US 4,498,220 AGranted

Method for pre-expanding heat exchanger tube

AssigneeThe Trane Company

InventorsDonald S. Fiegen, Chester D. Ware

Life of this patent

Estimating the term…

Loading patent…

Abstract

This invention is a method for pre-expanding a heat exchanger tube prior to its insertion into a tube sheet. A tubular mandrel having an elastic bladder sheath sealed at each end is inserted into the tube and positioned at the point where the tube is to be expanded. A die with an annular recess approximating the shape to which the tube is to be expanded is clamped around the outer surface of the tube, concentric to the mandrel. The elastic bladder is then pressurized with hydraulic fluid pumped through a passage in the mandrel, thereby deforming the tube outward so that it conforms to the recess in the die. A heat transfer enhancement treatment thereafter may be applied to the exterior of the tube between the expanded sections, without concern that it may crack off when the tube is installed in a tube sheet. In addition, the hydraulic pre-expansion process prevents or minimizes cracking of the tube which sometimes occurs when a tube is expanded to an equivalent diameter in a single operation.

Claims10

Dependent claims

A method of expanding a heat exchanger tube to which a nucleate boiling heat transfer enhancement treatment is to be applied, and seating the tube within a bore of a tube sheet or a tube support without significant degradation of the treatment, said method comprising the steps of:

a. inserting an elongate mandrel into the bore of the tube, said mandrel including an elastic bladder concentrically mounted on the mandrel and sealed at each end;
b. positioning the mandrel inside a section of the tube to be expanded;
c. positioning a die having an internal annular recess with a diameter approximately equal to or greater than the expected diameter of the tube where the nucleate boiling heat transfer enhancement treatment is to be applied, so that the recess concentrically encompasses the exterior of the tube where the mandrel has been positioned;
d. injecting a fluid under pressure through a passage in the mandrel, to expand the elastic bladder outward against the interior of the tube, causing the tube to deform and expand into the annular recess of the die;
e. reducing the pressure and removing the die and mandrel from the tube;
f. applying the nucleate boiling heat transfer enhancement treatment to the exterior of a section of the tube which is not expanded;
g. inserting the expanded section of the tube into a bore of the tube sheet or tube support;
and
h. mechanically roll swaging the expanded section radially outward so that the tube is in intimate contact with the inner surface of the bore.

6 more elements

Dependencies are inferred from the claim text.