Rong-Hua Yeh

Fins with temperature dependent surface heat flux—I. Single heat transfer mode

Abstract Involved in all possible types of heat transfer, the thermal characteristics of a single fin with and without heat transfer at its tip is studied. The heat transfer coefficient is assumed to vary with a power-law-type formula. Based on the value of the exponent, the problem is categorized into three regimes. The temperature distribution and heat transfer rate are given in implicit forms and solved exactly. No solution is found when the fin parameter exceeds a specific value for a negative exponent. Besides, two solutions are detected when the fin parameter is smaller than this value, which is related to the thermal instability. Results from analysis are compared with experimental data.

Fins with temperature dependent surface heat flux—II. Multi-boiling heat transfer

Abstract An analytical and experimental study is conducted for a fin when various types of boiling occur simultaneously at adjacent locations on its surface. The heat transfer coefficient is taken as a power function of wall superheat in each heat transfer mode. The temperature distribution as well as the variation of length in each section is calculated for different base temperatures. Hysteresis effects and the sudden change in total heat transfer rate are particularly noted. Experiments were carried out with 2.5 cm diameter copper rods with boiling liquids of water and isopropyl alcohol. The results from theory are compared with experimental data.

Errors in one-dimensional fin optimization problem for convective heat transfer

The purpose of this study is first to determine the optimum dimensions of a one-dimensional longitudinal rectangular fin and a cylindrical pin fin. To circumvent the tedious procedures in solving the two-dimensional fin problems, a modified one-dimensional solution for fin optimization is also presented. In addition, special cases of fins with insulated tips are also taken into account

Optimum longitudinal convective fin arrays

This study presents the optimum design for longitudinal fin arrays in forced convection. Rectangular, convex-parabolic-profile, triangular, and concave-parabolic-profile fins are taken into consideration in the analysis. The aspect ratio, interfin spacing, and heat transfer characteristics of the optimized fin arrays are investigated with a given geometry of base plate, fin area, and constant thermal properties. A comparison in the total heat duties as well as the efficiencies of the four different arrays is also made. The results of this work are presented in dimensionless form for the convenience of parametric study and design analysis.

Optimum configuration of a fin for boiling heat transfer

Abstract Based on the principle of minimum volume, an optimum shape of fin is proposed in this study. The outer appearance is essentially like a cylindrical fin and the excavated part is in the inner portion of the fin. First, the surface heat flux is assumed to follow a power-law dependence. With the aid of one-dimensional analysis, the temperature distributions and the profiles of the excavation hole are calculated for various single heat transfer modes. Secondly, the boiling curve of isopropyl alcohol on copper surface is used as an input to the model. The base temperature in the film boiling regine is taken and the optimum geometry is presented. Finally, the efficiency based on the volume and heat duty is discussed.

Analysis of thermally optimized fin array in boiling liquids

Abstract Considering temperature dependent heat transfer coefficient, an optimum longitudinal fin array is investigated. The heat transfer coefficient is assumed to vary with a power-law-type formula. The heat transfer from tips of an array fins is taken into consideration. For convenience of design, two approaches in the optimization of array system are given. The system is optimized by maximizing the heat dissipation of the fin array at a fixed total fin volume. It shows that the aspect ratios of fins for an optimized array is larger than that of a single optimum fin. The results of this work are all presented in dimensionless form for the convenience of design analysis. In addition, results from this study are compared with the experimental data of previous works.

On optimum spines

This article presents the optimum dimensions and heat transfer characteristics of spines for cylindrical, convex parabolic, conical, and concave parabolic profiles. With a derived solution form, the optimum base diameter, length, heat dissipation, temperature profile, and efficiency of spines are obtained by fin parameter and tip temperature. The temperature-dependent heat transfer coefficient is assumed to be a power-law type. It is found that the optimum dimensions of a spine are functions of fin volume, heat transfer coefficient at fin base, and thermal conductivity. For a fin with least material, the optimum conditions are also obtained. It shows that the results are solely related to the heat transfer mode on the fin surface. To facilitate the thermal design of heat transfer components, simple mathematical expressions as well as design charts are presented. 15 refs.

Optimum spines with temperature dependent thermal parameters

Abstract Based on the principle of minimum volume, an optimum shape of spine is proposed at a given heat duty, base temperature, and fin length. Both the thermal conductivity and heat transfer coefficient are temperature dependent. In this study, a power-law type wall heat flux is employed. A uniform temperature is assumed at the fin base whereas two kinds of boundary at the fin tip are considered. First, a specified heat transfer rate is prescribed at the free end. Second, the outer edge of the fin is also subject to a power-law type surface heat flux and dissipates energy to the ambient fluids. Special cases of negligible heat transfer from fin tip and zero tip temperature are investigated. The temperature distributions and the profiles of the optimum fins are calculated for various single heat transfer modes. The results are presented in non-dimensionalized form for the convenience of parametric study and design analysis.

Transient Three-Dimensional Analysis of Gas Tungsten Arc Welding Plates

In this study, a numerical scheme of Douglas-Gunn is employed to solve the three-dimensional transient heat conduction problem in welded plates. The heat transfer characteristics as well as the physical properties of base materials for this problem are affected by the moving heat source powered by input voltage. Therefore, to simulate the real situations, the intensity of the heat source is assumed to follow a Gaussian distribution in spatial coordinates. Various parameters such as heat input, welding speed, radius of heat source, dimension, and material of the welded plates are considered. In the welding of thin plates, the welding problem can be mostly assumed to be two-dimensional in heat transfer if full penetration of the weld pool is obtained. In addition, good quality of welding is obtained if the workpiece is properly preheated in welding 6061 aluminum plates. Finally, a series of experiments is conducted to verify the theoretical results.

Numerical Analysis of Laminar Flow and Heat Transfer in Internally Finned Tubes

In this study, fully developed laminar flow and convective heat transfer in an internally finned tube heat exchanger are investigated numerically. The flow is assumed to be both hydrodynamically and thermally developed with uniform outside wall temperature. Parameters of the thickness, length, and number of fins and thermal conductivity ratio between fin and working fluid are varied to obtain the friction factor as well as Nusselt number. The results show that the heat transfer improves significantly if more fins are used; however, the pressure drop turns out to be large in this heat exchanger. In addition, it is found that the emergence of closed-loop isotherms between the areas of two neighboring fins leads to heat transfer enhancement in the internally finned tube. When the fin number is smaller than 14, there appears a maximum Nusselt number at about 0.8 of the dimensionless fin length. Finally, an experiment is conducted to verify the numerical results.