Velimir Stefanovic

A model of a Serbian energy efficient house for decentralized electricity production

This paper presents architectural project and simulation of energy consumption and production of a model of Energy Efficient House for Decentralized Energy (DE). The house model is designed for the area of Serbia, based on the needs of an average Serbian family. The model is designed to investigate opportunities for DE of typical house geometry with advantages of passive solar architecture combined with active solar systems and heat pump. Simulation of the model was performed for the climate conditions for the city of Nis. Thermal load for designed net-zero energy efficient home for a period of one year was simulated by means of trnsys software. With respect to renewable energy sources in Serbia, production of electrical, heating, and cooling energy by solar photovoltaic/thermal collectors, heat pump, and heat storage is considered. The balance of simulated annual electricity production and consumption show that the house model can produce 51% of its energy demands. Simulation results are used to determin...

Ray Tracing Study of Optical Characteristics of the Solar Image in the Receiver for a Thermal Solar Parabolic Dish Collector

This study presents the geometric aspects of the focal image for a solar parabolic concentrator (SPC) using the ray tracing technique to establish parameters that allow the designation of the most suitable geometry for coupling the SPC to absorber-receiver. The efficient conversion of solar radiation into heat at these temperature levels requires a use of concentrating solar collectors. In this paper detailed optical design of the solar parabolic dish concentrator is presented. The system has diameter mm and focal distance mm. The parabolic dish of the solar system consists of 11 curvilinear trapezoidal reflective petals. For the construction of the solar collectors, mild steel-sheet and square pipe were used as the shell support for the reflecting surfaces. This paper presents optical simulations of the parabolic solar concentrator unit using the ray tracing software TracePro. The total flux on the receiver and the distribution of irradiance for absorbing flux on center and periphery receiver are given. The goal of this paper is to present the optical design of a low-tech solar concentrator that can be used as a potentially low cost tool for laboratory scale research on the medium-temperature thermal processes, cooling, industrial processes, polygeneration systems, and so forth.

EXPERIMENTAL INVESTIGATION OF THE CONVECTIVE HEAT TRANSFER IN A SPIRALLY COILED CORRUGATED TUBE WITH RADIANT HEATING

The Archimedean spiral coil made of a transversely corrugated tube was exposed to radiant heating in order to represent a heat absorber of the parabolic dish solar concentrator. The main advantage of the considered innovative design solution is a coupling effect of the two passive methods for heat transfer enhancement - coiling of the flow channel and changes in surface roughness. The curvature ratio of the spiral coil varies from 0.029 to 0.234, while water and a mixture of propylene glycol and water are used as heat transfer fluids. The unique focus of this study is on specific boundary conditions since the heat flux upon the tube external surfaces varies not only in the circumferential direction, but in the axial direction as well. Instrumentation of the laboratory model of the heat absorber mounted in the radiation field includes measurement of inlet fluid flow rate, pressure drop, inlet and outlet fluid temperature and 35 type K thermocouples welded to the coil surface. A thermal analysis of the experimentally obtained data implies taking into consideration the externally applied radiation field, convective and radiative heat losses, conduction through the tube wall and convection to the internal fluid. The experimental results have shown significant enhancement of the heat transfer rate compared to spirally coiled smooth tubes, up to 240% in the turbulent flow regime.

High pressure gas pipeline under the influence of radiation

This paper presents one of the possible hazardous situations during transportation of gas through the international pipeline. It describes case when at high pressure gas pipeline, due to mechanical or chemical effect, the crack and gas leakage appears and gas is somehow triggered to combusting. As a consequence of heat impingement on the pipe surface will be, change of material properties (decreasing of strength) at high temperatures. In order to avoid greater rapture a reasonable pressure relief rate needs to be applied. Standards in this particular domain of depressurizing procedure are not so exact (DIN EN ISO 23251; API 521). The main part of the work consists of two calculations. First is the numerical simulation of heat radiation of combustible gas which affects the pipeline, done by software FLUENT, and second in Matlab. There are also given conclusions according to achieved results.

COMBINED NATURAL GAS AND SOLAR TECHNOLOGIES FOR HEATING AND COOLING IN THE CITY OF NIS IN SERBIA

The use of conventional systems for heat and electricity production in Nis and Serbia means a constant waste of energy, and money. This problem is present in both industrial and public sector. Using conventional systems, means not only low‐energy efficient systems, and technologies, but also using very “dirty” technologies, which cause heavy environment pollution. The lack of electricity in our country, and region is also present. The gas pipeline in Nis was finished not long ago, and second gas pipeline is about to be made in the next couple of years. This opens a door for implementing new technologies and the use of new methods for production of heat and electricity, while preserving our environment. This paper reports discussion of this technology with management of public institutions, which use both heat and electricity.