1. Recent advances in ejector-enhanced vapor compression heat pump and refrigeration systems : a reviewSven Gruber, Klemen Rola, Danijela Urbancl, Darko Goričanec, 2024, original scientific article Abstract: The incorporation of ejectors into heat pump and refrigeration cycles has been the subject
of growing interest, largely due to their simple structure, high reliability, and cost-effectiveness. This
paper investigates the recent advancements in novel design concepts of ejector-enhanced vapor
compression heat pump and refrigeration cycles. An overview of novel single-stage and twostage compression cycles utilizing a single or multiple ejectors is provided. First, the system setup,
operational principles, description, and figures of the existing schemes are provided. Second, the
main results, such as the coefficient of performance (COP), volumetric heating capacity and exergy
destruction, are discussed. In conclusion, the paper presents a coherent summary of the current
developments, future prospects, and the current knowledge gap. A plethora of research is present
in developing theoretical systems with high efficiency. However, experimental tests for real-life
implementations are limited. This review aims to provide the reader with an overview of recent
theoretical and experimental studies.
Keywords: ejector, heat pump, refrigeration, vapor compression system, review
Published in DKUM: 03.09.2024; Views: 51; Downloads: 11
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2. Waste Lignocellulosic Biomass as a Source for Bioethanol ProductionKlemen Rola, Sven Gruber, Danijela Urbancl, Darko Goričanec, 2024, original scientific article Abstract: Synthetically produced biofuels play a critical role in the energy transition away from fossil fuels. Biofuels could effectively lower greenhouse gas (GHG) emissions and contribute to better air quality. One of these biofuels is bioethanol, which could act as a gasoline replacement. For this purpose, a simulation of bioethanol production through lignocellulosic biomass fermentation, focused on distillation, was carried out in simulation software Aspen Plus. Since the possibility of absolute ethanol production through distillation is limited by the ethanol–water azeotrope, pressure swing distillation (PSD) was used to obtain fuel-grade ethanol (EtOH) with a fraction of 99.60 wt.%. The flowsheet was optimised with NQ analysis, which is a simple optimisation method for distillation columns. We found that the PSD has the potential to concentrate the EtOH to a desired value, while simultaneously removing other unwanted impurities whose presence is a consequence of pretreatment and fermentation processes.
Keywords: bioethanol, distillation, lignocellulosic biomass, azeotrope, Aspen Plus
Published in DKUM: 14.08.2024; Views: 99; Downloads: 5
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3. Carbon-free heat production for high-temperature heating systemsSven Gruber, Klemen Rola, Danijela Urbancl, Darko Goričanec, 2023, original scientific article Abstract: The article presents a new carbon-free heat production technology for district heating, which consists of a combined heat and power generation fuel cell (FC CHP) with CO2 capture and a two-stage cascade high-temperature heat pump (TCHHP). The FC generates heat and electricity, the latter being used to drive the compressors of the TCHHP. During the winter period, the water temperature achieved can occasionally be too low, so it would be heated up with hydrogen gas boilers. The hydrogen would be produced by reforming natural gas, synthetic methane, or biogas. The results are presented with natural gas utilization—the ratio between the obtained heat flow transferred directly to the water for district heating and the input heat flow of natural gas. In the case of a return water temperature of 60 °C and district heating temperature of 85 °C, the TCHHP, whose heat source is groundwater, achieves plant efficiency of 270.04% in relation to the higher heating value (HHV) and 241.74% in relation to the lower heating value (LHV) of natural gas. A case with a TCHHP whose heat source is low-temperature geothermal water achieves a plant efficiency of 361.36% in relation to the HHV and 323.49% in relation to the LHV.
Keywords: carbon-free, decarbonization of district heating systems, fuell cell, high-temperature district heating, high-temperature heat pump
Published in DKUM: 10.05.2024; Views: 233; Downloads: 17
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4. Utilisation of renewable electricity to produce synthetic methaneKlemen Rola, Sven Gruber, Danijela Urbancl, Darko Goričanec, 2023, original scientific article Keywords: power-to-methane, P2M, synthetic methane, CO2 methanation, Aspen Plus, Aspen Adsorption
Published in DKUM: 18.04.2024; Views: 203; Downloads: 13
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5. Inovativen energetski sistem uporabe obnovljivih virov energije za visokotemperaturno ogrevanje : magistrsko deloSven Gruber, 2023, master's thesis Abstract: V zaključnem delu smo zasnovali novo procesno shemo sistema visokotemperaturnega daljinskega ogrevanja katerega cilj je učinkovito ter ogljično nevtralno delovanje.
Sistem je sestavljen iz gorivne celice vezane z dvostopenjsko kompresijsko toplotno črpalko. Gorivne celice so naprave za pretvorbo energije, ki proizvajajo elektriko (in toploto) neposredno iz plinastega goriva z elektrokemično kombinacijo goriva in oksidanta. V našem sistemu je gorivo zemeljski plin. Proizvedena elektrika iz gorivne celice samo zadostno oskrbuje toplotne črpalke ter hkrati proizvaja toploto, ki le te razbremenjuje.
Skonstruirali smo osnovno shemo in dve dodatni alternativi, z dodanim vmesnim prenosnikom in zaporedno vezanimi toplotnimi črpalkami in jih primerjali pri različnih pogojih. V primeru temperature povratka 60 °C in končni temperaturi ogrevanja 80 °C osnovna shema z vmesnim prenosnikom toplote obratujeta pri COP vrednostih 3,15 oz. 3,21. Najvišje vrednosti COP smo zasledili pri zadnji alternativi in sicer 3,86, vendar ta ni samo zadostna in tako nastanejo dodatni stroški nakupa elektrike. Konkurenčnost in inovativnost sistema ne moremo meriti le s COP vrednostjo. Najboljši rezultat dobimo z 'izkoristkom' zemeljskega plina. Omenimo, da ne gre za navaden izkoristek, ampak utilizacijo - razmerje med dobljenim toplotnim tokom, ki se neposredno prenese na ogrevano vodo in vloženim toplotnim tokom zemeljskega plina na podlagi HHV in LHV. V osnovni shemi in z vmesnim prenosnikom dosežemo 251,62 % oz. 261,37 % glede na HHV ter 225,21 % oz. 233,99 % glede na LHV. Alternativa z zaporedno vezanimi toplotnimi črpalkami dosega 277,41 % glede na HHV in 247,38 % glede na LHV, vendar ni samo zadostna.
Keywords: Visokotemperaturna toplotna črpalka, gorivna celica, SOFC, visokotemperaturno daljinsko ogrevanje, razogljičenje sistema daljinskega ogrevanja
Published in DKUM: 14.09.2023; Views: 618; Downloads: 0
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6. Računalniška simulacija subkritičnih in transkritičnih toplotnih črpalk : diplomsko delo univerzitetnega študijskega programa I. stopnjeSven Gruber, 2021, undergraduate thesis Abstract: Toplotne črpalke so naprave, ki izrabljajo nizkotemperaturne vire za visokotemperaturno gretje, navadno sanitarne vode. V diplomskem delu smo s pomočjo računalniškega paketa Aspen Plus V10 primerjali subkritične in transkritične toplotne črpalke s štirimi različnimi naravnimi hladilnimi sredstvi: ogljikov dioksid, amonijak, propan in izobutan. Simulacije so bile izvedene pri izstopnih temperaturah hladilnega sredstva iz kondenzatorja oz. plinskega hladilnika med 15 °C in 30 °C in temperaturah uparjanja od -30 °C do 10 °C. Za cilj smo si zastavili gretje konstantnega toka vode na temperaturo med 40 °C in 60 °C, s koraki po 10 °C.
Namen diplomske naloge je bil poiskati najučinkovitejše naravno hladilno sredstvo, ki bi predstavljalo ekonomsko ugodno rešitev in hkrati okolju prijazno alternativo trenutno uporabljenim toksičnim in okolju škodljivim hladilnim sredstvom.
Najvišje vrednosti COP smo zasledili pri temperaturi uparjanja 10 °C, temperaturi hladilnega sredstva po kondenzaciji 15 °C in najnižji tarčni izstopni temperaturi vode 40 °C. V transkritičnem ciklu je najučinkovitejše hladilno sredstvo ogljikov dioksid, v subkritičnem se pa je amonijak izkazal boljše od ostalih. Slednji je skupno boljši od transkritičnega ogljikovega dioksida, vendar ima določene slabe lastnosti kot so toksičnost v višjih koncentracijah, vnetljivost in nekompatibilnost z bakrom.
Keywords: toplotne črpalke, subkritičen cikel, transkritičen cikel, COP, naravna hladilna sredstva
Published in DKUM: 08.09.2021; Views: 941; Downloads: 112
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