Gilberto Espinosa-Paredes

Effect of foaming agents on the stability, rheological properties, drying kinetics and flavour retention of tamarind foam-mats

Abstract Tamarind foam-mats were prepared using as foaming agents ovalbumin, mesquite gum and a low molecular weight surface active blend, by themselves or in combination, in accordance to a 2 3 factorial experimental design. The stability, rheological properties (flow and viscoelasticity) and drying kinetics of the different foam treatments were evaluated. Sensory evaluation of the dried powders was performed. Response surface analysis yielded polynomial models that explain the influence of the foaming agents treatments on the selected foams response variables: drainage mean time, yield stress, apparent plastic viscosity, critical drying time, instantaneous elastic modulus, and mean retardation time. In general terms, the use of binary combinations of the foaming agents at their high usage level yielded foams that exhibited longer drainage mean times; higher yield stress, apparent plastic viscosity, instantaneous elastic modulus and mean retardation times; and a shorter onset of the critical drying time, that yielded dried tamarind powders with better sensory flavour perception. A close interrelationship existed between the drainage mean time and the apparent plastic viscosity, and between the critical drying time and the mean retardation time of the foams.

TEMPLOP/V.2: a computer program for estimation of fully transient temperatures in geothermal wells during circulation and shut-in

This paper describes the development, validation and application of the TEMLOPI/V.2 computer program. This program is a useful tool for estimating in-situ the transient temperature distribution of the fluids employed for drilling geothermal wells. TEMLOPI/V.2 is based on a mathematical model which is developed to consider two-dimensional transient heat transfer during drilling and shut-in conditions in and around a geothermal well. The solution of the partial dierential equations is based on the finite-dierence technique with an implicit scheme. This scheme serves to demonstrate the numerical solution procedure. Each radial grid node is placed in a dierent thermal region: flow inside the pipe, metal pipe wall, flow inside annulus, and the surrounding formation. The program was written in FORTRAN 77 using modular programming and runs on most IBM compatible personal computers. The software code, its architecture, input and output files, the solution algorithm, flow diagrams and source programs are described in detail. From validation tests, computed temperatures dier by less than 58C from analytically obtained temperatures. Comparison of results from the fully transient TEMLOPI/V.2 simulator and the pseudo-transient version, TEMLOPI/ V.1, with measured data shows that the fully transient model provides better results. Application of TEMLOPI/V.2 is demonstrated in a practical application study of well EAZ-2 from Los Azufres Mexican geothermal field. # 2001 Elsevier Science Ltd. All rights reserved.

Time-Fractional Telegrapher’s Equation (P1) Approximation for the Transport Equation

Abstract In this technical note we develop a new approximation from the solution of the time-dependent Boltzmann equation, which includes a fractional constitutive equation of the neutron current density, for a general medium. The fractional constitutive equation in combination with the conservation law that governs the particle collision and reaction processes (P1) approximation for the transport equation gives a time-fractional telegraphers equation (TFTE). The wave velocity found with this approximation is 3-γ/2 for γ < 1. The numerical results are compared with the exact solution and Heizlers approximation. We found that the TFTE gives the best estimate for a purely absorbing medium, where most approximations fail. The asymptotic diffusion coefficient was applied for a heterogeneous medium, and the results show that the behavior of the TFTE improves.

Effective thermal conductivity of Mexican geothermal cementing systems in the temperature range from 28°C to 200°C

The effective thermal conductivity of six Mexican cementing systems used in geothermal well completion were experimentally determined in the temperature range from 28°C to 200°C. Measurements were carried using the classical line-source method. The experimental system was calibrated by measuring the thermal conductivity of standard fused quartz samples. An experimental procedure for preparation of the cement specimen samples was also developed. Results show that thermal conductivity depends on the particular cement system and tends to increase with temperature for most cement systems. Experimental uncertainties of thermal conductivity were less than 4%. From this experimental work, new empirical equations for correlating thermal conductivity with temperature for geothermal cementing samples were obtained.

SBWR Model for Steady-State and Transient Analysis

This paper presents a model of a simplified boiling water reactor (SBWR) to analyze the steady-state and transient behavior. The SBWR model is based on approximations of lumped and distributed parameters to consider neutronics and natural circulation processes. The main components of the model are vessel dome, downcomer, lower plenum, core (channel and fuel), upper plenum, pressure, and level controls. Further consideration of the model is the natural circulation path in the internal circuit of the reactor, which governs the safety performance of the SBWR. To demonstrate the applicability of the model, the predictions were compared with plant data, manufacturer_s predictions, and RELAP5 under steady-state and transient conditions of a typical BWR. In steady-state conditions, the profiles of the main variables of the SBWR core such as superficial velocity, void fraction, temperatures, and convective heat transfer coefficient are presented and analyzed. The transient behavior of SBWR was analyzed during the closure of all main steam line isolation valves (MSIVs). Our results in this transient show that the cooling system due to natural circulation in the SBWR is around 70% of the rated core flow. According to the results shown here, one of the main conclusions of this work is that the simplified model could be very helpful in the licensing process.

Wavelet-Based Method for Instability Analysis in Boiling Water Reactors

Abstract This paper introduces a wavelet-based method to analyze instability events in a boiling water reactor (BWR) during transient phenomena. The methodology to analyze BWR signals includes the following: (a) the short-time Fourier transform (STFT) analysis, (b) decomposition using the continuous wavelet transform (CWT), and (c) application of multiresolution analysis (MRA) using discrete wavelet transform (DWT). STFT analysis permits the study, in time, of the spectral content of analyzed signals. The CWT provides information about ruptures, discontinuities, and fractal behavior. To detect these important features in the signal, a mother wavelet has to be chosen and applied at several scales to obtain optimum results. MRA allows fast implementation of the DWT. Features like important frequencies, discontinuities, and transients can be detected with analysis at different levels of detail coefficients. The STFT was used to provide a comparison between a classic method and the wavelet-based method. The damping ratio, which is an important stability parameter, was calculated as a function of time. The transient behavior can be detected by analyzing the maximum contained in detail coefficients at different levels in the signal decomposition. This method allows analysis of both stationary signals and highly nonstationary signals in the timescale plane. This methodology has been tested with the benchmark power instability event of Laguna Verde nuclear power plant (NPP) Unit 1, which is a BWR-5 NPP.

Theoretical derivation of the interaction effects with an eccentric cell model and void fraction propagation in two-phase flow

Abstract This paper was concerned with the dilute dispersion of gas bubbles in a continuous liquid phase. The starting point in the present study was the three-dimensional, transient averaged transport equations for inviscid incompressible and isothermal two-phase flow. For the evaluation of the averaged description, potential flow around bubbles was considered in order to get closure relationships, using an eccentric cell model approach. The resulting averaged equations are novel in the literature on two-phase flow. The closure averaged model was used to describe the features of the propagation of void fraction waves, and to investigate the linear stability of bubble flow regime. The hyperbolicity of the averaged wave equation was examined and demonstrated that the model is stable when the void fraction is smaller or equal to 2/7.

Estimation of static formation temperatures in geothermal wells

Stabilized formation temperatures were estimated at different depths in 40 wells from the Los Humeros geothermal field, Mexico, using the Horner and the spherical radial flow (SRF) methods. The results showed that the Horner method underestimates formation temperatures, while the SRF method gives temperatures that are closer to the true formation temperatures. This was supported by numerical simulation of a combined circulation and shut-in period in several wells, and results for well H-26 are presented. Numerical reproduction of logged temperature is more feasible if an initial temperature profile based on the SRF method is employed instead of using an initial temperature profile based on the Horner method.

Study on the flow production characteristics of deep geothermal wells

This paper describes a study on the potential flow production characteristics of three non-producing, deep (average depth 4000 m) geothermal wells in the Cerro Prieto geothermal field. The expected production characteristics of these wells were computed in order to determine whether their inability to sustain flow was due to: (1) heat loss effects in the well; (2) the influence of casing diameters; (3) transient temperature effects during the first days of well discharge, and/or (4) the effects of secondary low-enthalpy inflows. For the study, the conservation equations of mass, momentum and energy for two-phase homogeneous flow were solved for the wellbore, since homogeneous flow provides the simplest technique for analyzing two-phase flows when the flow patterns are not well established. The formation temperature distribution was computed assuming radial transient heat conduction. The numerical model was validated by comparison with analytical solutions and with measured pressure and temperature profiles of well H-17 from the Los Humeros geothermal field, Mexico. It was found that the wells should have sustained production. The early heat losses were so large that the flow needed to be induced, and flow will be sustained only after a few days of induced discharge. For well M-202, the analysis suggests that the inflow of secondary colder fluids was responsible for stopping the flow in this well.

Severe Accident Simulation of the Laguna Verde Nuclear Power Plant

The loss-of-coolant accident (LOCA) simulation in the boiling water reactor (BWR) of Laguna Verde Nuclear Power Plant (LVNPP) at 105% of rated power is analyzed in this work. The LVNPP model was developed using RELAP/SCDAPSIM code. The lack of cooling water after the LOCA gets to the LVNPP to melting of the core that exceeds the design basis of the nuclear power plant (NPP) sufficiently to cause failure of structures, materials, and systems that are needed to ensure proper cooling of the reactor core by normal means. Faced with a severe accident, the first response is to maintain the reactor core cooling by any means available, but in order to carry out such an attempt is necessary to understand fully the progression of core damage, since such action has effects that may be decisive in accident progression. The simulation considers a LOCA in the recirculation loop of the reactor with and without cooling water injection. During the progression of core damage, we analyze the cooling water injection at different times and the results show that there are significant differences in the level of core damage and hydrogen production, among other variables analyzed such as maximum surface temperature, fission products released, and debris bed height.