In the present study, the effects of different types thermal bridges formed by beams for floor-wall junctions in reinforced concrete structures, with and without balconies, and the optimum configuration of the insulation layers to avoid heat loss were investigated as numerically. Both insulation between the walls and internal insulation was selected for floor-wall junctions and internal insulation was used for floor-wall junctions with balcony. Fluent package program was used to solve the temperature domain numerically. Results showed that high heat transfer rates were obtained in the region of thermal bridges for all building models. It was also obviously obtained that heat transfer rate decreased with making insulation on the beam surfaces.

To able to employ nanofluids in engineering applications, it is essential to investigate heat transfer properties in addition to thermophysical characteristics. In this work, the convection heat transfer coefficient of graphene oxide-distilled water nanofluid along a circular copper tube having a constant heat flux at the outside surface has been investigated both numerically and experimentally under turbulent flow regime. While the nanofluid convection heat transfer and head loss of pressure have been evaluated in the experimental section, the tube wall surface temperature, the convection heat transfer coefficient and friction factor have been obtained by using finite volume method in the numerical part with a three-dimensional domain by assuming single-phase flow. Surface and fluid temperatures and pressure drop of the distilled water have been acquired and compared with the related output from the correlation. Besides, the variations of the tube surface temperatures and the convection heat transfer coefficients of the nanofluids have been examined as numerical and experimental comparisons. The contours of the temperatures, convection heat transfer coefficients and pressure distributions for fluids have been presented. The convection heat transfer performances of the nanofluids according to the different volumetric flow rates, concentrations and the heat flux values have been exhibited in this study. The heat transfer coefficient increment value for the nanofluid of 0.02 vol% concentration and with a flow rate of 1.5 l/min (Re = 5032) has been obtained as about 48% for 5073.244 W/m 2 (350 W) heat flux according to the distilled water.

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Original scientific paper https://doi.org/10.2298/TSCI160721151AIn the present work, the effect of the different geometric moist objects with straight and reverse semi-circular on the heat and mass transfer enhancement of the jet drying was conducted with a numerical analysis. The drying jet was a laminar 2-D jet stationed at a constant jet distance from the moist object. The diameter of the object, jet distance from the moist object and initial jet height were fixed in all cases. Temperature and mass distributions were obtained inside the object for different jet velocities. A finite volume method was used to solve the governing equations for momentum and energy by using ANSYS Fluent 17.0 software program. Calculations were performed for four different Reynolds numbers, namely, Re = 100, 200, 300, and 400. It was found good agreement with the experimental data available in the literature. The results showed that the geometry of straight semi-circular moist object had better performance of heat and mass transfer than that of the reverse moist object geometry. In addition, increasing Reynolds number showed a positive effect on heat and mass transfer. Locally, jet drying was found to be most effective near the stagnation point on the leading side of the objects.

Öz Bu çalışmada, plakalı kanatçıklı ısı değiştiricilerde ısı transferini artırmak için birleşik (taşınım ve iletim) ısı transferi yaklaşımıyla 2 mm kanatçık yükseklikli 30 o ve 60 o kanatçık açılı ve akışa dik yatay yönde 10 mm ötelenmiş dikdörtgensel kanatçıkların ısı transferi potansiyeli ve basınç düşüşü sayısal olarak incelenmiştir. Sayısal hesaplamalar, üç boyutlu Navier-Stokes ve enerji denkleminin FLUENT programı kullanılarak çözülmesiyle zamandan bağımsız olarak elde edilmiştir. Çalışma akışkanı olarak hava kullanılmıştır. Çalışma, Re= 400 için soğuk ve sıcak hava kanala giriş hızlarının sırasıyla 1,338 m/s ve 0,69 m/s, giriş sıcaklıklarının ise 27 o C ve 327 o C olarak alınmasıyla yapılmıştır. Sonuçlar soğuk akışkan sıcaklığının ters akış durumunda 30 o kanatçık açılı kanalın çıkışında düz kanala göre %9 artırıldığını göstermektedir. Çalışmada, paralel ve ters akış şartlarında Reynolds sayısının farklı değerlerinin ve farklı kanatçık yükseklikleri ve kanatçık aralıklarının ısı transferi artışı üzerindeki etkisi ve ayrıca kanalın dış yüzeyinin soğuk ve sıcak akışkan taraflarındaki sıcaklık dağılımları da 30 o ve 60 o kanatçık açıları için incelenmiştir. Anahtar Kelimeler: Plakalı ısı değiştirici, Sayısal ısı transferi, Kanat Abstract In the present study, the heat transfer potential of rectangular fins with 30 o and 60 o angle and 2 mm fin height and 10 mm offset from the horizontal direction perpendicular to flow for heat transfer enhancement with the use of a conjugated heat transfer approach and pressure drop are numerically evaluated in the plate fin heat exchangers. The numerical computations are performed by solving a steady, three-dimensional Navier-Stokes equation and an energy equation by using Fluent software program. Air is taken as a working fluid. The study is carried out at Re= 400 and inlet temperatures, velocities of cold and hot air are fixed as 27 o C, 327 o C and 1.338 m/s, 0.69 m/s, respectively. The results * Sorumlu yazar