Journal of Thermodynamics The latest articles from Hindawi Publishing Corporation © 2014 , Hindawi Publishing Corporation . All rights reserved. Thermohydraulic Performance of a Series of In-Line Noncircular Ducts in a Parallel Plate Channel Sun, 21 Sep 2014 09:21:24 +0000 Heat transfer and fluid flow characteristics for two-dimensional laminar flow at low Reynolds number for five in-line ducts of various nonconventional cross-sections in a parallel plate channel are studied in this paper. The governing equations were solved using finite-volume method. Commercial CFD software, ANSYS Fluent 14.5, was used to solve this problem. A total of three different nonconventional, noncircular cross-section ducts and their characteristics are compared with those of circular cross-section ducts. Shape-2 ducts offered minimum flow resistance and maximum heat transfer rate most of the time. Shape-3 ducts at Re < 100 and Shape-2 ducts at Re > 100 can be considered to give out the optimum results. Siddharth D. Mhaske, Soby P. Sunny, Sachin L. Borse, and Yash B. Parikh Copyright © 2014 Siddharth D. Mhaske et al. All rights reserved. Second Law Analysis for Third-Grade Fluid with Variable Properties Mon, 08 Sep 2014 00:00:00 +0000 This paper investigates the entropy generation in a third-grade fluid flow with variable properties through a channel. Approximate solutions to the nonlinear boundary-value problem are obtained using Adomian decomposition method (ADM). Variation of important parameters on the fluid velocity, temperature distribution, entropy generation and irreversibility ratio are presented graphically and discussed. Samuel O. Adesanya Copyright © 2014 Samuel O. Adesanya. All rights reserved. Effect of Initial Stress on the Propagation Characteristics of Waves in Fiber-Reinforced Transversely Isotropic Thermoelastic Material under an Inviscid Liquid Layer Tue, 26 Aug 2014 05:16:48 +0000 The present investigation deals with the propagation of waves in fiber-reinforced transversely isotropic thermoelastic solid half space with initial stresses under a layer of inviscid liquid. The secular equation for surface equation in compact form is derived after developing the mathematical model. The phase velocity and attenuation coefficients of plane waves are studied numerically for a particular model. Effects of initial stress and thickness of the layer on the phase velocity, attenuation coefficient, and specific loss of energy are predicted graphically in the certain model. A particular case of Rayleigh wave has been discussed and the dispersion curves of the phase velocity and attenuation coefficients have also been presented graphically. Some other particular cases are also deduced from the present investigation. Rajneesh Kumar, Sanjeev Ahuja, and S. K. Garg Copyright © 2014 Rajneesh Kumar et al. All rights reserved. Thermodynamic Properties of Vapors from Speed of Sound Mon, 21 Jul 2014 07:46:46 +0000 A numerical procedure for deriving the thermodynamic properties , , and of the vapor phase in the subcritical temperature range from the speed of sound is presented. The set of differential equations connecting these properties with the speed of sound is solved as the initial-value problem in domain . The initial values of and are specified along the isotherm with the highest temperature, at a several values of [0.1,‚ÄČ1.0]. The values of are generated by the reference equation of state, while the values of are derived from the speed of sound, by solving another set of differential equations in domain in the transcritical temperature range. This set of equations is solved as the initial-boundary-value problem. The initial values of and are specified along the isochore in the limit of the ideal gas, at several isotherms distributed according to the Chebyshev points of the second kind. The boundary values of are specified along the same isotherm and along another isotherm with a higher temperature, at several values of . The procedure is tested on Ar, N2, CH4, and CO2, with the mean AADs for , , and at 0.0003%, 0.0046%, and 0.0061%, respectively (0.0007%, 0.0130%, and 0.0189% along the saturation line). Muhamed Bijedić and Sabina Begić Copyright © 2014 Muhamed Bijedić and Sabina Begić. All rights reserved. Pedagogical Visualization of a Nonideal Carnot Engine Mon, 21 Jul 2014 06:32:05 +0000 We have implemented a visualization tool for the demonstration of a nonideal Carnot engine, operating at finite time. The cycle time can be varied using a slide bar and the pressure-volume, temperature-entropy, power-time, and efficiency-time diagrams change interactively and are shown on one screen. We have evaluated the visualization tool among engineering students at university level during an introductory course on thermodynamics and we review and discuss the outcome of the evaluation. Jonas Johansson Copyright © 2014 Jonas Johansson. All rights reserved. Studies on Thermophysical Properties of CaO and MgO by -Ray Attenuation Tue, 15 Apr 2014 00:00:00 +0000 The study on temperature dependent γ-ray attenuation and thermophysical properties of CaO and MgO has been carried out in the temperature range 300 K–1250 K using different energies of γ-beam, namely, Am (0.0595 MeV), Cs (0.66 MeV), and Co (1.173 MeV and 1.332 MeV) on γ-ray densitometer fabricated in our laboratory. The linear attenuation coefficients (μl) for the pellets of CaO and MgO as a function of temperature have been determined using γ-beam of different energies. The coefficients of temperature dependence of density have been reported. The variation of density and linear thermal expansion of CaO and MgO in the temperature range of 300 K–1250 K has been studied and compared with the results available in the literature. The temperature dependence of linear attenuation coefficients, density, and thermal expansion has been represented by second degree polynomial. Volume thermal expansion coefficients have been reported. A. S. Madhusudhan Rao and K. Narender Copyright © 2014 A. S. Madhusudhan Rao and K. Narender. All rights reserved. Performance Evaluation of Refrigeration Units in Natural Gas Liquid Extraction Plant Tue, 25 Mar 2014 09:24:29 +0000 This paper has applied thermodynamics principles to evaluate the reliability of 390 m3/hr natural gas processing plant. The thermodynamics equations were utilized in the evaluation, characterization, and numerical simulation of key process parameters in natural gas liquid extraction plant. The results obtained show the comparison of the coefficient of performance, compression ratio, isentropic work, actual work, electrical power requirements, cooling water consumption in intercoolers, compressor power output, compressor capacity, and isentropic, volumetric, and mechanical efficiency of the two-stage refrigeration unit with a flash gas economizer and these were compared with the designed specifications. The second law of thermodynamics was applied in analyzing the refrigeration unit and the result shows that exergetic losses or lost work due to irreversibility falls within operating limit that is less than 1.0%. Similarly, the performance of expansion turbine (expander) parameters was monitored and the results indicate a considerable decrease in turbine efficiencies as the inlet gas pressure increases resulting in an increased power output of the turbine leading to a higher liquefaction rate. Awajiogak Anthony Ujile and Dirina Amesi Copyright © 2014 Awajiogak Anthony Ujile and Dirina Amesi. All rights reserved. Acoustic and Volumetric Properties of Mixture of (N,N-Dimethylacetamide + Ethyl Acrylate) with 1-Butanol or iso-Butanol or t-Butanol at 308.15 K Thu, 27 Feb 2014 07:03:26 +0000 Densities, , and ultrasonic speeds, of mixtures of 1-butanol or iso-butanol or t-butanol with equimolar mixture of (N,N-dimethylacetamide + Ethyl acrylate) over the entire composition range have been measured at  K. Using the experimental results, deviation in ultrasonic speed, , deviation in isentropic compressibility, , excess molar volume, , excess intermolecular free length, , and excess acoustic impedance, , have been calculated. The variation of these properties with composition of the mixtures has been discussed in terms of molecular interactions in these mixtures. The deviation/excess properties have been fitted to Redlich-Kister type polynomial and the corresponding standard deviations have been calculated. Negative values of , , and and positive values of , and are observed over the entire composition range. The observed negative and positive values of deviation/excess properties are attributed to the strong interactions between the unlike molecules of the mixtures. Further theoretical values of sound velocity in the mixtures have been evaluated using various theories and compared with experimental sound velocities to verify the applicability of such theories to the systems studied. Theoretical ultrasonic velocity data has been used to study molecular interactions in the systems investigated. M. Kondaiah, K. Sreekanth, D. Sravana Kumar, and D. Krishna Rao Copyright © 2014 M. Kondaiah et al. All rights reserved. Thermophysical Properties of Binary Mixtures of Dimethylsulfoxide with 1-Phenylethanone and 1,4-Dimethylbenzene at Various Temperatures Mon, 24 Feb 2014 13:40:56 +0000 This research article reports the experimental results of the density, viscosity, refractive index, and speed of sound analysis of binary mixtures of dimethylsulfoxide (DMSO) + 1-phenylethanone (acetophenone) and + 1,4-dimethylbenzene (para-xylene) over the whole composition range at 313.15, 318.15, 323.15, and 328.15 K and at atmospheric pressure. The excess molar volumes (), viscosity deviations (), excess Gibbs energy of activation (), deviations in isentropic compressibility (), deviations in speed of sound (), and deviations in the molar refraction () were calculated from the experimental data. The computed quantities were fitted to the Redlich-Kister equation to derive the coefficients and estimate the standard error values. The viscosities have also been correlated with two, and three-parameter models, that is, Heric correlation, McAllister model, and Grunberg-Nissan correlation, respectively. Harmandeep Singh Gill and V. K. Rattan Copyright © 2014 Harmandeep Singh Gill and V. K. Rattan. All rights reserved. Thermal Performance and Economic Analysis of 210 MWe Coal-Fired Power Plant Wed, 12 Feb 2014 11:10:02 +0000 This paper presents the thermal and economic performance of a 210 MWe coal-fired power plant situated in North India. Analysis is used to predict coal consumption rate, overall thermal efficiency, mass flow rate of steam through boiler, and Net present value (NPV) of plant for given load. Thermodynamic analysis was carried out using mass and energy equations followed by empirical correlations. Predicted mass flow rate of steam, coal consumption rate, and thermal efficiency give fair agreement with plant operating data. The economic analysis includes operational activities such as equipment cost, fuel cost, operations and maintenance cost, revenue, and plant net present value. From economic point of view, the effect of condensate extraction pump redundancy on net present value is observed to be sensitive than boiler feed pump redundancy. Ravinder Kumar, Avdhesh Kr. Sharma, and P. C. Tewari Copyright © 2014 Ravinder Kumar et al. All rights reserved. Second Law Analysis of Laminar Flow in a Circular Pipe Immersed in an Isothermal Fluid Tue, 31 Dec 2013 12:31:34 +0000 Entropy generation and pumping power to heat transfer ratio (PPR) of a laminar flow, for a circular tube immersed in an isothermal fluid, are studied analytically in this paper. Two different fluids, namely, water and ethylene glycol, are chosen to study the influence of fluid properties on entropy generation and PPR. The expressions for dimensionless entropy generation, Bejan number and PPR are derived in a detailed way and their variations with Reynolds number, external Biot number, and the dimensionless temperature difference are illustrated. The results of the analysis are compared with those for a laminar flow in a circular tube with uniform wall temperature boundary condition. Finally, a criterion is established to determine which type of thermal boundary conditions is more suitable for a particular fluid, with respect to its influence on entropy generation. Vishal Anand and Krishna Nelanti Copyright © 2013 Vishal Anand and Krishna Nelanti. All rights reserved. Nonlinear Closure Relations for Electron Transport in Hydrodynamical Models Mon, 23 Dec 2013 09:29:15 +0000 Closure relations problem of hydrodynamical models in semiconductors is considered by expressing third- and fourth-order closure relations for the moments of the distribution function in terms of second-order Lagrange multipliers using a generalized Maxwell-Boltzmann distribution function within information theory. Calculation results are commented and compared with others to justify the accuracy of the approach developed in this paper. The comparison involves, in the first part with good agreements, the closure relations results obtained within extended thermodynamics which were checked by means of Monte Carlo simulations, in the second part, the results obtained by Grad's method which expands the distribution function up to fourth-order in Hermite polynomials. It is seen that the latter method cannot give any restriction on closure relations for higher-order moments, within the same conditions proposed in our approach. The important role of Lagrange multipliers for the determination of all closure relations is asserted. A. Salhoumi Copyright © 2013 A. Salhoumi. All rights reserved. MHD Stagnation-Point Flow of Casson Fluid and Heat Transfer over a Stretching Sheet with Thermal Radiation Thu, 10 Oct 2013 18:42:04 +0000 The two-dimensional magnetohydrodynamic (MHD) stagnation-point flow of electrically conducting non-Newtonian Casson fluid and heat transfer towards a stretching sheet have been considered. The effect of thermal radiation is also investigated. Implementing similarity transformations, the governing momentum, and energy equations are transformed to self-similar nonlinear ODEs and numerical computations are performed to solve those. The investigation reveals many important aspects of flow and heat transfer. If velocity ratio parameter (B) and magnetic parameter (M) increase, then the velocity boundary layer thickness becomes thinner. On the other hand, for Casson fluid it is found that the velocity boundary layer thickness is larger compared to that of Newtonian fluid. The magnitude of wall skin-friction coefficient reduces with Casson parameter (β). The velocity ratio parameter, Casson parameter, and magnetic parameter also have major effects on temperature distribution. The heat transfer rate is enhanced with increasing values of velocity ratio parameter. The rate of heat transfer is enhanced with increasing magnetic parameter M for B > 1 and it decreases with M for B < 1. Moreover, the presence of thermal radiation reduces temperature and thermal boundary layer thickness. Krishnendu Bhattacharyya Copyright © 2013 Krishnendu Bhattacharyya. All rights reserved. Two Temperature Magneto-Thermoelasticity with Initial Stress: State Space Formulation Mon, 30 Sep 2013 10:27:12 +0000 Magneto-thermoelastic interactions in an initially stressed isotropic homogeneous elastic half-space with two temperatures are studied using mathematical methods under the purview of the L-S model of linear theory of generalized thermoelasticity. The formalism deals with the state space approach with the purpose of counteracting the difficulties of handling the displacement potential functions. Of specific concern here is the propagation of waves owing to ramp type increase in temperature and load. The medium is considered to be permeated by a uniform magnetic field. The expressions for different field parameters such as displacement, temperature, strain, and stress in the physical domain are obtained by applying a numerical inversion technique. Results of some earlier workers have been deduced from the present formulation. Numerical work is also performed for a suitable material with the aim of illustrating the results. Sunita Deswal and Kapil Kumar Kalkal Copyright © 2013 Sunita Deswal and Kapil Kumar Kalkal. All rights reserved. Effect of Size and Shape on the Vibrational and Thermodynamic Properties of Nanomaterials Thu, 19 Sep 2013 13:13:45 +0000 A simple theoretical model is developed to study the size and shape dependence of vibrational and thermodynamic properties of nanomaterials. To show the real connection with the nanomaterials we have studied Debye temperature, Debye frequency, melting entropy, and enthalpy in different shapes, namely, spherical, nanowire, and nanofilm of -Fe, Sn, Ag, and In. The results obtained are compared with the experimental data. A good agreement between the model predictions and the experimental data supports the theory developed in the present paper. R. Kumar, G. Sharma, and M. Kumar Copyright © 2013 R. Kumar et al. All rights reserved. Batch Sorption Experiments: Langmuir and Freundlich Isotherm Studies for the Adsorption of Textile Metal Ions onto Teff Straw (Eragrostis tef) Agricultural Waste Tue, 17 Sep 2013 10:48:03 +0000 Adsorption of heavy metals (Cr, Cd, Pb, Ni, and Cu) onto Activated Teff Straw (ATS) has been studied using batch-adsorption techniques. This study was carried out to examine the adsorption capacity of the low-cost adsorbent ATS for the removal of heavy metals from textile effluents. The influence of contact time, pH, Temperature, and adsorbent dose on the adsorption process was also studied. Results revealed that adsorption rate initially increased rapidly, and the optimal removal efficiency was reached within about 1 hour. Further increase in contact time did not show significant change in equilibrium concentration; that is, the adsorption phase reached equilibrium. The adsorption isotherms could be fitted well by the Langmuir model. The value in the present investigation was less than one, indicating that the adsorption of the metal ion onto ATS is favorable. After treatment with ATS the levels of heavy metals were observed to decrease by 88% (Ni), 82.9% (Cd), 81.5% (Cu), 74.5% (Cr), and 68.9% (Pb). Results indicate that the freely abundant, locally available, low-cost adsorbent, Teff straw can be treated as economically viable for the removal of metal ions from textile effluents. Mulu Berhe Desta Copyright © 2013 Mulu Berhe Desta. All rights reserved. Studies on Excess Volume, Viscosity, and Speed of Sound of Binary Mixtures of Methyl Benzoate in Ethers at and  K Mon, 26 Aug 2013 10:10:49 +0000 Densities, viscosities, and speed of sound have been determined at T = (303.15, 308.15, and 313.15) K for the binary mixtures of methyl benzoate with tetrahydrofuran, 1,4-dioxane, anisole, and butyl vinyl ether over the entire range of composition. Using these measured values, excess volume , deviation in viscosities , excess Gibb’s free energy of activation for viscous flow , and deviation in isentropic compressibility have been calculated. These calculated binary data have been fitted to Redlich-Kister equation to determine the appropriate coefficients. The values of excess volume and deviation in viscosities are negative over the entire range of composition for all the binary systems at the studied temperatures. The behavior of these parameters with composition of the mixture has been discussed in terms of molecular interactions between the components of liquids. M. V. Rathnam, Devappa R. Ambavadekar, and M. Nandini Copyright © 2013 M. V. Rathnam et al. All rights reserved. Stagnation Point Flow of a Nanofluid toward an Exponentially Stretching Sheet with Nonuniform Heat Generation/Absorption Sun, 18 Aug 2013 14:14:00 +0000 This paper deals with the steady two-dimensional stagnation point flow of nanofluid toward an exponentially stretching sheet with nonuniform heat generation/absorption. The employed model for nanofluid includes two-component four-equation nonhomogeneous equilibrium model that incorporates the effects of Brownian diffusion and thermophoresis simultaneously. The basic partial boundary layer equations have been reduced to a two-point boundary value problem via similarity variables and solved analytically via HAM. Effects of governing parameters such as heat generation/absorption λ, stretching parameter ε, thermophoresis , Lewis number Le, Brownian motion , and Prandtl number Pr on heat transfer and concentration rates are investigated. The obtained results indicate that in contrast with heat transfer rate, concentration rate is very sensitive to the abovementioned parameters. Also, in the case of heat generation , despite concentration rate, heat transfer rate decreases. Moreover, increasing in stretching parameter leads to a gentle rise in both heat transfer and concentration rates. A. Malvandi, F. Hedayati, and G. Domairry Copyright © 2013 A. Malvandi et al. All rights reserved. Excess Molar Volumes and Viscosities for the Binary Mixtures of n-Octane, n-Decane, n-Dodecane, and n-Tetradecane with Octan-2-ol at 298.15 K Tue, 25 Jun 2013 17:08:51 +0000 Experimental values of densities (ρ) and viscosities (η) in the binary mixtures of n-octane, n-decane, n-dodecane, and n-tetradecane with octan-2-ol are presented over the whole range of mixture composition at  K. From these data, excess molar volume (), deviations in viscosity , and excess Gibbs free energy of activation have been calculated. These results were fitted to Redlich-Kister polynomial equations to estimate the binary coefficients and standard errors. Jouyban-Acree model is used to correlate the experimental values of density and viscosity at  K. The values of have been analyzed using Prigogine-Flory-Patterson (PFP) theory. The results of the viscosity composition are discussed in the light of various viscosity equations suggested by Grunberg-Nissan, Tamara and Kurata, Hind et al., Katti and Chaudhri, Heric, Heric and Brewer, and McAllister multibody model. The values of have also been analyzed using Bloomfield and Dewan model. The experiments on the constituted binaries are analyzed to discuss the nature and strength of intermolecular interactions in these mixtures. Arvind R. Mahajan and Sunil R. Mirgane Copyright © 2013 Arvind R. Mahajan and Sunil R. Mirgane. All rights reserved. Effects of Exothermic/Endothermic Chemical Reactions with Arrhenius Activation Energy on MHD Free Convection and Mass Transfer Flow in Presence of Thermal Radiation Sun, 23 Jun 2013 10:36:35 +0000 A local similarity solution of unsteady MHD natural convection heat and mass transfer boundary layer flow past a flat porous plate within the presence of thermal radiation is investigated. The effects of exothermic and endothermic chemical reactions with Arrhenius activation energy on the velocity, temperature, and concentration are also studied in this paper. The governing partial differential equations are reduced to ordinary differential equations by introducing locally similarity transformation (Maleque (2010)). Numerical solutions to the reduced nonlinear similarity equations are then obtained by adopting Runge-Kutta and shooting methods using the Nachtsheim-Swigert iteration technique. The results of the numerical solution are obtained for both steady and unsteady cases then presented graphically in the form of velocity, temperature, and concentration profiles. Comparison has been made for steady flow () and shows excellent agreement with Bestman (1990), hence encouragement for the use of the present computations. Kh. Abdul Maleque Copyright © 2013 Kh. Abdul Maleque. All rights reserved. Thermo Physical Properties for Binary Mixture of Dimethylsulfoxide and Isopropylbenzene at Various Temperatures Mon, 29 Apr 2013 09:04:43 +0000 Density, refractive index, speed of sound, and viscosity have been measured of binary mixture dimethylsulfoxide (DMSO) + isopropylbenzene (CUMENE) over the whole composition range at 298.15, 303.15, 308.15, and 313.15 K and atmospheric pressure. From these experimental measurements the excess molar volume, deviations in viscosity, molar refractivity, speed of sound, and isentropic compressibility have been calculated. These deviations have been correlated by a polynomial Redlich-Kister equation to derive the coefficients and standard error. The viscosities have furthermore been correlated with two or three parameter models, that is, herric correlation and McAllister model, respectively. Maninder Kumar and V. K. Rattan Copyright © 2013 Maninder Kumar and V. K. Rattan. All rights reserved. Modified Lennard-Jones Potentials with a Reduced Temperature-Correction Parameter for Calculating Thermodynamic and Transport Properties: Noble Gases and Their Mixtures (He, Ne, Ar, Kr, and Xe) Mon, 15 Apr 2013 16:12:39 +0000 The three-parameter Lennard-Jones potential function is proposed to calculate thermodynamic property (second virial coefficient) and transport properties (viscosity, thermal conductivity, and diffusion coefficient) of noble gases (He, Ne, Ar, Kr, and Xe) and their mixtures at low density. Empirical modification is made by introducing a reduced temperature-correction parameter to the Lennard-Jones potential function for this purpose. Potential parameters (, , and ) are determined individually for each species when the second virial coefficient and viscosity data are fitted together within the experimental uncertainties. Calculated thermodynamic and transport properties are compared with experimental data by using a single set of parameters. The present study yields parameter sets that have more physical significance than those of second virial coefficient methods and is more discriminative than the existing transport property methods in most cases of pure gases and of gas mixtures. In particular, the proposed model is proved with better results than those of the two-parameter Lennard-Jones potential, Kihara Potential with group contribution concepts, and other existing methods. Seung-Kyo Oh Copyright © 2013 Seung-Kyo Oh. All rights reserved. Thermodynamic and Acoustic Study on Molecular Interactions in Certain Binary Liquid Systems Involving Ethyl Benzoate Mon, 25 Mar 2013 10:09:49 +0000 Speeds of sound and density for binary mixtures of ethyl benzoate (EB) with N,N-dimethylformamide (NNDMF), N,N-dimethyl acetamide (NNDMAc), and N,N-dimethylaniline (NNDMA) were measured as a function of mole fraction at temperatures 303.15, 308.15 K, 313.15 K, and 318.15 K and atmospheric pressure. From the experimental data, adiabatic compressibility (), intermolecular free length (), and molar volume () have been computed. The excess values of the above parameters were also evaluated and discussed in light of molecular interactions. Deviation in adiabatic compressibilities and excess intermolecular free length () are found to be negative over the molefraction of ethyl benzoate indicating the presence of strong interactions between the molecules. The negative excess molar volume values are attributed to strong dipole-dipole interactions between unlike molecules in the mixtures. The binary data of , , and were correlated as a function of molefraction by using the Redlich-Kister equation. B. Nagarjun, A. V. Sarma, G. V. Rama Rao, and C. Rambabu Copyright © 2013 B. Nagarjun et al. All rights reserved. Second Law Analysis of a Gas-Liquid Absorption Film Mon, 25 Feb 2013 10:17:28 +0000 This paper reports an analytical study of the second law in the case of gas absorption into a laminar falling viscous incompressible liquid film. Velocity, temperature, and concentration profiles are determined and used for the entropy generation calculation. Irreversibilities due to heat transfer, fluid friction, and coupling effects between heat and mass transfer are derived. The obtained results show that entropy generation is mainly due to coupling effects between heat and mass transfer near the gas-liquid interface. Total irreversibility is minimum at the diffusion film thickness. On approaching the liquid film thickness, entropy generation is mainly due to viscous irreversibility. Nejib Hidouri, Imen Chermiti, and Ammar Ben Brahim Copyright © 2013 Nejib Hidouri et al. All rights reserved. Maximum Power Point Characteristics of Generalized Heat Engines with Finite Time and Finite Heat Capacities Thu, 20 Dec 2012 17:00:22 +0000 We revisit the problem of optimal power extraction in four-step cycles (two adiabatic and two heat-transfer branches) when the finite-rate heat transfer obeys a linear law and the heat reservoirs have finite heat capacities. The heat-transfer branch follows a polytropic process in which the heat capacity of the working fluid stays constant. For the case of ideal gas as working fluid and a given switching time, it is shown that maximum work is obtained at Curzon-Ahlborn efficiency. Our expressions clearly show the dependence on the relative magnitudes of heat capacities of the fluid and the reservoirs. Many previous formulae, including infinite reservoirs, infinite-time cycles, and Carnot-like and non-Carnot-like cycles, are recovered as special cases of our model. Abhishek Khanna and Ramandeep S. Johal Copyright © 2012 Abhishek Khanna and Ramandeep S. Johal. All rights reserved. CFD Analysis for Heat Transfer Enhancement inside a Circular Tube with Half-Length Upstream and Half-Length Downstream Twisted Tape Tue, 11 Dec 2012 17:15:58 +0000 CFD investigation was carried out to study the heat transfer enhancement characteristics of air flow inside a circular tube with a partially decaying and partly swirl flow. Four combinations of tube with twisted-tape inserts, the half-length upstream twisted-tape condition (HLUTT), the half-length downstream twisted-tape condition (HLDTT), the full-length twisted tape (FLTT), and the plain tube (PT) with three different twist parameters (, 0.27, and 0.38) have been investigated. 3D numerical simulation was performed for an analysis of heat transfer enhancement and fluid flow for turbulent regime. The results of CFD investigations of heat transfer and friction characteristics are presented for the FLTT, HLUTT, and the HLDTT in comparison with the PT case. R. J. Yadav and A. S. Padalkar Copyright © 2012 R. J. Yadav and A. S. Padalkar. All rights reserved. Temperature Dependence of the Raman Frequency of an Internal Mode for SiO2-Moganite Close to the α-β Transition Sun, 09 Dec 2012 15:10:47 +0000 The temperature dependence of the 501 cm−1 frequency of the vibrational mode is analyzed for SiO2-moganite. The experimental data for the heating and cooling cycles of moganite from the literature is used for our analysis. The coexistence of α-β moganite is obtained over a finite temperature interval, and the α-β moganite transition at around 570 K is studied, as observed experimentally. Mustafa Cem Lider and Hamit Yurtseven Copyright © 2012 Mustafa Cem Lider and Hamit Yurtseven. All rights reserved. Two-Dimensional Analytical Solution of the Laminar Forced Convection in a Circular Duct with Periodic Boundary Condition Thu, 29 Nov 2012 10:56:08 +0000 In the present study analytical solution for forced convection heat transfer in a circular duct with a special boundary condition has been presented, because the external wall temperature is a periodic function of axial direction. Local energy balance equation is written with reference to the fully developed regime. Also governing equations are two-dimensionally solved, and the effect of duct wall thickness has been considered. The temperature distribution of fluid and solid phases is assumed as a periodic function of axial direction and finally temperature distribution in the flow field, solid wall, and local Nusselt number, is obtained analytically. M. R. Astaraki and N. Ghiasi Tabari Copyright © 2012 M. R. Astaraki and N. Ghiasi Tabari. All rights reserved. Pippard Relations Close to the Melting Point in the Premelting Region of Hexadecane Tue, 13 Nov 2012 17:14:17 +0000 We examine here the validity of the Pippard relations close to the melting point in the premelting region of hexadecane. For this verification, we analyze the observed data for the thermal expansivity obtained for various pressures at constant temperatures of 302 and 325 K in this system. By calculating the isothermal compressibility and the specific heat in the same pressure region of the premelting region of hexadecane, we obtain that varies linearly with and also that varies linearly with for this system. This indicat es that some molecular organic compounds, such as solid hexadecane studied here, can exhibit -phase transitions prior to melting which are expected to verify the Pippard relations. Hamit Yurtseven, Özcan Tilki, and Mustafa Kurt Copyright © 2012 Hamit Yurtseven et al. All rights reserved. Conductometric Studies of Thermodynamics of Complexation of Co2+, Ni2+, Cu2+, and Zn2+ Cations with Aza-18-crown-6 in Binary Acetonitrile-Methanol Mixtures Sun, 11 Nov 2012 10:38:29 +0000 The complexation reactions between aza-18-crown-6 (A18C6) and Co2+, Ni2+, Cu2+, and Zn2+ ions were studied conductometrically in different acetonitrile-methanol mixtures at various temperatures. The formation constants of the resulting 1 : 1 complexes were calculated from the computer fitting of the molar conductance-mole ratio data at different temperatures. Selectivity of A18C6 for Co2+, Ni2+, Cu2+, and Zn2+ cations is sensitive to the solvent composition. At 20°C and in acetonitrile solvent, the stability of the resulting complexes varied in the order but the order was reversed byadding 20% methanol. The enthalpy and entropy changes of the complexation reactions were evaluated from the temperature dependence of formation constants. It was found that the stability of the resulting complexes decreased with increasing methanol in the solvent mixture. The TΔS° versus ΔH° plot of thermodynamic data obtained shows a fairly good linear correlation indicating the existence of enthalpy-entropy compensation in the complexation reactions. In addition, binding energies of Ni2+, Cu2+, and Zn2+ complexes with A18C6 were calculated at B3LYP/6-31G level of theory. Mehdi Taghdiri, Mahmood Payehghadr, Reza Behjatmanesh-Ardakani, and Homa Gha'ari Copyright © 2012 Mehdi Taghdiri et al. All rights reserved.