Modeling and analyzing rheological behavior of sour lemon juice concentrate using image processing methods

In this study, temperature-concentration related rheological behavior of sour lemon juice concentrate (SLJC) were investigated. Lemons were squeezed, and lemon juices were obtained. SLJC samples were produced by two methods: atmospheric and vacuum conditions. The rheological properties of SLJC at 10, 20, 30, 40, and 50°C for each 31, 36, 41, 46, 51 °Bx were measured with rheometer. Firstly, it was determined that the SLJC showed Newtonian flow behavior at measured concentrations and temperatures. Then, viscosity of SLJC produced under vacuum conditions was determined higher than SLJC produced under atmospheric conditions. This difference was calculated statistically significant (p < .05). Furthermore, activation energy values of samples produced under atmospheric and vacuum conditions ranged between 13.6–24.0 kJ/mol and 9.0–17.9 kJ/mol, respectively. Finally, temperature-concentration dependent viscosity variations were modeled by surface equations, and the data predicted were transformed into images to provide visual analysis. It was determined by images that the viscosity change is proportional to concentration while inversely proportional to temperature. Ascorbic acid value was found higher under vacuum conditions than atmospheric conditions. In contrast, the HMF value was detected in low quantities under vacuum conditions.     

Entropy generation due to conjugate natural convection in enclosures bounded by vertical solid walls with different thicknesses

Entropy generation due to conjugate natural convection heat transfer and fluid flow has been studied inside an enclosure with bounded by two solid massive walls from vertical sides at different thicknesses. Enclosure is differentially heated from vertical walls and horizontal walls are adiabatic. Governing equations which are written in streamfunction-vorticity form solved by finite difference technique for the governing parameters as Rayleigh number, 10³ ≤ Ra ≤ 10⁶, length ratio of solid walls as ₁ (for left vertical wall) and ₂ (for right vertical wall) and thermal conductivity ratio of solid to fluid (k), 1 ≤ k ≤ 10. Entropy generation contours due to fluid friction and heat transfer irreversibility, isotherms, streamlines, Nusselt numbers and velocity profiles were obtained. It is found that entropy generation increases with increasing of thermal conductivity ratio and thicknesses of the walls. Entropy generation due to heat transfer is more significant than that of fluid flow irreversibility for all values of thickness of the solid vertical walls.     

The dependence of lamellar spacings and microhardness on the growth rate in the directionally solidified Bi-43 wt.% Sn alloy at a constant temperature gradient

Bi-43 wt.% Sn eutectic samples were directionally solidified upward with five different growth rates (V = 8.3–164.8 μm/s) at a constant temperature gradient (G = 3.55 K/mm) in a Bridgman type directional solidification furnace. The lamellar spacings (λ) and microhardness values (HV) were measured from the quenched samples; the directionally solidified Bi-43 wt.% Sn eutectic alloy and the minimum undercoolings (ΔT) were determined from the Jackson-Hunt eutectic theory. The dependency of lamellar spacings (λ), microhardness (H_ν) and undercooling (ΔT) on the growth rate (V) were analyzed. According to these results, it has been found that the value of λ decreases with the increasing value of V and that the values of HV and ΔT increase for a constant G. The values of λ²V, λΔT and ΔT V^−0.5 were determined by using the values of λ, ΔT and V. The results obtained in the present work have been compared with those predicted by the Jackson-Hunt eutectic theory and with similar experimental results.     

Slip-flow heat transfer in microtubes with axial conduction and viscous dissipation – An extended Graetz problem

This study is an extension of the Graetz problem to include the rarefaction effect, viscous dissipation term and axial conduction with constant-wall-heat-flux thermal boundary condition. The energy equation is solved analytically by using general eigenfunction expansion. The temperature distribution and the local Nusselt number are determined in terms of confluent hypergeometric functions. The effects of the rarefaction, axial conduction and viscous dissipation on the local Nusselt number are discussed in terms of dimensionless parameters such as the Knudsen number, Peclet number and Brinkman number.     

Determination of laminar and turbulent flow ranges through vertical packed beds in terms of particle friction factors

Despite the presence of a variety of studies dealing with the magnitude of particle Reynolds number, Re_p defining transition from laminar to turbulent regime for flow through packed beds, the manner is still one of the unknowns. An approach based on the experimental data concerning upward airflow through fixed cylindrical packed beds is presented in this paper. The utilized packed beds had the following ranges of; sphericity, Φ, 0.55 ? Φ ? 1.00, packing material diameter to bed length ratio, D_p/L, 0.04 ? D_p/L ? 0.72, and bed porosity, ε, 0.36 ? ε ? 0.56. The test cases covered the ranges of particle Reynolds number, Re_p 708 ? Re_p ? 7772 and particle Froude number; Fr_p 2.86 ? Fr_p ? 10.39. The measurements of pressure drop through packed bed; ΔP_Bed and superficial mean exit velocity; U are used to determine bed frictional effects in reference to the available literature on particle friction factors, f_p. The magnitude of Re_p defining transition is assumed to be 2000 with particular emphasis to the flow dynamics. The definitions of Bird et al. [R.B. Bird, W.E. Stewart, E.N. Lightfoot, Transport Phenomena, John Wiley and Sons, NY, 1960] are used to calculate f_p. The calculated f_p for the covered test cases are given as a function of pressure coefficient, ΔP* and Re_p, Fr_p, Φ, ε, D_p/L in the approximate ranges of laminar and turbulent flow for Re_p < 2000 and Re_p > 2000, respectively. The proposed separate equations of f_p = f_p(ΔP*, Re_p, Fr_p, Φ, ε, D_p/L) are satisfied for laminar and turbulent flows with corresponding average error margins of ±7.6% and ±18%. Furthermore ranges of transitional and fully rough flow through packed beds are estimated as 2000 ? Re_p ? 4000 and Re_p > 5000 with an analogy to the well-known Moody Chart in pipe flows.     

Characterisation and vapour sensing properties of spin coated thin films of anthracene labelled PMMA polymer

In the present article thin films of poly (methyl methacrylate) (PMMA) polymer labelled with anthracene (Ant-PMMA) prepared by spin coating are characterised by UV–visible spectroscopy, surface plasmon resonance (SPR), spectroscopic ellipsometry (SE) and Atomic Force Microscopy (AFM) and their organic vapour sensing properties are investigated. Ant-PMMA films' thickness are determined by performing theoretical fitting to experimental data measured using SPR and SE. Results obtained show that the spin-cast films are of good uniformity with an average thickness of 6–8 nm. Organic vapour sensing properties are studied using SPR technique during exposures to different volatile organic compounds (VOCs). Ant-PMMA films' response to the selected VOCs has been examined in terms of solubility parameters and molar volumes of the solvents, and the films were found to be largely sensitive to benzene vapour compared to other studied analytes.     

Source rock characteristics of Eocene bituminous shales and the effect of redox conditions on source rock potential,Nallıhan (Ankara) Central Anatolian Basin

Eocene bituminous shales within the Çamalan Formation of Paleocene-Eocene aged K?z?lçay Group exposing around Tekirler (Nall?han, Ankara), central Anatolia, were deposited under oxic and suboxic redox conditions and have Corg values in the range of 2.37 to 12.42 wt% (average 6.32 wt%). Samples are represented by Type-I kerogen and their maturity level is immature-early mature. Eocene bituminous shales are enriched in some major and trace elements, such as Ca, Mg, Si, Na, K, V, Ni, U, Th, P, S, Mo, Cu, Zn, Cr, Co, Pb, Au, Ag, As, Re, La, Ce, Pr, Nd, Li, Sm, and Y. Paleoredox indicators (e.g., V/(V+Ni), Ni/Co, U/Th, V/Sc, Mo/Mn) yield that Eocene bituminous shales were mostly deposited oxic–suboxic conditions.     

Kinetics of emulsifier–free emulsion polymerization of methyl methacrylate

The influences of polymerization temperature, initiator and monomer concentrations, ionic strength of the aqueous phase, as well as ethylene glycol dimethacrylate (EGDM) co-monomer, on the kinetics of the emulsifier-free emulsion polymerization of methyl methacrylate (MMA) and on the properties of the resulting poly(methyl methacrylate) (PMMA) lattices were studied. The polymerizations were carried out using potassium persulfate (KPS) as the initiator. Monodisperse PMMA lattices with particle diameters varying between 0.14–0.37 μm and polymer molecular weights of the order 0.4 × 10⁶ to 1.2 × 10⁶ g/mol were prepared. The initial rate of polymerization increases with increasing temperature, KPS-MMA mole ratio, EGDM content, or with decreasing ionic strength of the aqueous phase. It was shown that the bead size can be limited by reducing the monomer concentration or by using the cross-linking agent EGDM. The ionic strength of the aqueous phase has a dominant effect on final particle diameter and polymer molecular weight. The uniformity of the latex particles increases as the temperature increases or as the initiator concentration decreases. The experimental results can be reasonably interpreted by the homogeneous nucleation mechanism of the emulsifier-free emulsion polymerization of MMA. © 1996 John Wiley & Sons, Inc.     

Formation of tangential pre-stress as a residual stress and its influence on the tribological performance of nodular cast irons

Since any state of residual stress influences the service behavior of a material, it is of particular interest for engineers and designers to know its benefits to machine parts, and where it can be utilized successfully. From this point of view, mechanical tangential pre-stress as circumferential compressive residual stress has been investigated for wear performance. For this purpose, a thick walled cylinder specimen model was established as a tribo-element, and the force, which will form the desired tangential pre-stress representing residual stress, has been calculated by the rules of elasticity theory. In order to compare the effect of residual stress on the wear performance under dry and lubricated conditions, 0.8 R_e (R_e: unidirectional yield strength) were applied to the nodular cast iron (DDK-40, DDK-60) specimens. Wear test results have been evaluated in terms of two different stress levels, 0 R_e and 0.8 R_e, formed on the specimen.     

Unperturbed molecular dimensions and the theta temperature of dextran in dimethylsulfoxide (DMSO) solutions

Summary The unperturbed molecular dimensions of dextran samples have been determined in dimethylsulfoxide (DMSO) solutions from intrinsic viscosity measurements at different temperatures. The unperturbed dimension parameter, K_o, has been calculated from extrapolation methods.The unperturbed root-mean-square end-to-end distance, <r²>_o ^1/2, found for the polymer samples in DMSO solutions, indicate that the polymer coils are contracted. This distance varies from 3.25 × 10⁻⁷ cm to 2.94 × 10⁻⁷ cm for the sample T 40 and from 8.28 × 10⁻⁷ cm to 7.48 × 10⁻⁷ cm for the sample T 500, in the chosen solvent as the temperature is raised from 25°C to 45°C. In the system of dextran/DMSO, the long-range interaction parameter, B, was also determined and a significant decrease is observed between 25°–45°C. The theta temperatures, Θ, were obtained as Θ= 327.25 K, Θ= 327.41 K and Θ= 323.38 K from the temperature dependence of the interaction parameter in Kurata-Stockmayer-Fixman, Berry and Inagaki-Suzuki-Kurata equations, respectively. Received: 19 January 1998/Revised version: 9 June 1998/Accepted: 10 June 1998