Experimental and modeling study of kinetics for methane hydrate formation in a crude oil-in-water emulsion

A low-viscosity emulsion of crude oil in water can be believed to be the bulk of a flow regime in a pipeline.To differentiate which crude oil would and which would not counter the blockage of flow due to gas hydrate formation in flow channels,varying amount of crude oil in water emulsion without any other extraneous additives has undergone methane gas hydrate formation in an autoclave cell.Crude oil was able to thermodynamically inhibit the gas hydrate formation as observed from its hydrate stability zone.The normalized rate of hydrate formation in the emulsion has been calculated from an illustrative chemical affinity model,which showed a decrease in the methane consumption（decreased normalized rate constant） with an increase in the oil content in the emulsion.Fourier transform infrared spectroscopy（FTIR） of the emulsion and characteristic properties of the crude oil have been used to find the chemical component that could be pivotal in selfinhibitory characteristic of the crude oil collected from Ankleshwar,India,against a situation of clogged flow due to formation of gas hydrate and establish flow assurance.

Simulation of Cement Hydration and Porous Structures by the Hydration-Pixel Probability Model

This research proposes a new pixel-based model called the hydration-pixel probability model which aims to simplify cement hydration as a probability problem.The hydration capacity of cement,the solution within pores,and the difiusion of solid particles are represented by three probability functions derived from experimental data obtained through electrical resistivity and hydration heat measurements.The principle of the model is relatively simple,and the parameters have clear physical meanings.In this research,the porous structures of difierent cement pastes with w/c ratios of 0.3,0.4,and 0.5 are investigated.The results indicate that the porosity of the cement paste decreases during the first few hours,followed by a rapid decline,and eventually reaches a steady state.The porosity of the paste decreases as w/c ratio decreases,and the rate of decrease is more rapid in the early stages.Referring to the porosity curves,the average degree of hydration and depth of hydration can be derived.The simulation results show that the hydration degree of paste composed of irregular particles is higher than that of the paste composed of round particles.The trend in the development of the average hydration depth is similar to that of the average hydration degree.Upon analyzing the average growth rate of the hydration depth,it is observed that there are two peaks in the curves,which correspond to the three characteristic points in the electrical resistivity test.

A Model for Temperature Infl uence on Concrete Hydration Exothermic Rate (Part one: Theory and Experiment)

Recent achievements in concrete hydration exothermic models based on Arrhenius equation have improved computation accuracy for mass concrete temperature field. But the properties of the activation energy and the gas constant （Ea/R） have not been well studied yet. From the latest experiments it is shown that Ea/R obviously changes with the hydration degree without fixed form. In this paper, the relationship between hydration degree and Ea/R is studied and a new hydration exothermic model is proposed. With those achievements, the mass concrete temperature field with arbitrary boundary condition can be calculated more precisely.

A Simple Cement Hydration Model Considering the Influences ofWater-to-Cement Ratio and Mineral Composition

A simple hydration model is used here by taking the composition of the cement and the initial water: cementratio (w/c) into account explicitly. Its conceptual basis is a combination of the Avrami equation and Bentz’s modelbased on simple spatial considerations. In this model, the Avrami equation determines the initial reaction, andBentz’s model describes the following hydration stage. The model favors engineers for it relies on one experimentalparameter and has a reliable approximation in the practice.

Hydration Mechanism of Cement-based Materials with Different Si-rich Mineral Admixtures

Early hydration mechanism of cement-based materials with silica fume, nano-SiO2 and silica sol of different contents was investigated, and the detailed effect of these Si-rich mineral admixtures in three stages of early hydration（NG, I, D） using kinetics model was focused. The results showed that silica fume, nano-SiO2, and silica sol have significant effect on kinetic parameters n, k1, k2 and k3, the fineness and existing form of SiO2 particles in these Si-rich mineral admixtures are two important factors to affect the hydration process and on the parameters. Through integrated use of methods of hydration heat-Krstulovic-Dabic Modelsynthetical thermal analysis, data of hydration heat were collected, hydration degree was characterized, as well as the resulting crystallization behavior of early hydration, to build a numerical relationship between parameter n and CH contents that n decreases with increasing CH, and thus, a direct connection between hydration heat release behavior and crystallization behavior has been established.

Simplified mathematical model of proton exchange membrane fuel cell based on horizon fuel cell stack

This paper presents a simplified zero-dimensional mathematical model for a self-humidifying proton exchange membrane(PEM)fuel cell stack of 1 k W.The model incorporates major electric and thermodynamic variables and parameters involved in the operation of the PEM fuel cell under different operational conditions.Influence of each of these parameters and variables upon the operation and the performance of the PEM fuel cell are investigated.The mathematical equations are modeled by using Matlab-Simulink tools in order to simulate the operation of the developed model with a commercial available 1kW horizon PEM fuel cell stack(H-1000),which is used for the purposes of model validation and tuning of the developed model.The model can be extrapolated to higher wattage fuel cells of similar arrangements.New equation is presented to determine the impact of using air to supply the PEM fuel cell instead of pure oxygen upon the concentration losses and the output voltage when useful current is drawn from it.

Analysis of Compressive Strength Development of Ultra-high Performance Concrete

A numerical procedure was presented for evaluating the compressive strength development of ultra-high performance concrete(UHPC) with cement-silica fume-slag binder.This numerical procedure started with initial packing behavior of designed UHPC using a random sequential packing method.Furthermore,synergistic effect of combined mineral admixtures was addressed with respect to hydration heat.Accordingly,hydration degree of cement and reaction degrees of mineral admixtures were determined based on a blended cement hydration model.Finally,a compressive strength evolution model was proposed and the evolution of compressive strength of three mixes with different binder recipes was compared.The results showed that the both initial packing behavior of UHPC mixes and synergistic effect of mineral admixtures are critical for predicting the properties of UHPC.A remarkable void fraction of 0.2042 was observed for UHPC mix designed by optimization algorithms under random packing.Furthermore,a negative synergistic effect of the combination of silica fume and slag was obtained with regarding to compressive strength.In addition,for a given mineral admixture replacement of 20%,the formulation of mineral admixture should be carefully tailored where the UHPC incorporating 5%silica fume and 15%slag shows the highest compressive strength.