Integrated heat exchanger and muffler unit

An integrated heat exchanger and muffler unit (50,120,140) is provided for transferring heat between a first fluid and a second fluid, and for muffling the noise of the first fluid. The unit includes a housing (52) including a first inlet (60) for the first fluid, a first outlet (62) for the first fluid, a second inlet (64) for the second fluid, and a second outlet (66) for the second fluid. The unit (50,120,140) further includes a resonator (76) in the housing (52) and connected between the first inlet and outlet (60,62) to muffle noise in the first fluid, and a heat exchanger core (11,122) in the housing (52) connected to the first and second inlets and outlets to transfer heat between the first and second fluids. In one embodiment, the heat exchanger core surrounds the resonator. In another embodiment, the resonator surrounds the heat exchanger core.

FIELD OF THE INVENTION

This invention relates to integrated heat exchangers and mufflers, and in more particular applications to integrated heat exchangers and mufflers for use in a pressurized fuel cell system at a location downstream from the air compressor for the cathode air flow.

BACKGROUND OF THE INVENTION

In a pressurized fuel cell system where air is needed as oxidant, an air compressor is generally in place to supply the air at higher pressure above the atmosphere. What comes with this compression process are the annoying noises due to the compressor's internal cyclic moving or rotating parts, as well as the high temperature air output. Therefore, in a typical system design of this kind, a noise reduction silencer/muffler usually follows the gas compressor to muffle the noise down to a certain acceptable level. A gas cooler in series then cools the hot gas down to protect the downstream equipment.

SUMMARY OF THE INVENTION

An object of this invention is to design an air compressor aftercooler that not only meets the heat transfer performance requirements but also satisfies the compressor noise reduction specification. By designing the two functions in one component, the fuel cell system is simplified and its cost is reduced.

A broader object of the invention is to provide a new and improved integrated heat exchanger and muffler unit.

It should be understood that while certain objects of the invention have been expressly described herein, every embodiment of the invention may not achieve all of the expressly described objects.

To achieve at least some of the objects of the invention, a compressed air aftercooler merges into itself the function of an air compressor muffler/silencer without adding many extra parts. Resonator holes need to be drilled or formed through the side bars (bar-plate type) or tube walls (charged air cooler type), and baffle plates are added if more than one resonator is desirable. The overall dimensions of the heat exchanger/muffler are comparable with the original heat exchanger design, only slightly longer longitudinally to achieve better muffling results.

In accordance with one feature of the inventions, an integrated heat exchanger and muffler unit is provided for transferring heat between a first fluid and a second fluid, and for muffling the noise of the first fluid.

In one feature, the unit includes a housing extending along an axis between a first end and a second end, the housing including an first inlet for the first fluid, a first outlet for the first fluid, a second inlet for the second fluid, and a second outlet for the second fluid, with the first inlet located in the first end of the housing and configured to direct a flow of the first fluid parallel to the axis, and the first outlet located in the second end and configured to direct a flow of the first fluid parallel to the axis. The unit further includes an expansion chamber in the housing and connected to one of the first inlet and outlet for the transfer of the first fluid between the expansion chamber and the one of the first inlet and outlet; a first fluid flow path in the housing and extending parallel to the axis between the first inlet and outlet and connected to the expansion chamber for the transfer of the first fluid between the first fluid flow path and the expansion chamber; a resonator in the housing and connected to the first fluid flow; and a second fluid flow path in the housing and extending between the second fluid inlet and the second fluid outlet in heat transfer relation with the first fluid flow path.

As one feature, the first and second fluid flow paths surround the at least one resonator.

As a further feature, the second fluid flow path surrounds the first fluid path.

According to one feature, the housing includes an outer cylindrical wall, an inner cylindrical wall, and an intermediate cylindrical wall located radially between the inner and outer cylindrical walls. The inner and intermediate cylindrical walls define the first fluid flow path, and the intermediate and outer cylindrical walls define the second fluid flow path.

In one feature, a fin is located in the first fluid flow path between the inner and intermediate cylindrical walls.

As one feature, the inner cylindrical wall defines a resonator chamber of the resonator, and a plurality of resonator orifices extend through the inner cylindrical wall to connect the first fluid flow path to the resonator chamber.

In accordance with one feature, the first and second flow paths are defined by a plurality of spaced parallel planar surfaces, and the resonator includes a resonator chamber that surrounds the first and second flow paths. In a further feature, the unit further includes a plurality of parallel plates interleaved with a plurality of bars, with the plurality of spaced parallel planar surfaces being surfaces of the plurality of parallel plates. In yet a further feature, the resonator further includes a plurality of orifices in selected ones of the plurality of bars, the selected ones enclosing the first flow path.

As one feature, the unit includes another expansion chamber in the housing and connected to the other of the first inlet and outlet and to the first fluid flow path to transfer the first fluid between the first fluid flow path and the other of the first inlet and outlet.

According to one feature, the unit includes another resonator in the housing and connected to the first fluid flow path.

In accordance with one feature of the invention, the unit includes a housing including an first inlet for the first fluid, a first outlet for the first fluid, a second inlet for the second fluid, and a second outlet for the second fluid. The unit further includes a first expansion chamber in the housing and connected to the first inlet to receive the first fluid therefrom; a second expansion chamber in the housing and connected to first outlet to direct the first fluid thereto; a first fluid flow path in the housing and extending from the first expansion chamber to the second expansion chamber; a resonator in the housing and connected to the first fluid flow path between the first and second expansion chambers; and a second fluid flow path in the housing and extending between the second fluid inlet and the second fluid outlet in heat transfer relation with the first fluid flow path, the first and second fluid flow paths surrounding the resonator.

In one feature, the unit includes an additional resonator in the housing and connected to the first fluid flow path between the first and second expansion chambers. In a further feature, the housing extends along an axis between and first end and a second end, each of the resonators includes a resonator chamber having a length dimension extending parallel to the axis, and the length dimension of one of the resonator chambers is unequal to the length dimension of the other resonator chamber.

According to one feature, the housing extends along an axis between a first end and a second end, and further including a plurality of resonators in the housing and connected to the first fluid flow path, each of the resonators including a resonator chamber having a length dimension parallel to the axis. In a further feature, the unit includes a fin located in the first fluid flow path and having a length parallel to the axis that is at least as long as the length dimension of any one of the resonator chambers, but is unequal to the combined length dimensions of all of the resonator chambers.

In accordance with one feature of the invention, the unit includes a housing including an first inlet for the first fluid, a first outlet for the first fluid, a second inlet for the second fluid, and a second outlet for the second fluid. The unit further includes a first expansion chamber in the housing and connected to the first inlet to receive the first fluid therefrom; a second expansion chamber in the housing and connected to first outlet to direct the first fluid thereto; a first fluid flow path in the housing and extending from the first expansion chamber to the second expansion chamber; a second fluid flow path in the housing and extending between the second fluid inlet and the second fluid outlet in heat transfer relation with the first fluid flow path; and a resonator in the housing and connected to the first fluid flow path between the first and second expansion chambers. The first and second flow paths are defined by a plurality of spaced parallel planar surfaces.

In a further feature, the resonator includes a resonator chamber that surrounds the first and second flow paths.

As a further feature, the unit includes a plurality of parallel plates interleaved with a plurality of bars, the plurality of spaced parallel planar surfaces being surfaces of the plurality of parallel plates.

According to one feature, the resonator further includes a plurality of orifices in selected ones of the plurality of bars, the selected ones enclosing the first flow path.

In accordance with one feature of the invention, the unit includes a housing including an first inlet for the first fluid, a first outlet for the first fluid, a second inlet for the second fluid, and a second outlet for the second fluid; a resonator in the housing and connected between the first inlet and outlet to muffle noise in the first fluid; and a heat exchanger core surrounding the resonator, the heat exchanger core connected to the first and second inlets and outlets to transfer heat between the first and second fluids.

As one feature, the unit further includes at least one additional resonator connected between the first inlet and outlet to muffle noise in the first fluid and surrounded by the heat exchanger core.

In accordance with one feature of the invention, the unit includes a housing including an first inlet for the first fluid, a first outlet for the first fluid, a second inlet for the second fluid, and a second outlet for the second fluid: a heat exchanger core in the housing and connected to the first and second inlets and outlets to transfer heat between the first and second fluids; and a plurality of resonators in the housing, each of the resonators connected between the first inlet and outlet to muffle noise in the first fluid, each of the resonators including a resonator chamber that surrounds the heat exchanger core and a plurality of resonator orifices in the heat exchanger core to connect the resonator chamber to a flow path for the first fluid. As one feature, the heat exchanger core includes a plurality of spaced planer surfaces that define flow paths for the first and second fluids.

According to one feature, the heat exchanger core is a bar-plate type construction.

Other objects, features, and advantages of the invention will become apparent from a review of the entire specification, including the appended claims and drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In an earlier conceptual design of an air aftercooler10, a heat exchanger core11of bar-plate construction and all its air and coolant manifolds12and14, respectively, could be brazed at one time using a cylindrical tube housing16and some internal baffle plates18A-18D.FIG. 1shows one possible configuration as an example of this design. The intention of the design was to avoid welding inlet/outlet distribution tanks on both the air side and coolant side of the heat exchanger core11for simplified manufacturing purpose.

In addition to its aforementioned welding free merit, the configuration of this design also gives the chance to incorporate some noise reduction function in it without affecting its design performance as a heat exchanger. According to the plain wave acoustical theory, there are two basic types of noise reduction mechanism: expansion chamber and resonator, as illustrated inFIGS. 2A and 2B, respectively. The mechanism of the expansion chamber type muffler20is to reflect the sound pressure back towards its source and therefore reduce the transmitted noise level when sound wave propagation encounters area change. A typical resonator-type muffler22consists of an enclosed volume24surrounding a wave propagation pipe26, the volume24being connected to the pipe26through orifices28. The pressure fluctuations in the pipe26are branched off to the volume chamber24through the two small connecting orifices28, with the transmitted noise level being thereby reduced. In practical muffler design, the two basic mechanism can also be combined to reach required noise reduction performance.

Referring back toFIG. 1, an inlet/outlet diffuser30or32(tube housing on both ends) could act as an expansion chamber type muffler, and the enclosed air volume between the two middle baffle plates18B and18C could be a resonator's34enclosed volume36if proper holes38(shown in phantom) are drilled through the side bars40. If more resonators34are desirable from the sound muffling standpoint, additional baffle plates18can be added to separate the total enclosed volume into the desired number of resonator volumes without affecting its heat exchange performance.FIG. 3, for example, demonstrates a two-resonator type model based on the designed heat exchanger ofFIG. 1. Additionally,FIGS. 4 and 5diagrammatically illustrate two practical muffler models that could readily be implemented in the heat exchanger design show inFIG. 1. Acoustically, they consists of, in sequence, a first expansion chamber (inlet diffuser)30, two/three resonators34, and a second expansion chamber (outlet diffuser)32. For simplicity, they are referred to a two-resonator model and three-resonator model respectively, dependent on the number of resonators they have.

FIGS. 6 and 7show one form of an integrated heat exchanger and muffler unit50made according to the invention by making suitable modification to the aftercooler10ofFIG. 1. The unit50includes a housing52including a cylindrical outer wall53extending along an axis54between a first end56and a second end58. The housing includes an inlet60in the end56and an outlet62in the end58for a first fluid that is carrying noise, such as an air flow from a compressor. The housing52also includes an inlet64and an outlet66for a second fluid which passes through the heat exchanger core11in heat exchange relation with the first fluid. In the illustrated embodiment, the second fluid is a suitable coolant for cooling the air flow from a compressor, such as, for example, the WEG flow of a fuel cell system. The unit50further includes an inlet expansion chamber68A and an outlet expansion chamber68B, with the inlet60and outlet62configured to direct the first fluid flow parallel to the axis54to/from the expansion chambers68A and68B, respectively. The unit50further includes a first fluid flow path, shown schematically by the arrow72, in the housing52, and extending parallel to the axis54for directing the first fluid through the heat exchanger11, and a second fluid flow path for the second fluid, shown schematically by the arrow74, in the housing52for the directing the second fluid flow through the heat exchanger core11. The unit50also includes three resonators76A,76B and76C, with76A being a high frequency resonator,76B being a medium frequency resonator, and76C being a low frequency resonator. Each of the resonators76A-76C includes a resonator chamber78A,78B and78C defined between the exterior of the heat exchanger core10and the interior of the cylindrical outer wall53, and a plurality of resonator orifices80A,80B and80C which are formed by providing holes in the side walls of the flow passages for the first fluid in the heat exchanger core11. Baffles82A,82B,82C,82D,82E and82F are provided in the housing in the form of disk-shaped plates each with a lip for mating with the interior surface of the cylindrical wall53and a central opening that conforms to the exterior shape of the heat exchanger core10. In the embodiment ofFIG. 6, the expansion chamber68A is defined between an end cap84and the baffle82A, and the expansion chamber68B is defined between an end cap86and the baffle82F. Each of the resonator chambers78A,78B and78C is defined between the exterior of the heat exchanger core11and the interior of the cylindrical wall53in the radial direction and between two of the baffles82A-82F in the axial direction. The unit50also includes an inlet manifold88A for the second fluid and an outlet manifold88B for the second fluid, with the inlet manifold88A being defined between the exterior of the heat exchanger core11and the interior of the cylindrical wall53in the radial direction and between the baffles82E and82F in the axial direction, and the outlet manifold88B being defined between the exterior of the heat exchanger core10and the interior of the cylindrical wall53in the radial direction and between the baffle plates82A and82B in the axial direction.

As previously discussed, the core11can either be a bar-plate type or a charge air cooler type with tubes. With reference toFIG. 7, the core11of the illustrated embodiment is a bar-plate type and includes a plurality of parallel plates92spaced by bars94and96, with the volume enclosed by the plates92and the bars94defining individual flow passages98for the flow path72, and the volumes enclosed by the plates92and the bars96defining individual passages99for the flow path74. Preferably, surface enhancements such as fins or turbulators are included in the flow passages, with serpentine fins100being shown in the flow passages of the illustrated embodiment. As also seen inFIG. 7, the exterior of the housing50can be coated with an acoustic damping material, and the resonator chambers can be filled with a suitable insulation.

FIGS. 8A-10Billustrate three examples of additional embodiments of integrated heat exchanger and muffler units according to the invention, with like numbers indicating like components in the figures. Specifically,FIGS. 8A and 8Billustrate a unit102including two resonators76and one expansion chamber68,FIGS. 9A and 9Billustrate a unit104having two resonators76and two expansion chambers68, andFIGS. 10A and 10Billustrate a unit106having three resonators76and one expansion chamber68.

FIG. 11illustrates another embodiment of an integrated heat exchanger and muffler unit120, with like reference numbers indicating like components. The unit120differs from the previously described embodiments in that it has a heat exchanger core122that surrounds the resonators76, rather than having the resonators76surround the heat exchanger core10as in their prior embodiments. In this embodiment, the heat exchanger core is defined by an outer cylindrical wall106, an inner cylindrical wall108and an intermediate cylindrical wall110located between the outer and inner cylindrical walls106and108, with the first fluid flow path72being defined between the inner and intermediate cylindrical walls108and110, and the second fluid flow path74being defined between the outer and intermediate cylindrical walls106and110. Preferably, a surface enhancement such as a serpentine fin112is provided in the fluid passage72, and another surface enhancement such as fin114is provided in the fluid flow passage74. The unit120includes baffles82A,82B,82C and82D which differ from the baffles82of the prior embodiments in that they do not have any central opening and they engage the inner cylindrical wall108, rather than an outer cylindrical wall53. Furthermore, the resonator chambers78A-78C are defined between the interior surface of the inner cylindrical wall108and the respective baffles82A-82D, and the resonator orifices80A-80C extend through the inner cylindrical wall108to connect the resonator chambers78A-78C to the fluid flow path72.

FIG. 12shows another embodiment of an integrated heat exchanger and muffler unit140that is similar to the unit120ofFIG. 7, but differs in that it includes expansion chambers68A and68B on either side of the heat exchanger core122.

FIG. 13shows an alternate embodiment of the unit140ofFIG. 12, wherein the walls106and108have been lengthened so that they do extend past the length of the fins112and114, with the unfinned area between the outer cylindrical wall106and the intermediate cylindrical wall110defining inlet and outlet manifolds for the second fluid that can aid in fluid distribution.

To analyze the feasibility of the nose reduction muffler design implemented into a heat exchanger configuration such as shown inFIG. 1, and as implemented in the integrated heat exchanger and muffler units50,120and140ofFIGS. 6-13, the linear acoustical plane wave theory was adopted to analytically predict the sound pressure attenuation characteristics of the two muffler models shown inFIGS. 4 and 5. The effects of inlet/out expansion chambers, diameter of the cylindrical outer housing, total heat exchanger core length and the split ratio of total enclosed volume between the resonators on the attenuation characteristics were studied using the acoustical analytical model. The analytical model assumes the sound of speed of air is 434.5 m/s @ Tair=200° C. In order to use the plain wave theory, the geometrical dimensions of the expansion chambers must be small compared to the wavelength of the sound, and the lumped-impedance theory is valid if the length of a resonator chamber is less than ⅛ of the wavelength, which, for example, for a 1,200 Hz frequency is calculated as: sound wavelength=λminc/f=434.5/1200=0.362 [m]=14.26 [inch]. The analytical model was used to perform a design parametric study for the three resonator model shown inFIG. 5and included the following:Effects of the inlet and outlet expansion chamberCase studies included no inlet expansion chamber, no outlet expansion chamber and the effects of the length of the two expansion chambers.Effects of the canister diameterCase studies included changing the canister (outer cylindrical wall) diameter, and adjusting the orifices of the three chamber respectively in order to keep the resonance frequencies of the three resonators unchanged as the canister diameter changes.Effects of the total heat exchanger lengthCase studies included changing the canister diameter, and adjusting the orifices of the low frequency chamber in order to keep the resonance frequencies of the three resonators unchanged as the total heat exchanger length changes.Effects of the volume split ratio between different resonatorsCase studies included fixing the high frequency chamber and splitting the remaining volume at different ratios between low and medium frequency chamber. The orifice sizes have to change to maintain the same low and medium resonance frequency at these chambers.

In the curves shown inFIGS. 14-18, the theoretical predicted results are presented to show the possibility of the aftercooler10functioning also as the muffler, with the features incorporated inFIGS. 6-13.FIG. 14shows a typical attenuation curve for three resonator designs based onFIG. 5.FIG. 15illustrates the effects of the first and second expansion chambers30and32in three resonator designs based onFIG. 5.FIG. 16illustrates the effects of outer cylindrical wall diameter in three resonator designs based on ofFIG. 5.FIG. 17illustrates the effects of heat exchanger core length in three resonator designs based onFIG. 5.FIG. 18illustrates the effects the resonator volume ratio for three resonator designs based onFIG. 5.

Based on the results of the case studies, a number of conclusions were reached. First, the expanders broaden the frequency response between the resonator frequency design points and low frequency attenuation, with longer expander lengths improving attenuation performance. Additionally, the larger the canister diameter, the broader the frequency response between resonator frequency design points. Furthermore, the design is relatively insensitive to heat exchanger length, but performance improves slightly with longer heat exchanger designs. Additionally, skewing the design in favor of a larger volume low frequency resonator can broaden the frequency response at low frequencies. Finally, literature searches indicate that a tapered inlet diffuser can act as a horn and reduce the effectiveness of the muffler.