Očuvanje vitamina C, likopena i ugljenih hidrata u plodovima paradajza sušenim u tunelskom tipu sušara

The aim of this study was to find an optimal way of tomato drying in a tunnel type dryer, in order to achieve the lowest possible losses in nutritive value of dried tomato products. Domestic variety of tomato (SP-109) was used in this research. Drying was performed in three ways, applying five temperature regimes, as follows: cocurrent system (variant 1 at 70-80 oC; variant 2 at 90-75 oC), countercurrent system (variant 1 at 55-65 oC, variant 2 at 65-75 oC) and combined system (85-55 oC and 55-65 oC). In these systems, the kinetic of changes in nutritive value of tomato fruits was monitored by measuring the content of carbohydrates, lycopene and vitamin C. Different influences of temperature regimes on nutritive value of dried tomato were observed at the level of statistical difference (LSD 0.05; 0.01) in the researched systems. Cocurrent system was statistically significant for differences in temperature modes (variant 1 and variant 2). Monitoring of the tomato drying kinetics showed that, in all variants, period of constant drying rate lasted about 3.5 h and that the total drying was the fastest in parallel cocurrent flow of non-saturated hot air and material. The content of total carbohydrates in tomato was dependent on the temperature regime of the tested drying systems. The carbohydrate content obtained in tomato samples dried at lower temperatures was higher compared to the values observed in the samples dried at higher drying temperatures. Significant losses of vitamin C were determined in all drying systems. The lycopene content under all experimental conditions generally showed a tendency to decrease slightly. Comparing its content in dry and fresh tomato fruits, the loss ranged from 4.94% to 19.98% but did not reach the significant level as the occurrence remained below 95% of cases.Cilj ove studije bio je pronalaženje optimalnog načina sušenja paradajza u tunelskom tipu sušara kako bi se smanjili gubici vrednosti nutritijenata kod sušenog proizvoda paradajza. U ovom istraživanju korišćena je domaća sorta paradajza (SP-109). Istraživanje je izvedeno u tunelskom tipu sušara na tri načina u pet temperaturnih režima. Sušenje je izvedeno u sistemu paralelnog (varijanta 1 na 70-80 oC, varijanta 2 na 90-75 oC), suprotnosmernom (varijanta 1 na 55-65 oC, varijanta 2 na 65-75 oC) i kombinovanog sistema strujanja vazduha (85-55 oC i 55- 65 oC). U ovim sistemima sušenja praćena je kinetika promena nutritivnih vrednosti ploda paradajza: sadržaj ugljenih hidrata (%), likopena i askorbinske kiseline (vitamin C). Utvrđeni su različiti uticaji temperaturnih režima na nivou statističke razlike (LSD 0.05; 0.01) ispitivanih sistema za nutritivnu vrednost sušenog paradajza. Paralelni sistem je bio statistički značajan za razlike u varijanti temperature 1 i varijanti 2. Prateći kinetiku sušenja paradajza utvrđeno je da u svim varijantama period konstantnog sušenja traje oko 3,5 časa i da je za ukupno sušenje najbrži paralelni protok toplog vazduha i materijala. Sadržaj ugljenih hidrata u uzorcima paradajza koji su sušeni na nižim temperaturama bio je veći u poređenju sa sadržajem ugljenih hidrata koji je utvpđen u uzorcima osušenim na višim temperaturama sušenja. Na nižim temperaturama njihov sadržaj je bio veći nego kod viših temperatura sušenja. Značajni gubici vitamina C određeni su u svim sistemima sušenja. Vrednost likopena u svim eksperimentalnim uslovima sušenja pokazuje tendenciju blagog smanjenja. Poredeći sadržaj u suvim i svežim plodovima paradajza, gubitak je bio od 4,94% do 19,98%, ali ne na značajnom nivou

Пренос масе у инверзно флуидизованом слоју

In this work, the coefficient of fluid-wall mass transfer in an inverse fluidized bed was determined using the adsorption method. The experiments were carried out in a column with a diameter of 45 mm with spherical and non-spherical particles of polypropylene and polyethylene with a diameter of 3.3-4.9 mm and a density of about 930 kg m-3. A diluted solution of methylene blue was used as a fluidization medium, which was adsorbed on part of the surface of the column on silica gel. The obtained results showed that the presence of particles during inverse fluidization does not contribute significantly to mass transfer compared to the influence of particles on transfer in conventional fluidized beds. Therefore, the pseudofluid concept was introduced into the analysis and an empirical correlation was performed to determine the mass transfer coefficient. The obtained results were compared with literature correlations for inverse and conventional fluidized beds.У овом раду је одређиван коефицијент преноса масе флуид-зид у инверзнофлуидизованом слоју применом адсорпционе методе. Експерименти су вршени у колони пречника 45 мм са сферичним и несферичним честицама полипропилена и полиетилена пречника 3.3-4.9 мм и густине око 930 кг м-3. Као флуидизациони медијум коришћен је разблажени раствор метиленски плавог који је адсорбован на делу површине колоне на силикагелу. Добијени резултати показали су да присуство честица при инверзној флуидизацији не доприноси значајно преносу масе у поређењу са утицајем честица на пренос масе у конвенционално флуидизованим слојевима. Због тога је у анализу уведен концепт псеудофлуида и изведена је емпиријска корелација за одређивање коефицијента преноса масе. Извршено је поређење добијених резултата са литературним корелацијама за инверзну и конвенционалну флуидизације

Analogija prenosa količine kretanja, toplote i mase pri vertikalnom hidrauličkom transportu inertnih čestica

Wall-to-bed momentum, heat and mass transfer in the vertical liquid-solids flow, as well as in the single phase flow, were studied. The aim of this investigation was to establish the analogy among those phenomena. Also, effect of particle concentration on momentum, heat and mass transfer was studied. The experiments in hydraulic transport were performed in 25.4 mm I.D. cooper tube equipped with a steam jacket, using spherical glass particles of 1.94 mm in diameter and water as a transport fluid. The segment of the transport tube used for mass transfer measurements had internal coating made of benzoic acid. In the hydraulic transport two characteristic flow regimes were observed: turbulent and parallel particle flow regime. The transition between two characteristic regimes (Y* = 0), occurs at a critical voidage ε ≈ 0.85. The vertical two-phase flow was con­sidered as the pseudofluid, and modified mixture-wall friction coefficient (fw) and modified mixture Reynolds number (Rem) were introduced for system characterization. Experimental data show that the wall-to-bed momentum, heat and mass transfer coefficients, in vertical flow of pseudofluid, for the turbulent regime are significantly higher than in parallel regime. Wall-to-bed, mass and heat transfer coefficients in hydraulic transport of particles were much higher than in single-phase flow for lower Reynolds numbers (Re LT 15000), while for high Reynolds numbers (Re > 15000), there was not significant difference. The experimental data for wall-to-bed momentum, heat and mass transfer in vertical flow of pseudofluid in parallel particle flow regime, verify analogy among these three phenomena.U ovom radu prikazani su rezultati eksperimentalnih ispitivanja prenosa količine kretanja, toplote i mase zid-fluid u vertikalnom hidrauličkom transportu inertnih čestica i pri strujanju fluida u cevi istog prečnika. Eksperimentalna ispitivanja vršena su istovremenim merenjem potrebnih parametara za definisanje navedenih prenosa. Cilj ovih ispitivanja bio je određivanje koeficijenata prenosa pri vertikalnom hidrauličkom transportu inertnih čestica i uspostavljanje analogije tri prenosa. Eksperimentalni sistem predstavljala je vertikalna transportna cev prečnika 25,4 mm snabdevena omotačem za zagrevanje parom, kao i segmentom transportne cevi prepariranim rastopom benzoeve kiseline. Kao fluid korišćena je voda, a vršen je transport staklenih sfernih čestica prečnika 1,94 mm. U rezultatima su prikazani dobijeni koeficijenti trenja, prelaza toplote i prelaza mase. Korišćenjem koncepta pseudofluida, pokazano je postojanje analogije prenosa količine kretanja, toplote i mase u transportnoj cevi za paralelni režim strujanja

Momentum-heat-mass transfer analogy in gas-solid packed bed at elevated temperatures

The experimental values of the friction factor (fp) at ambient and elevated temperatures as well as of the heat transfer coefficient (hp) were used to establish the analogy among momentum and heat transfer in gas-solid packed beds of mono-sized spherical glass particles, as jH=fp/22 or jHε=fp/50. Also, Chilton-Colburn type of momentum-mass transfer analogy was confirmed. These findings are valid for the range of the modified Reynolds number Re’p≈20-130. The experiments related to fp were performed by measuring the pressure drop across the packed bed of particles (0.58, 0.92, 1.04, 1.20, 1.94, 2.98, 3.91 and 4.91 mm diameters) heated to the desired temperature by hot air (temperatures from 20ºC to 350ºC). The range of gas superficial velocity was from 0.05 to 0.99 m/s and the bed porosities were from 0.357 to 0.430. The experiments related to hp were performed by recording the temperatures of the cold aluminium test spheres (6, 12 and 20 mm dimeters) with embedded K-type (Ni/Al) thermocouples, immersed into the hot packed bed of particles (1.20, 1.94 and 2.98 mm diameters at temperatures from 100 to 300ºC) until the thermal equilibrium was reached. The superficial gas velocity and bed porosity varied from 0.30 to 0.79 m/s and from 0.392 to 0.406, respectively.  New correlation for prediction of the heat transfer factor has been proposed in the form jHε=0.30(Re’p)-0.30.The analogies defined in this way leave the possibility of determining the value of the heat and mass transfer coefficients on the basis of the value of the friction factor, which is more common in the literature

Preservation of vitamin C, lycopene and carbohydrate content in tomato dried in a tunnel type dryer

The aim of this study was to find an optimal way of tomato drying in a tunnel type dryer, in order to achieve the lowest possible losses in nutritive value of dried tomato products. Domestic variety of tomato (SP-109) was used in this research. Drying was performed in three ways, applying five temperature regimes, as follows: cocurrent system (variant 1 at 70-80 oC; variant 2 at 90-75 oC), countercurrent system (variant 1 at 55-65 oC, variant 2 at 65-75 oC) and combined system (85-55 oC and 55-65 oC). In these systems, the kinetic of changes in nutritive value of tomato fruits was monitored by measuring the content of carbohydrates, lycopene and vitamin C. Different influences of temperature regimes on nutritive value of dried tomato were observed at the level of statistical difference (LSD 0.05; 0.01) in the researched systems. Cocurrent system was statistically significant for differences in temperature modes (variant 1 and variant 2). Monitoring of the tomato drying kinetics showed that, in all variants, period of constant drying rate lasted about 3.5 h and that the total drying was the fastest in parallel cocurrent flow of non-saturated hot air and material. The content of total carbohydrates in tomato was dependent on the temperature regime of the tested drying systems. The carbohydrate content obtained in tomato samples dried at lower temperatures was higher compared to the values observed in the samples dried at higher drying temperatures. Significant losses of vitamin C were determined in all drying systems. The lycopene content under all experimental conditions generally showed a tendency to decrease slightly. Comparing its content in dry and fresh tomato fruits, the loss ranged from 4.94% to 19.98% but did not reach the significant level as the occurrence remained below 95% of cases

Prenos mase zid-fluid u partikulativno fluidizovanim slojevima

Mass transfer in fluidized beds is an important operation for separation processes. Two effects can be achieved by using fluidized beds in mass transfer processes increasing interface area and relative movement between the phases. These effects are both desirable because they lead to greater process rates. This paper presents an experimental investigation regarding mass transfer from the wall of a column to the fluid in a fluidized bed of inert spherical particles. The experiments were conducted in column 40 mm in diameter with spherical particles 0,8-3 mm in diameter and water as one fluidizing fluid. The method of dissolution of benzoic acid was used to provide very low mass flux. The average wall-to-fluid mass transfer coefficients were determined for two systems: single-phase fluid flow and a fluidized bed of inert particles The measurements encompassed a Reynolds number range from 100-4000 for single-phase flow and 600-4000 in fluidized beds. The mass transfer coefficients for both systems were calculated from weight loss of benzoic acid. The effects of superficial liquid velocity and particle diameter on the mass transfer coefficient were investigated. It was found that mass transfer was more intensive in the fluidized bed in comparison with single phase flow. The best conditions for mass transfer were reached at a minimum fluidization velocity, when the mass transfer coefficient had the greatest value. The experimental data were correlated in the form: jd = f(Re), where jd is the dimensionless mass transfer factor and Re the Reynolds number.Ispitivan je prenos mase sa zida kolone na fluid u fluidizovanom sloju inertnih sfernih čestica. Eksperimenti su izvršeni u fluidizacionoj koloni prečnika 40 mm, sa sfernim česticama od stakla prečnika 0,8-3 mm i vodom kao fluidizacionim medijumom. Određivan je koeficijent prelaza mase zid kolone-fluidizovani sloj metodom rastvaranja benzoeve kiseline. Ispitivan je uticaj brzine strujanja fluida i karakteristika čestica na koeficijent prelaza mase. Opseg ispitivanih Rejnoldsovih brojeva bio je za strujanje fluida bez čestica (jednofazni tok) od 100-4000, a u fluidizovanom sloju od 600-4000. Rezultati su prikazani kao zavisnosti bezdimenzionog faktora prenosa mase /d od Rejnoldsovog broja Re i Rejnoldsovog broja za česticu Rep. Na osnovu eksperimentalnih rezultata postavljena je korelacija za određivanje koeficijenta prelaza mase u obliku zavisnosti JD = f(Re)

Prenos mase fluid-uronjeni objekat u pakovanim i fluidizovanim slojevima tečnost-čestice

The mass transfer coefficient between fluid and an immersed sphere in liquid packed and fluidized beds of inert spherical particles have been studied experimentally using a column 40 mm in diameter. The mass transfer data were obtained by studying the transfer of benzoic acid from the immersed sphere to flowing water using the dissolution method. In all runs, the mass transfer rates were determined in the presence of inert glass particles 0.50-2.98 mm in diameter. The influence of different parameters, such as: liquid velocity, particles size and bed void age, on the mass transfer in packed and fluidized beds is presented. The obtained experimental data for mass transfer in the packed and particulate fluidized bed were correlated by a single correlation, thus confirming the similarity between the two systems.U ovom radu je eksperimentalno ispitivan prelaz mase između uronjene sfere i fluida u prisustvu pakovanih i fluidizovanih čestica. Za određivanje koeficijenta prelaza mase korišćena je metoda praćenja rastvaranja slabo rastvorne supstance- benzoeve kiseline u vodi. Korišćena je kolona prečnika 40 mm, uronjena sfera prečnika 21 mm, a pakovane i fluidizovane slojeve su činile staklene sfere prečnika 0,5-2,98 mm. Ispitivanja u pakovanim slojevima izvršena su u sistemima sa različitim pakovanjima - retkom i gustom. Prikazani su uticaji različitih parametara, kao što su brzina fluida, veličina čestica i poroznost slojeva na koeficijent prelaza mase. Pokazane su razlike i sličnosti u prenosu mase kada su u sloju prisutne nepokretne i fluidizovane čestice. Data je završna eksperimentalna korelacija koja je zajednička i za pakovane i za fluidizovane slojeve. Korelacija je data kao veza bezdimenzionih grupa Rep/(1-ε)i jDε koje nisu tipične za korelisanje podataka u fludizovanim slojevima. Ova korelacija ukazuje da postoji sličnost mehanizama prenosa mase u pakovanim i partikulativno fludizovanim slojevima

Mass and momentum transfer in packed beds of spherical inert particles

Mass transfer coefficients between fluid and immersed sphere in liquid dense and loose packed beds of spherical inert particles have been studied experimentally using column 40 mm in diameter. Mass transfer data were obtained by studying transfer of benzoic acid from a large spherical particle to flowing water using the disssolution method. In all runs mass transfer rates were determined in the presence of inert spherical glass particles 0.54, 0.68, 1.20, 1.94, 2.98 and 4.98 mm in diameter. Measurements have covered a particle Reynolds number range from 0.35 to 400 and one Schmidt number (25°C) 969. Experimental data are correlated by the widely used general form, j D = f(Re p ). The resulting correlation for packed beds, which covers dense and loose packed beds, is j D = 0.395ε -1,2 Re p -0,39 . In the same experimental systems a relationship between friction factor and particle Reynolds number has been studied. The results indicate that numerical constants in Ergun equation are system specific

Wall effects on the velocities of a single sphere settling in a stagnant and counter-current fluid and rising in a co-current fluid

Experimental results were obtained on the steady settling of spheres in quiescent media in a range of cylindrical tubes to ascertain the wall effects over a relatively wide range of Reynolds number values. For practical considerations, the retardation effect is important when the ratio of the particle diameter to the tube diameter (lambda) is higher than about 0.05. A new empirical correlation is presented which covers a Reynolds number range Re = 53-15,100 and a particle to tube diameter ratio lambda lt 0.88. The absolute mean deviation between the experimental data and the presented correlation was 1.9%. The well-known correlations of Newton, Munroe and Di Felice agree with the presented data reasonably well. For steady settling of spheres in a counter-current water flow, the slip velocity remains practically the same as in quiescent media. However, for rising spheres in a co-current water flow, the slip velocity decreases with increasing co-current water velocity, i.e., the wall factor decreases with increasing co-current water velocity. Consequently, the drag coefficient for rising particles in co-current water flow increases with increasing water velocity