LG-e
VDI Heat Atlas eReference 11th edition
Absolute roughness K in mm for various materials
|
Drawn glass, lead, copper and brass tubes |
|
0 – 0.0015 |
|
Drawn steel tubes |
New Cleaned after long service Moderately rusted or slightly fouled Heavily fouled |
0.04 (0.02 – 0.1) 0.15 – 0.20 ≤ 0.40
≤ 3.0 |
|
Galvanized sheet steel Galvanized steel tubes |
Smooth (air ducts) Normally galvanized |
0.07 0.15 |
|
Welded steel pipes |
New New bituminized Used, cleaned Uniformly rusted Slightly fouled Heavily fouled |
0.05 (up to 0.1) 0.05 0.15 – 0.20 ≤ 0.40 1 – 1.5 2 – 4 |
|
Riveted steel pipe |
|
0.9 (0.5 – 10) |
|
Cast iron pipes |
New New bituminized Slightly rusted Fouled |
0.26 (up to 1) 0.10 – 0.15 1.0 – 1.5 1.4 – 4.0 |
|
Concrete conduits |
Smooth finish Rough |
0.3 (up to 0.8) 1.2 (up to 3) |
|
Fibrous concrete pipes |
(Eternit; Toschi) |
0.05 –0.1 |
|
Wooden boards |
Unplaned Planed |
0.7 0.2 |
|
Brickwork |
Normal bonds |
1.3 |
|
Plastic tubes |
|
≤ 0.0015 |
The so-called homogeneous model is based on the idea that vapor and liquid phase are evenly distributed over the pipe cross-section and flow at the same velocity (without slip). Although bubble or fog flow comes closest to this idea, some model variants are also successfully used for other flow forms.
The heterogeneous model is based on the idea that vapor and liquid phase flow at different velocities through different cross-sectional parts of the pipe. The interaction between the phases is not considered separately in most model variants, but is included in the adjusted coefficients of the correlations.
For the frictional pressure loss, the VDI Heat Atlas proposes model-based approaches for flows according to the homogeneous or heterogeneous model as well as an empirical approach according to Müller-Steinhagen and Heck. The aim of the authors was to create a much easier to handle and yet well-founded calculation rule compared to model-based approaches, which are often difficult to implement. Despite the actually very simple structure, this correlation, which is still widely used today, always shows very good agreement even with newer experimental data.