Patent Grant
10179637
Field of the Invention
This invention relates to the improvement of heat transfer in a marine keel cooler, and in particular to improving heat transfer of the internal coolant flowing through keel cooler coolant tubes.
Discussion of the Prior Art
Heat-generating sources in marine vessels are often cooled by water, other fluids, or water mixed with other fluids. In marine vessels, cooling fluid or coolant flows through the engine or other heat generating source where the coolant picks up heat and then flows to another part of the plumbing circuit. The heat must be transferred from the coolant to the ambient surroundings, such as the body of water in which the vessel is located. For small vessels having outboard motors, the raw ambient water being pumped through the engine is a sufficient coolant. However, as the vessel power demand gets larger, ambient water pumped through the engine serves as a source of significant contamination damage, particularly if the ambient water is corrosive salt water and/or carries abrasive debris.
There have been developed various apparatuses for cooling engines and other heat sources of marine vessels. One such apparatus that uses coolant in a closed-loop plumbing circuit is a keel cooler. Keel coolers were developed more than 70 years ago for attachment to a marine hull structure, an example of which is described in U.S. Pat. No. 2,382,218 (Fernstrum). A keel cooler is basically composed of a pair of spaced headers secured to the hull and separated by a plurality of heat conduction or coolant tubes. In the plumbing circuit of a vessel, hot coolant flows from the engine and into the keel cooler header located beneath the water level (i.e., below the aerated water level), and then into the coolant tubes. The coolant flows through the coolant tubes to the opposite header, and the cooled coolant returns through the plumbing circuit to the engine. The headers and coolant tubes disposed in the ambient water operate to transfer heat from the coolant, through the walls of the coolant tubes and headers, and into the ambient water. The foregoing type of keel cooler is referred to as a one-piece keel cooler, since it is an integral unit with its major components being welded or brazed in place. However, other types of keel coolers are known, including demountable keel coolers having spiral tube configurations wherein the major components, including coolant tubes, are detachable
An important aspect of a keel cooler is the ability to efficiently transfer heat from the coolant flowing through the inside of the coolant tubes into the cooler ambient water around the outside. There are several factors that impact keel cooler heat transfer, one of which is the rate at which the heat flows into, or out from, either the interior fluid (i.e., coolant) or exterior fluid (i.e., ambient water). A high resistance to heat flow in either fluid will produce a slow overall rate of heat transfer. For the coolant, the inside heat transfer (Hi) is a function of coolant thermal properties, inside tube geometry, coolant flow rate, coolant flow distribution per tube, coolant flow characteristics (i.e., laminar or turbulent), and inside wall friction coefficients. For the ambient water, the outside heat transfer (Ho) is a function of outside fluid thermal properties, outside tube/keel cooler geometry, flow characteristics and restrictions, tube assembly, location on the hull, and speed and direction of ambient water passing over the keel cooler. Other factors to consider in overall heat transfer include the coolant tube wall thickness and the thermal conductivity of the tube material.
One known way to improve overall heat transfer is to increase the effective area of the keel cooler in order to increase the conductive barrier provided for heat flow. In other words, a larger keel cooler area will result in a greater amount of heat that will flow in a given time with a given temperature differential. Keel coolers are usually disposed in recesses at the bottom of the hull of the vessel, and sometimes are mounted on the side of the vessel, but always below the water line. The area on the vessel hull which is used to accommodate a keel cooler is referred to as the “footprint.” However, an important aspect of keel coolers for marine vessels is the requirement that they have as small a footprint as possible, while fulfilling or exceeding their heat exchange requirement and minimizing pressure drops in coolant flow. As such, keel coolers in the prior art have minimized their footprint by utilizing rectangular tubes and spacing them relatively close to each other to create a large heat flow surface area. Accordingly, keel coolers in the prior art often have a total of eight rectangular coolant tubes extending between the two headers, including six intermediate tubes and two outer-side tubes, which usually have cross-sectional dimensions of either 1.375 in.×0.218 in., 1.562 in.×0.375 in., or 2.375 in.×0.375 in. However, demands for improving engine fuel efficiency and payload capacity of vessels have resulted in higher engine output temperatures and a greater demand on keel cooler heat transfer efficiency, and since the keel cooler must maintain as small a footprint as possible, there exists a need to improve the heat transfer efficiency of the keel cooler in other ways.
Another way to improve keel cooler heat transfer is to enhance the flow rate and flow distribution of the internal coolant. It is well known that the flow rate of the coolant flowing through the coolant tubes has a velocity upon which the heat transfer is partially dependent. Moreover, it is also well known in the keel cooler art that the two outer-side tubes have the greatest area of exposure to the external ambient water, and that increasing flow distribution to these outer tubes would also improve keel cooler efficiency. However, keel coolers with rectangular headers and rectangular heat conduction tubes may provide imbalanced coolant flow among the parallel tubes, which can lead to both excessive pressure drops and inferior heat transfer. In particular, coolant flowing through the heat exchanger may have limited access to the outer-side tubes even in the presence of orifices designed for passing coolant to these outer-side tubes. As such, the vast majority of keel cooler developments in the past 15 years have focused on improving heat transfer efficiency by enhancing as well as equalizing the flow rate through the side tubes and intermediate tubes. For example, U.S. Pat. No. 6,575,227 (having the same assignee as the present application) was directed toward a keel cooler having a beveled bottom wall with outer-side tube orifices being in the natural flow path of coolant flow for improving flow rate and flow distribution to the coolant tubes. U.S. Pat. No. 6,896,037 (also having the same assignee) additionally provided in the header a fluid flow diverter for facilitating coolant flow towards both the inner tubes and the outer-side tubes. U.S. Pat. No. 7,055,576 (Fernstrum) was directed toward an apparatus for enhancing keel cooler efficiency by increasing the flow rate of coolant through side tubes by using apertures in an arrow-shaped design. However, as already mentioned, the demand on keel cooler efficiency continues to increase, and there exists a need for a new development in the art of keel coolers, which is satisfied by the present invention.
An approach for improving keel cooler heat transfer that has received no attention in the prior art is through the enhancement of turbulent flow of the internal coolant flowing through coolant tubes. In most modern keel cooler designs, the rectangular coolant tubes have a relatively smooth inner surface that promotes laminar flow of the cooling fluid at or near the coolant tube interior walls. Laminar flow is defined as a flow condition where a viscous fluid flows in contact with a tube surface at a low velocity so as not to produce any intermixing of the fluid. In a laminar flow regime, the fluid in contact with the tube wall will have its velocity reduced by viscous drag or friction, which produces a “boundary layer” that acts as a region of high viscous shear stress. This viscous shear layer, or boundary layer, acts to retard the passage of fluid along the pipe through the no-slip condition at the wall. Within the boundary layer, these viscous, frictional stresses cause energy dissipation into the bulk fluid, which appears as heat. In other words, the boundary layer not only inhibits mixing in the bulk fluid, but also acts as an insulative heat generating layer at the coolant tube interior wall (i.e., the heat transfer surface), therefore reducing the overall heat transfer of the keel cooler.
On the other hand, enhancing turbulence within the coolant can help to minimize the thermally resistant boundary layer. Turbulence is generally defined as the flow regime in which the fluid exhibits chaotic property changes, such as rapid fluctuations in velocity and pressure of the fluid about some mean value. Whether fluid flow will result in laminar or turbulent flow is primarily determined by the Reynolds number, which may be defined as the ratio between the inertial force and viscous force of the fluid. As such, the Reynolds number is a function of the fluid velocity, and as fluid velocity increases, a transition region can be reached in which the inertial forces dominate over the viscous forces. This may allow for the development of turbulent eddies in the fluid which can impact and destroy the boundary layer, resulting in a decrease in boundary layer thickness. As turbulence is further increased, eddying motion can become increasingly unsteady, causing the eddies to burst from the wall and mix with the bulk fluid (i.e., the region of fluid outside of the boundary layer that is further from the tube wall). The turbulent eddies that are formed can transport large quantities of thermal energy. Therefore, heat transfer can be increased where the eddies bursting from and/or impacting the tube wall act to disrupt or destroy the boundary layer insulation and take large amounts of cooler fluid from the wall and distribute it into the hotter bulk fluid regions.
While the science behind turbulence is not considered a well-understood art, it is generally believed that increasing turbulent flow inside of a keel cooler tube will result in an increase in the pressure drop of the coolant. This is believed to be caused by the turbulent eddies of various sizes interacting with each other as they move around, exchanging momentum and energy, and consuming the fluid's mechanical energy as the bulk fluid is forced to drive these unsteady eddy motions. In other words, in the keel cooler art, it is believed that enhancing turbulence will result in increased drag and pressure drop due to the increased transverse motion of fluid particles that oppose the direction of bulk fluid flow. In the keel cooler art, increasing system pressure drop is considered devastating to keel cooler performance and detracts from the overall usefulness of the keel cooler. This is because keel coolers on marine vessels are generally limited by the pumping capacity of the marine motor and do not usually have external pumps that can compensate for increased pressure drop. In other words, unlike land-based heat exchanger systems that can accommodate larger footprints with external pumps, keel coolers have strict size and payload constraints that practically preclude the use of an external pump. It is for this reason that developments in the keel cooler art have traditionally avoided enhancing coolant turbulence, for concerns over increasing pressure drop.
The only known keel cooler on the market that allegedly attempts to disrupt the coolant flow pattern inside of a rectangular keel cooler tube is an apparatus having a plurality of roughness elements on the interior surface of the coolant tube. The roughness elements of this known apparatus are small protrusions in the form of bumps arranged on the coolant tube interior wall. The bumps of this apparatus are about 0.015 inches in height, with a diameter of 0.022 inches, and spaced evenly by 0.060 inches in a staggered configuration. It is believed that the purpose of these roughness elements is to disrupt the boundary layer insulation at the coolant tube interior wall. However, it is well known in the keel cooler industry that this apparatus significantly increases pressure drop with de minimus improvement in heat transfer. Therefore, it is believed that this device does not enhance turbulent coolant flow and/or generate unsteady eddying motions as to effectively mix the bulk coolant to improve heat transfer. Instead, this apparatus acts to increase surface roughness of the coolant tube wall, which increases the friction factor according to the well-known Moody diagram, and therefore results in the observed increase in pressure drop. The introduction of this apparatus into the keel cooler market has only further detracted those skilled in the art from pursuing coolant flow characteristics as an avenue for successfully increasing heat transfer.
As it generally pertains to keel cooler heat transfer, there are known keel coolers of only general interest that use external fins to improve the outside heat transfer (Ho) with the ambient water. For example, U.S. Pat. No. 3,841,396 (Knaebel) provides for a marine vessel heat exchanger having a series of radially extending external fins connected to a longitudinal member. The Knaebel invention provides these external fins to increase the surface area of the heat exchanger and does not teach turbulent flow to improve internal heat transfer (Hi). In U.S. Pat. No. 3,240,179 (Van Ranst), a marine heat exchanger is disclosed providing a bottom sheet portion in a transverse sinuous configuration. The Van Ranst invention is intended to provide a relatively large effective heat exchange area in proportion to the complete unit. The Van Ranst invention further provides for a smooth flow path of the inner coolant fluid, which is described as “optimal” and is believed to teach away from promoting turbulent fluid flow. In U.S. Pat. No. 3,650,310 (Childress), a combination boat trim tab and heat exchanger is provided having elongated fins secured to the bottom of the outside of the body to increase heat exchange area. Childress further provides an internal serpentine passageway and internal cooling fins to further increase the heat exchange area between the cooling liquid and the body. The invention in Childress does not disclose the use of turbulent coolant flow to increase heat transfer. U.S. Pat. No. 3,177,936 (Walter) provides a marine heat exchanger that includes a fluted heat exchange tube with an internal helical baffle. The fluted tube of the Walter invention is intended to increase heat exchange surface area, as well as improve the flow of external seawater over the tubes. The helical baffle in the Walter invention is intended to mechanically agitate the coolant and to partition the tubes into at least two stream passages of a serpentine form. The Walter invention does not disclose promoting turbulent flow of the coolant, as this term was well known in the art at the time of that invention. More particularly, Walter does not teach enhancing turbulence through naturally occurring eddying motions to improve bulk fluid mixing, and instead merely mechanically agitates the coolant to some unknown degree. Moreover, such partitioning inside of the coolant tube is believed to restrict coolant flow, which would result in a substantial increase in pressure drop compared to a similarly situated tube without the flutes and baffle. Therefore, as can be seen by these shortcomings in the keel cooler prior art, there exists a need to further improve heat transfer without increasing pressure drop, which can be achieved by the present invention through the provision of turbulence enhancers for use in the internal coolant.
Turbulators, which are known as inserts, tube inserts, impediments, or static mixers, are known to be arranged inside of a tube in order to promote and/or enhance turbulent fluid flow. Although turbulators are known to enhance turbulence and promote bulk fluid mixing to improve heat transfer, they are also known to detrimentally increase pressure drop. Because those skilled in the keel cooler art have been taught to avoid increased pressure drop due to the pumping constraints of marine motors, the use and teachings of turbulators have generally been confined to land-based heat exchanger systems where pressure loss can be compensated by external pumping means. Moreover, the relatively slow rate of innovation in the keel cooler art, combined with the lack of understanding of turbulence, has only further detracted those persons with ordinary skill in the keel cooler art from logically commending their attention to other heat exchanger systems.
Accordingly, there have been various patents of only general interest pertaining to turbulators which have issued over the years. U.S. Pat. No. 3,981,356 (Granetzke) describes a heat-exchange tube with a strip of expanded metal arranged in a helix to form a turbulator. This arrangement is alleged to direct a portion of the liquid toward the inner wall surface to control heat flow, however, it also results in increased pressure drop. The Granetzke invention alleges to regulate this increase in pressure drop by modifying the expanded metal configuration. Referring next to U.S. Pat. No. 6,578,627 (Liu et al.), this patent discloses a fin-pattern of ribbed vortex generators for an air conditioner system having a plurality of prism-like structures on the fin. The structures have different heights for improving heat transfer while allegedly causing little pressure drop-off. Similarly, U.S. Pat. No. 7,637,720 (Liang) provides a turbulator for use with a turbine blade of a gas turbine engine having an inverted V-shape with a diffusion slot between adjacent turbulators. In U.S. Pat. No. 4,865,460 (Friedrich), a static mixing device is disclosed having a plurality of rows of spaced parallel tubes extending across the conduit. The tubes are arranged so that adjacent tubes are located at right angles to each other, which provides a tortuous path for the viscous resin medium to be mixed. The Friedrich invention requires the product to be fed through the tortuous path of the static mixer at “high pressure,” and does not disclose the effect of pressure loss.
In light of the foregoing, it should be understood that keel coolers with the smallest footprint, greatest overall heat transfer, and least internal pressure drop are considered the most desirable. However, despite the various efforts to enhance turbulence and increase heat transfer using turbulators in general heat exchangers, there has been no known development in this area with respect to marine keel coolers. The demand on keel cooler efficiency is increasing as marine motors must become more efficient and carry heavier payloads. If turbulence enhancers can be selected to increase heat transfer while not substantially increasing pressure drop to an unacceptable level, there could be significant economic savings in the keel cooler industry. Therefore, there exists a long-felt, yet unsatisfied need for a keel cooler that improves heat transfer by enhancing turbulent coolant flow inside of the coolant tubes without a substantial increase in pressure drop. Such a keel cooler with improved heat transfer could further reduce the size required of the keel cooler, the cost of acquiring keel coolers, and the manufacturing costs associated with keel coolers.
The present invention satisfies the various long-felt, yet unsatisfied needs in the keel cooler art through the provision of a keel cooler assembly comprising a header and at least one coolant tube, which includes a means for enhancing the turbulence of the coolant for improving heat transfer without substantially increasing pressure drop of the coolant, and also without increasing the footprint of the keel cooler. The header may comprise an upper wall, an end wall, a bottom wall, opposing sidewalls, and an inclined surface operatively connecting upper wall, bottom wall and sidewalls, and also having spaces to receive each inner coolant tube. Each coolant tube may extend in a longitudinal direction from the header and comprises an elongated body portion including an interior surface forming an internal channel for allowing flow of the coolant, and also configured for enhancing turbulence. Each coolant tube may have at least one inlet for ingress of the coolant and at least one outlet for egress of the coolant. In some preferred embodiments there may be eight or more of these coolant tubes.
Another aspect of the invention relates to a provision wherein means for enhancing turbulence comprises a means for generating turbulent wakes in the coolant for increasing eddying motion and for improving heat transfer without substantially increasing pressure drop. In a preferred embodiment, means for generating turbulent wakes is provided in the bulk region of the coolant, the bulk region being the region of fluid outside of the boundary layer that is further from the coolant tube wall.
Yet another aspect of the invention is a provision wherein means for enhancing turbulence comprises a means for generating and propagating turbulent vortexes in the coolant for enhancing bulk coolant mixing for improving heat transfer without substantially increasing pressure drop.
Still another aspect of the invention is to achieve the foregoing means through the provision of a plurality of turbulence enhancers extending inwardly into the coolant tube internal channel from the coolant tube interior surface and being arranged in a predetermined pattern. Turbulence enhancers may be provided through the provision of turbulators having various configurations. Turbulators may be provided as inserts, such as cylindrical inserts with round, ellipsoid, or oval cross sections; hollow inserts, such as inserts with interior channels; inserts in the form of a rectangular parallelepiped, such as with square or rectangular cross sections; pyramidal inserts, such as with triangular cross sections; flat bars; bars having a wing-shaped configuration; inserts with polygonal configurations; inserts having one or more rounded surfaces; inserts having a configuration with combined rounded and flat surfaces; or any variety of inserts having irregular cross sections. The invention is not limited to having inserts as turbulators and could, for example, comprise coolant tubes with walls having internal turbulators as an integral part of the respective walls.
Another aspect of turbulence enhancers according to embodiments of the invention is through the provision of turbulators as impediments to coolant flow. Such impediments could be, amongst others, pins of various configurations, impediments sloped as chevrons, vane configurations having tear drop-shaped cross sections, impediments with or without orifices, impediments having undulating shapes, impediments having star-shaped cross sections, and the like. The impediment(s) could extend from the interior wall surface part-way into the coolant tube interior, or could extend into and be attached to two or more attachment points in the tube interior. In some situations, the impediment(s) could extend longitudinally in the respective tubes and may not be attached to coolant tube interior surface.
The invention further relates to the dimensions of the turbulators for respective sizes and shapes of the keel cooler tube in which turbulators are to be placed.
Another aspect of the invention is the distance between the respective turbulators in a keel cooler tube, the position of each turbulator in a keel cooler tube, the spacing between turbulators, and the pattern of turbulators in a keel cooler tube—all for increasing heat transfer while minimizing increase in pressure drop of the coolant, and while not unreasonably increasing the footprint of the keel cooler.
The foregoing turbulators could face in different directions inside the keel cooler tube, depending on the nature of the coolant, the shape and size of the keel cooler tube, the pressure of the coolant, amongst other factors.
Another aspect of the invention relates to the provision of a coolant tube for a keel cooler comprising an elongated body portion having an interior surface forming an internal channel and comprising a plurality of turbulators extending from the interior surface. The turbulators are configured to interact with the coolant for enhancing turbulence to improve heat transfer without substantially increasing pressure drop, and potentially to result in a decrease in the footprint of the keel cooler of which coolant tube constitutes a component. In a preferred embodiment, the respective coolant tubes have a rectangular cross section, which may include cross-sectional dimensions common to the industry. The coolant tube may be a keel cooler inner coolant tube or an outer coolant tube and may have various inlets and/or outlets depending on the particular configuration.
Through the provisions and embodiments discussed herein, it is a general object of the invention to increase the heat transfer in a keel cooler while minimizing any increase of the pressure drop of the coolant flowing through the keel cooler.
Another object of the invention is to enhance the turbulence of coolant flowing through keel cooler tubes while not substantially increasing the pressure drop of the coolant. Yet another object of the invention is to naturally generate turbulent wakes in the coolant; and further still, an object is to generate turbulent vortexes in the coolant, all while not substantially increasing pressure drop. In preferred embodiments, an object of the invention is to generate turbulent wakes and/or turbulent vortexes through naturally occurring eddy motions in the bulk region of the coolant without substantially increasing pressure drop.
Another object of the invention is to enhance turbulence for improving heat transfer independent of the bulk fluid velocity or flow rate. In a preferred embodiment, turbulence is enhanced and heat transfer improved without substantial pressure drop even when coolant tube interior walls are substantially smooth between respective turbulence enhancers.
It is yet another object of the present invention to provide a turbulence enhancer for a keel cooler tube for increasing the heat transfer capability of the keel cooler.
It is an additional object of the invention to enhance the turbulence inside a keel cooler tube to increase the heat transfer capability of the keel cooler, to thereby decrease the size of the footprint of the keel cooler to therefore reduce costs for the vessel owner where the keel cooler is to be incorporated.
A general object of the present invention is to increase the efficiency and effectiveness of keel coolers in an economical and practical manner.
These and other objects should be apparent from the description to follow and from the appended claims.
The present invention may take physical form in certain parts and arrangement of parts, the preferred embodiments of which will be described in detail in the specification and illustrated in the accompanying drawings which form a part hereof, and wherein:
The fundamental components of a keel cooler system for a water-going or marine vessel are shown in
In the discussion above and to follow, the terms “upper”, “inner”, “downward”, “end,” etc. refer to the keel cooler, coolant tubes, or header as viewed in a horizontal position as shown in
Turning to
Keel cooler 10 is connected to the hull of a vessel through which a pair of nozzles 20 extend. Nozzles 20 have nipples 21 at the ends and cylindrical connectors 22 with threads 23. Nozzles 20 discharge coolant into and out of keel cooler 10. Large gaskets 26 each have one side against headers 30 respectively, and the other side engages the hull of the vessel. Rubber washers 25B are disposed on the inside of the hull when keel cooler 10 is installed on a vessel, and metal washers 25A sit on rubber washers 25B. Nuts 24 which typically are made from metal compatible with the nozzle 20, screw down on sets of threads 23 on connectors 22 to tighten the gaskets 26 and rubber washers 25B against the hull to hold keel cooler 10 in place and seal the hull penetrations from leaks. The gaskets 26 are provided for three essential purposes. First, they insulate the header to prevent galvanic corrosion. Second, they eliminate infiltration of ambient water into the vessel. Third, they permit heat transfer in the space between the keel cooler tubes and the vessel by creating a distance of separation between the keel cooler and the vessel hull, allowing ambient water to flow through that space. Gaskets 26 are generally made from a polymeric substance. In typical situations, gaskets 26 are between one-quarter inch and three-quarter inches thick.
The plumbing from the vessel is attached by means of hoses to nipple 21 and connector 22. A cofferdam or sea chest (part of the vessel) at each end (not shown) contains both the portions of the nozzle 20 and nut 24 directly inside the hull. Sea chests are provided to prevent the flow of ambient water into the vessel should the keel cooler be severely damaged or torn away, where ambient water would otherwise flow with little restriction into the vessel at the penetration location. The keel cooler described above shows nozzles for transferring heat transfer fluid into or out of the keel cooler. However, there are other means for transferring fluid into or out of the keel cooler. For example, in flange mounted keel coolers, there are one or more conduits such as pipes extending from the hull and from the keel cooler having end flanges for connection together to establish a heat transfer fluid flow path. Normally, a gasket is interposed between the flanges. There may be other means for connecting the keel cooler to the coolant plumbing system in the vessel. This invention is independent of the type of connection used to join the keel cooler to the coolant plumbing system.
Turning to
Referring to
Because keel coolers are sometimes used in corrosive salt-water environments, keel coolers are typically made from 90-10 copper-nickel alloy, or some other material having a large amount of copper. This makes the keel cooler a relatively expensive article to manufacture and an object of the present invention to reduce the size of keel cooler would be advantageous for reducing overall material and manufacturing costs.
Turning to
Also as shown in the embodiment of
Also as shown in
Turbulence enhancers are an important aspect of the present invention and provide a number of important advantages to the keel cooler. As mentioned previously, whether fluid flow will result in turbulent flow is primarily determined by the Reynolds number, which is in part dependent on the velocity of the cooling fluid. In general, at a given fluid viscosity, a fluid flowing at a low velocity will provide laminar flow, and as the velocity of the fluid is increased, the fluid can become more turbulent. In a laminar flow regime, the coolant in contact with surfaces will have its velocity reduced by viscous drag, which forms an insulating boundary layer that can reduce heat transfer. However, as the fluid becomes more turbulent, the static and insulative boundary layer becomes unstable due to the fluid inertial forces overpowering the fluid viscous forces. This can cause the fluid to form turbulent eddies where the boundary layer breaks away from the wall, therefore disrupting or destroying the thermally insulative layer to improve heat transfer. Enhancing turbulence at a given fluid velocity or flow rate in order to disrupt, thin-down, or destroy the boundary layer is one way in which an embodiment of the present invention improves heat transfer.
Turbulence enhancers according to an embodiment of the present invention can achieve the foregoing means through the provision of inserts or impediments extending inwardly from a coolant tube interior surface into the coolant. As described herein, inserts may include separate parts and impediments may be integral with a coolant tube. A tremendous variety of inserts for turbulence enhancer are available. Among the factors regarding the inserts are the shape of the inserts, the placement of the inserts within the keel cooler tube, the pattern of inserts along the keel cooler tube, and the size of the respective inserts. An aspect of turbulence enhancers according to the invention is the provision of inserts having various configurations, such as cylindrical inserts with round, ellipsoid, or oval cross sections; hollow inserts, such as inserts with interior channels; inserts in the shape of a rectangular parallelepiped, such as with square or rectangular cross sections; pyramidal inserts, such as with triangular cross sections; flat bars; bars having a wing-shaped configuration; inserts with polygonal configurations; combinations of different configurations; or any variety of inserts having irregular cross sections. Inserts could be attached to the keel cooler walls in a number of ways depending in part on the nature of the insert and the type of wall involved. The inserts could be welded to the walls, the walls themselves could have a configuration which could convert part of them into impediments to cause heat transfer, having the inserts extend across the walls, and protrude through the walls where they could be welded or brazed in place so as to prevent any coolant leakage, and the like. The inserts could even extend in the longitudinal direction of the respective coolant tubes with appropriate supports.
Another aspect of turbulence enhancers is the provision of impediments to coolant flowing through the keel cooler tubes. Such impediments could be, amongst others, pins of various configurations, impediments sloped as chevrons, vane configurations having tear drop-shaped cross sections, impediments with or without orifices, impediments having undulating shapes, impediments having star-shaped cross sections, and the like. It should be understood that there are many factors which determine the best type of insert or impediment to increase heat transfer while not substantially increasing the pressure drop to a level that detracts from the overall performance and usefulness of the keel cooler. Some of these factors are the size and shape of the keel cooler tubes, the viscosity of the coolant, the temperature differential between the coolant and ambient water, and the like. In addition, the foregoing inserts or impediments could face in different directions inside the keel cooler tube, depending on the nature of the coolant, the shape and size of the keel cooler tube, the pressure of the coolant, amongst other factors. In preferred embodiments, inserts or impediments could be disposed in the bulk coolant for effecting turbulence enhancement.
An object of the present invention is that turbulence enhancers do not cause a substantial increase in pressure drop of the coolant to a level that detracts from the overall usefulness of the keel cooler. An acceptable pressure drop level may, of course, depend on the design considerations and pumping capacity of the particular marine engine or heat source to which keel cooler is plumbed. However, for many marine applications, a substantial increase in pressure drop may be defined as no greater than about a 10-percent increase over the pressure drop of a standard, or baseline, coolant tube configuration that lacks turbulence enhancers, such as those prior art coolant tubes having a generally rectangular cross section as shown in
Another aspect of turbulence enhancers according to an embodiment of the invention includes the arrangement of turbulence enhancers inside of the coolant tube, which includes the spacing between respective turbulence enhancers and the pattern and placement of turbulence enhancers within the coolant tube. Such patterns could be, amongst others, symmetrical or asymmetrical; parallelogram patterns, such as rectangular, square or diamond; triangular patterns; polygonal patterns; spiral, undulating and/or sinuous patterns; irregular or random patterns; and the like.
According to an embodiment of the invention, the arrangement of turbulence enhancers can affect the flow characteristics and pressure drop of the coolant in a manner that can be explained by the well-known Moody diagram (which is incorporated herein by reference in its entirety). According to the Moody diagram, for a given relative roughness factor of the surfaces over which the coolant flows, the friction factor will decrease as the Reynolds number increases (increasing turbulence), up to a limit defined by wholly turbulent flow. The friction factor can be defined as a resistance to flow, such that a reduction in friction factor will generally result in minimizing or reducing substantial pressure drop. Thus, turbulence enhancers according to a preferred embodiment of the invention provides a means for enhancing turbulence in order to minimize or reduce friction factor (and pressure drop). More particularly, one manner in which turbulence enhancers can achieve these means is through the arrangement of a plurality of turbulence enhancers in a narrow configuration for effecting a constriction of coolant flow in the areas between adjacently arranged turbulence enhancers. Constricting the coolant flow in this manner causes the coolant velocity to reach a maximum where there is a minimum cross-sectional spacing between adjacent turbulence enhancers, particularly where coolant flow is normal to the spacing between transversely adjacent turbulence enhancers. The increased velocity increases the Reynolds number of the coolant flowing between turbulence enhancers, and according to the Moody diagram, this reduces the friction factor to minimize or reduce the amount of pressure drop. However, turbulence enhancers should not be so narrowly arranged as to restrict coolant flow and increase pressure drop.
Turbulence enhancer structures and/or the arrangement of turbulence enhancers according to an embodiment of the invention can also minimize or reduce substantial pressure drop of the coolant by providing a means for enhancing turbulence through generating turbulent wakes in the coolant, which can also improve heat transfer. Turbulence enhancers can provide a means for generating these turbulent wakes through the provisions of inserts and/or impediments, as described above. In a preferred embodiment, turbulence enhancers extend from the coolant tube interior wall(s) into the bulk coolant to effect the development of turbulent wakes in the bulk coolant flow. When the coolant flows around a turbulence enhancer, the fluid flow is distorted and a boundary layer may be formed on the turbulence enhancer body in the same way as the boundary layer is formed at the coolant tube interior wall. As the coolant approaches the vertical boundaries of the turbulence enhancer body, fluid separation can develop leading to highly distorted fluid chunks, which may begin to rotate if they travel far enough downstream. At increased velocities (higher Reynolds numbers), the inertia of the fluid particles passing over a turbulence enhancer body can overcome the fluid viscosity, and the highly distorted fluid particles can separate to form a turbulent wake region extending downstream from the turbulence enhancer body. The turbulent wake region thus formed can interact with boundary layers that have developed on downstream turbulence enhancer bodies and coolant tube walls. Since the boundary layers can be a source of high resistance due to frictional shear, the enhanced eddying motion and increased Reynolds number of the turbulent wake region that acts to disrupt, thin-down, or destroy the boundary layers on downstream surfaces can lead to a reduced friction factor according to the Moody diagram, as described above. Moreover, disruption of the boundary layer in this manner destroys the thermal insulation, which increases heat transfer.
If coolant flow in the turbulent wake region becomes highly unsteady, large eddies or vortexes can be shed downstream from the turbulence enhancer body. This may require sufficient spacing in the arrangement between respective turbulence enhancers to allow turbulent vortexes to develop. Development of turbulent vortexes in the coolant can also increase Reynolds number and thus reduce friction factor on coolant tube walls and downstream turbulence enhancers, as described above. Therefore, yet another aspect of the turbulence enhancer structure and/or the arrangement of turbulence enhancers according to an embodiment of the present invention is to provide a means for enhancing turbulence by generating turbulent vortexes in the coolant for improving heat transfer without substantially increasing the pressure drop of the coolant. As used herein, the term vortex is defined as a region within a fluid where the flow is mostly a spinning or swirling motion about an imaginary axis, straight or curved. Therefore, the characteristic swirling motion of a turbulent vortex formed by turbulence enhancers can provide an effective means for mixing the bulk coolant and increasing eddying motion. Since, eddies can transport large quantities of thermal energy as they are mixed with the fluid, increasing eddying motion through turbulent vortex mixing can increase heat transfer by disrupting the boundary layer insulation and by taking large amounts of cooler fluid from the coolant tube wall region and distributing it into the hot bulk fluid regions.
It should be understood that aspects of turbulence enhancers according to preferred embodiments of the invention could provide benefits even where the coolant tube interior walls are smooth between respective turbulence enhancers. The smoothness of the coolant tube interior surface can be defined according to the relative roughness factor of the Moody diagram, such that a smooth tube according to an embodiment of the invention has a relative roughness factor between 9.74×10−5 and 1.978×10−4, and more preferably between 9.7×10−5 and 1.2×10−4. In certain embodiments, it may be preferable to have smooth coolant tube interior walls, since an increase in the relative roughness factor can restrict flow and increase friction factor (according to the Moody diagram), which could substantially increase pressure drop. It is believed that known prior art keel coolers having a plurality of roughness elements in the form of small protrusions or bumps on the coolant tube interior walls demonstrates this adverse phenomena, as it is known to suffer from substantial pressure drop.
It should also be understood that aspects of turbulence enhancers according to preferred embodiments of the invention can provide improvements regardless of whether the bulk coolant flow is laminar or turbulent. In other words, regardless of whether the flow rate is low and provides laminar flow, or whether the flow rate is increased to promote more turbulence, turbulence enhancers according to preferred embodiments of the invention can still improve heat transfer without a substantial increase in pressure drop. For example, where the bulk coolant flow is generally laminar, the insulative boundary layer at the coolant tube interior wall may be thicker (compared to when flow is more turbulent), however, turbulence enhancers according to preferred embodiments can still effectively cool the hot bulk fluid by providing a means for enhancing naturally occurring eddying motions through the generation of turbulent wakes and/or turbulent vortexes that effectively mix the coolant. Even as the coolant velocity increases to become more turbulent, turbulence enhancers that generate turbulent wakes and/or turbulent vortexes still enhance eddying motion and improve heat transfer. Therefore, it should be understood that an object of turbulence enhancers is to increase heat transfer independently of coolant velocity or flow rate.
It should also be understood that the corresponding structures, materials, acts, and equivalents of all means plus function elements of turbulence enhancers in the claims below are intended to include any structure, material, or acts for performing the functions in combination with other claimed elements as specifically claimed. Thus, for example, although turbulence enhancers have been described through the provision of inserts or impediments, and through other aspects such as spacing and patterns, other structures and arrangements may be provided. Accordingly, any specific embodiments pertaining to the structure or arrangement of turbulence enhancers through the provision of turbulators, including previously described inserts and impediments, should be understood to be non-limiting embodiments of the present invention.
Turning now to
As shown in the embodiment of
In the embodiment shown in
A series of experiments were conducted to evaluate the effect of turbulator 175 according to several embodiments of the present invention. The experimental apparatus comprised a 32 inch long segment of a keel cooler coolant tube disposed inside of a chamber that flowed “external” cooling water over the exterior surface of the coolant tube segment. The coolant tube flowed internal coolant (the coolant being water) through its interior channel. Although keel cooler coolants typically comprise a glycol mixture, the viscosity and characteristics of water were sufficiently similar for the purposes of experimental comparison. Thermocouples were placed throughout the apparatus to measure the coolant tube shell (exterior wall) temperature, the coolant inlet temperature and coolant outlet temperature. Based on the thermocouple readings, the logarithmic mean temperature difference (LMTD) was calculated. Based on the calculated LMTD, measured flow rate and fluid specific heat, the overall heat transfer coefficient was calculated for various internal and external flow rates. Pressure transducers located at the inlet and outlet ports measured pressure drop of the coolant across the coolant tube segment. In each experiment, the coolant tube material and dimensions remained constant. The test was conducted over a range of flow rates with a coolant inlet temperature of 98° F. and an ambient shell temperature of 75° F. The coolant tube segment in each series of experiments was substantially the same, having a rectangular cross section measuring 0.375 inches wide by 2.375 inches in height. The coolant tube segment was made of a 90-10 copper-nickel alloy and had a wall thickness of about 0.062 inches. The surface roughness or relative roughness factor of the coolant tube interior walls was substantially equivalent for each setup, and ranged from about 63 to 125 micro-inches.
Three configurations were tested in the experimental apparatus. The first configuration was a coolant tube lacking turbulators, which represented the baseline condition (hereinafter, the “baseline configuration”). The second configuration comprised turbulators 175 according to the embodiment depicted in
The effect of turbulators and turbulator pattern spacing ratio (β) on heat transfer coefficient versus flow rate is shown in the graph of
The effect of turbulators and turbulator pattern spacing ratio (β) on pressure drop versus flow rate is shown in the graph of
It is believed that the narrow turbulator configuration (β=1) yields larger Reynolds numbers (increased turbulence) because of the closer spacing of respective turbulators constricting the fluid to effect an increase in fluid velocity, as previously explained. The spacing in this configuration is not so narrow as to restrict fluid flow and cause a substantial increase in the resistance to flow or pressure drop. As shown in the schematic of
In order to visually verify the development of turbulent wakes (W) and/or turbulent vortexes (V) according to the above experimental results, a replica of the coolant tube segment and turbulator configuration could be made with a clear material, such as polycarbonate. Each of the same turbulator configurations could be tested, whereby coolant (e.g., water) could be flowed at the same flow rates and a dye could be injected into the flow stream for visual identification of the flow characteristics. Where the fluid would display rapid fluctuations in the dyed flow stream in an extended wake region downstream from the turbulator body, a turbulent wake region would be considered developed. Where the dyed fluid would display a swirling vortex motion, a turbulent vortex would be considered developed. Such testing is easy to conduct and is commonly utilized for characterizing fluid flow. These tests could even precede the above-mentioned heat transfer experiments as an adequate screening tool.
In certain preferred and non-limiting embodiments of the invention, turbulators may be arranged in a staggered turbulator pattern wherein the spacing ratio (β) is preferably in the range between about 0.75 to 9, and more preferably in the range between about 1 to 7. In some preferred embodiments, it may be beneficial to improve heat transfer as much as possible without a substantial increase in pressure drop, which may correspond to a wide turbulator configuration wherein the spacing ratio (β) is preferably greater than about 3.5, and more preferably in the range between about 3.5 and 9. In still other preferred embodiments, it may be beneficial to minimize or reduce the pressure drop according to a narrow turbulator configuration wherein the spacing ratio (β) is preferably in the range between about 0.75 to 3.5, and more preferably in the range between about 1 to 3. As shown in the embodiment of
It should be understood that turbulators according to preferred embodiments of the present invention may have different geometric configurations and/or different turbulator patterns within a coolant tube for enhancing turbulence to improve heat transfer without substantially increasing pressure drop. In another preferred embodiment of the invention, shown in
Turning to
It should be understood according to objects of the present invention that turbulence enhancers or turbulators, including the provisions of inserts and/or impediments, may be incorporated into the coolant tubes of different types of keel coolers. For example, a keel cooler 200 according to an embodiment of the invention is shown in
Still referring to
Also as shown in
Another embodiment of a keel cooler 300 according to the invention is shown in
Turning to
It should also be understood that the importance and function of turbulence enhancers or turbulators according to the present invention may have advantages in other keel cooler systems as well. Referring to
An embodiment of two-pass keel cooler 600 shown in
Another embodiment of the present invention is shown in
Further as shown in the embodiment of
Multiple keel coolers can be combined in various combinations. For example, there can be two or more one-pass systems as shown in
The invention has been described in detail with particular reference to the preferred embodiments thereof, with variations and modifications which may occur to those skilled in the art to which the invention pertains.
This application is a continuation of U.S. patent application Ser. No. 14/508,091 filed Oct. 7, 2014, which is a continuation of International Application No. PCT/US2014/027440, filed Mar. 14, 2014, which claims priority to U.S. Provisional Application Ser. No. 61/784,977, filed Mar. 14, 2013, all of which are incorporated herein by reference in their entireties.
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| Number | Date | Country | |
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| Number | Date | Country | |
|---|---|---|---|
| Parent | 14508091 | Oct 2014 | US |
| Child | 14663044 | US | |
| Parent | PCT/US2014/027440 | Mar 2014 | US |
| Child | 14508091 | US |
