Search results for "35"
showing 10 items of 2413 documents
Numerical Investigation of a Wood-Chip Downdraft Gasifier
2019
Biomass gasification is regarded as one of the most promising technology in the renewable energy field. The outcome of such operation, i.e. the synfuel, can be exploited in several ways, for example powering engines and turbines, and is considered more flexible than the biomass itself. For this reason, a careful analysis of the gasification performance is of paramount importance for the optimization of the process. One of the techniques that can be used for such a purpose, is the numerical analysis. CFD is indeed a tool that can be of great help in the design and study of the operation of the gasifier, allowing for an accurate prediction of the operating parameters. In this work, a downdraf…
A study of solar panel efficiency in Latvian climate conditions
2020
With solar panels increasingly used in nearly zero energy building solutions it is important to clarify if the panels can achieve the efficiency indicators specified by their producers in real operation conditions. To determine the efficiency of poly- and monocrystalline panels depending on their spatial orientation and the seasons a set of test panels was installed in 2018 in Riga, Latvia for long-term monitoring of the amount of generated power and produced energy. Here we summarize the results of the first year of monitoring. Data indicate that orientation has high significance, very small amounts of energy are generated in autumn/winter and that there is a good correspondence of the act…
Long-term abundance dynamics of coastal zooplankton in the Gulf of Riga
1998
The dynamics of three most abundant mesozooplankton species in the coastal zone of the Gulf of Riga — Bosmina longispina, Synchaeta baltica, Keratella quadrata — is analyzed to detect the regulating environmental factors. The only significant downward trend of species abundance was found for S. baltica in autumn. Statistically significant correlation was estimated only between the summer salinity and the abundance of B. longispina. K. quadrata though showed a negative correlation with summer salinity. The abundance of S. baltica had only nonsignificant correlations with the environmental factors. The abundance of coastal mesozooplankton species is determined by the combination of hydrologic…
The possibilities of energy storage in bulk materials
2018
The increased demand for energy from renewable sources entails the development of storage systems. The purpose of these systems is to supply energy on demand during periods which may not be concurrent with the time of the most efficient production of this energy. Various systems are being developed for storing energy in various forms and over various lengths of time.This paper presents selected projects and the results of studies into thermal energy storage. The results of the present author's own research into the transport of thermal energy in granular beds are also presented. The curves of temperature distribution have been determined; they are essential for the design of the thermal sto…
Catalytic activity of humic substances in condensation reactions
1998
Abstract Humic substances (HS) have considerable impact on the fate of organic xenobiotics in natural environments. This paper reports on the catalytic activity of HS in condensation reactions of carbonyl compounds with active methylene compounds, using Knoevenagel and Claisen-Schmidt reactions as examples. Of the HS, the aquatic fulvic acids are the most active, but the velocity of condensation reactions depends also on the temperature, concentration and form of HS (free or salt) used, and the solvent.
Metals in sediments of lakes in Latvia
1995
Abstract The concentrations and speciation forms of Pb, Cu, Ni, Cd, Zn, and Mn have been determined in sediments from 49 lakes thoroughout Latvia to study the impact of different pollutant sources and to estimate the background pollution level. Regional variation in pollutant distributions of Pb, Cu, and Cd concentrations is due to anthropogenic load. The enrichment of metals in the top layer of sediments is an estimate of the environmental pollution level. In regions with no known pollution sources, this enrichment was not typical. Another factor that determines metal concentrations in sediments is the organic matter production and sedimentation in eutrophic water bodies.
The consequences of the inappropriate use of ventilation systems operating in indoor swimming pool conditions - analysis
2018
Increasingly more leisure facilities, such as water parks or indoor swimming pools are being built in Poland nowadays. In order to ensure the air quality required by standards for such leisure facilities it is necessary to fit them with effectively functioning ventilation. For the removal of excess humidity, as well as chlorine ions occurring as a result of the disinfection of water as well as the carbon dioxide emitted by people using the facility, the ventilation system needs to be appropriately designed and efficient. For this reason, studies into the air quality in such facilities were undertaken. The paper presents the causes and consequences of the inappropriate operation and maintena…
Computation of vertically averaged velocities in irregular sections of straight channels
2015
Abstract. Two new methods for vertically averaged velocity computation are presented, validated and compared with other available formulas. The first method derives from the well-known Huthoff algorithm, which is first shown to be dependent on the way the river cross section is discretized into several subsections. The second method assumes the vertically averaged longitudinal velocity to be a function only of the friction factor and of the so-called "local hydraulic radius", computed as the ratio between the integral of the elementary areas around a given vertical and the integral of the elementary solid boundaries around the same vertical. Both integrals are weighted with a linear shape f…
Electrificación, desarrollo rural y Buen Vivir. Un análisis a partir de las parroquias Taday y Rivera (Ecuador)
2017
El acceso a la energía eléctrica pretende mejorar las condiciones de vida de los habitantes rurales y disminuir la inequidad social. Bajo esta premisa, analizamos la electrificación como vía para alcanzar el Buen Vivir y favorecer el desarrollo productivo en las parroquias rurales de Taday y Rivera (Ecuador). Las entrevistas con la población local, sector privado, técnicos de las administraciones públicas y políticos locales muestran la importancia de este servicio por su impacto positivo en la salud y educación de las personas, en la participación de la mujer en el mercado de trabajo, en la reducción de la exclusión social y, en la actividad económica local. En este contexto, la agencia co…
MICROBIAL FUEL CELL WITH Ni-Co CATHODE AND KMnO4 CATHOLYTE
2017
The improving standard of living causes the increases in energy consumption and waste or wastewater production. The possibility of combining wastewater treatment and electricity production can be accomplished by means of a microbial fuel cell. The possibility of wastewater treatment using the Ni-Co alloy as cathode catalyst with KMnO4 catholyte for microbial fuel cells was presented in this paper. The measurements covered the comparison of changes in the concentration of COD, NH4+ and NO3- in the reactor without aeration, with aeration and using a microbial fuel cell (with Ni-Co cathode and KMnO4 catholyte). The reduction time for COD using a microbial fuel cell with the Ni-Co catalyst (and…