U.S. patent application number 10/431574 was filed with the patent office on 2004-02-19 for heat exchanger.
This patent application is currently assigned to SMITHS GROUP PLC. Invention is credited to Wilson, George.
Application Number | 20040031599 10/431574 |
Document ID | / |
Family ID | 9936209 |
Filed Date | 2004-02-19 |
United States Patent
Application |
20040031599 |
Kind Code |
A1 |
Wilson, George |
February 19, 2004 |
Heat exchanger
Abstract
A multi-plate dual flow path heat exchanger includes a plurality
of stacked plates 70 each having a central section 71 provided with
a number of longitudinal channels 72 separated by upstanding
zig-zag walls 75, the channels 72 being provided on their floors
72A with ridges 74, the floors and the ridges being of undulating
form along the flow paths. Shallow ribs 75 extend laterally across
the flow paths and in combination with the undulations assist in
disruption of boundary layer flow.
Inventors: |
Wilson, George; (Harrogate,
GB) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
1100 N GLEBE ROAD
8TH FLOOR
ARLINGTON
VA
22201-4714
US
|
Assignee: |
SMITHS GROUP PLC
London
GB
|
Family ID: |
9936209 |
Appl. No.: |
10/431574 |
Filed: |
May 8, 2003 |
Current U.S.
Class: |
165/166 ; 165/69;
165/81 |
Current CPC
Class: |
F28F 2250/108 20130101;
F28D 9/0068 20130101; F28D 9/0031 20130101; F28F 3/046
20130101 |
Class at
Publication: |
165/166 ; 165/81;
165/69 |
International
Class: |
F28F 003/00; F28F
007/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 8, 2002 |
GB |
0210434.7 |
Claims
1. A heat exchanger including a plurality of plate members stacked
parallel above one another to define two separate fluid flow paths
between alternate pairs of adjacent plate members wherein each
plate member has an undulating surface along the respective fluid
flow path sufficient to reduce the boundary layer effect and
wherein each plate member has a series of laterally-extending
surface formations along the flow paths.
2. A heat exchanger according to claim 1 wherein each
laterally-extending formation is in the form of a shallow rib.
3. A heat exchanger according to claim 1 wherein each
laterally-extending formation is no more than 1 mm in height.
4. A heat exchanger according to claim 1 wherein the surface of
each plate member is textured.
5. A heat exchanger according to claim 1 wherein each plate member
is formed with a plurality of channels defined between upwardly
projecting walls and providing floors therebetween.
6. A heat exchanger according to claim 5 wherein each channel is
provided with a plurality of equi-spaced ridges upstanding from the
floor and extending in parallel and longitudinally along the
channel between the walls and being of lower height than the walls,
the ridges and the floor of each channel undulating along the
length thereof.
7. A heat exchanger according to claim 6 wherein the undulations in
the floor and the ridges are of shallow and multiple form to
provide a plurality of hills and valleys along each channel.
8. A heat exchanger according to claim 5 wherein the upwardly
projecting walls bounding the channels are of zig-zag form in the
longitudinal direction of the plate members.
9. A heat exchanger according to claim 8 wherein the zig-zag
formations are offset as between one plate member and an adjacent
plate member.
10. A heat exchanger according to claim 6 wherein the support
members are provided on at least one ridge in each channel and are
upstanding therefrom and are adapted to support an adjacent plate
member.
11. A heat exchanger according to claim 6 wherein the support
members are disposed at spaced intervals longitudinally of the
ridges.
12. A heat exchanger according to claim 11 wherein the support
members are formed of the material of the plate member and are in
the form of elongate projections extending parallel to the
direction of fluid flow.
13. A heat exchanger according to claim 10 wherein support members
are provided on more than one ridge and the support members on one
ridge are offset from those on the other ridge.
14. A heat exchanger according to claim 10 wherein the support
members on one plate member are offset from the support members on
an adjacent plate member.
15. A heat exchanger according to claim 1 wherein triangular
regions at opposite ends providing adjacent inlet and outlet faces
inclined relative to one another and meeting at an apex.
16. A heat exchanger according to claim 15 wherein at least one
elongate resilient member extending vertically along the apex and
having fingers interdigitated between plate members, the exchanger
having elongate clamping members extending along opposite sides of
the or each resilient member and compressing the or each resilient
member therebetween.
16. A heat exchanger including a plurality of plate members stacked
parallel above one another to define two separate fluid flow paths
between alternate pairs of adjacent plate members wherein each
plate member has an undulating surface along the respective fluid
flow path and is textured and wherein each plate member has a
series of laterally-extending ribs.
17. A heat exchanger including a plurality of plate members stacked
parallel above one another to define two separate fluid flow paths
between alternate pairs of adjacent plate members wherein each
plate member is formed with a plurality of channels defined between
upwardly projecting walls and providing floors therebetween, each
channel is provided with a plurality of equi-spaced ridges
upstanding from the floor and extending in parallel and
longitudinally along the channel between the walls and being of
lower height than the walls, the ridges and the floors of each
channel undulating along the length thereof, and wherein each plate
member has a series of laterally-extending ribs.
Description
[0001] This invention relates to heat exchangers.
[0002] The invention is more particularly concerned with heat
exchangers for use in building ventilation systems.
[0003] Heat exchangers are used in building ventilation systems to
transfer heat from warm air extracted from the building to cold air
supplied to the building. In this way, the amount of energy needed
to maintain the temperature within the building can be
minimized.
[0004] A common form of heat exchanger used in building ventilation
systems comprises a stack of thin parallel plates spaced from one
another to form two separate flow paths between alternate pairs of
plates. The warm air is supplied along one path and a part of its
heat is conducted through the thickness of the plates to the cold
air supplied along the other path.
[0005] The ideal heat exchanger should have a high efficiency of
thermal transfer, preferably above about 90% and should produce
only a low back pressure so as to reduce energy expenditure by the
fans used to pass the air through the exchanger. The exchanger
should also have a low leakage between the two air paths and be
easy to manufacture at low cost.
[0006] One example of a heat exchanger is described in GB
0121865.0
[0007] It has proved difficult to produce heat exchangers having a
high efficiency and a low leakage without a relatively high back
pressure. An important factor in increasing the efficiency of heat
exchangers is the reduction in boundary layer effect.
[0008] It is an object of the present invention to provide an
alternative heat exchanger.
[0009] According to one aspect of the present invention there is
provided a heat exchanger including a plurality of plate members
stacked parallel above one another to define two separate fluid
flow paths between alternate pairs of adjacent plate members, the
plate members having an undulating surface along the fluid flow
path sufficient to reduce the boundary layer effect and each plate
member having a series of laterally-extending surface formations
along the flow paths.
[0010] The surface formations are preferably spaced at intervals of
between about 20 mm and 35 mm and, in particular, are preferably
spaced at intervals of about 25 mm. The surface formations are
preferably shallow ribs. The plate members are preferably textured,
such as with an orange-peel texture in the manner produced by
coarse sand casting. Each plate member may have a plurality of
support members distributed over its surface and formed from
material of the plate members. The support members may be elongate
projections extending parallel to the direction of fluid flow. The
support members of one plate member are preferably located close to
but not in alignment with support members of an adjacent member so
that the support members do not nest with one another but so that
contact of the support members with adjacent plate members provides
vertical support in a stack of plate members. The plate members
preferably have a plurality of substantially straight
longitudinally-extending ridges, the ridges preferably being
arranged in groups separated from one another by support ridges of
zigzag shape, the support ridges being higher than the straight
ridges and arranged out of phase with zigzag ridges in adjacent
plates. The heat exchanger preferably has triangular regions at
opposite ends providing adjacent inlet and outlet faces inclined
relative to one another and meeting at an apex. The exchanger
preferably has at least one elongate resilient member extending
vertically along the apex and having fingers interdigitated between
plate members, the exchanger having elongate clamping members
extending along opposite sides of the or each resilient member and
compressing the or each resilient member therebetween.
[0011] According to another aspect of the present invention there
is provided a plate member for a heat exchanger according to the
above one aspect of the invention.
[0012] A heat exchanger assembly according to the present
invention, will now be described, by way of example, with reference
to the accompanying drawings, in which:
[0013] FIG. 1 is a schematic plan view of the assembly;
[0014] FIG. 2 is a perspective view of the heat exchanger unit;
[0015] FIG. 3 is a perspective view of a side panel of the
exchanger housing;
[0016] FIG. 4 is a plan view of a lower type of heat exchanger
plate;
[0017] FIG. 5 is a plan view of an upper type of heat exchanger
plate;
[0018] FIG. 6 is an elevation view showing an edge part of a heat
exchanger plate to an enlarged scale;
[0019] FIG. 7 is a simplified longitudinal elevation view showing
how the support peaks on the plates are positioned;
[0020] FIG. 8 is a simplified lateral elevation view showing how
the support peaks on the plates are positioned;
[0021] FIGS. 9A and 9B are simplified plan views of A and B type
plates respectively showing the relative positions of the support
peaks;
[0022] FIG. 10 is a simplified plan view illustrating the
out-of-phase nature of the zigzag walls on the A and B type of
plates;
[0023] FIG. 11 is a sectional side elevation view of the exchanger
showing how the edges of the plates locate with the side
panels;
[0024] FIG. 12 is a perspective view of a foam sealing strip used
in the exchanger;
[0025] FIGS. 13 and 14 FIGS. 13 and 14 are perspective views of two
clamp strips used with the foam strip of FIG. 12; and
[0026] FIG. 15 is a simplified elevation view illustrating a step
in the assembly of the foam strips.
[0027] With reference first to FIGS. 1 and 2, the heat exchanger
assembly has an outer housing 1 with two inlets 2 and 3 and two
outlets 4 and 5 located at four corners of the housing. A heat
exchange unit 6 is located in the housing 1 and defines two
separate air flow paths 7 and 8 through the housing. The first flow
path 7 extends from the inlet 2 through the exchange unit 6 to the
outlet 4 in the opposite corner and, in use, receives warm air
exhausted from a room. The second flow path 8 extends from the
other inlet 3 to the other outlet 5 and, in use, receives cold air
from outside. The exchange unit 6 operates to transfer heat from
the air flowing along the first flow path 7 to air flowing along
the second flow path 8 so that the fresh air supplied to the
building is warmed. The assembly includes two conventional electric
fans 10 and 11 located in the housing 1 at the two outlets 4 and 5
to draw air along the respective flow paths 7 and 8.
[0028] The heat exchange unit 6 is of the counter-flow type having
two parallel, vertical sides 61 and 62 and four end faces 63 to 66
providing the two inlets and outlets. The unit 6 has a horizontal
base 67 and top 68. Operation of the two fans 10 and 11 causes warm
air drawn in through the inlet 2 of the housing to flow in the
inlet face 63, through the unit 6 and out of the diagonally
opposite outlet face 65, from where it flows to the outlet 4. Cold
air drawn in through the inlet 3 passes in the inlet face 64,
through the unit 6 and out of the diagonally opposite outlet face
66, from where it passes to the outlet 5.
[0029] With reference now also to FIGS. 3 to 11, the heat exchange
unit 6 comprises a parallel stack of forty-seven, six-sided heat
exchanger plates 70, in twenty-three pairs and one single plate.
Other exchangers may have different numbers of plates. Typically,
the plates are about 300 mm wide and about 650 mm long between the
apexes. The plates 70 are contained within a base panel 12, a top
panel 13, and two side panels 14 and 15. The heat exchanger plates
70 are vacuum formed from a thin sheet of carbon-loaded uPVC of a
black colour, which has a high thermal conductivity and is an
efficient thermal radiator. The plates 70 are moulded with surface
formations that act to enhance heat transfer and support the plates
with one another. The heat exchanger plates 70 are of two different
types: a lower type A and an upper type B. These are joined with
one another in pairs having four sides sealed together by welding
and two diagonally opposite sides open for inlet and outlet of air.
The pairs of joined plates A and B are stacked one above the other.
The space between the upper surface of the lower plate A in a pair
and the lower surface of the upper plate forms a part of the first
flow path 7. The space between the upper surface of the upper plate
and the lower surface of the lower plate in an adjacent pair of the
stack forms a part of the second flow path 8. The configuration of
the lower type of plate 70A will now be described with reference to
FIG. 4.
[0030] The plate 70A has a main section 71 of rectangular shape
divided into eight parallel, longitudinal channels 72 separated
from one another by upwardly-projecting walls 73 of triangular
profile and a zigzag configuration. The walls 73 serve to support
and space adjacent plates from one another in a manner that will
become apparent later. Extending along each channel 72 are five
parallel ridges 74 equally spaced from one another across the width
of each channel. The ridges 74 have a triangular profile but are
only about half the height of the walls 73. The lower edges of the
ridges 74 are contiguous with one another, with the peaks of the
ridges being separated from one another by valleys of triangular
section, as shown in FIG. 6. The ridges 74 are straight when viewed
from above but the floor 72A of the channels 72 and the ridges have
an undulating profile along their length forming a series of about
fourteen hills and valleys, as shown in FIG. 7. The peak-to-peak
height of the undulations is about 0.5 mm. The ridges 74 serve to
channel air smoothly along the channels 72 and increase the surface
area of the plate 70A contacted by the air. The walls 73 and ridges
74 also increase the longitudinal stiffness of the plates. The
undulating floor 72A of the channel 72 has been found to be
particularly important in helping to reduce boundary layer effects
by increasing the buffeting of air between the plates as it flows
along the channels.
[0031] The channels 72 are also interrupted by a series of fifteen
ribs 75 extending laterally across the width of the plate. The ribs
75 are shallow compared with the ridges 74, only being no more than
1 mm high and extend across both the ridges and the walls 73. The
spacing between adjacent ribs 75 is between about 20 mm and 35 mm
and is preferably about 25 mm. The purpose of the ribs 75 is also
to reduce boundary layer effects by increasing disturbance of air
flow at intervals. Without a similar formation, a boundary layer
will build up over a distance of about 32 mm so the spacing of the
ribs is preferably chosen to be slightly less than this.
[0032] Each channel 72 also includes fourteen support members or
peaks 80 spaced along the channels. The peaks 80 are of
substantially rectangular shape when viewed from above, being about
9 mm long and 1 mm wide, and have a triangular profile. The peaks
80 project upwardly on the ridges 74 and, in particular, are formed
equally spaced from one another alternately on the second and
fourth ridges across each channel 72. The purpose of the peaks 80
is to maintain the spacing between adjacent plates 70, in
particular, to maintain the spacing at about 3 mm.
[0033] As shown in FIGS. 6 and 11, the edges 81 and 82 of the
rectangular section 71 have an inner boundary wall 83 and a
longitudinal depression 84 of semicircular profile extending along
their length about halfway across the width of the edge. The upper
surface of the edges 81 and 82 is welded to the upper plate 70B in
a manner described in more detail later.
[0034] At opposite ends of the main section 71, the plate 70A has
an inlet and outlet section 90 and 91, both of triangular shape.
One side 92 of the inlet section 90 is closed by welding to the
upper plate 70B; the other side 93 is open. The surface of the
inlet section 90 is ribbed with shallow, parallel ribs 94 extending
laterally of the plate and generally transversely to the direction
of air flow. The inlet section 90 also has six higher raised walls
95 extending perpendicular to the open side 93 and forming a
continuation of the zigzag walls 73. These ribs 94 and walls 95 act
to channel air entering the open side 93 substantially evenly
across the row of ends of the channels 72. The ribs 94 also
introduce a small amount of turbulence into the air flow.
[0035] The outlet section 91 similarly has a closed, welded side 96
and an open side 97. The outlet section 91 also has ribs 98 and
walls 99 to help channel air emerging from the channels 72 to the
open side 97 of the section.
[0036] All the ridges, walls and other formations on the plate 70A
are formed by moulding from the material of the plate so that the
thickness of the plate is constant over its surface and each
formation on one surface of the plate has a corresponding inverted
formation on the opposite surface. The entire upper and lower
surfaces of the plate are textured with a granular, orange peel
texture. This texture is preferably produced directly in the vacuum
forming mould tool by leaving this as a rough, coarse sand-cast
finish. This texture has been found further to discourage the
formation of boundary layers on the plates.
[0037] The upper type of plate 70B (FIG. 5) has similar surface
formations on its upper surface, which are given the same number as
the formations for plate 70A with the addition of a prime. The
plates 70B have a pattern of zigzag walls 73' identical with the
walls 73 except that they are out of phase with one another. In
this way, the walls 73 and 73' in adjacent plates cross one another
and support the plates relative to one another, as illustrated in
FIG. 10. The ridges 74' on the plate 70B extend in alignment with
the corresponding ridges on the lower plate. The distribution of
the peaks 80', however, is slightly different from those on the
lower plate 70A in that they are aligned laterally but are
displaced longitudinally by a distance equal to a peak length, as
shown in FIGS. 6 to 8. This displacement is sufficient to ensure
that the peaks 80 and 80' do not nest with one another but the
spacing is sufficiently close that the column of peaks provides
some vertical strength to the stack of plates 70.
[0038] The triangular left and right sections 90' and 91' of the
upper plate 70B are similar to those of the lower plate 70A except
that the upper surface of the left section 90' is configured to
provide an outlet whereas the right section 91' is configured to
provide an inlet. Different ones of the sides 92', 93', 96' and 97'
are open and closed and the internal ribs 94', 98' and walls 95',
99' act to channel air from the open side 96' via the ends of the
channels 72' to the open side 92'.
[0039] The two plates 70A and 70B in each pair are welded together
around four sides. The edges 81' and 82' of the upper plate 70B
along the sides of the rectangular section 71' are flat and are
welded to the edges of the lower plate 70A along opposite sides of
the semicircular depression 84 so that the open side of the
depression is closed and sealed, thereby forming it into an
air-filled longitudinal seal. At the same time, the closed sides 91
and 92 of the lower plate 70A are welded to the sides 91' and 92'
of the upper plate 70B. The pairs of plates 70 are held together
with one another in a stack by means of the bottom panel 12, top
panel 13 and side panels 14 and 15. The side panels 14 and 15
(shown most clearly in FIGS. 3 and 11) are imperforate and moulded
of a rigid, black ABS plastics material with twenty-two parallel
slots 100 extending horizontally along their length. The width of
the slots 100 is selected so that the welded edges 81 and 82 of the
pair of plates are retained as a tight push fit, with the
semicircular formation 84 on the lower plate 70A providing an
effective seal against passage of air around the edges of the
plates. The spacing of the slots 100 provides accurate spacing
between adjacent pairs plates; accurate spacing between the A and B
plates of a pair is ensured by the surface shapes of the lower A
plate.
[0040] The unit 6 is assembled by clipping the side panels 14 and
15 into the base panel 12 and then sliding a pair of heat exchange
plates 70A and 70B into the slots 100 along the side panels. When
all the pairs of plates 70 have been slid into position, the top
panel 13 is clipped onto the upper edge of the side panels 14 and
15. The top panel 13 has a series of recesses 180 on its lower
surface located in positions corresponding to the peaks 80' on the
upper plate 70B of the stack. The peaks 80' are received in the
recesses 180 so as to ensure that the peaks do not space the plate
70B away from the top panel 13 and allow too great a proportion of
air to flow between the plate and the top panel.
[0041] With the plates 70 stacked together, the open edges 93 and
93' of the lower and upper plates 70A and 70B are welded to the
respective upper and lower plates of adjacent pairs, so that air
cannot flow between the upper plate of one pair and the lower plate
of the adjacent pair at the face 63. Similarly, the edges 97 and
97' are welded together at the face 65.
[0042] Because there is a transition at each apex 101 in the stack
of plates 70, between the extracted and supply air flows, it is
particularly important that this region is effectively sealed to
prevent leakage between the two paths 7 and 8. This is achieved by
means of two foam sealing strips 102, as shown in FIG. 11, cut
along one edge with a series of short cuts 103 extending at right
angles to the edge (as shown in FIG. 12). The number of cuts 103 is
equal to the number of plates 70 in the stack. The strips 102 are
assembled on either side of the apex 101 in the manner shown in
FIG. 1550 that fingers 104 of the strip between each cut 103 extend
between the plates 70 at the apex 101. Two clamping strips 105 and
106, as shown in FIGS. 13 and 14 are then positioned along opposite
sides of the foam strips 102, as shown in FIG. 15, and are clamped
together so as to compress the foam strips into an effective seal
with the plates 70.
[0043] Similar foam strips (not shown) are used at the corners 110
to 113, where the exchanger plates 70 project from the slots 100 in
the side panels 14 and 15. Vertical clamping strips 114 are used to
compress the foam strips and hold them in place so as to reduce
leakage of air along the slots 100.
[0044] The arrangement of the present invention enables a heat
exchanger of high efficiency to be provided without a high back
pressure. The arrangement can also reduce cross leakage between the
two air flows.
* * * * *