WO1999020969A1

WO1999020969A1 - A product tube bend for tube heat exchangers

Info

Publication number: WO1999020969A1
Application number: PCT/SE1998/001875
Authority: WO
Inventors: Anders Sjöström
Original assignee: Tetra Laval Holdings & Finance S.A.
Priority date: 1997-10-23
Filing date: 1998-10-20
Publication date: 1999-04-29
Also published as: SE9703865L; AU9658398A; SE9703865D0

Abstract

The invention relates to a product tube bend (7) for a tube heat exchanger. The tube heat exchanger is of the type in which a bundle of heat transfer tubes (10) intended for product is surrounded by a jacket tube (4) intended for the heat transfer medium. These heat exchanger elements (1) are interconnected into a flow system. Product bends (7) are disposed to transport the product between two adjacent heat exchanger elements (1). The product bend (7) constitutes 180° and has, in both of its ends, a circular cross section. The centre of the product bend (7), at 90°, has an elliptical cross-sectional area (10). The product bend (7) is fully drainable regardless of how it is mounted in a heat exchanger.

Description

A PRODUCT TUBE BEND FOR TUBE HEAT EXCHANGERS

TECHNICAL FIELD

The present invention relates to a product tube bend for tube heat exchangers of the type which interconnects two adjacent heat exchange elements with heat transfer tubes disposed in the tube bundle, and in which the product bend makes up 180°.

BACKGROUND ART Tube heat exchangers are a common type of heat exchanger which are often employed for highly viscous products but also for less viscous products, or alternatively for products containing fibres or particles. A tube heat exchanger consists of one or more heat exchanger elements which are interconnected to form a flow system. The heat exchanger elements comprise one or more heat transfer tubes surrounded by an outer casing or jacket tube. The heat transfer tubes are interconnected into a product flow insert, the inserts in turn being interconnected by means of product tube bends in order to circulate the product which is to be heated or cooled, depending upon the process for which the heat exchanger is employed. The heat transfer tubes are enclosed in a jacket or casing tube which houses the heat transfer medium which may consist of water at various temperatures, steam or other types of liquids or gases. One such tube heat exchanger is described in detail in Swedish Patent Specification SE 501 908.

Heat exchangers of the above-outlined type are put to use in various processing industries and this type of heat exchanger is very common within the food industry. When being employed for foods, the demands on hygiene and washability of the tube heat exchanger are stringent in the extreme.

When the product flows between the different heat exchanger elements in the product tube bends intended therefore, it is vital to maintain the flow rate which the product has when it first enters the bend. A reduction in flow rate may entail a stagnation of the product in the bend and consequential problems with hygiene and difficulties in being able to wash the product bends satisfactorily.

In order to maintain the flow rate, use has normally been made of tapered tube sections between the heat exchanger elements and the product bends. These tapered tube sections have, however, given rise to another problem. The heat exchanger is not fully drainable, but the product bends must be released from their tube mountings in each respective heat exchanger element. When the heat exchanger is assembled in the factory, it is normally trial run with water in order to test its function. After the trial run, a minor quantity of water invariably remains in the tapered sections between the product bends and the heat exchanger elements, with the result that the heat exchanger, on storage outdoors or on transport under unfavourable weather conditions has fractured as a result of freezing.

OBJECTS OF THE INVENTION

One object of the present invention is to realise a product tube bend which permits maintained flow rate for the product and which gives full drainage capability for the heat exchanger regardless of how the product tube bends are mounted in a complete tube heat exchanger. The drainage capability for a heat exchanger is, in addition, a requirement placed by the authorities in certain countries.

The product tube bend must also satisfy the stringent requirements on washability and it must also be capable of being made with the precision required in the manufacture of product tube bends.

SOLUTION

These and other objects have been attained according to the present invention in that the product tube bend of the type described by way of introduction has been given the characterizing features that the bend has, in both ends, a circular inner cross sectional area which corresponds to the inner area of the heat transfer tube bundle, and that the centre of the bend, at

90°, has a cross sectional area which is elliptical.

Preferred embodiments of the present invention have further been given the characterizing features as set forth in the appended subclaims.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

One preferred embodiment of the present invention will now be described in greater detail hereinbelow, with reference to the accompanying

Drawings. In the accompanying Drawings: Fig. 1 shows, partly in section, a portion of a state-of-the-art tube heat exchanger; Fig. 2 shows, partly in section, a portion of a tube heat exchanger according to the present invention;

Fig. 3 shows, partly in section, a product tube bend according to the present invention; Fig.4 is a partial section taken along the C-C in Fig. 3;

Fig. 5 shows a horizontal mounting of a product tube bend according to the present invention; and

Fig. 6 shows a vertical mounting of a product tube bend according to the present invention. The accompanying Drawings show only those parts and details essential to an understanding of the present invention, and the tube heat exchanger in its entirety, which is well-known to a person skilled in the art, has been omitted.

DESCRIPTION OF PREFERRED EMBODIMENT

Both Fig. 1 and Fig. 2 show heat exchanger elements 1 which are interconnected to a flow system which constitutes a complete tube heat exchanger. Each heat exchanger element 1 consists of a number of heat transfer tubes 2 which are united into a bundle and are interconnected at each end of the heat exchanger element 1 by the intermediary of a tube plate 3. The bundle of heat transfer tubes 2 is surrounded by a jacket or casing tube 4. The jacket tubes 4 are interconnected pairwise with communicating tube sections 5.

The jacket tubes 4 enclose the heat transfer medium, i.e. the gas or liquid which is to heat or cool the product being processed in the tube heat exchanger. The heat transfer tubes 2 in their turn enclose the product which is to be processed.

Two adjacent heat exchanger elements 1 are interconnected by product bends 6, 7, of which Fig. 1 shows a state-of-the-art product bend 6 and Fig. 2 shows a product bend 7 according to the present invention.

The prior art product bend 6 displays tapered tube sections 8 between the bend 6 proper and the heat exchanger element 1, as has been necessary according to prior art technical solutions, in order to maintain the flow rate of the product through the bend 6. However, the tapered sections 8 have prevented the tube heat exchanger from being fully drainable, and regardless of how the product bends were mounted in the tube heat exchanger, a minor quantity of water has remained in the tapered sections 8 after trial running ex works, and on transport or storage under unfavourable conditions, this has given rise to fracture of the tube heat exchanger as a result of freezing. Also in production, these tapered tube sections have given rise to product being entrapped and remaining in the bend, which in turn has given rise to poorer hygienic conditions.

The product bend 7 according to the present invention (which is shown in detail in Figs. 3 and 4) consists of a 180° bend. Both ends of the bend 7 display circular cross section, with an inner diameter A. The diameter A is as great as the inner diameter D of the total bundle of heat transfer tubes 2. The product bend 7 is intended to be secured in one end of a heat exchanger element 1, for example by means of flange union 9.

From the circular cross section at both ends of the product bend 7, the cross section progressively changes so that the centre of the bend 7, at 90°, displays an elliptical cross section 10. The elliptical cross section 10 has a maximum diameter A and a minimum diameter B. As a result, a reduced cross section will be obtained which permits the flow rate through the product bend 7 to be maintained. By maintaining the flow rate through the product bend 7, stagnation points 11 are avoided where the product may be arrested and adhere to the walls of the bend, which jeopardises the hygiene of the process. A common stagnation point 11 is at the centre of the bend 7 at its inner wall.

The maximum diameter A of the elliptical cross section 10 should be placed such that it is always parallel with an imaginary plane M. The extent of the plane M is shown in Figs. 3 and 4. Consequently, the minimum diameter B of the elliptical cross section 10 will always be placed at right angles to the imaginary plane M.

By placing the elliptical cross section 10 in the above-described manner, there will be obtained, also in horizontal mounting of the product bend 7 between two heat exchanger elements 1 (Fig. 5), full drainage capability for the tube heat exchanger. In this case, the lower defining surface 12 of the bend is wholly parallel with the horizontal plane, so that no liquid remains in any part of the bend 7. An alternative mounting of the product bend 7 is vertical mounting (Fig. 6). Also in this position, the tube heat exchanger is completely drainable. The minimum diameter B of the elliptical cross section 10 should suitably be selected such that the area of the elliptical cross section is approximately equal to the total cross sectional area of all of the heat transfer tubes 2 included in the tube bundle. Novel technology, such as hydroforming, i.e. utilising a liquid which directly acts on the body which is to be formed, permits the forming of a product bend 7 according to the present invention in a relatively simple and economical manner. Hydroforming also permits manufacture of a product bend 7 with the high precision which is required for the bend 7 to fit in mounting into two adjacent heat exchanger elements 1.

As will have been apparent from the foregoing description, the present invention realises a product bend 7 in which the product may, with retained flow rate, be transported between two adjacent heat exchanger elements 1. As a result of the design of the bend 7, the tube heat exchanger is moreover completely drainable, regardless of in which position the product bend 7 is mounted.

The present invention should not be considered as restricted to that described above and shown on the Drawings, many modifications being conceivable without departing from the scope of the appended Claims.

Claims

WHAT IS CLAIMED IS:

1. A product tube bend (7) for tube heat exchangers of the type which interconnects two adjacent heat exchange elements (1) with heat transfer tubes (2) disposed in the tube bundle, and in which the product bend (7) makes up 180┬░, characterized in that the product bend (7) has, in both of its ends, a circular inner cross sectional area which corresponds to the inner area of the heat transfer tube bundle; and that the centre of the bend (7), at 90┬░, has a cross sectional area (10) which is elliptical.

2. The product tube bend (7) as claimed in Claim 1, characterized in that the elliptical cross sectional area (10) has a maximum diameter A which is equal to the diameter A of the circular cross sectional area; and that it has a minimum diameter B.

3. The product tube bend (7) as claimed in Claim 2, characterized in that the diameter A is always placed parallel with an imaginary plane M; and that the diameter B is always placed at right angles to the imaginary plane M.

4. The product tube bend (7) as claimed in any of the preceding Claims, characterized in that the elliptical cross sectional area (10) is approximately equal to the total cross sectional areas of the heat transfer tubes (2) included in the tube bundle.