Original scientific paper A new geometric form of fins (needle fins) for finned heat exchangers of gas-liquid type is described. It achieves a higher heat transfer coefficient and lower mass of the heat exchange surface relative to the heat exchangers with circular fins which in this case served as a basis for comparison. For the analysis of the heat transfer, the computational fluid dynamics analysis with ANSYS Fluent software was applied. Numerical simulation was performed for the round fins and fins with a new, innovative geometric shape at air flow speeds of 1 m/s to 5 m/s. The results of numerical simulations, with regard to the exchanged heat and pressure drop were verified by the correlations available in the literature and compared to the simulation results for tubes with innovative fins. Results show an increase in the amount of Nu from 20 % to 30 % for 2300 >Re > 12000 while reducing mass of heat exchange surfaces of 23,8 %.Keywords: finned heat exchanger; heat exchange; heat exchanger efficiency; needle fins; numerical simulation Razvoj novog tipa lamelnog izmjenjivača toplineIzvorni znanstveni članak Opisan je novi geometrijski oblik lamele (igličaste lamele) za orebrene cijevne izmjenjivače topline plin -tekućina pomoću kojeg se postiže veći koeficijent prijelaza topline, a time i manja masa izmjenjivačkih površina u odnosu na izmjenjivače topline s okruglim lamelama koji su u ovom slučaju poslužili kao baza za usporedbu. Za analizu izmjene topline i pada tlaka primijenjena je računalna dinamika fluida s programom ANSYS Fluent. Numerička simulacija provedena je za slučaj zagrijavanja zraka koji struji oko cijevi s lamelama novog geometrijskog oblika te oko cijevi s lamelama konvencionalnog kružnog oblika brzinama od 1 m/s do 5 m/s. Rezultati numeričke simulacije obzirom na izmijenjenu toplinu i pad tlaka za cijevi s okruglim lamelama provjereni su pomoću korelacija dostupnih u literaturi te su uspoređeni s rezultatima simulacije za cijevi s inovativnim lamelama. Rezultati pokazuju povećanje iznosa Nu značajke od 20 % do 30 % za 2300 > Re > 12000 uz smanjenje mase izmjenjivačkih površina od 23,8 %.

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Today, there is a growing awareness of the need for environmental protection and a healthy ecological environment. Given the growing popularity of renewable energy sources, they should be familiar with their environmental impact. Each renewable energy source has more or less environmental impacts that are most often compared to the influence of conventional fuels on the environment. The aim of this article is to show the potential impacts of geothermal power plants on the environment both in the construction phase and in the phase of regular work. Environmental impacts may be temporary or irreversible and include changes in habitats and land use, atmospheric emissions, increased noise, impact on surface and groundwater, land subsidence, occurrence of seismicity and solid waste disposal. The magnitude of the influence depends on the characteristics of the geothermal source, the applied thermodynamic cycle, and the applied abatement systems.

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Abstract. The article compares the tube heat exchanger with annular fins with innovative star shaped fins. For the analysis of the heat transfer and pressure drop, the computational fluid dynamics analysis with ANSYS Fluent software was applied. Through the tubes flow the hot water and heat the cold air flowing around the fins and tubes. The validation of selected turbulence models (k-ω SST and k-ε Realizable) was performed by annular fins comparing with the results in the literature. The results of the numerical analysis for star shaped fins for 2200