with respect to the drawings wherein like reference characters designate like or similar elements throughout the several figures of the drawings , the schematic of fig1 represents an assembly of five multisegmented process cells 10 in serial alignment along a photosensitive material ( psm ) 12 process traveling route . in typical sequence , the first cell will circulate developer solution , the second cell will circulate fixer solution and the remaining cells circulate wash water . in an embodiment of the invention preferred for processing two - sided psm having radiation exposed , photosensitive emulsion coated on the two opposite surfaces of the substrate 12 , a process cell 10 comprises upper and lower plates 20 and 30 , respectively . a rotatively driven pair of squeegee rolls 14 are positioned on the outflow side of each cell 10 to nip the psm 12 dry of the preceding process solution and pull the psm through the cell . physical dimensions of a cell may vary greatly . for example , a wash cell in a 35 mm film development sequence may comprise only one segment and measure only about 1 inch in the psm travel direction and only about 1 . 5 inch transversely of the travel direction . conversely , a developer cell in an enlargement sequence may measure 15 inches in the psm travel direction and 30 inches transversely . plates 20 and 30 and rolls 14 respective to a single cell 10 are located above a corresponding overflow tray 16 which may or may not be in circulation circuit with the process solution of the respective cell unit 10 . see fig8 . the primary function of trays 16 is as catch - basins for excess or sealing flow of process solution from within the respective cell . in most cases , this is oxidized or contaminated solution not desired for recirculation . with respect to the sectional elevation of fig2 and the pictorial of fig6 the internal volume between upper and lower plates 20 and 30 is floored by a saw - tooth surface characterized by a plurality of tooth edges 31 along the planar intersection of respective ramp faces 33 and rise faces 35 . these tooth surfaces are oriented with the ramp surface 33 rising to the tooth edge 31 in the downstream psm 12 flow direction . spacing between adjacent tooth edges may be from about 0 . 25 to about 2 . 0 inches and preferably from about 0 . 50 to about 1 . 0 inches . tooth edge rise may be from 0 . 05 inches to about 0 . 25 inches and preferably from about 0 . 070 to about 0 . 10 inches . upper plate tooth edges 21 characterize the internal cell volume roof with a periodic spacing and rise similar to that below . additionally , each upper tooth edge 21 is backfaced with a gas riser channel 23 . the riser channels are vented to atmosphere at vents 24 . in the fig3 configuration of the invention , the vents 24 are connected with a conduit manifold 25 and controlled , whether open or closed , by a valve 26 . spacing between a first plane common to the upper tooth edges 21 and a second plane common to the lower tooth edges 31 is within about 0 . 005 inches to 0 . 10 inches with the range of about 0 . 01 to 0 . 05 preferred . although the tooth period of upper and lower plates 20 and 30 , respectively , is substantially the same , the relative tooth alignment along the psm traveling direction may be offset 0 to 50 % and preferably about 0 to 25 %. bottom plates 30 are also provided with process solution distribution channels 37 and 39 . with respect to the circulation diagram of fig8 and 9 , circulation pump 40 supplies the plate inlet channel 37 via supply conduits 42 and withdraws solution from channel 39 via the return conduits 44 . flow between distribution channels 37 and 39 is predominately parallel with the tooth edge line 31 . similarly , upper plates 20 include process solution distribution channels 27 and 29 respectively connected with supply conduits 42 and return conduits 44 via parallel connected supply conduits 22 and 19 . as with the lower plate , process solution flow is predominately parallel with the tooth edge line 21 . however , the true nature of the solution flow is considerably more complex due to the moving , wetted surface of the psm which carries some solution out of the cell and stimulates local turbulence . fig1 illustrates an alternative embodiment of an upper plate 20 having a multiplicity of solution circulation conduits 47 and 49 serving the distribution channels 27 and 29 , respectively , in alignment with each tooth ridge 21 defined transverse flow channel . obviously , the same multiple circulation conduit embodiment may also be applied to a bottom plate 30 design . the fig8 process solution circulation system respective to each cell 10 in the process line also includes solution and wash water reservoirs 46 and 48 , respectively , connected by conduits 41 and 43 . a discharge conduit 45 connects the circulation system to a sewer or waste recovery vessel 59 . controller 50 receives operating flow data from meters 53 and 54 . normally closed valves 56 , 57 and 58 are opened in response to controller 50 signal commands and pump motor 51 is regulated to maintain a predetermined cell solution flow rate or circulation velocity . as a percentage of the cell cavity volume between the floor and roof and between the solution distribution channels , that circulation may be in the range of 25 % to 800 % per minute . preferably , the volumetric flow rate should be in the range of 50 % to 500 % per minute . vertical spacing between the upper and lower tooth edge planes is controlled by the plate 20 and 30 end faces 28 and 38 , respectively . in assembly , these two end faces are aligned and secured in juxtaposition . gaskets , not shown may also be used to skim the desired separation distance and to seal the cell ends fluid tight . blade squeegees 68 and 69 , as seen in fig2 along the cell exit opening also contribute to internal fluid confinement and to wiping the psm surface . a trailing doctor blade 67 conditions the upper squeegee roll 14 while flush water supply 66 supports the doctor blade cleaning and conditioning function . although it is not possible to entirely seal the internal cavity volume from process solution leakage , it is possible to minimize that leakage by solution fluid surface tension and cavity volume pressure control . since the cell sides are sealed , solution is mostly lost only across the psm entrance and exit openings . by controlling the clearance of the tooth edges above and below the psm , liquid surface tension and meniscus forces will confine a sufficient pressure head to flood coat the psm upper surface : if there are no air bubbles against the cell roof . it is concern for roof bubbles and the need to vent them from the cell cavity that is addressed by the gas riser channels 23 and vents 24 . with such a minimum volume process solution system as disclosed hereby , the presence of a roof bubble can greatly distort cell solution distribution , concentration and reactivity . as a general rule , a cell cavity volume will be flooded to about the root of the tooth 21 which is at the intersection of the plane extended from the tooth backface . this will exert an escape head at the entrance and exit of about 0 . 05 inch to about 0 . 125 inch , the tooth riser distance . process solution level and flow rate may be controlled by a pair of dual contact resistance probes 61 and 62 bedded into the upper plate 20 . each probe represents a pair of physically spaced insulated electrical contacts that are exposed to the solution liquid at respective distances from the psm traveling plane . probe 61 sensing point is high in the riser channel 23 whereas probe 62 is midway along the tooth backface . when no solution bridges a contact set , measured resistance across the contacts is considerably greater than the resistance measured when immersed in the process solution . analysis of the relative resistance states provides a data base for operating the flow control motor 51 to achieve a relatively steady - state level within the cell . when a cell is emptied for maintenance or cleaning , refilling necessarily would trap new air in the transverse flow channel between the tooth ridges 21 except for the gas riser channels 23 . hydrostatic forces naturally press the air into these channels 23 and the vent apertures 24 . at a distance removed from the psm traveling plane by the rise of a cell tooth , the air / solution interface area is sufficiently small to be reactively insignificant and of no disruption to the transverse solution flow . normally , atmospherically open vents 24 are preferred as providing immediate visual verification of roof purging and solution flow rate adjustment . certain processes and solutions , however , may be better controlled as shown by fig1 with a conduit 25 confined vent system that is controlled by a valve 26 . the valve 26 may also be automatically or remotely operated . once the cell is full as sensed by probes 61 and 62 , the valve 24 can be closed and the solution will be essentially protected from any further exposure to additional air . the dashed line 18 corner boundary of fig1 represents an outer housing enclosing the cell processing line having internal air temperature and circulation control . to maintain close temperature control over variables influencing the psm process , an integrated heat control system as schematically represented by fig1 may be used to keep the air surrounding the processing cell units 10 within a desirable range . within the enclosure 18 is a fan 70 driven by motor 71 to circulate internal enclosure 18 air across heating element 73 . a temperature sensing probe 74 is positioned within the enclosure 18 and connected to an a / d converter to provide digital signal data to the system data processing controller 80 corresponding to the temperature of the air surrounding the cells 10 . responsive to set - point comparisons , the data processing controller 80 emits motor and heater operating commands to a power controller 82 . as an additional subsystem to the overall temperature control , each lower plate 30 is temperature regulated by means illustrated with fig1 and 19 . the underside of the lower plate 30 is recessed 90 to receive an electric heating pad 92 . more deeply recessed into the lower plate 30 structure is a bedding channel 94 for a temperature sensing probe 96 and signal carrier wire . an insulating cover plate 93 is secured in place by a flange plate 95 . fasteners not shown , located through and around the flange plate perimeter are threaded into the bottom cell plate 30 to unitize the assembly . a / d converter 97 transmits corresponding temperature data in a form compatible with the data process controller 80 for set - point comparison . responsive to signals from the power controller 99 , resistance elements within the pad 92 are energized to conductively heat the structure of cell bottom plate 30 . if required or desired , the same cell plate temperature control system described above with respect to bottom plate 30 may also be implemented with respect to top plate 20 with due consideration given to the structural complication presented by the riser channels 23 and air vents 24 . process solution make - up flow is temperature regulated by means of a liquid bath system as shown by fig1 . a containment vessel 100 for a liquid medium suitable for heat storage such as water or ethylene glycol is provided with an internal medium circulation system which includes a pump 101 . motor controller 102 is actuated by signals from the data processing controller 80 . analog signals from a temperature sensing probe 103 are converted by an a / d converter 104 to corresponding digital data and transmitted to the data processing controller 80 for set - point comparison . responsively , controller 80 transmits a control signal to the heating element power controller 105 . immersed within the liquid volume contained by vessel 100 are heat exchange coils 110 respective to each solution make - up stream respective to developer , fixer and wash , for example , that is to be maintained at the set - point temperature of this bath . there may be several solution make - up temperature control baths respective to different solution make - up streams and set - point temperatures . these immersed heat exchange coils 110 are in conduit connection with respective solution make - up systems 41 that are regulated by the controller 50 to fig8 and meters 53 and valves 56 . those of skill in the art will recognize that controller 50 of fig8 may be the same as controller 80 of fig1 and 19 , it or both being a pre - programmed , digital microprocessor . nor is this to preclude the use of dedicated analog controllers for this purpose . one of the objects and advantages of the present invention in placing all of the process variables such as solution flow rate , level control and temperature under a single control logic is the capacity to coordinate solution flow to actual usage and the particular psm in process movement . at the extremely small cavity volumes corresponding to the psm travel opening and clearance taught hereby , the flow demand differential between an interval with no psm in transit and an interval with maximum psm caliper in transit may be considerable . additionally , normal maintenance procedures and cycles may be preprogrammed . for example , the controller or controllers may be programmed to terminate developer and fixer circulation at a certain time of day and to automatically flush the respective cell with water for a predetermined period of time . moreover , a developer or fixer solution circulation may be abruptly replaced by water circulation to that respective cell thereby displacing the developer in the cavity and service conduits as a plug flow without opening the cavity to the atmosphere . thereafter , water could be circulated through the developer cell during a non - service or non - attendance period . by repeating the plug flow displacement of water by the developer solution when required , the cell would never be allowed to dry out , or otherwise permit the entry of atmospheric air . fig1 through 16 represent a few of the numerous geometric permutations of the invention with respect to ridge and cell cavity shape . fig1 illustrates an upper cell plate 120 with rounded ridge lines 122 defining a sinusoidal cavity with transverse flow channels 121 therebetween . air vents 124 penetrate the upper reaches of the flow channels . rounded ridge lines 127 . with respect to the psm traveling direction , the upper and lower ridge lines 122 and 127 are vertically aligned with a 0 % offset . the fig1 embodiment of the invention illustrates top and bottom cell plates 130 and 135 , respectively , having a diamond shaped cavity volume formed by flow channels 131 and 136 between vertically aligned , top and bottom , symmetrical tooth , ridge lines 132 and 137 . the upper flow channel 131 is penetrated by air vents 134 . fig1 represents the symmetrical tooth geometry of the preferred embodiment in vertical alignment with a 0 % psm travel direction offset . fig1 illustrates a simplified form of the invention having only a tooth ridged bottom plate 145 matched to a flat roof 141 top plate 140 . fig1 represent the inverse of fig1 with asymmetrical tooth ridges 151 defining flow channels 152 transversely of the psm traveling direction aligned against a flat floor 156 of the bottom plate 155 . the invention embodiment of fig1 is particularly distinctive with a mesh 163 drawn across tooth ridges 166 in bottom plate 165 beneath a similar mesh 164 secured to the bottom of the flat roof 161 of a top plate 160 . this bottom mesh 163 is secured at the first tooth base and may or may not be secured at the mesh trailing and 168 . suitable materials for these mesh elements 163 and 164 include nylon , rayon , polyester , polypropylene and polyethylene . a mesh grid of 30 to 300 strands per inch is useful and a mesh of 50 to 200 strands per inch preferred . such strands may range from 0 . 030 mm to 0 . 250 mm in diameter although a strand diameter of 0 . 050 mm to 0 . 150 is preferred . solution flow through transverse channels 169 between the tooth ridges 166 and under the mesh 163 supports a complex , localized circulation and in some cases , a microturbulence within the mesh perforations to replenish the reactivity solution strength in direct contact with the psm emulsion surface . the upper mesh 164 provides improved surface transport characteristics for the psm which may otherwise adhere to the top surface . if laid loosely across the tooth ridges 166 , the mesh will find its own best proximity to the psm surface . if drawn tightly and secured at downstream point 168 the mesh surface elements may be given precisely controlled proximity to a psm of known thickness . obviously , the fig1 embodiment is preferentially used with 1 side psm . a 2 side psm processing cell may include an upper and lower asymmetric tooth ridge configuration as taught by fig2 with a mesh 163 drawn across both upper and lower tooth ridges . it should also be understood that the bottom mesh 163 may be secured at both the front and trailing ends but only loosely laid in between to allow some controlled , mid - span movement of the mesh .