Air bath jet tube 300
The IYPT problems are open-ended and enquiry-based. We are working to clarify how the special, breathtaking features of such problems have been coined.
Before 1994, the IYPT probelms were circulating mostly in Russian. In many cases, no “standard” English editions existed, and not all “standard” Russian editions have been yet found. When re-published or translated in the past, the problems suffered from omissions and inaccuracies, and many problems were even misattributed. This section presents the problems for the early IYPTs, as they are restored from all traced multilingual sources. After 1993, the problems already existed in unique, “standard” English versions, that have been almost continuously preserved up to now.
The committee for problem selection would need the early problems for “ a simple check of possible repeating of problems ”, as decided in 2007. The historical IYPT problems, however, are useful for a much wider, global audience. The problems have been repeatedly credited as source of ideas for laboratory tasks , thematic activities in schools , graduation research projects , or even everyday physics teaching .
In an aspirator, fluid (liquid or gaseous) flows through a tube that first narrows and then expands in cross-sectional area. When the tube narrows, the fluid pressure decreases. In this narrow area the fluid velocity must increase to conserve mass continuity. Where the tube narrows, a vacuum is drawn because of the Venturi effect.
If a liquid is used as the working fluid, the strength of the vacuum produced is limited by the vapor pressure of the liquid (for water, 3.2 kPa or 0.46 psi or 32 mbar at 25 °C or 77 °F ). If a gas is used, however, this restriction does not exist. The industrial steam ejector (also called the "steam jet ejector", "steam aspirator", or "steam jet aspirator") uses steam as a working fluid.
In order to avoid using too much steam, a single steam-ejector stage is generally not used to generate vacuum below approximately 10 kPa (75 mmHg ).  To generate higher vacuum, multiple stages are used; in a two-stage steam ejector , for example, the second stage provides vacuum for the waste steam output by the first stage. Condensers may be used between stages to reduce the load on the later stages. Steam ejectors with two, three, four, five and six stages may be used to produce vacuums down to 2.5 kPa , 300 Pa, 40 Pa, 4 Pa, and 0.4 Pa, respectively.