Abstract: The thermal conductivity of nanofluids has been studied experimentally using the transient hot-wire method, and it is shown that a significant increase can be obtained. Existing methods for the prediction and correlation of the thermal conductivity are discussed. It is shown that a lot of work still needs to be done in this area. © Springer Science+Business Media, LLC 2006.

Abstract: The available experimental data for the density and viscosity of liquid aluminum and iron have been critically examined with the intention of establishing a density and a viscosity standard. All experimental data have been categorized into primary and secondary data according to the quality of measurement specified by a series of criteria. The proposed standard reference correlations for the density of the aluminum and iron are characterized by standard deviations of 0.65% and 0.77% at the 95% confidence level, respectively. The overall uncertainty in the absolute values of the density is estimated to be one of ± 0.7% for aluminum and 0.8% for iron, which is worse than that of the most optimistic claims but recognizes the unexplained discrepancies between different methods. The standard reference correlations for the viscosity of aluminum and iron are characterized by standard deviations of 13.7% and 5.7% at the 95% confidence level, respectively. The uncertainty in the absolute values of the viscosity of the two metals is thought to be no larger than the scatter between measurements made with different techniques and so can be said to be ± 14% in the case of aluminum and ± 6% in the case of iron. © 2006 American Institute of Physics.

Abstract: The transient hot-wire technique was employed to measure the thermal conductivity of the solid part of five different hollow bricks from Greece. Consequently a finite-elements procedure was developed in order to obtain the apparent thermal conductivity of the whole brick. The advantages of this technique for the optimum design of perforation patterns are demonstrated.

Abstract: The thermal conductivity of three thermal-conductivity reference materials, Pyrex 7740, Pyroceram 9606, and stainless steel AISI 304L, has been studied. The technique employed is the transient hot-wire technique, and measurements cover a temperature range from room temperature up to 570 K. The technique is applied here in a novel way that eliminates all remaining contact resistances. This allows the apparatus to operate in an absolute way. The method makes use of a soft silicone paste material between the hot wires of the technique and the solid of interest. Measurements of the transient temperature rise of the wires in response to an electrical heating step in the wires over a period of 20 ?s up to 20 s allow an absolute determination of the thermal conductivity of the solid, as well as of the silicone paste. The method is based on a full theoretical model with equations solved by a two-dimensional finite-element method applied to the exact geometry. At the 95% confidence level, the standard deviation of the thermal conductivity measurements is 0.1% for Pyrex 7740, 0.4% for Pyroceram 9606, and 0.2% for stainless steel AISI 304L, while the standard uncertainty of the technique is less than 1.5%.

Abstract: In this paper, the OSPM model is employed for the calculation of the PM10 concentration levels in the historical centre of the city of Thessaloniki (Greece). Although measurements of the background concentration are available at a suburban station, and a few measurements of PM10 concentrations do exist at particular areas inside the historical city centre, further assumptions had to be made (e.g., for the traffic load) in order to implement OSPM. To validate this approach, NOx and NO2 measurements were employed in addition to data for PM10. The good agreement observed allowed the prediction of PM10 concentrations in all streets in the historical city centre. The very high PM10 concentration levels obtained in almost all streets are indicative of the city's situation today. Finally, developments in vehicle's technology are invoked to model possible future scenarios.

Abstract: Air quality in urban environments can today be modelled by a large number of computer models (empirical, box models, CFD). OSPM (Operational Street Pollution Model) is one of the most widely used empirical-box models due to its simplicity and its very good performance. However, in most cases the necessary data, even for such simple computations, are not all available, leading to large errors, especially when employed for future planning. The City of Thessaloniki (Greece) was studied as an example, as although few input-data are available, there are enough measurements to validate the model's results. The current work proposes a methodology for dealing with this lack of data, confirmed by comparison with measured values. Following that, a sensitivity analysis for the most common input parameters is presented. Finally, OSPM is employed to predict the air quality in some highly-possible future scenarios. © 2007 WIT Press.

Abstract: Until recently, the modelling of airflows and gas contaminants dispersion in urban environments was concentrated on the atmospheric pollution generated from the greenhouse effect gases (CO2, NOx etc.). Modern cities face modern threats/problems. Accidental or intentional release of lethal toxic gases is one of them. A new computer model was constructed for the calculation of toxic gases dispersion in urban terrains in micro scale, extended to an area of 1 km x 1 km. The model consists of three individual modules: a mesh-generator (structured mesh of linear quadrilateral elements), a processor (flow and advection-diffusion solver) and a post-processor (graphical representation of the phenomena). The well-established finite element method was used to solve firstly the Navier-Stokes equation in order to acquire the steady-state velocity profile and secondly the advection-diffusion equation to acquire the transient concentration distribution. All three modules of the model were implemented to a computer software by using the Microsoft . NET® programming environment. In order to evaluate the model’s preliminary results in 2D, numerous simulations were collected from wind tunnel experiments and other CFD software. The model’s main algorithms and its advantages are presented in this work.