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Wind tunnel for studies of latent heat storage
Tesař, Václav
When a heated solid body temperature reaches the melting point, temperature stops increasing and remains constant until the whole body is completely molten. The heat input during this melting is spent on freeing the body molecules. This latent heat of melting remains inside the body and may be released when the body is cooled and solidifies. This heat was suggested, already several decades ago, for storing thermal energy. The advantage it offers is avoiding high temperature differences - which otherwise decrease effectiveness of storage (by inevitable heat escape by conduction). Also the mass of the body needed to store a given amount of heat is much smaller. For investigations of the melting and solidification processes a special wind tunnel has been designed and is being built in this study. The tested sample of phase change material, encapsulated in a spherical shell, will be exposed in the tunnel to recirculating hot air flow in a 140 mm x 140 mm test section. Sudden decrease in air flow temperature is made by shifting away the whole closed-circuit part of the tunnel and exposing the test section to flow of cold (room temperature) air.
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Recent advances in characterisation of subsonic axisymmetric nozzles
Tesař, Václav
Nozzles are devices generating jets. They are widely used in fluidics and also increasingly often in active control of flows past bodies. Being practically always a component of larger system, design and optimisation needs nozzle properties characterisation by an invariant quantity. Perhaps surprisingly, no suitableinvariant has been so far introduced. This article surveys approaches to characterisation quantities and presents several examples of their typical use such as parallel operation of two nozzles, matching a nozzle to its fluid supply source, apparent resistance increase in flows with pulsation, and the secondary invariants of a family of quasi-similar nozzles.
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