Applied Mechanics and Materials Vol. 831

Abstract: The suspensions consisted of fluid phase and solid particles have been used for over 100 years. However, these tests concerned only the particles of dimension scale of mili-or micrometer, and application of such mixtures has caused serious problems that were a consequence of sedimentation of solid particles, wall erosion, clogging of the conduits or creating of sediments. The nanotechnology development has caused a vast availability of particles with dimensions less than 100 nm. Suspensions consisting of base fluid and particles (beads, filaments, plates) with dimensions less than 100 nm were given a name of nanofluids [1].

Abstract: In contrast to the very rich literature on modeling and the determination of the thermal conductivity of nanofluids the forced convection data are limited. This work presents preliminary results of the experimental investigation of the forced convection heat transfer of water-Al₂O₃ nanofluids inside stainless steel tube with 8 mm internal diameter and 2000 mm length. Nanoparticles were tested at the concentrations of 0.01%, 0.1%, 1% and 5% by weight and the Reynolds number range encompasses laminar as well as turbulent flows.

Abstract: In the paper the author presents the possibilities of the application of the electrolytic technique for the investigation of heat transfer coefficients in channels with nanofluids. The electrolytic technique called the limiting current method enables to obtain mass transfer coefficients on the basis of the electrochemical processes and the laws governing these physical phenomena. The exemplary graph presenting the limiting currents values resulting from the experiment is shown in Fig. 1. These are the voltammograms at different Reynolds numbers and the ion concentration C_b. Heat transfer coefficients can be calculated using the correlations describing the analogy of mass and heat transfer processes. Some cases of the possible application of the electrolytic technique and factors influencing the mass transfer experiment including the state of the electroactive surface, change in ion concentration and thickness of the diffusion layer are discussed in [1]. In this work the author focused on the mass transfer experiment with the application of the nanofluid. Special properties of the nanofluid should be taken into account in the investigations. The paper presents the preliminary results of the experiment with nanofluid in the annular channel.

Abstract: The paper presents the preliminary design of the special heat exchanger. The device under consideration is the kind of immersed coil heat exchangers. It consists of three vertical coils: two coils are standard, water is used as a heating medium; one coil is filled by the refrigerant R134a which transfers the waste heat from refrigeration and air conditioning system during the boiling processes. In order to prevent the possible refrigerant leakage, the special buffer layer filled with the nanofluid is mounted in the Freon coil. Thermophysical properties of the nanofluid cause the intensification of the heat transfer through the buffer layer and the same increase of the heat transfer rate. Calculations of thermal power were made. Correlations of heat transfer coefficients in curved tubes, pressure drop correlations for flow through helical coil tubes and correlations describing the heat transfer in the buffer layer, were applied. Results of the calculations indicate of the influence of of Freon coil on the exchanger heat transfer rate. Heat power of Freon coil is about 7 – 25% of water coil thermal power. Thus, the waste heat applied significantly increases the exchanger heat transfer rate.

Abstract: The paper presents the results of experimental investigation of the ORC system with a droplet separator (which was used to improve the quality of working medium vapour), a radial microturbine and a multi-fuel boiler. The research aimed at verifying the correctness of prototype microturbine performance in the ORC installation, equipped with a heat source in the form of the multi-fuel boiler. During these tests, a detailed assessment of the functioning of the microturbine and the boiler has been devoted more attention. The paper contains the characteristics of the heat exchangers installation that were obtained for the ORC system variant using a regenerative cycle. The multi-fuel boiler was fired with biomass (wood pellets). Two series of measurements were conducted for various flow rates and several selected temperatures of the working medium, glycol solution and thermal oil. On the basis of research carried out on the ORC with a radial microturbine, one can say that, physicochemical parameters of the HFE7100 medium obtained during the first measuring series, were as follows: temperature at the microturbine inlet 158.9 °C, pressure at the microturbine inlet 9.66 bar, flow rate 178.9 g/s at the microturbine discharge pressure of 1.75 bar. The second series of measurements gave the following results: temperature at the microturbine inlet 163.2 °C, pressure at the microturbine inlet 9.86 bar, flow rate 179.2 g/s at the microturbine discharge pressure of 1.88 bar. The maximum electrical power generated with the use of radial microturbine working in the regenerative ORC system reached about 1150 W_e.

Abstract: The paper presents the results of experimental investigation on the ORC system with a droplet separator (which was used to improve the quality of working medium vapour) and two scroll expanders, which operated individually. The research aimed at verifying the correctness of scroll expanders performance in the ORC installation, equipped with the electric flow heater for thermal oil as a heat source. The paper contains the characteristics of the heat exchangers installation that were obtained for the ORC system variant using a regenerative cycle. The tests were conducted for selected flow rates and various temperatures of the working medium HFE7100, glycol solution and thermal oil. The unit with a gear pump and a magnetic coupling functioned as a circulating pump. Following the results of tests carried out on two scroll expanders it may be concluded that the electric power output that was measured at the generator terminals was approximately 750 W. The maximum voltages generated by the expanders amounted to around 200 V and the maximum current was about 4 A.

Abstract: The article presents an analysis of the possibilities of co-combustion of two fuels in truck diesel engines. The goal of usage two different fuels is to lower coast of exploitation heavy duty trucks and buses. The two systems were introduced In first the ignition in cylinder is initiated by diesel oil small dose then main dose of methane is burned. In the alternative system the share of diesel oil is much greater and the mixture of propane butane is only additional fuel. Measurement results of first inwestigations has been presented. The important remarks about setting pilot injection dose and injection time angle were munched.

Abstract: Stirling engine is a device that produces mechanical energy using heat from any source of energy, without the need of combustion of any fuel inside the device. Renewable energy sources, which are mostly low-temperature energy sources, can be used to produce mechanical and electrical energy in Stirling engines. The paper presents an overview of the existing prototype Stirling engines designed for using of low-temperature energy sources, including renewable energy sources. Commercial devices for electric power generation offered for use in home, usually do not exceed 1 kW. Using the Schmidt model, the analyze of influence of temperature working fluid in the expansion space (heater) on the efficiency and the electric power generated in the Stirling engine of alpha type has been presented in the paper.

Abstract: In the paper presented is a concept to utilize waste heat from the power plant with the aid of the low-temperature ORC cycle. The ORC system is heated from two heat sources, the first one being the flow rate of waste heat obtained from the exhaust gases. Subsequently, the working fluid in the cycle is additionally heated by the condensing steam from the low pressure turbine extraction points increasing in such way the level of temperature of working fluid before turbine to 120°C. Examination of the results enables to conclude that the overall efficiency of the cycle increased from =51.958% to =52.304%. That is due to the fact that additional heat enabled to evaporate more working fluid. The total generated power increased to the value of N_elRU=915.85MWe, which corresponds to about 1.5% increase in power.

Abstract: A numerical method is proposed to calculate earth-energy of earth-air-pipe heat exchanger during winter heating. The proposed method is based on using numerical computation developed on Scilab a free open source software. Authors showed the comparison between their simple numerical model called Heatground with the well-known Amitrano results. The comparison is given for different parameters as the airflow, the pipe length, the depth of buried pipe, the pipe diameter.