The effects of orientation of an inclined enclosure on laminar natural convection

Natural convective laminar flow is numerically investigated in a two-dimensional and square enclosure at various angles of inclination respect to horizontal. Two adjacent walls of the enclosure are insulated and the other two are kept at different temperatures. The influence of Rayleigh number representing the effects due to the differential heating of the enclosure walls as well as the effect of inclination angle on natural convection flow are studied. The flow field and isothermal lines show different patterns at high Rayleigh numbers. The average Nusselt number, maximum stream function and average temperature appear to be a little affected by the inclination angle at low Rayleigh numbers. However, as the Rayleigh numbers rises, these parameters behave differently at various inclination angles. In this study, the effects of inclination on the temperature along the centerline of the enclosure and the local Nusselt number along the cold wall are also examined. The results show negligible effects of inclination angle at low Rayleigh numbers and considerable effects at high Rayleigh numbers

Interaction effects between surface radiation and double-diffusive turbulent natural convection in an enclosed cavity filled with solid obstacles

The work reported here is a 2D numerical study on the buoyancy-driven low speed flow of humid air inside a rectangular cavity partially filled with solid cylindrical objects and whose vertical walls are maintained at 1.2 and 21 oC. This is a case of double diffusion where both temperature and concentration gradients are significant. Detailed calculations were carried out and results compared with reliable data, with the aim of investigating the influence of surface emissivity on heat and moisture transport. The Rayleigh number of the fluid mixture (air and water vapour) based on the height of the vertical wall is found to be 1.45 x 109. In the computations, turbulent fluxes of the momentum, heat and mass were modelled by low-Re (Launder-Sharma) k-ε eddy viscosity model. The effect of radiation has been found to be significant even for the moderate temperature difference of 19.8 oC between the hot and the cold walls with the humid air participating in the radiation heat transfer. Variations of average Nusselt number and buoyancy flux are analysed and profiles of turbulent quantities are studied in order to observe the net effect of the intensity of turbulence. It has been found that a change in surface emissivity influences the humidity distribution and heat transfer within the cavity. It was also observed that during natural convection process the air/water vapour combination results in an increase in the heat transfer as compared to pure natural convection. An increase in heat transfer is observed using thermo-physical materials of higher surface emissivity. It can thus be implied that with the appropriate choice of components, the fluid flow, heat and mass transfer due to natural convection can be increased passively

Review of the Baffle Effects on Natural Convection Heat Transfer in an Enclosure Filled with Nanofluid

تم عرض مراجعة شاملة حول مجموعة واسعة من الدراسات حول انتقال الحرارة بالحمل الطبيعي وخاصة على للدراسات التي اجريت على الحيز المغلق والذي يحتوي على مادة نانوية متناهية الصغر والتي درست تحت ومتغيرات ظروف حرارية مختلفة على جدران الحيز. تمت مناقشة التفاصيل المتعلقة بالطرق المستخدمة في تعزيز النقل الحراري باستخدام تلك المواد النانوية داخل منطقة حيز الدراسة. أيضًا تم عرض الدراسات التجريبية والعددية المتعلقة بالانتقال الحراري بالحمل الطبيعي لتلك السوائل النانوية. حيث ان دراسة هذه المواضيع لها أهمية عملية وعلمية للعديد من التطبيقات الهندسية، مثل المنشآت الصناعية للتخزين البارد والعزل للمباني. لقد جذب الباحثون اهتمامهم بدراسة الخصائص الفيزيائية الحرارية للجسيمات النانوية أكثر من أي شيء آخر من الدراسات ولم يركزوا على خصائص انتقال الحرارة بواسطة هذا السائل الجديد. كانت هناك سلسلة من التحقيقات والعديد من الدراسات التجريبية والعددية تم التحقيق داخل حيز مربع الشكل باستخدام السوائل النانوية استخدمت كوسيط نقل ومع تأثير حاجز ذات موصلية جيدة ودراسة تأثير تغيير طول الحاجز على الجدار الأفقي السفلي. لقد وجد أن هناك الكثير من الأشياء التي يجب دراستها لدراسة حجم الجسيمات النانوية وتأثيرها على انتقال الحرارة الحراري الطبيعي داخل الحيز المغلق.A comprehensive review on wide range of studies on natural convection was published relevant to enclosures especially for the nanofluid enclosures which were exposed to different conditions on its boundary wall. The papers related to the ways that used to enhancement the natural convection heat transfer of a nanofluid within an enclosure region had been discussed in full details. Also contains the experimental and numerical studies related to natural convection heat transfer of a nanofluid. It is of practical and scientific importance to several engineering applications, such as industrial cold-storage installations and insulation for buildings. There are researchers attracted their attention and interested in studying the thermophysical characteristics of the nanoparticle more than anything else of the studies and did not focus on the characteristics of heat transfer by this new fluid. There was a series of investigations and several experimental and numerical studies were investigating within a square shape cavity using nanofluids as working fluid and with the effect of the conductive baffle has a variable-length attached to the bottom horizontal wall. It was found that there is a lot of things need to be investigated for studying the nanoparticle size and shape influence on the natural convection heat transfer inside an enclosure

Natural convection in an inclined parallelogram-shaped enclosurecontaining internal energy source with linearly heated sidewall

The main objective of this paper is to study the natural convection flow inside a parallelogram enclosure having uniform internal heat generation. The left inclined wall is linearly heated while the right inclined wallis kept at cold temperature (Tc) and top and bottom walls are thermally insulated. Steady state, two-dimensional numerical study is carried out by using the finite volume technique after the equations are put into dimensionless forms. The governing parameters studied are external Rayleigh number, internal Rayleigh number and inclination angle from horizontal axis which are varied from 103≤RaE≤106, 0≤RaI≤108and 0o≤Φ≤45o. Air is used as a working fluid with a Prandtl number of 0.71. Efforts are focused on the interaction between the internal Rayleigh number (heat generation) and external Rayleigh number (temperature difference between the sidewalls) for various inclination angles. The accuracy of the numerical method compared with the previous published works shows an excellent agreement. The obtained results show that the maximum heat transfer performance occurs at zero inclination angle and low values of external heating. Keywords: Natural convection; heat generation; linear heating; parallelogram enclosure; finite volume

Heat and mass source effect on MHD double-diffusive mixed convection and entropy generation in a curved enclosure filled with nanofluid

This paper examines the two-dimensional laminar steady magnetohydrodynamic doublediffusive mixed convection in a curved enclosure filled with different types of nanofluids. The enclosure is differentially heated and concentrated, and the heat and mass source are embedded in a part of the left wall having temperature Th (>Tc) and concentration ch (>cc). The right vertical wall is allowed to move with constant velocity in a vertically upward direction to cause a shear-driven flow. The governing equations along with the boundary conditions are transformed into a nondimensional form and are written in stream function-velocity formulation, which is then solved numerically using the Bi-CGStab method. Based on the numerical results, the effects of the dominant parameters such as Richardson number (1 ≤ Ri ≤ 50), Hartmann number (0 ≤ Ha ≤ 60), solid volume fraction of nanoparticles (0.0 ≤ ϕ ≤ 0.02), location and length of the heat and mass source are examined. Results indicate that the augmentation of Richardson number, heat and mass source length and location cause heat and mass transfer to increase, while it decreases when Hartmann number and volume fraction of the nanoparticles increase. The total entropy generation rises by 1.32 times with the growing Richardson number, decreases by 1.21 times and 1.02 times with the rise in Hartmann number and nanoparticles volume fraction, respectively

Computational study of heat transfer in solar collectors with different radiative flux models

2D steady incompressible laminar Newtonian viscous convection-radiative heat transfer in a rectangular solar collector geometry is considered. The ANSYS FLUENT finite volume code (version 17.2) is employed to simulate the thermo-fluid characteristics. Extensive details of computational methodology are given to provide engineers with a framework for simulating radiative-convection in enclosures. Mesh-independence tests and validation are conducted. The influence of aspect ratio, Prandtl number (Pr), Rayleigh number (Ra) and radiative flux model on temperature, isotherms, velocity, pressure is evaluated and visualized in colour plots. Additionally, local convective heat flux is computed, and solutions are compared with the MAC solver for various buoyancy effects achieving excellent agreement. The P1 model is shown to better predict the actual influence of solar radiative flux on thermal fluid behaviour compared with the limited Rosseland model. With increasing Ra, the hot zone emanating from the base of the collector is found to penetrate deeper into the collector and rises symmetrically dividing into two vortex regions with very high buoyancy effect. With increasing Pr there is a progressive incursion of the hot zone at the solar collector base higher into the solar collector space and simultaneously a greater asymmetric behaviour of the dual isothermal zones

Numerical Analysis Of Natural Convection In A Two-Dimensional Enclosure : The Effects Of Aspect Ratio And Wall Temperature Variation

Penyelidikan ini tertumpu kepada pengkajian berangka ke atas perolakan tabie yang beraliran mantap bagi suatu aliran udara dengan nombor Prandtl, Pr = 0.71 di dalam satu ruang tertutup dua-dimensi. This research is focused on the numerical investigation of a steady laminar natural convection flow of air with Prandtl number, Pr = 0.71 in a two-dimensional enclosure