Analysis of flux-base fins for estimation of heat transfer coefficient

Exact solutions are given for the transient temperature in flux-base fins with the method of Green’s functions (GF) in the form of infinite series for three different tip conditions. The speed of convergence is improved by replacing the steady part by a closed-form steady solution. For the insulated-tip case, a quasi-steady solution is presented. Numerical values are presented and the conditions under which the quasi-steady solution is accurate are determined. An experimental example is given for estimation of the heat transfer coefficient (HTC) on a non-rotating roller bearing, in which the outer bearing race is treated as a transient fin.     

Data dependent systems technique: a methodology with an application to human systems

The objective of this paper is to introduce the application of Data Dependent Systems (DDS) methodology to the field of ergonomics. Many current techniques in ergonomics utilize static models, which can have significant limitations. DDS is a stochastic modelling and analysis technique that can be used to capture the dynamics of a system through quantitative analysis of the available data. DDS has been successfully applied to the analysis of manufacturing processes and the surfaces generated by those processes. In this research, DDS was used to analyse time-based hand-skin temperature data for the evaluation of two types of glove liners to be used underneath latex gloves. DDS was able to capture the differences between the two glove liners and the two subjects. The implications of the results and the potential of the DDS methodology are discussed.     

Thermal models of railroad wheels and bearings

The rolling surface for railroad wheels can be a heat source that may have an impact on the performance of the wheel bearing. In this study, experimental data from an electrically-heated railroad wheel set is analyzed by constructing thermal models of the wheel set. A steady finite-element model, a steady-analytical model, and a transient lumped-parameter model are discussed. Model parameters are determined from careful comparisons with the experimental data. The lumped-parameter model given here is intended as a simple predictive tool for determining when wheel heating caused by rail operations will have an impact on bearing temperature. The model parameters found in this study will also be useful as experimentally-validated boundary conditions in ongoing finite-element studies of heated wheels.     

Bi-site Analysis of Meteorological Drought Duration: Theoretical Modeling and Application

Droughts are regional incidents that threat the environment and limit most of the socio-economic activities. Given the dry and wet state sequences for two sites, X_t^{( 1 )}X_t^{\left( 1 \right)} and X_t^{( 2 )}X_t^{\left( 2 \right)} , this paper presents a procedure to reduce the two sequences X_t^{( 1 )}X_t^{\left( 1 \right)} and X_t^{( 2 )}X_t^{\left( 2 \right)} to one sequence Z _t for the purpose of simplifying the analysis of drought duration at two sites jointly. Theoretical models to evaluate the expected value and the variance of the process Z _t and the occurrence probability of the dry state at two sites jointly are presented and verified using simulation experiments. Historical data for the period 1939–2005 and generated rainy season precipitation data for two gauging sites in Central Jordan, namely Amman Airport and Madaba, is used in the present study to investigate the occurrence of droughts. The joint analysis of drought duration obtained using the historical precipitation at the two sites appears to be inconsistent especially for droughts of duration longer than 3 years. On the other hand, the joint analysis of drought duration obtained theoretically by employing the characteristics of the process Z _t are found to match well with the more reliable drought statistics obtained empirically by analyzing the long generated precipitation. Considering 25 years planning horizon, droughts of 1, 2, and 3 years duration are the most frequent droughts in the region of Central Jordan. The return period of such regional droughts ranges from 8–30 years.     

Investigation of the effect of superheating on the performance of a refrigeration system using low temperature different refrigerant blends in porous media

A comparative experimental investigation on the effect of superheating of R‐22, R‐404A, R‐407C, and R‐422A as low‐temperature refrigerant blends on the performance of a vapor compression refrigeration system is conducted. Empty and porous evaporators with porosities of (40%, 43%, and 45%) are used during the tests, to predict good alternatives to the refrigerant R‐22, which has high ozone depletion potential and high global warming potential. Condensation, evaporation temperatures, degree of subcool are kept constants at 40°C, ?26°C, and 6°C (±0.5°C), respectively. The effect of superheating on the compressor discharge temperature, evaporating pressure drop, evaporating capacity, volumetric refrigeration capacity and coefficient of performance (COP) of these refrigerants has been analyzed. Refrigerants, R‐422A and R‐404A showed greater performances than that of R‐22. The percentages of increase in evaporation capacities of R‐407c, R‐22, R‐404A, and R‐422A are approximately 144%, 168%, 146.3%, and 161.5%, respectively, when changing the degrees of superheat from 6°C to 16°C and changing the porosity from empty evaporator to 40%. The percentages of increase in COP are approximately 319%, 320%, 312%, and 350%, respectively. The percentages of increase in evaporation capacities of R‐422A and R‐404A when compared with R‐22 under the same conditions are 18.6% and 8.8%, respectively, while the percentages of increase in COP when compared with R‐22 are 17% and 12%, respectively.     

Magnetic energy-based feature extraction for low-quality fingerprint images

In fingerprint recognition systems, feature extraction is an important part because of its impact on the final performance of the overall system, particularly, in the case of low-quality images, which poses significant challenges to traditional fingerprint feature extraction methods. In this work, we make two major contributions: First, a novel feature extraction method for low-quality fingerprints images is proposed, which mimics the magnetic energy when attracting iron fillings, and this method is based on image energies attracting uniformly distributed points to form the final features that can describe a fingerprint. Second, we created a new low-quality fingerprints image database to evaluate the proposed method. We used a mobile phone camera to capture the fingerprints of 136 different persons, with five samples for each to obtain 680 fingerprint images in total. To match the computed features, we used the dynamic time warping and evaluated the performance of our system based on k-nearest neighbor classifier. Further, we represent the features using their probability density functions to evaluate the method using some other classifiers. The highest identification accuracy recorded by several experiments reached 95.11% using our in-house database. The experimental results show that the proposed method can be used as a general feature extraction method for other applications.     

Deeply Buried Thermoplastic Pipe Field Performance over Five Years

This paper presents the updated long-term field performance data from the thermoplastic pipe deep burial study that the writers first initiated in the summer of 1999. The data from the past four to five years are presented in terms of pipe deflections and soil pressure measured at the pipe crown. Examinations of the historic field performance data revealed pipe-soil interaction behavior that had not been reported previously. The long-term pipe performance of both polyvinyl chloride and high density polyethylene pipes installed under at least 6.1?m (20?ft) of soil fill was characterized with nearly constant deflections/circumferential shortening and fluctuating soil pressures. Review of the long-term soil pressure data revealed some interesting trends regarding the relationships among pipe material type, pipe wall design, and fill height. Detailed review of the soil pressure data also led to a reasonable speculation that the seasonal fluctuations of environmental (air temperature, soil moisture) conditions caused the fluctuations in the peripheral soil pressure. Theoretical analysis based on the full-field elastic solutions showed that the temperature most likely had a much larger influence on the soil pressure fluctuations than the changes in the soil moisture conditions.     

TD-DFT and optical properties of 9,9-dioctyl-9Hfluorene-based oligomer in a thin film and design of DFB laser using ellipsometry studies

Journal of Materials Science: Materials in Electronics - 9,9-dioctyl-9H-fluorene (9DOF) is one of the most important molecule structures with unique photophysical properties. We investigated the...     

Spatial climate variation pattern and regional prediction of rainfall in Jordan

Currently Jordan is facing various water problems accompanied by rapid population growth, urbanisation and industrialisation. It is of outmost importance to search for water resources augmentation possibilities leading to decision‐making procedures by addressing the rainfall sources as the main water resources in Jordan, through refined techniques. Point cumulative semivariogram (PCSV) samples are analysed in order to identify the regional dependence of the rainfall phenomena. Amman station is taken as a pivot site because of its location in the centre of the Kingdom, where the samples of the PCSV are calculated for eight systematic directions. Standard regional dependence function (SRDF) is obtained from the sample PCSV and the weighted average procedure is applied with the help of SRDF to predict the rainfall amounts. The radius of rainfall influence is determined for Amman in each direction. The cross‐validation methods are used to predict the rainfall in Amman using different samples representing along each direction. The result of cross‐validation method is acceptable in all samples with relative error not exceeding 10%, except in the desert sides where larger errors indicate weak regional dependence.     

Effect of Darcy,Reynolds, and Prandtl Numbers on the Performance of Two‐Phase Flow Heat Exchanger Filled with Porous Media

Experimental investigation of two‐phase laminar forced convection in a single porous tube heat exchanger is presented. The effect of Darcy, Reynolds, and Prandtl numbers on the performance of this heat exchanger during the condensation process of carbon dioxide at different test conditions were investigated. Gravel sand with different porosities is used as a porous medium. The flow in the porous medium is modeled using the Brinkman–Forchheimer‐extended Darcy model. Parametric studies are also conducted to evaluate the effects of porosity and Reynolds and Prandtl numbers on the heat transfer coefficient and the friction factor. A dimensionless performance parameter is developed in order to be used in evaluating the porous tube heat exchanger based on both the heat transfer enhancement and the associated pressure drop. The study covers a wide range of inlet pressure (P_in), mass flow rate (), porosity of gravel sand (ε), and Darcy number (Da) which ranged: 34.5 ≤ P_in ≤ 43 bars, 8 * 10^{? 5} ≤ ≤ 16 * 10^{? 5} kg/s, 34.9% ≤ ε ≤ 44.5%, 1.6 * 10^{? 6} ≤ Da ≤ 5 * 10^{? 6}, respectively. The study predicted the combined effect of the Reynolds number, Darcy number, porosity, and Prandtl number on the heat transfer and pressure drop of carbon dioxide during the condensation process in a porous medium. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21117