Chaoslike states can be expected before and after logistic growth

Instabilities associated with population growth can be simulated by putting the logistic growth curve in a discrete form. In contrast to the usual derivation of chaos, which can only explain instabilities at the top of the curve, this method can also account for fluctuations during the early phases of the niche-filling process. Precursors, a steep initial rise, and final instabilities can all be interrelated. Industrial examples are given of logistic growth alternating with periods of chaotic fluctuations.

Research on High-Pressure Hydrogen Pre-Cooling Based on CFD Technology in Fast Filling Process

In the fast filling process, in order to control the temperature of the vehicle-mounted storage tank not to exceed the upper limit of 85 °C, it is an effective method to add a hydrogen pre-cooling system upstream of the hydrogenation machine. In this paper, Fluent is used to simulate the heat transfer process of high-pressure hydrogen in a shell-and-tube heat exchanger and the phase change process of refrigerant R23. The accuracy of the model is proven by a comparison with the data in the references. Using this model, the temperature field and gas volume fraction in the heat transfer process are obtained, which is helpful to analyze the heat transfer mechanism. At the same time, the influence of hydrogen inlet temperature, hydrogen inlet pressure, and refrigerant flow rate on the refrigeration performance was studied. The current work shows that the model can be used to determine the best working parameters in the pre-cooling process and reduce the operating cost of the hydrogen refueling station.

2D CFD Modeling of Rapid Water Filling with Air Valves Using OpenFOAM

The rapid filling process in pressurized pipelines has been extensively studied using mathematical models. On the other hand, the application of computational fluid dynamics models has emerged during the last decade, which considers the development of CFD models that simulate the filling of pipes with entrapped air, and without air expulsion. Currently, studies of CFD models representing rapid filling in pipes with entrapped air and with air expulsion are scarce in the literature. In this paper, a two-dimensional model is developed using OpenFOAM software to evaluate the hydraulic performance of the rapid filling process in a hydraulic installation with an air valve, considering different air pocket sizes and pressure impulsion by means of a hydro-pneumatic tank. The two-dimensional CFD model captures the pressure evolution in the air pocket very well with respect to experimental and mathematical model results, and produces improved results with respect to existing mathematical models.

Application of Lean Methodology to Increase Productivity through Value Stream Mapping

Productivity plays a vital role for business because it controls the real income that is needed to meet obligations to customers, employees, shareholders, and government through taxes and still remain competitive in the marketplace. An effective way to increase productivity is to eliminate waste in the manufacturing process, therefore using lean methodology. This study aims to use one of the lean tools which are value stream mapping (VMS) to identify wastes and improve the efficiency of the sachet filling process in manufacturing company. In conjunction with state mapping, re-engineering of the manufacturing setup was also developed. The future state map shows that after the streamlining process non value added time was reduce by 43.13%. Total lead time was also reduced from 118.63 hrs to 64.96 hrs and total man-hours were reduced from 189.26 hrs to 105.93 hrs which provide significant savings to the organization with respect to labor cost.

Thermodynamic Analysis of CNG Fast Filling Process of Composite Cylinder Type IV

Due to ecological and economic advantages, natural gas is used as an alternative fuel in the transportation sector in the form of compressed natural gas (CNG) and liquefied natural gas (LNG). Development of infrastructure is necessary to popularize vehicles that use alternative fuels. Selected positive factors from EU countries supporting the development of the CNG market were discussed. The process of natural gas vehicle (NGV) fast filling is related to thermodynamic phenomena occurring in a tank. In this study, the first law of thermodynamics and continuity equations were applied to develop a theoretical model to investigate the effects of natural gas composition on the filling process and the final in-cylinder conditions of NGV on-board composite cylinder (type IV). Peng–Robinson equation of state (P-R EOS) was applied, and a lightweight composite tank (type IV) was considered as an adiabatic system. The authors have devised a model to determine the influence of natural gas composition on the selected thermodynamic parameters during fast filling: Joule–Thomson (J-T) coefficient, in-cylinder gas temperature, mass flow rate profiles, in-cylinder mass increase, natural gas density change, ambient temperature on the final natural gas temperature, influence of an ambient temperature on the amount of refueled natural gas mass. Results emphasize the importance of natural gas composition as an important parameter for the filling process of the NGV on-board composite tank (type IV).