Heat transfer and pressure drop in tubes with enhanced structures: synthetic review of the latest correlations

The aim of this report is to list and take a critical look at methods for calculating heat exchange coefficients and coefficients of friction when using improved-structure tubes in single-phase and two-phase flows (evaporation and condensation).

This document is available exclusively to GRETh members who requested a report on this topic at the 2020 Annual General Meeting.

In this report, we have focused on the tube technologies that are most widely studied and likely to be used in industry. In this context, the technologies studied in this report concern :

• twisted oval tubes,
• tubes with high and low fins,
• micro-winged tubes and porous coatings,
• The tubes are alternately flattened.

In general terms, this report provides, after a thorough screening of scientific publication databases, methods for calculating heat exchange coefficients and coefficients of friction in the form of correlations, making them easy to use.

The publications selected are those that we have judged to be the most relevant according to the following main criteria:

• A geometry that is applicable and viable in the industrial field,
• Wide range of operating conditions and geometries.

In terms of content: beyond writing the correlations and their descriptions (construction and validity domain) and the unique analysis of the publication, points which are obviously included in this report, we set out to make :

• Comparisons of the selected correlations with known and recognized correlations applicable to the same conditions and improved geometries in order to judge the quality of the results obtained with older methods;
• As far as possible, comparisons with reference correlations in smooth tubes, under similar operating conditions, in order to judge the quality of the intensifications provided by the surface structuring studied.

The results presented in this report, in the form of graphs showing the evolution of the transfer coefficient and friction coefficient as a function of Reynolds number, are therefore the result of coding and calculating the new correlations (as well as the usual correlations) in the specific cases mentioned in the figure legends and in the body of the text.

We hope this report will provide you with concrete elements that can be incorporated into your heat exchanger sizing codes and/or complete system simulations.

This document is available exclusively to GRETh members.