Enthalpy

The aim of the methods described is to calculate the properties of turbulent reactive flow fields. At each point in the flow field, a complete statistical description of the state of the fluid is provided by the velocity-composition joint pdf. This is the joint probability density function (pdf) of the three components of velocity and of the composition variables (species mass fractions and enthalpy). The principal method described is to solve a modelled transport equation for the velocity-composition joint pdf. For a variable-density flow with arbitrarily complex and nonlinear reactions, it is remarkable that in this equation the effects of convection, reaction, body forces and the mean pressure gradient appear exactly and so do not have to be modelled. Even though the joint pdf is a function of many independent variables, its transport equation can be solved by a Monte Carlo method for the inhomogeneous flows of practical interest. A second method that is described briefly is to solve a modelled transport equation for the composition joint pdf.The objective of the paper is to provide a comprehensive and understandable of the theoretical foundations of the pdf approach.

An enthalpy formulation based fixed grid methodology is developed for the numerical solution of convection-diffusion controlled mushy region phase-change problems. The basic feature of the proposed method lies in the representation of the latent heat of evolution, and of the flow in the solid-liquid mushy zone, by suitably chosen sources. There is complete freedom within the methodology for the definition of such sources so that a variety of phase-change situations can be modelled. A test problem of freezing in a thermal cavity under natural convection is used to demonstrate an application of the method.Une formulation enthalpique basée sur une méthodologie à grille fixe est développée pour la résolution numérique des problèmes de changement de phase avec une région trouble contrôlée par la convection. La méthode proposée repose sur la représentation par des sources convenablement choisies de l'évolution des chaleurs latentes et de l'écoulement dans la zone trouble liquide-solide. 11 y a une complète liberté dans la méthodologie pour la définition de telles sources de telle sorte qu'on peut modéliser une grande variété de situations. On étudie la congélation dans une cavité avec convection naturelle pour démontrer l'application de la méthode.Ein Festgitter-Verfahren, welches auf Enthalpiebilanzen basiert, wurde zur numerischen Lösung von Konvektions-Diffusionsgesteuerten Problemen des Phasenübergangs entwickelt. Der grundlegende Unterschied der vorgestellten Methode liegt in der Berücksichtigung der Entstehung der latenten Wärme und der Strömung in der Fest-flüssig-Übergangszone durch geeignet gewählte Wärmequellen. Für die Definition solcher Quellen hat man vollkommene Freiheit, sodaβ eine Vielzahl von Phasenwechselvorgängen modelliert werden kann. Ein Testproblem des Gefriervorganges in einem thermischen Einschluβ unter natürlicher Konvektion wird benutzt, um die Anwendung dieser Methode zu zeigen.Ha ocнoвe энтaльпийнoй фopмyлиpoвки иcпoльзyeтcя мeтoд нeпoдвижнoи ceтки для чиcлeннoгo peшeния зaдaч фaзoвoгo пepeчoдa c yчeтoм кoнвeкции и диффyзии. Чapaктepнoй чepтoй пpeдлaгaeмoгo мeтoдa являeтcя пpeдcтaвлeниe yдeльнoй тeплoты фaзoвoгo пepeчoдa и пoтoкa в зoнe фaзoвoгo пepeчoдa твepдoe тeлo-жидкocть c пoмoщью cooтвeтcтвeннo выбpaнныч иcтoчникoв. Bыбop этич иcтoчникoв пpeдпoлaгaeтcя тaким, чтo пoзвoляeт мoдeлиpoвaть paзличныe cлyчaи фaзoвыч пpeвpaщeний. B кaчecтвe иллюcтpaции paccмaтpивaeтcя зaдaчa o зaмepзaнии в пoлocти пpи ecтecтвeннoй кoнвeкции.

Adsorption of fluoride on waste carbon slurry was investigated. Waste carbon slurry was obtained from fuel oil based generators of a fertilizer industry. The work involves batch experiments to investigate the effects of contact time, pH, temperature and adsorbent dose on the extent of adsorption by carbon slurry. The contact time and pH for maximum fluoride uptake were found 1 h and 7.58, respectively. Maximum adsorption capacity (4.861 mg g−1) of fluoride on carbon slurry was observed at 15.00 mg L−1 initial fluoride concentration using 1.0 g L−1 adsorbent dose. Among four applied models, the experimental isotherm data were found to follow Langmuir equation more closely. Thermodynamically, adsorption was found endothermic with values 7.348 kJ mol−1, −25.410 kJ mol−1 and 0.109 kJ mol−1 K−1 for enthalpy, free energy and entropy, respectively showing the feasibility of adsorption process. From kinetic analysis, the adsorption was found to follow second-order mechanism with rate constant 49.637 g mg−1 min−1. The rate-controlling step of the adsorption was found pore diffusion controlled. In order to investigate the potential of this adsorbent on industrial scale, column and desorption experiments were carried out. The breakthrough capacity of column was calculated 4.155 mg g−1 with at a flow rate of 1.5 mL min−1. The proposed adsorbent has been used to remove fluoride from groundwater and wastewater. Desorption has been achieved under alkaline conditions (pH 11.6) from exhausted carbon slurry. The performance of carbon slurry was compared with many other reported adsorbent for fluoride removal and it was observed that proposed adsorbent is effective in terms of performance and cost especially.

The adsorption of a reactive dye, Ariazol Scarlet 2G (AS2G) (C.I.: Reactive Red 234), onto compost, from aqueous solutions, was studied in a batch system. The effects of initial dye concentration, initial pH and sorbent mass have been studied. Four two-parameter isotherm models–Langmuir, Freundlich, Temkin and Harkins Jura – were used to fit the experimental data using a nonlinear trial-and-error method. The best fi t of the adsorption isotherm data was obtained using the Langmuir model (X 2 = 1.97E−03). A comparison of kinetic models applied to the adsorption of AS2G on compost was evaluated using the pseudo-second order, Elovich and Lagergren first-order kinetic models. Results showed that the pseudo-second order kinetic model was found to agree well with the experimental data. An intra-particle diffusion model analysis showed multi-linearity with two steps and a non-zero intercept which indicated the intra-particle diffusion model is not a dominant rate controlling mechanism in the sorption of AS2G by compost.

The kinetics and mechanism of methylene blue adsorption onto raw pine cone biomass (Pinus radiata) was investigated under various physicochemical parameters. The extent of the methylene blue dye adsorption increased with increases in initial dye concentration, contact time and solution pH but decreases with the amount of adsorbent, salt concentration and temperature of the system. Overall the kinetic studies showed that the methylene blue adsorption process followed pseudo-second-order kinetics among various kinetic models tested. The different kinetic parameters including rate constant, half-adsorption time and diffusion coefficient are determined at different physicochemical conditions. Equilibrium data were best represented by Langmuir isotherm among Langmuir and Freundlich adsorption isotherm. The maximum monolayer adsorption capacity of pine cone biomass was 109.89 mg/g at 30°C. The value of separation factor, R L, from Langmuir equation and Freundlich constant, n, both give an indication of favourable adsorption. Thermodynamic parameters such as standard Gibbs free energy (∆G 0), standard enthalpy (∆H 0), standard entropy (∆S 0) and the activation energy (A) were calculated. A single-stage batch absorber design for the methylene blue adsorption onto pine cone biomass has been presented based on the Langmuir isotherm model equation.

In the present study, the aptitudes of cedar (Cedrus atlantica Manatti) sawdust and crushed brick to remove copper(II) ions from aqueous solutions were investigated. Kinetic results and equilibrium removal isotherms were determined. The influence of pH and ionic strength on the sorption of copper was also studied. The removal of copper by both sorbents increased with an increase in contact time and pH (from 1 to 6) and decreased with an increase in ionic strength. Various kinetic models such as the pseudo-first and pseudo-second order rate equations, Boyd model, and external mass-transfer expression were tested. It was concluded that, for both sorbents, copper sorption occurs through a film diffusion mechanism and the kinetic results were best described by the pseudo-second order kinetic model. The equilibrium data has been correlated with both Langmuir and Freundlich isotherms. The results indicate that the Langmuir model fits the data better. The Freundlich model does not lead to a correct determination of the maximum sorption capacity. Thermodynamic parameters such as the changes in free energy, enthalpy, and entropy of sorption of the copper-sorbent systems were also evaluated. The negative values of the change in free energy indicate the feasibility and spontaneous nature of the process, and the negative heats of the change in enthalpy suggest the exothermic nature of the process. Additionally, different types of chemical treatments were applied: alkaline treatments (NaOH, KOH), acidic treatments (H2SO4, H3PO4, CH3COOH), treatments with mineral salts (NaCl, KCl, Na2HPO4, NaHCO3), treatment with urea, and phosphorylation treatment (urea + H3PO4) in order to enhance the sorption aptitudes of the both sorbents. Among the studied chemical treatments applied, treatments with mineral salts (Na2HPO4, KCl, NaCl, and NaHCO3) for crushed brick and alkaline treatments by NaOH and KOH for cedar sawdust were the most effective.

A new microencapsulated phase change material slurry based on microencapsulated Rubitherm RT6 at high concentration (45% w/w) was tested. Some heat storage properties and heat transfer characteristics have been experimentally investigated in order to assess its suitability for the integration into a low temperature heat storage system for solar air conditioning applications. DSC tests were conducted to evaluate the cold storage capacity and phase change temperature range. A phase change interval of approximately 3 °C and a hysteresis behaviour of the enthalpy were identified. An experimental set-up was built in order to quantify the natural convection heat transfer occurring from a vertical helically coiled tube immersed in the phase change material slurry. First, tests were carried out using water in order to obtain natural convection heat transfer correlations. Then a comparison was conducted with the results obtained for the phase change material slurry. It was found that the values of the heat transfer coefficient for the phase change material slurry were higher than for water, under identical temperature conditions inside the phase change interval.

Rheological, thermal and structural changes in high pressure (HP) treated Basmati rice flour dispersions were studied as function of pressure level (350–650 MPa), slurry concentration (with 1:5, 1:3 and 1:2 flour-to-water ratios) and holding time (7.5–15 min). Rice flour dispersions exhibited a gradual liquid–solid gel transformation as they gelatinized and/or denatured and behaved as viscoelastic fluid following HP treatment. Mechanical strength (G′) of pressurized gel increased with applied pressure and rice concentration. Differential scanning calorimeter (DSC) thermograms of rice slurry measured after pressure treatment indicated a reduction in peak enthalpy in proportion with the extent of gelatinization and/or denaturation of starch and proteins. Pressure-treated rice samples had a progressively lower gelatinization temperature. A 15 min pressure treatment at 550 MPa was found sufficient to complete gelatinization of protein free isolated rice starch while the slurry required 650 MPa. The presence of proteins might have been responsible for the slower starch gelatinization in the rice slurry during pressure treatment. The sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Fourier-transform infrared (FTIR) spectroscopy results indicated some minor changes in protein subunits and secondary structure of rice protein. This study has provided complementary information on pressure-induced changes in physical (thermal stability, overall structure) and molecular level (secondary structure) of rice protein.