In this study, the forced convection properties of teardrop-shaped dimpled fins, Fe3O4/H2O ferrofluid, and constant magnetic field parameters were investigated numerically and experimentally. The study consists of two parts. In the first part, a numerical simulation was conducted, incorporating all relevant parameters, and the results were analyzed. In the second part, the experimental setup was completed for the scenario that yields the highest performance evaluation criterion value, as determined from the numerical results. The Reynolds number (10000 <= Re <= 50000), the size of the teardrop-shaped dimple (BTD, MTD and STD), dimples distance (30 <= P <= 50), constant heat flux (q" = 20 kW/m2), ferrofluid concentration ratio (0.0 <= 4Vvol.<= 2.0) and the constant magnetic field strength applied at x/D = 20 location (0 T <= B0 <= 0.3 T) were studied experimentally and numerically. The findings showed that the DT9 case increased the thermal performance change by 36.18 % compared to the smooth tube. The highest heat transfer rate occurred in the magnetic field strength B0 = 0.3 T. The magnetic field strength caused an improvement in heat transfer of 5.12 % and 7.32 % in the Nusselt number, respectively, in the numerical and experimental results. The highest PEC was obtained by using 4Vvol. = 2.0% Fe3O4/H2O nanofluid in case DT9 (STD, P = 50 mm) at Re = 10000 and B0 = 0.3 T, with a contribution of 32.45% compared to the smooth tube. The compound effect amounts of teardrop-shaped dimples, ferrofluid, and constant magnetic field were obtained numerically and experimentally as 55.41% and 55.37% in Nusselt number, while obtained as 29.15% and 32.45% in PEC, respectively, compared to a smooth tube, using H2O and the absence of a constant magnetic field.

In this paper, thermo-hydraulic performance and entropy generation (EnG) of the teardrop-dimpled tube (DT) was computationally performed under turbulent flow conditions which Reynolds numbers (Re) ranging between 10,000 ≤ Re ≤ 50,000 using Fe3O4/H2O ferrofluid (FF) (0 ≤ φ ≤ 2.0). The analyses were carried out under constant heat flux conditions of 20 kW/m2. Three sizes and spacing (P = 30, 40, and 50 mm) of the teardrop dimples were investigated parametrically. Moreover, in this study thermo-hydraulic performance and EnG effects were scrutinized for smooth and nine different teardrop DT cases. As a result of the simulations and calculations, the highest performance evaluation criterion (PEC) has been recorded in the case of DT9, and this case performed an increment of 28

This study experimentally and analytically investigated the freeze-drying kinetics of five medicinally important plant species (Viburnum opulus, Berberis crataegina, Ajuga reptans, Trachystemon orientalis, and Petasites hybridus) to determine the most suitable drying models. Valuable plants used in traditional and modern medical treatment methods were chosen, and freeze drying, a hygienic drying method, was applied to extend the shelf life of these plants and increase their accessibility. Experimental drying data were analyzed using MATLAB to evaluate eight common kinetic models based on RMSE, X2, and R2 values. The lowest chi-square (X2) values ranged from 6.79x10-6 to 1.055x10-4, and RMSE values ranged from 0.002607 to 0.01027, with high coefficients (R2 >= 0.9993). The Diffusion model was identified as the best fit for V. opulus, A. reptans, and P. hybridus, while the Wang and Sing model suited B. crataegina, and the Page model best described T. orientalis. These findings provide crucial insights for optimizing freeze-drying processes for these sensitive medicinal plants.

This study examines the challenges associated with freezing conditions in air-source heat pump systems (ASHP), with a focus on defrost methods and the experimental evaluation of a poppet-type solenoid valve (PTV) as an alternative to the traditional four-way valve (FWV). In case of the outdoor temperature falls below the dew point, frost formation is possible on ASHP evaporators depending on various operational and environmental factors. This experimental study compared the performance of a heat pump system using a poppet valve to one with a four-way valve, emphasizing defrost duration and its impact on system efficiency. Both systems operated in cooling mode for 10 min, followed by a one-minute defrost cycle, repeated over 10 cycles. Results showed the poppet valve system achieved a coefficient of performance (COP) of 6.07, outperforming the four-way valve system’s COP of 5.42 by 11.99

Background: This study experimentally and numerically addresses magnetohydrodynamic forced convection including dimpled fins, Fe3O4/water ferrofluid, and DC magnetic field. In this research, focusing on the thermohydraulic performance improvement of a sudden expansion tube. It has been used different inlet diameters, dimple sizes, ferro nanoparticle concentrations, and magnetic field strengths to examine the heat transfer and fluid dynamics characteristics of the system. Methods: The study consists of two parts, i) experimental and ii) numerical. Steady-state, incompressible, Newtonian flow were considered but chemical reaction, viscous dissipation, buoyancy, and radiative heat transfer were neglected in this study. On the other hand, numerical solutions were carried out for single-phase method. This study was first compared with the studies in the literature on the flow in a sudden expansion tube without dimpled fins and the error rate was found to be less than 10%. In the analysis, dimpled fins with d=3, 5, and 7 mm at each P=15 mm (P/d=5.0, 3.0, and 2.14) have been used. As working fluid, Fe3O4/water ferrofluid with volume concentration of phi=1.0 % and 2.0% have been analyzed. Additionally, DC magnetic fields, which strength of Ha=0.1, 0.3, 0.5, 1.1, 3.2, and 5.3 (B =0.01, 0.03, 0.05, 0.1, 0.3, and 0.5T), have been applied on the sudden expansion tube surface as external force. Significant findings: Dimpled fins enhance the heat transfer by disrupting the boundary layer and forming secondary flows, while the ferrofluid increases the thermal conductivity and viscosity of the base fluid. Based on these explanations, dimpled fins increased the convective heat transfer rate at the rate of 96.0% compared with smooth tube. In addition, Fe3O4/water ferrofluid with phi=2.0 % performed the highest performance and performance evaluation criteria increased by 8.5%. The magnetic field also contributes to the heat transfer enhancement by inducing Lorentz force and mixing the flow. Excessive increasing of magnetic field strength adversely affected the system performance, and the highest performance evaluation criterion is acquired at Ha=3.2 by increasing 3.9%. Compared with smooth tube, compound effect of dimpled fins, Fe3O4/water ferrofluid, and magnetic field improved the average Nusselt number and performance evaluation criterion at the rate of 279.8 % and 207.9%, respectively.

Purpose The purpose of this study is to analyse the magnetic field effect on Fe3O4/H2O Ferrofluid flowing in a sudden expansion tube, which has specific behaviour in terms of rheology, with convex dimple fins. Because the investigation of flow separation is a prominent application in performance, the effect of magnetic field and convex dimple on the thermo-hydraulic performance of sudden expansion tube are examined, in detail. Design/methodology/approach During the solution of the boundary conditions of the sudden expansion tube, finite volume method was used. Analyses have been conducted considering the single-phase solution, steady-state, incompressible fluid and no-slip condition of the wall under forced convection conditions. In the analyses, it has been assumed that the flow was developing thermally and has been fully developed hydrodynamically. Findings The present study focuses on exploring the influence of the magnetic field, nanofluid concentration and convex dimple fins on the thermo-hydraulic performance of sudden expansion tube. The results indicate that the strength of the magnetic field, nanofluid concentration and convex dimple fins have a positive effect on the convective heat transfer in the system. Originality/value The authors conducted numerical studies, determining through a literature search that no one had yet investigated enhancing heat transfer on a sudden expansion tube using combinations of magnetic fields, nanofluids and convex dimple fins. The results of the numerical analyses provide valuable information about the improvement of heat transfer and system performance in electronic device cooling and heat exchangers.

In this study, it is examined to prevent the formation of toxins by providing drying of the kanlica mushroom, which is unique to Karabuk, by freezing, to extend the shelf life, to take measures against early decay and spoilage. As the dried product, kanlica mushroom, which is an endemic plant, contains high amounts of protein and amino acids. In this study, the 5 mm thick cut kanlica mushroom was placed in a freeze-drying device and the drying process was initiated. Weight losses during drying were recorded and kinetic models were created. In the experiment lasting 14 hours in total, 100 gr. The weights of the canlica mushrooms were measured every two hours and MR (Moisture rates) were calculated. According to our results, the lowest chi-square (X-2) was 1.851 x10(-4) and the estimated standard error (RMSE) value was 0.01358. The correlation value (R-2) was calculated as 0.9988, close to one. The best Page model gave these results from the kinetic models. The effective diffusivity for the Kanlica Mushroom with 5 mm thicknesses can be calculated at about 3.2035x10(-10) m(2)/s. It was confirmed that the calculated effective diffusivity value was within the reference range mentioned in the literature (10(-12) m(2)/s - 10(-8) m(2)/s) for food products.

This study tests freeze-drying (FD) technology (Scanvac Coolsafe model, Labogene brand) to preserve hawthorn fruit. First, 100g hawthorn slices were frozen and then freeze-dried. Kinet-ic models were applied, and hawthorn’s moisture ratio and weight loss were noted after every two hours during the 14-hour freeze-drying process. Matlab program is used to perform a to-tal of eight kinetic drying models. Results show that the root mean square error was 0.011063, the highest determination coefficient was 0.9987, the least chi-square was 1.959x10-4, and the effective diffusivity was 2.33742x10-10m2/s. The diffusion approach is the best among the eight models.

This study was performed to define the kinetic drying model and to define the effective diffusivity coefficient of the fruit, which is called ottoman strawberries in the literature. In the study, strawberries by the weight of 100 g and with a thickness of 5 mm were placed in the drying device, and the data were processed by observing the weight loss every two hours after being subjected to the drying process for 14 hours. 8 different kinetic drying models were applied to the acquired data using the MATLAB program. As a result of the application, the estimated standard errors (RMSE), chi-square (X2), regression coefficients (R2) were calculated, error analysis was performed, R2, X2, and RMSE values were found, as 9,998×10-1, 6,993×10-5 and 0.7242×10-2. According to these results, the model of strawberry was determined that the most suitable model is the Page model. Also, the effective diffusivity coefficients for ottoman strawberries were calculated as 2.73286 × 10-10 m2/s. It was confirmed that the calculated effective diffusivity value was within the reference range mentioned in the literature (10-12 m2/s – 10-8 m2/s) for food products.

This study was performed to define the kinetic drying model and to define the effective diffusivity coefficient of the fruit, which is called Diospyros kaki in the literature, from the family of Ebonaceae known as the Persimmon in our country. In the study, blueberries by the weight of 100 g and with a thickness of 5 mm were placed in the drying device, and the data were processed by observing the weight loss every two hours after being subjected to the drying process for 14 hours. 8 different kinetic drying models were applied to the acquired data using the Matlab program. As a result of the application, the estimated standard errors (RMSE), chi-square (X2), regression coefficients (R2) were calculated, error analysis was performed, R2, X2, and RMSE values were found, as 0.019483, 5.062 x 10-4 and 0.9558. According to these results, it was determined that the most suitable model is the Page model. Also, the effective diffusivity coefficients for Persimmon (Diospyros Kaki) were calculated as 1.79775 × 10-10 m2/s.

The aim of this study is to examine the hydrothermal behavior of Fe3O4 Ferrofluid flowing under the effect of uniform magnetic field (0 T <= B <= 0.3 T). In addition, magnetic field locations were changed for each experiment to observe effect of the magnetic field locations (x/D = 20, 40, 60) on the hydrothermal behavior of the proposed system. Fe3O4 Ferrofluid was prepared in phi = 1.0% volume concentration in water and flows under the laminar regime (1131 <= Re <= 2102). Comparisons of the hydrothermal behavior of the novel proposed parameters were performed according to combinations of the different magnetic field locations and magnitudes. It is concluded that the highest Nusselt number was obtained using B = 0.3 T for the magnetic field location of x/D = 20 for both in smooth and dimpled tubes. Compared to B = 0 T, the Nusselt number enhancement was detected by 64.03% for smooth tube for the magnetic field location of x/D = 20 for B = 0.3 T whereas Nusselt number wasaugmented by 45.40% for dimpled tube for the same input parameters. Furthermore, no considerable changes in friction factor was determined under magnetic field effect when the application of magnetic field locations was changed. As a result of these findings, the highest increase in Performance Evaluation Criteria belonging dimpled tube was calculated by 33.54% at Re = 2102 for B = 0.16 T for the magnetic field location of x/D = 20. As a general conclusion, this study can shed light on investigating ferrofluids behavior under magnetic field applied in var-iable magnetic field locations.

In the study, the kiwi fruit was sliced into various thicknesses as 5 mm and 7 mm, and those sliced specimens were put in the freeze-drying device. the mass losses of the specimens were measured and saved during the drying process and kinetic drying models were performed using those measurements. The mass losses of each kiwi slices in 100 g mass were measured every two hours in the experiment lasting 14 hours in total and moisture ratios (MR) were calculated as well. Considering the experimental results, 8 different kinetics drying models were performed using MATLAB software. As a result, the lowest reduced chi-square (X2) values for 5 mm and 7 mm thicknesses were calculated about 8.261x10-6 and 1.705x10-5 respectively, the root means square error values (RMSE) were about 0.002865 and 0.004146, respectively. Also, the coefficient of determination (R2) for both thicknesses was calculated as 0.9999 which was the highest result closest to 1. Among the 8 different kinetic drying models, the Logarithmic model was chosen as a proper kinetic drying model for kiwi products. When the moisture contents and drying rates were considered it was seen that the drying rate of kiwi slices with 7 mm thickness exhibited slow behavior because of the higher moisture content. Besides, it was determined that the effective diffusivity coefficients for specimens with 5 mm and 7 mm thickness were calculated as 2.25 × 10-10 m2/s and 3.28 × 10-10 m2/s respectively.

Abstract The current study presents a novelty with focusing on the magnetic field effect on a sudden expansion tube with expansion ratio, total length, and pitch length of the dimpled fin is 2.5, 1500 mm, and 3.0, respectively. The magnetizable Fe3O4/H2O Ferrofluid with different nanoparticle volumetric concentrations (φ = 1.0% and 2.0%) were used as a heat transfer fluid, and magnetohydrodynamic effects were elaborately investigated in this study. The numerical analysis was conducted under laminar flow regime and the DC magnetic field (B0 = 0.03T, 0.05T, 0.3T, and 0.5T). The present study provided a comprehensive investigation, which presented the thermo-hydraulic performance of difference dimpled fins, Fe3O4/H2O Ferrofluid, and magnetic field. According to the results, dimple fins showed the best increment within heat transfer enhancement techniques. The heat transfer enhancement rate of the dimple tube and Fe3O4/H2O Ferrofluid were respectively acquired as 22.62% and 5.43%-6.28% (φ = 1.0% and 2.0%). When dimpled fin and Fe3O4/H2O Ferrofluid were used, the increment in Performance Evaluation Criteria was calculated as 21.31% and 4.85%-9.79% (φ = 1.0% and 2.0%). Although the highest average Nusselt number was obtained at B0 = 0.5T, the highest performance evaluation criteria were detected at B0 = 0.3T due to the friction factor showing an increment.

Sudden expansion geometry plays an important role in the design of many engineering applications such as heat exchangers to avoid thermal stress on welded joints. While the heat transfer in these geometries is maximized at the reattachment points, it decreases to a minimum in the recirculation regions created by the fluid. To prevent this situation and improve the performance of the expansion tubes, nanofluid, and expanded surfaces can be used. For this purpose, forced convection of magnetite nanofluid flow in various expansion ratios has been investigated numerically in this study. Analyses have been performed on Reynolds ( Re ) numbers ranging from 100 to 2000, constant and uniform heat flux at 600 W/m(2), and volume concentrations (1.0 <=phi <= 2.0 vol.%). The result showed that while the Nu number increases with increasing Re number , the most efficient case is Dimpled Tube ( DT ) 9, and the highest value of performance evaluation criteria (PEC) has been obtained at phi= 2.0 vol.%. Compared with the water, the highest Nu number value has been obtained as 3.34% increased at Re = 20 0 0 and phi= 2.0 vol.%. When compared to the DT9 and Smooth Tube ( ST ) 1 where water was used as the working fluid at Re = 20 0 0 and phi= 2.0 vol.%, the PEC value increased by 8.66% and 110.31%, respectively. In addition, the bottom wall of the DT9 case performs higher convective heat transfer rate than the top wall.(c) 2022 Elsevier Ltd. All rights reserved.

In this study, heat transfer enhancement by natural convection Al 2 O 3 /water mono and Al 2 O 3 –SiO 2 /water hybrid nanofluid in an enclosure cavity have been performed utilizing the finite element method. For numerical computations, the homogeneous nanofluid approach was considered. The cavity was heated from the left vertical wall and cooled from the right vertical wall while the top and bottom walls were taken as adiabatic. The effects of some related factors such as the Rayleigh number (10 3 ≤ Ra ≤ 10 6 ) and nanoparticles’ volume fraction (0 ≤ φ ≤ 0.05) on the heat transfer by natural convection were examined. To discuss fluid characteristics of mono and hybrid type nanofluid under natural convection effect, the obtained results were presented as streamlines and isotherms. Also, variations of local and average Nusselt numbers were examined in detail. It was obtained that an increase in the nanoparticle volume fraction leads to the enhancement of convective heat transfer for all Rayleigh numbers. It was also indicated that the highest increment in heat transfer by convection occurs in the nanoparticle volume fraction of 2% for Al 2 O 3 /water and 4% for Al 2 O 3 –SiO 2 /water. The present study results are also consistent with the literature results.

In this numerical study, heat transfer characteristics and hydrodynamical analysis have been performed for a circular tube inserted with twisted tape, which has different twisted pitch ratios (TPR=0, 50, 100, and 200). As a working fluid Al2O3/water nanofluid is used which has different volumetric concentrations (0.0≤φ≤3.0 vol. %). The numerical analysis has been carried out under the constant wall heat flux (q′′) of 4357 W/m2 for laminar flow ranging the Reynolds (Re) number from 1000 to 2000. According to numerical results, the highest average Nusselt number (Nu) and average Darcy friction factor (ff) have realized in twisted pitch ratio (TPR) 50. The reason is that when the twisted pitch ratio gradually decreases, stronger secondary flows and a higher velocity can be obtained. When compared with water, the highest Nu for TPR=50 has been obtained at φ=3.0 vol. % concentration as 61.15%. Also, when compared with TPR=0, the highest thermal performance enhancement (TPE) was realized at φ=3.0 vol. % concentration and Re=2000 conditions as 61.15% for TPR=50. Keywords: CFD Convective heat transfer Laminar flow Al2O3/water Twisted tape

In current study, the freeze-drying (FD) method has been investigated. This method is the healthiest drying method that used in recent years by extending the shelf life of the products and preserving the beneficial flavors in its content. Antioxidant, antimicrobial, antidiabetic, anti-inflammatory, antiseptic, etc., are the most emphasized role among the berries. Thus, blueberry is one of the great aspects to be a case for drying. Blueberry (Vaccinium Myrtillus), which is an opulent source of many phenolic compounds with known properties, has been determined. In the study, blueberries by the weight of 100 g and with a thickness of 5 mm were placed in the drying device, and the data were processed by observing the weight loss every two hours after being subjected to the drying process for 14 hours. 8 different kinetic drying models were applied to the acquired data using the Matlab program. As a result of the application, the estimated standard errors (RMSE), chi-square (X2), regression coefficients (R2) were calculated, error analysis was performed, R2, X2, and RMSE values were found, as 1.4686 ×10-2, 2.875×10-4 and 9.978 ×10-1. According to these results, it was determined that the most suitable model is the Page model. Also, the effective diffusivity coefficients for blueberries were calculated as 2.57665 × 10-12 m2/s.

: This study has been carri ed out with the “Freeze Drying" topic and freeze - drying technology (FD), which proved to be a healthy drying model that increases the shelf life of the products and preserve s their aroma values . The product that we have dr ied is Rosehip, which is utilized for the cook ing jam in winter, brew tea, which contains hi gh nutritional values and countless merits for human health. We started the study with the experiment of drying the rose hips, which were cut into 5 mm slices and removed from the seeds, by keeping them in the refrigerator. By recording the experiments of the rose hips, which were placed in our drying device in 7 samples of 100 grams, one by one. The weights of the 2, 4, 6, 8-, 10-, 12- and 14- hour experiments were measured , and a kinetic model was created also calc ulate the moisture ratio (MR). A total of 8 different kinetic drying models were studied by using the MATLAB program in the presence of experimental data, and according to the results of the experiment, X 2 : 2,156×10 -4 , RMSE: 0.011874 value was regulated. I t has been observed that the closest value of R 2 to1 is R 2 with the amount of R 2 =0.9985 . According to the results of the experiment, it was determined as the Diffusion Approach model that gave the best results among eight models. Also, we have found the effective diffusivity value, which was 1 , 99828×10 -10 m 2 /s for the mentioned Rosehip slices. It was confirmed that the calculated effective diffusivity value was within the reference range mentioned in the literature (10 -12 – 10-8 m 2 /s) for food products.