A total linearization method for solving viscous free boundary flow problems by the finite element method

In this paper a total linearization method is derived for solving steady viscous free boundary flow problems (including capillary effects) by the finite element method. It is shown that the influence of the geometrical unknown in the totally linearized weak formulation can be expressed in terms of boundary integrals. This means that the implementation of the method is simple. Numerical experiments show that the iterative method gives accurate results and converges very fast

Melting of PCM in a thermal energy storage unit: Numerical investigation and effect of nanoparticle enhancement

The present paper describes the analysis of the melting process in a single vertical shell-and-tube latent heat thermal energy storage (LHTES), unit and it is directed at understanding the thermal performance of the system. The study is realized using a computational fluid-dynamic (CFD) model that takes into account of the phase-change phenomenon by means of the enthalpy method. Fluid flow is fully resolved in the liquid phase-change material (PCM) in order to elucidate the role of natural convection. The unsteady evolution of the melting front and the velocity and temperature fields is detailed. Temperature profiles are analyzed and compared with experimental data available in the literature. Other relevant quantities are also monitored, including energy stored and heat flux exchanged between PCM and HTF. The results demonstrate that natural convection within PCM and inlet HTF temperature significantly affects the phase-change process. Thermal enhancement through the dispersion of highly conductive nanoparticles in the base PCM is considered in the second part of the paper. Thermal behavior of the LHTES unit charged with nano-enhanced PCM is numerically analyzed and compared with the original system configuration. Due to increase of thermal conductivity, augmented thermal performance is observed: melting time is reduced of 15% when nano-enhanced PCM with particle volume fraction of 4% is adopted. Similar improvements of the heat transfer rate are also detecte

An Economics-Based Second Law Efficiency

Second Law efficiency is a useful parameter for characterizing the energy requirements of a system in relation to the limits of performance prescribed by the Laws of Thermodynamics. However, since energy costs typically represent less than 50% of the overall cost of product for many large-scale plants (and, in particular, for desalination plants), it is useful to have a parameter that can characterize both energetic and economic effects. In this paper, an economics-based Second Law efficiency is defined by analogy to the exergetic Second Law efficiency and is applied to several desalination systems. It is defined as the ratio of the minimum cost of producing a product divided by the actual cost of production. The minimum cost of producing the product is equal to the cost of the primary source of energy times the minimum amount of energy required, as governed by the Second Law. The analogy is used to show that thermodynamic irreversibilities can be assigned costs and compared directly to non-energetic costs, such as capital expenses, labor and other operating costs. The economics-based Second Law efficiency identifies costly sources of irreversibility and places these irreversibilities in context with the overall system costs. These principles are illustrated through three case studies. First, a simple analysis of multistage flash and multiple effect distillation systems is performed using available data. Second, a complete energetic and economic model of a reverse osmosis plant is developed to show how economic costs are influenced by energetics. Third, a complete energetic and economic model of a solar powered direct contact membrane distillation system is developed to illustrate the true costs associated with so-called free energy sources.Center for Clean Water and Clean Energy at MIT and KFUPM (Project R13-CW-10

Production of Biodiesel from Locally Available Spent Vegetable Oils

The depletion of fossil fuels prompted considerable research to find alternative fuels. Due its environmental benefits and renewable nature the production of biodiesel has acquired increasing importance with a view to optimizing the production procedure and the sources of feedstock. Millions of liters of waste frying oil are produced from local restaurants and houses every year, most are discarded into sewage systems causing damage to the networks.  This study is intended to consider aspects related to the feasibility of the production of biodiesel from waste frying oils which will solve the problem of waste frying oil pollution and reduce the cost of biodiesel production.This research studies the conversion of locally available spent vegetable oils of different origins and with different chemical compositions into an environmentally friendly fuel. The biodiesel production requirements by base catalyzed trans-esterification process for the different feed stocks are determined according to the measured physical properties. The quality of the produced biodiesel is compared to petro diesel in terms of established standard specifications

A cost-effective steam-driven RO plant for brackish groundwater

Desalination is a costly means of providing freshwater. Most desalination plants use either reverse osmosis (RO) or thermal distillation. Both processes have drawbacks: RO is efficient but uses expensive electrical energy; thermal distillation is inefficient but uses less expensive thermal energy. This work aims to provide an efficient RO plant that uses thermal energy. A steam-Rankine cycle has been designed to drive mechanically a batch-RO system that achieves high recovery, without the high energy penalty typically incurred in a continuous-RO system. The steam may be generated by solar panels, biomass boilers, or as an industrial by-product. A novel mechanical arrangement has been designed for low cost, and a steam-jacketed arrangement has been designed for isothermal expansion and improved thermodynamic efficiency. Based on detailed heat transfer and cost calculations, a gain output ratio of 69-162 is predicted, enabling water to be treated at a cost of 71 Indian Rupees/m3 at small scale. Costs will reduce with scale-up. Plants may be designed for a wide range of outputs, from 5 m3/day, up to commercial versions producing 300 m3/day of clean water from brackish groundwater

ENHANCING THE ESTERIFICATION CONVERSION USING PERVAPORATION

Coupling of a pervaporation membrane unit with an esterification reactor has been undertaken with a view to improve the overall efficiency of the esterification process through removal of one of the products. The esterification reaction of acetic acid with methanol in the presence of two alternative heterogeneous catalysts Nafion resin (NR) and silica sulfuric acid (SSA) is investigated on the laboratory scale. The system consists of a batch reactor externally coupled with pervaparation (PV) module containing a Nafion membrane. The effect of different parameters on the esterification / pervaporation system is explored. The studied parameters include reactants molar ratio, temperature, and catalyst weight percent. The results show that the water diffusion through the PV membrane helps to break the thermodynamic equilibrium barrier of reversible esterification reaction and improve the reaction conversion. The maximum conversion reached 96.76 % after 60 min at 60 ºC, 3% silica sulfuric acid as catalyst, with a reactant to acid molar ratio of 8:1, and a membrane surface area to reactor volume of 1.3 cm-1.

Overview of a Cyber-enabled Wireless Monitoring System for the Protection and Management of Critical Infrastructure Systems

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/84821/1/OverviewSHMTech.pd

Mathematical modelling of thickness and temperature dependent physical aging to O2/N2 gas separation in polymeric membranes

Polymeric membranes are glassy materials at non-equilibrium state and inherently undergo a spontaneous evolution towards equilibrium known as physical aging. Volume relaxation characteristic during the course of aging is governed by the surrounding temperature in which the polymeric material is aged. Although there are studies to understand how polymeric materials evolve over time towards equilibrium at different operating temperatures, the theories have been developed merely in response to experimental observations and phenomenological theory at bulk glassy state without the implementation of sample size effects. Limited work has been done to characterize the physical aging process to thin polymeric films using reasonable physical parameters and mathematical models with incorporation of thermodynamics and film thickness consideration. The current work applies the Tait equation of states and thickness dependent glass transition temperature, integrated within a simple linear correlation, to model the temperature and thickness dependent physical aging. The mathematical model has been validated with experimental aging data, whereby a small deviation is observed that has been explained by intuitive reasoning pertaining to the thermodynamic parameters. The mathematical model has been further employed to study the gas transport properties of O(2) and N(2), which is anticipated to be applied in oxygen enriched combustion for generation of cleaner and higher efficiency fuel in future work