A thermal separation process driven by a desuperheater applied to a vapor-compression heat pump

Abstract

A thermally driven device that separates a volatile constituent from a liquid mixture that contains both the volatile constituent and one or more non-volatile constituents. The device includes a heat pump and a regenerator.

Description

Atty. Dkt. No. 01296-0088A Thermal Separation Process Driven by a Desuperheater applied to a Vapor-Compression Heat PumpRELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional Patent Application No. 63 / 744,522. filed January 13. 2025 and entitled ' Thermal Separation Process Driven by Heat Recovered from a Desuperheater applied to a Vapor-Compression System7’, the contents of which are incorporated herein by reference in their entirety.FIELD OF THE INVENTION

[0002] This invention is directed to thermal separation processes, and in particular to vaporcompression heat pumps.BACKGROUND

[0003] Since the pioneering work of Willis Carrier at the start of the 20th century, vaporcompression air conditioners (VC-AC) have been the dominant cooling technology for indoor comfort conditioning in all climates. Although technology advances have produced ever more efficient VC-ACs, a fundamental inefficiency has remained: VC-ACs serve very high latent loads (i.e., moisture loads) by first over-cooling air to condense moisture and then reheating the air to maintain the proper balance of sensible and latent cooling. Since reheating reduces the amount of total cooling provided by the VC-AC, this method of dehumidifying air wastes some of the work performed by the VC-AC’s compressor.

[0004] Desiccants are materials that have a strong attraction for water vapor. This attraction allows desiccants to dehumidify without overcooling the air. Since all desiccants have a finite capacity to absorb water, a practical air conditioner that applies desiccants to dehumidification must provide a means to either continuously or cyclically regenerate the desiccant (i.e., drive the absorbed water off the desiccant).

[0005] Desiccants are commonly regenerated by heating them. U.S. Patent Nos.7, 269, 966 and 10,655,870 disclose means of applying liquid desiccants to a VC-AC where heat recovered from the VC-AC’s refrigerant condenser is used to regenerate the desiccant. In the first of these patents, heat is transferred to the desiccant by flowing it over the outside surface of a heat exchanger that has refrigerant vapor condensing within it. In the second, the air that is heated by the VC-AC’s condenser flows through a pad of contact media that is wetted with the desiccant. In both cases, the liquid desiccant releases water as it heats.Atty. Dkt. No. 01296-0088

[0006] There are at least two venture-backed companies attempting to commercialize liquiddesiccant air conditioners that use the preceding approaches to regenerating a liquid desiccant. Blue Frontier has licensed the technology for desiccant regeneration disclosed in U.S. Patent No. 11,029,045 assigned to the Alliance for Sustainable Energy. The independent claim in this patent requires “routing the desiccant that is diluted with the moisture through the condenser to heat the desiccant and evaporate the moisture.” In this configuration the condenser has a two-phase, vapor / liquid flow of refrigerant within a heat exchanger while liquid desiccant flows over the outer surfaces of the heat exchanger.

[0007] Mojave Energy Systems, in their U.S. Patent Application No. 20230332780, describe the process for desiccant regeneration that is used in their ArctiDiy liquid-desiccant air conditioner applied as a Dedicated Outdoor Air System (DO AS). As described in the patent application “[t]he liquid desiccant system includes a regeneration airflow path passing through the desorbing unit and forming a desorber liquid / air interface... [and a] heat exchanger [which is later claimed to be the condenser of a VC-AC] is thermally coupled to the regeneration airflow path adding heat to the regeneration airflow upstream of the desorber unit.”

[0008] Also relevant to the invention described herein are heat exchangers described as desuperheaters. The refrigerant discharged by the compressor in a VC-AC will have a temperature higher than the refrigerant’s saturation temperature (i.e., the refrigerant is superheated). This superheated refrigerant vapor can be used to heat a second fluid up to a temperature that can approach the maximum temperature of the superheated refrigerant vapor. The most common application for a desuperheater applied to a VC-AC is to heat water for homes, commercial buildings and industrial processes.

[0009] In U.S. Patent No. 4,887,438, Meckler discloses a means for regenerating a liquid desiccant that is assisted by heat transferred from refrigerant vapor to the liquid desiccant in a desuperheater. Referring to Figure 3 in the Meckler patent, the high pressure, superheated refrigerant discharged by the compressor [element 33 in the Meckler patent] of a vaporcompression air conditioner is divided into two flows. One flow' is directed to a condensing heat exchanger

[0034] where the refrigerant vapor condenses and the heat released as the refrigerant condenses is transferred to a flow of air

[0022] , thus raising the air’s temperature. The second flow of superheated refrigerant discharged by the compressor is directed to a desuperheater

[0028] where the refrigerant is cooled towards saturation as it transfers heat to a flow of w eak liquid desiccant. The weak liquid desiccant that is heated in the desuperheater then flows to a spray bar

[0027] that spreads the hot desiccant over the surfaces of a porous core

[0021] through which flows the air

[0022] that has been heated in the condensing heat exchangerAtty. Dkt. No. 01296-0088

[0034] , The hot desiccant releases water as it flows downward through the porous core

[0021] and flows off the core into a sump

[0029] as concentrated, regenerated desiccant.

[0010] An essential feature of the Meckler patent is that the saturated or near-saturated refrigerant vapor that leaves the desuperheater

[0028] is drawn back to the suction side of the compressor

[0033] , As explained by Meckler “[t]his cooler desuperheated gas returns to the compressor and is mixed with the discharge gas to produce a cooler, more dense mixture that passes over the motor and its windings to remove more heat than possible with gas that is not desuperheated. Despite its potential performance advantages, the technology disclosed in the Meckler patent has never been incorporated into a commercial product — possibly because of its complexity.SUMMARY OF THE INVENTION

[0011] One objective of the invention disclosed herein is to greatly simplify the application of a desuperheater to the task of regenerating a liquid desiccant by eliminating separation of the refrigerant vapor discharged by the compressor into two streams (for example, as disclosed in Meckler) — one that flows to a condenser and the other that flows first to a desuperheater and then returns to the compressor. As described herein, the present invention requires that all refrigerant vapor that releases heat to a liquid desiccant in a desuperheater must then How to a condenser where the vapor converts to liquid.

[0012] A thermally driven system that separates a volatile constituent from a liquid mixture that contains both the volatile constituent and one or more non-volatile constituents according to an exemplary embodiment of the present invention comprises: a heat pump with (a) an evaporator in which liquid refrigerant absorbs heat and converts to a vapor, (b) a compressor that compresses the refrigerant that leaves the evaporator to a higher pressure, (c) a desuperheater in which a liquid mixture absorbs thermal energy from the higher pressure refrigerant discharged from the compressor which then raises the temperature of the liquid mixture and decreases the temperature of the refrigerant to or towards its saturation temperature, (d) a condenser in which the higher pressure refrigerant vapor that leaves the desuperheater further releases heat and converts to a liquid, and the heat released as the refrigerant condenses raises the temperature of a coolant, (e) an expansion valve across which the pressure of the liquid refrigerant that leaves the condenser decreases to a lower value before entering the evaporator as a two-phase (liquid / vapor) fluid; a separation component (alternately referred to as a regenerator) comprising (a) porous contact media, which may be configured as one or more beds, blocks or pads, whose surface is readily wettable by the liquid mixture, (b)Atty. Dkt. No. 01296-0088a means of delivering the liquid mixture that has been heated in the desuperheater to an upper region of the porous contact media from where the liquid mixture flows downward, (c) a flow of scavenging air that passes through the porous contact media so that the volatile component released by the heated liquid mixture is collected by the scavenging air and discharged to the local ambient, and (d) a sump, tray or pan functioning as a receiving reservoir that collects the liquid mixture after it has released a portion of its volatile constituents to the scavenging air.

[0013] In an exemplary embodiment the liquid mixture and the higher-pressure refrigerant that exchange thermal energy in the desuperheater flow counter to each other.

[0014] In an exemplary embodiment the liquid mixture is a liquid desiccant with a volatile constituent that is water and a non-volatile constituent that is an ionic salt or ionic liquid, the liquid desiccant flowing out of the regenerator being characterized as either strong, concentrated or water-lean and the liquid desiccant flowing into the regenerator being characterized as either weak, dilute or water-rich.

[0015] In an exemplary embodiment the heat pump is part of a vapor-compression air conditioner with an evaporator that cools a stream of air that is supplied to a building or process and a condenser that heats a stream of air that is discharged to ambient; and the liquid mixture is a liquid desiccant that is regenerated using heat recovered from the air conditioner’s desuperheater.

[0016] In an exemplary embodiment the heat pump is part of a vapor-compression air conditioner that uses heat recovered from a desuperheater to regenerate a liquid desiccant that is used to increase the dehumidification provided by the air conditioner.

[0017] In an exemplary' embodiment the heat pump is part of a vapor-compression air conditioner that uses heat recovered from a desuperheater to regenerate a liquid desiccant that is stored for use at a later time.

[0018] In an exemplary embodiment the coolant to which the condenser releases heat is a stream of air, and all or a portion of this air is used as the scavenging air, which is discharged to the local ambient after collecting the volatile component released by the mixture.

[0019] In an exemplary' embodiment the scavenging airflows horizontally through the porous contact media.

[0020] In an exemplary embodiment the scavenging air flows vertically upward through the porous contact media.

[0021] In an exemplary' embodiment the porous contact media is of a ty pe commonly referred to as random fill, which can be rashig rings, bed saddles or some other geometry; and theAtty. Dkt. No. 01296-0088random fill is enclosed within a container with walls that have openings through which the scavenging air can pass.

[0022] In an exemplary embodiment the porous contact media is of a type commonly referred to as structured media, which can be composed of corrugated sheets, folded sheets or other repeating geometry’.

[0023] In an exemplary embodiment the contact media is ceramic.

[0024] In an exemplary embodiment the contact media includes sheets of metal wire screens.

[0025] In an exemplary embodiment the scavenging air first flows through a particulate filter before it flows through the contact media.

[0026] In an exemplary' embodiment the desuperheater is embedded within the porous contact media so that the liquid mixture that flows downward on the surfaces of the contact media, cooling as the volatile component evaporates, is either continuously or intermittently reheated.

[0027] In an exemplary embodiment the desuperheater that is embedded within the porous contact media is composed of multiple, spaced apart, vertical, microchannel plates with refrigerant flowing within the microchannels and scavenging air flowing in the gaps between plates; and the contact media is formed as thin layers on the surfaces of the plates.

[0028] In an exemplary embodiment the desuperheater that is embedded within the porous contact media is configured like the wicking-substrate heat and mass exchanger described in U.S. Patent No. 7,269,966.

[0029] In an exemplary embodiment the desuperheater is a component of a vapor-compression air conditioner with an air-cooled condenser and the flow rate of the cooling air is varied to either increase or decrease the refrigerant vapor pressure within the condenser, thereby increasing or decreasing the temperature of the refrigerant vapor discharged by the compressor to the desuperheater.DESCRIPTION OF THE FIGURES

[0030] FIG. 1 is a conceptual block diagram of an exemplary embodiment of the invention.

[0031] FIG. 2 is a conceptual block diagram of an exemplary' embodiment of the invention in which a portion of the air that collects rejected heat from the condenser is used to scavenge released volatile constituents.

[0032] FIG. 3 is a conceptual block diagram of an exemplary embodiment of the invention as part of a liquid-desiccant, vapor-compression air conditioner in which liquid desiccant is used to enhance dehumidification.Atty. Dkt. No. 01296-0088

[0033] FIG. 4 is a drawing of a regeneration component with contact media that is berl saddles.

[0034] FIG. 5 is an example of structured contact media composed of corrugated sheets that are affixed to each other.

[0035] FIG. 6 is a drawing of a regeneration component with a filter that removes particulates from the scavenging air.

[0036] FIG. 7 is a sectional drawing of a regeneration component with a desuperheater formed from microchannel plates that are embedded within the porous contact media.DETAILED DESCRIPTION

[0037] Although desuperheaters can heat a second fluid to a temperature that is much higher than the refrigerant’s saturation temperature, the amount of energy available is significantly less than that released in a VC-AC’s condenser (where the refrigerant condenses at an almost constant temperature). For a VC-AC with R410A refrigerant operating with suction and discharge saturation temperatures of 52°F and 119°F, the maximum amount of energy released in a refrigerant desuperheater is 32% of that released as the refrigerant condenses.

[0038] When assessing the value of the invention claimed here it is important to understand that a regenerator that directly heats the desiccant is more thermally efficient than one that first heats air that then heats the desiccant. As will be illustrated in a later example, a desiccant regenerator that is driven by air that has been heated by a VC-AC s condenser might have a thermal efficiency on the order of 0.5 to 0.7, while one that directly heats the desiccant might have a thermal efficiency on the order of 1.1 or higher. (The thermal COP for regeneration compares the amount of energy driving the regeneration with the amount of energy for converting an equivalent amount of water from liquid to vapor; a thermal efficiency of one indicates one pound of water is released by the desiccant for every 1050 Btu of thermal energy driving the process.)

[0039] Figure 1 shows a vapor-compression heat pump, generally designated by reference number

[0200] , according to an exemplary embodiment of the present invention. The heat pump

[0200] is made up of a single refrigerant circuit composed of the following elements: a compressor

[0204] , a desuperheater

[0206] , a condenser

[0208] , an expansion valve

[0210] and an evaporator

[0202] , This heat pump provides a cooling effect at its evaporator

[0202] (i.e., heat is absorbed) and a heating effect at its condenser

[0208] (i.e., heat is released) through the operation of its compressor

[0204] that draws in refrigerant vapor from the evaporator

[0202] and discharges higher pressure refrigerant. This compression of the refrigerant vapor raises its temperature so that the discharged refrigerant vapor is superheated, i.e., the temperature of theAtty. Dkt. No. 01296-0088refrigerant vapor is higher than its saturation temperature. The refrigerant vapor discharged by the compressor

[0204] rejects heat in the desuperheater

[0206] and leaves the desuperheater at a temperature equal to or close to its saturation temperature. This saturated or near-saturated refrigerant vapor then enters the condenser

[0208] where further heat rejection to a coolant

[0220] first converts the refrigerant vapor to a saturated liquid and then, in many instances, further subcools the liquid refrigerant to a temperature slightly below its saturation temperature. The subcooled refrigerant liquid that leaves the condenser

[0208] drops in pressure as it flows through the expansion valve

[0210] , This drop in pressure causes some of the liquid refrigerant to flash to vapor, and a two-phase (liquid / vapor) refrigerant vapor enters the evaporator

[0202] , In the evaporator

[0202] the two-phase refrigerant converts to vapor as it absorbs heat from a fluid stream

[0230] , The refrigerant vapor leaving the evaporator is drawn into the compressor

[0204] , thus completing the refrigeration cycle.

[0040] Separation processes in which a volatile component evaporates from a liquid mixture composed of the volatile component and one or more non-volatile components typically are endothermic. Furthermore, the efficiency of the separation process (i.e., kilograms per second of volatile produced per Watt of thermal energy) increases as the temperature of the mixture increases since the vapor pressure of the volatile component usually increases exponentially with temperature. This fact is relevant for the embodiment shown in Figure 1 because the highest temperature for the refrigerant occurs at its entrance to the desuperheater

[0206] , The embodiment shown in Figure 1 exploits this high temperature by rejecting heat from the superheated refrigerant in the desuperheater

[0206] to a fluid

[0310] that is a mixture of volatile and non-volatile constituents. After leaving the desuperheater, the hot fluid mixture [31 Oh] is delivered to a regenerator

[0300] where it spreads out over a porous contact media

[0304] that is within the regenerator. In the regenerator, the hot mixture releases the volatile component which then is carried out of the regenerator to a discharge location by the stream of scavenging air

[0306] that flows through the porous contact media. The mixture, now depleted in the volatile component, flows out of the regenerator

[0300] into a collection reservoir

[0308] that can be configured as a sump, tank, tray, gutter, pan or similar fluid-storage element.

[0041] Those skilled in the art of heat exchanger design will appreciate that the liquid mixture

[0310] can be heated to a higher temperature by circuiting the desuperheater

[0206] so that the liquid mixture flows counter to the high pressure, high temperature refrigerant.

[0042] Those skilled in the art of distillation and thermal separation will recognize that the invention can be applied to many different liquid mixtures, as long as at least one constituent of the mixture is volatile and at least one is either non-volatile or has a very low volatility.Atty. Dkt. No. 01296-0088Thus, the invention can be used to convert a water-rich liquid desiccant to a water-lean liquid desiccant. For liquid desiccants, the volatile component will be water, and the non-volatile component can be an ionic salt, including but not limited to potassium acetate, calcium chloride, potassium formate, lithium chloride, magnesium chloride; mixtures of ionic salts; or ionic liquids.

[0043] For HVAC applications where a liquid desiccant provides dehumidification, a portion of the concentrated liquid desiccant that is collected by the sump, tray or pan can be stored in a tank so that dehumidification can be provided when the desuperheater is not operating.

[0044] Figure 2 shows an exemplary’ embodiment in which the coolant

[0220] that absorbs heat from the refrigerant vapor in the condenser

[0208] is a stream of air, and the scavenging air

[0306] that flows through the contact media

[0304] is all or a portion of this stream of air.

[0045] In HVAC applications the heat pump

[0200] may be part of a vapor-compression air conditioner. In these applications, the fluid stream

[0230] leaving the evaporator

[0202] in Figures 1 and 2 is cooled air that provides comfort conditioning to a building. As shown in Figure 3, this fluid stream

[0230] , after leaving the evaporator

[0202] , can be further dehumidified by flowing it through an absorber

[0320] that has contact media

[0304] to which has been supplied liquid desiccant [310c] that has been concentrated in the regenerator

[0300] ,

[0046] In the exemplary7embodiment shown in Figure 1, as well as most other embodiments of the invention, the porous contact media

[0304] within the regenerator

[0300] can be rashig rings, berl saddles or some other geometry commonly referred to as random fill. Figure 4 shows a regenerator

[0300] within w hich the contact media is berl saddles that are wetted by the hot liquid mixture [31 Oh], Since random fill is composed of relatively small pieces that are not joined to each other, the fill is enclosed within a container

[0312] with walls that have openings through which the scavenging air

[0306] can pass. The loose random fill enclosed within the container can be described as a column or bed of contact media.

[0047] In the exemplary embodiment shown in Figure 1, as well as most other embodiments of the invention, the porous contact media

[0304] can be of a ty pe commonly referred to as structured media. One example of structured media is the corrugated sheets shown in Figure 5. The structured media applied as the porous contact media

[0304] within the regenerator

[0300] can be described as a bed, block or pad of contact media.

[0048] In general, contact media commonly used in the chemical process industry can be used as the contact media

[0304] in all embodiments of invention as long as the contact media is easily wetted by the liquid mixture and compatible with the liquid mixture over its operating temperature range.Atty. Dkt. No. 01296-0088

[0049] In many applications it will be advantageous to increase the rate at which the volatile constituent is released by the mixture. This increase in volatile release rate can be achieved by increasing the temperature of the mixture that is supplied to the contact media. However, this approach to increasing the volatile release has a practical limit: the mixture cannot be heated to a temperature higher than the temperature of the refrigerant vapor that enters the desuperheater.

[0050] For a fixed refrigerant vapor pressure at the inlet to a heat pump’s compressor

[0204] , the temperature of the compressed refrigerant vapor will increase as the discharged pressure increases. However, this increase in discharged pressure will degrade the COP of the heat pump

[0200] (where the COP of the heat pump is the ratio of the total heat released by the refrigerant in desuperheater and the condenser divided by the power consumed by the compressor).

[0051] There may be applications where the increase in the volatile release rate from the mixture provided by the higher temperature of refrigerant vapor entering the desuperheater

[0206] justifies the degraded COP. In these applications, the heat pump can be controlled to run with a higher compressor discharge pressure.

[0052] When the heat pump has an air-cooled condenser, a higher compressor

[0204] discharge pressure can be produced by reducing the flow rate of the air

[0220] that cools the condenser. When the flow rate of air that cools the condenser is decreased, the temperature of the condensing refrigerant increases so that the condenser rejects heat at the required rate (i.e., the condenser must reject heat at a rate equivalent to cooling effect provided by the evaporator plus the work performed by the compressor). This increase in condensing temperature must be accompanied by an increase in compressor discharge pressure that then increases the temperature of the refrigerant vapor entering the desuperheater

[0206] ,

[0053] For applications where the invention is part of a R410a VC-AC, the temperature of the refrigerant vapor leaving the compressor

[0204] and entering the desuperheater

[0206] can be as high as 185°F. Since it may be advantageous for the liquid mixture to flow7counter to the refrigerant in the desuperheater so that it leaves the desuperheater at a temperature close to that of the entering refrigerant, the contact media must not degrade when flooded with a liquid mixture that may be as hot as 185°F (or hotter depending on the refrigerant and the operation of the refrigerant cycle). The preferred contact media for high-temperature applications such as this one may be made of a ceramic that can w ithstand the high temperature or a metal w ire screen that is compatible with the hot liquid mixture.Atty. Dkt. No. 01296-0088

[0054] When air cools the condenser of a heat pump, the air often carries airborne particulates. If this air is used to scavenge the water released by a hot desiccant as it flows over the surfaces of contact media, the particulates may be captured by and foul the desiccant-wetted surfaces. An exemplary embodiment of the invention that addresses this potential fouling problem is shown in Figure 6. As shown in this figure, the scavenging air first passes through a particulate filter

[0314] before passing through the openings of the container and the desiccant-w etted contact media.

[0055] The hot desiccant supplied to the contact media cools as it desorbs w ater. The decrease in the rate of water release by the desiccant caused by this cooling can be minimized by embedding the desuperheater within the porous contact media so that the desiccant that flow s downward on the surfaces of the contact media is either continuously or intermittently reheated. In the exemplary embodiment shown in Figure 7, the desuperheater that is embedded within the porous contact media is composed of multiple, spaced apart, vertical, microchannel plates

[0318] with hot refrigerant vapor

[0316] flowing upward within the microchannels and scavenging air

[0306] flowing in the gaps between plates (out of the page in Figure 7); and the contact media

[0304] is formed as thin, wettable layers on the surfaces of the plates

[0318] ,

[0056] In an alternative to the exemplary embodiment shown in Figure 7, the desuperheater that is embedded within the porous contact media is configured like the wicking-substrate heat and mass exchanger shown in Figure 1 of U.S. Patent No. 7,269,966, the contents of which are incorporated herein by reference in their entirety.

[0057] Unitary vapor-compression air conditioners, such as the 30-ton, packaged roof-top unit (RTU) in the example next presented, are rated under Standard 340 / 360 published by the Air-Conditioning, Heating and Refrigeration Institute. Under this standard the rated performance of an air conditioner is measured at high load, summer conditions with the cooling air entering the condenser at 95°F and 0.014 Ib / lb humidity ratio and process air entering the evaporator at 80°F and 0.011 Ib / lb humidity ratio. These air conditions are referred to as the A Rating Point.

[0058] Prophetic Example

[0059] At the A Rating Point, a 30-ton RTU that processed 12,000 cfm of air might supply 360,000 Btu / h total cooling and 72.8 Ib / h of water removal (i.e. , dehumidification). Under these operating conditions, the high-pressure refrigerant discharged by the compressor might have a saturation temperature of 119°F and be superheated to 170°F. At this condition, the superheat thermal energy7in the refrigerant vapor leaving the compressor (i.e., the thermal energy released when the refrigerant cools from a superheated vapor at 170°F to a saturatedAtty. Dkt. No. 01296-0088vapor at 119°F) will be 104,800 Btu / h, which is about 24% of the total heat rejected by the RTU’ s condenser.

[0060] U.S. Patent No. 10,655,870 describes a means of enhancing the dehumidification provided by a vapor-compression air conditioner in which “an absorber comprising a porous bed of contact media the surface of which is wetted by a first flow of liquid desiccant that is supplied to the absorber and through which flows the [process] stream of air after it has been cooled in the [evaporator]7’. For the 30-ton RTU, an absorber located behind the evaporator that is composed of a 4” deep bed of corrugated fiberglass contact media similar to Munters 5090 Glasdek, the absorber wetted by a 2.5 gpm flow of 20% (by weight) aqueous solution of lithium chloride, will absorb an additional 31.4 Ib / h of water from the process air. This water absorption by the desiccant is a 43% increase in the total dehumidification provided by the RTU.

[0061] The diluted desiccant flowing out of the absorber can be returned to its original 20% concentration in a regenerator driven by thermal energy recovered from a desuperheater installed in the RTU's refrigeration circuit. In one design for the desuperheater regenerator, a 1.3 gpm flow of diluted desiccant is first heated to 140°F in the desuperheater. With superheated refrigerant vapor entering the desuperheater at 170°F, the desiccant’s temperature approaches to 30°F of the maximum temperature of the refrigerant vapor. If the diluted desiccant is drawn from a sump at 86°F, the desuperheater operates at an effectiveness of 64%. The total heat transfer to the desiccant is about 29% of the maximum thermal energy available as superheat in the refrigerant vapor discharged by the compressor.

[0062] The flow of hot desiccant is delivered to a pad of fiberglass contact media similar to Munters 5090 Glasdek with dimensions of 24” (H) x 24” (W) x 4” (D). A 387-cfm flow of warm, 116°F air leaving the RTU’s condenser flows horizontally through the desiccant-wetted pad and scavenges the released water. (The scavenging air flow is less than 2% of the total air flow cooling the RTU’s condenser. Although more difficult to implement in practice, the volumetric flow rate of scavenging air could be further reduced by flowing the air upward through the desiccant-wetted pad and counter to the flow of desiccant.)

[0063] This example illustrates an important advantage for using a desuperheater to heat a stream of liquid desiccant to a high temperature before the liquid desiccant is delivered to a scavenging-air regenerator: the regeneration process will have a very high COP, which in this example is 1.1. (The COP for liquid-desiccant regeneration is defined as the ratio of the thermal energy for converting 31.4 Ib / h of liquid water to vapor at 1050 Btu / lb divided by the 30,200 W of desiccant heating provided by the desuperheater).Atty. Dkt. No. 01296-0088

[0064] A persistent problem for HVAC engineers in humid climates is the inability of conventional RTUs to maintain indoor humidity at comfortable and safe levels when indoor latent loads are high (i.e., there are large sources of indoor humidity) or the required make-up fresh air is very humid. While the 43% increase in dehumidification provided by an RTU that employs the liquid-desiccant desuperheater regenerator described herein could address high indoor humidity, conventional means are available. In particular, an RTU can be modified to overcool the supply air so that additional water vapor is condensed. However, if comfort is to be maintained, the supply air must be reheated after overcooling so that the indoor temperature stays within comfortable limits. The required overcooling increases the size of the RTU’s refrigeration system and the need to reheat requires an additional refrigerant condenser and controls for its operation.

[0065] An important advantage for an RTU that employs the liquid-desiccant desuperheater regenerator described herein is that dehumidification is enhanced with no increase in either the size of the refrigeration component (i.e., compressor, condenser and evaporator) or the power drawn by the compressor. By comparison, an overcool / reheat RTU that matches the 43% increased dehumidification will need a 14% larger evaporator, a 17% larger compressor and a reheat condenser; and its power draw will be 17% higher

[0066] The illustration herein of exemplary’ embodiments of the invention applied to a heat pump with a single refrigerant circuit that has one compressor, one condenser and one evaporator should not be construed as limiting the invention to this single-circuit type of heat pump. It is common for large vapor-compression heat pumps to have multiples of each major component. For these larger vapor-compression heat pumps, multiple desuperheater regenerators could be applied or the superheated refrigerant from multiple compressors could be combined before entering one desuperheater regenerator.

[0067] According to an exemplary embodiment of the present invention, a thermally driven device that separates a volatile constituent from a liquid mixture that contains both the volatile constituent and one or more non-volatile constituents comprises: (I) a heat pump comprising: (a) at least one evaporator in which liquid refrigerant absorbs heat and converts to a vapor, (b) at least one compressor that compresses the refrigerant that leaves the at least one evaporator to a higher pressure, (c) at least one desuperheater in which a liquid mixture absorbs thermal energy from the higher pressure refrigerant discharged from the at least one compressor which then raises the temperature of the liquid mixture and decreases the temperature of the refrigerant to or towards its saturation temperature, (d) at least one condenser in which the higher pressure refrigerant vapor that leaves the at least one desuperheater further releases heatAtty. Dkt. No. 01296-0088and converts to a liquid, and the heat released as the refrigerant condenses raises the temperature of a coolant, (e) at least one expansion valve across which the pressure of the liquid refrigerant that leaves the at least one condenser decreases to a lower value before entering the at least one evaporator as a two-phase fluid; and (II) a regenerator comprising: (a) porous contact media comprising a surface that is readily wettable by the liquid mixture, (b) a means of delivering the liquid mixture that has been heated in the desuperheater to an upper region of the porous contact media from where the liquid mixture flows downward, (c) a flow of scavenging air that passes through the porous contact media so that the volatile constituent released by the heated liquid mixture is collected by the scavenging air and discharged to local ambient, and (d) a reservoir that collects the liquid mixture after it has released a portion of its volatile constituent to the scavenging air.

[0068] In an exemplary embodiment, the liquid mixture and the higher-pressure refrigerant that exchange thermal energy in the desuperheater flow counter to each other.

[0069] In an exemplary7embodiment, the liquid mixture is a liquid desiccant and the volatile constituent is water and the liquid desiccant comprises anon-volatile constituent that is an ionic salt or ionic liquid, the liquid desiccant flowing out of the regenerator being characterized as either strong, concentrated or water-lean and the liquid desiccant flowing into the regenerator being characterized as either weak, dilute or water-rich.

[0070] In an exemplary embodiment, the heat pump is part of a vapor-compression air conditioner in which the at least one evaporator cools a stream of air that is supplied to a building or process and the at least one condenser heats a stream of air that is discharged to ambient.

[0071] In an exemplary embodiment, the concentrated liquid desiccant that flows out of the regenerator is delivered to an absorber with desiccant-wetted, porous contact media located downstream of the at least one evaporator so that the air stream leaving the at least one evaporator is dehumidified as it flows through the absorber.

[0072] In an exemplary7embodiment, a portion of the concentrated liquid desiccant flowing out of the regenerator is delivered to a storage tank.

[0073] In an exemplary embodiment, the coolant to which the condenser releases heat is a stream of air, and all or a portion of the air is used as the scavenging air, which is discharged to the local ambient after collecting the volatile constituent released by the mixture.

[0074] In an exemplary embodiment, the flow of scavenging air passes horizontally through the porous contact media.Atty. Dkt. No. 01296-0088

[0075] In an exemplary embodiment, the flow of scavenging air passes vertically upward through the porous contact media.

[0076] In an exemplary embodiment, the porous contact media is of a t pe commonly referred to as random fill; and the random fill is enclosed within a container with walls that have openings through which the scavenging air can pass.

[0077] In an exemplary embodiment, the random fill has a rashig ring or berl saddle geometry.

[0078] In an exemplary embodiment, the porous contact media is of a type commonly referred to as structured media.

[0079] In an exemplary embodiment, the structured media is composed of corrugated sheets, folded sheets or other repeating geometry.

[0080] In an exemplary embodiment, the contact media is ceramic.

[0081] In an exemplary embodiment, the contact media comprises sheets of metal wire screens.

[0082] In an exemplary embodiment, the scavenging air first flows through a particulate filter before it flows through the contact media.

[0083] In an exemplary’ embodiment, the desuperheater is embedded within the porous contact media so that the liquid mixture that flows downward on the surfaces of the contact media, cooling as the volatile component evaporates, is either continuously’ or intermittently reheated.

[0084] In an exemplary’ embodiment, the desuperheater that is embedded within the porous contact media is composed of multiple, spaced apart, vertical, microchannel plates with refrigerant flowing within the microchannels and scavenging air flowing in the gaps between the plates: and the contact media is formed as thin layers on the surfaces of the plates.

[0085] In an exemplary embodiment, the desuperheater that is embedded within the porous contact media is configured as a wicking-substrate heat and mass exchanger.

[0086] In an exemplary’ embodiment, the desuperheater is a component of a vapor-compression air conditioner and the at least one condenser is an air-cooled condenser; and the flow rate of the cooling air is varied to either increase or decrease the refrigerant vapor pressure within the at least one condenser, thereby increasing or decreasing the temperature of the refrigerant vapor discharged by the at least one compressor to the desuperheater.

[0087] In an exemplary embodiment, the reservoir is a sump, tray or pan.

[0088] Having thus described the present invention in detail, it is to be appreciated and will be apparent to those skilled in the art that many physical changes, only a few’ of w’hich are exemplified in the detailed description of the invention, could be made w ithout altering the inventive concepts and principles embodied therein. It is also to be appreciated that numerous embodiments incorporating only part of the preferred embodiment are possible which do notAtty. Dkt. No. 01296-0088alter, with respect to those parts, the inventive concepts and principles embodied therein. The present embodiment and optional configurations are therefore to be considered in all respects as exemplary and / or illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all alternate embodiments and changes to this embodiment which come within the meaning and range of equivalency of said claims are therefore to be embraced therein.

Claims

Atty. Dkt. No. 01296-0088Claims:

1. A thermally driven device that separates a volatile constituent from a liquid mixture that contains both the volatile constituent and one or more non-volatile constituents comprising:(I) a heat pump comprising: (a) at least one evaporator in which liquid refrigerant absorbs heat and converts to a vapor, (b) at least one compressor that compresses the refrigerant that leaves the at least one evaporator to a higher pressure, (c) at least one desuperheater in which a liquid mixture absorbs thermal energy from the higher pressure refrigerant discharged from the at least one compressor which then raises the temperature of the liquid mixture and decreases the temperature of the refrigerant to or towards its saturation temperature, (d) at least one condenser in which the higher pressure refrigerant vapor that leaves the at least one desuperheater further releases heat and converts to a liquid, and the heat released as the refrigerant condenses raises the temperature of a coolant, (e) at least one expansion valve across which the pressure of the liquid refrigerant that leaves the at least one condenser decreases to a lower value before entering the at least one evaporator as a two-phase fluid; and(II) a regenerator comprising: (a) porous contact media comprising a surface that is readily wettable by the liquid mixture, (b) a means of delivering the liquid mixture that has been heated in the desuperheater to an upper region of the porous contact media from where the liquid mixture flows downw ard, (c) a flow of scavenging air that passes through the porous contact media so that the volatile constituent released by the heated liquid mixture is collected by the scavenging air and discharged to local ambient, and (d) a reservoir that collects the liquid mixture after it has released a portion of its volatile constituent to the scavenging air.

2. The device of claim 1 wherein the liquid mixture and the higher-pressure refrigerant that exchange thermal energy in the desuperheater flow counter to each other.

3. The device of claim 1 wherein the liquid mixture is a liquid desiccant and the volatile constituent is w ater and the liquid desiccant comprises a non-volatile constituent that is anAtty. Dkt. No. 01296-0088ionic salt or ionic liquid, the liquid desiccant flowing out of the regenerator being characterized as either strong, concentrated or water-lean and the liquid desiccant flowing into the regenerator being characterized as either weak, dilute or water-rich.

4. The device of claim 3 wherein the heat pump is part of a vapor-compression air conditioner in which the at least one evaporator cools a stream of air that is supplied to a building or process and the at least one condenser heats a stream of air that is discharged to ambient.

5. The device of claim 4 wherein the concentrated liquid desiccant that flows out of the regenerator is delivered to an absorber with desiccant-wetted, porous contact media located downstream of the at least one evaporator so that the air stream leaving the at least one evaporator is dehumidified as it flows through the absorber.

6. The device of claim 3 wherein a portion of the concentrated liquid desiccant flowing out of the regenerator is delivered to a storage tank.

7. The device of claim 1 wherein the coolant to which the condenser releases heat is a stream of air, and all or a portion of the air is used as the scavenging air, which is discharged to the local ambient after collecting the volatile constituent released by the mixture.

8. The device of claim 1 wherein the flow of scavenging air passes horizontally through the porous contact media.

9. The device of claim 1 wherein the flow of scavenging air passes vertically upward through the porous contact media.

10. The device of claim 1 wherein the porous contact media is of a type commonly referred to as random fill; and the random fill is enclosed within a container with walls that have openings through which the scavenging air can pass.

11. The device of claim 10, wherein the random fill has a rashig ring or berl saddle geometry.Atty. Dkt. No. 01296-008812. The device of claim 1 wherein the porous contact media is of a type commonly referred to as structured media.

13. The device of claim 12, wherein the structured media is composed of corrugated sheets, folded sheets or other repeating geometry.

14. The device of claim 1 wherein the contact media is ceramic.

15. The device of claim 1 wherein the contact media comprises sheets of metal wire screens.

16. The device of claim 1 wherein the scavenging air first flows through a particulate filter before it flows through the contact media.

17. The device of claim 1 wherein the desuperheater is embedded within the porous contact media so that the liquid mixture that flows downward on the surfaces of the contact media, cooling as the volatile component evaporates, is either continuously or intermittently reheated.

18. The device of claim 17 wherein the desuperheater that is embedded within the porous contact media is composed of multiple, spaced apart, vertical, microchannel plates with refrigerant flowing within the microchannels and scavenging air flowing in the gaps between the plates; and the contact media is formed as thin layers on the surfaces of the plates.

19. The device of claim 17 wherein the desuperheater that is embedded within the porous contact media is configured as a wicking-substrate heat and mass exchanger.

20. The device of claim 1 wherein the desuperheater is a component of a vapor-compression air conditioner and the at least one condenser is an air-cooled condenser; and the flow rate of the cooling air is varied to either increase or decrease the refrigerant vapor pressure within the at least one condenser, thereby increasing or decreasing the temperature of the refrigerant vapor discharged by the at least one compressor to the desuperheater.

21. The device of claim 1, wherein the reservoir is a sump, tray or pan.

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