[0001] This invention relates to heat exchangers and particularly to heat exchangers of
the kind having a plurality of parallel tubes enclosed within a shell and having an
inlet and an outlet for passing fluid through the tubes. A plurality of fin elements
extend across the tubes to form secondary heat exchange surfaces and another fluid
is fed between the tubes to pass over the secondary surfaces.
[0002] Heat exchangers of this kind have been disclosed in British Patents 717,613 and 1,544,927.
In some cases the secondary surface fin elements have been formed with louvres or
slits to improve the heat transfer characteristics of the heat exchanger.
[0003] It has also been proposed in British Patent 818,589 to provide fin and tube heat
exchangers in which the tubes pass through the fins and in the spaces between the
tubes the fins are formed with pairs of flanges.
[0004] It is an object of the invention to provide a heat exchanger of the kind described
in which the heat exchange characteristics are enhanced.
[0005] According to the invention a heat exchanger comprises a plurality of circular-section
tubes parallel to and spaced from one another, a shell disposed around the tubes,
an inlet and an outlet for passing fluid through the tubes, a plurality of secondary
surface fin elements lying in parallel planes extending transverse to the tubes, and
inlet and outlet means for feeding a further fluid through the spaces between the
tubes and over the elements in a direction generally parallel thereto, the elements
each being formed with openings between the tubes and the openings being flanked by
tags extending transverse to the planes of the elements, the tubes being arranged
with spacings between the tubes to achieve a substantially constant cross-section
in the direction of flow of said further fluid. In an arrangement of tubes in which
the tubes are in rows transverse to the direction of flow and the tubes of alternate
rows are staggered by one half the pitch of the tubes in each row, the spacing of
the tubes in each row from one another is greater than the spacing of the tubes in
one row from the tubes in adjacent transverse rows. Preferably the spacing of tubes
from one another in each row is twice the spacing of the tubes in each row from tubes
in adjacent rows. In this way the velocity of said further fluid is kept relatively
constant and acceleration and deceleration of the fluid is avoided with consequent
reduction in pressure loss across the heat exchanger.
[0006] Conveniently the tags lie generally parallel to the direction of flow of said further
fluid over the elements and the tags are formed in pairs so that one tag lies to each
side of said opening.
[0007] Preferably, by the use of baffles, the further fluid is constrained to pass in a
generally sinuous path through the space between the tubes and over the fin elements.
[0008] Further features of the invention will appear from the following description of an
embodiment of the invention given by way of example only and with reference to the
drawings, in which:-
Fig. 1 is a part sectional side elevation of a heat ezchanger.
Fig. 2 is an elevation of a fin element of the heat ezchanger of Fig. 1.
Fig. 3 is an enlarged view of part of the fin of Fig. 2, and
Fig. 4 is a section on the line 4-4 in Fig. 3.
[0009] Referring to the drawings and firstly to Fig. 1, a heat exchanger includes a cylindrical
shell 10 at the ends of which are manifolds 11 including an outlet pipe 12 and an
inlet pipe 13 for fluid acting as a heat transfer medium; for example the fluid may
be water.
[0010] A plurality of circular-section tubes 14 extend between tube plates 15 bounding the
manifolds 11 to conduct the water or other fluid between the inlet and outlet and
the tubes lie parallel to and spaced from one another. The tube plates 15 close off
the spaces between the tubes 14 from the manifolds 11.
[0011] A series of intermediate baffles 17a to 17e are located between the manifolds at
right angles to the tubes and spaced from one another. The baffles are spaced alternately
from the upper and lower walls of the shell 10.
[0012] A plurality of secondary heat exchanger fin elements 20 lie at right angles to and
across the tubes 14 and are regularly spaced from one another in the direction of
the tubes, the upper and lower edges of the elements 20 being spaced from the upper
and lower walls of the shell 10. Inlet and outlet pipes 21 and 22 are located in the
upper part of the shell 10 at opposite ends thereof to admit heat exchange medium,
for example oil, to the spaces around the tubes. The presence of the baffles 17a to
17e and the fins 20 ensures that the flow path of the oil or other fluid is sinuous
and generally parallel to the planes of the elements 20. The fluid flows first down
from the inlet 21 over the fins 20, under the baffle 17a, upwards over the fins 20
and over the baffle 17b, and so on, until the fluid leaves the shell upwardly through
the outlet 22.
[0013] It will be seen, in particular from Fig. 2, that the tubes 14 are arranged to lie
in horizontal rows R in one direction, and in a direction at a right angle to said
rows R the tubes are in vertical rows S. The rows R lie transverse to the general
direction of flow F and the tubes in alternate rows R are staggered by one half the
pitch of the tubes in the rows R. If, as seen in Figs. 2 and 3, the spacing of the
tubes in the rows R is y, the spacing of each tube in a row R from the tubes in adjacent
rows R is x and the relationship between x and y is such that x is less than y, and
preferably of the order of y = 2x. Such a spacing ensures that the cross-sectional
area of the flow of fluid around the tubes remains substantially constant and the
velocity of the fluid is therefore substantially constant thereby avoiding acceleration
and deceleration of the fluid. Accordingly pressure loss in the heat exchanger is
kept low.
[0014] The fins 20 are formed with openings 25 and associated tags 26 as seen in Figs. 3,
4 and 4. Openings are formed between adjacent tubes 14 in rows R and at the ends of
rows R. The tags 26 are formed in pairs out of bent over portions of the fin elements
20 and lie at right angles to the planes of the fins. The tags 26 also lie generally
parallel to the general direction of flow F and the openings 25 are formed as rectangular
openings by the action of forming the tags.
[0015] The tags 26 and associated openings 25 provide edges to the fluid thereby reducing
boundary layer thickness of fluid on the fins. High heat transfer rates can be achieved
without undue pressure losses being created.
1. A heat exchanger comprising a plurality of circular section tubes 14 parallel to
and spaced from one another, a shell 10 disposed around the tubes, an inlet 13 and
an outlet 12 for passing fluid through the tubes 14, a plurality of secondary surface
fin elements 20 lying in parallel planes extending transverse to the tubes, and inlet
and outlet means 21, 22 for feeding a further fluid through the spaces between the
tubes and over the elements in a direction F generally parallel to the elements, characterised
in that the elements 20 are each formed with openings 25 located between the tubes
and the openings are flanked by tags 26 extending transverse to the planes of the
elements 20, the spacings between the tubes being arranged to achieve a substantially
constant cross-section in the direction of flow F of said further fluid over the elements
20.
2. A heat exchanger according to claim 1 characterised in that the tubes 14 are in
rows R arranged transverse to the direction of flow F of said further fluid and the
tubes of alternate rows R are staggered by one half the pitch of the tubes in each
row.
3. A heat exchanger according to claim 2 characterised in that the spacings of the
tubes 14 in each row R from one another is greater than the spacing of the tubes in
one row R from tubes in adjacent transverse rows R.
4. A heat exchanger according to claim 3 characterised in that the spacing of tubes
14 from one another in each transverse row R is twice the spacing of the tubes in
each transverse row R from tubes in adjacent transverse rows R.
5. A heat exchanger according to any one of the preceding claims characterised in
that the tags 26 lie generally parallel to the direction of flow F of said further
fluid over the elements 20.
6. A heat exchanger according to any one of the preceding claims characterised in
that the tags 26 are in pairs so that a tag lies to each side of said opening 25.
7. A heat exchanger according to any one of the preceding claims characterised in
that the shell 10 contains baffles 17a, 17b, 17c, 17d, 17e whereby the further fluid
is constrained to pass in a generally sinuous path F through the space between the
tubes 14 and over the fin elements 20.