Les je v krožnem biogospodarstvu prepoznan kot obetavna surovina, saj ima sposobnost skladiščenja ogljika, ki pa je pogojena z življenjsko dobo izdelka. Podaljšanje življenjske dobe lesa lahko ...dosežemo z ustrezno zaščito, pogosto z uporabo kemikalij, ki so lahko okolju in ljudem nevarne. Mineralizacija lesa s hidroksiapatitom predstavlja potencial za okolju prijazno zaščito lesa. Na primeru Plečnikove parkovne klopce, mineralizirane s hidroksiapatitom, sta bili izvedeni LCA in LCC analizi. Analiza LCA je temeljila na standardih EN ISO 14040 in EN ISO 14044, analiza LCC je bila prilagojena po vmesniku Evropske komisije za javna naročila. Pri primerjavi mineraliziranega lesa z življenjsko dobo 16 oz. 24 let z referenčnim (nemineraliziranim) lesom so rezultati pokazali, da je mineraliziran les z življenjsko dobo 24 let okolju najprijaznejša in hkrati najcenejša izbira. Največje negativne vplive na okolje je predstavljal mineraliziran les z življenjsko dobo 16 let, najdražja alternativa je bil referenčni les.
V prispevku smo s pomočjo sistema za avtomatizirano vrednotenje zlepljenosti (ABES) ugotavljali razvoj strižne trdnosti ribjega kleja pri lepljenju lesa. Uporabili smo bukov (Fagus sylvatica L.) ...furnir, ki smo ga lepili pri konstantnem tlaku 12 barov, medtem ko smo spreminjali temperaturo in čas stiskanja. Temperatura je znašala med 25 °C in 100 °C, z intervalom 25 °C, čas stiskanja pa od 1 minute do 60 minut. Dosežena maksimalna strižna trdnost je znašala okoli 10 N/mm2, dosegli smo jo pri vseh štirih proučevanih temperaturah stiskanja. Na podlagi rezultatov študije smo ugotovili, da strižna trdnost ribjega kleja pri različnih temperaturah segrevanja neenakomerno narašča. Pri višjih temperaturah segrevanja hitreje dosežemo maksimalne strižne trdnosti. Strižne trdnosti spoja lepila iz ribjega kleja smo ugotavljali tudi po standardih EN 204 in EN 205.
•The heat transfer coefficient (HTC) is improved with surface structuring.•The largest manufactured cavities were most successful at increasing the HTC.•The highest density of nucleation cavities ...resulted in the highest HTCs.•The onset of boiling, HTC and critical heat flux were not directly correlated.•The laser textured surfaces improved the HTC compared to the bare silicon surface.
Pool boiling experiments were performed using saturated double-distilled and degassed water on 10 × 10 mm silicon samples, which were (i) untreated; (ii) laser structured; or (iii) modified with etched artificial nucleation cavities. The etched silicon surfaces were fabricated with differently sized micro nucleation cavities (5–30 µm) and pitches (0.125–2 mm) to allow a comparative analysis of the fabricated surfaces. The heat transfer coefficient (HTC) comparative analysis conducted at the heat flux of 200 kW/m2 exhibits the highest enhancement of 244% during nucleate boiling on the silicon sample with etched nucleation cavities with a 30 µm diameter and a 0.125 mm pitch. The experimental results consistently show that HTC increases with decreasing the pitch and increasing the size of the nucleation cavities in the range of the experimental conditions. The superheat required for the onset of nucleate boiling and the critical heat flux were not substantially affected with the structured surfaces. However, the boiling phenomena propagates more promptly to the entire available silicon surface, when the sample is laser treated or etched compared to the reference bare silicon sample.
•Boiling on functionalized steel foils was investigated by high-speed IR imaging.•Wall-temperature distributions were calculated at various heat fluxes.•Distributions’ parameters revealed important ...differences in boiling performance.•Surface with microcavities provided the lowest standard deviation of wall superheat.•Compared to coatings, laser texturing didn’t increase heaters’ thermal resistance.
Nucleate boiling was examined on Joule heated stainless steel foils, functionalized by PDMS-silica coating and/or nanosecond-laser texturing. The nucleating bubbles and transient temperature fields were visualized through high-speed IR and video recordings. The differences in boiling performance were evaluated through wall-temperature distributions. Results confirmed that smooth surfaces require high activation temperatures and produce larger bubbles, while wall-temperature distributions display higher standard deviations, higher local superheats, and bimodal shapes. Similarly, relatively high activation temperatures were observed on the superhydrophilic surface, where the enhanced liquid replenishment on the active nucleation sites reduces the bubble departure diameters and prevents formation of local hotspots. Consequently, the analyzed temperature distributions have negative skewness and decreased standard deviation. The highest heat transfer coefficient was achieved on a laser textured surface with non-uniform wettability and multi-scale microcavities. Here, nucleation site density was as high as 200cm−2 at 300kW/m2, while wall-temperature distributions demonstrated by far the lowest standard deviation. The temperature distributions also proved that annealed PDMS-silica coating significantly increased the thermal resistance of the entire heater. On the contrary, laser textured surfaces provided an even better boiling performance compared to coated surfaces and did not increase heater’s thermal resistance. This additionally endorses the coating-free, direct laser texturing method as a cutting-edge technology in the development of surfaces capable of significantly enhanced boiling heat transfer.
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