Laboratory Apparatus

Small scale equipment for simulating a solid-liquid separation process in the laboratory. Objective is to obtain data concerning the separation behavior of the suspension and the dimensioning of full-scale scale equipment. Since certain machine parameters of the envisioned large scale apparatus cannot be simulated in a laboratory apparatus, like a special stirring machine, testing with a so-called pilot plant is frequently conducted on semi-technical scale for proper plant dimensioning.

Lace Weave

Weave in linen or twill weave where the warp and weft threads, crossing at right angles, have different diameters.

Lambda Value

The term lambda value λ is used in the modeling of the demoisturing of filter cakes in the centrifugal field. It is defined as a dimensionless kinetic parameter taking into account the cake thickness hc, the liquid viscosity ηL, the liquid density ρL, the centrifugal value (C-value), the earth‘s acceleration g, the mean hydraulic radius (hydraulic diameter) of the cake pores rh and the demoisturing time t2:

Lamella Clarifier

Apparatus for gravitational sedimentation. The clarifying area is increased with tilted, parallel plates separated by only a small distance of several mm up to a few cm between each other. The gap width determines the sedimentation path of the particles on the plate beneath it. The clarified liquid rises over special rising channels and exits on the upper side of the apparatus. If a lamella clarifier is applied as a thickener, a sludge collecting space beneath the plate assembly is required with sufficient height for the formation of a compression layer. Lamella clarifiers can be operated in co-current flow (particle and liquid) or in counter-current flow. In addition, they can be employed in special designs for the separation of a second liquid phase (e.g. oil and water).

Laminar Flow

A laminar flow is defined as the movement of a liquid or a gas, where individual volume elements move past each other without mixing. This flow type is stable only up to a certain Reynolds number. In the laminar flow of particles in sedimentation for example the particle Re number is made up of its settling velocity w, the particle diameter x, the liquid’s density ρL and dynamic viscosity η as follows:

If this value is < 0.2, which is the so-called Stokes’ region, the flow is laminar.


The Laplace-equation describes the capillary pressure pc of a system consisting of two non miscible fluid phases (at least one liquid) by linkage of the interfacial tension of the liquid γL, and both main curvature radiuses of the liquid surfaces R1 and R2:

For a cylindrical capillary with the radius r and the contact angle δ resultsthe following:

Layer Thickness

Thickness of a bulk formed in a separation apparatus. This can be either a filter cake or a sediment.

Leaching Out
Leading Edge

The leading edge of filter cells at rotary filters in the direction of the rotation, characterized by the fact that it has the shortest cake formation time, i.e. the cake thickness there is at its lowest value. If the filter cells are not too wide this effect is not significant. At disc filters with relatively few cells, however, the zone of the leading edge, that is close to the cell foot, can cause a problem during the demoisturing as more than 50 % of the total amount of air can penetrate this extremely small filter area.

Leaf Filter

Collective name for discontinuously working, cake forming overpressure filters with leaf shaped, sequentially arranged filter elements with up to several square meters of filter area. The filter leafs are made out of several layers of wire cloth. The outer layer is a closely meshed, woven filter cloth, the middle layer a coarse weave, in order to drain the filtrate. Leaf filters are usually operated with pressures of up to 6 bar and used in the separation of difficult to filter suspensions. The solids discharge can be carried out either as an extremely thickened suspension or a filter cake breaking in lumps. Leaf filters are also being operated as fine filters with precoat as well as deep bed filters. A well-known example for a leaf filter is the so-called Niagara filter.

Leakage Air
Secondary Air
Leaving Filter Belt

A filter cloth for the discharge of a filter cake from a drum filter that is guided away from the drum around a small diameter spindle. The cloth returns to the drum via tension and deflection rollers. A running cloth is typically used for strongly adhesive and cloth contaminating filter cakes, as the sharp deflection around the spindle breaks off the cake. The cloth can be washed subsequently on both sides with high-pressure nozzles before returning to the drum.

Level Controller

Sensor in vertical and horizontal discontinuous filter centrifuges for controlling of the filling process with suspensions. Generally, the level controller employs a water ski-like sensor, that is mounted on a pivot and that glides on the surface of the rotating drum while pressed on by a spring. The pivoting caused by the increase in fill height can be measured by an electronic position sensor and utilized for the regulation of the filling valve. Objective is to avoid overfilling of filter drum. At some variants the basic level indicator is combined with a thermal sensor capable of registering differences in frictional heats between suspension and solids, respectively, and thus it is able to indicate when the demoisturing step of the cake begins.

Light Weight Segment

Specially designed filter segment by the BOKELA company for the BoVac Disc filters. The weight reduction of the disc filter segments makes maintenance work easier especially at large diameter disc filters. Compared to a standard filter segment the light weight segment has even a better rigidity.

Linen Weave
Plain Weave
Liquid Bridge
Interstitial Liquid
Liquid-Liquid-Solid Separation
Three Phase Separation
Liquid Load

A measure for the liquid amount remaining in the solid bulk after separation. Generally, the load B is defined as the ratio of liquid mass mL and solid mass ms:

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