A Hybrid Method for the cross flow compact heat exchanger design
( 2016 - Applied Thermal Engineering - Elsevier UK ) ( http://dx.doi.org/10.1016/j.applthermaleng.2016.10.018 )
Giuseppe Starace, Maria Fiorentino, Matteo Pietro Longo, Emanuela Carluccio
Despite their limitations, the cross flow compact heat exchangers are generally modeled by the eps-NTU and LMTD methods and this mainly leads to the absence of effective consideration on the heat transfer geometry at the micro scale. At the same time, numerical analysis applied to compact cross flow heat exchangers, having different and complex finned surfaces respectively at the hot and cold sides, involves high computational costs. A powerful alternative design procedure is here proposed that takes advantage of both numerical and analytical approaches. Hot and cold sides are numerically modeled and predictor functions for heat transfer and fluid dynamic performance are obtained with regression technique, for both sides. The whole cross flow heat exchanger is divided into a set of control volumes, including the fins geometry 3D accurate description of both sides and their separation wall. An analytic iterative method is then used to find a wall temperature distribution throughout and to determine the mass flow rate distributions on both sides starting from the results of the numerical analysis at the micro scale. The multi-scale approach leads to a better accuracy level with respect to the full-scale one and allows to profitably investigate different fins influence on flow distributions, local heat transfer and pressure losses through both sides of the heat exchanger.
Numerical analysis of a cross-flow compact heat exchanger for vehicle applications
( 2005 - Applied Thermal Engineering - Elsevier UK - http://dx.doi.org/10.1016/j.applthermaleng.2004.11.013 )
Emanuela Carluccio, Giuseppe Starace, Antonio Ficarella, Domenico Laforgia
A numerical thermo-fluidynamic study of a compact crossed flows heat exchanger (HX), used to cool the high-pressure oil used in hydraulic circuits of earth-movement industrial vehicles, was performed.
The numerical analysis was carried out to verify the influence of the hydrodynamic regimes of the fluids involved in the heat transfer process, induced by fins in the channels, on the performance of the whole HX. The analysis was developed through three steps of increasing complexity. After a simple model built to evaluate the consistent boundary conditions of temperature, a small scale analysis of the fluid–dynamic phenomena inside the HX was carried out, taking into account geometrical periodical units at oil (OS) and at air side (AS). With the results obtained in this way, the HX performances were evaluated on an overall scale, extrapolating the data up to the real dimensions in terms of heat transfer and pressure loss.
With the “small scale” approach at the OS the local heat flux and the pressure losses were quantified, using a laminar scheme and a high detail in the geometry description of the turbulence generators. With the “full scale” approach, then, simulations were performed considering a porous media with characteristics set up on the previous analysis. The global heat transfer coefficient and the pressure losses were so accounted for.
At the AS, the schematization was limited to two periodic portions of the flow and results allowed to evaluate both local and overall heat transfer coefficients. Results were again extrapolated to the real dimensions of the channels. The results come out from the AS detailed analysis were, then, related to the output of the ones at OS. This was done to obtain crossed confirmations of the overall results in terms of thermo-fluid–dynamic performance of the HX at design conditions.
Automotive Compact Supercharge-air Intercooler Numerical Analysis
A compact aluminium intercooler for supercharge air for use in cars and trucks was numerically studied moving from an overall approach to a deep insight in finnings.
( 2006 IHTC-13 - Sidney - Begell House inc. - doi:10.1615/IHTC13.p22.330 )
Giuseppe Starace, Emanuela Carluccio, Domenico Laforgia
The influence of different input values of cooling and supercharge air flowrates was observed, investigating microscopic effects on the flow field, on heat transfer local convective coefficients and macroscopic effects on performance variations in terms of heat transfer and pressure losses.
Triangular wavy finnings, trapezoidal offset strip finnings ( squared and rounded, single or coupled ) and inside finned tubes efficiencies were calculated with reference to the different input conditions, useful for possible correlation equations among adimensional parameters for future design and sizing activities.
Un nuovo pannello solare termico a nanofluidi
( 2009-Congresso nazionale ATI - L'Aquila - link )
Gianpiero Colangelo, Ernani Favale, Arturo de Risi, Giuseppe Starace, Domenico Laforgia
Obiettivo del lavoro è l’analisi del fenomeno della sedimentazione dei nanofluidi all’interno di pannelli solari piani, finalizzata ad adottare gli accorgimenti necessari alla sua attenuazione o alla sua completa eliminazione. Lo studio è condotto su pannelli a tubi trasparenti attraverso analisi ottica. In una fase iniziale si è realizzato un pannello solare piano a tubi trasparenti, con le dimensioni di un classico pannello disponibile in commercio, all’interno del quale si è fatto fluire un nanofluido a base di acqua e ossido di alluminio ( Al2O3 ). Le zone interessate dalla sedimentazione della fase solida erano il tubo collettore di ingresso, quello collettore di uscita e i tubi traversi La quantità di fase solida depositata è risultata essere dipendente dalla velocità del nanofluido nei tubi di ingresso e di uscita. Nella fase successiva si è realizzato un pannello solare piano, delle stesse dimensioni del precedente, con una modifica sui tubi di ingresso e di uscita, volta a eliminare il fenomeno della sedimentazione per effetto di una opportuna variazione di velocità del nanofluido. La forma era tale da garantire una velocità costante lungo tutta la loro lunghezza. Essa è stata ottenuta agendo sulla sezione di passaggio all’interno dei tubi attraverso l’introduzione di un solido opportunamente sagomato. Il nanofluido utilizzato era a base di acqua e Al2O3 ed era alimentato nelle stesse condizioni adottate per il pannello della prima fase. Per effetto delle modifiche apportate il fenomeno di sedimentazione si è ridotto a livelli trascurabili e, in certi punti, è stato completamente eliminato. Il pannello solare modificato, dotato di tubi a sezione variabile, è stato oggetto di domanda di brevetto per invenzione industriale depositata all’Ufficio Italiano Brevetti e Marchi ( N° LE2010A000006 ) e successivamente è stata depositata anche la domanda di brevetto internazionale ( Application number: PCT/IB2011/051988 ).
(Proceedings of ESDA2006 8th Biennial ASME Conference on Engineering Systems Design and Analysis, Paper no. ESDA2006-95604 pp. 383-390) - dx.doi.org/10.1115/ESDA2006-95604)
Paolo Maria Congedo, Giuseppe Starace
Numerical and Experimental Characterization of a Plate Compact Multipass Counter-Flow and Locally Cross-FLow Recuperator
A compact and efficient heat exchanger for exhaust gas recovery energy was needed to raise the total efficiency of a thermo-photovoltaic system TPV ( Thermo-Photo-Voltaic ) for automotive applications ( see  ). In order to respect the strict condition of a high heat transfer surface to volume ratio, a heat exchanger configuration with a plate compact multi-pass counter flow and locally cross-flow recuperator has been chosen. The goal of this work is the understanding of the behaviour of the heat exchanger with numerical andexperimental analysis for different geometrical and operating conditions. A high number of dimensions and manufacturing constraints was evaluated before reaching a definite design of a compact and efficient heat exchangerto be tested in the lab for initial experiments.
The experimental work was needed in order to validate the numerical model. As the material needed for the real application could not be easily manufactured and instrumented in a workshop, a simplified real model, made of brass, was built, in order to compare numerical results and experimental findings. It was supposed that results obtained in this way would be sufficient to be considered valid when extrapolated in the real heat exchanger high temperature operating conditions and manufacturing material. The experimental results have been successfully compared with numerical ones obtained with the Fluent CFD code.
Curves of performance ( epsilon-NTU diagram plotted as a function of the ratio between the minimum and the maximum thermal capacities of the flows and pressure drop -mass flowrate diagram as a function of the average temperature ) have been obtained and were useful to choose the adequate configuration for different applications, depending on the requested heat transfer and maximum allowable pressure drop. The output of the investigation was: heat transfer, outlet temperatures for both air flows, heat exchanger efficiency, differential pressure drop for both hot andcold sides. After this validation final numerical simulations have been carried out in order to understand the dependence of the heat exchanger efficiency on other geometrical parameters and operating conditions such as plates dimensions, numbers and height of vanes, operating pressure and so on.