Heat transfer prediction of air‐to‐refrigerant two‐phase flow boiling of alternatives to HCFC‐22 inside air/refrigerant enhanced surface tubing

In this paper, an experimental study on the heat transfer characteristics of two‐phase flow boiling of some alternative refrigerants to HCFC‐22, on air/refrigerant horizontal enhanced surface tubing, is presented. Correlations have been proposed to predict the heat transfer characteristics such as average heat transfer coefficients, as well as pressure drops of alternatives to R‐22; such as R‐507, R‐404A, R‐407C, R‐410A and R‐408A in two‐phase flow boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixture's pressure drop is a weak function of the mixture's composition. It was found that the correlations were applicable to the entire heat and mass flux, investigated in the present study, for the proposed blends under question. The deviation between the experimental and predicted values for the heat transfer coefficient and pressure drop were less than ±20, and ±35 per cent, respectively, for the majority of data. Copyright © 2000 John Wiley & Sons, Ltd.     

Modelling of capillary tubes behaviour with HCFC 22 ternary alternative refrigerants

In this paper, a numerical model is presented for predicting capillary tube performance using new ternary mixtures proposed as alternatives to R 22. The model has been established after the fluid flow conservation equations written for a homogeneous refrigerant fluid flow under saturated, subcooled and two- pase conditions. Numerical results showed that the proposed model in question fairly simulated experimental on ternary refrigerant mixtures and fairly predicted the capillary tube behaviour under the investigated; subcooled, saturated, and two-phase flow conditions. © 1998 John Wiley & Sons, Ltd.     

Segmented thermoelectric generator: exponential area variation in leg

The innovative design of segmented thermoelectric generator with exponential area variation is introduced. Thermal efficiency and power output are assessed for various values of the design parameter (a = (L/x) ln[A_a/A(x)], where A_a is constant, and a is the dimensionless geometric parameter, L is the pin length, and A(x) is the pin cross‐sectional area), external load parameter (R_L/R₀, ratio of external electrical resistance to reference electrical resistance), and temperature parameter (θ = T_low/T_high, ratio of cold junction temperature to high junction temperature). The device efficiency obtained is validated through the previous experimental data for various hot and cold junction temperature differences. The findings reveal that thermal efficiency resulted from the current study agrees well with the experimental data. The innovative design of the segmented thermoelectric generator with exponentially decaying pin configuration enhances the thermal efficiency and output power as compared with the device having a single material pin configuration. Increasing temperature ratio results in the reduction in the thermal efficiency and the output power of thermoelectric generator. In addition, lowering the external load parameter improves the thermal efficiency and the output power of the thermoelectric device. The design parameter that maximizes the thermal efficiency of the thermoelectric generator does not maximize the device output power.     

Differential transform solution for Hall and ion‐slip effects on radiative‐convective Casson flow from a stretching sheet with convective heating

Magnetohydrodynamic (MHD) materials processing is becoming increasingly popular in the 21st century as it offers significant advantages over conventional systems, including improved manipulation of working fluids, reduction in wear, and enhanced sustainability. Motivated by these developments, the present work develops a mathematical model for Hall and ion‐slip effects on non‐Newtonian Casson fluid dynamics and heat transfer toward a stretching sheet with a convective heating boundary condition under a transverse magnetic field. The governing conservation equations for mass, linear momentum, and thermal (energy) are simplified with the aid of similarity variables and Ohm's law. The emerging nonlinear‐coupled ordinary differential equations are solved with an analytical technique known as the differential transform method. The impact of different emerging parameters is presented and discussed with the help of graphs and tables. Generally, aqueous electroconductive polymers are considered, for which a Prandtl number of 6.2 is employed. With increasing Hall parameter and ion‐slip parameter, the flow is accelerated, whereas it is decelerated with greater magnetic parameter and rheological (Casson) fluid parameter. Skin friction is also decreased with greater magnetic field effect, whereas it is increased with stronger Hall parameter and ion‐slip parameter values.     

Valorisation of olive mill wastewater by enhancement of natural hydroxytyrosol recovery

Recovery of natural and simple phenolic compounds with high added value was performed successfully from olive mill wastewater. Three types of olive mill wastewater were assayed in bioconversion at 15 and 40 L in mechanically stirred systems for 2 h at 50 °C. Maximum hydroxytyrosol concentrations of about 1.53, 0.83 and 0.46 g L^?1 were obtained in the presence of 5 IU Aspergillus niger β‐glucosidase per milliliter of OMW in North OMW, MSP and MCC, which were 2.70‐, 1.38‐ and 1.77‐fold higher than the controls, respectively. Enzymatic pretreatment was followed by two tangential flow membrane separation steps, microfiltration (MF) and ultrafiltration (UF), and concentration procedures for the ultrafiltration permeate. The latter exhibited a COD level of 48.44 g L^?1. The UF permeate concentration increased the hydroxytyrosol concentration to 7.2 g L^?1. Hence, this innovative work described an environmently friendly process; pilot‐scale has allowed producing a new and natural product which obeyed the dietary requirements; it contains some minerals beneficial to health and does not contain heavy metals or chemicals. Overall, this chemical‐free large‐scale process proved efficient for recovery of natural hydroxytyrosol.     

A heat and mass transfer study—analysis of continuous processes for the coloration of polyester fabric. I. Heat transmission to the fabric system—fabric,fiber, and dye particles

The three continuous processes (thermosol, high temperature steaming, and heat transfer printing) for the coloration of polyester and the involved equipment are briefly reviewed. A simple model for the transient heating of a body is developed, the model [eq.(22)] comprises a specific area of transfer parameter (A_s): area through which transport (of heat) takes place per unit mass of the body. This model is used in order to estimate the relative heating rates for the different geometrical approximations present in the fabric system: plate (fabric), cylinder (fiber), and sphere (dye particle). Results obtained from the more exact numerical analysis solution are used for investigating the limitations of the simple heat transfer model.     

Use of Front-Face Fluorescence Spectroscopy to Differentiate Sheep Milks from Different Genotypes and Feeding Systems

The objective of the present study was to assess the potential of front-face fluorescence spectroscopy coupled with chemometric tools for the evaluation of the quality of milk samples according to the feeding system and genotype. Fifty (n = 50) ewe's milk samples were scanned after excitation set at 250, 290, 322, and 380 nm and emission set at 410 nm. Thirty out of the 50 samples composed the first trial and were obtained from two different genotypes (i.e., Comisana versus Sicilo-Sarde); the second trial was composed of 20 samples obtained from the Sicilo-Sarde genotype with two different feeding systems in pen (soybean versus scotch bean). Milk samples were divided into four groups named Sicilo-Sarde with pasture feeding (Spas), Comisana with pasture feeding (Cpas), Sicilo-Sarde feeding on scotch bean (Ssco), and Sicilo-Sarde feeding on soybean (Ssoy). The factorial discriminant analysis was applied to the: (i) four groups (i.e., Spas, Ssco, Ssoy, and Cpas) and (ii) three groups composed only of Sicilo-Sarde genotype (i.e., Spas, Ssco, and Ssoy). Considering the four groups, the best result was obtained with the excitation vitamin A spectra since correct classification amounting to 76% was observed. When the factorial discriminant analysis was performed with the three groups belonging to the Sicilo-Sarde genotype, the best result was obtained again with vitamin A spectra (i.e., emission and excitation spectra) since 88.6% of correct classification was observed. Concatenation technique applied to the five fluorescence spectra improved the rate of classification between the four groups since 44 out of 50 samples were correctly classified. No misclassification was observed between milk samples collected from ewes with pasture feeding from the pen feeding. It was concluded from the obtained results that fluorescence spectroscopy could be considered as a powerful tool for differentiating between raw milks according to both genotype and feeding system.     

Comparison of methods in the recovery and amplificability of DNA from fresh and processed sardine and anchovy muscle tissues

An important condition for a successful PCR amplification is an efficient DNA-extraction procedure out of a complex biological matrix such as canned fish. In this study we compared six extraction methods, including commercial kit, in terms of DNA yield, purity and time requirement. Such methods were applied to distinguish small pelagic fish species (Sardina pilchardus and Engraulisencrasicolus) among commercial canned products. The quantity and quality of DNA extracted were evaluated using the ratio A₂₆₀/A₂₈₀. Data were submitted to principal component analysis (PCA) in order to assess the differences between PCR results of fresh and processed anchovy and sardine muscles. Two main PC characterised the PCR of sardine and anchovy (70% and 69% of all variance): principal component 1 (PC1) (4% and 60%) and principal component 2 PC2 (66.0% and 9%) for sardine and anchovy, respectively. According to the PC1, the PCI/SDS and Chelex extractions (in decreasing order) were positively correlated with results of PCR for both species.     

Characterization and technological properties of Staphylococcus xylosus strains isolated from a Tunisian traditional salted meat

The technological properties of strains of Staphylococcus xylosus were studied to select the most suitable for use as starter cultures for the production of dried fermented meat products. Strains of S. xylosus were isolated from traditional salted Tunisian meat and were identified by biochemical and molecular methods. Thirty strains of S. xylosus were studied to evaluate their catalase, nitrate reductase, lipolytic, proteolytic and antibacterial activities as well as growth ability at different temperatures, pH's and NaCl concentrations. All strains of S. xylosus had catalase activity and were able to reduce nitrates to nitrites. The nitrate reductase activity increased when the strains were kept under anaerobic conditions. Proteolytic activity on milk and on gelatin agar was demonstrated for 100% and 83.3% of the S. xylosus isolates, respectively. However extracellular proteolytic activity as assessed by the azocasein method was poor in all the strains. Lipolytic activity as assessed by the agar method showed that 76.6% of strains of S. xylosus could hydrolyze Tween 20 against 33.3% that could hydrolyze tributyrin. Tween 80 was hydrolyzed by only 10% of strains. Strains of S. xylosus hydrolyzed pork fat better than beef and lamb fat. The majority of strains had antibacterial activity against Salmonella arizonae, Staphylococcus aureus, Pseudomonas aeuroginosa, Escherichia coli and Enterococcus faecalis.