CA1218645A - Rotating heat exchanger - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The invention concerns a rotating heat-exchanger comprising a cylinder having an inner jacket, and outer jacket and a section intermediate the jackets, for the heat-exchanging medium. The heat-exchanger is par-ticularly intended for use in paper-making machines and paper converting machines. The invention solves the problem in such cylinders or rollers of reducing the rotating mass. In accordance with the teachings of the invention this is made possible by rotating only the outer jacket whereas the inner jacket and the central shaft or equivalent means are stationary.

Fig. 1

Description

6'~;

A Rotating Heat Exchang~r lh~ su~j~c~ invention relatcs to a rotating heat exchanger in the ~orrn of a cylindsr having dauble jacketst comprising a heat exchangEr s~ctio~ for passag~~through of the fluid ser~ing a3 th~ heat exchanging ~edium in the space botwqen th~ cylindrical outer and inner jacks~s.
Prior art h~at exchanga~s of th~ type deflned ~bove are constructed in such a manner that th~ entir0 cylinder rotates both whsn it is supported by a through shaft or - more frequ~ntly - by a pair of stub axles secured to the cylindar snds~ This meaes that shafts and axle bearings must bs di~nsian~d on the basis of th~ total weight of the cylindar. Cylind~rs of this kind aro used for instance in machine~ f~r production and drying oF pap~r and in machines o~ this and similar nature ths cylinders may hav~ a length of up to 7 meters; a diameter o~ 1.5 matr~s and a weight o~ approximately 5 tons. The considerable weight p.resents additional disadvantages which are more import~nt than the ons already mentioned~ i.s. the necassity to us~
lar~e-sizs axle bearingsO
One such additional disadvant~g~ is due to the n~cessity o~ ~upplying and leading off ths hsat-exchanging medium via rotating seals. The latter must be replaoed or repaired comparatively frequently due to con~iderable damagcs caused to them from wear, as a rule by imp~riti~s preeent in tha haat-exchaning medlum which ln the case o~ papermaking machinss generally consists of water or 30 steam, Replac~ents moan operational standstills and ln addition are costly in themselves, since packing boxes designod for rotating axles are axpensive.
A third disadvantage connected with the consider-able weight of t,~e cylindar is the following ono. The cxternal face of the outer jacket must have a v~ry ~mooth surface fini~h~ particularly wh0n the cylinder ie used in calender rolling mills and in similar applications.
Whcn u~ed in mills of this kirld also comparativ~ly ~inor scratches in the surface might make the cylinder un~it for us~. When damages lika these occur, the cylinder must be liftsd off the machine with the aid of an ovsrhead crane and the er1tirs cylinder unit be tran~ported to a workshop to bs repaired. Whila the cylin~er unit is being repairHd a complete spare cylind~r unit must be used.
A furth~ disadvantage connectad with the great cylinder weight is the corraspandingly graat inertial mass7 which oftan makas it impossible to use the paper w~b or ~quivalsnt means to drivc the cylind~rs. Instead, the latter mu~t be driven by motor and the drive ~otors requira complicated synchronization mechanisms which ars s~nsitive to disturbances and which usually ~re thyristor-~ontrolledO
The invention is ba~Hd on the roaliz~tion that it 20 i9 possiole to eliminate the above-mentiond disadvantages by constructlng the cylinder in such a manner that only its outer jacket rotates while th~ inner jackst and the rest of the cylinder unit co~ponents are stationary.
~y constructing the cylinder in this mann~r several lmportant advantages are obtained. Firstly, reduction o~
the mass of the movable components is c~ider~e~ allowing use of smaller and less oxpen~ive bearings. Secondly, ~limination of the rotating saaling member~, because the cylinder compri~es stationary p~rts through which the msdlu~ may be supplied and rs~oved~ Thirdly, when damages are mada to the outer jacket the latter may be conv~niently and readily dismantled from the cylinder, while all other ~omponents remain in position, which drastioally reducss th~ handling and actual repair costs.

Fourthly, the rotatil,s mase is so small that as a rule the web itaelf will be capable of drivir-lg the cylinder jackst, whareby the need for drive Motors for ~everal cylinders ~nd synchronizing me~ns therefor become superfluou~.
The arrangatn~nt in accordance with the invention 9iU8S additional advantnges which will be deeeribed in the following~ However~ orle should be montioned already at this point. Because the heat-nxchar7ging medium passes through a space inside the cylind0r, one of the large delimiting walls of which, the inner ja~ket, is stationary while the other large rJelimiting wall~ the outer jacket, is rotating, a relativ~ ~n~ent i~ ganerated in the peripheral direction between the mediusn atld the outer jacket. The practical consequence o~ this phenomenon is that the he~t r-~xchange no longer is affected exclu~ively by condurtion b~t is supplementsd to a largn extent by convection.
A pronounced turbulent flow of tha heat-axchanging 20 medium i8 generated~ resulting in excellsnt exchange of heat between tha medium and ths outer jacket.
The heat exchanger in accordance with the invan~
t~on i9 characterizad in that the inner stationary jacket i~ formed along it~7 ~xternal face with one or several helically extending ribs designed to guids the heat-_raxchanging medium in a helical flow path through the heat-exchangillg section and thus imparting to the latter a component of velocity in the peripheral dirsction of ths cylinder, that the outer jacket is arrangQd to rotate relatiue to the inner jacket in a direction counter to tha peripheral component o~ velocity or the hent~exchanging medium in order to ganerate a turbulent flow of the heat--exchanging medium tl7rough the heat exchanging sec-tion, and that ~tationary channels are arranged to conduct the heat--exchanging medium to and ~rom the haat excharlging section~

6~5 The inv~r)tiol- will be descrlbe~ in closer detail in the f~llowilly with refertllce to the accomp~nyirlg cirawings, whereil-l Fig~ 1 is a partly brokell perspective view of ons end of a rotatirlg heat excharlger in accsrdatlse with the ~bjsct invention~
Fig. 2 is a cross-sectional view through a d~tail oP the heat~exchanger in accordance with Fig, 13 Fig~ 3 is a cross-sectional view corrrdspon~ing 1U to Fig. 2 of a modified embodiment of She invention, Fig. 4 is a schematic overall view of a further embodiment of the inv0rltiorl9 Figs 1 - 3 illustrats one erld wall o~ the cylin~er but the opposite wall i8 of identical design and con~truction with the exception that no drivs means are provided at this end, As mentioned in the afors ~oing the heat exchanger in accordance with th~ invention i8 of the type consisting of a ylinder comprising an inner jacket 1 and an outer jacket 2 with a section 3 between the jackets for a heat-exchanging medium, such as water or steam. By means of suitable, not illustr~ted conduit means th0 medium is supplied to the cylinder~ e.g. by pu~ping, at the point illustrated by arrow A where the medium ~lowa ~5 into a stationary shaft 4 supporting the inner jacket 1.
The shaft 4 is tubular, defining an axial pa3sageway 5 in~ide the shaft.
On the sh3ft 4 is mounted a spherical roller bearing 6 it~ inner carrier ring 7 being ~hrunk onto the 3ha~t 4. The outer carrier ring 8 of the roller bearing supports an end-wall closing lid 9 which supports a tubular sectiOn 10~ A driven wh~l 11 ia mount0d on the tubular soctiorl 10 and may be secured thereto in any suitable manner, such a8 by mean~ of bolta. A smaller lid 12 surrounding the shaft 4 is attached tn end-w~ll Iid 9 ir)tern~lly of the rollar ~earing 6~ S~als 1~ are prouid~d b~twe~rl the lid 12 and th~ shaft ~, The end--wall lid 9 and the lid 12 con~sequantly ar~
rot~tior1ally mounted relatiue to the stationary shaft 4.
fladially sxterl1ally of the end-wall lid 7 is a retainer ring 14 which is provided with a plerality of axially extendirlg, threaded bores which engar~a the threads of acrew~ 75. In accordance with the embedimant illustrated in the drawings9 the~e are forraed wlth heads of Allen-sr,rew type, which ~ count~rsunk in aperture~ in a double-con0 clamping ring 16 which upon tightening of the screwe cooperates in a wedging-eFfect faahion with a conical ring 17, Wherl tha screws 15 are tightened the ring 17 i5 forced radially nutward~ and in doing 90 retains the outer jacket 2 in po3itien, ~ rora the passageway 5 ln the interior of the shaft 4 tha heat-3xchanging medium i9 conducted through a numbes of openings 1~ formed in the ~haft wall into a~ssntially radially extending, stationary channal~ 20 which are ~upported by the sha~t 4 and are Formed at their oppo~ite ends with outlet mouths 21, the latter being positioned in a radial plane in relation to shaft 4.
The heat-exchanging medium ~lows through the passageway 57 the openings 19~ the channele 20 and the outlet mouths 21 to the eectiorl 3 formad between the jackets 1 and The inner jacket 7 i~ formad with a helically extendig rib 22 which ~orces the medium to flow in a helical path from ons end of the cylir1der to tha other instead of aseuming an axial ~low path. In thi~ mannar the medium is imparted a motion which po 8e~8e9 a c~n~iderabla componerlt of valocity in the p~ripheral direction of the cylirdsr.
Tho rib 22 axert~ a vane-like efFect on the medium flow and thus contributes to generating turbulence in the flo~.
It i po~sible to provid~ more than one rib 22 in which casn the ribq are arranged in a manner cDrre~ponding to the -threa(,is 0~' multiple~ ~hr'~ ;(,rt,'W'~. :L-t ~rlay be advisable -to ~orm condui~ts for 1,tLe rn~i~rl in this rnanner in which case each conduit starts at the mou-th 21 of a channel 20~
The section 3 :i,3 limi-ted at its ends b~y the annular seal 14 and by a seal ~3 disposed between the rotatably mounted end-wall lid 9 and the inner stationary jacket ~. 'L'he seal 23 :is f`ormecl by a sealing member 24 which is retained in posi-tion by means of a screw 25 which is screwed into -the inner jacket 1 and retains a locking ring 2~, the latter in turn exerting a reta,ining clamping action on -the sealing rnembers 24 in conjunction with a ring 27. In -this man~er -the seal 23 will be positioned close -to the periphery of the cylinder to preven-t the heat-exchanging medium *rom penetrating into the cylinder interior.
~ig. 3 shows a somewhat different embodiment of the inven-tion. The seals 23 at -the ends of the section 3 have been eliminated and been replaced by seals 30 positioned in the area where the end wall 9 is mounted on the shaft 4. The seals 30 are retained in position by means of spacer elernen-ts 31 whlch are arranged on the shaft 4. In accordance with the embodiment shown in this drawing f'igure the medlum has access to the space 32 internally of the end wall 9. 'The seal 30 will be exposed to less velocity ana frictional stress than the seal 23.
As appears f'rom the drawings and the aforegoing ,it is only the comparatively thin outer jacke-t 2 and -the end-wall lids 9 supporting thc jacket -tha-t are rotatably mounted whereas the rest of the en-tire cylinder unit, above all the shaft 4 and the inner jacket ~ are stationary.
This principle of construction means that -the drawbacks mentioned initially with respect -to prior-art rotatin~
heat exchangers of -the ty~e comtemp1a-ted herein have been ~2~

eliminated as has been described above. When -the medlum is s-team it may be eonducted from the ~,ylinder into a condensor in which it is conden.sed to recover -the heat generated when steam is formed. In many cases it may- be suitable to position adjustab:le turbine blades (not shown) at -the entrance to the section 3.
In prior-art rota-ting heat exchangers, cons-tr~c-ted as cylindrical rollers all of which is rotational, the guide ribs 22 may abut against the inner f'ace of -the outer jacket. In rollers constructed in accordance with -the inven-tion ln which the inner jacket 1 and -the outer jacke-t 2 rQay movc relative one another it is obviously not possible to arrange the guide ribs in abutment agains-t -the outer jacke-t. Instead it is necessary to provide for some radial play between the ribs 22 and the outer jacket 2~ In principle, this could be achieved by two princ.ipally different me-thods, or by a combination of the two. The f'irst principle resides in dimensioning the outer jacket walL sufficiently -to prevent that the latter is deformed radially inwards by a reverse roller during operation with consequential loss of the play. In practice, this mean~s -that the material thickness of the outer jacket must be between 12 and 20 r~m. The second me-thod is to construct the outer jacket with a thin wall, which gives improved heat trans~fer and as a resul-t the hea-t-e~changing medium generates the required forces of :reaction. This is achieved by subjecting the medium to a s-tatic overpressure effected for instance by throttling on the medi~ exit side. When -the outer jacke-t suppor-ts one o,r -two turbhE_'blade supporting rings these actively con-tribu-te to stiffening the jacket radially.
~ t should also be noted -tha-t the outer jacket need not be pos,itively driven bu-t on the contrary one of -the ad~antages of the subject invention is -that owing -to the greatly reduced inertial mass the ou-ter jaclcet may also be driven by -the web trave'Lllrlg be-lween the jacket and i-ts reverse ro:LLer, for instance in a papermaklng machine. This mean,s tha-t no-t only does -the need ~or driving mèchal~isms become superfluo1ls 'but that the same is true as regards -the otherwise necessary synchroni-zation mechanisms.
Irl prior-art heat exchanger rollers cunstructed with an inner jacket and an outer jacket which rota-te together, the hea-t-exchanging medium is imparted essential-ly the same peripheral velocity as -the ~oller. The in,signiflcant difference that does exist depends wholly on the ~low resistance, This means that the heat transfer that takes place between the medium and the ou-ter jacket occurs exclusively -through conduction, In a heat=
-exchanger roller in accordance with the in-vention the medium has no componen-t of velocity at all in the periph-eral direction upon its entrance into the space 3 ~orJ
in the case turbine blades are used, only a negligible compon~n-t of -this kind), Withou-t -the provision of the ribs 22 the medium, in principle no-t rota-ting, would have flowed axially from one end o~ -the roller to the oppo,site one~ Since the outer jacket rotates a relative motion in thejperipheral direction is created be-tween the medium and the outer jacketO The result o~ this dif~erence in velocity i~ aturbulent flow which is generated in the heat e~changing medium and that the exchange o* heat will occur not only b~ conductio~ but also through con~ectionO This effect i~ ~urther hightened by o~ientating the ribs 22 in such a manner tha-t the peripheral component of the medium ~low velocit~ around the inner jacket 1 is counter to the rotational speed o:~ the outer jacke-t 2, i.e. the -to-tal dif-'~erence in velocity 'between the medium and the outer jacket equals the sum of these two veloci-ties.
Fig. 4 shows schematically another pos,si'ble embodiment of the invention. The heat exchanger in accordance wi-th -this embodimen-t of the in~ention compri~es s-tationary channels ~ at the centre of` the heat exchanger, -these channels 33 bei,ng designe~ in the same manner as channels 20 to lead the medium from -the axlal passageway 5 in the ~ha~-t 4 to -the hea-t-exchanging section 3 formed between the inner and outer jacke-ts ~, 2. ~rom the outlet of -the channels 33 the medium will divide into two flows, f~lowing in opposi-te directions into the heat-exchanging section 3O Pre~erably, ri'bs 22 are positioned in such a manner -that both medium flows will be impa~ted a compon~nt of veloci-ty in the same direction in the peripheral direction in the jacket 2.
This makes it possible to rotate the outer jacket 2 counter to this compon~n-t of ve]ocity of the medium.
In accordance with thls embodiment of the invention stationary channels 34 are provided at the two end walls 9 of -the heat exchanger to carry away the medium ~rom the gap 3. ~edium may be carried to the channels 33 as shown in ~ig. 4, through the passageway 5. An annular channel 35 preferably is provided about -the shaft 4 to carry away -the medium from one of the end walls o~ the heat exchanger, At the opposite end wall the medium is led off in the conve~tional manner. I-t is likewise possible to arrange for the supply flow of heat-exchanging medlum through a separa-te central tube which is positioned inside the passageway 5 and is provided wi-th radial spokes connecting i-t to the channels 33. In accordance with this em'bodimen-t the annular channel 35 becomes superfluous since medium may be led off -through the passageway 5~ The embodimen-t of the invention shown in Fig~ 4 has -the advantage over those shown in Flgs. 1-3 that the -two énd walls of -the heat exchanger are exposed -to equal pressure from the hea-t--sxchanging medium.

l'rel'erably, the temperature on the external face of -the ou-te-r jacke-t 2 sho-llld be equaL, at 'bo-th ends of'-this jacke-t and preferabLy it sho1lld be uniform throughou-t -the entire Ieng-th of'-the jacke-t. This co-uld be ach-ieved :~'or installce by forrrling the channel delimited by the rib 22 in a tapering fashion in its lengthwise extension9 wi-th the res-ul-t -that -the velocity of the heat-exchanging medium increases and -that it becomes po.ssible to control it in such a manner t~la-t the external temperature of the ou-ter jacket 2 remains constant9 despite -the gradual cooling of the heat--exchanging medi-um. In the Swedish Patent Specification No 367 666 are described both this method of controlling the external temperature oY the outer jacket 2 a-nd other ways of achieving the same effect which may be used together with the subject invention.
~ inally should be emphasized that in the prac-tical applications of the subJect in~ention it is possible to de~ia-te from the constructio-nal and functional designs which by way of examples have 'been illustrated in the drawings. The medium may be a liquid, generally water, steam, or a gas, It could be also a two-phase medi-um.
'~he number of channels 20, 33 may be chosen according to need. Also, -they could be constructed wi-th a changing cross-sec-tion, for instance such tha-t they are comparatively wide in the area o-~ the outle-t mouths 21 in the peripheral direction 'but narrow in the axial direotion bu-t at their inlets 19 essen-tially square or round.
A heat e~changer roller in acco:rdance with -the invention may be used in a variet,y of applications. At present, the most important one is considered to 'be in papermaking machines~ 0-ther applications are in paper--converting machines, for example in laminating or 'I 1 impregna-ting paper and in printing and textile machines.
~he invention is a1sv applicabl~ in rollers and calanders in the plastics and rubber industrie,s, in the ~'ood--production industry and in the pharmace1ltical industryO
As an example of use in -the food-produc,tion industry could be mentioned the -type of roller used in the conf'ectionary industry for -the production of p:ralines.
Rolleræ foY this purpose are ~ormed with recesses on their external face. So~t chocolate is poured to suc-cessively fill into the recesses which at every ins-tant a:re posi-tioned on the upper face of the ,rotating roller~
A~ter rotation of the roller o-ve~ half a turn -the chocolate must be set, allowing the finished pralines -to ~all downwards by gravi-ty. 'rhis is one example o*
many o* an area where efficient e~change of hea-t between the outer jacket and the medium~ in -this case a cooling medium, is desired.
When -the invention is applied to particularly papermaking machines it is, as mentioned above, o:~ten possible to eliminate separate roller driving and synchronizing mechanismsthanks to the decreased rotating ,mass and instead -the paper web or corresponding means is allowed to drive the roller. When a web has no-t ye-t ~ormed, which is the case when the sheet is being threaded through the machine, the rollers must, however, be driven in some o-ther way~ In this case i-t is an advantage to use -turbine blades. When -the blades are adjustable their angle o~ incidence may be se-t to ensure tha-t the rotational speed imparted b~ the -tur'bine in the outer jacket is somewhat less the speed corresponding to the peripheral speed of -the web. In this manner protec-tion is obtained against occ1rrence o~ undesirable tensile stresses in the web, also without -the use of synchro-nizing mechanisms. Alter~ati~el~ af`ter completion o~ the sheet-threading i-t is possible to set -the blades -to a zero angle of incidence.

Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

1. A rotating heat exchanger in the form of a cylinder having double jackets, comprising a heat exchanger section for passage-through of the fluid serving as the heat--exchanging medium in the space between the outer jacket and the inner jacket, said inner jacket being stationary, c h a r a c t e r i s e d i n t h a t the inner stationary jacket is formed along its external face with one or several helically extending ribs designed to guide the heat-exchanging medium in a helical flow path through the heat-exchanger section and thus imparting to the latter a component of velocity in the peripheral direction of the cylinder, that the outer jacket is arranged to rotate relative to the inner jacket in a direction counter to the peripheral component of the velocity of the heat-exchanging medium in order to generate a turbulent flow of the heat--exchanging medium through the heat exchanging section, and that stationary channels are arranged to conduct the heat-exchanging medium to and from the heat exchanging section.

2. A rotating heat exchanger in accordance with claim 1, c h a r a c t e r i s e d i n t h a t the inner jacket is non-rotationally mounted on a shaft, that said shaft is provided with an internal passageway, the stationary radial channels in the cylinder communicating said passage-way to the heat-exchanging section between the two jackets.

3. A rotating heat exchanger as claimed in claim 2, c h a r a c t e r i s e d i n t h a t the outer jacket is rotatably mounted on the shaft and that the jacket mounting means is a rotatably mounted end-wall lid provided at the end parts of the cylinder.

4. A rotating heat exchanger according to any one of the preceding claims, c h a r a c t e r i s e d i n t h a t the stationary channels designed to conduct heat-exchanging medium to the heat exchanging section are positioned at the centre of the cylinder, and in that the channels designed to conduct heat-exchanging medium from the heat exchanging section are positioned at the cylinder end walls.

5. A rotating heat exchanger according to any one of claims 1 - 3, c h a r a c t e r i s e d i n t h a t the stationary channels designed to conduct heat-exchanging medium to and from the heat-exchanging section are positioned at the end walls of the cylinder.