CROSS REFERENCE TO RELATED APPLICATION
The present application is a Non-Provisional and claims priority from U.S. Provisional Application Ser. No. 61/774,184 filed Mar. 7, 2013, entitled “Membrane Support Assembly for an Energy Exchanger, which related and claims priority from U.S. Provisional Application Ser. No. 61/692,793 filed Aug. 24, 2012, entitled “Membrane Support Assembly for an Energy Exchanger,” which is hereby expressly incorporated by reference in its entirety.
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OF THE DISCLOSURE
Embodiments of the present disclosure generally relate to an energy exchange system for conditioning air in an enclosed structure, and more particularly, to a membrane support assembly for an energy exchanger.
Enclosed structures, such as occupied buildings, factories and the like, generally include a heating/ventilation/air conditioning (HVAC) system for conditioning outdoor ventilated and/or recirculated air. The HVAC system typically includes a supply air flow path and an exhaust air flow path. The supply air flow path receives pre-conditioned air, for example outside air or outside air mixed with re-circulated air, and channels and distributes the pre-conditioned air into the enclosed structure. The pre-conditioned air is conditioned by the HVAC system to provide a desired temperature and humidity of supply air discharged into the enclosed structure. The exhaust air flow path discharges air back to the environment outside the structure. Without energy recovery, conditioning the supply air typically requires a significant amount of auxiliary energy, particularly in environments having extreme outside air conditions that are much different than the required supply air temperature and humidity. Accordingly, energy exchange or recovery systems are used to recover energy from the exhaust air flow path. Energy recovered from air in the exhaust flow path is utilized to reduce the energy required to condition the supply air.
Conventional energy exchange systems may utilize energy recovery devices (for example, energy wheels and permeable plate exchangers) or heat exchange devices (for example, heat wheels, plate exchangers, heat-pipe exchangers and run-around heat exchangers) positioned in both the supply air flow path and the return air flow path. Liquid-to-air membrane energy exchangers (LAMEEs) may be fluidly coupled so that a desiccant liquid flows between the LAMEEs in a run-around loop, similar to run-around heat exchangers that typically use aqueous glycol as a coupling fluid.
In general, a LAMEE transfers heat and moisture between a liquid desiccant solution and air through a thin flexible membrane. A flat plate LAMEE includes a series of alternating liquid desiccant and air channels separated by the membrane. Typically, the pressure of the liquid within a liquid channel between membranes is higher than that of the air pressure outside of the membranes. As such, the flexible membranes tend to outwardly bow or bulge into the air channel(s).
In order to avoid excessive restriction of the air flow due to membrane bulge, air channels of a LAMEE are relatively wide compared to the liquid channels. Moreover, a support structure is generally provided between membranes to limit the amount of membrane bulge. However, the relatively wide air channels and support structures typically diminish the performance of the LAMEE. In short, resistance to heat and moisture transfer in the air channel is relatively high due to the large air channel width, and the support structure may block a significant amount of membrane transfer area. Accordingly, a large amount of membrane area is needed to meet performance objectives, which adds costs and results in a larger LAMEE. Moreover, the support structure within an air channel may produce an excessive pressure drop, which also adversely affects operating performance and efficiency of the LAMEE.
The transfer of heat from an air channel to membranes within a parallel plate LAMME is described by the following:
where qs is the heat flux at the membrane per unit area, h is the local heat transfer coefficient, Ts is the local membrane temperature, and Tm is the local bulk mean temperature of the air. For a given temperature difference, (Ts−Tm), the rate at which heat is transferred to the membrane depends on the transfer coefficient h, which is related to the air channel width and air flow properties. The transfer of mass (for example, moisture) is governed by an analogous relationship. That is, the mass flux depends on a mass transfer coefficient hm, and the difference in concentration (for example, humidity) between the bulk air flow and the air at the surface. The coefficients h and hm are related to one another through the heat and mass transfer analogy for a given channel geometry and flow condition. The transfer coefficient is described by a dimensionless parameter referred to as the Nusselt number:
where Dh is the hydraulic diameter of the air channel, which is equal to twice the air channel width for parallel plates, and k is the thermal conductivity of the air. A typical LAMEE creates laminar flow (that is, smooth, steady air flow with no turbulence) in the air channels
A known LAMEE includes metal, glass, or plastic rods placed in the air channels to maintain the width of the air channel. Additionally metal screens are used as extra support structures between the membranes and the rods. The metal rods may be sandwiched within an air channel between metal screens, which, in turn, are sandwiched between the rods and the membranes. In general, the longitudinal axes of the rods are parallel to the air flow. Air flow through the air channel is typically laminar. However, the rods typically take up considerable space in the air channel. Additionally, it has been found that laminar air flow through the air channels produces relatively low heat and moisture transfer rates between the air channel and the membrane.
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OF THE DISCLOSURE
Certain embodiments of the present disclosure provide a membrane support assembly configured to be used with an energy exchanger, such as a liquid-to-air membrane energy exchanger, an air-to-air membrane exchanger, a liquid-to-liquid membrane energy exchanger, or even a non-membrane heat exchanger. The membrane support system is configured to be positioned within a fluid channel, such as an air or liquid channel, between first and second membranes. The membrane support assembly may include at least one support member configured to span between the first and second membranes. The support member(s) is configured to maintain the spacing of the fluid channel. The membrane support assembly may also include at least one turbulence promoter connected to the support structure(s). The turbulence promoter(s) is configured to promote fluid turbulence within the fluid channel. The fluid turbulence within the fluid channel enhances energy transfer between the fluid channel and the first and second membranes.
The turbulence promoter(s) may be perpendicular to the support member(s). The turbulence promoter(s) may be centered about a longitudinal axis of the support member(s). The turbulence promoter(s) may be offset with respect to a longitudinal axis of the support member(s). The turbulence promoter(s) may connect to the support member(s) proximate a lateral edge of the support member(s). The support member(s) may include at least one planar support strut.
The turbulence promoter(s) may include a rounded leading end (such as a semi-elliptical shape) connected to a blunted end through an intermediate portion. Alternatively, the turbulence promoter(s) may include a cylindrical post, a block-shaped post, an elliptical-shaped post, a triangular-shaped post, and/or a perforated screen. The perforated screen may be parallel with a longitudinal axis of the support member(s).
The support member(s) may include a waved support member having rounded peaks and valleys. The support member(s) may include a scalloped support member having connection beams connected to connection joints that are wider than the connection beams. The support member(s) may include a plurality of openings formed therethrough.
The turbulence promoter(s) may include at least one turbulence-promoting connection joint. The support member(s) may include parallel support beams connected to the turbulence-promoting connection joint(s).
The turbulence promoter may include a perforated screen. The perforated screen may be parallel to a longitudinal axis of the support member(s). Further, the support member(s) may include a perforated screen positioned along at least a portion of the support member(s).
Certain embodiments provide an energy exchange system configured to exchange energy between a first fluid, such as an air stream or liquid stream, and a second fluid, such as an air stream or a liquid stream. The energy exchange system may include first and second membranes defining first and second liquid channels, an air channel defined between the first and second membranes, wherein the air channel is configured to allow air to pass therethrough, and wherein the air contacts the membranes to exchange energy between the air and liquid within the first and second liquid channels, and a membrane support assembly positioned within the air channel between the first and second membranes.
BRIEF DESCRIPTION OF THE DRAWINGS
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FIG. 1 illustrates a schematic view of an energy exchange system, according to an embodiment of the present disclosure.
FIG. 2 illustrates a side perspective view of a liquid-to-air membrane energy exchanger, according to an embodiment of the present disclosure.
FIG. 3 illustrates a front view of panels within an energy exchange cavity of a liquid-to-air membrane energy exchanger, according to an embodiment of the present disclosure.
FIG. 4 illustrates a front view of a membrane support assembly between membranes of a liquid-to-air membrane energy exchanger, according to an embodiment of the present disclosure.