P. Yianoulis

Fabrication of evacuated glazing at low temperature

Abstract An indium-based seal augmented with an adhesive, developed to maintain a vacuum between two sheets of glass, avoids the high temperatures required to produce a seal in evacuated glazings to date. An experimentally-validated three-dimensional transient model has been used to predict heat transfer for an indium/adhesive sealed 1xa0m 2 area evacuated window with a highly insulating frame. An overall heat loss coefficient of 0.9xa0Wxa0m −2 xa0K −1 , with a midplane value of 0.36xa0Wxa0m −2 xa0K −1 , can be achieved with 0.72 visible transmittance for two 6xa0mm panes separated by 0.2xa0mm diameter pillars 40xa0mm apart. The conduction through a 3xa0mm edge-seal was 1.14xa0Wxa0m −2 xa0K −1 . Detailed three-dimensional isothermal contour plots through the system are presented.

Integrated collector-storage systems with suppressed thermal losses

Abstract Stationary concentrating solar devices, of the integrated collector and storage (ICS) type, that consist of a cylindrical tank placed horizontally in a properly shaped, curved mirror envelope, were designed. Prototype models were constructed, tested, and compared with conventional solar water heaters. In this article we describe the design of the ICS solar units with respect to the minimization of thermal losses from the absorber to the ambient. Experimental results were derived from the constructed models, a conventional concentrating stationary ICS prototype, and flat plate collectors of the thermosiphon type. Finally some conclusions regarding the practical application of the integrated units are presented.

Nano-tubular cellulose for bioprocess technology development.

Delignified cellulosic material has shown a significant promotional effect on the alcoholic fermentation as yeast immobilization support. However, its potential for further biotechnological development is unexploited. This study reports the characterization of this tubular/porous cellulosic material, which was done by SEM, porosimetry and X-ray powder diffractometry. The results showed that the structure of nano-tubular cellulose (NC) justifies its suitability for use in “cold pasteurization” processes and its promoting activity in bioprocessing (fermentation). The last was explained by a glucose pump theory. Also, it was demonstrated that crystallization of viscous invert sugar solutions during freeze drying could not be otherwise achieved unless NC was present. This effect as well as the feasibility of extremely low temperature fermentation are due to reduction of the activation energy, and have facilitated the development of technologies such as wine fermentations at home scale (in a domestic refrigerator). Moreover, NC may lead to new perspectives in research such as the development of new composites, templates for cylindrical nano-particles, etc.

Industrial scale modelling of the thermochemical energy storage system based on CO2 + 2NH3 ↔ NH2COONH4 equilibrium

Abstract The thermochemical storage of energy by the system carbon dioxide, ammonia and ammonium carbamate is studied in detail. In particular, the kinetics and the thermodynamics of the reversible reaction is studied. We give two industrial models for the operation of this system. In the first, the separation of the gases NH3 and CO2 is achieved by compression and liquefaction of NH3. In the second, a method of separation of the gases is proposed which is based on the solubility of NH3 in ethanol while CO2 is practically insoluble. The operation of this system is examined both in closed form and in the case in which CO2 is rejected in the atmosphere, and it is taken from alcoholic fermentation or from the combustion gases of power plants burning lignite. The mass and energy balance is given, for each case, and the amount of energy losses by the use of this storage system is calculated. Finally, we give some estimates for the area of solar collectors and the amount of chemicals which are required in order to cover the energy needs of a community.

CPC solar collectors with multichannel absorber

Abstract Stationary CPC solar collectors with symmetric and asymmetric mirrors have been studied and tested. In these collectors the distribution of solar radiation on the absorber surface is not uniform, with areas of low and high intensity, variable and depending on the position of the Sun relative to the collector. This effect can be used to improve the efficiency of the collector if the absorber is flat and divided in several sections, which form the channels of fluid flow. By selecting the channels with the higher radiation density, the working fluid can be heated to higher operating temperatures. Here we present work on the optical analysis and experimental tests on models consisting of four channel absorbers. The results show that efficient operation at temperatures in the range of 100–200°C can be achieved with relatively simple types of concentrating solar collectors.

Modelling line-axis solar concentrators in the medium temperature range

Simple correlation based models used extensively for the prediction of the performance of solar energy systems have little spatial accuracy and do not generally allow detailed investigation into modifications in system design. The recent development of powerful low cost computers has allowed the development of tools using computational fluid dynamics for predicting the performance of solar energy systems. These models allow predictions of the spatial variation of temperature air velocity and pressure within the concentrator system to be made and realistic theoretical investigations into the effects of design modifications to be undertaken.

Conditional probabilities of daily relative sunshine data and the dependence on the weather of the previous day

Abstract In this paper, the conditional probabilities p11(m, x) and p01(m, x) of the daily relative sunshine (DRS) are estimated for each month m, using available data for 30 years. p11(m, x) (p01(m, x)) is the probability that the DRS of a day for a certain month is greater than x, (o

The reaction coefficient of an enclosure to the solar energy collection

Abstract A dimensionless reaction coefficient Ra is defined which gives a measure of the solar energy collectivity of a room with opaque external walls. This number is defined as the ratio between the absorbed solar energy by the wall and the correspondent thermal gain of the room, and depends on the thermal and structural characteristics of the room and its environment. The reaction coefficient Ra is reduced to a simple expression and provides a simple way of estimating the amount of the net radiation energy gain by the room, when the amount of radiation, which is falling or absorbed by the wall, is given. This analytical relation has been confirmed experimentally especially with respect to the influence of the wall total thermal conductance on the reaction coefficient Ra.

Influence of kind of raw materials used for industrial production of alcohol on air and water pollution

Abstract In this paper, the influence of the kind of raw materials which are (or can be) used in Greece for industrial production of ethanol on the characteristics of liquid and gas wastes has been studied. Raisin and molasses, which are used today, as well as straw and sugar beets which have been proposed recently, have been examined. From this study, it was found that the more suitable raw material from the point of view of air and water pollution is the sugar beet.