Chimneys in wooden roofs: a 3D steady numerical model for the prediction of the temperatures

Chimneys convey exhaust gas produced in domestic heat appliances to the external environment and to do this they have to pass through floors and roofs: if these elements are made up of flammable materials, the fire hazard may occur. This article presents the verification of a 3D numerical model set for the determination of the stationary temperatures reached on the flammable materials in the vicinity of chimneys. The verification has been done comparing the temperatures measured in experimental tests with those estimated by means of the numerical model. Results show that the 3D numerical model is a valid tool for the analysis of heat transfer between chimney and roof. Since in the experimental tests it is not always possible to reach stationary temperatures, a lumped element model to estimate them is also proposed and it could support the chimney certification

Studio numerico su modelli termofluidodinamici della regione bifase nella solidificazione di acciaio in cavita' chiuse

Dottorato di ricerca in energetica. 12. ciclo. Relatore G. P. Beretta. Coordinatore G. AngelinoConsiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome; Biblioteca Nazionale Centrale - P.za Cavalleggeri, 1, Florence / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Data on temperature-time curves measured at chimney-roof penetration

Data on temperature-time curves measured at chimney-roof penetration are reported here. The tests were performed in different configurations in order to reproduce all the possible conditions in which a chimney may operate. To do this, a chimney was installed in a corner test structure and in an axi-simmetric test structure, and in three roofs of different thickness, thermal resistance, and layers position. The space between chimney and roof was left open, sealed with metal sheets, sealed with insulating panels, and filled of insulating material respectively

Interplay of Casting and CFD Software for Improved Accuracy of the Simulation

The advantages of using two simulation codes in casting simulations have been investigated: a fnite element code designed to simulate casting pro-cesses, and a fnite volume CFD code designed to simulate thermal and uid-dynamic boundary conditions. The temperature-time curve at an important injection point of a mould system has been measured: in this point, the agreement between numerical and experimental results is very sensitive to the specific boundary conditions that are assumed in the casting simulation. It has been demonstrate that the agreement is good if instead the choice of boundary condition parameters are chosen and tuned to experimental data with the help of a CFD code

Computing the Exergy of Solar Radiation From Real Radiation Data

The decrease of fossil fuels availability and the consequent increase of their price have led to a rapid evolution of renewable market and policy frameworks in recent years. Renewable resources include solar radiation, which is of considerable interest as it is inexhaustible, free, and clean. In order to calculate how much work can be obtained from solar radiation, several methods have been proposed in the literature and are here reviewed. In this paper, a single exergy factor to be applied to the total radiation measured on horizontal surface in a given place is proposed. The factor is estimated from both direct and diffuse radiation

DISPOSITIVO ISOLANTE PER CANNE FUMARIE INSTALLATE IN STRUTTURE EDILIZIE

DISPOSITIVO ISOLANTE PER CANNE FUMARIE INSTALLATE IN STRUTTURE EDILIZIE La presente invenzione ha come oggetto un dispositivo per limitare la temperatura dei materiali infiammabili di tetti attraversati da canne fumarie. Il dispositivo della presente domanda di brevetto è destinato al settore dell’evacuazione fumi nel settore delle costruzioni edile e/o industriale, da impiegarsi laddove si ravvisano condizioni di pericolo di incendio per la presenza di materiali combustibili, come ad esempio solai o tetti in legno. Scopo dell’invenzione è limitare la temperatura dei materiali combustibili in prossimità di una canna fumaria, evitare la formazione di ponti termici, e generare un recupero del calore proveniente dalla canna fumaria. Il dispositivo deve essere montato sulla superficie esterna della canna fumaria nel punto in cui quest’ultima attraversa elementi edilizi quali solai e/o tetti. Il dispositivo è costituito da elementi in materiale isolante ed elementi in materiale conduttivo che per la loro forma e posizione consentono di limitare la temperatura dei materiali infiammabili del tetto in cui è installata la canna fumaria

Design of a 5th Generation District Heating Substation Prototype for a Real Case Study

The evolution of district heating networks is moving toward low temperatures in heat distribution with so called 4th generation networks. However, the lowest heat transfer fluid temperatures in district heating are achieved through ultra-low temperature networks, referred to as 5th generation district heating networks (5GDHNs). Low temperatures in heat distribution results in an extremely different configuration of 5GDHN compared to traditional district heating network, especially in the grid substation due to the inability to directly couple the grid with the buildings. This paper presents a detailed design of a 5th generation substation prototype, which is carried out to verify the proper operation and monitor the performance of this type of substation in a real case study. The prototype is fed by low-temperature waste heat, currently dissipated through evaporative towers, and will be built in the city of Brescia, Italy. The layout of the substation prototype, consisting of a bidirectional pumping system, a reversible water-to-water heat pump, an inertial thermal energy storage and a heat exchanger, is presented. An analysis is performed to figure out which refrigerant offers the best performance of the heat pump. In addition, fixed the refrigerant, the performance of the grid connected heat pump is found to be increased from 29.5% to 55.5% for both heating and cooling compared with a stand-alone air-to-water heat pump solution. Finally, the process flow diagram and the piping and instrumentation diagram of the substation are presented and commented

Design of a 5th Generation District Heating Substation Prototype for a Real Case Study

The evolution of district heating networks is moving toward low temperatures in heat distribution with so called 4th generation networks. However, the lowest heat transfer fluid temperatures in district heating are achieved through ultra-low temperature networks, referred to as 5th generation district heating networks (5GDHNs). Low temperatures in heat distribution results in an extremely different configuration of 5GDHN compared to traditional district heating network, especially in the grid substation due to the inability to directly couple the grid with the buildings. This paper presents a detailed design of a 5th generation substation prototype, which is carried out to verify the proper operation and monitor the performance of this type of substation in a real case study. The prototype is fed by low-temperature waste heat, currently dissipated through evaporative towers, and will be built in the city of Brescia, Italy. The layout of the substation prototype, consisting of a bidirectional pumping system, a reversible water-to-water heat pump, an inertial thermal energy storage and a heat exchanger, is presented. An analysis is performed to figure out which refrigerant offers the best performance of the heat pump. In addition, fixed the refrigerant, the performance of the grid connected heat pump is found to be increased from 29.5% to 55.5% for both heating and cooling compared with a stand-alone air-to-water heat pump solution. Finally, the process flow diagram and the piping and instrumentation diagram of the substation are presented and commented

Safety at chimney-roof penetration : A numerical investigation

Chimneys convey exhaust gas produced in heat generators to the external ambient. To do this, they cross building elements such as floors and roofs, which can be made of flammable materials such as wood, wood fiber, cellulose, etc. This represents a dangerous condition that can lead to the overheating of the structure and, consequently, to possible fires. In recent years, numerous roof fires have occurred in Europe due to the presence of a chimney, and some of these have also involved certified chimneys. The aim of the certification procedure is the determination of the distance between chimney and flammable structures to avoid fires. This paper describes an investigation performed to understand the causes of the high number of fires and to propose solutions to the roof fires problem. The study was carried out numerically and experimentally, and consisted of three steps. Firstly, the chimney certification procedure was investigated to highlight possible weaknesses. Then, by means of a 2D and a 3D numerical models, the variables affecting heat transfer at chimney-roof penetration were identified. Finally, solutions and prescriptions to prevent roof fires are proposed. The solutions consist of a set of tables for checking chimney installations, and a universal device to be installed between chimney and roof to prevent the overheating of the latter, also in very critical conditions represented by soot fires, and installations in very thick and insulating roofs.publishedVersionPeer reviewe