Riccardo Martino

Hydropower Potential in Water Distribution Networks: Pressure Control by PATs

Pressure control is one of the main techniques to control leakages in Water Distribution Networks (WDNs) and to prevent pipe damage, improving the delivery standards of a water supply systems. Pressure reducing stations (PRSs) equipped by either pressure reducing valves or motor driven regulating valves are commonly used to dissipate excess hydraulic head in WDNs. An integrated new technical solution with economic and system flexibility benefits is presented which replaces PRSs with pumps used as turbines (PATs). Optimal PAT performance is obtained by a Variable Operating Strategy (VOS), recently developed for the design of small hydropower plants on the basis of valve time operation, and net return determined by both energy production and savings through minimizing leakage. The literature values of both leakages costs and energy tariffs are used to develop a buisness plan model and evaluate the economic benefit of small hydropower plants equipped with PATs. The study shows that the hydropower installation produces interesting economic benefits, even in presence of small available power, that could encourage the leakage reduction even if water savings are not economically relevant, with consequent environmental benefits.

An improved affinity model to enhance variable operating strategy for pumps used as turbines

ABSTRACT The use of pumps operating as turbines (PATs) is attractive to optimize the equipment costs of small hydropower plants. Unfortunately, the lack of information on the performance of PATs restricts the wide use of this technology. If a single characteristic curve is available, the behaviour of a PAT can be predicted by the application of the turbomachinery affinity law. In this paper, the reliability of the affinity law to predict the behaviour of a machine under variable speeds is discussed, and the results of this model are compared with an experimental database which includes the performance curves of five PATs operating at different speeds. The results show that the difference between the theoretical model and the experimental results is significant. Therefore, a new model, based on a relaxation of the affinity equations, has been proposed, in order to minimize the errors between the predicted and measured characteristic curves.

Pressure Coefficient in Dam-Break Flows of Dry Granular Matter

AbstractThe propagation of dry granular flows, such as rock and snow avalanches, can be described by depth-averaged models. Different from classical shallow-water equations, these models take into account the anisotropy of normal stresses inside the flowing pile through using an earth pressure coefficient in the pressure term. A new regularization function for calculating the pressure coefficient in the Savage-Hutter-type models at the early stages of dam-break flows and collapses is proposed. In such circumstances the flow lines are significantly curved with respect to the basal surface and a special treatment of the earth-pressure coefficient is required for obtaining a satisfactory agreement with experimental data. The comparison between numerical simulations and laboratory experimental data shows an apparent improvement in describing the early stages of dam-break waves over rough beds. The comparison with experiments over smooth bed surface exhibits minor evidence of improvement. Nonetheless, in this ...

A two-layer depth-averaged approach to describe the regime stratification in collapses of dry granular columns

The dynamics of dry granular flows is still insufficiently understood. Several depth-averaged approaches, where the flow motion is described through hydrodynamic-like models with suitable resistance laws, have been proposed in the last decades to describe the propagation of avalanches and debris flows. Yet, some important features of the granular flow dynamics cannot be well delivered. For example, it is very challenging to capture the progressive deposition process, observed in collapses and dam-break flows over rough beds, where an upper surface flow is found to coexist with a lower creeping flow. The experimental observations of such flows suggest the existence of a flow regime stratification caused by different momentum transfer mechanisms. In this work, we propose a two-layer depth-averaged model, aiming at describing such a stratification regime inside the flowing granular mass. The model equations are derived for both two-dimensional plane and axi-symmetric flows. Mass and momentum balances of each...

Assessment of Rheological Characteristics of a Natural Bingham-Plastic Mixture in Turbulent Pipe Flow

Estimating rheological parameters of a non-Newtonian fluid is performed with rheometers, but experiments are limited to fine sediments, in the absence of appreciable sedimentation. An approach based on pipe flow measurements may be more flexible and convenient. The aim of this paper is to experimentally verify the latter approach in order to assess the rheology of natural mixtures of heavy materials with high tendency toward sedimentation.

Optimization of Osmotic Desalination Plants for Water Supply Networks

Water scarcity and the poor quality of water resources are leading to a wider diffusion of desalination plants using the Reverse Osmosis (RO) process. Unfortunately, the cost of a cubic meter of fresh water produced by an RO plants is still high and many efforts are in progress to increase the efficiency of the membranes used in osmotic plants and to limit the energy required by the process. A further reduction of the energy cost could be obtained by an optimal operation of the desalination plant so reducing the hourly energy cost, or by coupling the RO plant with an energy production plant based on direct osmosis (Pressure Retarded Osmosis PRO).The economic viability of the desalination process has been analyzed until now without accounting for the integration of the RO plant with the existing water network. This analysis is developed in the present paper with reference to a hypothetical change of water supply in a real network, where a desalination plant is used to satisfy the fresh water demand. Several scenarios will be analyzed to assess the minimum cost of fresh water production and water supply to the network, including the use of energy recovery systems, such as an integrated use of RO and PRO processes, or the regulation of pressure at the network intake by a micro hydro power plant.

Performance of Slurry Flow Models in Pressure Pipe Tests

AbstractNew experimental data on pressure-pipe flow of slurries, together with some literature data, are used to evaluate the performance of four resistance models based on different interpretations of the process. The experiments were performed on a mixture of water and uniform sediment showing a shear-thinning rheological behavior. The literature datasets refer to a Bingham plastic mixture and to a shear-thickening mixture. Two of the tested models assume a fully stratified flow and express the total resistances as the sum of the bed and of the vehicle contribution. The third and the fourth models are based on a rheological approach that considers an equivalent homogenous fluid.

Estimating Leakages in Water Distribution Networks Based Only on Inlet Flow Data

AbstractThe estimate of current real losses in water distribution networks (WDN) is crucial to plan investments for rehabilitation, assess the rise of leakage over time, and possibly drive procedur...

Field Scale Water Content Measurement by TDR Technique

The paper presents an extended version of TDR technique for distributed large scale measurement of water content. Long Distance Reflectometry (LDR) technique is based on the propagation of electromagnetic waves through a transmission line consisting of two rods inserted in the soil horizontally and on the interpretation of the reflected signal for the assessment of the water retention curve. The lack in precision determined by the signal attenuation as an effect cables length is well balanced by the economical advantage of obtaining a low cost field scale representation of water content. Experiments confirm LDR capability in revealing variations in soil water contents, even in presence of sharp water retention curves.