SHEAR FLOW CONDENSER

Abstract

A plate-fin condenser includes a plate body defining an interior channel having a fluid inlet, a first interior channel section having a first cross-sectional area in fluid communication with the inlet, a second interior channel section downstream of the first interior channel section, and a fluid outlet in fluid communication with the converging interior channel. The second interior channel section has a second cross-sectional area that is smaller than the first cross-sectional area.

Description

BACKGROUND

1. Field

The present disclosure relates to heat exchangers, more specifically to condensers for condensing fluids in their vapor state.

2. Description of Related Art

Condensers can include an arrangement whereby a working fluid, i.e. a vapor, is cooled by a cooler stream (coolant) such that the amount of heat removed by the coolant is used to condense all or some of the vapor flow. A plate fin condenser includes the cooling and condensing fluid flow in alternating layers which are separated by solid sheets, called parting sheets.

Each plate of a typical plate fin condenser includes an interior channel(s) for routing a working fluid (vapor) flow therethrough. The flow space for the condensing vapor is between parting sheets. Both the vapor and coolant flow spaces include a series of conductive fins which are metallurgically or otherwise bonded to both sides of each space. For example, each plate can be connected together and/or separated by thermal transfer fins which create fin channels for a coolant to pass therethrough.

The thermal transfer fins and the fin channel defined thereby can be arranged such that coolant flows orthogonally to the working fluid flowing within the interior channel of the plates. The condensing working fluid can contain a pure or mixture of condensable vapors and, in some cases, non-condensable gases (e.g., fluids that will not condense at the operating temperature of the condenser).

Traditionally, the interior channel is defined within the plates as linear channels of constant cross-sectional area. However, as portions of the working fluid condense on the walls of the interior channel, the remaining vapor flow slows down. In some cases, this creates a buildup of condensate within the interior channel in such a manner that the thickness of the condensate film grows non-uniformly along the length of the interior channel.

The condensation layer is the principle resistance to heat transfer, such that a thickened layer significantly reduces the efficiency of the condenser. The reduced local heat transfer will require longer channels to condense the working fluid completely and/or a large enough temperature gradient to negate these effects. Also, non-condensates gases will blanket the local condensing surfaces when the vapor velocities are too small and this can further limit the efficiency of the condenser.

Local non-condensable gases are convectively transferred to the condensate surface with the condensing vapor flow. This mechanism enriches the non-condensable fraction near the condensing surface and inhibits the condensation rate because the partial pressure of the vapor is reduced and the vapor must diffuse through the layer.

Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved condensers. The present disclosure provides a solution for this need.

SUMMARY

In at least one aspect of this disclosure, a plate condenser includes a plate body defining an interior channel having a fluid inlet, a first interior channel section having a first cross-sectional flow area in fluid communication with the inlet, a second interior channel section downstream of the first interior channel section, and a fluid outlet in fluid communication with the second interior channel. The second interior channel section has a second cross-sectional flow area that is smaller than the first cross-sectional area.

The plate body is in thermal communication with fin thermal transfer devices and channels laterally defined thereby. The second interior channel can be tapered in cross-sectional flow area. The second interior channel can be uniform in cross-sectional area. The interior channel can be connected together with one or more headers, wherein each header directs flow from one interior channel to another interior channel to change the direction of flow.

The plate condenser can further include an intermediate interior channel section between the first and second interior channel sections that converges, such that the intermediate and second channel sections successively reduce in cross-sectional area. The first interior channel can be defined by uniform shaped walls parallel with an axial direction of flow within the first interior channel.

The intermediate and second interior channel sections can be defined by at least one wall that is angled relative to the axial direction of flow. The intermediate and second interior channel sections can include two tapered converging channel sections, wherein the at least one wall is a single angled wall defining the two tapered converging channels.

In at least one aspect of this disclosure, a method of condensing a fluid includes increasing a velocity of a working fluid (e.g., uncondensed vapor) within an interior channel of a plate condenser between a fluid inlet and a fluid outlet thereof while condensing the working fluid on the walls of the interior channel. Increasing the velocity of the working fluid can include routing the working fluid through a converging cross-sectional area of the interior channel of the plate condenser. In certain embodiments, increasing the velocity of the working fluid can include routing the working fluid through a uniformly converging cross-sectional area of the interior channel of the plate condenser. In other embodiments, increasing the velocity of the working fluid can include routing the working fluid through a non-uniformly converging cross-sectional area of the interior channel of the plate condenser.

These and other features of the systems and methods of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those skilled in the art to which the subject disclosure appertains will readily understand how to make and use the devices and methods of the subject disclosure without undue experimentation, embodiments thereof will be described in detail herein below with reference to certain figures, wherein:

FIG. 1A is a schematic, perspective view of an embodiment of a plate condenser in accordance with this disclosure, depicting a working fluid flowing therethrough within the interior channel thereof;

FIG. 1B is a partial, schematic, exploded view of the plate condenser shown in FIG. 1A, depicting a plurality of plates assembled together;

FIG. 2 is a schematic view of a uniformly tapered channel in accordance with this disclosure, showing in principle, shear flow condensing on walls thereof; and

FIG. 3 is a graph depicting the flow patterns that occur over a range of liquid and vapor mass flows in a closed channel which are applicable to flow in a condenser. Flow patterns are the vapor-liquid phase distribution such as bubbles within a liquid flow or liquid flowing as a film on wall with a vapor core.

DETAILED DESCRIPTION

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, an illustrative view of an embodiment of a plate condenser in accordance with the disclosure is shown in FIG. 1A and is designated generally by reference character 100. The systems and methods described herein can be used to at least partially condense vapor flow of a working fluid (e.g., a refrigerant).

In at least one aspect of this disclosure, referring to FIGS. 1A and 1B, a plate-fin condenser 100 includes a plate body 101 defining an interior channel having channel sections 103, 105, and 107. The interior channel includes a fluid inlet 109 in fluid communication with a vaporized working fluid 119 (e.g., from a heat sink with the working fluid flowing therethrough).

A first interior channel section 103 has a first cross-sectional area in fluid communication with the inlet 109. Vapor can flow through the inlet 109 into the first interior channel section 103. As shown in FIG. 1A, the first interior channel section 103 includes a uniform cross-sectional area with walls that are parallel with an axial direction of flow, but it is contemplated that the cross-sectional area of the first interior channel section 103 can be variable along the length of the first channel section 103.

The condenser 100 further includes a second interior channel section 107 downstream of the first interior channel section 103. At least a portion of the second interior channel section 107 includes a second cross-sectional area that is smaller than the first cross-sectional area of the first interior channel section 103. For example, second interior channel section 107 includes a tapered shape defined by wall 107a. In other embodiments, it is contemplated that the second interior channel section 107 can include a uniform cross-sectional area along its length with the cross-sectional area smaller than that of first interior channel section 103. In certain embodiments, the cross-sectional area of the second interior channel section 107 can be defined such that vapor flow, condensate thickness, and/or liquid flow are optimized for thermal transfer efficiency.

An approach to optimize the cross-section would reduce the passage size in a proportional manor to the vapor that in uncondensed. For example if the vapor flow at the end of the section is estimated to be half that of the inlet, the flow area at the end would be sized to be half the value at the start of the passage. Since liquid densities greatly exceed vapor densities, to a first order the vapor velocity will remain nearly constant. With a near constant vapor velocity the condensate film will be thinned by the “shear” force of the vapor flow and the heat transfer coefficient and subsequent condensation rate will be enhanced over a channel of uniform cross-sectional area. Because the condensation rate, film thickness, and vapor velocity are dependent quantities, the tapering rate for near uniform vapor velocity must be determined iteratively or alternately by a numerical model which determines the local conditions like the condensation heat transfer coefficient and condensation rate.

A prescribed optimum area profile is not necessary to improve the condensation process over a non-tapered design. Any design with a reducing (e.g., tapered) flow area in the direction of flow will improve the heat exchange process, resulting in a smaller device needed or a required coolant-to-vapor temperature difference.

A fluid outlet 111 is in fluid communication with the second interior channel section 107. The fluid outlet 111 can also be connected to a suitable heat exchanger location (e.g., recycled to a heat sink to absorb heat and convert the liquid working fluid 121 into vapor).

As shown in FIG. 1A, one or more intermediate channel sections 105 are disposed between the first interior channel section 103 and the second interior channel section 107, however, it is contemplated that the first and second interior channel sections 103, 107 be directly adjacent with no intermediate channel section 105 therebetween. The intermediate interior channel section 105 can have any suitable cross-sectional area (e.g., uniform or variable) and can also be tapered (e.g., defined by the opposite side of wall 107a).

The interior channel sections 103, 105, 107 are connected together with one or more headers 113. Each header 113 directs flow from one interior channel to another interior channel to change the direction of flow in a labyrinth manner within the plate body 101. As would be appreciated the headers 113 can be integrated as part of the plate body 101 instead of a separate component as shown.

Referring to FIG. 1B, a core of the condenser 100 with alternating vapor passages (i.e., interior channel sections 103, 105, 107 defined in plate body 101) and fin channels 117 (i.e., defined by the fins 115) is shown. The plate body 101 can be in thermal communication with fin thermal transfer devices 115 and fin channels 117 laterally defined thereby. As shown in FIGS. 1A and 1B, the fin thermal transfer devices are formed by accordion shaped sheet metal. In addition, as shown in FIG. 1B, a plurality of plate bodies 101 as described above can be assembled together around one or more fin thermal transfer devices 115. Any other suitable thermal transfer device and/or shape thereof is contemplated herein instead of or in conjunction with the fin thermal transfer devices 115.

As shown, a coolant flow 123 can be passed through the fin channels 117 in any suitable manner to remove heat from the vaporized working fluid 119 in order to convert the vaporized working fluid 119 to liquid working fluid 123. While, the interior channel sections 103, 105, 107 are shown to be circular with decreasing size, the interior channel sections 103, 105, 107 can be any suitable shape (e.g., non-circular cross-section) and can have fins therein. Also, each plate body 101 can be in thermal communication with multiple fin thermal transfer devices 115.

Referring to FIG. 2, the phenomena and flow patterns of a converging cross-sectional area for condensation is illustrated. The vapor core, with a high velocity extends far down the tube length. This flow pattern, with the liquid on the wall as a film is termed annular and it is the preferred condition for condensation. Of note are two other flow regimes, plug and chug. These regimes describe conditions where there is an oscillating nature to flow, with mostly liquid “slugs” are followed by large bubbles. This flow distribution is not favorable to condensation.

FIG. 3 shows a “flow map” which describes the flow patterns for a vapor and liquid flowing in a tube with various mass fluxes. Mass flux is the mass flow rate (˜kg/sec) divided by the tube flow area (˜m²). FIG. 3 is one of several semi-empirical “flow regime maps” that predicts the flow pattern for a given vapor flux and liquid flux. As can be seen, a plate condenser 100 having a tapered cross-sectional area as the embodiment of FIG. 1A maintains a higher vapor flux with higher liquid flux than a non-tapered traditional system. As can be seen, the flow is annular inside the interior channel in this condition, which is beneficial for heat transfer. Plate condenser 100 with a tapered cross-section allows for transition from annular flow to frothy and or bubbly flow which provides near-ideal heat transfer and condensation. For contrast, traditional plate condensers allow for annular flow to transition into slug flow, and then into a plug flow for less than ideal heat transfer.

In at least one aspect of this disclosure, a method of condensing a fluid includes increasing (or slowing the rate of decrease) a velocity of a vaporized working fluid 119 within an interior channel (e.g., second interior channel section 107) of a plate condenser 100 between a fluid inlet 109 and a fluid outlet 111 thereof while condensing the working fluid within the interior channel. Not significantly decreasing the working fluid velocity can include routing the working fluid through a converging cross-sectional area of the interior channel of the plate condenser. In certain embodiments, increasing the velocity of the working fluid can include routing the working fluid through a uniformly converging cross-sectional area of the interior channel of the plate condenser. In embodiments, increasing the velocity of the working fluid can include routing the working fluid through a non-uniformly converging cross-sectional area of the interior channel of the plate condenser.

The plate condenser 100 can be utilized in any suitable thermal transfer application. For example, two-phase thermal management systems are becoming widely used for cooling computer systems, electronics, weapons, actuation devices, etc. In these systems, the heat must be rejected by condensation to an outside heat sink (e.g., water, air or fuel in a condenser). Similarly in vapor-cycle refrigeration or air conditioning, the heat from the loop must be rejected in a condenser. Also, Rankine power generation cycles also require a condenser for waste heat rejection.

A shear flow condenser is most applicable to any of these applications where the condenser cannot be readily drained by gravity, and/or a size and/or weight reduction is advantageous. For example, shear flow condensers are highly relevant to the μ-gravity environment of space.

Another advantage to tapering the condensing vapor core is the increased stability of flow between condenser passages and into and out of the headers. The higher velocities that occur in a tapered design increase the pressure drop which has a stabilizing effect. Without taper, the deceleration of the vapor results into a momentum recovery and a smaller pressure drop. Flow reversal can occur in condensers that have small or no pressure drops. These stability issues can reduce condenser performance and impact system operation.

The methods and systems of the present disclosure, as described above and shown in the drawings, provide for a plate condenser with superior properties including improved thermal efficiency relative to traditional devices. While the apparatus and methods of the subject disclosure have been shown and described with reference to embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the spirit and scope of the subject disclosure.

Claims

1. A method of condensing a fluid, comprising: increasing a velocity of a working fluid within an interior channel of a plate condenser between a fluid inlet and a fluid outlet thereof while condensing the working fluid within the interior channel.

2. The method of claim 1, wherein increasing the velocity of the working fluid routing the working fluid through a converging cross-sectional area of the interior channel of the plate condenser.

3. The method of claim 1, wherein increasing the velocity of the working fluid routing the working fluid through a uniformly converging cross-sectional area of the interior channel of the plate condenser.

4. The method of claim 1, wherein increasing the velocity of the working fluid routing the working fluid through a non-uniformly converging cross-sectional area of the interior channel of the plate condenser.