cooling or heating, and in industrial applications involving immediate transient thermal response, leading to a lack of local thermal equilibrium (LTE). Therefore, for the sake of appropriately conduct the technological process, it has become necessary to examine the validity of the LTE assumption before deciding which energy model should be used. Indeed, the legitimacy of the LTE hypothesis has been widely investigated in different applications and different modes of heat transfer, and many criteria have been developed. This paper summarises the studies that investigated this hypothesis in forced, free, and mixed convection, and presents the appropriate circumstances that can make the LTE hypothesis to be valid. For example, in forced convection, the literature shows that this hypothesis is valid for lower Darcy number, lower Reynolds number, lower Prandtl number, and/or lower solid phase thermal conductivity; however, it becomes invalid for higher effective fluid thermal conductivity and/or lower interstitial heat transfer coefficient.</p

The appearance of oscillatory flows within a horizontal packed bed partly heated from below

We report on a numerical investigation of the unsteady mixed convective flow in a channel through a horizontal porous layer under localised isothermal heating from below to probe the oscillatory flow and thermal characteristics. The study was carried out for water flow within a plane channel containing stainless steel spherical particles. For this study, the channel height/particle diameter ratio was H/d=100 and the porosity was ɛ=0.35. The effects of the imposed pressure-driven flow characterised by the Péclet number (0.1≤Pe≤1000), and heating represented by the Rayleigh number (105≤Ra≤2×107), are investigated. The results reveal that for low Péclet numbers, steady free convective flows are dominant, while for high Péclet numbers, steady forced convective flows dominate. Importantly, no oscillatory flows are found to develop in the free and forced convection regimes. However, for moderate Péclet numbers, oscillatory mixed convective flows occur with different periodic, quasi-periodic, and chaotic flow behaviours. In addition, for low Rayleigh numbers, Ra≤106, the Nusselt number is not influenced by the Péclet number for Pe≤1. Nevertheless, for high Rayleigh numbers, Ra≥2×106, it is observed that there always exists a critical Péclet number for which the Nusselt number is a minimum. The effects of the Péclet and Rayleigh numbers on the local and average temperature disparity between the fluid and solid phases are then investigated

-2548G&gt;A LEP Polymorphism Is Positively Associated with Increased Leptin and Glucose Levels in Obese Saudi Patients Irrespective of Blood Pressure Status

Background and Objectives: In this study, we aimed to investigate the link between common -2548G&gt;A (rs7799039) promoter variant of the human leptin gene (LEP) with leptin and serum glucose leptin levels in obese Saudi patients. Materials and Methods: A total of 206 Saudi adults (80 obese normotensive nondiabetics, 76 obese hypertensive with Type 2 Diabetes and 50 normotensive nondiabetic controls) were genotyped for -2548G&gt;A LEP polymorphism using the polymerase chain reaction-restriction fragment-length polymorphism technique. Results: Participants with minor AA genotype had significantly higher blood glucose levels (6.8 &plusmn; 0.55 mmol/L vs. 5.8 &plusmn; 0.30 mmol/L; p &lt; 0.04) and HOMA-IR (4.1 &plusmn; 0.84 vs. 2.6 &plusmn; 0.67; p = 0.03) against those carrying major GG genotype. Participants with heterozygous GA genotype had significantly higher serum leptin levels against those carrying major GG genotype (40.0 &plusmn; 2.6 ng/mL vs. 29.6 &plusmn; 2.6 ng/mL; p = 0.04). Further investigation showed that individuals with AA, GA, GA + AA genotypes are at greater risk of developing hyperglycemia compared to those with GG genotype [OR 3.7(1.6&ndash;8.4), p = 0.001; 3.2 (1.2&ndash;8.6), p = 0.03; 3.5 (1.6&ndash;7.7), p = 0.001, respectively]. Additionally, the -2548AA allele was shown to be a risk factor for hyperglycemia [OR 1.9 (1.2&ndash;3.0), p = 0.006]. Our data revealed no relationship between this variant of the LEP gene with systolic and diastolic BP, signifying that this genetic variant is not a significant marker of obesity and hypertension in the Saudi population. Conclusions: AA and GA genotypes and LEP gene -2548AA alleles may signify potent risk factors predisposing healthy individuals to develop T2DM regardless of blood-pressure profile

Metabolic Alteration of MCF-7 Cells upon Indirect Exposure to <i>E. coli</i> Secretome: A Model of Studying the Microbiota Effect on Human Breast Tissue

According to studies, the microbiome may contribute to the emergence and spread of breast cancer. E. coli is one of the Enterobacteriaceae family recently found to be present as part of the breast tissue microbiota. In this study, we focused on the effect of E. coli secretome free of cells on MCF-7 metabolism. Liquid chromatography–mass spectrometry (LC-MS) metabolomics was used to study the E. coli secretome and its role in MCF-7 intra- and extracellular metabolites. A comparison was made between secretome-exposed cells and unexposed controls. Our analysis revealed significant alterations in 31 intracellular and 55 extracellular metabolites following secretome exposure. Several metabolic pathways, including lactate, aminoacyl-tRNA biosynthesis, purine metabolism, and energy metabolism, were found to be dysregulated upon E. coli secretome exposure. E. coli can alter the breast cancer cells’ metabolism through its secretome which disrupts key metabolic pathways of MCF-7 cells. These microbial metabolites from the secretome hold promise as biomarkers of drug resistance or innovative approaches for cancer treatment, either as standalone therapies or in combination with other medicines