METHOD OF BENDING OF FLAT TUBES FOR HEAT EXCHANGERS AND BENT FLAT TUBE
A heat exchanger, bent flat tube and method for bending of flat tubes for heat exchangers. The flat tube is initially formed as a straight flat tube and is bent in its central portion about a side end by an angle of about 180°. In bending the flat tube, the overall cross-sectional area and height of the flat tube is maintained in the bent central portion. Additionally, the top and bottoms side walls of the flat tube are maintained planar and parallel with one another. When provided in a heat exchanger with other bent flat tubes, fins are located between adjacent flat tubes and are provided in the curved central portion. The bent flat tubes also connect to a header located on one side of the heat exchanger.
1 . A method for bending of flat tubes for heat exchangers, whereby the flat tube is provided with an inflow portion. a curved central portion, and a return flow portion for a refrigerant co-planar therewith, the heat exchanger being provided with a header having separate portions to distribute and collect the refrigerant. at least two flat tubes stacked in relation to one another being connected to the header and fins being located between the flat tubes, the method comprising the following steps:
forming a straight flat tube having a longitudinal axis;
bending the flat tube at a central portion about a side end of the flat tube by an angle of about 180° relative to the longitudinal axis;
processing the flat tube at an inner bending radius;
making the flat tube longer at an outer bending radius during bending;
generally maintaining the overall total cross-sectional area and the thickness of the flat tube in the curved central portion, whereby the top side wall surface and the bottom side wall surface of the flat tube are maintained planar and aligned parallel to each other.
2 . The method of claim 1 wherein bending is carried out in a temperature range of between about 20° C. and 150° C.
3 . The method of claim 1 wherein the step of bending the flat tube includes the step of securing the cross-sectional area of the flat tube.
4 . The method of claim 1 wherein the step of bending the flat tube includes the step of securing the flat tube relative to a mandrel and using a bending device.
5 . The method of claim 1 wherein the step of bending the flat tube includes the step of overbending the flat tube because of the backspring of the flat tube.
6 . A bent flat tube for a fin and tube heat exchanger, the bent flat tube comprising: a flat tube defining a longitudinal axis and including an inflow portion, a curved central portion and a return flow portion configured for a refrigerant to flow therethrough, the central portion of the flat tube having a plane bend at an angle in the range of 160° to 180°, whereby throughout the curved central portion a substantially constant overall cross-sectional area and thickness of flat tube exists, the top side wall surface of the flat tube being planar and parallel to the bottom side wall surface in the curved central portion.
7 . The bent flat tube of claim 6 incorporated in a heat exchanger.
8 . The invention of claim 7 wherein the heat exchanger includes a plurality of bent flat tubes stacked adjacently on top of one another.
9 . The invention of claim 8 wherein the plurality of bent flat tubes are parallel to one another and at least one fin is located between adjacent ones of the bent flat tubes.
10 . The invention of claim 9 wherein the at least one fin is provided in the curved central portion.
11 . The invention of claim 7 wherein the heat exchanger includes a header on one side thereof and the inflow portions and return flow portions of the plurality of flat tubes are connected to the header.
12 . The invention of claim 7 wherein the bent flat tube defines a plurality of passageways therethrough.