The present analysis is pertaining to an experimental investigation, using an infrared thermography (IR) of fluid dynamics and heat transfer in forced air flows over a surface enhanced by different geometry and scale structures. Heat transfer, in forced convection inside rectangular channels, is a very interesting matter for industry. It is encountered in critical heat transfer applications such as turbine-blade cooling as well as in devices which are largely used in compact exchangers like plate -fins. Enhancing heat transfer in these situations would mean the operating limits are increased and thus a more efficient and compact device is created. In reality, this work deals with only the local measures in external forced convection on a ribbed surface skimmed over by turbulent flow. Moreover, by means of this internal geometry, we can only obtain a global vision of the problem by effectuated measurement: obtaining local data useful for an exact analysis is much more complex, so it is necessary to use external pattern . To sum up, the present study is an investigation of the average thermal performances under an external flow condition, of surfaces by square cross-section ribs with different dimensions, different pitches (progress ratio: 10, 20, 40, 13.3), and different configurations (continous, “machened”). Experimental analysis consists in evaluating the mean heat transfer characteristics of forced air-flows over a surface, with the plane wall enhanced with ribs variously configured and arranged according to the flow direction. Surfaces will be operated under fixed heat flux conditions, and air flow rates will be varied so that the Raynolds numbers can range between 40000 and 200000. This investigation is of upmost importance to industry, as it is encountered in many devices which are widely used in many applications, such as compact heat exchangers and turbine blade cooling devices. The aim of the work was to study the effect of rib spacing on the thermal performance of the ribbed channel. It is note, on the other hand, that the three-dimensional secondary motion produced by the transverse ribs distorted the mean flow pattern and enhance the heat transfer performances till up 200%.
Obiettivo del Lavoro è lo studio, sperimentale, in convezione forzata esterna, dell’incremento di scambio termico su superfici investite da flussi turbolenti, mediante l’uso di nervature di varia forma (spigolo di 3 e 4 [mm]) e configurazione (progress ratio: 10, 20, 40, 13.3) in modalità continua ed interrotta. Lo studio si e’ stato supportato da misure locali mediante termografia infrarossa (IR). Si e’tentato di raffinare lo studio del fenomeno della turbolenza e dei metodi di filtraggio supportando la fase sperimentale con una buona base teorica. E’ opportuno precisare che tale analisi è principalmente orientata allo studio della termo-fluidodinamica nella convezione forzata all’interno di canali con superfici variamente strutturate. Tale approccio, tuttavia, pur essendo un buon estimatore di misure globali, poco si presta alla realizzazione di studi locali, per i quali si ricorre ad assetti alternativi. Nel caso in esame, ci si è rivolti alla geometria esterna. L’analisi sperimentale consisterà nella determinazione delle caratteristiche medie di scambio termico di flussi ad elevati Reynolds, su superfici che riproducono in scala alcune situazioni tecnologiche d’interesse. In riferimento a canali a sezioni rettangolari, le superfici corrugate operano con condizioni al contorno di flusso imposto, mentre le altre due generalmente sono considerate adiabatiche. La portata d’aria e’ fornita da un ventilatore e può essere variata in modo tale da avere un finestra operativa di numeri di Reynolds compresi tra 40000e 200000. Operativamente, i provini “corrugati”, sono stati opportunamente inseriti in camera di prova, mediante un supporto aerodinamico costruito ad hoc ed investiti da un flusso in convezione forzata. Le prove sono state condotte a differenti regimi di moto con nervature di varia natura disposte in differenti configurazioni. Noto e’, che la presenza di corrugazioni porta a un incremento di scambio termico, rispetto al caso lastra piana, compreso tra il 100% ed il 200%. E’ stato interessante comprendere come la forma o la disposizione di tali nervature abbiano esaltato lo scambio termico, turbolenziando il flusso.
Analisi dello scambio termico in convezione forzata su superfici corrugate
CIMINA', SUSANNA
2010/2011
Abstract
The present analysis is pertaining to an experimental investigation, using an infrared thermography (IR) of fluid dynamics and heat transfer in forced air flows over a surface enhanced by different geometry and scale structures. Heat transfer, in forced convection inside rectangular channels, is a very interesting matter for industry. It is encountered in critical heat transfer applications such as turbine-blade cooling as well as in devices which are largely used in compact exchangers like plate -fins. Enhancing heat transfer in these situations would mean the operating limits are increased and thus a more efficient and compact device is created. In reality, this work deals with only the local measures in external forced convection on a ribbed surface skimmed over by turbulent flow. Moreover, by means of this internal geometry, we can only obtain a global vision of the problem by effectuated measurement: obtaining local data useful for an exact analysis is much more complex, so it is necessary to use external pattern . To sum up, the present study is an investigation of the average thermal performances under an external flow condition, of surfaces by square cross-section ribs with different dimensions, different pitches (progress ratio: 10, 20, 40, 13.3), and different configurations (continous, “machened”). Experimental analysis consists in evaluating the mean heat transfer characteristics of forced air-flows over a surface, with the plane wall enhanced with ribs variously configured and arranged according to the flow direction. Surfaces will be operated under fixed heat flux conditions, and air flow rates will be varied so that the Raynolds numbers can range between 40000 and 200000. This investigation is of upmost importance to industry, as it is encountered in many devices which are widely used in many applications, such as compact heat exchangers and turbine blade cooling devices. The aim of the work was to study the effect of rib spacing on the thermal performance of the ribbed channel. It is note, on the other hand, that the three-dimensional secondary motion produced by the transverse ribs distorted the mean flow pattern and enhance the heat transfer performances till up 200%.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/26861