Convective drying process is among the most energy-intensive ones; therefore, every kind of its improvement may result in a significant reduction of energy consumption, which contributes to sustainable energy planning. Intermittent drying, often accomplished by periodical temperature lowering and/or stopping the air flow completely, is one of the most popular measures for energy saving. Herein, intermittent regime was carried out only by temperature variation, keeping the heater turned on for 60 min, and then turned off for another 30 min, while the fan was turned on all the time. Temperature lowering in certain periods saves energy, but some extension of total drying time is also expected. The aim of the article was to explore the possibility of energy saving with no significant time extension and the influence of different effective diffusivities in that context. Hence, the drying materials with different properties were chosen-walnuts, chestnuts with and without shell, pumpkin, and potatoes. Drying of walnuts was described in more detail to briefly explain the basic idea of the analysis, whereas other materials were analyzed only in terms of energy saving. The research showed the noticeable effective diffusivity influence on energy saving, and only materials with its high value are suitable for such a treatment

Usled ekonomske situacije u Srbiji kotlovi starog tipa se koriste. Njihov tačan udeo na tržištu nije poznat. Ova konstrukcija je razvijena u 70-tim godinama, funkcioniše, jeftina je, ali ima nižu efikasnost i više emisije nego moderni kotlovi. Često se ovi kotlovi ugrađuju u zatvorene sisteme toplovodnog grejanja. To nije u skladu sa sigurnosnim pravilima iz standarda. Ovakva praksa može da dovode do eksplozija, ljudskih žrtava i materijalne štete. Slučajna anketa o načinu instaliranja kotlova na čvrsto gorivo je urađena. Ovaj rad pokušava da objasni razloge ove štetne prakse, kroz odgovaranje sledećih pitanja. Da li ISPRAVAN sigurnosni ventil može da spreči eksploziju kotla? Da li regulator promaje može da reguliše temperaturu potisa vode pri SVIM režimima? Da li je kotao bezbedan bez sistema za odvođenje VIŠKA toplote? Da li postoji SIGURNA instalacija kotla u prostorije u kojima nema vodovodne mreže? Koji tip kotla na čvrsto gorivo MOŽE biti ugrađen u zatvoren sistem grejanja?

Original scientific paper https://doi.org/10.2298/TSCI190120272D This research concerns the convective intermittent drying of in-shell walnuts, as well as the comparison between intermittent and continuous regimes. The collected data from the continuous drying experiment served as the basis for the modeling of intermittent drying, where the kinetic semi-theoretical model was implemented. Mathematical model for the intermittent drying precedes the computer simulation and experimental procedure for a single layer. As the validity of the proposed model is confirmed, deep fixed bed drying simulation was included as well. Intermittent drying regimes with shorter tempering periods gave better results compared to the longer ones. Deep bed simulations showed that a fixed bed of walnuts should not be bigger than 15-20 cm.

Prilikom donošenja odluka uobičajeno je da se uradi analiza koja će u obzir uzeti različite kriterijume. Pošto postoji nekoliko poznatih načina za sušenje oraha, postavlјa se pitanje koji od njih odabrati. U radu je obavljena analiza na osnovu kriterijuma različite vrste koji bi donosiocu odluke mogli da pomognu u donošenju odgovarajuće odluke. Analizirani su aspekti koji mogu da utiču na formiranje i odabir odgovarajućih kriterijuma, a analiza je sprovedena i na konkretnom primeru.

The paper presents the results of an experimental investigation of air pressure drop while flowing through wheat straw beds. According to Darcy?s law, the smaller the porosity of the bed is, the bigger the pressure drop will be. The investigation was conducted using three different porosities (or three bed densities), and for two different air flow rates. After determining porosity (which is directly measurable), the permeability of straw could be found. For high flow velocities, such as the velocity of air flowing through a straw bale, the Forchheimer equation becomes more relevant as a correction of Darcy?s law with inertial effects included. Otherwise, the permeability tensor depends only on the geometry of the porous medium. With permeability known, the Forchheimer equation coefficients can be easily estimated. These results may be important for the future development of efficient biomass combustion facilities. The measurement methods and facility characteristics are described in more detail.