Simplified Mathematical Expressions Research Articles

Prediction of Gas-Pulsation Frequency To Reduce Slug Length in Gas/Liquid Horizontal-Pipe Flow

Summary Very long slugs reaching several hundreds of pipe diameters may appear when transporting gas and liquid in horizontal pipes. Such slugs may cause serious operational and system failures. One could avoid the long slugs by pulsating the gas phase at the inlet at a specific range of frequencies. The present paper provides a simplified mathematical expression for the optimum gas-pulsation frequency. Predictions of the pulsation frequency for different flow conditions and pipe diameters are presented. Comparisons with available experiments are satisfactory.

Sizing and Economic Analysis of Standalone PEM Fuel Cell Systems for Residential Utilization

This study discusses the economic utilization of proton exchange membrane fuel cell (PEMFC) based on cost of energy (COE) to supply residential electrical and thermal loads. The fuel cell system is sized using simplified mathematical expressions considering the stack degradation and the system salvage value at the end of its life time. The study is based on a 5 kWh/day residential loads with a peak load power of 1300W. Two scenarios for economic survey are studied. The first scenario is to find the commercial price for each FC component considering that the supply fuel is hydrogen. The other scenario is for a complete FC system commercial price considering that the supply fuel is natural gas. The economic analyses are based on the actual sale prices in the market. The COE of the fuel cell system is compared with previous work by the authors for the same residential ratings but supplied from a stand-alone photo voltaic system (SAPV). The analysis results show that the COE relies heavily on the capital cost of the system.

Sizing and economic analysis of stand-alone PEM fuel cell systems for residential utilization

This study discusses the economic utilization of proton exchange membrane fuel cell (PEMFC) based on cost of energy (COE) to supply residential electrical and thermal loads. The fuel cell system is sized using simplified mathematical expressions considering the stack degradation and the system salvage value at the end of its life time. The study is based on a 5 kWh/day residential load with a peak load power of 1300 W. Two scenarios for economic survey are studied. The first scenario is to find the commercial price for each FC component considering that the supply fuel is hydrogen. The other scenario is for a complete FC system commercial price considering that the supply fuel is natural gas. The economic analyses are based on the actual sale prices in the market. The COE of the fuel cell system is compared with previous work by the authors for the same residential ratings but supplied from a stand-alone photo voltaic system (SAPV). The analysis results show that the COE relies heavily on the capital cost of the system.

Lexicographic fuzzy multi-objective model for minimisation of exceptional and void elements in manufacturing cell formation

This research proposes a lexicographic fuzzy multi-objective model based on perfect grouping for concurrent solving the part-family and machine-cell formation problems in a cellular manufacturing system. New simplified mathematical expressions of exceptional and void elements are proposed, opposing conventional quadratic and absolute functions. The main objectives of the proposed solution model, that is, the minimisation of both the number of exceptional elements and the number of void elements is defined by fuzzy goals as pre-emptive ordering. A lexicographic fuzzy goal model is developed to enhance cell performance and machine utilisation simultaneously. A satisfactory efficient solution can easily be obtained, and alternative solutions can also be generated by capturing flexibility of the proposed fuzzy multi-objective programming model. The formulated model can be solved by existing integer programming solvers. Finally, the evaluation of cell formation problems is briefly discussed to show the performance of the proposed model.

Technical performance evaluation of stand-alone photovoltaic array for outdoor field conditions of New Delhi

In this communication, an attempt has been made to investigate the performance assessment of a solar photovoltaic (PV) array system based on electrical energy output and power conversion efficiency. Simplified mathematical expressions for evaluating performance indices using experimental observations for entire PV array and its individual component subarrays on daily, monthly and annual basis have also been developed. Experiments have been carried out on two individual 1.2 kW p and 1.12 kW p component subarrays of 2.32 kW p stand-alone PV array system for climatic condition of New Delhi (latitude: 28°35′N, longitude: 77°12′E and an altitude of 216 m above mean sea level). Individual performances of both component subarrays were evaluated and its effect on the actual performance of entire PV array has been presented. Numerical computation was carried out for a typical clear day in the month of July 2010. It was found from experimental results that daily power conversion efficiency of entire PV array and its component subarrays1 and 2 were 6.24%, 9.5% and 3.9% respectively. For more effective performance assessment of PV array/subarrays, on field experimental performance results have been compared with the rated (max.) results estimated at STC and also with the maximum performance results estimated for actual climatic conditions as obtained during experimentation.

Simplified method of sizing and life cycle cost assessment of building integrated photovoltaic system

This paper presents methodology to evaluate size and cost of PV power system components. The simplified mathematical expressions are given for sizing of PV system components. The PV array size is determined based on daily electrical load (kWh/day) and number of sunshine hours on optimally tilted surface specific to the country. Based on life cycle cost (LCC) analysis, capital cost (US$/kW P) and unit cost of electricity (US$/kWh) were determined for PV systems such as stand-alone PV (SAPV) and building integrated PV (BIPV). The mitigation of CO 2 emission, carbon credit and energy payback time (EPBT) of PV system are presented in this paper. Effect of carbon credit on the economics of PV system showed reduction in unit cost of electricity by 17–19% and 21–25% for SAPV and BIPV systems, respectively. This methodology was illustrated using actual case study on 2.32 kW P PV system located in New Delhi (India).

Leak Detection in a Pipeline Using Modified Line Volume Balance and Sequential Probability Tests

The use of statistical tools to improve the decision process within leak detection is becoming a common practice in the area of computer pipeline monitoring. Among these tools, the sequential probability ratio test is one of the most named techniques used by commercial leak detection systems (Zhang and Di Mauro, 1998, “Implementing a Reliable Leak Detection System on a Crude Oil Pipeline,” Advances in Pipeline Technology, Dubai, UAE). This decision mechanism is based on the comparison of the estimated probabilities of leak or no leak observed from the pipeline data. This paper proposes a leak detection system that uses a simplified statistical model for the pipeline operation, allowing a simple implementation in the pipeline control system (Di Blasi, M., 2004, “Detección y localización de fugas en sistemas de transporte de fluidos incompresibles,” MS thesis, Universidad Nacional de La Plata, Buenos Aires, Argentina). Applying real-time recursive linear regression to volume balance and average pipeline pressure signals, a statistically corrected volume balance signal with reduced variance is derived. Its average value is zero during normal operation whereas it equals the leak flow under a leak condition. Based on the corrected volume balance, differently configured sequential probability ratio tests are presented to extend the dynamic range of detectable leak flow. Simplified mathematical expressions are obtained for several system performance indices, such as spilled volume until detection, time to leak detection, minimum leak flow detected, etc. Theoretical results are compared with leak simulations on a real oil pipeline. A description of the system tested over a 500 km oil pipeline is included, showing some real data results.

Lipase Surface Diffusion Studied by Fluorescence Recovery after Photobleaching

We have analyzed surface diffusion properties of a variant of Thermomyces lanuginosa lipase (TLL) on hydrophilic silica and silica methylated with dichlorodimethylsilane (DDS) or octadecyltrichlorosilane (OTS). For this study a novel method for analysis of diffusion on solid surfaces was developed. The method is based on fluorescence recovery after photobleaching using confocal microscopy. When a rectangular area of the sample was photobleached, fluorescence recovery could be analyzed as one-dimensional diffusion, resulting in simplified mathematical expressions for fitting the data. The method was initially tested by measuring bovine serum albumin diffusion on glass, which led to a diffusion coefficient in good correspondence to earlier reports. For the analysis of TLL diffusion, ellipsometry data of TLL adsorption were used to calibrate fluorescence intensity to surface density of lipase, enabling measurements of the diffusion coefficient at different surface densities. The average diffusion coefficient was calculated in two time intervals after adsorption. Mobile fraction and diffusion coefficient were lowest on the OTS surface, when extrapolated to infinite surface dilution. Moreover, the diffusion rate decreased with time on the hydrophobic surfaces. Our observations can be explained by the surface dependence on the distribution of orientations and conformations of adsorbed TLL, where the transition from the closed to the catalytically active open and more hydrophobic structure is important.

A Study on Residential Clothes Drying Using Waste Heat Rejected from a Split-Type Room Air Conditioner (RAC)

This article reports on a study of developing a novel residential clothes dryer using waste heat rejected from a room air conditioner. An experimental rig has been set up and extensive experimental work under various operating conditions carried out. A simplified mathematical expression (SME) for the clothes drying process using rejected waste heat from a RAC has also been developed and validated by the experimental results. The study results showed that in tropical or sub-tropical regions, where air conditioning is operated for at least 7–8 months in a year, the use of waster heat from an air cooled RAC can achieve both effective clothes drying and energy use reduction.

A quantitative framework for evaluating the mass balance of in-stream organic debris

A quantitative framework is developed for analyzing the mass budget of in-stream woody debris. Wood budgets are necessary for defining the relative importance of different recruitment processes over short and long periods, for designing spatially explicit simulation models, and for estimating the range of variability. The framework is used to analyze century-long patterns of large woody debris in streams that are governed by episodic forest death (fire and wind), forest growth and chronic mortality, bank erosion, mass wasting, decay, and stream transport. Simplified mathematical expressions are used to represent climatic, hydrologic, geomorphic, and biotic processes. Results are expressed in terms of time series and probability distributions. Predictions include that in areas of longer fire rotation (500 years) toppling of fire-killed trees comprises only 15% of the long-term wood budget yet chronic stand mortality that affect the large standing forest biomass ensures continuous large volumes of wood in streams. In contrast, toppling of fire-killed trees in forest environments with shorter fire rotations (150 years) comprise about 50% of the wood budget and indicates that field observers have a significantly higher chance of encountering low wood volumes in streams. Wood recruitment by bank erosion should increase irregularly downstream and bank erosion recruitment should exceed mortality recruitment at a bank erosion rate of approximately 5 cm per year. Recruitment from debris flows represents the single largest point source of woody debris to streams. The rarity of debris flows, in conjunction with a 3% per year annual decay rate, limits the contribution of wood from debris flows to about 12% of the long-term wood budget. Fluvial transport of wood promotes an increase in both inter-jam spacing and jam volume downstream. The proportion of woody debris transported into a reach in comparison to lateral recruitment approaches an asymptotic maximum of 50% when tree height approaches channel width. The relationships among process rates, their spatial variance across landscapes, and the resulting probability distributions of long-term patterns of wood abundance are proposed as a set of general theoretical principles. New data on wood supply and storage at the network scale are needed to fully test the predictions made in this analysis.

Voltage-based maximum power point tracking control of PV system

Photovoltaic (PV) generators exhibit nonlinear v-i characteristics and maximum power (MP) points that vary with solar insulation. An intermediate converter can therefore increase efficiency by matching the PV system to the load and by operating the solar cell arrays (SCAs) at their maximum power point. An MP point tracking algorithm is developed using only SCA voltage information thus leading to current sensorless tracking control. The inadequacy of a boost converter for array voltage based MP point control is experimentally verified and an improved converter system is proposed. The proposed converter system results in low ripple content, which improves the array performance and hence a lower value of capacitance is sufficient on the solar array side. Simplified mathematical expressions for a PV source are derived. A signal flow graph is employed for modeling the converter system. Current sensorless peak power tracking effectiveness is demonstrated through simulation results. Experimental results are presented to validate the proposed method.

Neural Networks for Chemical Engineering Unit Operations

Application of artificial neural networks in simulation of chemical engineering unit operations are studied. On the basis of the present work it is suggested that the raw data describing the phenomenon should be processed so that the relationships of the input variables are studied and if relationships are found, such as dimensionless numbers, these relationships are set as inputs in the neural network. Further, if the phenomenon can be described by a simplified mathematical expression, the value calculated by such simplified solution is set as one of the inputs. The method is demonstrated by three examples, namely, by turbulent fluid flow in a tube, breakthrough curve of adsorption, and by suspension crystallization. In all cases the method presented in this work results in a more accurate simulation and in easier training of the neural network.

Performance analysis of a local area network hybrid protocol

Abstract This paper presents the performance analysis of a oocal area network communication protocol, comparing the results of the analytic model with those obtained by simulation. Additionally, a new approach is presented that provides simplified mathematical expressions for throughput and delay in special situations. The last part of the paper shows the structure of the simulator developed.

A study of the characteristic analysis of high speed journal bearings. Optimum design of journal bearings.

This paper describes an optimum design of hydrodynamic journal bearings under laminar and turbulent operating conditions. Simplified mathematical expressions are presented for the eccentricity ratio, friction force and whirl onset speed as a function of the Sommerfeld number or eccentricity ratio. The radial clearance, slenderness ratio and viscosity of lubricants which optimize both the oil flow rate and the oil film temperature rise in hydrodynamic journal bearings under the constant load are determined numerically for a wide range of journal speeds.

An Optimum Bid Approximation Model

A competitive bidding model is presented which enables the practitioner to approximate an optimum bid with little computational effort. Elementary calculus is used to derive a simplified mathematical expression which yields and accurate approximation of the solution to a bidding problem.

Direct methanation of coal

The direct production of methane from coal by reaction with synthesis gas and steam constitutes the basis of the two-stage super-pressure gasifier being developed with support by the Office of Coal Research, U.S. Department of the Interior. Results of continuous flow experiments using steam and synthesis gas containing various amounts of hydrogen have been reported earlier. In these laboratory-scale experiments, temperatures were maintained at 960°C and the total system pressure was varied between 50 and 80 atm. Observed yields of methane were dependent on coal type and hydrogen partial pressure, but were relatively uninfluenced by time over the range studied. The present paper reports a further kinetic analysis of data from these continuous flow experiments, and of the observations of previous investigators concerning the rapid heating of coal in the presence of hydrogen. Moseley and co-workers have postulated that, in addition to gaseous pyrolysis products, an active but transient species is formed which undergoes rapid reaction with hydrogen to produce additional methane. In this paper a simplified mathematical rate expression based on this postulate is used to derive a relation between methane yield and hydrogen partial pressure that is applicable over all ranges of hydrogen pressure. The relation not only furnishes insight into the mechanism of the direct methanation of coal by hydrogen, but also provides a simple and reliable equation for design of future process and equipment development research.

Weight Considerations for Deep Submersibles

Conventional shallow submersible vehicles depend on the pressure hull for buoyancy, but deep submersibles depend on some type of bulk material for buoyancy. As a consequence, the design of very deep submersibles requires new considerations on the vehicle weight. The purpose of this paper is to evaluate the many parameters which affect the boat weight to see which ones are most influential on total weight. To accomplish this objective, a simplified mathematical expression is derived which describes the total weight for a deep submergence vehicle. The expression contains both structural and nonstructural weight items. The structural items include the pressure capsule, outer hull, foundations, and hard tanks. The nonstructural items are the equipment, buoyancy material, and payload. Each weight item is then examined in detail to determine what parameters affect the boat weight. The results show that the greatest weight reduction is possible with the equipment. This is because the state-of-the-art equipment used for deep submersibles has a weight almost equal to three times its displacement, and to furnish sufficient buoyancy material in the boat to float such equipment results in a large weight penalty.