Heat exchange – Tubular structure – With discrete heat transfer means
Patent
1990-12-28
1991-09-10
Flanigan, Allen J.
Heat exchange
Tubular structure
With discrete heat transfer means
1651091, F28F 120
Patent
active
050465562
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a surface enlarging element for heat-exchanger tubes of the type defined in the preamble to claim 1.
When heat is being exchanged between media of greatly differing thermal exchange content, the heat exchanger surface in contact with the medium with lower thermal exchange content is normally provided with surface enlarging elements so that the heat flow balances that which can be achieved on the opposite side of the heat exchanger.
Such is the case, for instance, with steam or hot-water boilers or with economisers connected after such boilers, where water passes through the tubes while flue gases or other hot fluids travel along the exterior of the tubes, usually in a direction perpendicular to the longitudinal axis of the tubes. (Longitudinal flow is also known.)
Various surface enlarging elements have been developed over the years, comprising pins, fins, plates and strips which are welded perpendicular to or along the tubes, as well as elements in ribbon form being applied helically around and along the tube.
With known surface enlarging elements it has proved difficult to limit production costs for the heat exchangers and at the same time offer heat exchangers which can relatively easily be kept clean on the outside and are subject to negligible deformation during operation.
One object of the invention is therefore to propose a surface enlarging element for heat exchanger tubes of the above type, which element can be produced easily and at low cost and can be simply and cheaply welded to the tube, resulting in a construction which can be efficiently cleaned and is subject to a negligible deformation during operation.
Although the invention is described above and in the following as pertaining to heat exchangers for exchanging heat between flue gases and water for steam production, it should be obvious that the surface enlarging element according to the invention can perfectly well be used for heat exchangers designed for other fluids.
Heat exchangers of the type under consideration generally comprise parallel tubes arranged with equal spacing between them, the surface enlarging elements on adjacent tubes substantially abutting each other in common normal planes to the tube axes so that the surface enlarging elements in each such common plate together substantially define a complete screen, these screens guiding the gas flow through the heat exchanger. The surface enlarging elements on a tube therefore suitably cover a rectangular, preferably square surface, centered around the tube.
There are conventionally two main types of surface enlarging elements, differing in the manner in which they are secured to the tube. One type consists of plates having a central hole in which the tube is placed and secured to the plates. The other type comprises substantially rectangular plates with a length substantially twice the width. These plates have a substantially semi-circular recess in one long side and are designed to be resistance welded to the tube so that the plates suitably lie in a normal plane to the axis of the tube. The plates are preferably welded in pairs to opposite sides of the tube in a common plane.
However, we have realized that, from the production aspect the second type of plate is necessary. However, we have found from experience that the known surface enlarging elements of this type do not function satisfactorily. They exhibit an unsatisfactory thermal balance, for instance, resulting in deformation during operation. Such deformation entails an uncontrolled rise in flow resistance in the heat exchanger, as well as the risk of dirt and soot being more quickly deposited on the plates, which in turn necessitates more frequent cleaning. We have thus established that the heat flow in the surface enlarging element becomes unevenly distributed around the tube in the known surface enlarging elements.
We have discovered that to achieve economic production and good function of the heat exchangers, i.e. to achieve the object of the invention, the surface enlarging element
REFERENCES:
patent: 2402262 (1946-06-01), Sewell
patent: 4648443 (1987-03-01), Szucs et al.
Flanigan Allen J.
Gadelius Sunrod AB
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