M. Dell'Isola

Measurement of high-pressure natural gas flow using ultrasonic flowmeters

Abstract A number of analyses have been carried out on both the installation effects and the calibration problems of transit time multipath flowmeters. There is, however, only a somewhat sketchy knowledge of their field operation, their long-term performance, and their compatibility with traditional instruments and measurement techniques. In this paper, the authors, prior to analysing the principal problems regarding transit time ultrasonic flowmeters, describe the results of an experimental field investigation into the use of multi-path flowmeters for measuring large flows of high pressure natural gas. Reference is also made to the future objectives of research on this type of device.

An experimental verification of saturated salt solution-based humidity fixed points

The high instability and hysterisis of the relative humidity sensors currently available on the market render necessary simple and economic calibration methodologies that can be used as a secondary of working standards. The chemical equilibrium-type systems based on saturated aqueous salt solutions, even though simple and economical, are not always metrologically satisfactory for calibration. They can, in fact, be unreliable, when some fundamental requirements are neglected: also, unacceptable discrepancies continue to exist in the equilibrium relative humidity reference data of saturated aqueous salt solutions furnished by both literature and standards. To highlight the factors that increase the reliability of calibrations with saturated aqueous salt solutions, the authors of this paper have redetermined the equilibrium relative humidity reference data of 11 saturated aqueous salt solutions at ambient pressure and temperature. The solutions chosen were the ones generally used as fixed points to obtain a relative humidity calibration scale.

High Order Explicit Solutions for the Transient Natural Convection of Incompressible Fluids in Tall Cavities

The performance of the artificial compressibility (AC) version of the characteristic based split (CBS) scheme for the solution of transient free convection in tall cavities is analyzed. A dual time-stepping procedure is used to recover the transient solution. The true transient term is discretized explicitly up to the fourth order of approximation, with consequent possibility to adopt larger true time-steps and to gain in accuracy and computing efficiency. In order to obtain the present results, the novel stability analysis recently developed by the authors for the steady-state AC-CBS scheme is here extended to the transient algorithm. Cavities with three different aspect ratios have been considered: 8:1, 10:1, and 16:1. The obtained results have been compared with the analytical and numerical data available in the literature.

Optimum choice of measurement points for sensor calibration

This paper deals with the choice of a sensor calibration plan, with the aim of reducing the calibration curve uncertainty. This uncertainty reduction is achieved by minimizing either the standard deviations of the regression curve coefficients or the standard deviation of the whole estimated calibration curve. Tables and figures are given to aid in choosing the experimental plan in terms of the number of calibration points, number of repetitions for each calibration point and calibration point location. Optimum solutions are highlighted as well as uncertainty amplification which can arise by adopting unsuitable calibration plans. In particular, the optimum location of calibration points in the case of cubic and fourth-order curves proves to be quite different from the equally spaced one, even if the equally spaced location never gives unacceptable uncertainty amplifications. Finally, some numerical examples concerning real sensor calibrations are given with the aim of quantifying the results of the proposed optimization criteria in some practical applications.

The effect of natural ventilation strategy on indoor air quality in schools

In order to reduce childrens exposure to pollutants in classrooms a proper ventilation strategy need to be adopted. Such strategy is even more important in naturally ventilated schools where the air exchange rate is only based on the manual airing of classrooms. The present work aimed to evaluate the effect of the manual airing strategy on indoor air quality in Italian classrooms. For this aim, schools located in the Central Italy were investigated. Indoor air quality was studied in terms of CO2, particle number and PM concentrations and compared to corresponding outdoor levels. In particular two experimental analyses were performed: i) a comparison between heating and non heating season in different schools; ii) an evaluation of the effect of scheduled airing periods on the dilution of indoor-generated pollutants and the penetration of outdoor-generated ones. In particular, different airing procedures, i.e. different window opening periods (5 to 20min per hour) were imposed and controlled through contacts installed on classroom windows and doors. Results revealed that the airing strategy differently affect the several pollutants detected in indoors depending on their size, origin and dynamics. Longer airing periods may result in reduced indoor CO2 concentrations and, similarly, other gaseous indoor-generated pollutants. Simultaneously, higher ultrafine particle (and other vehicular-related pollutants) levels in indoors were measured due to infiltration from outdoors. Finally, a negligible effect of the manual airing on PM levels in classroom was detected. Therefore, a simultaneous reduction in concentration levels for all the pollutant metrics in classrooms cannot be obtained just relying upon air permeability of the building envelope and manual airing of the classrooms.

The influence of reference condition correction on natural gas flow measurement

This paper discusses the influence of thermodynamic correction parameters on measuring the flow rate of natural gas in the reference condition. In particular, the principal aim is to experimentally evaluate the uncertainties of the correction parameters on volumetric flow rate measurement in the reference condition by means of conventional methods. An experimental analysis was carried out on the Italian distribution system which is very interesting from a metrological point of view since there are four different types of natural gas with a pressure and temperature range comprised respectively between 1.1 to 71 bar and 0 to 30°C.

Finite element analysis of pressure distortion coefficient and piston fall rate in a simple pressure balance

A finite element method (FEM) developed by the University of Cassino and the Istituto di Metrologia G. Colonnetti (IMGC, Turin) to optimize the design and use of simple pressure balances was applied while the most important operating and design parameters of the piston-cylinder units were varied. In particular, the influence of size, geometrical uncertainties and superficial roughness on the pressure distortion coefficient and on the piston fall rate was considered. Finally an analysis was carried out using the real clearance profile of the IMGC-100-NNtc unit based on dimensional measurements made at the IMGC. The comparison between the experimental values obtained at the IMGC and the numerical values, of both the pressure distortion coefficient and the piston fall rate, show excellent agreement.

A Comparison of Ideal and Real Moist Air Models for Calculating Humidity Ratio and Relative Humidity in the 213.15 to 473.15 K Range and up to a Pressure of 1 MPa

This study evaluates how the ideal mixture model of moist air approximates a real mixture model when determining both humidity ratio and relative humidity for the 0.1- to 1-MPa pressure range and the -60 to 200°C temperature range. The relevant thermodynamic properties are calculated using, among others, a specific algorithm based on the relationships proposed by Hyland and Wexler corrected for the new ITS-90 temperature scale.

An optimized approach to sensor calibration design

The authors highlight some aspects of the calibration design that could aid in the optimization of sensor characterization. The focus is on the minimization of the regression curve uncertainty by minimizing the standard deviation of its coefficients. Some formulas and tables are given for an easy choice of the experimental plan in terms of number of observations, calibration points and repetitions. A general solution to the problem of calibration point location is provided. An experimental validation of the results is given.<<ETX>>

Hydrogeological study and numerical model of the Suio-Castelforte hydrothermal area (central Italy)

A numerical simulation has been performed through the natural geothermal system of Suio-Castelforte (LT) in order to investigate the hydothermal area and assess its geothermal potentiality. Starting from geological and hydrogeological data a 2D conceptual model has been built. For numerical purpose, the latter idealizes and simplifies the natural system. The area has been affected by a temperature gradient, from low to medium enthalpy, related to the Quaternary volcanism. By a FEM (Finite Element Model) method, using the COMSOL MULTIPHYSICS® software, a homogeneous and isotrope media have been assumed, simulating the groundwater flow and simultaneous heat transfer. Using the porous media approach, Darcy and heat transfer laws have been applied in steady-state conditions. The results have been compared with the collected data and bibliography.