Absorption cooling devices using LiBr and H2O as working media

U radu je prikazan povijesni razvoj apsorpcijskih rashladnih uređaja, od prvih eksperimenata u kojima je uočeno da neke kapljevine imaju sposobnost apsorpcije vodene pare i ostalih plinova pa sve do uređaja koji su doživjeli masovnu proizvodnju i postali temeljem za moderne apsorpcijske rashladne sustave. U teorijskom dijelu opisan je apsorpcijski rashladni proces te je dan proračun realnog apsorpcijskog rashladnog uređaja. Cilj rada bio je ispitati primjenjivost teorijskog modela za izračun termodinamičkih parametara binarne smjese LiBr/H2O uz konstantne koeficijente koje su predložili znanstvenici Dong – Seon Kim i Infante Ferreira. Izračunati parametri korišteni su za proračun apsorpcijskog rashladnog procesa u uvjetima rada solarnog rashladnog postrojenja namijenjenog hlađenju poslovne zgrade Vodovoda Dubrovnik. Putem sustava za daljinsko mjerenje tehničkih parametara instaliranog solarnog postrojenja prikupljeni su eksperimentalni podaci koji su zatim uspoređeni s računski dobivenim podacima na temelju čega je potvrđeno da model zadovoljavajuće opisuje realni sustav uz mala odstupanja koja su rezultat pretpostavke idealnog prijenosa topline.This paper contains a historical review of absorption cooling devices, starting from the first experiments revealing that some liquids are capable to absorb aqueous vapour and some other gases all through the mass producted devices that have become forerunners of many modern absorption systems. The paper also contains a theoretical review of absorption cooling process and a calculation of real absorption cooling device. The aim of this study was to test the theoretical model by calculating thermodynamic properties of binary mixture LiBr/H2O using the constant coefficients given by scientists Dong – Seon Kim and Infante Ferreira. Model based parameters were used for calculation of absorption cooling process in working conditions of the solar cooling plant which is installed for cooling of the business building of 'Vodovod Dubrovnik'. The technical parameters of solar cooling plant were collected by using the long distance measurement system. The experimental data was then compared to the data which was calculated using the model and the comparison has confirmed that the theoretical model can be applied in this case taking into account slight deviations which are result of ideal heat transfer assumption

The modelling of a real absorption cooling process powered by solar energy

Cilj rada bio je projektirati, dimenzionirati i matematički modelirati konkretan apsorpcijski rashladni uređaj koji kao radni medij koristi binarnu smjesu LiBr/voda. Proučavani uređaj instaliran je u sklopu solarnog rashladnog postrojenja u Dubrovniku namijenjenog hlađenju poslovne zgrade tvrtke Vodovod Dubrovnik. Potrebnu energiju za pokretanje apsorpcijskog rashladnog procesa uređaj dobiva putem polja solarnih kolektora površine 60 m^2, a za ublažavanje oscilacija Sunčevog zračenja i/ili oscilacija rashladne energije, u sustav su također ugrađeni spremnici vrele i hladne vode volumena 3 i 1 m^3. Za projektiranje i dimenzioniranje uređaja razvijen je matematički model u softverskom paketu ChemCAD te je validiran na nezavisnom skupu eksperimentalnih podataka iz literature. Model je nakon validacije korišten za određivanje površina izmjene topline te ukupnih koeficijenta prijelaza topline pojedinih procesnih jedinica unutar uređaja. Tako dobiveni podaci korišteni su zatim za razvoj matematičkog modela u softverskom paketu MATLAB koji je nakon validacije primijenjen za određivanje optimalnih radnih uvjeta uređaja pri kojima postiže nominalni rashladni učin od 17,5 kW. Na temelju razvijenih matematičkih modela provedene su analize osjetljivosti kojima je utvrđeno da na ostvareni rashladni učin i stupanj iskorištenja procesa najveći utjecaj imaju ulazne temperature vanjskih ogrjevnih i hladnih struja. Analizom je također utvrđeno da povišenje temperature na izlazu iz kondenzatora i apsorbera dovodi do smanjenja rashladnog učina i stupnja iskorištenja procesa, dok im povišenje temperature na izlazu iz isparivača pogoduje. Osim toga, efikasnost rada uređaja bit će veća što je viša izlazna temperatura jake otopine LiBr na izlazu iz generatora te što je veća efikasnost izmjenjivača topline.The aim of this paper was designing, dimensioning and mathematical modelling of a real absorption cooling device which uses binary mixture LiBr/water as working media. The studied device is installed as a part of the solar cooling plant in Dubrovnik in order to provide cooling for an office building of Vodovod Dubrovnik company. The energy needed for starting the absorption cooling process is provided through the solar field with total absorption area of 60 m^2. Besides that, 3 m^3 hot water tank and 1 m^3 chilled water tank are also embedded into the plant to reduct oscillations of Solar radiation and/or cooling capacity. In order to design and determine the dimensions of the device, a mathematical model was developed in ChemCAD software package and validated using an independent set of experimentally data from literature. After the validation, the model was used for the calculation of heat transfer area and coefficients of every process unit inside the device. This calculated data was then used during the MATLAB mathematical model development which was also validated and then used for determination of optimal working conditions of the device in order to achieve nominal cooling capacity of 17.5 kW. Sensitivity study was also done using the developed mathematical models. The results have shown that inlet temperatures of hot and cold utility streams have the main effect on the obtained cooling capacity and coefficient of performance of the system. Furthermore, it has also been found that temperature rise at the condenser and absorber outlet has negative effect on cooling capacity and coefficient of performance, while temperature rise at the evaporator outlet improves them. Besides that, higher temperature at the generator outlet and higher heat exchanger efficiency will also contribute to more efficient device operation

Absorption cooling devices using LiBr and H2O as working media

U radu je prikazan povijesni razvoj apsorpcijskih rashladnih uređaja, od prvih eksperimenata u kojima je uočeno da neke kapljevine imaju sposobnost apsorpcije vodene pare i ostalih plinova pa sve do uređaja koji su doživjeli masovnu proizvodnju i postali temeljem za moderne apsorpcijske rashladne sustave. U teorijskom dijelu opisan je apsorpcijski rashladni proces te je dan proračun realnog apsorpcijskog rashladnog uređaja. Cilj rada bio je ispitati primjenjivost teorijskog modela za izračun termodinamičkih parametara binarne smjese LiBr/H2O uz konstantne koeficijente koje su predložili znanstvenici Dong – Seon Kim i Infante Ferreira. Izračunati parametri korišteni su za proračun apsorpcijskog rashladnog procesa u uvjetima rada solarnog rashladnog postrojenja namijenjenog hlađenju poslovne zgrade Vodovoda Dubrovnik. Putem sustava za daljinsko mjerenje tehničkih parametara instaliranog solarnog postrojenja prikupljeni su eksperimentalni podaci koji su zatim uspoređeni s računski dobivenim podacima na temelju čega je potvrđeno da model zadovoljavajuće opisuje realni sustav uz mala odstupanja koja su rezultat pretpostavke idealnog prijenosa topline.This paper contains a historical review of absorption cooling devices, starting from the first experiments revealing that some liquids are capable to absorb aqueous vapour and some other gases all through the mass producted devices that have become forerunners of many modern absorption systems. The paper also contains a theoretical review of absorption cooling process and a calculation of real absorption cooling device. The aim of this study was to test the theoretical model by calculating thermodynamic properties of binary mixture LiBr/H2O using the constant coefficients given by scientists Dong – Seon Kim and Infante Ferreira. Model based parameters were used for calculation of absorption cooling process in working conditions of the solar cooling plant which is installed for cooling of the business building of 'Vodovod Dubrovnik'. The technical parameters of solar cooling plant were collected by using the long distance measurement system. The experimental data was then compared to the data which was calculated using the model and the comparison has confirmed that the theoretical model can be applied in this case taking into account slight deviations which are result of ideal heat transfer assumption

Absorption cooling devices using LiBr and H2O as working media

U radu je prikazan povijesni razvoj apsorpcijskih rashladnih uređaja, od prvih eksperimenata u kojima je uočeno da neke kapljevine imaju sposobnost apsorpcije vodene pare i ostalih plinova pa sve do uređaja koji su doživjeli masovnu proizvodnju i postali temeljem za moderne apsorpcijske rashladne sustave. U teorijskom dijelu opisan je apsorpcijski rashladni proces te je dan proračun realnog apsorpcijskog rashladnog uređaja. Cilj rada bio je ispitati primjenjivost teorijskog modela za izračun termodinamičkih parametara binarne smjese LiBr/H2O uz konstantne koeficijente koje su predložili znanstvenici Dong – Seon Kim i Infante Ferreira. Izračunati parametri korišteni su za proračun apsorpcijskog rashladnog procesa u uvjetima rada solarnog rashladnog postrojenja namijenjenog hlađenju poslovne zgrade Vodovoda Dubrovnik. Putem sustava za daljinsko mjerenje tehničkih parametara instaliranog solarnog postrojenja prikupljeni su eksperimentalni podaci koji su zatim uspoređeni s računski dobivenim podacima na temelju čega je potvrđeno da model zadovoljavajuće opisuje realni sustav uz mala odstupanja koja su rezultat pretpostavke idealnog prijenosa topline.This paper contains a historical review of absorption cooling devices, starting from the first experiments revealing that some liquids are capable to absorb aqueous vapour and some other gases all through the mass producted devices that have become forerunners of many modern absorption systems. The paper also contains a theoretical review of absorption cooling process and a calculation of real absorption cooling device. The aim of this study was to test the theoretical model by calculating thermodynamic properties of binary mixture LiBr/H2O using the constant coefficients given by scientists Dong – Seon Kim and Infante Ferreira. Model based parameters were used for calculation of absorption cooling process in working conditions of the solar cooling plant which is installed for cooling of the business building of 'Vodovod Dubrovnik'. The technical parameters of solar cooling plant were collected by using the long distance measurement system. The experimental data was then compared to the data which was calculated using the model and the comparison has confirmed that the theoretical model can be applied in this case taking into account slight deviations which are result of ideal heat transfer assumption

The modelling of a real absorption cooling process powered by solar energy

Cilj rada bio je projektirati, dimenzionirati i matematički modelirati konkretan apsorpcijski rashladni uređaj koji kao radni medij koristi binarnu smjesu LiBr/voda. Proučavani uređaj instaliran je u sklopu solarnog rashladnog postrojenja u Dubrovniku namijenjenog hlađenju poslovne zgrade tvrtke Vodovod Dubrovnik. Potrebnu energiju za pokretanje apsorpcijskog rashladnog procesa uređaj dobiva putem polja solarnih kolektora površine 60 m^2, a za ublažavanje oscilacija Sunčevog zračenja i/ili oscilacija rashladne energije, u sustav su također ugrađeni spremnici vrele i hladne vode volumena 3 i 1 m^3. Za projektiranje i dimenzioniranje uređaja razvijen je matematički model u softverskom paketu ChemCAD te je validiran na nezavisnom skupu eksperimentalnih podataka iz literature. Model je nakon validacije korišten za određivanje površina izmjene topline te ukupnih koeficijenta prijelaza topline pojedinih procesnih jedinica unutar uređaja. Tako dobiveni podaci korišteni su zatim za razvoj matematičkog modela u softverskom paketu MATLAB koji je nakon validacije primijenjen za određivanje optimalnih radnih uvjeta uređaja pri kojima postiže nominalni rashladni učin od 17,5 kW. Na temelju razvijenih matematičkih modela provedene su analize osjetljivosti kojima je utvrđeno da na ostvareni rashladni učin i stupanj iskorištenja procesa najveći utjecaj imaju ulazne temperature vanjskih ogrjevnih i hladnih struja. Analizom je također utvrđeno da povišenje temperature na izlazu iz kondenzatora i apsorbera dovodi do smanjenja rashladnog učina i stupnja iskorištenja procesa, dok im povišenje temperature na izlazu iz isparivača pogoduje. Osim toga, efikasnost rada uređaja bit će veća što je viša izlazna temperatura jake otopine LiBr na izlazu iz generatora te što je veća efikasnost izmjenjivača topline.The aim of this paper was designing, dimensioning and mathematical modelling of a real absorption cooling device which uses binary mixture LiBr/water as working media. The studied device is installed as a part of the solar cooling plant in Dubrovnik in order to provide cooling for an office building of Vodovod Dubrovnik company. The energy needed for starting the absorption cooling process is provided through the solar field with total absorption area of 60 m^2. Besides that, 3 m^3 hot water tank and 1 m^3 chilled water tank are also embedded into the plant to reduct oscillations of Solar radiation and/or cooling capacity. In order to design and determine the dimensions of the device, a mathematical model was developed in ChemCAD software package and validated using an independent set of experimentally data from literature. After the validation, the model was used for the calculation of heat transfer area and coefficients of every process unit inside the device. This calculated data was then used during the MATLAB mathematical model development which was also validated and then used for determination of optimal working conditions of the device in order to achieve nominal cooling capacity of 17.5 kW. Sensitivity study was also done using the developed mathematical models. The results have shown that inlet temperatures of hot and cold utility streams have the main effect on the obtained cooling capacity and coefficient of performance of the system. Furthermore, it has also been found that temperature rise at the condenser and absorber outlet has negative effect on cooling capacity and coefficient of performance, while temperature rise at the evaporator outlet improves them. Besides that, higher temperature at the generator outlet and higher heat exchanger efficiency will also contribute to more efficient device operation

Phase Separation in La0.5Sr0.5MnO3 System

Perovskiti su tema brojnih znanstvenih istraživanja zbog svojih primjenskih svojstava, kao što su električna vodljivost, feromagnetičnost i reduktivnost. Svojstva perovskita dodatno se mogu poboljšati dopiranjem te formiranjem strukturnih defekata. Cilj ovog rada bio je istražiti mogućnost pripreme stroncijem dopiranog lantanova manganita kemijske formule La0,5Sr0,5MnO3 postupkom koprecipitacije. Dio materijala žaren je na 1200 °C/2h, a dio je prešan u tabletu i sinteriran na istim uvjetima. Iako je rendgenska difrakcijska (PXRD) analiza žarenog praha ukazivala na nastanak čiste faze, morfološkom analizom lomne površine tablete uočene su dvije faze. Energijski razlučujuća rendgenska spektrometrija pokazala je da je svjetlija faza SrMnO3, dok je tamnija La0,76Sr0,24MnO3. Tableta je usitnjena te analizirana PXRD-om. Iako su se maksimumi poklapali sa standardnom rendgenskom karticom faze La0,5Sr0,5MnO3, Rietveldovom metodom utočnjavanja potvrđen je udio Sr od 0,24 i nastanak faze La0,76Sr0,24MnO3. Ostatak stroncija dodanog tijekom sinteze kristalizirao je u SrMnO3 fazu. Time je potvrđeno da je supstitucija moguća do određene mjere nakon koje postoji opasnost od izdvajanje nove faze, pogotovo ako je uzorak pripremljen u obliku tablete.Perovskites are investigated as potential working materials in new technologies, such as solid oxide fuel cells, thermochemical energy storage, and magnetic refrigerators. They are interesting due to their application properties, such as electrical conductivity, ferromagnetic properties, and reducibility. Properties of perovskites can be improved by doping and the formation of structural defects. The aim of this work was to investigate the possibility of preparing Sr-doped lanthanum manganite with the chemical formula La0.5Sr0.5MnO3 by coprecipitation procedure, and to analyse the observed phase separation. The material was prepared by coprecipitation procedure in which sources of metal cations (La3+, Sr2+, Mn2+) were dissolved in 0.5 M HNO3. The nitrate solution was added dropwise in 10 wt% NH4HCO3 solution, both solutions being heated to 65 °C. To achieve coprecipitation of all present metal cations, the pH value was maintained at 8 by the addition of aqueous ammonia. The obtained precipitate was filtered and dried to obtain the precursor powder. One part of the prepared powder was calcined at 1200 °C/2 h (sample CL_Sr0.5_p), while the other part was pressed into a tablet and sintered in the same conditions (sample CL_Sr0.5_tab). Even though FTIR and PXRD analyses of the sample CL_Sr0.5_p (Figs. 1A-C) showed the formation of the pure phase, light and dark spots were observed during the SEM analysis of the tablet (CL_Sr0.5_tab) fracture surface (Fig. 2). These spots were analysed by energy-dispersive spectroscopy (EDS). EDS analysis (Table 1) showed that the light spots were SrMnO3 phase, while the dark spots were La0.76Sr0.24MnO3 phase. The tablet was then ground and FTIR and PXRD analyses were conducted. The obtained FTIR results (Figs. 1A and 1B) showed some bands characteristic for the SrMnO3 phase, and low-intensity maxima originating from the SrMnO3 phase were observed on the diffractogram (Fig. 1C) of CL_Sr0.5_tab sample, confirming the existence of separated phase. This was additionally investigated by the Rietveld refinement analysis (Table 1), and it was determined that Sr concentration was 0.24 instead of the targeted 0.5. Therefore, the La0.76Sr0.24MnO3 phase was formed, while the rest of added strontium during the synthesis crystallised in the SrMnO3 phase. Since successful preparation of La0.5Sr0.5MnO3 by hydrothermal synthesis was reported by multiple authors, it can be concluded that the coprecipitation procedure is not suitable for high concentration doping of LaMnO3 due to the separation of Sr into the secondary phase, especially when in tablet form

Perovskite Oxides for Energy Applications

Industrial and population growth is constantly increasing energy consumption. Since 81.3% of consumed energy is produced from fossil fuels, the high pollution and emission rates are leading to climate changes resulting in extreme weather conditions. The development of new materials and technology is necessary to achieve sustainable societal growth and development. In the field of new materials, perovskites are the main subject of much scientific research conducted in the last decade. Perovskites are usually divided into two groups: halides and oxides. The application of perovskite halides in photovoltaic and solar cells is already well-known and investigated. On the other hand, perovskite oxides do not possess optical and light-absorption properties comparable to perovskite halides, but they have promising electrical and magnetic properties and high reducibility rates. This review is dedicated to the perovskite oxides, preparation methods of this material and their application for energy transformation and storage applications. The perovskite oxides have high potential as working materials in solid oxide fuel cells (SOFC), Ca batteries, thermochemical energy storages (TCES) and ambient temperature magnetic refrigerators (MR)

Chitosan/collagen/Mg, Se, Sr, Zn-substituted calcium phosphate scaffolds for bone tissue engineering applications : A growth factor free approach

According to the biomimetic bone scaffold design paradigm, a scaffold resembling natural bone tissue with molecular, structural and biological compatibility is needed to allow effective regeneration of bone tissue. Continuing our previous studies regarding scaffolds with chitosan matrix containing Mg, Se, Sr, Zn-substituted calcium phosphates (CaPs), the focus of this work was to further improve the properties of these growth factor-free scaffolds. By addition of collagen into the chitosan matrix at weight ratios of 100:0, 75:25, 50:50, 25:75 and 0:100, we aimed to better resemble natural bone tissue. Highly porous composite scaffolds based on chitosan and collagen, with 30 wt% of Mg, Se, Sr, Zn-substituted CaPs, were prepared by the freeze-gelation method. The scaffolds show a highly porous structure, with interconnected pores in the range of 20–350 μm and homogeneously dispersed CaPs. The added collagen further enhanced the stability measured during 28 days in simulated biological conditions. Live/dead and CyQUANT assays confirmed good viability and proliferation of human bone marrow-derived mesenchymal stem/stromal cells, while successful osteogenic differentiation was confirmed by alkaline phosphatase quantification and type I collagen immunocytochemical staining. Results indicated that the addition of collagen into the chitosan matrix containing Mg, Se, Sr, Zn-substituted CaPs improved the physicochemical and biological properties of the scaffolds.publishedVersionPeer reviewe

Sr-doped calcium and barium manganites as catalysts in heterogeneous oxidation of volatile organic compounds

Sr-doped CaMnO3 and BaMnO3 were prepared by autocombustion (CNA) and coprecipitation and investigated as catalysts for catalytic oxidation of benzene, toluene, ethylbenzene and o-xylene mixture in a fixed-bed reactor. Ethylbenzene and o-xylene were completely removed by all prepared catalysts. Toluene was completely removed by BaMnO3 and Ba0.5Sr0.5MnO3 catalysts prepared by CNA synthesis, while conversions of ∼98% or higher were obtained for all the other prepared catalysts. The highest benzene conversion of 86.43% at 723 K was obtained for the Ba0.7Sr0.3MnO3 catalyst prepared by CNA synthesis. The differences in catalytic activities can be ascribed to Sr-doping, oxygen nonstoichiometry and morphological differences