GB2232749A

GB2232749A - Water heaters using waste heat: cleaning heat exchangers

Info

Publication number: GB2232749A
Application number: GB8912521A
Authority: GB
Inventors: Matthew Stephen Rutherford
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-05-31
Filing date: 1989-05-31
Publication date: 1990-12-19
Also published as: GB8912521D0

Abstract

A heat exchanger (61) suitable for use with a domestic hot water shower comprises a casing (2), and an element assembly (6). Warm waste water from the shower is passed through the casing (2) cavity over the element assembly (6) and acts to warm the flow of primary water which passes through the element assembly (6). A pump may act to increase the velocity of the waste water relative to the element assembly (6) and/or the casing (2), and to prevent the build up or deposition of sludge and/or dirt therein/thereon. The pumping action may be provided by a cleaner (64) comprising one or more rotating areas (8) fitted with flexible fibres (9). Energy extracted from the primary water flow may be used to power the pump/cleaner. A valve may be provided for maintaining the predetermined level of waste water within the casing cavity. <IMAGE>

Description

HEAT EXCHANGER This invention relates to heat exchangers and particularly but not exclusively to heat exchangers used in processes which involve hot water consumption.

Whenever a process involving the consumption of hot or heated water is carried out, for example a washing process, it is often the case that a flow of used warm water is allowed to flow to waste. This represents a loss of potentially useful thermal energy.

In certain circumstances, a heat exchanger could be beneficially utilized to reclaim some of the thermal energy which would otherwise be lost. A particular application for such a heat exchanger occurs when cold water is heated to produce warmer water instantaneously, ie at the rate at which it is consumed in the process itself. A heat exchanger could then be employed to transfer heat from the warm waste water (waste water) to the incoming cold water forming the process supply (primary water). This is shown diagrammatically in figure 1.This situation lends itself particularly well to the application of a heat exchanger because the primary water flow rate is of a similar order to that of the waste water, and because the waste water flow occurs simultaneously with the primary water flow, eliminating the need for storage of either of the same.

A particular application for such a heat exchanger would be that of the domestic shower, either of the 'mixer' type, which mixes stored pre-heated water with cold primary water, or of the direct heat-input type such as the electric shower.

The invention provides that there is associated with either type of heat exchanger means such that heat transfer takes place from the waste water to the primary water, to pre-heat the same.

The present invention will now be more particularly described by way of example only with reference to figures 1 to 6 of the accompanying drawings, in which: Figure 1 is a diagrammatic representation of a water using process to which the present invention may be applied.

Figure 2 is a cross-sectional view of one particular embodiment of the present invention, which is the heat exchanger shown in Figure 1.

Figure 3 is an enlarged partial view of figure 2.

Figure 4 is a cross-sectional view of a second particular embodiment of the present invention, which is the heat exchanger shown in Figure 1.

Figure 5 is an enlarged partial view of figure 4.

Figure 6 is a cross-sectional view of a third particular embodiment of the present invention, which is the heat exchanger shown in Figure 1.

In the first embodiment, referring to the drawings in general, but in particular to figure 2 and figure 3, waste water enters the heat exchanger (61) through an inlet pipe (1), part of the casing (2). The inlet pipe (1) projects into the interior of the casing (2), and a rotating collar (3), which is free to rotate about the axis of the pipe (1), is located on it. Means for driving the collar (3) to rotate, such as a ring gear (4) (shown), or a pulley (not shown) is provided. A funnel-shaped projection (5) may be fitted onto the end of the inlet pipe (1), to guide the flow of waste water smoothly onto surface of the heat exchanger element assembly (6) (element assembly). Waste water entering the heat exchanger (61) impinges on the element assembly (6). Thereon, it flows with a free surface on the upper surface of the element assembly (6), towards the outlet of the heat exchanger (61).It will be appreciated that in this document, the phrase 'with a free surface' is taken to imply 'with a surface in contact with the air above the liquid, this surface finding its own profile, instead of assuming that of the walls of the vessel containing it'. The advantages of allowing the waste water to flow with a free surface on the element assembly (6) are as follows.

Because the waste water flowing through the heat exchanger finds its own depth, and because there will usually be free space above the surface for it to become deeper, and no obvious restrictions to flow, such as valves, in the flow path, the heat exchanger (61) can pass if necessary a high waste water flow-rate with a low pressure-drop across it. Also with free surface flow, the waste water, by actually resting on the element assembly (6) surface, is ensured always to be in intimate contact with it, promoting heat transfer to the element assembly (6). Also, fluid friction in the waste water will be generated in the main only on the element assembly (6) surface, where it in any case promotes a higher rate of heat transfer to the element assy (6). In the main, fluid friction is not incurred by virtue of contact of waste water with the casing (2).This tends to minimize the power requirement of any waste water pump provided. A further advantage is that only one face of the element assembly (6) outer surface, and part of the casing (2) inner surface contacted by the waste water need be kept clean, and only part of the pump arm(s) (8) and/or its fibres need be immersed in the dirty waste water, their remainder being in the airspace above the waste water surface. This will reduce the chance of hairs or other debris becoming tangled around the pump arms (8).

In the example shown, waste water flow occurs in the general direction away from the axis 'a-a' of the heat exchanger (61), generally down the slope of the element assembly (6), which is in the form of an inverted bowl. However, the heat exchanger (61) could be designed so that the flow was towards the axis of the heat exchanger (61), with the element assembly (6) in the form of an upright bowl (in this case the inlet pipe (1) and outlet pipe (11) would have to be resituated). In the latter two arrangements, gravity would tend to assist the flow of waste water through the heat exchanger (61), to a degree depending on the angle of slope down which the water flowed, ie there might be zero assistance if the bowl shape were flattened (a plate), and perhaps even an adverse gradient for flow if the element assembly were so designed.The heat exchanger might even be designed such that waste water flow occurred axially through the element assembly (6) (this situation not shown), if gaps in it were provided. The waste water eventually flows over the periphery of, or through the element assembly (6), past possibly the mechanical support(s) (10) (two shown) for the element assembly (6) and thence onto the lower surface of the casing (2). Thence, the waste water flows out of the casing (2), via an exit pipe (11).

As the waste water flows on the element assembly (6) surface, it may tend to have its have velocity increased by a pump/cleaner (64). In this embodiment, this pump/cleaner (64) takes the form of one or more arms (8) (two shown), in contact with the waste water. These arms (8), if fitted, are caused to translate or rotate by attachment to, or contact with, a moving member, such as the rotating collar (3). They may be guided at point(s) along their length, such that they are free to carry out their agitating function while receiving mechanical support. The arms (8), if fitted, may be provided with flexible fibres (9) (shown in part for clarity), to improve their effectiveness in their possible actions as described above.The flexible fibres (9) would tend to assume the profile of the element assembly (6) surface, and perhaps of the casing (2) surface, thus forming naturally a water-sealing barrier across the element assembly (6) surface, in line with the arm (8). This moving barrier, sweeping around the element assembly (6) as the arm rotated, would tend to pump the waste water along its course, ie tend to increase its flow velocity. This action would tend to increase the rate of heat transfer from the waste water to the element assembly (6), and to minimize the possibility that any dirt or sludge which settles out of the waste water whilst in the heat exchanger will remain therein without being washed away by the waste water flow. The arms (8) may also serve to brush and/or scrape the element assembly (6) and/or casing (2) clean.

Alternatively, the pump/cleaner (64) may be intermittent in operation during heat exchanger (61) use, such that the main reason for its provision is to physically brush or scrape against part or all of the internal surfaces of the heat exchanger contacted by the waste water, to physically remove the dirt therein/thereon, thereby cleaning them.

Alternatively, the pump/cleaner (64) may not be fitted at all. In these latter two cases, a pure pump (not shown) (so called in this document because it has the pumping function of the pump/cleaner (64) (of increasing the waste water velocity) without having a direct scraping or brushing action), may be provided, possibly for continous operation during periods of heat exchanger (61) usage.

Raised contours (7) on the surface of the element assembly (6) (fins shown), and/or on the internal surface of the casing (2) (not shown) if provided, and in the form of concentric circles (spiral shown), tend to retain waste water in the valley (66) formed between each contour (7) until a point when the waste water starts to overflow over the contour (7) into the downstream adjacent valley (66), so increasing the average length of time spent by a waste water particle in the heat exchanger (61). This tends to increase the amount of heat transferred by each waste water particle to the element assembly (6). The contours (7) on the element assembly (6) also tend to increase the effective area for heat exchange of the element assembly (6).The contours (7) may take a spiral locus, providing a path(s) for waste water flow in the heat exchanger (61), leading generally from waste water inlet to outlet. The tendency to provide a path would be enhanced in this case if waste water did not spill over the upper extremities (67) of the contours. Such a path(s) would tend, in conjunction with the action of the pump/cleaner (64) which sweeps along the path(s) formed by the contours (7), to cause dirt to be swept through, and/or waste water to be pumped out of the heat exchanger (61), at a rate, ceteris paribus, determined by the rotational rate of the pump arm.If the rotational rate of the pump/cleaner (64) were arranged to be coupled to the primary water flow rate, for example by using a hydraulic motor or turbine, whose speed was coupled to the primary water flow rate, to extract energy from the primary flow to power the pump/cleaner (64), and one assumes the primary water flow rate to be coupled to the waste water flow rate, the pump/cleaner (64) could be arranged to pump the waste water through the heat exchanger (61) at or near the rate at which is was being generated. This would help to prevent any build-up of the waste water before the heat exchanger (61), or the pumping of waste water through the heat exchanger (61) at too high a rate.

Primary water enters the element assembly (6) via a pipe (12). The water then flows inside inside the element assembly (6), absorbing heat from the waste water through its walls. In the example shown, the water follows a spiral path within the element assembly (6), following a path generally towards its inner diameter. Various other flow paths could be illustrated, however, such as are well known within the art, and not discussed further here. The warmed primary water then exits the element assembly (6) via a pipe (13) (shown dashed in part for clarity) which passes through some point in the casing (2) A hydraulic motor or turbine (14) may be provided somewhere in the primary water flowline. If fitted, this extracts energy from the flow of the primary water, which may used to power the pump/cleaner (64) or the pure pump, if fitted.Alternatively, some other source of motive power such as an electric motor (not shown) or an (intermittent) manual force, transmitted via a pull-cord (not shown), or other suitable means, may be provided. Whichever, the mechanical power is transmitted inside the casing (2) by means of a shaft (15) with a cog (16) on the end, which engages the ring gear (4) on the rotating collar (3), or by other means well known within the art, to power the motion of the pump/cleaner (64) or pure pump.

The end of the shaft (15), if fitted, may be supported by a lug (17) attached to the inside of the casing (2). Means, such as a seal (18) between casing (2) and shaft (15), or even some form of magnetic drive operating across the casing (2) may be provided to render the casing (2) airtight, apart from the inlet and exit pipes (1) and (11). This, in conjunction with the fact that the inlet pipe (1) projects into the casing, and that the exit pipe (11) opens into the casing cavity at a lower level than the inlet pipe (1) mouth, will tend to ensure that an air pocket is trapped in the part(s) of the casing (2) cavity above the level of the inlet pipe (1) mouth, into which the waste water never rises.By arranging that the bearing surfaces between parts with relative motion such as the collar (3) and inlet pipe (1) and/or the drive mechanism of the collar (3) are situated within this air pocket, provision will be made that they do not become contaminated by contact with the waste water, and/or dirt therein.

To assist thIs, means to reduce splashes of waste water entering the airlock region may be provided. In the example, a ring (19) co-axial with the axis 'A-A' is shown in part, which projects from the casing (2) towards the collar (3), with which it forms a small clearance. The chances of a splash of waste water penetrating through the small clearance, and impinging on the protected areas are minimal, thus the anti-splash action mentioned above is provided.

In a second embodiment, referring to the drawings in general, but in particular to figure 4, and to figure 5 which is an enlarged view of part of figure 4, waste water enters the heat exchanger (62) through an inlet pipe (20), part of the casing (21). The inlet pipe (20) projects into the interior of the casing (21) and a rotating collar (22), which is free to rotate about the axis of the pipe (20), is located on it. A funnel-shaped projection (24) may be fitted onto the end of the inlet pipe (20), to guide the flow of waste water smoothly onto the surface of the heat exchanger element assembly (25). Waste water entering the heat exchanger (62) impinges on the heat exchanger element assembly (25) (element assembly).

Thereon, it flows on its surface with a free surface, towards the outlet of the heat exchanger (62). Note that a large part of the exterior wall of the heat exchanger (62) is formed by the element assembly (25) itself, of which the outside surface is directly exposed to atmosphere. In the example shown, flow occurs in the general direction away from the axis 'B-B' of the heat exchanger (62), into a gulley (29) whence it flows or is swept into the exit pipe (30), and the element assy (25) is flat. Similar permutations of flow directions and element assy (25) configurations could be provided, however, as are described in the description of operation of the embodiment depicted in figure 2, including the provision that the exit pipe (30) may communicate with the casing (21) interior at the axis of the heat exchanger in cases when waste water flow is towards the axis.The advantages of allowing the waste water to flow on the element assembly (25) with a free surface are enunciated in the description of operation of the embodiment illustrated in figure 2 A pump/cleaner (66), possibly consisting of one or more arms (27) (two shown) possibly provided with flexible fibres (28), and attached to or contacting a moving member, such as the rotating collar (22) performs a function substantially similar to that described in the decription of the operation of the embodiment depicted In figure 2.

Alternatively, the pump/cleaner (66) as described above may be intermittent in operation during heat exchanger (62) use, such that the main reason for its provision is to physically brush or scrape against part or all of the internal surfaces of the heat exchanger (62) contacted by the waste water, to physically remove the dirt therein/thereon, thereby cleaning them. Alternatively, the pump/cleaner (66) may not be provided at all. In this case, a pure pump (not shown) may be provided, possibly for continous operation during periods of heat exchanger (62) usage.

Raised contours (26) (fins shown), (if fitted) on the surface of the element assembly (25), whether circular or spiral or other, perform similar respective functions to those described in the decription of the operation of the embodiment depicted in figure 2.

Primary water enters the element assembly (25) via a pipe (31).

The water then flows inside inside the element assembly (25) in a manner substantially similar to that described in the description relating to the embodiment described in figure 2. The warmed primary water then exits the element assembly (25) via a pipe (34).

The element assembly (25) may be designed in more than one part, with one particular part, the vessel carrying the primary water, not directly immersed in or in contact with the waste water, but in intimate thermal contact with a part of the element assembly (25) which is, heat being conducted directly or indirectly from the latter to the former. In the example shown, a contoured plate (32) is actually in contact with the waste water, whereas a pipe (33) in intimate thermal contact with the contoured plate (32) actually carries the primary water. This design provides a barrier to separate the waste water from the primary water (ie plate (32) and pipe (33) wall) more robust than that which separates the waste water from the atmosphere (ie plate (32) ).This protects the vessel carrying the primary water against being caused to leak by the erosive or abrasive action of the pump/cleaner (66) and/or the waste water flow, by virtue of the fact that abrasion or erosion acting equally on the contoured plate (32) surface will cause a leak of waste water to atmosphere (signalling that the device needs overhaul) before any likelihood of erosion or abrasion right through the primary water vessel wall occurs, causing a leak of primary water.

A hydraulic motor or turbine (35) (connecting pipework not shown), or other source of motive power such as an electric motor or manual power may be provided, in addition to power transmission means such as the shaft (36) and cog (37), which functions in a manner substantially similar to that described in the description of operation of the embodiment described in figure 2.

The end of the shaft (36), if fitted, may be supported by a lug (38) attached to the inside of the casing (21). Means may be provided to render the casing (21) airtight, which in conjunction with the design of the heat exchanger, tends to cause an air pocket protecting against contamination by waste water which functions in a manner substantially similar to that described in the description of operation of the embodiment described in figure 2.

A third embodiment is now described, with reference to the drawings in general, but in particular to figure 6. Waste water enters the heat exchanger (63) through an inlet pipe (40), part of the casing (41). Waste water entering the heat exchanger (63) tends to fill the interior of the casing (41), thereby tending to immerse the heat exchanger element assembly (42) in waste water. When the waste water reaches a pre-determined level, a mechanism (43), which tends to maintain the waste water level at a pre-determined level, allows the waste water to flow out of the casing (41) interior via an exit pipe (44), which communicates with the casing (41) cavity at a level lower than that of the inlet pipe (40), at a level in fact at or nearly at the lowest part of the casing (41) Interior.In the example shown, flow occurs in the general direction from the periphery to the axis 'c-c' of the heat exchanger (63) with the element and casing generally in the form of an upright bowl. The heat exchanger (63) could however be designed so that flow was from axis 'c-c' to periphery, with an element assembly (42) in the form of an inverted bowl. One of the essential points of design of this embodiment is that a mechanism regulates the level of waste water in the casing (41) in which the element assembly (42) is located. Thus the degree of immersion of the element assembly (42) in the waste water is also regulated. Also, the overall direction of flow of the waste water is down the gravitational incline from inlet to outlet, with the outlet at or near the lowest point of the casing cavity.Some or all of the internal surfaces of the heat exchanger (63) components may slope down towards the outlet. This arrangement will mean that dirt and sludge, if it settles out, ( being for the most part denser than water ) will tend under the action of gravity, superimposed on any other action, to migrate down the slope of the surface on which it settled to a point at or near the lowest part of the casing (41), which by definition is near the opening of the outlet pipe (44) Here, the waste water velocity, as it approaches the outlet pipe (44), increases. Thus the settled-out sludge and dirt will tend eventually to be swept out of the heat exchanger (63) by the waste water flow.

In the example shown1 the level control mechanism (43) is in the form of a valve (45) which opens only when the magnitude of the force due to the hydrostatic pressure of the waste water acting on the valve seat area, in a direction down the valve stem (arrow 46), overcomes the force of the pre-compressed spring (47) which tends to keep the valve (45) seated. Other methods of controlling the waste water level could be employed, such as a float valve, whereby a float (not shown), floating on the surface of the waste water, tends to lift an outlet valve off its seat at waste water levels above a pre-determined value, or such means as are well-known within the art, and not discussed further here.

A pump/cleaner (48) may be provided, shown as consisting of two main parts, each formed by an outer ring (49) and (50) respectively, located in a bearing on the casing (41), which is connected by a series of fingers (51) to an inner ring (52) and (53) respectively. However, other arrangements could be provided, which are well known within the art, and not discussed further here. The arms, if fitted, may be provided with fibres (not shown). The function of the pump/cleaner (48) and/or fibres is substantially similar to that described in the description of operation of the device illustrated in figure 2.

Alternatively, the pump/cleaner (48) may be intermittent in operation during heat exchanger (63) use, such that the main reason for its provision is to physically brush or scrape against part or all of the internal surfaces of the heat exchanger (63) contacted by the waste water, to physically remove the dirt therein/thereon, thereby cleaning them.

Alternatively, the pump/cleaner (48) may not be provided at all. In this case, a pure pump (not shown) may be provided, possibly for continous operation during periods of heat exchanger (63) usage.

Raised contours (not shown) on the surface of the element assembly (42), whether circular or spiral or other, if provided, perform similar respective functions to those described in the decription of the operation of the embodiment depicted in figure 2.

Primary water enters the element assembly (42) via a pipe (54).

The water then flows inside inside the element assembly (42), in a similar manner to that described in the decription of the operation of the embodiment depicted in figure 2.

A hydraulic motor or turbine (56) (connecting pipework not shown) or other source of motive power, such as an electric motor or manual power may be provided, in addition to power transmission means such as a shaft (57) and cog (58) which engages a ring gear(s) (59) on each outer ring (49) and (50). These function in a substantially similar manner to that described in the decription of the operation of the embodiment depicted in figure 2.

The end of the shaft (57), if fitted, may be supported in a bearing located in the casing (41). Means, such as a seal (60) between casing (41) and shaft (57) may be provided to render the casing (41) airtight, apart from the inlet and exit pipes (40) and (44). This, in conjunction with the design of the heat exchanger (63), will tend to ensure that an air pocket is trapped in the upper part of the casing (41) cavity, such that the bearing surfaces between parts with relative motion do not become contaminated by contact with the waste water, and/or dirt therein, as described in the decription of operation of the embodiment depicted in figure 2.

Claims

1. A heat exchanger comprising an element assembly with primary water on one surface and waste water on part or whole of its other surface, housed in a casing, which transfers heat from warm waste water to colder primary water, and a pump which tends to increase the velocity of the waste water relative to the element assembly and casing, so tending to increase the rate of heat transfer from the waste water to the element assembly, and to minimize the possibility that any dirt and sludge which settles out of the waste water whilst in the heat exchanger will remain therein without being washed away by the waste water flow.

2. A heat exchanger as claimed in claim 1, where a scraper or brush is provided which can be made to physically scrape or brush against all or part of the internal surfaces in the heat exchanger wetted by the waste water, to physically remove the dirt therefrom.

3. A heat exchanger as claimed in claim 2, where the brush/scraper also serves to pump the waste water.

4. A heat exchanger as claimed in claim 1, 2 or 3, where the waste water flows with a free surface whilst on the element assembly.

5. A heat exchanger as claimed in claim 1, 2 or 3, where the waste water exits the casing through an exit pipe which communicates with the casing cavity at a lower level than that at which the inlet pipe does, at a level at or near the lowest part of the casing interior, with a level control mechanism which regulates the level in the casing of the waste water, thereby regulating the immersion of the element assembly in the waste water, with the waste water flow generally down the gravitational incline from inlet to outlet.

6. A heat exchanger as claimed in claim 5, in which some or all of the solid surfaces of the heat exchanger slope down the incline towards the waste water outlet.

7. A heat exchanger as claimed in claim 4 in which raised surface contours on the element assembly tend to retain waste water in the heat exchanger, so increasing the average length of time spent by a waste water particle in the heat exchanger.

8. A heat exchanger as claimed in claim 7 in which the raised contours are substantially circular in their locus.

9. A heat exchanger as claimed in claim 4 or 5 in which raised contours on the casing and/or element assembly provide a path leading generally from waste water inlet to outlet.

10. A heat exchanger as claimed in claim 9 in which the path-providing contours are spiral in their locus.

11. A heat exchanger as claimed in claim 10, where the spiral contours in conOunction with the action of the rotating pump/cleaner or pure pump, tend to cause dirt to be swept through, and/or waste water to be pumped out of, the heat exchanger.

12. A heat exchanger as claimed in claim 11, in which the rotational rate and hence, ceteris paribus, the flow rate pumped by the pump/cleaner or pure pump is arranged to be coupled to the primary water flow rate, so that assuming the waste water flow rate is coupled to the primary water flow rate, the pumping of the waste water through the heat exchanger is at the rate at which it is generated.

13. A heat exchanger as claimed in claims 1, 2, 3, 4, or 5, where the energy for pumping is extracted from the flow of the primary water by means of a hydraulic motor or turbine.

14. A heat exchanger as claimed in claims 1, 2, 3, 4 or 5, where the design of the heat exchanger ensures the trapping in part of the casing cavity of an air pocket, into which the general level of waste water never rises, so that bearing surfaces located in the air pocket do not become contaminated by contact with waste water and/or dirt therein.

15. A heat exchanger as claimed in claim 4, where the element assembly is designed in more than one part, with the vessel carrying the primary water not directly immersed in or in contact with the waste water, but in intimate thermal contact with a part of the element assembly which is, heat being conducted from the latter to the former.

16. A heat exchanger as claimed in claim 15 or claim 1, where the element assembly is designed so that the vessel carrying the primary water is protected against being caused to leak by the erosive or abrasive action of the brush/scraper or waste water flow, by providing a more robust physical barrier separating waste water from primary water than that separating waste water from atmosphere, and by providing that the outside surface of the element assembly is exposed to atmosphere, so that if errosion or abrasion occured, a leak of waste water to atmosphere would become noticeable, signalling the necessity of device overhaul, before the likelihood of a leak of primary to waste water occured.

17. Any heat exchanger substantially as depicted in figures 2 cr 4 or 6, or as described in their relevant descriptions.