DESCRIPTION

Technical Description

Convection is one of the three basic types of heat transfer. The heat transport is substance-bound. In the convection process, the whole fluid is moving. So-called bulks of fluid move (and thus transfer heat) from warm zones into cold zones. The different temperatures lead to density differences in the fluid so that a flow develops. In the case of free convection, the density differences result in a rather slow flow of the fluid with a more intensive heat transfer. In the case of forced convection, the flow is generated by a fan or pump. In this case, the heat transfer to fluid particles is lower, but more heat is transported than with free convection due to the much larger mass flow.

The core element of the WL 352 experimental unit is a vertical duct into which a heating element is inserted. Air flows past the heating element and absorbs heat in the process. Three heating elements with different surfaces are available: a flat plate, a tube bundle or fins. For experiments on forced convection, an additional fan has to be activated.

Sensors record the flow velocity of the air, the heating power and the temperatures at all relevant points. The measured values can be read on digital displays. At the same time, the measured values can also be transmitted directly to a PC via USB. The data acquisition software is included.

The well-structured instructional material sets out the fundamentals and provides a step-by-step guide through the experiments.

Learning Objectives / Experiments

- free and forced convection
- heat transfer at different surfaces:
* flat plate
* pipe bundle
* fins
- temperature distribution in the heat exchanger
- determination of the Reynolds and Nusselt numbers
- calculation of heat transfer coefficient for free and
forced convection