Heat exchanger

Abstract

A heat exchanger comprises a conduit defining an inlet flow path for a fluid; a heat exchanger matrix disposed to receive a flow from the inlet flow path; and a swirler disposed within the conduit and arranged to improve dispersion of a flow from the inlet flow path over the heat exchanger matrix.

Claims

1. A heat exchanger comprising: a conduit defining an inlet flow path for a fluid; a heat exchanger matrix disposed to receive a flow from the inlet flow path; and a swirler disposed within the conduit and arranged to improve dispersion of a flow from the inlet flow path over the heat exchanger matrix; wherein the heat exchanger matrix has a polygonal cross section in the direction of the flow path, and wherein the swirler is arranged to direct flow streams from the flow path towards each of the corners of the polygonal cross section; wherein the swirler comprises a plurality of blades; and wherein the blades wind helically around more than 90 degrees and are disposed across an entire cross-section of the flow path so that no unobstructed path exists for fluid flow directly through the swirler along the conduit.

2. A heat exchanger as claimed in claim 1, wherein the plurality of blades define a helical flow path within the conduit.

3. A heat exchanger as claimed in claim 1, wherein the blades are separated from each other by equal angles.

4. A heat exchanger as claimed in claim 1, wherein the heat exchanger matrix has a quadrilateral cross section in the direction of the flow path, and wherein the swirler comprises four blades arranged to direct flow from the flow path towards each of the four corners of the cross section.

5. A heat exchanger as claimed in claim 1, wherein the heat exchanger matrix comprises an array of channels providing multiple flow paths for the fluid in heat exchange with another fluid, and the swirler is arranged to disperse the flow from the inlet flow path across the array of channels.

6. A heat exchanger as claimed in claim 1, wherein the swirler comprises a sleeve portion providing a friction fit within the conduit.

7. A heat exchanger as claimed in claim 1, wherein the heat exchanger is arranged to carry a fluid flow with a speed of greater than 300 m/s via the conduit.

8. A heat exchanger as claimed in claim 1, wherein the swirler is disposed proximate an end of the conduit.

9. A heat exchanger as claimed in claim 1, wherein the swirler has been formed by additive manufacturing.

10. An aircraft in combination with a heat exchanger as claimed in claim 1.

11. A method for distributing flow in a heat exchanger that includes a conduit defining an inlet flow path for a fluid, a heat exchanger matrix disposed to receive a flow from the inlet flow path, and a swirler disposed within the conduit and arranged to improve dispersion of a flow from the inlet flow path over the heat exchanger matrix, the method comprising: using the swirler to disperse the flow from the inlet flow path over the heat exchanger matrix, wherein the heat exchanger matrix has a polygonal cross section in the direction of the flow path, and wherein using the swirler includes directing flow streams from the flow path towards each of the corners of the polygonal cross section and wherein the swirler comprises a plurality of blades and wherein wind helically around more than 90 degrees and are disposed across an entire cross-section of the flow path so that no unobstructed path exists for fluid flow directly through the swirler along the conduit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Certain exemplary embodiments of the invention will be described below by way of example only and with reference to the accompanying drawings in which:

(2) FIG. 1 shows a schematic of a heat exchanger according to the prior art;

(3) FIG. 2 shows a schematic of a heat exchanger with a swirler;

(4) FIG. 3A shows a plot of fluid flow intensity in a heat exchanger;

(5) FIG. 3B shows an alternative view of the plot of fluid flow intensity of FIG. 3A;

(6) FIG. 3C shows a cross-section of the plot of fluid flow intensity of FIGS. 3A and 3B over a plurality of channels;

(7) FIG. 3D shows a distribution of mass flow rate of fluid for the plurality of channels of FIG. 3C;

(8) FIG. 4A shows a plot of fluid flow intensity in a heat exchanger with a swirler;

(9) FIG. 4B shows an alternative view of the plot of fluid flow intensity of FIG. 4A;

(10) FIG. 4C shows a cross-section of the plot of fluid flow intensity of FIGS. 4A and 4B over a plurality of channels;

(11) FIG. 4D shows a distribution of mass flow rate of fluid for the plurality of channels of FIG. 4C;

(12) FIG. 4E shows views of swirler;

(13) FIG. 5 shows a swirler at various stages of manufacture by additive manufacturing;

(14) FIG. 6 shows plots analogous to those of FIGS. 4A to 4E but for an alternative swirler; and

(15) FIG. 7 shows plots analogous to those of FIGS. 4A to 4E but for another alternative swirler.

DETAILED DESCRIPTION

(16) FIG. 1 shows a typical heat exchanger 10, comprising a conduit 11 and a heat exchanger matrix 12. Fluid 14 flows through the conduit 11 into a volume defined by the tank of the heat exchanger 12 and disperses throughout the volume.

(17) FIG. 2 shows a heat exchanger 100 comprising a conduit 110, a heat exchanger matrix 120, and a swirler 130. Fluid 140 flows along the conduit 110 at a higher speed than is usual for heat exchangers. The fluid 140 then flows through the swirler 130 and is dispersed thereby into a volume defined by the heat exchanger matrix 120.

(18) FIG. 3A shows the speed of fluid in a heat exchanger without a swirler. Fluid 140 flows along conduit 110 at speeds of more than 1000 m/s, up to speeds of 1300 m/s. Fluid 140 reaching the volume of the heat exchanger matrix 120 disperses into the volume, over channels 122 of the heat exchanger matrix 120. The channels 122 may carry a second fluid (not shows) so as to be in heat exchange with the first fluid 140.

(19) FIG. 3B shows an end-on view of the heat exchanger 100 of FIG. 3A. The channels 122 run horizontally, substantially perpendicular to the flow path of fluid 140 so as to maximise contact therewith. Dispersal of the fluid 140 into the volume defined by the heat exchanger matrix 120 is indicated by the flow lines.

(20) FIGS. 3C and 3D show the magnitude of the speed of the fluid 140 distributed across the channels 122. Without a swirler, the distribution is focussed in a localised region, such that high velocity fluid 140 impinges on the channels primarily in one place within the heat exchanger matrix 120. This causes thermal expansion of the channels 122 in the region of the focus, resulting in fatigue of the matrix 120, and leading to micro-fractures and leakages.

(21) FIGS. 4A to 4D show analogous plots to those of FIGS. 3A to 3D but for a heat exchanger 100 which includes a swirler 130. FIG. 4E shows a perspective view of the swirler 130 for the embodiment of FIG. 4.

(22) The swirler 130 comprises four blades 132 in a right-handed spiral, spaced equidistantly about the axis of the conduit 110. Each of the blades 132 sweeps 90 degrees about the axis of the conduit 110, so that the swirler 130 covers an entire cross section of the conduit 110. The swirler 130 is rotated within the conduit 110 relative to the heat exchanger matrix 120 so that the end of one of the blades is at an angle of 22.5 degrees to the side of the heat exchanger matrix 120.

(23) The fluid 140 is directed by the swirler 130 in four adjacent helical fluid paths within the conduit 110. Upon leaving the swirler 130 and entering the heat exchanger matrix 120, the angular momentum imparted to the fluid by the swirler 130 carries the fluid in four diverging streams outward from the axis of the conduit 110. The alignment of the swirler 130 within the conduit 110, directs each of these four streams respectively approximately towards each of the four corners of the heat exchanger matrix 120. These streams are clearly visible in FIG. 4B.

(24) FIG. 4C shows that the highest fluid velocities are thus disposed approximately in each of the four corners of the heat exchanger matrix 120. The heat exchanger matrix 120 thus experiences less thermal expansion and fatigue in the centre of the matrix 120. Instead, a greater proportion of the thermal expansion and fatigue is applied near the edges of the matrix, where the heat exchanger is better able to withstand the resultant stresses.

(25) FIG. 4D shows the distribution of the fluid speeds across the channels 122, from the top to the bottom of the heat exchanger 120. A fully uniform flow is in indicated by the dashed black line. The uniformity index for the swirler 130 of FIG. 4E is 80.38%, compared to that of 79.05% for the heat exchanger 100 without a swirler.

(26) The uniformity index (UI) is a measure of how evenly the flow is distributed e.g. across a heat exchanger matrix face. It is calculated as a fraction and quoted as a percentage, with 100% representing perfectly uniform mass flow distribution. A value for the uniformity index may be calculated by dividing the face of the heat exchanger matrix into cells, finding a sum over all of the cells of the differences between a cell velocity and the average velocity, and dividing this sum of differences by the average velocity over all of the cells which make up the heat exchanger matrix face. The uniformity index may then be calculated using the expression:

(27) $\mathrm{Uniformity}\mathrm{index}=1-\frac{\underset{f}{\overset{}{.Math.}}.Math.{}_f-\stackrel{\_}{}.Math.A_f}{2.Math.\stackrel{\_}{}.Math.\underset{f}{.Math.}{A}_f}$
where .sub.f is the velocity value of a cell, is the average velocity, and A.sub.f is the area of a cell of the heat exchanger matrix face.

(28) FIG. 5 shows a swirler 130 in various stages of production by an additive manufacturing process. The swirler 130 comprises four blades 132 and a sleeve portion 134 surrounding the blades. The swirler 130 is formed by the addition of incremental layers, defining the blades 132 and sleeve portion 134. The completed swirler 130 may be made to the desired dimensions retrofit to existing heat exchanger conduits 110 to improve the flow distribution of fluid therefrom during use.

(29) FIG. 6 shows plots corresponding to those of FIGS. 3 and 4, for a swirler 130 with four blades 132 sweeping a 90 degree angle. The swirler 130 of FIG. 6 has an increased length along the conduit 110 compared to the swirler of FIG. 4. The swirler 130 is also aligned with the heat exchanger matrix 120 so that the ends of the blades are vertical and horizontal.

(30) The increased length of the swirler 130 prevents the four streams entering the volume of the heat exchanger matrix 120 from diverging as much as the four streams formed by the swirler 130 of FIG. 4. The velocity of the fluid 140 is then distributed in a hot spot but also across a corner of matrix 120. The uniformity index is increased to 79.31%.

(31) FIG. 7 shows corresponding plots to those of FIGS. 3, 4 and 6, but for an alternative swirler 130, comprising four blades 132 with a 90 degree sweep in a left-handed helical orientation. The ends of the blades 132 are aligned vertically and horizontally with the heat exchanger matrix 120.

(32) The swirler 130 of FIG. 6 is the same length in the conduit 110 as the swirler 130 of FIG. 4, and consequently the four streams of fluid 140 entering the matrix 120 diverge more than those of FIG. 6. Although the uniformity index of the embodiment of FIG. 7 is only 77.00%, the flow distribution is improved since it is spread around the edges of the matrix 120, avoiding a single central hot spot.

(33) The alignment of the swirler 130 within the conduit 110 with the heat exchanger matrix 120 will affect the resulting distribution of the fluid 140 over the matrix 120. The position of the conduit 110 relative to the heat exchanger 120 will also affect the final distribution. It may therefore be advantageous to align the swirler 130 so that the resulting streams are distributed approximately evenly over a cross-section of the heat exchanger 120, for example by directing the streams to the corners of the heat exchanger 120.