Dead space

The dead space (also dead space or dead space ) is an undesirable volume within fittings or equipment containing a medium.

Fluid energy machines

The dead space in fluid energy machines is the volume in the cylinder of a piston machine (e.g. compressor ) between the cylinder head or cover and the piston at dead center .

The gases in the dead space reduce the possible efficiency of a working machine , since gases compressed in the cylinder head first expand before new gas mass can be sucked in. There it has the effect of damaging the mass flow and reduces the efficiency , but not with pumps for liquids (since these are approximately incompressible).

The dead space can be determined by the given geometric and technical conditions. When using a piston engine that requires high compression, this can be so limited by the dead space that a technologically less favorable combustion chamber shape has to be selected, for example in the case of a diesel engine . With compressors, the effective dead space is reduced by the multi-stage technology.

Due to their design, Stirling engines have a large dead space, therefore low compression, and need a high mean operating pressure with high power density.

In steam locomotives with cylinders that are not horizontally but upright or inclined, the spring travel also creates harmful space, since the cylinders are attached to the vehicle frame, but the connecting rods are attached to the crank pins of the drive wheels.

Fittings

In the case of shut-off valves , for example, the space between the ball and the housing of a ball valve is referred to as dead space, into which fluid penetrates when the valve is closed and which is trapped there when the valve is fully open.

literature

• Wolfgang Kalide: Pistons and flow machines. 1st edition, Carl Hanser Verlag, Munich Vienna, 1974, ISBN 3-446-11752-0