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The electrorheological effect and its possible uses
29
Journal of Non-Newtonron Flurd Mechanrcs, 8 (1981) 29-41 Elsevler Sclentlfic Pubhshmg Company, Amsterdam - Pnnted m The Netherlands
THE ELECTRORHEOLOGICAL
Z P SHULMAN,
R G GORODKIN,
EFFECT
USES
E V KOROBKO and V K GLEB
Lulkov Heat and Mass Transfer Institute, (Recewed
AND ITS POSSIBLE
BSSR Academy
of Sciences,
Mmsk, (V S S R )
July 17,198O)
Summary Expenmental results for the electrorheological effect are cited and its possible apphcatlons m science, technology and different mdustnal branches are described. The hydraulic designs suggested are discussed m detail m terms of flow and heat-transfer characteristics of lowconductivity alumosllicate suspensions as a function of external electric field mtensity.
I. Introduction The development of scientific knowledge m the field of electrical physics and electrical engmeermg, as well as electrification and automation m all branches of mdustnal and agricultural production, has stimulated the development of novel processes employmg strong electric fields. Thus the electrorheological effect (ERE), a reversible change m the rheological characteristics of low-conductivity dispersed compounds, seems to be very promismg and deserves greater interest from scientists and engmeers. Thorough investigation of ERE has been carried out at the Heat and Mass Transfer Institute for the last 5-7 years and it has been found that the apparent viscosity of electrorheological suspensions (ERS) may increase some orders of magmtude, up to apparent sohdlfication of the medium. This involves mtemal structural rearrangement in suspensions, giving rise to nonNewtonian behavior and, m particular, to the appearance of a plastic-flow component. Marked thlxotropy, vlscoelasticlty and other properties inherent m complex media have also been observed. The nature of the observed phenomena is attributed to the competition between the hydrodynamic and electnc onentations of polarized particles 111 the suspension flow movmg across the external electric field, deformation and interaction of diffuse shells, overlappmg double electnc layers around the 0377-0257/81/0000-0000/$2
50 @ 1981 Eleevler Sclentlflc
Pubhshmg Company
30
particles, and oscillation and structunzatlon of the solid phase m the mterelectrode gap [ 5,6]. The last circumstance 1s shown to be of the greatest importance due to very large interaction energy of fibnl bridge, dendrite and coagulation structures, formed by particles m the field, whose destruction requires appreciable flow energy. The analysis of ERS programs allows the rheological equation of state to be chosen m the form of a four-parameter model of a nonlinear vlscoplastic medium (7
Sign
Ty
= ?A’” + (r),i
slgn
yp
,
(1)
where ro, Q,, n, m - f(E). This ensures successful solution of the problem of a single-phase flow and heat transfer m plane and coaxial cyhndncal channelcapacitors. The results of calculations were supported experimentally and allowed simple qualitative relationships to be established for the charactenstICSof flow (flow rate, heat) and heat transfer (convective heat transfer coefficient a(E), Nu(E) on the electric field mtensity). It has also been noticed that the volume of the fixed suspension bed, with electric field applied, increases markedly up to some value m proportion to the electric field mtensity, rather than randomly as is the case with the Reynolds dilatation. The process 1s reversible and the suspension bed recovers its volume when the electric field is turned off. The above data on ERS properties have been used to design and unplement various new, efficient, and economical mstruments and devices. Usmg direct application of electricity across the test medium (without intermediate transformations), mechanical, electromechamcal and other known systems have been successfully replaced by simple electrorheologmal devices that show an appreciable improvement m response, working hfe, output charactenstics (strength, frequency), energy consumption, etc. II. Apphcations We now consider the basic types of devices developed at the Institute m terms of their applications. Hydrauk
valves wrth electrorheologlcal fluld
Whenever an electrorheological suspension is pumped through a channel capacrtor with sufficient potential difference between its walls, resistance to its motion can be regulated (depending on the field intensity) up to apparent sohdlfication, i.e. complete stop of the flow. This channel may serve as a throttle and a valve m an ERS-filled hydraulic system. Bullough and Stringer et al. [2,3] have devised and patented hydrauhc devices using flat and coaxial, cylmdr~aI valves. We have developed a new
31
Fig 1 Dlelectrlc suspension pump (for explanation of symbols, see text)
screw valve [ 81 havmg electrodes that are stnp spiral spnngs. Usmg the same dlmenslons as the pass valves, the output pressure drop m the valve Increases several times. A number of devices usmg plane and coaxial, cylmdncal valves are suggested, mcludmg the dlelectnc suspension pump [ 91 sketched m Fig. 1. Dlelectrlc suspension pump Two valves (3 and 4) are mcorporated m the cylmder. The suction valve (3) may perform reclprocatmg motion induced by the dnve (l), while the delivery valve (4) ISngldly fixed m the cylmder and mamtams pressure m the pumpmg system. When the suction valve moves to the dehvery valve, the required electnc voltage (2) 1ssupphed to the former valve to provide maximum mcrease m the apparent vlscoslty of the ERsuspenslon up to the lockmg point. The valve, now servmg as a piston, repels the fluid from the mtervalve gap, through the delivery valve, to the system. When the “dead” point 1sreached by the suction valve, electnc voltage is applied across the dehvery valve to prevent pressure drop m the system, rehevmg pressure m the suction valve. For reverse motion, the test fluid flows via the suction valve and fills up the mtervalve gap. The repetition of these cycles results m the suspension bemg pumped out. By varymg the apphed voltage, one may contmuously adJust the flow rate and pressure m the system. Mom tormg device The construction of an ERS-feeder to be used for ERS supply to bunkers and for special ER-mecharusms m the production process ISshown m Fig. 2 [lo]. It consists of a set of tapered, plane, metal frames - condenser plates (1). With voltage (2) apphed, they form, with the suspension (3) sohdlfled m the gaps, the wall of a cavity filled with electrorheolo@cal suspension (ERS). Successive downwards smtchmg-off of the plates frees the suspension batches between adJacent plates and provides discharge mto the mam channel. Thus the fluid can be momtored, as requned, when any set of plates 1s switched off.
32
Fig 2 Momtormg
dewce (for explanation
Fig 3 Dlstrlbutor
(for explanation
of symbols,
see text)
of symbols, see text)
Dlstrrbu tor This contams a cyhnder (5) vvlth one inlet, two outlets (I-l, 11-2) and two discharge onfices (I-3,11-4) [ll] (Fig. 3) The device suggested has 4 fixed valves (A, B, C, D) each between two successnre cylmdncal orlflces controlled by a high-voltage pulse operator (7). The device operates m the followmg fashion an electnc pulse of the required duration 1s supphed to the electrode pairs AC and BD. The suspension moves from the central mlet orifice, through the open middle valve, to the hydraulic discharge line and after performing some work (for example, movmg the power cylmder piston) returns to the discharge onflce. The use of fixed valves ehmmates the fnctlon and wear of movmg pistons and increases the speed of response and the hfetune of the dlstnbutor. Flurd hydrauhcs monrtors The electrorheolo@;lcal effect and devices based on it are employed m this class of apparatus to obtam the requved secondary effect. In contrast to the devices of the first class, which have restncted apphcatlon owmg to lunlted use of rheolo@cal suspensions, these devices are very promlsmg. The following are examples: Perlstaltlc pump (See Fig 4) [12] The appropriate voltage (5) 1s applied across the electrodes (2 and 1) of
33
5
Fig 4 Perlstaltlc pump (for explanation of symbols, see text) Fig 5 Safety device (for explanation of symbols, see text)
the workmg element of a membrane transducer (3) filled wrth ERS (4). This results m contractron of the walls made of elastic hose (6) and the squeezmgout of pumped fluid (7). Successwe apphcatlon of a movmg electnc field across the workmg elements wrll mduce shrftmg of the material to be transported. The frequency of electnc pulses supphed to the electrodes and, hence, the frequency of the membrane “compressron-extensron” can be monitored m any known way. Safety device (See Fig 5 [13]) Dependmg on the voltage applied, the ERS m the plpelme 1sm a quaslsolid state and can endure a certam liquid or vapor pressure m the pipeline. Once a prescribed cntlcal pressure ISachieved, a safety membrane (3), made of any low-strength mater& (paper, film), is destroyed and, when the valve (1) is broken, 1sremoved from the plpelme (4) to the discharge onflce with the suspension (6) flowmg out through the gaps between the electrodes (5), thus ensurmg free passage for liquid (au). Crltlcal pressure 1smonitored by varymg the apparent ERS vrscoslty which depends on the electnc voltage (2) applied across the valve. Llqurd pressure oscdlator (See Frg 6 [14]) In the cylinder (1) ERS (4) flows through the gaps of the valve (2) to the discharge onflce. Whenever a high-voltage electnc pulse 1ssupphed from the oscillator (6), the valve moves (together with the rod (3) and the piston (5)), because of the mcreasmg pressure due to the mcrease m hydraulic resistance Under equrhbnum condltlons, the piston throttles the flow of liquid (7) to the drscharge ordlce. With the valve movmg, the piston falls until the forces
Fig 6 Llquld pressure oscillator (for explanahon of symbols, see text)
actmg upon it become equal. Thus the discharge flow rate decreases, while the output pressure applied across the test element mcreases. Once the pressure is relieved, the valve, together with the piston, 1s unpelled by the sprmg and outlet liquid pressure correspondmgly decreases In the case of possible undesvable ERS flow-rate changes, due to foreign forces, the flow meter registers this change and transmits it along the cmxut to the osctiator, which generates greater or lower amphtude high-voltage signals to monitor the hydraulic resxtance of the ER-valve and to stabilize outlet osctiatlons. The amplitude and frequency of the forced liquid-pressure osclllatlons at the outlet are slmllar to the pressure varlatlons of the ERS-flow and change m the valve motion of the rod and piston. Osclllatlons may have different shapes (smusoldal, peaking and rectangular). Power deorces and au tomatlc elements Klass [ 151 (followed by other authors [4,16]) reported possible apphcatlons of electrorheologlcal suspensions for obtammg appreciable magmtudeand duratloncontrolled forces m various dampmg and antlshock devices, as well as m vibratory devices for testmg full-scale spacecraft and rockets. Several improved versions of such devices and vibrators (m particular refs. [ 1,171) are here suggested and new mechanisms of brakmg as well as fnctlonal devices and automatic elements are described.. Electrohydrauhc brake pusher (See Fig 7 [18J) By rotatmg the wheel (2), the electric motor (1) mduces a suspension flow through the cylinder (3), the electrorheologlcal valve (4), the pumpmg channel
35
1
Fig 7 Electrohydrauhc
-
brake pusher (for explanation
Fig 8 Trackmg dewce for copytng machmes
“Y
of symbols, see text)
(for explanation
of symbols, see text)
(6), and to the cylinder mlet under the rotary wheel. With the electnc field apphed, the valve, operatmg as a piston, moves together with the connected rod (5). The rod transfers the force to a system of brake levers. Removmg the electric voltage at the valve electrodes and reapplymg It at the required mstant allows ready control of the brake, v&l-~the tune of response to an electnc pulse not exceeding 0.05 s.
Tracking device for copymg machrnes (See Fig 8 [19]) This device comprises the probe (4), oil pump (9), fluid dlstnbutor and
fluld cylmder (7) with a piston (8) ngldly connected to the mlllmg head (11). The machine board (1) with the sample (2) and the blank (3) moves to the left at constant speed V,. The probe travels along the axis OY and, together mth the board movmg along the axis OX, yields a curvllmear motion m the plane OXY, correspondmg to the sample shape. When the rod moves up, an electnc potential regulated by rheostat (5) 1ssupplied to the hydrodlstnbutor valve, the openings m piston (8) close and the piston due to the ERS pressure moves upward. The mllhng head also moves up, thus producmg the requved work m the plane OXY m the scale of the model The speed of the mdhng-head response depends on the operation tune of the electrorheologlcal valve of any design (coaxial-cylinder, screw, etc.) and 1scontrolled by the electnc clrcult (6), the operation of which depends on the probe. When only honzontal operations are needed, the electnc field must be smtched off, while vertical processmg of the work requires stoppmg the dvectmg board.
36
Fig 9 Packmg dewce (for explanation of symbols, see text) Fig 10 Cawon (for explanation of symbols, see text)
Packmg device (See Fig 9 [20] ) Designed for packmg hydrauhc mams, this device mcludes a hollow elastic rmg (l), a metal flttmg (2), a currentconductmg bed (3), which covers the unremforced wall of the packing chamber, and an electrorheological suspension (4) flllmg the hollow rmg. It ISplaced inside the casmg (5) to pack the gap between the casmg and the work (6). When electric voltage 1sapphed across the metal fittmgs and the current-conducting bed, the ERS-volume increases due to the electrodllatant effect, the unreinforced walI of the packmg chamber is bent towards the work and adheres to it. Wide-range vanation of the applied voltage allows smooth change of the degree of packmg, dependmg on the pressure of gas and liquid tendmg to penetrate mto the gap between the casmg and the work. This device 1ssunpler than those in existence, provides smooth control of the degree of packing, and reduces energy consumption. Carsson (See Fag 10 [21] ) In building, some constructions must be recessed mto the ground (for example, skip pits for blast furnaces, etc.). It 1scommon practice m these cases to use thixotroplc suspensions for reducmg the drag between the ground and the obJect. ER-suspensions make it possible to control the rate of ObJect recession. The carsson, using ERS, contams a metal body (l), filler (2), pipelines (3) to fill the gap between the external caisson wall and the ground wrth ERS (4), and metal plates (5) set on the external waU of the caisson. A high-voltage source (6) 1smounted at some distance from the caisson. The carsson LSset on the ground surface and then lowered as the ground 1s taken out. Sunultaneously, electrorheological suspension sensitive to electric field 1spumped mto the gap between the ground and external caisson wall.
37
Electnc voltage apphed across plates (5) allows wide-range vanatlon of the fnctronal force between the ground and the carsson walls and thus allows vanatlon of the penetration speed up to a complete stop. This makes it posslble to avoid cracking and farlure of the cauxon. Fan (See Fig 11 [22] ) The wmd rotates the wmd dnve (l), the electrorheolo@;lcal clutch-stablhzer (3), high-voltage generator (4) and working wheel (5) of the fan fixed on the shaft (2). The rotor of the osmllator, when rotatmg with the dnve shaft, generates hrgh-voltage current m the stator wmdmgs, which is then conducted to the stabrhzer bushing. The gap between the stabtizer bushmg and the shaft 1sfilled with ERS. Due to the change m ERS vrscoslty, the rotation speed of the shaft controllmg the oscillator potential changes under the effect of electnc field. The higher (lower) the rot&on speed, the greater (smaller) 1sthe potential from the oscillator and hence more (less) pronounced 1sthe decrease m the speed of rotation of the shaft mth the fixed workmg wheel. By connectmg the constant high-voltage source m senes with the cucult, one can vary the electnc field mtenslty m the gap of the electrorheologlcal clutch and rotation speed of the fan wheel (i.e. the performance of the device ) .
Fig 11 Fan (for explanation of symbols, see text) Fig 12 Concentrahon text)
meter for dlelectrlc composhons
(for explanation of symbols, see
38
Measurmg devices Solrd-phase concentration meter for drelectrrc composrtrons (See Fig 12 ~231) Solid-phase concentration measurements m dielectric (m particular, mineral) dispersed systems is based on the effect of dielectric rotor movement m a low-conductivity medium m a capacitor field. As a result of the Qumcke effect, the dielectric rotor (3) m the field of plane capacitor (2), whose gap is filled with lowconductivity fluid (4), starts rotating when high voltage is apphed across the capacitor plates. Other conditions being equal, the speed of rotation depends on the electric field mtensity, composition and properties of the test fluid, and rotor material. Thus the nomograms for the number of dielectric rotor rotations vs. the test fluid composition, when available, permit the determination of solid suspension concentration from the speed of rotation. In some cases this concentration meter is more convenient and reliable than other known devices. (This is the case when, for example, measurements of the concentration of suspended substances are made using a photoelectric absorption meter measuring light sorption and scattering m the medmm to be analysed.) Sumlar methods can be used to measure the moisture content of dielectric materials [24] (Fig 12) In this mstance, the dielectric cylmder (3) is immersed m the mixture of nonconductmg fluid and dispersed dielectric material (4) which fills a hollow plexiglass cylinder (1) contammg electrodes (2) The rotation speed of a dielectric cylinder (3) set m bearings (5) is determined, say, with the aid of an illummated perforated disc (6), and a photocell (7), with signals bemg read off by a frequency meter (8). A constant electric field may be induced by a power source (9) of type BC-23, for instance. When the electric field is applied, the rotor starts rotating at a speed proportional to the moisture content of the test material (Fig. 13). Rotary vlscometer (See Fig 14 [25] ) Test fluid (3) is placed in the gap between cylinders 1 and 2 and electrorheological suspension (6) m the cavity between cylinders 4 and 5. Cylinders 2 and 5 are then set moving by one drive (7). Cyhnders 1 and 4 will be affected by the resistance forces appearing m the fluids and the degree of rotation on their axes will depend on the fluid viscosity Continuous increase of the electric voltage allows matching of the indicator (8) with the scale (9). ERS viscosity correspondmg to a certain electric voltage is found from the calibration table composed before the experimental measurements. The vlscometer allows measurement of fluid viscosities m a wide range (5-500 cps) for a short time, both under laboratory and plant conditions Sensitivity and accuracy of measurement using this rotary viscometer depends essentially on the quality of the measuring system.
39
J
9
7
5
Q,’ a
11
Fig 13 Dlelectra rotor rotations (nl) vs material moisture content (for explanation of symbols see text) Fig 14 Rotary wscometer (for explanations of symbols, see text)
Recuperatwe
heat exchangers
By varymg the electric field mtennty, surface fmtlon of dlelectmc suspensions can be altered over a wide range. This also has slgnlfxant effects on the
---
_
-----
-e_ --p__ z --
--
-
_ _
-
--
-
-
Electrorheologml -
SUSDWlSIOn
Newtonm neat corr,er
----
_A--
_---
-+-
_-
018
--
Fig 15 Longltudrnal section of a recuperative heat exchanger Fig 16 Effectwe thermal conductwty mtenslty (E)
of alumoskate
suspensions (A) vs electric field
40
flow structure and, especially, on hydrodynamic resistance. The method can also serve as an effective means for changmg temperature fields and convective heat transfer charactenstlcs m tubes, channels and heatengineenng devices [26]. If ERS or any other Newtonian fluid moves on both sides of a thm metal partition of a recuperative heat exchanger (whose longitudmal section IS shown m Fig. 15), then the ERS velocity and heat convection change considerably under the effect of the apphed electnc field. Thus it is possible to vary heat-transfer mtenslty between fluids over a wide range. These heat exchangers improve heat-transfer characteristics and lower energy consumption. For dlatomlc suspensions m transformer oil, the heat transfer coefficient changes considerably with mcreasmg electric field (Fig. 16). By varying X, one can control heat removal from the heated body. III. Conclusions The specific properties of electrorheological fiuids make it possible to develop nonstandard approaches to the problem of mechanical energy transfer and control, and to design totally new devices. The foregoing mechamsms do not exhaust all the possibilities of ERE application. The ER effect appears to be promising in hqmd electric generators, current transducers, electrokinetic balances, separators and scrubbers, TV sets with plane screens, and cinema proJectors usmg discrete systems whose transparency changes when electric fields are applied. Notation
m
4
E Nu c 4
nonlinear vlscoplastlclty indices electric field mtenslty (V/m) Nusselt number solid phase concentration (o/o) number of rotations (r.p.m.)
Greek symbols 7 70 VP
(Y x 9
shear stress (N/m2) untlal shear stress (N/m2) plastic viscosity analog (N s/cm2) heat transfer coefficient (W/m2 deg) effective thermal conductnnty (W/m deg) Sohd phase moisture content (% weight)
References 1 A V Lwkov, Electrorheologmd Effect 2 US Patent No 26611596 Cl 60-52
Nauka I Tekhn
Mmsk, 1972
41 3 W A Bullough and J D Strmger, Proc 3rd Intern Fluid Power Symp , Tunn, 1973, Paper F3, p. 37 4 H T Strandrat, Proc Hydr and Pneumat ,1966, pp. 139-143 5 Z P Shulman, A D Matsepuro and B.M Smolsky, Vest1 AN BSSR, Ser FIZ Energ Nauk. 1 (1974) 60 6 Z P Shulman, A D Matsepuro and V A Kuzmm, Vest1 AN BSSR, Ser FIZ Energ Nauk, 2 (1974) 130 7 Z P Shulman and E V Korobko, Inst J Heat Mass Transfer, 21 (1978) 543 8 U S S R Apphcatlon for InventIon No 2548871/08,31 August 1978 9 U S S R Author’s Certlflcate No 606001, Bull Invent No 17,1978 10 U S S R Apphcatlon for InventIon No 2795322/10 11 U S S R Apphcatlon for InventIon No 2585128/06 12 U S S R Apphcatlon for InventIon No 2481802/03,18 August 1978 13 U S S R Author’s Certlflcate No 625091, Bull Invent No 35, 1978 14 U SS R Apphcatlon for InventIon No 245992/06,30 March 1979 15 D L Klass, New Sclentlst, (1967) 664 16 W A Bullough and M B Foxon, Report of the Department of Mechamcal Engmeermg, Umv Sheffield Press, 1974 17 U S S R Apphcatlon for InventIon No 2448116/23, 29 March 1978 18 U S S R Author’s Certlflcate No 625073, Bull Invent No 35,1978 19 U S S R Apphcatlon for InventIon No 2654710/08, 28 February 1979 20 U S S R Apphcatlon for InventIon No 2618342/08,26 December 1978 21 U S S R Apphcatlon for Inventlon No 1803767/14 22 U S S R Apphcatlon for Inventlon No 2645774/24, 31 May 1978 23 U S S R Apphcatlon for InventIon No 1830881 24 U S S R Author’s Certificate No 572698, Bull Invent No 34.1977 25 U S S.R Apphcatlon for InventIon No 2509285/25,8 February 1978 26 Z P Shulman, E A Zaitsgendler and V K Gleb, Proc 6th Int Heat Transfer Conf , Toronto, 1978
Journal of Non-Newtonron Flurd Mechanrcs, 8 (1981) 29-41 Elsevler Sclentlfic Pubhshmg Company, Amsterdam - Pnnted m The Netherlands
THE ELECTRORHEOLOGICAL
Z P SHULMAN,
R G GORODKIN,
EFFECT
USES
E V KOROBKO and V K GLEB
Lulkov Heat and Mass Transfer Institute, (Recewed
AND ITS POSSIBLE
BSSR Academy
of Sciences,
Mmsk, (V S S R )
July 17,198O)
Summary Expenmental results for the electrorheological effect are cited and its possible apphcatlons m science, technology and different mdustnal branches are described. The hydraulic designs suggested are discussed m detail m terms of flow and heat-transfer characteristics of lowconductivity alumosllicate suspensions as a function of external electric field mtensity.
I. Introduction The development of scientific knowledge m the field of electrical physics and electrical engmeermg, as well as electrification and automation m all branches of mdustnal and agricultural production, has stimulated the development of novel processes employmg strong electric fields. Thus the electrorheological effect (ERE), a reversible change m the rheological characteristics of low-conductivity dispersed compounds, seems to be very promismg and deserves greater interest from scientists and engmeers. Thorough investigation of ERE has been carried out at the Heat and Mass Transfer Institute for the last 5-7 years and it has been found that the apparent viscosity of electrorheological suspensions (ERS) may increase some orders of magmtude, up to apparent sohdlfication of the medium. This involves mtemal structural rearrangement in suspensions, giving rise to nonNewtonian behavior and, m particular, to the appearance of a plastic-flow component. Marked thlxotropy, vlscoelasticlty and other properties inherent m complex media have also been observed. The nature of the observed phenomena is attributed to the competition between the hydrodynamic and electnc onentations of polarized particles 111 the suspension flow movmg across the external electric field, deformation and interaction of diffuse shells, overlappmg double electnc layers around the 0377-0257/81/0000-0000/$2
50 @ 1981 Eleevler Sclentlflc
Pubhshmg Company
30
particles, and oscillation and structunzatlon of the solid phase m the mterelectrode gap [ 5,6]. The last circumstance 1s shown to be of the greatest importance due to very large interaction energy of fibnl bridge, dendrite and coagulation structures, formed by particles m the field, whose destruction requires appreciable flow energy. The analysis of ERS programs allows the rheological equation of state to be chosen m the form of a four-parameter model of a nonlinear vlscoplastic medium (7
Sign
Ty
= ?A’” + (r),i
slgn
yp
,
(1)
where ro, Q,, n, m - f(E). This ensures successful solution of the problem of a single-phase flow and heat transfer m plane and coaxial cyhndncal channelcapacitors. The results of calculations were supported experimentally and allowed simple qualitative relationships to be established for the charactenstICSof flow (flow rate, heat) and heat transfer (convective heat transfer coefficient a(E), Nu(E) on the electric field mtensity). It has also been noticed that the volume of the fixed suspension bed, with electric field applied, increases markedly up to some value m proportion to the electric field mtensity, rather than randomly as is the case with the Reynolds dilatation. The process 1s reversible and the suspension bed recovers its volume when the electric field is turned off. The above data on ERS properties have been used to design and unplement various new, efficient, and economical mstruments and devices. Usmg direct application of electricity across the test medium (without intermediate transformations), mechanical, electromechamcal and other known systems have been successfully replaced by simple electrorheologmal devices that show an appreciable improvement m response, working hfe, output charactenstics (strength, frequency), energy consumption, etc. II. Apphcations We now consider the basic types of devices developed at the Institute m terms of their applications. Hydrauk
valves wrth electrorheologlcal fluld
Whenever an electrorheological suspension is pumped through a channel capacrtor with sufficient potential difference between its walls, resistance to its motion can be regulated (depending on the field intensity) up to apparent sohdlfication, i.e. complete stop of the flow. This channel may serve as a throttle and a valve m an ERS-filled hydraulic system. Bullough and Stringer et al. [2,3] have devised and patented hydrauhc devices using flat and coaxial, cylmdr~aI valves. We have developed a new
31
Fig 1 Dlelectrlc suspension pump (for explanation of symbols, see text)
screw valve [ 81 havmg electrodes that are stnp spiral spnngs. Usmg the same dlmenslons as the pass valves, the output pressure drop m the valve Increases several times. A number of devices usmg plane and coaxial, cylmdncal valves are suggested, mcludmg the dlelectnc suspension pump [ 91 sketched m Fig. 1. Dlelectrlc suspension pump Two valves (3 and 4) are mcorporated m the cylmder. The suction valve (3) may perform reclprocatmg motion induced by the dnve (l), while the delivery valve (4) ISngldly fixed m the cylmder and mamtams pressure m the pumpmg system. When the suction valve moves to the dehvery valve, the required electnc voltage (2) 1ssupphed to the former valve to provide maximum mcrease m the apparent vlscoslty of the ERsuspenslon up to the lockmg point. The valve, now servmg as a piston, repels the fluid from the mtervalve gap, through the delivery valve, to the system. When the “dead” point 1sreached by the suction valve, electnc voltage is applied across the dehvery valve to prevent pressure drop m the system, rehevmg pressure m the suction valve. For reverse motion, the test fluid flows via the suction valve and fills up the mtervalve gap. The repetition of these cycles results m the suspension bemg pumped out. By varymg the apphed voltage, one may contmuously adJust the flow rate and pressure m the system. Mom tormg device The construction of an ERS-feeder to be used for ERS supply to bunkers and for special ER-mecharusms m the production process ISshown m Fig. 2 [lo]. It consists of a set of tapered, plane, metal frames - condenser plates (1). With voltage (2) apphed, they form, with the suspension (3) sohdlfled m the gaps, the wall of a cavity filled with electrorheolo@cal suspension (ERS). Successive downwards smtchmg-off of the plates frees the suspension batches between adJacent plates and provides discharge mto the mam channel. Thus the fluid can be momtored, as requned, when any set of plates 1s switched off.
32
Fig 2 Momtormg
dewce (for explanation
Fig 3 Dlstrlbutor
(for explanation
of symbols,
see text)
of symbols, see text)
Dlstrrbu tor This contams a cyhnder (5) vvlth one inlet, two outlets (I-l, 11-2) and two discharge onfices (I-3,11-4) [ll] (Fig. 3) The device suggested has 4 fixed valves (A, B, C, D) each between two successnre cylmdncal orlflces controlled by a high-voltage pulse operator (7). The device operates m the followmg fashion an electnc pulse of the required duration 1s supphed to the electrode pairs AC and BD. The suspension moves from the central mlet orifice, through the open middle valve, to the hydraulic discharge line and after performing some work (for example, movmg the power cylmder piston) returns to the discharge onflce. The use of fixed valves ehmmates the fnctlon and wear of movmg pistons and increases the speed of response and the hfetune of the dlstnbutor. Flurd hydrauhcs monrtors The electrorheolo@;lcal effect and devices based on it are employed m this class of apparatus to obtam the requved secondary effect. In contrast to the devices of the first class, which have restncted apphcatlon owmg to lunlted use of rheolo@cal suspensions, these devices are very promlsmg. The following are examples: Perlstaltlc pump (See Fig 4) [12] The appropriate voltage (5) 1s applied across the electrodes (2 and 1) of
33
5
Fig 4 Perlstaltlc pump (for explanation of symbols, see text) Fig 5 Safety device (for explanation of symbols, see text)
the workmg element of a membrane transducer (3) filled wrth ERS (4). This results m contractron of the walls made of elastic hose (6) and the squeezmgout of pumped fluid (7). Successwe apphcatlon of a movmg electnc field across the workmg elements wrll mduce shrftmg of the material to be transported. The frequency of electnc pulses supphed to the electrodes and, hence, the frequency of the membrane “compressron-extensron” can be monitored m any known way. Safety device (See Fig 5 [13]) Dependmg on the voltage applied, the ERS m the plpelme 1sm a quaslsolid state and can endure a certam liquid or vapor pressure m the pipeline. Once a prescribed cntlcal pressure ISachieved, a safety membrane (3), made of any low-strength mater& (paper, film), is destroyed and, when the valve (1) is broken, 1sremoved from the plpelme (4) to the discharge onflce with the suspension (6) flowmg out through the gaps between the electrodes (5), thus ensurmg free passage for liquid (au). Crltlcal pressure 1smonitored by varymg the apparent ERS vrscoslty which depends on the electnc voltage (2) applied across the valve. Llqurd pressure oscdlator (See Frg 6 [14]) In the cylinder (1) ERS (4) flows through the gaps of the valve (2) to the discharge onflce. Whenever a high-voltage electnc pulse 1ssupphed from the oscillator (6), the valve moves (together with the rod (3) and the piston (5)), because of the mcreasmg pressure due to the mcrease m hydraulic resistance Under equrhbnum condltlons, the piston throttles the flow of liquid (7) to the drscharge ordlce. With the valve movmg, the piston falls until the forces
Fig 6 Llquld pressure oscillator (for explanahon of symbols, see text)
actmg upon it become equal. Thus the discharge flow rate decreases, while the output pressure applied across the test element mcreases. Once the pressure is relieved, the valve, together with the piston, 1s unpelled by the sprmg and outlet liquid pressure correspondmgly decreases In the case of possible undesvable ERS flow-rate changes, due to foreign forces, the flow meter registers this change and transmits it along the cmxut to the osctiator, which generates greater or lower amphtude high-voltage signals to monitor the hydraulic resxtance of the ER-valve and to stabilize outlet osctiatlons. The amplitude and frequency of the forced liquid-pressure osclllatlons at the outlet are slmllar to the pressure varlatlons of the ERS-flow and change m the valve motion of the rod and piston. Osclllatlons may have different shapes (smusoldal, peaking and rectangular). Power deorces and au tomatlc elements Klass [ 151 (followed by other authors [4,16]) reported possible apphcatlons of electrorheologlcal suspensions for obtammg appreciable magmtudeand duratloncontrolled forces m various dampmg and antlshock devices, as well as m vibratory devices for testmg full-scale spacecraft and rockets. Several improved versions of such devices and vibrators (m particular refs. [ 1,171) are here suggested and new mechanisms of brakmg as well as fnctlonal devices and automatic elements are described.. Electrohydrauhc brake pusher (See Fig 7 [18J) By rotatmg the wheel (2), the electric motor (1) mduces a suspension flow through the cylinder (3), the electrorheologlcal valve (4), the pumpmg channel
35
1
Fig 7 Electrohydrauhc
-
brake pusher (for explanation
Fig 8 Trackmg dewce for copytng machmes
“Y
of symbols, see text)
(for explanation
of symbols, see text)
(6), and to the cylinder mlet under the rotary wheel. With the electnc field apphed, the valve, operatmg as a piston, moves together with the connected rod (5). The rod transfers the force to a system of brake levers. Removmg the electric voltage at the valve electrodes and reapplymg It at the required mstant allows ready control of the brake, v&l-~the tune of response to an electnc pulse not exceeding 0.05 s.
Tracking device for copymg machrnes (See Fig 8 [19]) This device comprises the probe (4), oil pump (9), fluid dlstnbutor and
fluld cylmder (7) with a piston (8) ngldly connected to the mlllmg head (11). The machine board (1) with the sample (2) and the blank (3) moves to the left at constant speed V,. The probe travels along the axis OY and, together mth the board movmg along the axis OX, yields a curvllmear motion m the plane OXY, correspondmg to the sample shape. When the rod moves up, an electnc potential regulated by rheostat (5) 1ssupplied to the hydrodlstnbutor valve, the openings m piston (8) close and the piston due to the ERS pressure moves upward. The mllhng head also moves up, thus producmg the requved work m the plane OXY m the scale of the model The speed of the mdhng-head response depends on the operation tune of the electrorheologlcal valve of any design (coaxial-cylinder, screw, etc.) and 1scontrolled by the electnc clrcult (6), the operation of which depends on the probe. When only honzontal operations are needed, the electnc field must be smtched off, while vertical processmg of the work requires stoppmg the dvectmg board.
36
Fig 9 Packmg dewce (for explanation of symbols, see text) Fig 10 Cawon (for explanation of symbols, see text)
Packmg device (See Fig 9 [20] ) Designed for packmg hydrauhc mams, this device mcludes a hollow elastic rmg (l), a metal flttmg (2), a currentconductmg bed (3), which covers the unremforced wall of the packing chamber, and an electrorheological suspension (4) flllmg the hollow rmg. It ISplaced inside the casmg (5) to pack the gap between the casmg and the work (6). When electric voltage 1sapphed across the metal fittmgs and the current-conducting bed, the ERS-volume increases due to the electrodllatant effect, the unreinforced walI of the packmg chamber is bent towards the work and adheres to it. Wide-range vanation of the applied voltage allows smooth change of the degree of packmg, dependmg on the pressure of gas and liquid tendmg to penetrate mto the gap between the casmg and the work. This device 1ssunpler than those in existence, provides smooth control of the degree of packing, and reduces energy consumption. Carsson (See Fag 10 [21] ) In building, some constructions must be recessed mto the ground (for example, skip pits for blast furnaces, etc.). It 1scommon practice m these cases to use thixotroplc suspensions for reducmg the drag between the ground and the obJect. ER-suspensions make it possible to control the rate of ObJect recession. The carsson, using ERS, contams a metal body (l), filler (2), pipelines (3) to fill the gap between the external caisson wall and the ground wrth ERS (4), and metal plates (5) set on the external waU of the caisson. A high-voltage source (6) 1smounted at some distance from the caisson. The carsson LSset on the ground surface and then lowered as the ground 1s taken out. Sunultaneously, electrorheological suspension sensitive to electric field 1spumped mto the gap between the ground and external caisson wall.
37
Electnc voltage apphed across plates (5) allows wide-range vanatlon of the fnctronal force between the ground and the carsson walls and thus allows vanatlon of the penetration speed up to a complete stop. This makes it posslble to avoid cracking and farlure of the cauxon. Fan (See Fig 11 [22] ) The wmd rotates the wmd dnve (l), the electrorheolo@;lcal clutch-stablhzer (3), high-voltage generator (4) and working wheel (5) of the fan fixed on the shaft (2). The rotor of the osmllator, when rotatmg with the dnve shaft, generates hrgh-voltage current m the stator wmdmgs, which is then conducted to the stabrhzer bushing. The gap between the stabtizer bushmg and the shaft 1sfilled with ERS. Due to the change m ERS vrscoslty, the rotation speed of the shaft controllmg the oscillator potential changes under the effect of electnc field. The higher (lower) the rot&on speed, the greater (smaller) 1sthe potential from the oscillator and hence more (less) pronounced 1sthe decrease m the speed of rotation of the shaft mth the fixed workmg wheel. By connectmg the constant high-voltage source m senes with the cucult, one can vary the electnc field mtenslty m the gap of the electrorheologlcal clutch and rotation speed of the fan wheel (i.e. the performance of the device ) .
Fig 11 Fan (for explanation of symbols, see text) Fig 12 Concentrahon text)
meter for dlelectrlc composhons
(for explanation of symbols, see
38
Measurmg devices Solrd-phase concentration meter for drelectrrc composrtrons (See Fig 12 ~231) Solid-phase concentration measurements m dielectric (m particular, mineral) dispersed systems is based on the effect of dielectric rotor movement m a low-conductivity medium m a capacitor field. As a result of the Qumcke effect, the dielectric rotor (3) m the field of plane capacitor (2), whose gap is filled with lowconductivity fluid (4), starts rotating when high voltage is apphed across the capacitor plates. Other conditions being equal, the speed of rotation depends on the electric field mtensity, composition and properties of the test fluid, and rotor material. Thus the nomograms for the number of dielectric rotor rotations vs. the test fluid composition, when available, permit the determination of solid suspension concentration from the speed of rotation. In some cases this concentration meter is more convenient and reliable than other known devices. (This is the case when, for example, measurements of the concentration of suspended substances are made using a photoelectric absorption meter measuring light sorption and scattering m the medmm to be analysed.) Sumlar methods can be used to measure the moisture content of dielectric materials [24] (Fig 12) In this mstance, the dielectric cylmder (3) is immersed m the mixture of nonconductmg fluid and dispersed dielectric material (4) which fills a hollow plexiglass cylinder (1) contammg electrodes (2) The rotation speed of a dielectric cylinder (3) set m bearings (5) is determined, say, with the aid of an illummated perforated disc (6), and a photocell (7), with signals bemg read off by a frequency meter (8). A constant electric field may be induced by a power source (9) of type BC-23, for instance. When the electric field is applied, the rotor starts rotating at a speed proportional to the moisture content of the test material (Fig. 13). Rotary vlscometer (See Fig 14 [25] ) Test fluid (3) is placed in the gap between cylinders 1 and 2 and electrorheological suspension (6) m the cavity between cylinders 4 and 5. Cylinders 2 and 5 are then set moving by one drive (7). Cyhnders 1 and 4 will be affected by the resistance forces appearing m the fluids and the degree of rotation on their axes will depend on the fluid viscosity Continuous increase of the electric voltage allows matching of the indicator (8) with the scale (9). ERS viscosity correspondmg to a certain electric voltage is found from the calibration table composed before the experimental measurements. The vlscometer allows measurement of fluid viscosities m a wide range (5-500 cps) for a short time, both under laboratory and plant conditions Sensitivity and accuracy of measurement using this rotary viscometer depends essentially on the quality of the measuring system.
39
J
9
7
5
Q,’ a
11
Fig 13 Dlelectra rotor rotations (nl) vs material moisture content (for explanation of symbols see text) Fig 14 Rotary wscometer (for explanations of symbols, see text)
Recuperatwe
heat exchangers
By varymg the electric field mtennty, surface fmtlon of dlelectmc suspensions can be altered over a wide range. This also has slgnlfxant effects on the
---
_
-----
-e_ --p__ z --
--
-
_ _
-
--
-
-
Electrorheologml -
SUSDWlSIOn
Newtonm neat corr,er
----
_A--
_---
-+-
_-
018
--
Fig 15 Longltudrnal section of a recuperative heat exchanger Fig 16 Effectwe thermal conductwty mtenslty (E)
of alumoskate
suspensions (A) vs electric field
40
flow structure and, especially, on hydrodynamic resistance. The method can also serve as an effective means for changmg temperature fields and convective heat transfer charactenstlcs m tubes, channels and heatengineenng devices [26]. If ERS or any other Newtonian fluid moves on both sides of a thm metal partition of a recuperative heat exchanger (whose longitudmal section IS shown m Fig. 15), then the ERS velocity and heat convection change considerably under the effect of the apphed electnc field. Thus it is possible to vary heat-transfer mtenslty between fluids over a wide range. These heat exchangers improve heat-transfer characteristics and lower energy consumption. For dlatomlc suspensions m transformer oil, the heat transfer coefficient changes considerably with mcreasmg electric field (Fig. 16). By varying X, one can control heat removal from the heated body. III. Conclusions The specific properties of electrorheological fiuids make it possible to develop nonstandard approaches to the problem of mechanical energy transfer and control, and to design totally new devices. The foregoing mechamsms do not exhaust all the possibilities of ERE application. The ER effect appears to be promising in hqmd electric generators, current transducers, electrokinetic balances, separators and scrubbers, TV sets with plane screens, and cinema proJectors usmg discrete systems whose transparency changes when electric fields are applied. Notation
m
4
E Nu c 4
nonlinear vlscoplastlclty indices electric field mtenslty (V/m) Nusselt number solid phase concentration (o/o) number of rotations (r.p.m.)
Greek symbols 7 70 VP
(Y x 9
shear stress (N/m2) untlal shear stress (N/m2) plastic viscosity analog (N s/cm2) heat transfer coefficient (W/m2 deg) effective thermal conductnnty (W/m deg) Sohd phase moisture content (% weight)
References 1 A V Lwkov, Electrorheologmd Effect 2 US Patent No 26611596 Cl 60-52
Nauka I Tekhn
Mmsk, 1972
41 3 W A Bullough and J D Strmger, Proc 3rd Intern Fluid Power Symp , Tunn, 1973, Paper F3, p. 37 4 H T Strandrat, Proc Hydr and Pneumat ,1966, pp. 139-143 5 Z P Shulman, A D Matsepuro and B.M Smolsky, Vest1 AN BSSR, Ser FIZ Energ Nauk. 1 (1974) 60 6 Z P Shulman, A D Matsepuro and V A Kuzmm, Vest1 AN BSSR, Ser FIZ Energ Nauk, 2 (1974) 130 7 Z P Shulman and E V Korobko, Inst J Heat Mass Transfer, 21 (1978) 543 8 U S S R Apphcatlon for InventIon No 2548871/08,31 August 1978 9 U S S R Author’s Certlflcate No 606001, Bull Invent No 17,1978 10 U S S R Apphcatlon for InventIon No 2795322/10 11 U S S R Apphcatlon for InventIon No 2585128/06 12 U S S R Apphcatlon for InventIon No 2481802/03,18 August 1978 13 U S S R Author’s Certlflcate No 625091, Bull Invent No 35, 1978 14 U SS R Apphcatlon for InventIon No 245992/06,30 March 1979 15 D L Klass, New Sclentlst, (1967) 664 16 W A Bullough and M B Foxon, Report of the Department of Mechamcal Engmeermg, Umv Sheffield Press, 1974 17 U S S R Apphcatlon for InventIon No 2448116/23, 29 March 1978 18 U S S R Author’s Certlflcate No 625073, Bull Invent No 35,1978 19 U S S R Apphcatlon for InventIon No 2654710/08, 28 February 1979 20 U S S R Apphcatlon for InventIon No 2618342/08,26 December 1978 21 U S S R Apphcatlon for Inventlon No 1803767/14 22 U S S R Apphcatlon for Inventlon No 2645774/24, 31 May 1978 23 U S S R Apphcatlon for InventIon No 1830881 24 U S S R Author’s Certificate No 572698, Bull Invent No 34.1977 25 U S S.R Apphcatlon for InventIon No 2509285/25,8 February 1978 26 Z P Shulman, E A Zaitsgendler and V K Gleb, Proc 6th Int Heat Transfer Conf , Toronto, 1978