Free convection heat transfer in finned heat exchangers

Moor, G., 1992. Free convection heat transfer in finned heat exchangers. MPhil, Nottingham Trent University.

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Abstract

The steady state heat transfer, from a vertical, extended surface heat exchanger, under the influence of free convection has been investigated. The investigation used a liquid crystal approach, in conjunction with acrylic models. The models represented a cast iron heat exchanger, with base dimensions of 200 mm wide X 160 mm high, these dimensions being maintained throughout the investigation. The extended surfaces used were vertical fins of 3 mm width, their spatial separation being altered between 11 mm and 37 mm, and their length being altered between 15 mm and 30 mm.

The method used, in this investigation, was to pre-heat the heat exchange model, and allow it to cool in free convection, whilst recording the isotherms onto video tape. The timing data, deduced from the video recordings, were analysed using a one dimensional transient technique. The resultant local heat transfer coefficient values are plotted to give contour maps. The validity of the technique is verified, giving good agreement to previously published correlations for vertical flat surfaces in free convection, with the presented data giving a non-dimensional correlation of.

Nux = 0.805 Pr1/4 Grx1/6

The investigation defines an optimal spatial separation, for the fins, of 14 mm, based upon volumetric optimisation. There is also a dependency shown, for the increase in heat transfer, above that of a vertical flat plate, to the total volume of the fins added to a flat plate. The equation given is with reference to an overall total fin volume of 60 x 10-6 < VfTOT < 165 x 10-6, the equation being.

Qinc = -25367 (VfTOT X103)2 + 9.313 V fTOT X106 - 300.293

This equation is expanded to provide a correlation between the fin length and increase in heat transfer, above that of the vertical flat plate, giving

Qinc = -228303 H2 L2 + 27939 H L N - 300.293

and the maximum number of fins given as an integer value, being related to the spatial separation and base width by.

Nmax = BW/0.003 + S

Item Type:	Thesis
Description:	In collaboration with Baxi Partnership Ltd.
Creators:	Moor, G.
Date:	1992
ISBN:	9781369324518
Identifiers:	Number Type PQ10290202 Other
Rights:	© Copyright Notice: This copy of the thesis has been supplied under the condition that anyone who consults it is understood to recognise that its copyright rests with its author and that no quotations from it may be published without the authors prior consent.
Divisions:	Schools > School of Science and Technology
Record created by:	Linda Sullivan
Date Added:	16 Jun 2021 13:40
Last Modified:	17 Oct 2023 13:38
URI:	https://irep.ntu.ac.uk/id/eprint/43092

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