AU2010289019A1

AU2010289019A1 - Plate heat exchanger

Info

Publication number: AU2010289019A1
Application number: AU2010289019A
Authority: AU
Inventors: Peter Albring; Bodo Burandt; Marcus Honke; Frank Schoepe; Gregor Trommler
Original assignee: Inst fur Luft und Kaltetechnik Gemeinnutzige GmbH; Institut fuer Luft und Kaeltetechnik Gemeinnuetzige GmbH
Current assignee: Institut fuer Luft und Kaeltetechnik Gemeinnuetzige GmbH
Priority date: 2009-08-25
Filing date: 2010-08-23
Publication date: 2012-04-12
Also published as: WO2011023191A3; EP2470852A2; WO2011023191A4; DE102009038836A1; WO2011023191A2

Abstract

The invention relates to a plate heat exchanger for transferring heat between two phase-changing mass flows or between a phase-changing mass flow and a liquid mass flow, usually in conjunction with water or low-boiling liquids, e.g., seawater. The heat exchanger comprises several identical heat exchanger plates (4), which are arranged one behind the other and between which evaporator seals and condenser seals are inserted in alternation. The evaporator seals and condenser seals are compressed by end plates (1, 11) clamped by means of tie rods. The evaporator seals and the condenser seals are designed as frame profiled elements (12, 13) having a trapezoidal cross-section and/or the frame profiled elements (12, 13) are provided with several elongated, parallel openings, which together with the heat exchanger plates (4) form channels connected in series, which channels are used for flow through the evaporator chambers (2) and/or condenser chambers (3) in a multi-flow manner. High heat transfer coefficients can be achieved by means of the heat exchanger; the heat exchanger is corrosion-resistant, can be produced cheaply, and can be removed and cleaned without great effort.

Description

Plate Heat Exchanger The invention relates to a plate heat exchanger for transferring heat between two phase alternating mass flows, usually in conjunction with water or low boiling liquids. It is 5 particularly suitable for use in water distillation apparatus, seawater desalination plants, water purification systems, and refrigeration systems or heat pumps in which water is used as the coolant. The heat exchanger is corrosion-resistant, can be cost-effectively produced, and is easy to clean. Moreover, it is characterized by low spray losses. 0 Plate heat exchangers are frequently used for process engineering applications in which both condensation and evaporation are carried out in an apparatus, wherein the thermal energy from the condensing mass flow is used for evaporating the liquid mass flow. To better utilize the heat of condensation, most plate heat exchangers of this type are embodied as multiple stage, i.e., as having several separate evaporator chambers and 5 condenser chambers, which are thermally coupled by means of heat exchange surfaces, and are arranged alternatingly one in front of the other. Heat exchangers of this type are used primarily for applications in which the evaporation and condensation of water are used either to clean water by way of distillation, as in the 0 case of seawater desalination, for example, or to thicken liquids, as in the case of sugar production, for example. The production of plate heat exchangers that comprise multiple evaporator chambers and condenser chambers has heretofore been a material-intensive and technologically 5 complex process. With heat exchangers for low boiling working substances such as water (high specific volume in the ambient temperature range), a relatively large plate distance is necessary to keep the pressure losses of the vapor influx low; additionally, in each evaporator chamber, the liquid to be evaporated must be distributed uniformly in a thin layer across the entire heat exchange surface. In addition, with the necessary 0 spraying or dripping of the liquid, drops of liquid find their way directly into the vapor collecting channel, thereby necessitating drop separation, at additional cost.

2 It is known to connect the individual heat exchange plates to one another by either welding, soldering or screws. In plate heat exchangers that must be suitable for operating with corrosive liquids, such 5 as plate heat exchangers for seawater desalination plants, for example, soldered and/or welded connections can be used only conditionally due to the increased risk of corrosion, and therefore, heat exchangers connected by screws are increasingly being used. 0 In heat exchangers having plates connected by screws, support structures are ordinarily formed in the heat exchange plates, with flexible sealing elements being inserted into said structures. For instance, DE 31 48 375 Al discloses a plate evaporator having a plurality of heat 5 exchange plates, which are arranged essentially vertically spaced and opposite one another in such a way that evaporation channels and heating medium channels are alternatingly produced between them. On the pairs of plates arranged in series, which form the evaporation channels, bulges, such as ribs, for example, are formed, as a result of which the cross-sectional area of the evaporation channels increases in the .0 direction of flow while the perimeter thereof decreases. Due to the increasing cross-sectional area in the direction of flow in the evaporation chambers, the flow conditions in the plate evaporator are improved, thereby increasing the heat transfer coefficients thereof, however, the attachment or formation of the ribs on ?5 the heat exchange plates is relatively complex and costly. GB 2 089 666 A discloses a plate evaporator having a plurality of essentially vertically aligned heat exchange plates, which are arranged in such a way that evaporator channels and channels for a heating medium are alternatingly formed. The evaporator 0 channels are formed in such a way that in the direction of flow, the area of their cross section increases, while their perimeter decreases. This is achieved by way of spacing 3 elements, which have a trapezoidal cross-section, wherein, in order to achieve a sealing of the channels, the spacing elements are equipped with flexible seals. Neither of the two described solutions suggests designing the heat 5 exchanger/evaporator as having multiple channels; moreover, the heat exchanger cannot be reconfigured to a multi-channel heat exchanger without considerable expense. Furthermore, GB 859 876 A proposes an evaporator for increasing the concentration of 0 liquids, in which the channels for the liquid are connected in pairs at their upper ends, whereby the channel for the heating medium is formed, and are similarly connected to one another at their lower ends, whereby an inlet for the liquid to be evaporated and an outlet for the concentrated liquid and for the residual material are formed. The evaporator can contain channels that are connected to one another in parallel or are 5 meandering, which enable a multi-channel flow through the evaporator. None of the above-mentioned plate evaporators is suitable for a heat exchange between two mass flows, in each of which a transfer between liquid and gaseous phase occurs (combined evaporation/condensation). 0 The problem addressed by the invention is that of overcoming the disadvantages of the prior art. The goal is to devise a plate heat exchanger having good heat transfer coefficients, which is suitable for transferring heat between two phase alternating mass flows; at the same time, it is to be ensured that the evaporator cells and condenser cells !5 are durably sealed, simple in design, cost-effectively producible, and uncomplicated to clean; further, it should be possible to configure the plate heat exchanger as multi channel without great design expense. This problem is solved according to the invention by the features of claim 1; 0 advantageous embodiments and uses of the invention are found in claims 2 to 10.

4 The heat exchanger according to the invention consists of a number of identical heat exchange plates arranged one in front of the other, between which condenser seals and evaporator seals are alternatingly arranged. With every two heat exchange plates and the evaporator seal enclosed therein, an evaporator chamber is formed, or with two 5 adjoining heat exchange plates and the condenser seal, a condenser chamber is formed. The smallest functional heat exchanger consists of three heat exchange plates, wherein in the two intermediate spaces, one condenser seal and one evaporator seal are 0 inserted. For optimal operation, it is provided to construct the heat exchanger from ten or more heat exchange plates. The stack formed from heat exchange plates and seals is pressed together by two end plates, which are arranged at the two ends of the stack and are clamped together by 5 means of tie rods. The heat exchange plates are equipped in their edge regions with at least three openings that have a relatively small cross-sectional area, and with at least two openings that have a relatively large cross-sectional area. The openings having a 0 smaller cross-sectional area are provided for conducting the liquid media and optionally the inert gases, and the openings having a larger cross-sectional area are provided for conducting the gaseous media, such as water vapor, for example. In the case of heat exchangers that are used for distilling seawater, the heat exchange 5 plates are equipped in their exterior region with four openings having a small cross section, wherein three openings are used for conducting the untreated water, the distillate and the brine. The fourth opening is used for discharging the inert gas. Two openings having a larger cross-section are provided for conducting the water vapor streams. 0 5 In accordance with the basis of the invention, plate-shaped frame profiles made of a flexible material are used both as evaporator seals and as condenser seals, which serve simultaneously to space the heat exchange plates. 5 The seals embodied as frame profiles therefore do not serve merely to seal the evaporator chambers and condenser chambers, as has previously been customary, but are also simultaneously structural elements. The frame profiles have the same outer contours as the heat exchange plates. In this manner, a compact stack of heat exchange plates and seals is formed, which makes an additional housing superfluous. 0 According to the invention, either frame profiles having a trapezoidal cross-section are used, wherein, because the frame profiles must have approximately the shape of a plate, the height of the trapezoid is substantially larger than the two parallel sides of the trapezoid - which allows the uncomplicated production of heat exchangers in which the 5 evaporator chambers widen toward the top whereas the condenser chambers become narrower toward the top - or the frame profiles of the evaporator chambers and/or the frame profiles of the condenser chambers are provided with a plurality of elongated recesses extending in parallel, wherein in connection with the heat exchange plates, channels connected one in front of the other are formed, by means of which the medium 0 is conducted past the heat exchange plates on a meandering path (multi-channel flow). In the multi-channel embodiment, the frame profiles have a rectangular or trapezoidal cross-section, depending upon their use. The use of frame profiles having a trapezoidal cross-section offers several advantages. 5 First, as a result of the evaporator chambers that widen toward the top, high flow rates of the vapor in the upper region of the evaporator chambers are largely prevented, which would otherwise occur on the basis of the increase in volume with the evaporation of the medium used. As a result, heat exchange is improved, and the entrainment of 0 liquid drops with the vapor is prevented. The use of evaporator chambers of this type is particularly advantageous in cases involving operation with water, as the volume of water is increased approximately 1,000 times in the transition from the liquid to the 6 gaseous state. In other coolants that are used, the volumetric ratio of liquid to vapor is only 1:10 to 1:100. Second, the shape of the condenser chambers that narrow toward the top allows the 5 condensate to drain rapidly off of the inclined heat exchange plates. As a result, the formation of thick condensate layers on the surfaces of the heat exchange plates is prevented, and effective heat transfer is ensured. With the heat exchangers embodied as single-channel, the frame profiles of the 0 evaporator chambers and the condenser chambers contain through openings over large areas at their center; together with the heat exchange plates, they form the evaporator chambers and condenser chambers. At the edges of the frame profiles, additional openings are provided, which, in combination with the condenser plates, form channels for the infeed, discharge, and distribution of the liquid and gaseous media to the 5 evaporator chambers and condenser chambers. With heat exchangers embodied as multi-channel, assuming they are constructed from frame profiles having a trapezoidal cross-section, the direction of flow of the meandering channels is chosen such that in the evaporator chambers, the cross-section of each 0 channel widens in the direction of flow, and in the condenser chambers, the cross section is correspondingly decreased. Thus by using frame profiles having a trapezoidal cross-section, the same advantages can be achieved using heat exchangers embodied as multi-channel as with heat exchangers embodied as single-channel. Heat exchangers embodied as multi-channel have the additional advantage that, with a 5 suitable choice of the number and the width of the channels for nearly any media, said heat exchangers can be used to achieve optimal heat exchange behavior. Stud bolts between the heat exchange plates, in addition to the frame profiles, ensure an increase in mechanical stability and a limitation of the pressure acting on the frame 0 profiles.

7 It is provided that all frame profiles of the evaporator chambers have the same shape and the same thickness. The same is true of the frame profiles of the condenser chambers. 5 If the heat exchanger will be used for methods in which varying flow cross-sections are necessary within the heat exchanger, the frame profiles have different thicknesses and have different sizes of center recesses, which determine the size of the evaporator chambers and/or condenser chambers. These frame profiles are made of flexible materials that have different Shore hardness ratings. For instance, it is advantageous to 0 produce thicker frame profiles from a material having a higher Shore hardness and thinner frame profiles from a material having a lower Shore hardness, so that all frame profiles end up with similar spring constants. In principle, the heat exchanger according to the invention can also be used as an 5 evaporator, in which the liquid to be evaporated is dripped across the heat exchange plates of the evaporator chambers and hot water flows through the condenser chambers (water heated evaporator), or as a condenser, in which the vapor to be condensed flows through the condenser chambers and cold water flows through the evaporator chambers (water cooled condenser). In those cells through which hot or cold water flows, built-in 0 elements are installed, or the cells are embodied as multi-channel, so that high flow rates and heat transfer coefficients are ensured. The frame profiles of the evaporator/condenser chambers are then approximately two to three times thicker than the frame profiles of the cells through which hot/cold water flows. !5 In what follows, the invention will be specified in greater detail in reference to an embodiment example; the figure shows a schematic illustration of a single-channel plate heat exchanger with trapezoidal frame profiles, from a side view. As is clear from the figure, five heat exchange plates 4, spaced by frame profiles 12, 13, 0 are located in each case between the front and rear cover plates 1, 11. The evaporator frame profiles 12 together with the two adjoining heat exchange plates 4 form the evaporator chambers 2, and the condenser frame profiles 13 together with the heat 8 exchange plates 4 correspondingly form the condenser chambers 3. The cross-sections of the condenser frame profile 12.1, which is located at the start of the heat exchanger, and of the evaporator frame profile 13.1, which is located at the end of the heat exchanger, each have the shape of a rectangular trapezoid, whereas the cross-sections 5 of the remaining condenser frame profiles 13.2 and evaporator frame profiles 12.2 each have the shape of an equilateral trapezoid. The acute angles of all trapezoids (and therefore also all obtuse angles of the equilateral trapezoids) are equal in size. The frame profiles 12, 13 are rotated alternatingly 1800 in 0 relation one another, so that in each case, one long and one short parallel side of the trapezoid lie side by side in the heat exchanger. In this manner, a square plate heat exchanger is formed, the evaporator chambers 2 of which widen toward the top, and the condenser chambers 3 of which become narrower toward the top. 5 In addition to the spacing, the frame profiles 12, 13 also produce a hermetic seal (apart from the supply and discharge lines) of the chambers 2, 3 against the surrounding environment and the adjoining chambers 2, 3. The frame profiles 12, 13 therefore function simultaneously as sealing and structural elements. The frame profiles 12, 13 contain recesses, which, together with the heat exchange plates 4, form the channels for 0 the supply and discharge of the liquid and gaseous media in the evaporator chambers 2 and condenser chambers. When vapor is introduced into the condenser chambers 3, it condenses and releases the resulting heat of condensation to the two heat exchange plates 4. The heat that is 5 released flows to the sides of the heat exchange plates 4 on the evaporator side, onto which liquid is dripped, whereby a part of this liquid is evaporated. The resulting vapor rises, is collected in the vapor channel 5, and is discharged from the heat exchanger via the vapor nozzle 6. 0 The vapor to be condensed is introduced into the individual condenser chambers 3 via the nozzle 7. The vapor enters the chamber beneath the condenser chambers 3, and is forced, as a result of a partial pressure difference occurring there, against the cool heat 9 exchange plates 4, where it precipitates. In this, drops form, which fall or flow under the force of gravity in the direction of the floor of the condenser chambers 3. The condensate ultimately finds its way to the collecting line 9, via the end holes 8, and is transported out of the heat exchangers through the nozzle 10. 5 The liquid to be dripped is supplied via the nozzle 14 and is conducted through the channel 15 that is incorporated into the condenser frame profile 13.1 to the liquid chamber 17. The liquid travels through finely distributed holes 16 formed in the heat exchange plates 4 into the two adjoining evaporator chambers 2, whereby the heat 0 exchange plates 4 are dripped uniformly into the evaporator chambers 2.

10 List of Reference Signs Used 1 Front cover plate 2 Evaporator chamber 5 3 Condenser chamber 4 Heat exchange plate 5 Vapor channel 6 vapor port (outlet) 7 vapor port (intake) 0 8 Outflow opening 9 Collecting line 10 Nozzle (condensate) 11 Rear cover plate 12 Evaporator frame profile 5 12.1 Evaporator frame profile with perpendicular trapezoidal cross-section 12.2 Evaporator frame profile with equilateral trapezoidal cross-section 13 Condenser frame profile 13.1 Condenser frame profile with perpendicular trapezoidal cross-section 13.2 Condenser frame profile with equilateral trapezoidal cross-section 0 14 Nozzle (for the liquid to be dripped) 15 Channel 16 Hole 17 Liquid chamber 5

Claims

1. A plate heat exchanger, consisting of three or more identical heat exchange 5 plates (4) arranged one in front of the other, between which evaporator seals and compressor seals are alternatingly inserted, wherein two heat exchange plates (4) form each of the evaporator chambers (2) and the compressor chambers (3) of the heat exchanger, the stack that is formed thereby is pressed together by end plates (1, 11), which are clamped together by tie rods or comparable means, and the heat exchange 0 plates (4) have, in their outer region, at least three openings having a relatively smaller cross-sectional area for the liquid media and at least two openings having a relatively larger cross-sectional area for the gaseous media, wherein the evaporator seals and the condenser seals are frame profiles (12, 13) that space the heat exchange plates (4), said seals being made of a flexible material and having the same outer contour as the 5 heat exchange plates (4), wherein the frame profiles of the evaporator chambers (12) and condenser chambers (13) have large, central openings, which, combined with the heat exchange plates (4), form the evaporator (2) and condenser chambers (3), and have smaller openings arranged at the edges of said profiles, by which, in conjunction with the heat exchange plates (4), channels for the infeed, discharge, and distribution of 0 the liquid and gaseous media to the evaporator chambers (2) and condenser chambers (3) are formed, wherein - the frame profiles (12, 13) have a trapezoidal cross-section, with the height of the trapezoid being greater than the length of the two parallel sides of the trapezoid, wherein the frame profiles (12, 13) are shaped such that evaporator chambers (2) that become 5 wider toward the top and condenser chambers (3) that become narrower toward the top are formed, from the inclined walls of which the condensate can rapidly drain, - and/or the frame profiles (12, 13) are provided with a plurality of elongated, parallel extending recesses, by which, together with the heat exchange plates (4), channels connected in series are formed, which create a multi-channel flow through the 0 evaporator chambers and compressor chambers. 12

2. The plate heat exchanger according to claim 1, characterized in that stud bolts are inserted between the heat exchange plates (4), and serve to space the heat exchange plates (4) from one another in a defined manner. 5

3. The plate heat exchanger according to claims 1 and 2, characterized in that different frame profiles (12, 13) are made of flexible materials having different Shore hardness ratings.

4. The plate heat exchanger according to claims 1 to 3, characterized in that the 0 frame profiles of the evaporator chambers (12) and condenser chambers (13) each have different thicknesses.

5. The plate heat exchanger according to claims 1 to 4, characterized in that the thicknesses of the frame profiles of the evaporator chambers (12) and condenser 5 chambers (13) increase or decrease depending on the position thereof in the heat exchanger.

6. The plate heat exchanger according to claims 1 to 3, characterized in that the thickness of all frame profiles of the evaporator chambers (12) and condenser chambers 0 (13) is the same.

7. The plate heat exchanger according to claims 1 to 6, characterized in that all frame profiles of the evaporator chambers (12) have the same geometry and all frame profiles of the condenser chambers (13) have the same geometry. 5

8. The plate heat exchanger according to claim 7, characterized in that the cross sections of the frame profiles (12.1, 13.1) at the start and at the end of the plate heat exchanger have the shape of rectangular trapezoids, and the cross-sections of the basic forms of the remaining frame profiles (12.2, 13.2) have the shape of equilateral 0 trapezoids, and in each case the acute angles of the rectangular and equilateral trapezoids coincide, wherein the frame profiles (12, 13) are arranged such that, in each case, the long and the short parallel sides of the trapezoid lie alternatingly side by side, 13 thereby forming a square plate heat exchanger, the evaporator chambers (2) of which become wider at the top, and the condenser chambers (3) of which become narrower toward the top. 5

9. The plate heat exchanger according to claims 1 to 8, characterized in that the frame profile of the evaporator chamber (12) has an opening that serves to supply the liquid that will be evaporated, which opening is connected to a horizontally arranged, narrow, rectangular opening, which is located above the large opening that adjoins the evaporator chamber (2) and is separated from said opening by a land-shaped section, 0 wherein the land-shaped section has, on its front side and its rear side, groove-shaped recesses that extend close to one another and connect the rectangular opening to the evaporator chamber (2), which recesses promote uniform dripping onto the two adjoining heat exchange plates (4). 5

10. The plate heat exchanger according to claims 1 to 8, characterized in that the frame profile of the condenser chamber (12) has an opening that serves to supply the liquid that will be evaporated, which opening is connected to a horizontally arranged, narrow, rectangular opening, which is located above the large opening that adjoins the condenser chamber (3) and is separated from said opening by a land-shaped section, !0 wherein, in the two adjoining heat exchange plates (4), closely adjoining, small holes (16) are provided at the height of the rectangular opening and extending across the length thereof, said holes serving to permit the passage of the liquid to be evaporated through the heat exchange plates (4) and a fine drip onto the back sides of the heat exchange plates (4) located in evaporator (2) chambers. !5