Theoretical Prediction With Numerical and Experimental Verification to Predict Crosswind Effects on the Performance of Cooling Towers

A simple theoretical model, validated against available numerical and experimental data in the literature, is presented to predict the effects of crosswind on the performance of natural draft dry cooling towers. The intersection of asymptote method, along with scale analysis, is used to find a closed-form solution for the airflow rate at the tower exit for given crosswind speeds. The total heat rejected under a windy condition is then calculated based on the air mass flow rate at the tower exit. This theoretical model allows for parametric studies and can generate accurate data. Interestingly, the model results, expected to be accurate within an order of magnitude, are more accurate than anticipated when compared to available experimental and numerical data in the literature. In fact, the maximum relative error is observed to be 15% when current theoretical predictions are compared to available experimental data. The results of this study will be useful for future work on the development of air-cooled condensers, especially for geothermal and solar thermal power plants in Australia.     

A Hybrid Finite-Element/Finite-Difference Scheme for Solving the 3-D Energy Equation in Transient Nonisothermal Fluid Flow over a Staggered Tube Bank

This article presents a hybrid finite-element/finite-difference approach. The approach solves the 3-D unsteady energy equation in nonisothermal fluid flow over a staggered tube bank with five tubes in the flow direction. The investigation used Reynolds numbers of 100 and 300, Prandtl number of 0.7, and pitch-to-diameter ratio of 1.5. An equilateral triangle (ET) tube pattern is considered for the staggered tube bank. The proposed hybrid method employs a 2-D Taylor-Galerkin finite-element method, and the energy equation perpendicular to the tube axis is discretized. On the other hand, the finite-difference technique discretizes the derivatives toward the tube axis. Weighting the 3-D, transient, convection-diffusion equation for a cube verifies the numerical results. The L² norm of the error between numerical and exact solutions is also presented for three different hybrid meshes. A grid independence study for the energy equation preceded the final mesh. The outcome is found to be in acceptable concurrence with those from the previous studies. After the temperature field is attained, the local Nusselt number is computed for the tubes in the bundle at different times. The isotherms are also obtained at different times until a steady-state solution is reached. The numerical results converge to the exact results through refining the mesh. The implemented hybrid scheme requires less computation time compared with the conventional 3-D finite-element method, requiring less program coding.     

Adsorption Characteristics of Congo Red from Aqueous Solution onto Tea Waste

The feasibility of using tea waste (TW) as a low-cost adsorbent for the adsorption of an anionic dye (Congo red) from aqueous solution has been investigated. Adsorption in a batch process was conducted to study the effect of adsorbent dosage, initial dye concentration, contact time, pH, and temperature. The experimental data were analyzed by the Langmuir, Freundlich, and Temkin models. The adsorption system was best described by the Langmuir isotherm (R ² > 0.99). Adsorption kinetics followed a pseudo-second-order model (R ² > 0.99). The effect of mechanical treatment (vibratory mill) was also studied. The experimental results showed that using this physical treatment leads to an increase in the adsorption capacity of TW from 32.26 to 43.48 mg/g. Thermodynamic analyses revealed that the adsorption of Congo red on TW was endothermic and spontaneous in nature. The results indicated that TW can be employed as a potential low-cost adsorbent for the removal of Congo red from aqueous solution.     

Optimization of Dynamic Interfacial Tension for Crude Oil–Brine System in the Presence of Nonionic Surfactants

In this study, interfacial tension (IFT) is measured between brine and crude oil (a sample of heavy oil from an Iranian oil reservoir) in the presence of two nonionic surfactants, KEPS 80 (Tween 80) and Behamid D, at different concentrations in order to optimize the concentrations of the surfactants. The surface response method is used to design the IFT measurement experiments. The experimental design and optimization is performed using the IFT as an objective function and temperature, concentration, and time as independent variables. In addition to the IFT measurement, various experiments such as stability tests of the surfactants in NaCl brine solutions, adsorption experiments on the carbonated rock surface, and phase behavior tests are performed to investigate the behavior of KEPS 80 and Behamid D in the enhanced oil recovery process. At the end, a model using the response surface statistical technique is designed for optimization of the concentrations of the surfactants, and a surfactant molecular migration mechanism is used for explanation of the dynamic IFT variation versus time. In the case of IFT experiments, the effect of surfactant concentration (at 1000, 3000, and 5000 ppm) on the dynamic IFT is investigated. The experiments are performed at four temperatures (25, 40, 50, and 67°C). The results show that the oil–brine IFT values can be reduced to about 4 mN m⁻¹ in the presence of Behamid D and to about 1 mN m⁻¹ in the presence of KEPS 80 at low concentrations.     

A novel high dynamic range differential LNA using quartet topology

In some applications such as short-range radars, a large target can desensitize the receiver. A high dynamic range low-noise amplifier (LNA), as a key component of a transmitter/receiver module, can improve the entire system performance. This study presents a high dynamic range differential LNA that uses a differential quartet topology for the first time. The LNA shows more linearity than the conventional differential common source LNAs. For a typical 0.18 µm CMOS technology, it achieves a power gain of about 5.5 dB at 24 GHz, a low noise figure (NF) of 3.5 dB, very good linearity performance, an input-referred third-order intercept point (IIP3) of +?6.3 dBm, and an input-referred 1 dB compression point (P1dB) of ??4.5 dBm.     

An analog circuit model for drive mode of MEMS vibratory gyroscope

Microsystem Technologies - In this paper, an analog circuit model for the drive mode of a two-degree-of-freedom MEMS vibratory gyroscope is presented. This model is implemented on a printed circuit...     

An optimized system of GMDH-ANFIS predictive model by ICA for estimating pile bearing capacity

The pile bearing capacity is considered as the most essential factor in designing deep foundations. Direct determination of this parameter in site is costly and difficult. Hence, this study presents a new technique of intelligence system based on the adaptive neuro-fuzzy inference system (ANFIS)-group method of data handling (GMDH) optimized by the imperialism competitive algorithm (ICA), ANFIS-GMDH-ICA for forecasting pile bearing capacity. In this advanced structure, the ICA role is to optimize the membership functions obtained by ANFIS-GMDH technique for receiving a higher accuracy level and lower error. To develop this model, the results of 257 high strain dynamic load tests (performed by authors) were considered and used in the analysis. For comparison purposes, ANFIS and GMDH models were selected and built for pile bearing capacity estimation. In terms of model accuracy, the obtained results showed that the newly developed model (i.e., ANFIS-GMDH-ICA) receives more accurate predicted values of pile bearing capacity compared to those obtained by ANFIS and GMDH predictive models. The proposed ANFIS-GMDH-ICA can be utilized as an advanced, applicable and powerful technique in issues related to foundation engineering and its design.

     

Optimal opportunistic routing and network coding for bidirectional wireless flows

There is growing interest in recent years in routing methods for wireless networks that leverage the broadcast nature of the wireless medium and the ability of nodes to overhear their neighbors’ transmissions. Such methods include opportunistic routing (OR), which generally choose the next hop on a routing path only after the outcome of the previous transmission is known; and wireless network coding (NC), which linearly combines packets from different flows coexisting in the network. In this paper, we study the potential benefits of forwarding schemes that combine elements from both the OR and NC approaches, when traffic on a bidirectional unicast connection between two nodes is relayed by multiple common neighbors. We present a theoretically optimal scheme that provides a lower bound on the expected number of transmissions required to communicate a packet in both directions as a function of link error probabilities, and demonstrate that this bound can be up to 20% lower than with either OR or NC employed alone even in a small network. Using simulation, we further explore the control overhead in a direct implementation of the scheme with a simple coordination mechanism and show that the optimal bound can be closely approached for a wide range of link error rates.     

Multiple expectations: assessing the assumed roles of theory in relation to urban design

Designers take different approaches when dealing with urban problems. Some find solutions in existing theories, some rely on their creativity, and many take a middle way. The questions here are what they expect from theory and how they follow their expectations. This paper examines the ways in which theory is being applied within the field of urban design following on from recent discussions on this topic. The paper then identifies four models for employing theory within urban design: as servant of innovation, as scientific formulation, as a means to control wicked problems, and finally as the subject for critique. In a comparison, these four models are assessed in relation to their use within both design and research contexts. The final part of this paper examines how urban design professionals employ theory in their work within practice and academia. The paper concludes by examining the advantages and disadvantages of each model, and adds that being confined to one model of employing theory would exacerbate urban problems. Reflecting on the interviews, the paper advocates multiple models be used, specifically chosen according to the problem in hand.