Transition of laminar flow into turbulent flow and its consequences
|Type of article||TIP&TRICK|
|Source for translation||2022-06-27|
Depending on the Reynolds number, laminar or turbulent flow is assumed for calculation. The Re number depends, among other things, on the flow velocity and the kinematic viscosity of the fluid, which in turn depends on its temperature. According to DIN EN 1264-2/A1:2012-06, the nature of the flow affects the determination of the heat flux density. Therefore, the user may encounter problems when trying to regulate radiant systems in the interactive calculations window (For more information, see:Interactive calculations of radiant systems) and when verifying tables of results, ie.:
- Insufficient heating with smaller spacing and overheating with larger spacing - higher heat output of the heating surface attained with smaller spacing;
- Reducing the temperature difference between supply and return decreases the output of the heating/cooling surface (instead of increasing it);
- Switching the status of the auto/manual button for the temperature difference between supply and return, without changing its value, changes the output of the heating/cooling surface.
In the cases as given above, lower heating surface output is reached due to the laminar flow. The flow regime is indicated in the Flow (laminar / turbulent) column in the Interactive calculations of radiant systems window, where:
- T - means that the flow under the given conditions is turbulent;
- L - means that the flow under the given conditions is laminar.
Information about the flow regime is also displayed when the cursor is positioned over the heating-cooling surface label:
In order to increase output, the temperature difference between supply and return must be gradually changed to a temperature at which the flow is turbulent. This will be the limit at which there will be a spike in output due to a change in the regime of the flow from laminar to turbulent.