A future design for intercoolers

Hybrid plate/tubes concept[/caption]

A number of alternative technologies are under investigation and show  potential for both performance improvements or cost reduction in intercooler technology for compressors. One is is the so called “Hybrid plate/fins” cooler. Hybrid plate/tubes heat exchangers are manufactured by piling and welding several corrugated plates with a given geometry so that cooling media can flow in closed loop path while gas can go through straight “channels” in cross flow.

This article contains excerpts from the paper, "Influence of inter-coolers technologies on the performance of isotherm centrifugal compressors," presented by Luca Porreca of MAN Diesel & Turbo Schweiz AG. Zürich, Switzerland.

With this design, the area ratio between the wetted surfaces of air and coolant is approximately equal to 1, which means that the heat transfer is significantly improved when compared with the classical tube/fins design. The air passages are designed so that they have the lowest pressure losses i.e. the passage is almost “see through”. While the water channels, where the pressure losses are much less important, is designed with bumps and curves to increase heat transfer coefficient. Simulations on the heat transfer coefficient shows that, keeping the same overall dimensions and flow parameters, the heat transfer of the Hybrid plate/tubes is ~200 W/m2K that means a factor 2.5 when compared with the tube/fins arrangement. As a consequence, investigation carried out on axial-radial isotherm compressor [13], with external coolers, shows that an equivalent Hybrid cooler (able to transfer the same overall heat) is approximately half in length compared with the “standard” tube/fins cooler bundle (Table 2 [12]).

In inline radial isotherm compressors, the size reduction of the intercoolers is much more beneficial because the casing size can be also decrease, while keeping the rotating component unchanged. A smaller casing design has also a big impact on the overall cost of the compressor, estimated in about 10%. The disadvantage of the Hybrid plate/tube design is the cost of such arrangement. Estimated cost is about >30% higher than conventional plate fin/tube arrangement.