G. Di Nicola

Development and optimization of a method for analyzing biodiesel mixtures with non-aqueous reversed phase liquid chromatography.

Biodiesel (a mixture of fatty acid esters) is normally analyzed using gas chromatography/flame ionization detection, as specified by the ASTM D6584 and EN14105 standards. This paper proposes a binary gradient method for analyzing biodiesel mixtures using non-aqueous reverse phase HPLC with a UV detector capable of overcoming the drawbacks of the gas chromatographic technique normally used. The new analytical method was developed by means of a statistical sensitivity analysis applied to the main parameters influencing the recording, using the full factorial design method combined with the Yates algorithm and the steepest ascent optimization procedure. The present study shows the influence of the main biodiesel mixture separation analysis parameters. The resulting tool proved valid for analyzing not only biodiesel but also any traces of unreacted oil.

CO2 + R23 Binary System: Virial Coefficients Derived from Burnett Measurements

Burnett PVT measurements were performed on trifluoromethane (R23) and mixtures of R23 with carbon dioxide (CO2). The Burnett apparatus was calibrated using helium. Fourteen expansions were performed for 5 isotherms and in a pressure range from 130 kPa to 6 MPa for R23. Second and third virial coefficients were derived from the collected data and compared with literature values; good agreement was found between them. PVTx measurements for the binary CO2+R23 system were carried out for five isotherms (303, 313, 323, 333, and 343 K). In all, 18 runs were performed in a pressure range from 150 kPa to 5.9 MPa. The composition of the mixtures was measured with a gas chromatograph after it had been calibrated using samples prepared gravimetrically. Second and third virial coefficients for the system were derived, together with the second and third cross virial coefficients, from experimental results using virial coefficients for CO2 from previous measurements (for the same sample as used in the present study). Samples for composition measurements were collected during the first Burnett expansion. Second virial coefficients for the system showed positive deviations from ideal values, while the third virials were negative. No previous experimental results were found for the PVTx properties of this binary system.

Numerical analysis of ball-type turbulators in tube heat exchangers with computational fluid dynamic simulations

In the tube heat exchangers, heat transfer enhancement by creation of turbulent flow has been investigated in a number of previous research using different turbulator forms and methods, whereas in the present work a novel ball-type turbulators is used as a new technique implementation to increase heat transfer rate by vortex generation in the flow. Numerical analysis is performed for proposed novel turbulator to probe heat and flow characteristics. Ball-type turbulators have been designed in three different ball diameters inside a tube exchanger. The effects of balls diameter, pitches and Reynolds number on the heat transfer, friction factors and also entropy generation are analyzed at four different Reynolds numbers between 5000 and 20,000. The Nusselt number and friction factor outcomes are compared with those of smooth tube under the same flow and thermal conditions to determine the heat transfer enhancement. From the numerical analysis, it is specified that the suggested turbulators generate a larger vortex flow at low Reynolds numbers, and consequently, more effective heat transfer can be obtained. Moreover, increasing the ball diameter will lead to more heat transfer rate due to the wider vortex region at behind of the ball.

Experimental characterization of a solar cooker with thermal energy storage based on solar salt

High temperature solar cooking allows to cook food fast and with good efficiency. An unavoidable drawback of this technology is that it requires nearly clear-sky conditions. In addition, evening cooking is difficult to be accomplished, particularly on the winter season during which solar radiation availability is limited to a few hours in the afternoon in most of countries. These restrictions could be overcome using a cooker thermal storage unit (TSU). In this work, a TSU based on solar salt was studied. The unit consists of two metal concentric cylindrical vessels, connected together to form a double-walled vessel. The volume between walls was filled with a certain amount of nitrate based phase change material (solar salt). In order to characterize the TSU, a test bench used to assess solar cooker performance was adopted. Experimental load tests with the TSU were carried out to evaluate the cooker performance. The obtained preliminary results show that the adoption of the solar salt TSU seems to allow both the opportunity of evening cooking and the possibility to better stabilize the cooker temperature when sky conditions are variable.