Nevin Celik

Heat Transfer and Friction Factor of Coil-Springs Inserted in the Horizontal Concentric Tubes

The goal of this investigation is to obtain definitive information about the heat transfer characteristics of circular coil-spring turbulators. This is achieved by measuring the wall temperatures on the inner tube of the exchanger. Also the inlet and outlet temperatures and pressure loss of the fluid are measured. These results are parametrized by Reynolds numbers (2500 <Re < 12, 000), outer diameters of the springs (D s = 7.2 mm, 9.5 mm, 12 mm, and 13 mm), numbers of the springs (n =4, 5, and 6), and the incline angles of the springs (θ=0 deg, 7 deg, and 10 deg). Additionally, another goal of this work is to quantify the friction factor f of the turbulated heat exchanger system with respect to aforementioned parametric values. As a result, it is found that increasing spring number, spring diameter, and incline angle result in significant augmentation on heat transfer, comparatively 1.5-2.5 times of the results of a smooth empty tube. By the way, friction factor increases 40-80 times of the results found for a smooth tube. Furthermore, as a design parameter, the incline angle has the dominant effect on heat transfer and friction loss while spring number has the weakest effect.

Exergy Analysis of Coil-Spring Turbulators Inserted in the Horizontal Concentric Tubes

In this study, to obtain definitive information about the effects of spring-type turbulators located in the inner pipe of a concentric heat exchanger, the rates of exergy transfer Nusselt number (Nu e ) and exergy loss (E * ) were obtained. The results were parametrized by the Reynolds number (2500<Re<12,000), the outer diameter of the spring (D s = 7.2 mm, 9.5 mm, 12 mm, and 13 mm), the number of the springs (n =4, 5, and 6), and the incline angle of the spring (θ = 0 deg, 7 deg, and 10 deg). It is found that increasing those parameters results in a significant augmentation on exergy transfer comparative to the results of a smooth empty tube. A new term, exergy transfer Nusselt number, is derived in this paper. This term includes both irreversibility due to temperature gradient on the heat transfer surface and irreversibility due to pressure loss of the system. Hence, it is observed that optimum values of independent parameters for a constant surface temperature tube can be determined by this value. With regard to the maintained data, the irreversibility of heat transfer and pressure loss increases with increasing Re. However, at a certain value of Re, the increment rate of the irreversibility of heat transfer decreases, while the increment rate of the irreversibility of pressure loss increases. These results will contribute to adjust the system parameters such as the pump power and other independent parameters more easily.

TAGUCHI METHOD AS A MEANS FOR EXTRACTING CAUSE AND EFFECT RELATIONS AND FOR IMPROVING THE EFFECTIVENESS OF NUMERICAL SIMULATION

The performance of the perforated plates in fluid-flow applications is evaluated by measuring the pressure drop of the working fluid. The purpose of this investigation is to determine how different parameters affect the capability of the perforated plates and modify the design by using a design of experiment analysis, namely Taguchi method for optimization. The flow characteristics, which were obtained by the Computational Fluid Dynamics (CFD) software package ANSYS-CFX, were used for this analysis. nThe design parameters which affect the pressure loss are Reynolds number (A), porosity (B), non-dimensional thickness of the plate (C) and hole pattern (D). The level of importance of the design parameters are determined by use of analysis of variance method, ANOVA. According to the analysis, the optimum values are obtained for the case A8B2C2D1 (Re = 15000, porosity = 50.3, t/D = 1, and staggered hole). The most effective design parameter on the results is found as porosity (92%), while the least effective is the hole pattern (0.2%). A special dividend of this work was to demonstrate the capabilities of the Taguchi Method as a powerful means of increasing the effectiveness of numerical simulation.The performance of the perforated plates in fluid-flow applications is evaluated by measuring the pressure drop of the working fluid. The purpose of this investigation is to determine how different parameters affect the capability of the perforated plates and modify the design by using a design of experiment analysis, namely Taguchi method for optimization. The flow characteristics, which were obtained by the Computational Fluid Dynamics (CFD) software package ANSYS-CFX, were used for this analysis. nThe design parameters which affect the pressure loss are Reynolds number (A), porosity (B), non-dimensional thickness of the plate (C) and hole pattern (D). The level of importance of the design parameters are determined by use of analysis of variance method, ANOVA. According to the analysis, the optimum values are obtained for the case A8B2C2D1 (Re = 15000, porosity = 50.3, t/D = 1, and staggered hole). The most effective design parameter on the results is found as porosity (92%), while the least effective is the hole pattern (0.2%). A special dividend of this work was to demonstrate the capabilities of the Taguchi Method as a powerful means of increasing the effectiveness of numerical simulation.