t/V = f(V) Method

Experimental method to determine the filter medium resistance and the cake permeability in a laboratory Nutsche Filter (BoFilTest) with the filter surface A. While a filter cake is formed under constant pressure Δp, the suspension concentration (kappa-factor) and the liquid viscosity ηL, the cumulative filtrate volume VL is recorded over time t. Then the curve t/VL over VL is plotted. It shows for nearly incompressible cake formation a straight line and the filter medium resistance Rm can be calculated from the intercept a. The specific cake permeability pc (or the specific cake resistance rc = 1/pc, respectively) are calculated from the slope b, as follows:

Generally, the specific cake resistance rc has values between 1011 and 1016 m–2; 1011 m–2 indicates extremely well filtering products (i.e. coarse salts, minerals) whereas 1016 m–2 characterizes very slowly filtering materials (bacteria, pigments).

Table Filter
Pan Filter
Tangled Fiber Fleece
Taylor Vortex

Under certain operating conditions in a coaxial dynamic crossflow filter annular vortices develop. They rotate as pairs against each other. If an axial velocity component is superimposed analogous to continuous filtration, then two continuously parallel and counter-rotating screw vortices evolve out of the individuals. This leads to an extremely complex velocity distribution.


Surface-active chemicals tend to gather on interfaces and thus to lower the interfacial tension. They mainly consist of a hydrophobic group (e.g. hydrocarbon chain with 10÷18 C atoms), or an acrylate group, and a hydrophilic group (e.g. -COOMe, -OSO3Me, SO3Me, NH2=NH). According to the polarity of the ionic group one can differentiate between anionic, cationic and non-ionic tensides. Problems are often posed in industrial applications by their limited biological decomposition as well as by a tendency to foam.

Tension Roller

Deflection roller for the filter cloth in belt filters, press filter automats or double belt presses, with an adjustment for tightening of the circulating filter medium.

Thermal Convection

Flows in a liquid caused by density differences in turn due to temperature gradients. Next to Brownian motion, they are the main reason why individual particles with a diameter of less than approximately 1 μm cannot settle out in the earth’s gravitational field.

Thermal Fixation

pre-treatment of synthetic fiber weaves, generally with hot air, to condition the cloth for dimensional stability during operation.

Gravity Thickener

denotes increasing the solids concentration of a diluted suspension to produce a still free-flowing sludge. The thickening represents a typical pretreatment process in solid-liquid separation, most of the time followed by a further demoisturing of the sludge with suitable equipment. Thereby the generally high-grade equipment downstream is no longer burdened with large volumes or streams of liquid. Both settling and filtering processes can be utilized for the thickening, i.e. sedimentation through gravity or centrifugal forces as well as cake filtration, crossflow filtration, and the deep bed filtration with regenerating beds.

Thickening Filter

works either discontinuously or continuously to produce a highly concentrated, still free-flowing sludge instead of discharging only a demoistured filter cake. They can be operated on the basis of cake filtration, crossflow filtration, or deep bed filtration. Generally, the thickened sludge has to be further demoistured in a machine especially designed for that purpose. The thickening filter represents an alternative to sedimentation through gravity or centrifugal forces.

Thin Layer Filtration
Sieve Filtration

Non-Newtonian flow behavior. With increasing duration of the acting shear forces the viscosity of the liquid decreases.

Three-Column Centrifuge

Batch operated filter centrifuge with perforated filter or solid bowl, a vertical ro-tational axis, and mounted on three spring-dampened legs for vibration absorption. The centrifuge drum itself is rigidly mounted in the spring-suspended housing. A ty-pical example for a three-column centrifuge is a peeler centrifuge. Three co-lumn centrifuges operate in the range of low 100 up to several 1,000 rpm and are furnished with approx. 0.5 up to 2 m drum diameter. They are well suited for smaller batches of frequently changing products, as often required in the chemical industry, because they are accessible and easy to clean.

Three Phase Boundary

Linear contact formed by three different phases with a physical interface between each other, e.g. solid/liquid/gas, solid/liquid/liquid or liquid/liquid/gas.

Three Phase Decanter

Decanter, i.e. a solid-bowl centrifuge, which aside from solid separation can also separate two immiscible liquids. The liquids separate from each other due to their density difference into layers that are coaxially stacked around the rotational axis of the decanter, and are removed out of the process chamber by dedicated discharge devices such as peeling discs. The applications for such machines are found, for example, in oil-saturated waste- water, or in the processing of vegetable oil.

Three Phase Filter Revamping

A special program developed by the BOKELA company for revamping of filter plants in three steps including the diagnostic step (step 1) i.e. determination of the optimization potential, the engineering step (step 2) i.e. an engineering study to verify the mechanical design of the changes, cost and time required for implementation as well as to verify the process improvements that will be achieved and the realisation step (step 3) i.e fabrication of new parts, installation of new equipment/parts and finally commissioning of the modified filter.

Three Phase Separation

A process to separate solid particles from two molecularly non-mixable liquids due to differences between their spec. weight. Such processes can be realized in the earth field but much more efficient in a centrifugal field three phase decanter.


Quantity based on mass or volume which is able to pass through a separation apparatus per time unit. The throughput can be related to the amount of suspension fed, or the filtrate or solids flows produced, respectively. Both moist and dry solids can be meant in the case of solids throughput. If a specific throughput is stated, then this value refers in addition to the employed filter area. For example the specific throughput of rotary filters is quoted in [kg/m2h].

Tilting Pan Filter

Quasi-continuously working vacuum filter of an older design made with individual suction box arranged horizontally in a circle around a central control valve. The suction boxes are further turned stepwise according to a time-controlled program. Following the last demoisturing step they are tilted and the cake drops out of the filter cell.

Titer Reduction
Bacteria Retaining Test
Titus Filter-Dryer
Filter Reactor
Titus Pneumatics
Peeling Pneumatics

is a term used in mechanics defined as the product of force and lever arm which is the perpendicular distance from the axis to the line of action of the force acting on a revolving rigid object.

Total Separation Degree

Θ measures the solids mG, separated out of a suspension, in relation to the solids amount in the feed mA:


indicates the direction perpendicular to the surface of a membrane from the concentrate to the permeate side of the medium.


indicates the direction parallel to the surface of a membrane of a cylindrical filter module from the point of entry of the suspension to the exit of the concentrate.

Tray Belt Filter

also denoted as belt filter with reversing vacuum trays is a special design of the belt filter that features vacuum trays covered with a continuous filter medium. This design is more elaborate than a basic belt filter with a rubber conveyor, but it offers considerably more freedom in the selection of suitable filter media, and it operates like a continuous vacuum filter.

Tromp Curve
Fractional Grade Efficiency
Tubular Centrifuges

Cylindrical sedimentation centrifuge of distinct slenderness ratio. They are operated with over flow until the solids collection space is filled up with separated solids. Tubular Centrifuges are used for separating extremely fine particles out of highly diluted suspensions with C-values of several 10,000’s.

Tumbler Centrifuge

Continuously working self-transporting centrifuge with a conicall opening and a cantilevered sieve basket. The transport of solids through this discharge centrifuge is accomplished with a tumbling motion of the sieve basket around its rotating axis. The machine is designed in such a way that at normal rotations the solids remain in place by adhesive friction. The solids are forced to slide intermittently by the tumbling movement to manage the otherwise difficult to control solids transport in sliding centrifuges.

Turbid Filtration Phase

occurs at the very first moment of filter cake formation. It is caused by fine solids particles that are able to pass through the pores of the filter medium before a bridge layer is formed, which serves as a filter agent for the remaining suspension.

Turbid Substances
Turbid Filtration Phase
Turbulent Flow

sets in when the critical Reynold’s number is exceeded as minor flow fluctuations are no longer attenuated and random turbulences disturb the fluid movement. These are small liquid or gas eddies that move volume elements diagonally to the flow direction, so that the liquid or gas layers are being mixed.

Twill Lace

Special form of twill weave, at which warp and weft (weave) have different diameters. This makes the weave stronger; in addition the mesh width can be modified.

Twill Weave

Special form of thread weave in a weave. A weft thread is bound over respectively two or more warp threads or reverted (weft- respectively warp thread). The interlacing points rise in a twill weave in uninterrupted diagonals, forming the twill marks. Within the pattern repeat one or more weave marks can exist. In a satin weave the interlacing points do not contact each other, so that a smooth, surface without structure is formed. Twill weaves often have uneven sides, if warp and weft are not equally distributed on the upper-and underside of the cloth.

Two-Phase Flow

in solid-liquid separation technology means often a mixed flow of liquid and gas in a bulk. In contrast to tubular two–phase flows, these fluids move to a large extent independently from each other in the fine pore channels of particle bulks. Thus the liquid volume is assigned to the solids when the gas flow is evaluated, since the shear stress induced by the friction of the gas into the liquid is generally smaller by several orders of magnitude than the capillary pressure which retains the liquid.

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