Occurrence Of Natural Convection Research Articles

Ternary Hybrid Nanofluid Flow Containing Gyrotactic Microorganisms over Three Different Geometries with Cattaneo–Christov Model

The movement of microorganism cells in fluid influences various biotic processes, including septicity and marine life ecology. Many organic and medicinal applications need to look into the insight of mechanism in nanofluids containing a microbial suspension. The current paper concerns the bioconvection of a ternary hybrid nanofluid (Al2O3-Cu-CNT/water) flow containing motile gyrotactic microorganisms toward three different geometries (a flat plate, a wedge, and a cone) in the occurrence of natural convection, radiation, and heat source/sink. The Cattaneo–Christov theory is employed to develop the model. The equations are solved by using the “bvp4c function in MATLAB”. The influence of the crucial significant factors on the motile microorganisms’ density, velocity, temperature, nanoparticles’ concentration, microbe density gradient, and transmission rates of heat and mass is discussed. The results depict that the heat transmission rate is highest for the flow toward the cone, whereas the mass transmission rate and microbe density gradient are highest for the flow toward the wedge. In addition, the higher estimates of the thermal relaxation parameter corresponding to the Cattaneo–Christov theory act to enhance the rate of heat transmission. The results of the current study will be useful to many microbial-enhanced oil recovery systems, carriage processes, architectural design systems, medicinal fields that utilize nanofluids, and so on.

Measurement and Scaling of Lake Surface Skin Temperatures

AbstractWater temperature microprofiles at the air‐water interface of a stratified lake were measured concurrently with moderate wind speeds of 0.8–8.2 ms−1 above the lake surface. The day‐time measurements revealed the cool skin effect of water surface temperatures that triggers the cooling of the lake surface and the occurrence of natural convection. Natural convection velocity scale mediates the thickness of the diffusive thermal sublayer and the corresponding net heat flux at the interface. The diffusive thermal sublayer thickness ranged from 0.7 to 3.6 mm. The temperature microprofiles and proposed parameterization of skin‐to‐bulk temperatures enable similarity scaling of temperature microprofiles over the diffusive thermal sublayer thickness. The proposed parameterizations allow for the estimation of diffusive thermal sublayer thickness and skin‐to‐bulk temperature difference in the presence of natural convection. Our results have the potential to facilitate the validation and integration of satellite‐derived lake surface temperatures.

Modelling the conditions for natural convection onset in open-cell porous Al/paraffin composite phase change materials: Effects of temperature, paraffin type and metallic structure geometry

Composite Phase Change Materials (PCMs) can be made combining a PCM, i.e., a material that is able store/release heat by its melting/solidification, and a low-amount of well distributed high-melting and high-thermal conductivity phase with the aim of improving the overall conductivity of the material and keeping its high heat storage capability. The composite made by a paraffin and a porous structure of aluminium (Al) has been considered as the representative of this material class. The design of these materials should not only take into account the melting temperature (Tm) and the volume fraction of the paraffin, but also the geometrical distribution and coarseness of the Al phase, which relate to the effective thermal conductivity of the composite as well as the occurrence of natural convection once the PCM is in the molten state. In the present paper, the inverse Body Centred Cubic (BCC) structure has been confirmed to be the most suitable to model high porosity Al foams. For their BCC modelled structure, an analytical equation is proposed for the evaluation of the overall thermal conductivity of the composite PCMs. Also, new best fit equations for predicting permeability of BBC structure are proposed. Analytical description is also given for the Rayleigh-Darcy number obtained as a product of material-dependent term (related to Tm and volume fraction of PCM) and the geometry dependent term (related to volume fraction of PCM, permeability as well as to material coarseness alternatively given in terms of pores per inch, pore size or unit cell length). The model has been validated by means of literature available experimental data. The proposed simplified model can further be adjusted to correlate the onset of natural convection through the local temperature gradient for the composite PCMs.

Development and validation of a stabilized immersed boundary CFD model for freezing and melting with natural convection

Numerous processes in the automotive, additive manufacturing or energy storage industries require an accurate prediction of the solidification (freezing) and melting (thawing) dynamics of substances. The numerical modeling of these phase changes is highly complex because it includes sharp moving interfaces and strong discontinuities in the material properties. This complexity is often exacerbated by the occurrence of natural convection, which induces a strong coupling between the motion of the liquid and the position of the solid–liquid interface. This leads to strongly coupled non-linear thermo-fluid problems which have to be solved in complex geometries.In this work, we introduce two novel stabilized finite element models to predict the phase change with natural convection. The first model uses a more classical viscosity approach to impose stasis in the solid region whereas the second one is based on an immersed boundary formulation to accurately describe the solid–fluid interface.The efficiency of the stabilization is first demonstrated by studying the Stefan problem. The two approaches to impose stasis are then compared using 2D test cases before they are both used to study melting in a rectangular (2D) and prismatic (3D) cavity. Significant differences are observed in the flow profiles and the solid–liquid interface position between the 2D and the 3D simulations.

Решение внутренней задачи о возникновении естественной конвекции жидкости

Решение внутренней задачи о возникновении естественной конвекции жидкости

Characterizing the performance of a single-layer fabric system through a heat and mass transfer model - Part II: Thermal and evaporative resistances

In Part I of this work, a heat and mass transfer model was developed to calculate the thermal and evaporative resistances of a single-layer fabric system. Using this model, the effects of environmental conditions, air gap, and material properties on the thermal and evaporative resistances have now been studied. The thickness of the air gap and that of the fabric layer were shown to contribute significantly to both the thermal resistance and evaporative resistance. The occurrence of natural convection in the air gap can cause decreases in thermal and evaporative resistances, and needs to be considered to determine the optimal air gap thickness. The porosity of the fabric layer has a distinct effect on the two resistances, and is an excellent property to help achieve both thermal protection and comfort. This work provides the fundamental basis for the optimization of garment fit and material properties to achieve good performance of the clothing system.

자성유체를 이용한 다이나믹형 빙축열 시스템에 관한 실험적 연구

In this study, It induced to a conclusion below by experiment consideration to regarding an effective supercooling ends method of the flow cooling water in a tube of continuous ice making method and the static cooling water in a tube of continuous Ice making method which used magneticfluid in a dynamic type Ice storage system. Continuous Ice making in a tube of the flow cooling water was shortened about 12 minutes until supercooling ends that case winch gave vertical eccentricity rotation magnetic field 120rpm than did not provide magnetic field by experimental result that was tested to supercooling ends effect from shape control of magneticfluid Continuous Ice making method in a tube of the static cooling water compared with and reviewed the case that was not provided with the magnetic field and exposed cooling surface instantaneously by magnetic field. It confirmed that supercooling degree ◁Te, ◁Ts sand ◁Tw became lower because of heat transfering increasing by the occurrence of natural convection between after cooling staffing progress tune 1-3 minutes if it did not give a magnetic field, and performed the supercooling ends when natural convection occurred confirmed that refrigerating capacity was better. That relation ◁Te and tε/(◁Te―◁Ts) after convection occurred, was not depended on Tb and initial temperature If the depth of water and thickness of magneticfluid were regular and It was possible to verify conjecture of tp from ◁ Ts and ◁Tc.

Occurrence of free convection in a plane layer in the presence of a chemical transport reaction

We consider the conditions for the occurrence of natural convection when a volatile compound is transported through a gaseous phase as a result of a chemical reaction with a solid substance. We determine the variation of the critical Rayleigh number for the principal level of instability as a function of the parameters of the process.

Natural Convection Within Porous Electrodes During Electrolysis

Depletion of reactive solute species from interior regions of a porous electrode during electrolysis can result in a density difference between the electrolyte within the porous electrode and the bulk solution. The density difference which may thus arise can in some cases provide the driving force necessary for natural convection flow of electrolyte through the porous electrode. A one‐dimensional steady‐state theoretical model has been developed to investigate system conditions under which density‐driven flows may be anticipated and to what extent these flows can enhance reaction rates. Calculations were conducted for three aqueous electrolyte systems: potassium hydroxide, sulfuric acid, and copper sulfate in excess sulfuric acid. The theoretical results predict conditions under which volumetric reaction rates may be increased significantly by the occurrence of natural convection. The results indicate that double‐ porosity high‐rate porous electrodes may be designed within which electrochemical reaction would occur primarily in the fine, high surface area, pores while natural convection of electrolyte would take place in the larger pore structure.