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This article describes a novel approach to generate increased turbulence levels in an incoming flow. It relies on a cost-effective and robust semi-active jet grid, equipped with flexible tubes as moving elements attached onto tube connections placed at the intersections of a fixed, regular grid. For the present study, these flexible tubes are oriented in counter-flow direction in a wind tunnel. Tube motion is governed by multiple interactions between the main flow and the jets exiting the tubes, resulting in chaotic velocity fluctuations and high turbulence intensities in the test section. After describing the structure of the turbulence generator, the turbulent properties of the airflow downstream of the grid in both passive and active modes are measured by hot-wire anemometry and compared with one another. When activating the turbulence generator, turbulence intensity, turbulent kinetic energy, and the Taylor Reynolds number are noticeably increased in comparison with the passive mode (corresponding to simple grid turbulence). Furthermore, the inertial subrange of the turbulent energy spectrum becomes wider and closely follows Kolmogorov's -5/3 law. These results show that the semi-active grid, in contrast to passive systems, is capable of producing high turbulence levels, even at low incoming flow velocity. Compared to alternatives based on actuators driven by servo-motors, the production and operation costs of the semi-active grid are very moderate and its robustness is much higher.

This article presents the principle of operation of an experimental indirect evaporative cooling system which applies liquid desiccant solution as a drying agent. This mobile system is going to be built for the investigation of the effects of different working parameters (e.g. regenerating temperature of the desiccant salt-solution, air flow rates, solution flow rates, droplet size and mixing path length, etc.) on the produced cooled and dehumidified air, as well as the effects of the initial hot-air parameters (temperature and humidity) on the effectiveness (cooling and dehumidification rate) of the system. In this paper the basic mechanisms of both the direct and indirect evaporative cooling systems are presented with their advantages and disadvantages. It is shown how the solar energy by means of solar collector(s) can be utilized as an energy source of the regeneration of the diluted desiccant solution. Besides the 3D drawing and the parts of the experimental cooler and air dryer system will be presented and explained.

Jelen tanulmányban a közel izotróp, homogén rács-turbulencia turbulens paramétereinek meghatározásra szolgáló összefüggéseket mutatjuk be. Szélcsatornákba beépített turbulencia generáló rácsokat alkalmaznak azért, hogy közel izotróp, homogén, elhaló turbulenciát hozzanak létre. Az ilyen áramlások segítségével olyan mérések végezhetők, amelyeknél elvárt követelmény a meghatározott turbulens paraméterekkel bíró áramlás. Ebből adódóan elsőként az így előállítható turbulencia feltérképezése szükséges. E célból az állandó hőmérsékletű légsebességmérő technikát alkalmaztuk. Az általunk fejlesztett aktív rács után az így kimért pillanatnyi sebesség-értékeket a MATLAB® programban írt script segítségével dolgoztuk fel. A script segítségével többek között a következő mennyiségeket határozhattuk meg: egy- és háromdimenziós turbulencia intenzitás, turbulens kinetikus energia, izotrópia-arány, integrál hosszskála, turbulens energiaspektrum, disszipációs ráta, Kolmogorov-skálák, Taylor-mikroskála, Turbulencia-Reynolds szám, Taylor-Reynolds-szám. Ezek kiszámítási módja mellett a fejlesztett aktív rács különböző beállításai esetén mért alapáramlás irányú energiaspektrumokat is bemutatjuk.

In this paper the principle of operation and preliminary laboratory measurements of a prototype of a high-efficiency electrical air heater unit is presented. Unlike conventional heaters, which apply Joule-heat formed by electrical resistance, the developed device uses thermoelectric modules for heating ambient air. Just like in case of resistance heaters, most of the heat is produced as a result of the internal ohmic resistance of the thermoelectric module (resistance heating), however, in case of appropriate air conditions our device is capable of transforming the latent heat of the air moisture into heat energy. In case of condensation mode, some of the moisture condensates on the cold side of the module while its latent heat is transferred to the hot side of the module where it heats the dried air. In this mode, the heating efficiency of the device (e.g., the ratio of the heat added to air and the consumed electricity) is over unity. Following the idea and basic equations of the operation of this device, the results of the laboratory measurements in a climate test chamber is presented.