Category CONGRESS

Thermodynamic process

The expansion (2-3) is considered as being isothermal. The theoretical effiency r] of this energy conversion can be described by /2,3/:

OV hy) ~ ^(sy &2<) – (Pe~ РкУРі

^ Оу ^5) + TE(S3- S2) – (pg – РкУРі

(h= enthalpy, s= entropy, p density, p= pressure, T = absolute temperature).

Therein, the pumping of the sodium to feed the sodium from the condensate pressure pK back to the high pressure level pE, is treated as reversible. The pump power (pE- pK)/pj is taken away from the energy gained and added to the heat input. The latter explains, why the energy h5 – hj has not to be delivered by the external heat source.

The electric tension U of an AMTEC can be calculated by

U – (M/zF)[(h3- h2t) – Tg^- S2O]

or with the Nemst equation:

U = ^ln(pE/p3)

( R = gas constant, F= Farady constan...

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-Alcali-Metall-Thermo-Electric-Converter-. Another Way to Harness Solar Energy for Electricidy Production

V. Heinzel, F. Huber, W. Peppier, H. WiU

Nuclear Research Center of Karlsruhe
Institute for Reactor Development
Dr. V. Heinzel
P. O. Box 3640
D-7500 Karlsruhe

Abstract

In an Alcali-Metal-Thenno-Electric Converter (AMTEC) sodium is expanded through an oxide ceramic electrolyte. The sodium penetrates as ion the electrolyte, which is an isolator for electrons. Therewith an electric current can be taken from electrodes on both sides of the electrolyte wall. The driving force for the sodium penetration are different potentials or a saturation pressure, i. e. temperatures difference.

Based on the realistic design of an experimental AMTEC-cell the theoretical efficiency and process losses were investigated as function of the process parameter...

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RESULTS

Equations 2 to 9 were solved with the finite difference technique. Temperature distributions along the length of a typical loop of concentrators were obtained for the working fluid, the absorber tube and the glass envelope. Since nominal design conditions for the solar power plant require a temperature raise from 304°C to 390°C for a masic flow of working fluid of 6.73 Kg/s per loop, this value of the masic flow was used in all of the simulations. Figure 3 shows the outlet temperatures of the working fluid in the solar field versus the solar time according to the season of the year (it must be remarked that all of the loops are assumed to be working under identical conditions)...

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SOLAR FIELD SIMULATION

The objective in simulating a system is to predict reasonably well its performance under several different conditions of operation. In the particular case of the solar field, it is desirable to predict: a) The outlet temperature of the working fluid when it leaves the solar field; and, b) The useful energy that the solar system will deliver.

To predict operation of the solar field, a mathematical model for a module of concentration was developed (Zamora, УаЫёз and V&zquez, 1991). This model consists of a system of three ordinary differential equations as a boundary value problem. Each one of these equations describes the heat transfer phenomena in each one of the principal components or parts of the concentration module: a) The working fluid; b) The absorber tube and c) The glass envelope...

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PREDICTING THE DIRECT SOLAR RADIATION

It has been shown that the only way to make approximate solar radiation predictions for short periods (for example hourly radiation), is by means of parametrized methods for clear days. Many of these have been verified in several regions of the world (Iqbal, 1983; Estrada-Cajigal, 1985).

Galv&n and others (1988) have shown that, for Mexico, the Hoyt’s model (Hoyt, 1980) can predict the direct solar radiation with acceptable precision. For a cloudless atmosphere, Hoyt proposed to evaluate the direct irradiance on a horizontal plane by mean of the following equation:

Подпись: 5 7-і (1)

Where Aj (j=l to 5) are the absorption ratios for the water vapor (j=1), carbon dioxide (j =2), ozone (j=3), aerosols (j=4) and oxygen (j=5); Tas and Tr are transmittance functions which depend on the radiation scattering du...

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BRIEF SYSTEM DESCRIPTION

As it was mentioned above, the SE6S may be divided into the two subsystems; the first one is the parabolic trough collectors field. In this field a fraction of the normal beam radiation is converted into useful energy to be used to heat the working fluid (thermal oil) from 304°C to 390°C. The second subsystem is the power block consisting of a conventional plant operating with a Rankine Cycle and capable of generating 80 MW. Both subsystems are interconnected with heat exchangers where the hot fluid is employed for steam generation at 100 bar and 371°C which in turn will be used to produce useful work in the turbine.

The basic components of the solar field are the parabolic trough collectors, which consist of three elements: a) The parabolic trough mirrors which concentrate part of the ...

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PRELIMINARY STUDY OF A SOLAR 80 MW PLANT PERFORMANCE. LOCATED IN THE NORTHWESTERN REGION OF MEXICO

A. Vald£s*, J. M. Zamora*, R. Almanza**, R. Lugo*
and V. Estrada-Cajigal**

*Depto. de IPH, Universidad Autdnoma Metropolitana,
Iztapalapa, Mexico D. F., 09340, Mexico
**Secc. Fluidos у Тйгтіса, Instituto de Ingenieria,
UNAM, Coyoacan, Mexico. D.F., 04510, Mexico

ABSTRACT

Results in predicting the performance of an 80 MWe Solar Electric Generating System (SEGS) without auxiliary natural gas boiler and hypothetically located at Hermosillo Son. city are presented in this paper. Simulations were made for four months: March, June, September and December. A parametrized method is used in estimating the solar beam radiation for clear days. The thermal behavior of the solar concentrators field is predicted by means of a model consisting of a system of three differential equations...

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FOLLOW-UP

The article was originally published in Canadian Geographic. The author was swamped with letters and telephone calls from readers across Canada. Cottagers too far from power lines wanted to run their water pumps. A fellow panning for gold in the Yukon and a trapper in northern Manitoba wanted to electrify their camps. Two students wanted to make a photovoltaic collector for a class project. They all wanted more details, electrical diagrams and lists of components.

And what about Long Dog? How did they fare after a year of electricity? Because of the nature of the installations, it would have been meaningless to monitor the systems. The best evaluation was simply to go back to talk to people. Aside from two burned out ballasts, everything was working fine...

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