Scale-model experiments

This chapter covers a description of conventional measurement techniques used in ventilation as well as othei related topics such as flow visualization, laser- based measurement techniques, and scale model experiments. 

Scaling laws If a full-scale test is not possible, reduced-scale experiments are a good alternative. However, certain scaling laws must be observed (see Section 12.4, Scale model experiments ). Correct scaling for isothermal flows is usually possible. However, scaling of buoyant flows in large rooms may be difficult, if not impossible. Then numerical simulation is the better choice. 

Scale model experiments (.Section 12.4) In the case where there is no site to carry out full-scale measurements (planning phase), or it would be too expensive or space-demanding to construct a full-scale experiment (large lacdities/rooms/buildings). 

In case experiments have been selected, the next step is to decide on the method visualization, full-scale measurements, or scale model experiments. Some features of these are listed in Table 12.1. 

All three experimental approaches are presented in this chapter visualization of airflow and contaminant dispersion (Section 12.2), measurement techniques including laser-based-techniques (Section 12.3), and scale model experiments (Section 12.4). 

Scale-model experiments have been used to study a variety of ventilation problems as air movement in a room, air movement around a building, energy flow in a building, contaminant distribution at an operator s workplace, and smoke movement in a building on fire. The theory is discussed at a general level in the references. 

The general conditions for scale-model experiments with flow in a room are... 

Model experiments where free convection is the important part of the flow are expressed by the Grashof number instead of the Archimedes number, as in Eq. (12.61). The general conditions for scale-model experiments are the use of identical Grashof number, Gr, Prandtl number, Pr, and Schmidt number,, Sc, in the governing equations for the room and in the model. 

FIGURE 12.34 Scale-model experiment with natural ventilation of a school building. 

S, Mierzwinski. Scale model experiments. In Ventilation of Large Spaces in Buildings (eds, R Heiselberg, S. Murakami, C.-A. Roulet). Aalborg University, Aalborg, Denmark, I99S. 

P. V. Nielsen. Airflow in a world exposition pavilion studied by scale-model experiments and computational fluid dynamics. ASHRAE Transactions, 101(2), 1118-1126, 1995. 

Another alternative is to conduct a scale model experiment in a centrifuge in which g is now increased [13]. Modifying both p and g in the model can allow the preservation of more groups. Thus, scaling in fire is not complete, but it is still a powerful tool, and there are many ways to explore it. Illustrations will be given later of successful examples in scale modeling and correlations to specific fire phenomena. 

The third example is for a Canadian Laker in a canal with sloping sides (t3T>ical canal). These data are from Tothil s 1 48 scale model experiments. The measured Yb = 0.93m for the ship traveling at 6.98kt (14 = 3.59m/s). Ship and channel features are listed in Table 26.5. 

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