US3493040A - Heat exchangers - Google Patents

Description

Feb. 3, 1970 w. DAVIDSON 3,493,040

HEAT EXCHANGERS I Filed Oct. 17, 1967 5 Sheets-Sheet 1 A llorn eys Feb. 3, 1970 w. DAVIDSON 3, 9 ,040,

HEAT EXGHANGERS V Filed Oct. 17. 1967 5 Sheets-Sheet 5 Min/ELL IV. dew/.050

A tlomeys Feb. 3 1970 M. w. bAv-lnsoN- HEAT EXCHANGERS- 5 Sheets-Sheet Filed Oct. 17, 1967 Feb; 3., 1910 Filed Oct. 17, 1967 m:::LAA\\\ llrl I M. W. DAV

IDS'ON. 3,493,040

HEAT EXCHANGERS 5 Sheets-Sheet 5 A florney United States Patent 3,493,040 HEAT EXCHANGERS Maxwell Wingate Davidson, Collinton, Edinburgh, Scotland, assignor, by mesne assignments, to Maxwell Davidson Evaporators Limited, a British company Filed Oct. 17, 1967, Ser. No. 675,832 Claims priority, application Grtzsast Britain, Oct. 19, 1966,

Int. Cl. F28d 3/00, 3/04; B01d 3/28 US. Cl. 165-115 8 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to improvements in or relating to evaporators, especially but not exclusively to evaporators for distillation plants for the desalination of sea water.

According to the present invention there is provided an evaporator in the form of a unit including a casing having inlet means for liquid to be evaporated and for heating fluid and housing a pair of vertically arranged spaced parallel plates, each plate comprising top, middle and bottom portions, the middle portions defining a central evaporating passage whilst the top portions are bent to provide together a pressure reducing orifice opening towards the central passage, the bottom portions being outwardly folded over to provide reservoirs for reception of condensed heating fluid; a pair of partitions each extending into a respective reservoir to define with the reservoir walls a U-leg arrangement in the reservoir and mounted in the casing such that, in combination with a quantity of condensate in each U-leg, they divide the interior of the casing into a high pressure zone and a low pressure zone, a portion of each partition defining with the middleportion of a respective plate a passage for heating fluid; and outlet means in the casing for fluids from the central passage and for condensate overflowing from the outer limb of the U-legs.

Preferably a plurality of pairs of parallel plates are arranged side-by-side in the casing, adjacent intermediate reservoirs being linked by a respective U-shaped partition.

According to another aspect of the present invention a multi-stage evaporator includes at least two of the evaporator units as aforesaid arranged in series communication one above the other, such that unevaporated fluid from the upper evaporator passes to the orifice of the lower evaporator whilst vapour and condensate from the upper evaporator passes to the heating fluid passages of the lower evaporator.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a side view of one heat exchanger plate of an evaporator.

FIG. 2 is a view in the direction of arrow A in FIG. 1

FIG. 3 is section 33 from FIG. 2.

FIGS. 4 and 5 are respectively an end view and an to view of a evaporator unit, both to a smaller scale, th tubular rods 17 shown in FIG. 4 being removed from FIG. 5 ftgr clarity.

FIG. is an enlarged schematic view showing tht diaphragm sealing arrangement for the sides of the hea exchanger plates.

FIG. 7 is an enlarged view of a reservoir of tilt evaporator unit showing the arrangement of the tubulai rod.

FIG. 8 shows schematically a multi-stage evaporatoi having a plurality of the evaporator units of FIGS. 4 and 5 arranged one above the other.

Referring to the drawings, the heat input and heal rejection sections of an evaporator unit of a desalination plant are formed by two vertically arranged parallel plates 10, one being a mirror image of the other, and each comprising top, middle and bottom portions. The end of the top portions of each plate is bent over as shown at 11, 12 and 13 such that when the plates are placed side by side a convergent-divergent orifice is formed by said top portions as shown clearly in FIG. 4. The bottom portions are kinked 14 and doubled back to form a channel 15 at the base of each plate and extending back up the plate but terminating at a level beneath the passage. The plates are provided with alternately inwardly and outwardly facing dimples 16 pressed from the plates, the dimples serving to space the plates apart when they are arranged side by side and to position the partitions to be referred to below.

A heat input or evaporating section is thus formed, this section being the space between the plates while the heat rejection or condensing section is the space outwith the plates.

Fluid to be desalinated is fed to the convergent portion of the passage formed by the top portions, this convergent portion serving as a reservoir. A tubular rod 17 (not shown in FIG. 5) is floated in this reservoir and automatically regulates the flow of fluid through the divergent portion of the passage into the heat input section. Referring to FIG. 7, a duct 25 for the supply of fluid to be evaporated is positioned above the rod 17: the arrangement is such that when the level of liquid in the reservoir falls to a minimum desired value, the rod 17 abuts the walls of the reservoir and fluid flow through the orifice ceases, whilst, when the level rises to a maximum desired value, the rod closes the mouth 26 of the duct. As the fluid passes through the orifice its pressure and hence its saturation temperature reduces.

I-Ieat from the heat rejection section is supplied to evaporate the fluid. The heat is supplied from water vapour supplied to the section and this vapour is at a greater pressure than the fluid within the heat input section the temperature of the vapour need only be saturation temperature.

Any of this heating vapour which condenses 0n the plates 10 runs down the plates and is collected in the channels 15, these channeis being provided with partitions, positioned by the inwardly facing dimples 16, which reach to almost the bottom of the channel to form a U- tube arrangement at the base of each plate. One limb 18 of a member in the form of an inverted U forms the innel partition, the other limb 19 forming a partition a further similar unit placed parallel to the above scribed unit. Several units are thus assembled within :asing 20 to form an evaporator unit as shown in FIG.

The casing has inlet openings 30 at the top above reservoirs formed by the opposed inturned plate parts and outlet openings 31 at the bottom below parallel plates. The openings 30 serve for passage of liquid to be evaporated to said iervoirs and for the passage of heating fluid to the cts between outer walls 11a of adjacent units or beeen the casing 20 and the outer walls 11w of the units jacent thereto. The openings 31 serve for the outw of vapor and unevaporated liquid from the central ssages and condensate overflowing from the U-legs fined by the channels 15 in combination with the abs 18, 19 of the partitions.

The unit is held together by varying an applied transrse clamping pressure on the plates by means of silient diaphragms 22, engaging the outer walls 11a the outermost plates 10; and which are supplied with essure air through inlets 32 such that the width of the vssage at the top of the plates may be varied by varyg the clamping air pressure. To seal the ends of the tges a resilient rubber diaphragm 21 (FIG. 6) is used, is diaphragm being forced into engagement with the ate ends and the ends of the U members by applying pressure to a chamber of which the diaphragm 21 rms one wall, this pressure being greater than the eatest anticipated pressure within the unit. If the unit operating under vacuum, then atmospheric pressure ting on the outside of the diaphragm would be flicient. Where it is necessary to supply pressure air to ther of the pairs of diaphragms 21 or 22, respective ints 32, 33 can be formed through the framework of sing 20 which serves to hold the diaphragms in position,

e diaphragm edges being behind and bolted or studded the respective part of the framework. The extremities f the rods 17 lie beneath the top plate of the framework I.

To form a desalination plant as shown, schematically FIG. 8, several of the FIG. 4 units are arranged, one )OVC the other with the reservoir of lower stage beneath 1d receiving fluid from the outlet 31 of the stage above .rough the inlet ducts 25 of FIG. 7 (not shown in FIG. which are arranged in the inlet openings 30 of the age.

Fluid to be desalinated is supplied to the reservoirs 1 the top of the plates of the uppermost exaporator unit 1d flows through the oriflce into the heat input section. ;eam is piped to the heat rejection sections and in giv- .g off heat to evaporate the fluid in the heat input section )me of this steam condenses and is collected in the mbs of the U-tube arrangement.

Residual fluid from the heat input section falls from le outlet 31 and through the inlet 30 into the reservoir E the next below stage and vapour from the heat input :ction flows to the heat rejection section of the next elow stage through inlets 30. Similarly condensate verflowing from the U-tube arrangement of the top nit flows via the outlets 31 of the top unit and the in- :ts 30 of the next below unit to between the diaphragms 2 and the outer walls 11a of the outermost units or etween the outer walls 11a of adjacent units to the heat ejection section of the unit below.

The pressure of the fluid in the heat rejection section f the second stage unit is thus the same as the pressure f the heat input section of the first unit. As the pressure f the fluid in the heat input section of the second stage nit is lower than this pressure, having been reduced in 1e orifice between the top portion of the plates means 11.181. be provided to maintain this pressure diiferential. This means is the U-tube arrangement, the levels of the ondensate in the limbs being different and this difference n head being equivalent to the pressure diflerential.

Thus if the pressure within the heat input section is p the pressure within the heat rejection section is p, and the difference in condensate levels in the U-tube arrangement is h, p =p +h. The means for maintaining the pressure differential between sections is thus self-adjustmg.

A desalination plant is thus provided which comprises basically a plurality of only three difierent types of component, namely the two plates and the U-shaped members.

The components can be easily and cheaply manufactured from any suitable thin sheet material, for example tinplate and replacement of a defective component or cleaning of the plant can be relatively cheaply and quickly affected.

1 claim.

1. An evaporator in the form of a unit including a casing having inlet means for liquid to be evaporated and for heating fluid and supporting therein at least one pair of vertically arranged spaced parallel plates below the inlet means, each plate comprising top, middle and bottom portions, the middle portions defining a central evaporating passage whilst the top portions are bent to provide together a pressure-reducing orifice arranged to receive the liquid to be evaporated from the inlet means and opening towards the central passage, the bottom portions being outwardly folded over to provide reservoirs for reception of condensed heating fluid; respective end partitions each extending into a respective reservoir to define with the reservoir walls a U-leg arrangement in the reservoir and supported in the casing whereby, in combination with a quantity of said condensed heating fluid in each U-leg, they divide the interior of the casing into a high pressure zone and a low pressure zone, a portion of each partition defining with the middle portion of a respective plate a passage for said heating fluid and arranged to receive said heating fluid flowing .via the inlet means; outlet means in the casing below the parallel plates for fluids from the central passage and for said condensed fluid overflowing from the U-legs; sealing means resiliently engaging the ends of the plates and partitions; and means for applying clamping pressure to the plates to control the width of said orifice.

2. An evaporator as claimed in claim 1, wherein each pressure-reducing orifice has an upper downwardly convergent portion and a lower downwardly divergent portion, the upper portion serving as a reservoir for the liquid to be evaporated, and a tubular member is floated in said reservoir for the liquid to be evaporated and is adapted both to shut off flow of the liquid to be evaporated from the inlet means and the flow of the liquid to be evaporated to the lower portion of the orifice when the liquid level in the reservoir for the liquid to be evaporated reaches desired maximum and minimum values respectively.

3. An evaporator as claimed in claim 1, wherein one plate of each pair is a mirror image of the other.

4. An evaporator as claimed in claim 1, wherein the plates are provided with alternately inwardly and outwardly facing dimples, the dimples serving both to space the plates apart when they are arranged side-by-side and to position the partitions.

5. An evaporator as claimed in claim 4, wherein said means for applying clamping pressure comprises resilient diaphragms at opposite sides of the casing parallel to the plates and engaging respective ones of the plates adjacent to the casing at positions adjacent to said orifices, and means for supplying pressure air to the sides of the diaphragms remote from the plates.

6. An evaporator as claimed in claim 1, wherein said sealing means comprises resilient diaphragms provided at the ends of the plates and partitions to seal the ends, the diaphragms being subjected to an external pressure greater than the greatest anticipated pressure within the high pressure zone.

7. An evaporator as claimed in claim 1, wherein a plurality of pairs of parallel plate are arranged side-byside in the casing, adjacent intermediate reservoirs being linked by a respective U-shaped partition.

8. A Inulti-stage evaporator including at least two of the evaporators according to claim 7 arranged in series communication one above the other, such that unevaporated fluid from the upper evaporator passes to the orifice of the lower evaporator whilst vapour and condensate from the upper evaporator passes to the heating fluid passages of the lower evaporator.

6 References Cited UNITED STATES PATENTS 3,351,119 11/1967 Rosenblad 165-l15 X 3,356,125 12/1967 Standiford 159l3 X ROBERT A. OLEARY, Primary Examiner ALBERT W. DAVIS, Assistant Examiner US. Cl. X.R.

l59l3; l65165; 202236; 20389

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