Numerical study of heat transfer of laminar air flow in perforated trapezoidal corrugated plate-fin ducts

A novel trapezoidal corrugated perforated fin core is proposed in this study. The porosity of the fin surface, or perforations, is indicated to promote the unusual behavior of increasing the heat transfer coefficient, while reducing the friction factor with respect to its non-perforated counterpart, primarily due to surface transpiration, which leads to better flow mixing and successive boundary layer disturbances. This allows the heat exchanger to be built much more compact with a smaller volume and a front area. To highlight this, the results of the computational simulations for velocity and temperature fields in typical trapezoidal corrugated perforated plate-fin ducts are presented. Constant property, fully or periodically developed laminar airflow [Formula: see text] with Reynolds number [Formula: see text] passing through inter-fin passages, with fins at constant wall temperature T, in which the fin walls have perforations equally spaced along the length of the duct, is considered and a parametric study of the effects of the duct geometry, including the variation of the inclination angle [Formula: see text] of the diverging plane, the aspect ratio of the channel or period length and fin density effects [Formula: see text] and the converging-diverging ratio of the plate [Formula: see text], is performed. The results of the Fanning friction factor and the Nusselt number over the wide range of the Reynolds number, which was treated in this study, show the improved performance. The improvement is assessed quantitatively by the area goodness factor ( j/ f) relative to Re, comparison with simple flat channels. It is seen that increasing ϕ to [Formula: see text] improves the core performance; As ϕ increases beyond [Formula: see text], performance starts to decrease. j/ f increases with increasing λ; and λ = 3.6 acts as an inflection point. It is better to have a large λ value for lower Re range and vice versa. As ε increases, the performance increases; so, the highest area goodness factor value occurs at [Formula: see text]. In case 11, with [Formula: see text], [Formula: see text], and [Formula: see text] at Re = 200, compared to the non-perforated channel, the friction factor decreases about 11%, and the area goodness factor increases about 72%. Thus, the area goodness factor of the perforated case reaches 0.37.

Valuation of Machines with a Random Service Life Based on the System of National Accounts – 2008

We propose a mathematical model describing the decrease in the market value of machines (depreciation) with age in a situation where its service life is random and has a Weibull distribution. We measure the depreciation of a used machinery item using a goodness factor, that is, the ratio of its value to the value of a similar new machinery item. The model is based on the principle of anticipation of benefits adopted in the valuation theory and the discounting cash flows method. The model takes into account that machine’s technical and economic characteristics deteriorate with age and its benefits are reduced according to the hyperbolic dependence adopted in the system of national accounts SNA‑2008. We have built the dependences of average machine's goodness factor on its relative age (the ratio of the actual age to the average service life). Calculations show that the discount rate and average service life have little effect on these dependencies. This made it possible to divide the machines into three categories and propose for each of them its own dependence of the goodness factor on the relative age, which is convenient for practical use in appraisal activities.

Thermal-Hydraulic Optimization of Open Cell Metallic Foams Used as Extended Surfaces

A one-dimensional analytical validated model for predicting temperature distribution, heat transfer, pressure drop, and fluid pumping power in an open cell metal foam (OCMF) fin is developed. A foam length optimization technique based on its performance factor (PF) is proposed. Every optimized foam's efficiency is shown to be 33.2%, regardless of its PPI or porosity. Although it can be applied to other porous materials, the model has been illustrated for aluminum foams with 5-40 pores per inch (PPI) and 0.88-0.96 porosity (e). The highest PPI, lowest porosity foam gives the best unit area goodness factor f_u=j_H/f, heat transfer, and heat transfer per unit volume Q ?_V, while the greatest goodness factor f (heat transfer rate to fluid pumping power) is achieved by the lowest PPI, lowest porosity foam. The highest PPI, highest porosity foam yields the best heat transfer per unit mass Q ?_M. Thus, optimum foam selections strongly depend on the application. An often used fin optimization criterion recommends that the fin effectiveness should equal or exceed 2. The present study shows that the effectiveness of any optimized foam always exceeds 2. However the converse, i.e., requiring the foam effectiveness to at least equal 2, does not guarantee an optimal foam, which implies that the PF-based optimization criterion is an inclusive one. It is also proved that a previously suggested optimization criterion of maximizing a foam's geometric mean efficiency will result in a sub-optimal foam design.

Analysis for Joint Delay-Power Tradeoff with Buffer/Channel-Aware and Its FPGA Implementation in Wireless Sensor Networks

In this paper, we aim to investigate the delay-power tradeoff problem which is attracting widespread interest due to its importance in wireless technology. This research has two main objectives. First, to assess the effect of different system parameters on the performance metrics. Second, to provide a solution for this optimization problem. A two-state, slow-fading channel is categorized into good and bad channel states. An adaptive transmission and random data arrivals are considered in our model. Each channel category has its own Markov chain, which is used in modeling the system. A joint Buffer-Aware and Channel-Aware (BACA) problem was introduced. In addition, an enhanced iterative algorithm was introduced for obtaining a sub-optimal delay-power tradeoff. The results show that the tradeoff curve is piecewise linear, convex and decreasing. Furthermore, a channel-aware system was investigated to provide analysis of the effect of system parameters on the delay and power. The obtained results show that the dominant factors that control the system performance are based on the arrival rate and the channel goodness factor. Moreover, a simplified field programable gate array (FPGA) hardware implementation for the channel aware system scheduler is presented. The implementation results show that the consumed power for the proposed scheduler is 98.5 mW and the maximum processing clock speed is 190 MHz.

Statistical Goodness Factor ‘ᴦ’ for Image Fusion Algorithm Based on UGGD Parameters

In this paper we propose a novel pyramid decomposition based Image fusion metric, Gamma Factor or Goodness of Fit ‘ᴦ’ which describes the statistically amount of information fused by the image fusion algorithm. We first apply steerable pyramid decomposition and then a fitting model for Univariate Generalised Gaussian Distribution (UGGD) parameter estimation. From the UGGD; P and S fitting model coefficients are computed. To estimate the optimum weights for computation a huge data set of complimentary images are used. Using these weights, amount of information contributed by each image to form a fused image can be estimated. Experimental results show the tremendous matching with the quantise information

Performance Improvement of a Fin-Tube Heat Exchanger Using Rectangular Winglet as Vortex Generator

Heat transfer performance of fin-tube heat exchanger can be augmented by using longitudinal vortex generators. Numerical simulations have been performed in the present work for investigating the effect of punching a rectangular winglet having hole from fin surface, on the heat transfer and flow resistance characteristics in a fin-tube heat exchanger. The concept of punching out a rectangular winglet having hole from the fin-plate surface is being proposed here and studied in two configurations namely, common flow down and common flow up. Comparisons on the basis of heat transfer and flow resistance characteristics have been drawn for all the configurations under consideration using Colburn’s factor (j), friction factor (f) and performance evaluation criterion (PEC) also known as area goodness factor (j/f). Investigations have been performed considering Reynolds number in the range of 1500 to 9000 and angle of attack as 45°. The result clearly indicates that punched out rectangular winglet with hole having common flow down configuration at upstream location as exhibiting the best thermal performance, followed by common flow up at upstream location and, common flow down at downstream location.

Numerical laminar forced convection modelling in a ceramic and concrete solar collector with non-circular duct

The paper presents simulations of laminar forced convection in non-circular piping of flat solar collectors made of ceramics or concrete, which are characterized by a low thermal conduction coefficient. The cross-sections of piping in the shape of a regular polygonal, elliptic, superellipse (Lamé curve) and Cassini oval were used for the calculations. In order to perform the simulation, a simplified two-dimensional model of laminar forced convection in a straight axis duct was used and the issue of H2 (constant axial wall heat flux with uniform peripheral wall heat flux) for materials with low thermal conductivity was applied. The calculations were made using the boundary element method (BEM) in a calculation program written by Fortran by the author. In the work, the number of Poiseuille, Nusselt and dimensionless parameters for the evaluation of heat exchangers such as the area goodness factor and the volume goodness factor were determined in the function of characteristic geometrical parameters of the assumed cross-sectional shapes of the flat solar collector piping.

Fanning friction (f) and colburn (j) factors of a louvered fin and flat tube compact heat exchanger

In the present study, the heat transfer and pressure drop characteristics of air over the louvered fins in a compact heat exchanger, used as a radiator in the automobiles have been experimentally investigated. The experiments were conducted at various flow rates of air and the results showed a decrease in goodness factor of 22.7% with respect to increase in Reynolds number from 231 to 495. The experimental results were compared with the CFD results and the ?f? and ?j? factors from the CFD analysis are in good agreement with the experimental data. Also, the experimental ?f? and ?j? factors were compared with the predicted values from the available correlations in the literature for the louvered fin and tube compact heat exchangers. The large deviation of the predicted results revealed that the correlations are not reliable for the design of the compact heat exchanger. Hence, the CFD analysis is more advantageous for the optimal design of compact heat exchanger, which also reduces the experimentation time and cost.