Ludger Fischer

Friction factors for fully developed laminar flow in ducts confined by corrugated parallel walls

Abstract Straight ducts of constant cross-section with sinusoidally curved walls may be found in plate heat exchangers as well as in packing structures used in mass transfer operations or in catalytic reactors. Frictional pressure drop, in the case of fully developed laminar flow, depends on the shape of the cross-section. It is characterized by a generalized form of Poiseuilles law: (ξ · Re) = K. Two types of cross-section formed by two parallel sinusoidally corrugated walls, with the amplitude a , the wave length A and the distance 2 a are regarded. The two sine walls may be either phase shifted by Π, so that the walls touch each other and form an arbitrary number of equal tubelike ducts, or they may be in phase, so that the duct is similar to the one formed by two parallel planes. In both limits the values of K were numerically calculated for a number of aspect ratios 2 a / A . The whole range of aspect ratios has been covered by fitting polynomials in order to allow for interpolation of the calculated values.

Characterization of High-Performance Structured Packing

Column packings applicable to the field of rectification are mainly characterized by their number of theoretical stages per meter NTSM (m –1 ), specific pressure drop per height Δ p (mbarm –1 or Pam –1 ), and capacity limits. A set of dimensionless numbers are derived by means of a simple model of dry gas flow within parallel plates (slit flow). Those numbers are dimensionless and able to describe measured values from various packing types and their recent improved performance only taking into account the specific surface. These numbers describe pressure drop, capacity and surface efficiency. Furthermore an approach is presented where the most important criteria describing packing performance are combined into one characteristic number to find a description within only one diagram. Examples of values from different packing types are presented. The recent developments of the ‘high-performance’ packings are included. Plotting these values allow extrapolation to ‘expected’ new packing types.

Shape factors for conductive heat flow in circular and quadratic cross-sections

Abstract The two-dimensional steady heat flow in bodies with different cross-sections and isothermal boundaries is a problem that has been investigated intensively in the literature. For the cross-section of two concentric circles the analytical solution of the shape factor as a function of the ratio of the outer diameter to the inner diameter is well known and can be found in most textbooks on heat transfer. For some simple well defined geometries it is possible to calculate the shape factor by the method of conformal mapping. But for arbitrarily shaped cross-sections numerical methods or correlations fitted to measured or calculated values have to be used. We applied the Method of Finite Elements and the Method of Finite Differences to calculate shape factors for cross-sections bounded by concentric circles and squares. By developing the shape factor for the investigated cross-sections analytical approximations for the shape factor are obtained. The approximations fulfil limiting cases and are close to the exact solutions when being fitted to the numerical values.

Storage of Heat, Cold and Electricity.

A promising energy storage system is presented based on the combination of a heat pump, a heat engine, a hot and a cold storage. It can be operated as a pure bulk electricity storage (alternative to Pumped Heat Electrical Storage (PHES)/Compressed Air Energy Storage (CAES)) or as combined storage of heat, cold and electricity. Both variations have been evaluated using a steady state, thermodynamic model and two promising concepts are proposed: A transcritical CO(2) cycle for the pure electricity storage and a subcritical NH(3) cycle for combined storage of electricity, heat and cold. Parametric studies are used to evaluate the influence of different parameters on the roundtrip efficiency of the storage system.