Kamil Kahveci

Buoyancy Driven Heat Transfer of Nanofluids in a Tilted Enclosure

Buoyancy driven heat transfer of water-based nanofluids in a differentially heated, tilted enclosure is investigated in this study. The governing equations (obtained with the Boussinesq approximation) are solved using the polynomial differential quadrature method for an inclination angle ranging from 0 deg to 90 deg, two different ratios of the nanolayer thickness to the original particle radius (0.02 and 0.1), a solid volume fraction ranging from 0% to 20%, and a Rayleigh number varying from 104 to 106. Five types of nanoparticles, Cu, Ag, CuO, Al2O3, and TiO2 are taken into consideration. The results show that the average heat transfer rate from highest to lowest is for Ag, Cu, CuO, Al2O3, and TiO2. The results also show that for the particle radius generally used in practice ( 0.1 or 0.02), the average heat transfer rate increases to 44% for Ra 104, to 53% for Ra 105, and to 54% for Ra 106 if the special case of 90 deg, which also produces the minimum heat transfer rates, is not taken into consideration. As for 90 deg, the heat transfer enhancement reaches 21% for Ra 104, 44% for Ra 105, and 138% for Ra 106. The average heat transfer rate shows an increasing trend with an increasing inclination angle, and a peak value is detected. Beyond the peak point, the foregoing trend reverses and the average heat transfer rate decreases with a further increase in the inclination angle. Maximum heat transfer takes place at 45 deg for Ra 104 and at 30 deg for Ra 105 and 106. DOI: 10.1115/1.4000744

Natural Convection in a Partitioned Vertical Enclosure Heated With a Uniform Heat Flux

This numerical study looks at laminar natural convection in an enclosure divided by a partition with a finite thickness and conductivity. The enclosure is assumed to be heated using a uniform heat flux on a vertical wall, and cooled to a constant temperature on the opposite wall. The governing equations in the vorticity-stream function formulation are solved by employing a polynomial-based differential quadrature method. The results show that the presence of a vertical partition has a considerable effect on the circulation intensity, and therefore, the heat transfer characteristics across the enclosure. The average Nusselt number decreases with an increase of the distance between the hot wall and the partition. With a decrease in the thermal resistance of the partition, the average Nusselt number shows an increasing trend and a peak point is detected. If the thermal resistance of the partition further declines, the average Nusselt number begins to decrease asymptotically to a constant value. The partition thickness has little effect on the average Nusselt number.

A Differential Quadrature Solution of Natural Convection in an Enclosure with a Finite-Thickness Partition

Natural convection in a rectangular enclosure divided by a partition with a finite thickness and conductivity is studied numerically. A temperature difference is imposed between the two isothermal vertical walls, and the other two walls are assumed adiabatic. Governing equations with the Boussinesq approximation are solved using the polynomial differential quadrature (PDQ) method. The results show that flow on either side of the enclosure is unicellular for low values of the aspect ratio. A multicellular flow forms the flow field in the bigger zone of the enclosure for higher aspect ratios. With increasing aspect ratio, heat transfer shows an increasing trend and reaches a maximum value. Beyond the maximum point, the foregoing trend reverses to decrease with further increase of the aspect ratio. The average Nusselt number decreases toward a constant value as the partition is distanced from the hot wall toward the middle of the enclosure. Decreasing the thermal conductivity ratio produces higher average Nusselt numbers. However, for higher aspect ratios, the increasing trend of the average Nusselt number with decreasing thermal conductivity ratio reverses to decrease as the thermal conductivity ratio is decreased further below a certain value.

Numerical simulation of natural convection in a partitioned enclosure using PDQ method

Purpose – This paper seeks to investigate the effect of a heat conducting vertical partition in an enclosure on natural convection heat transfer and fluid flow using the polynomial‐based differential quadrature (PDQ) method.Design/methodology/approach – The PDQ method with the non‐uniform Chebyshev‐Gauss‐Lobatto grid point distribution given below is used to transform the governing equations into a set of algebraic equations. After numerical discretization, the resulting algebraic equations are solved by the successive over‐relaxation iteration method.Findings – It is found that the average Nusselt number decreases towards a constant value as the partition is distanced from the hot wall towards the middle of the enclosure. Furthermore, with decreasing thermal conductivity ratio, the average Nusselt number first increases and passes a peak point and then begins to decrease. The average heat transfer rate exhibits little dependence on the width of the partition in the range taken into consideration in this ...

Determination of optimum operating conditions and simulation of drying in a textile drying process

In this study, drying behavior of viscose yarn bobbins was investigated experimentally to specify the optimum drying conditions and a drying model was proposed for simulation of drying. The experiments were conducted in a pressurized hot-air bobbin dryer, which was designed and manufactured based on the dryers used in the textile industry. Drying process was performed for various drying parameters: bobbin diameter, drying temperature, drying pressure, and volumetric flow rate of drying air. The results show that total drying time is strongly dependent on drying pressure, drying temperature, and volumetric flow rate and increase at these parameters shortens the drying time considerably. The results also show that the minimum energy consumption is for lower values of drying temperature and drying pressure and modest and higher values of volumetric flow rate. Simulation results show that the most appropriate model in describing the drying curves of viscose yarn bobbins is the stretched exponential model.

A Differential Quadrature Solution of MHD Natural Convection in an Inclined Enclosure With a Partition

Magnetohydrodynamics natural convection in an inclined enclosure with a partition is studied numerically using a differential quadrature method. Governing equations for the fluid flow and heat transfer are solved for the Rayleigh number varying from 10 4 to 10 6 , the Prandtl numbers (0.1, 1, and 10), four different Hartmann numbers (0, 25, 50, and 100), the inclination angle ranging from 0 deg to 90 deg, and the magnetic field with the x and y directions. The results show that the convective flow weakens considerably with increasing magnetic field strength, and the x-directional magnetic field is more effective in reducing the convection intensity. As the inclination angle increases, multicellular flows begin to develop on both sides of the enclosure for higher values of the Hartmann number if the enclosure is under the x-directional magnetic field. The vorticity generation intensity increases with increase of Rayleigh number. On the other hand, increasing Hartmann number has a negative effect on vorticity generation. With an increase in the inclination angle, the intensity of vorticity generation is observed to shift to top left corners and bottom right corners. Vorticity generation loops in each region of enclosure form due to multicelluar flow for an x-directional magnetic field when the inclination angle is increased further. In addition, depending on the boundary layer developed, the vorticity value on the hot wall increases first sharply with increasing y and then begins to decrease gradually. For the high Rayleigh numbers, the average Nusselt number shows an increasing trend as the inclination angle increases and a peak value is detected. Beyond the peak point, the foregoing trend reverses to decrease with the further increase of the inclination angle. The results also show that the Prandtl number has only a marginal effect on the flow and heat transfer.

Mathematical Modelling of Drying of Rough Rice in Stacks

In this study, drying behaviour of rough rice stacks up to 30 cm is simulated with several models. The suitability of models is determined by the statistical analysis by examining the values of correlation coefficient, standard deviation and mean squared deviation. The results showed that the best model to explain the drying characteristics of rough rice stack is the Midilli et al. model and the coefficients and exponent in the Midilli et al. model could be expressed as functions of drying temperatures and stack height. Statistical analyses also showed that among the models with two coefficients, that of Page, and among the models with three coefficients, that of Verma et al. and diffusion approach were acceptable models in expressing the drying behaviour of rough rice in stacks. Among the models considered here, the geometric model appeared to be the worst fit.

Heat Transfer in Continuous-Drive Friction Welding of Different Diameters

ABSTRACT Heat transfer in friction welding of similar and dissimilar cylindrical rods with different diameters is considered in the present study. The governing equations are solved numerically using an explicit finite-difference technique to determine the temperature field for various values of geometric and thermal parameters. The values of the parameters in the problem are selected as a = 1, 2, 4 for the aspect ratio, r k = 0.25, 1, 4 for the thermal conductivities ratio, and B 1 = 0.05, 0.01, 0.001 for the Biot number. The predicted temperature field is of similar form for all values of the parameters, but the radial and axial temperature gradients change at certain amounts for different values of parameters.

Microwave drying behaviour of apple slices

In this study, microwave drying behaviour of apple slices was investigated experimentally to determine the effect of microwave power on drying, energy consumption and colour quality. Microwave drying behaviour was simulated by a theoretical drying model. Suitability of several empirical and semi-empirical models in defining the microwave drying behaviour of apple slices was determined by statistical analysis. The experimental results show that the drying time, energy consumption and the colour quality of apple slices decrease considerably with an increase of microwave power. The modelling results indicate that theoretical model simulates microwave drying behaviour of apple slices very well and among the empirical and semi-empirical models, the Page model yields the best fit with the experimental data. The modelling results also show that the excess pressure inside the apple slices shows first an increasing trend and then begins to decrease as the moisture content takes lower values.

Mixed convection of water-based nanofluids in a square enclosure heated and cooled on adjacent walls

This study examines the mixed convection of water-based nanofluids in a lid-driven square enclosure heated from one side and cooled from the stationary adjacent side while the other sides are kept stationary and adiabatic. The conservation equations are solved numerically for the stream function, vorticity, and temperature using the differential quadrature method. The Grashof number is kept at a constant value of 10 4 in the present study, and the Reynolds number is varied so that the Richardson number will have values in the range of 0.1 to 10. Nanoparticles volume fraction φ is varied as 0%, 5% and 10% and the value of η the ratio of the nanolayer thickness to the original particle radius, is fixed to 0.1. The results show that the motion of the side wall and nanoparticle usage has significant effects on the flow and temperature fields. A significant increase in the average Nusselt number is seen with an increase in the volume fraction of nanoparticles and a decrease in the Richardson number.