Onorio Saro

Numerical analysis of heat and mass transfer in a passive building component cooled by water evaporation

Abstract In this paper, the behaviour of a special roofing system is investigated. It is a passive building component that consists of a ventilated roof with a maintained wet lower surface of the cavity over which flows the external air. The authors have carried out numerical simulations of the thermal field, flow field and water vapour concentration of air within the duct for thermal performance evaluation purposes. In order to obtain an estimate of the thermal cooling flux on the wet surface, suitable procedures were coded and linked to a commercial program for computational fluid dynamics (CFX 4.4). An original approach to solve a coupled heat and mass transfer problem is presented. Results of numerical simulations of the temperature field and the values of the mean specific heat and mass fluxes of the wet lower surface are shown. Numerical problems that have been dealt with, due to particular physical phenomena such as boundary coupled fields and radiation between cavity surfaces, are highlighted.

Improving the Energy Efficiency of Heating Systems in Europe’s Residential Buildings

Although the ultimate solution is the complete energy-related renovation of building, upgrades of heating and air-conditioning system components represent the quickest and least costly way to reduce significantly the heating and cooling energy requirements. Such upgrades can be implemented independently of the refurbishment of the building envelope. Numerical simulations of the thermal behaviour of existing buildings have been performed with reference to one-family and multi-family buildings in climate conditions typical of different European countries. The selected building models consider heating systems and envelopes with different thermal characteristics that are customary of existing buildings. A series of tools, such as tables and graphs, are presented in order to enable a rapid and effective preliminary assessment of the benefits rising from the replacement of one or more components of the system. On this basis, it is possible to estimate the increase in the energy efficiency resulting from a given heating system upgrade. For a more complete analysis of the energy-related upgrades, some economic aspects have been considered. In order to assess the cost-effectiveness, typical tools of the financial analysis have been used. Each upgrade has been treated as an investment with an initial outlay and a series of incoming cash flows, which correspond to the annual energy savings from the considered upgrade.

Water Droplets Behavior in Sprinkler Irrigation: Thermal-Fluid Dynamical Assessment and Quantum Considerations

The present paper is aimed at analyzing the behavior of water droplets traveling in air from the nozzle to the ground according to a traditional numerical and a quantum point of views. Considering a single-droplet system, an analytical model based on the Newtonian kinematics is here described, considering the most relevant parameters involved: droplet initial diameter, droplet initial velocity, water and air temperatures, diffusion coefficient of water in air, air relative humidity, environmental radiation, and presence of wind. The effect of those parameters on water evaporation is, hence, discussed. Differently, when a multi-droplet system in considered, the problem becomes even more complicated due to the difficulty of assessment of interdroplet reciprocal affections and both a Newtonian description and a numeric implementation are definitely hard to obtain. An alternative to traditional approaches to treat the water droplet dynamics is the quantum approach, which is here introduced and pointed out in order to give an as full as possible description of the whole phenomenon. Such an approach offers a more tight description of the microscopic phenomena that influence the evolution of the whole multi-droplet system.

Simplified Models for Assessing Heat and Mass Transfer in Evaporative Towers

The aim of this book is to supply valid and reasonable parameters in order to guide the choice of the right model of industrial evaporative tower according to operating conditions which vary depending on the particular industrial context: power plants, chemical plants, food processing plants and other industrial facilities are characterized by specific assets and requirements that have to be satisfied. Evaporative cooling is increasingly employed each time a significant water flow at a temperature which does not greatly differ from ambient temperature is needed for removing a remarkable heat load; its aim is to refrigerate a water flow through the partial evaporation of the same.

Utilization of phase change materials (PCM) for energy recovery in the steelmaking industry

The purpose of this study is to evaluate the possibility of recovery of energy, efficiently, from the off-gases of an Electric Arc Furnace (EAF). The system adopted provides the utilization of a phase change materials (PCMs) apparatus matched with an Organic Rankine Cycle (ORC) for electrical energy production. The solution proposed allows reduction of the temperature and mass flow rate variability of the off-gases. Results show an excellent reduction of the range of wall-temperatures, close to the off-gases and a relevant energy recovery.