A study on the internal convection in small turbochargers. Proposal of heat transfer convective coefficients

Nowadays turbochargers play an important role in improving internal combustion engines (ICE) performance. Usually, engine manufacturers use computer codes to predict the behaviour of both engine and turbocharger, the later by means of measured look-up maps. Using look-up maps different problems arise, being one of the most important the difference in heat transfer between the current operating condition and the conditions at which maps were measured. These effects are very important at low to medium turbocharger speeds (typical condition of urban driving conditions) where heat transfer can even be higher than mechanical power. In this work, the different convective heat transfer phenomena inside these kind of machines have been measured and analysed. Besides, general correlations for these flows, based on dimensionless numbers, are fitted and validated in three different turbochargers. The applicability of the model is shown by comparison the main results obtained when the model is used and not, improving up to 20 C the predicted turbine outlet temperature. The main advantages of applying these correlations rely on predicting fluids outlet temperatures (compressor, turbine, oil and coolant). The former is needed to feed accurately ICE model, turbine outlet temperature is important for aftertreatment device modelling while oil and coolant temperatures are important in order to design optimum cooling systems.This work has been partially supported by the Spanish Ministerio de Economa y Competitividad through grant no. TRA2012-36954. The equipment used in this work has been partially supported by FEDER project funds "Dotacion de infraestructuras cientifico tecnicas para el Centro Integral de Mejora Energetica y Medioambiental de Sistemas de Transporte (CiMeT), (FEDER-ICTS-2012-06)", framed in the operational program of unique scientific and technical infrastructure of the Ministry of Science and Innovation of Spain.Serrano Cruz, JR.; Olmeda González, PC.; Arnau Martínez, FJ.; Reyes Belmonte, MÁ.; Tartoussi, H. (2015). A study on the internal convection in small turbochargers. Proposal of heat transfer convective coefficients. Applied Thermal Engineering. 89:587-599. https://doi.org/10.1016/j.applthermaleng.2015.06.053S5875998

Quantifying heterogeneity of small test portion masses of geological reference materials by portable XRF spectrometry: implications for uncertainty of reference values

There is an increasing use of analytical macro-beam techniques (such as portable XRF, PXRF) for geochemical measurements, as a result of their convenience and relatively low cost per measurement. Reference materials (RMs) are essential for validation, and sometimes calibration, of beam measurements, just as they are for the traditional analytical techniques that use bulk powders. RMs are typically supplied with data sheets that tabulate uncertainties in the reference values by element, for which purpose they also specify a minimum recommended mass of material to be used in the chemical analysis. This minimum mass may not be achievable using analytical beam techniques. In this study, the mass of the test portion interrogated by a handheld PXRF within pellets made from three silicate RMs (SdAR L2, M2 and H1) was estimated using a theoretical approach. It was found to vary from 0.001 to 0.3 g for an 8 mm beam size and 0.0001 to 0.045 g for a 3 mm beam. These test portion masses are mainly well below the recommended minimum mass for these particular RMs (0.2 g), but were found to increase as a function of atomic number (as might be expected). The uncertainties caused by heterogeneity (UHET) in PXRF measurements of the three RMs were experimentally estimated using two different beam diameters for eighteen elements. The elements showing the highest levels of heterogeneity (UHET > 5%) seem generally to be those usually associated with either an accessory mineral (e.g., Zr in zircon, As in pyrite) or low test portion mass (associated with low atomic number). When the beam size was changed from nominally 8 to 3 mm, the uncertainty caused by heterogeneity was seen to increase for most elements by an average ratio of 2.2. These values of UHET were used to calculate revised uncertainties of the reference values that would be appropriate for measurements made using a PXRF with these beam sizes. The methods used here to estimate UHET in PXRF measurements have a potential application to other analytical beam techniques