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  • Author: P. Shipkovs x
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Solar energy is used not only at low latitudes, where it is available at large amounts, but also at higher latitudes, where height of sun and irradiance are significantly lower. On the other hand, the length of day at higher latitudes is longer in summer than at low latitudes, and also the path of the sun is longer.

The present research deals with seeking for new shapes of solar collectors capable of receiving more solar energy.

For designing and evaluating new shapes of solar collectors, it is necessary to have new methods for simple calculations of energy received from the sun by surface of any shape and direction. Such a method is explained in the present paper.

Based on calculations by the proposed method, a new form of solar collector – a cylindrical collector – has been worked out. This collector is intended for air heating, but main principles can also be used for water heating, and even for photovoltaics.

A cylindrical collector receives more energy in the morning and evening than a flat one, but at midday power of both collectors is equal, if effective areas are equal. Daily energy sum of the cylindrical solar collector is 1.5 times greater than that of the flat one.


Concentration measurements are important in bioethanol industries, in the R&D areas, for chemical, medical and microbiological analyses and processing as well as for diagnostics, manufacturing, etc. The overview shows development of the structural design of a system for measuring the concentration of solutions and mixtures consisting of two dielectric liquids. The basic principles of the system's design are given along with relevant equations. The concentration of dielectric liquids is measured using devices with capacitive sensors (1-300 pF). The operational frequency of the developed measuring system is 100.000 kHz. Configuration of the system excludes some errors usually arising at measurements, and broadens its applicability. For testing, the system was calibrated for measuring the concentration of anhydrous ethanol + de-ionized water mixture. Experimental results have shown a stable resolution of ±0.005 pF at measuring the sensor capacitance and a reproducible resolution better than ±0.01% at measuring the ethanol volume concentration


During the last 10 years biofuel production and utilization in the European Union have become more extensive owing to support provided by the relevant EU Directives. Achievement of the main targets defined by Directives was not simple, being confronted with various barriers. Latvia is one of the EU member-countries that have set an ambitious goal as to the production of biofuel and its use in transport. The authors summarize the major achievements of the country in this area and analyze the main barriers to implementation of biofuels in the transport sector, providing an outlook on the current status of the bioenergy and the transport situation in Latvia.


As known, many multi-purpose plants can be used in different industries. This research is focused on the possibilities to utilize hemp as feedstock for thermal insulation products. The most advantageous features of hemp insulation are associated with health and environmental safety. The thermal conductivity of commercially available hemp insulation products is comparable with that of other fibrous insulation materials; however, it is possible to develop new products that could be more efficient in terms of cost and due to other important features.

A Mathematical Model for the Temperature Field in the Absorber of a New Type Solar Collector

The temperature field problem described in the paper is analytically solved for the absorber of a new type solar collector. The absorber consists of two plates, one of them being flat and placed on top of the other plate made with a square profile. The temperature field is calculated for four areas using the Laplace equation under stationary conditions. For each area the boundary conditions are written and the Laplace equation solved. The resultant temperature fields are found for each area separately.


The paper presents the use of phase change material (PCM) in window application that was studied in the framework of the ERA-NET-LAC Project “Solar Hybrid Translucent Component for Thermal Energy Storage in Buildings” (SOLTREN). Increase of energy savings in buildings is the main aim of this study. To achieve the aim, it has been decided to create a theoretical model of the impact of the PCM on the characteristics of the window and, at the next stage, to experimentally test the model. Paraffin has been chosen as the most suitable and available material as PCM. Pure paraffin has high transparency in liquid phase, and dull white colour in solid phase. The paper shows results of total transmittance and absorption spectra for different thicknesses of paraffin with a melting temperature of 35°C, as well as absorption of the glass sample with PCM at different angles of incidence of light.

In the work, the temperature field model is developed for the absorber of a round-pipe collector. As distinguished from previous models when the temperature of liquid was assumed to be constant over the entire pipe crosssection, the results obtained clearly show the temperature variations in the absorber’s cross-section. In the work, optimal values are found in the work for geometrical parameters of the collector (i.e. the plate thickness and the pipe diameter) that allow the highest possible temperature of liquid to be achieved.


Information on the electrical-driven solar air conditioning (SAC) is rather scanty. A considerable body of technical data mostly concerns large-scale photo-voltaic solar air conditioning (PV-SAC) systems. Reliable information about the energy output has arisen only in recent years; however, it is still not easily accessible, and sometimes its sources are closed. Despite these facts, solar energy researchers, observers and designers devote special attention to this type of SAC systems. In this study, performance evaluation is performed for the PV-SAC technology, in which low-power (up to 15 kWp of cooling power on average) systems are used. Such a system contains a PV electric-driven compression chiller with cold and heat sensible thermal storage capacities, and a rejected energy unit used for preheating domestic hot water (DHW). In a non-cooling season, it is possible to partly employ the system in the reverse mode for DHW production. In this mode, the ambient air serves as a heat source. Besides, free cooling is integrated in the PV-SAC concept.


In Part 2 of the work we describe a modified measuring system for precise monitoring of the dehydration process of bioethanol production. This is based on the earlier proposed system for measuring the concentration of solutions and two-liquid mixtures using devices with capacitive sensors (1-300pF), which provides a stable measuring resolution of ± 0.005 pF at measuring the capacitance of a sensor. In this part of our work we determine additional requirements that are to be imposed on the measuring system at monitoring the ethanol dehydration process and control of bioethanol production. The most important parameters of the developed measuring system are identified. An exemplary calculation is given for the thermocompensated calibration of measuring devices. The results of tests have shown a good performance of the developed measuring system.


Adequate reconstruction of defects that are consequences of glossectomy is of primary importance for achieving satisfactory functional results and improving the quality of life.

AIM: The aim of this study was to report a case of free flap reconstruction of a subtotal glossectomy defect and discuss it in relation to other available methods.

CASE REPORT: A 48- year-old woman was operated on for a T4N0M0 squamous cell carcinoma of the tongue. A subtotal glossectomy via mandibular swing procedure with bilateral supraomohyoid neck dissection and reconstruction with a radial forearm free flap (RFFF) was performed. Surgery was followed by adjuvant radiotherapy.

RESULTS: The post-operative period was uneventful. The patient resumed intelligible speech evaluated as “excellent” and oral feeding. The donor site morbidity was acceptable. Present reconstructive options of the tongue include two categories: to maintain mobility or to provide bulk. In glossectomy with 30 to 50 percent preservation of the original musculature, maintaining the mobility of the remaining tongue by a thin, pliable flap is preferred. This can be achieved by infrahyoid myofascial, medial sural artery perforator flap, RFFF, anterolateral thigh and ulnar forearm flap. When the post-resectional volume is less than 30 percent of the original tongue, the reconstruction shifts to restoration of bulk to facilitate swallowing by providing contact of the neotongue with the palate. Flaps providing bulk include the free TRAM flap, latissimus dorsi myocutaneous free flap, pectoralis major musculocutaneous flap and trapezius island flap.

CONCLUSION: Surgical treatment of advanced tongue cancer requires adequate reconstruction with restoration of speech, swallowing and oral feeding. Free tissue transfer seems to achieve superior functional results with acceptable donor site morbidity when indicated.