Heat Capacity Of Gas Research Articles

Reverse engineering of fluid selection for thermodynamic cycles with cubic equations of state, using a compression heat pump as example

Fluid selection for thermodynamic cycles like refrigeration cycles, heat pumps or organic Rankine cycles remains an actual topic. Generally the search for a working fluid is based on experimental approaches or on a not very systematic trial and error approach, far from being elegant. An alternative method may be a theory based reverse engineering approach, proposed and investigated here: The design process should start with an optimal process and with (abstract) properties of the fluid needed to fit into this optimal process, best described by some general equation of state and the corresponding fluid-describing parameters. These should be analyzed and optimized with respect to the defined model process, which also has to be optimized simultaneously. From this information real fluids can be selected or even synthesized which have fluid defining properties in the optimum regime like critical temperature or ideal gas capacities of heat, allowing to find new working fluids, not considered so far. The number and kind of the fluid-defining parameters is mainly based on the choice of the used EOS (equation of state). The property model used in the present work is based on the cubic Peng–Robinson equation, chosen due to its moderate numerical expense, sufficient accuracy as well as a general availability of the fluid-defining parameters for many compounds.The considered model-process works between the temperature levels of 273.15 and 333.15 K and can be used as heat pump for supplying buildings with heat, typically. The objective functions are the COP (coefficient of performance) and the VHC (volumetric heating capacity) as a function of critical pressure, critical temperature, acentric factor and two coefficients for the temperature-dependent isobaric ideal gas heat capacity. Also, the steam quality at the compressor entrance has to be regarded as a problem variable. The results give clear hints regarding optimal fluid parameters of the analyzed process and deepen the thermodynamic understanding of the process. Finally, for the COP optimization a strategy for screening large databases is explained. Several fluids from different substance groups like hydrogen iodide (COP = 3.68), formaldehyde (3.61) or cyclopropane (3.42) were found to have higher COPs than the often used R134a (3.12). These fluids will also have to fulfill further criteria, prior to their usage, but the method appears to be a good base for fluid selection.

Performance Analysis of Power Generation by Producer Gas from Refuse Derived Fuel-5 (RDF-5)

At present, municipal and city corporation governments throughout the world are facing choices about how to manage the unending stream of waste generated by their residents and businesses. In many places landfills and dumpsites are filling up, and all landfills and dumpsites leak into the environment; due to increasing populations, the issue of waste becomes more urgent and more complicated. Many regions are already facing a waste crisis, and drastic measures are needed. In the past, the main approach to waste management operations is the landfill which is causes many environmental pollutions and health hazards. Furthermore, extending the land for land filling is the one of best solutions. This paper demonstrated the performance analysis of power generation producer gas from RDF-5 in Chiang Mai University, Thailand. The efficiency of different ratio waste composition and of RDF-5 was revealed. In addition, the humidity, density and heat capacity of RDF-5 are also focused. In order to analyze the compositions, heat capacity of producer gas, fuel consumption, efficiency of producer gas system, waste water and quantity of ash; RDF-5 have been tested by using producer gas in different ratio of oxygen and fuel. In term of automobile application, the performance of RDF-5 and Diesel-RDF-5 are compared; and the specific factors such as power, specific fuel consumption rate, carbon dioxide, sound level and fuel feeding were included that comparison. Consequently, this paper mainly focused and concerned with the production and properties of refuse derived fuel-5 for use in energy from waste technologies.

Thermodynamic properties of electron gas in complex-shaped quantum well

Thermodynamic properties of degenerate two-dimensional electron gas in complex-shaped quantum well are studied. We determine the equation of state, chemical potential, entropy and heat capacity of the electron gas. An influence of profile and parameters of the quantum well on thermodynamic characteristics are investigated.

Equation of state modeling for the vapor pressure of biodiesel fuels

The vapor pressure and liquid heat capacity of seven biodiesel fuels and its components (fatty acid methyl esters – FAMEs) were modeled using the advance Peng–Robinson equation of state. The dataset used for the modeling was obtained from the literature and included FAME properties and the composition, vapor pressure, and liquid heat capacity of the biodiesel fuels from different sources at temperatures from 50 to 130°C and −30 to 75°C, respectively. New values for the critical properties and acentric factor of FAMEs are introduced as well as new models for the ideal gas heat capacity for the FAMEs. The average AARD is 12% for vapor pressure and 3% for liquid heat capacity.

Experimental Measurements and Thermodynamic Modelling of Carbon Dioxide Capture with use of 2-(Ethylamino) Ethanol

Carbon dioxide solubility was studied in 2.5 mass % and 5 mass % aqueous 2 (Ethylamino)ethanol (EAE; CAS 110- 73-6) solution, an interesting secondary amine prepared mainly from renewable resources, at high loading rates, at three temperature ranges (293.00K, 313.15 K, 333.15 K), and in pressure range from 289 to 1011 kPa. In addition to that, heat capacity (cp) was measured of examined solution, allowing determination of temperature dependent coefficients of ideal gas heat capacity equation. Afterwards, the electrolyte Non Random Two-Liquid model’s parameters were determined to represent the thermodynamic behaviour of the CO2 – EAE – H2O system with use of ASPEN® Plus V8.0 simulation software, indicating a good correlation between experimental and simulation results. As a consequence, model based calculation of the carbon dioxide capture with use of 2-(Ethylamino) ethanol is possible.

Continuous Molecular Targeting–Computer-Aided Molecular Design (CoMT–CAMD) for Simultaneous Process and Solvent Design for CO2 Capture

Solvent-based separation systems have a substantial potential for improvement when the solvent and the process conditions are optimized simultaneously. The fully integrated design problem, however, leads to an optimization problem of prohibitive size and complexity owing to the many discrete degrees of freedom in selecting a solvent and the nonlinear nature of the process models. We here implement and extend the method of continuous molecular targeting–computer-aided molecular design (CoMT–CAMD) for the solvent and process optimization of a precombustion CO2-capture system with physical absorption. CoMT–CAMD is a deterministic procedure that does not require a preselection of solvent molecules. The process topology considered in our study includes all major process operations of an existing CO2-capture system: multistage absorption, desorption (two flash desorption stages with gas recycle) and CO2 compression. We measure the process performance with a single economic objective function. The objective function captures the process trade-offs and evaluates the potential process-solvent on a common basis. The solvent is represented as the pure component parameters of the perturbed-chain statistical associating fluid theory (PC-SAFT). The optimization problem is formulated with the pure component parameters of the solvent (PC-SAFT parameters) and with the process variables as degrees of freedom. Necessary auxiliary properties of the optimized solvent such as the ideal gas heat capacity and the molar mass are predicted with quantitative structure property relationship models, based on the pure component PC-SAFT parameters. As a result, one gets a unified thermodynamic framework for fluid properties based on the PC-SAFT model. With CoMT–CAMD we obtain a list of the best performing physical solvents for the considered CO2-capture application. The resulting list of best performing solvents contains state-of-the-art solvents and new green solvent molecules.

On the use of departure function correlations for hydrocarbon isobaric liquid phase heat capacity calculation

Constant pressure heat capacities for pure liquids and mixtures are by default evaluated indirectly, in process simulators and in general purpose calculations, using ideal gas isobaric heat capacity values to which equation of state based departure functions are added. As ideal gas heat capacities are known or can be calculated from theory with small uncertainties and typically comprise 75% of liquid heat capacity values, the large relative deviations present in departure function calculations appear to be tolerated or ignored because deviations between indirectly calculated and measured constant pressure liquid heat capacities are typically less than 15% and large deviations are uncommon. For hydrocarbon and petroleum applications, non-cubic equations of state have a limited range of application and a cubic equation of state departure function calculations possesses a systematic skew with respect to absolute and relative temperature. This provides application windows for stand alone departure function correlations: by Tyagi that requires the input properties (Tc, Pc, ω, M) at high reduced and absolute temperatures; and a difference calculation based on correlations by Dadgostar and Shaw (for hydrocarbon liquids) and Laštovka and Shaw (for ideal gases) which extend the range of fluids for which liquid state heat capacity departure functions can be evaluated to include poorly defined (Tc and M are available) individual hydrocarbons or mixtures or ill-defined (only elemental analysis is available) hydrocarbon mixtures. However, none of these approaches provides consistently low deviations from measurements and consequently, direct calculation of liquid phase heat capacities is recommended for detailed engineering calculations.

On the isobaric specific heat capacity of natural gas

A colorimeter equipped with a gas booster in conjunction with a PVT cell was used to measure the heat capacity of natural gas with different amounts of impurities. Based on new experimental and literature data, a general investigation of the isobaric specific heat capacity was carried out using the Jarrahian–Heidaryan equation of state (J–H-EOS). A model was obtained that is valid in wide ranges of pressures (0.1–40MPa) and temperatures (250–414K). The arithmetic average of the model’s absolute error is acceptable in engineering calculations and has superiority over other methods in its class.

A Fundamental Equation of State for Ethanol

The existing fundamental equation for ethanol demonstrates undesirable behavior in several areas and especially in the critical region. In addition, new experimental data have become available in the open literature since the publication of the current correlation. The development of a new fundamental equation for ethanol, in the form of Helmholtz energy as a function of temperature and density, is presented. New, nonlinear fitting techniques, along with the new experimental data, are shown to improve the behavior of the fundamental equation. Ancillary equations are developed, including equations for vapor pressure, saturated liquid density, saturated vapor density, and ideal gas heat capacity. Both the fundamental and ancillary equations are compared to experimental data. The fundamental equation can compute densities to within ±0.2%, heat capacities to within ±1%–2%, and speed of sound to within ±1%. Values of the vapor pressure and saturated vapor densities are represented to within ±1% at temperatures of 300 K and above, while saturated liquid densities are represented to within ±0.3% at temperatures of 200 K and above. The uncertainty of all properties is higher in the critical region and near the triple point. The equation is valid for pressures up to 280 MPa and temperatures from 160 to 650 K.

Vapor pressure and gaseous speed of sound measurements for isobutane (R600a)

The vapor pressures of isobutane (R600a) were measured from (259 to 406)K. The uncertainty of the vapor pressures was estimated to be less than 300Pa. The measured vapor pressures were correlated using a Wagner-type vapor pressure equation. The critical pressure, normal boiling point and acentric factor were then determined from the vapor pressure equation. The speed of sound in gaseous isobutane was also measured along seven isotherms from (270 to 330)K using a cylindrical resonator. The perturbations from the thermal and viscous boundary layer, the gas fill duct, the shell motion and the vibrational relaxation were corrected in the resonance frequency measurements. The longitudinal acoustic modes were used to determine the speed of sound. The relative standard uncertainty in the speed of sound was estimated to be less than 0.015%. The ideal gas heat capacities and the second acoustic virial coefficients for isobutane were deduced from the speed of sound data. The second virial coefficients were obtained from the measured acoustic data and the square-well intermolecular model.

Working fluid selection and preliminary design of a solar organic Rankine cycle system

A method for the selection of the working fluid and preliminary design of an Organic Rankine Cycle system driven by solar energy are reported in this article. The performances of nine working fluids in various working conditions were analyzed, based on the turbine inlet pressure and temperature. The results from the superheated and saturated cycles are compared; and the efficiencies for the nine working fluids in different cycles are calculated. Latent heat, critical temperature, liquid heat capacity and gas heat capacity show complicated effects on the efficiency of the cycle. The thermal stability experiment of the optimal candidate is also reported in the article, and the results show that MM (hexamethyldisiloxane) is stable with the material of the system up to 300°C. As a result, MM is chosen as the working fluid for this system. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 619–626, 2015

High-Throughput Calculations of Molecular Properties in the MedeA Environment: Accuracy of PM7 in Predicting Vibrational Frequencies, Ideal Gas Entropies, Heat Capacities, and Gibbs Free Energies of Organic Molecules

The atomistic and molecular simulation environment MedeA (MedeA: Materials Exploration and Design Analysis, version 2.14.6; Material Design, Inc.: Angel Fire, NM, 1998–2014; http://www.materialsdesign.com) in its functionalities and graphical user interface has been enhanced to prepare and submit on the order of 1000 simulations on different structures, and to collect and help in the analysis of the results. We illustrate this with the determination of the accuracy of the semiempirical (SE) package MOPAC2012 (Stewart, J. J. P. MOPAC2012; Stewart Computational Chemistry: Colorado Springs, CO, USA, 2012; http://OpenMOPAC.net) with the PM7 method (Stewart, J. J. P. Optimization of parameters for semiempirical methods VI: more modifications to the NDDO approximations and reoptimization of parameters. J. Mol. Model. 2013, 19, 1–32) to compute frequencies of vibration and thermodynamic properties, specifically the zero point energies, ideal gas heat capacity at constant pressure, entropy, and Gibbs free energy, between 200 and 1000 K for 795 organic molecules. The results were compared with experimental data and density functional theory (DFT) values (using B3LYP/TZVP and BP86/TZVP DFT methods). This comparison showed that the PM7 frequencies of vibration above 2500 cm–1 are systematically underestimated. An a posteriori correction using a linear relationship rescaling of the frequencies permitted resetting to zero the average relative deviations with respect to experimental reference values. This frequency correction also removed the bias from the zero point energies, ideal gas heat capacity, and entropy average deviations from the PM7 results. The root-mean-square deviation (RMSD) of PM7 and the DFT heat capacities of 160 organic molecules were equivalent with respect to experimental values, being about 5 %, 2.5 %, and 3 % at 300 K, 600 K, and 1000 K, respectively. The RMSD of PM7, when compared to the DFT values, became 4 %, 2 %, and 1 % for the same temperatures when the analysis was extended to a set of 795 molecules. In the case of the ideal gas entropies, the RMSD of the PM7 relative to DFT values were between 5 % and 4 % between 300 K and 1000 K, respectively. The RMSD of the Gibbs free energies of PM7 were 15 kJ mol–1 and 30 kJ mol–1 at 300 K and 1000 K, respectively. The efficiency of this semiempirical approach was tested on a set of approximately 5800 molecules. This set was processed in about a day, thus demonstrating the scalability of the approach to big data sets.

Isobaric specific heat capacity of natural gas as a function of specific gravity, pressure and temperature

Natural gas engineering entails production, processing, storage and transportation of natural gas. A good handling of the gas requires a sophisticated understanding of how its density, compressibility, pseudo-pressure and specific heat capacity vary with the gas condition. A variety of methods have been presented in petroleum and gas journals and a host of scholastic materials to evaluate other properties over a wide range of temperatures, however, the available correlation for isobaric specific heat capacity is for only 150 °F. We generated 200 samples of natural gas mixture with methane component ranging from 0.74 to 0.9985 using normally distributed experimental design. The variations of the respective specific heat capacity of the components and the effect of composition on the specific gravity and overall specific heat capacity of the gas were taken into consideration. The developed correlation reads in the specific gravity and temperature to generate the ideal gas specific heat capacity of the sample. The result yielded 99.75% accuracy at 150 °F when compared to experimental data, as against the result from isentropic coefficient method which overestimated the ideal gas specific heat capacity by 25% at the same temperature. The ideal gas specific heat capacity developed compared to 6000 data points generated from mixing rule at different temperatures resulted in correlation regression coefficient of 0.9999. To account for the deviation from ideal gas behaviour, this work presents 99.7% R squared value for dimensionless residual specific heat capacity as a function of reduced temperature and pressure compared to that calculated from Starling Carnahan equation of state. This model is the first explicit correlation for the residual specific heat capacity of natural gas to be derived.

Simultaneous Optimization of Working Fluid and Process for Organic Rankine Cycles Using PC-SAFT

Organic Rankine Cycles (ORCs) generate power from low temperature heat. To make the best use of the diverse low temperature heat sources, the cycle is tailored to each application. The objective is to maximize process performance by optimizing both process parameters and the working fluid. Today, process optimization and working fluid selection are typically addressed separately in a two-step approach: working fluids are selected using heuristic knowledge; subsequently, the process is optimized. Such an approach can lead to suboptimal solutions, since the optimal fluid might be excluded by the heuristics. We therefore present a framework for the holistic design of ORCs enabling the simultaneous optimization of the process and the working fluid based on process performance. The simultaneous optimization is achieved by exploiting the rich molecular picture underlying the PC-SAFT equation of state in a continuous-molecular targeting approach (CoMT-CAMD). To allow for the prediction of caloric properties, a quantitative structure–property relationship (QSPR) for the ideal gas heat capacity is proposed that relies on pure component parameters of PC-SAFT. The framework is used for the optimization of a geothermal ORC in a case study. A sound holistic design of process and working fluid is achieved.

Simulations of the PC boiler equipped with complex swirling burners

Purpose – The purpose of this paper is to show possible approaches which can be used for modeling complex flow phenomena caused by swirl burners combined with simulating coal combustion process using air- and oxy-combustion technologies. Additionally, the response of exist boiler working parameter on changing the oxidizer composition from air to a mixture of the oxygen and recirculated flue gases is investigated. Moreover, the heat transfer in the superheaters section of the boiler was taken into account by modeling of the heat exchange process between continuum phase and three stages of the steam superheaters. Design/methodology/approach – An accurate solution of the flow field is required in order to predict combustion phenomena correctly for numerical simulations of the industrial pulverized coal (PC) boilers. Nevertheless, it is a very demanding task due to the complicated swirl burner construction and complex character of the flow. The presented simulations were performed using the discrete phase model for tracking particles and combustion phenomena in a dispersed phase, whereas the Eulerian approach was applied for the volatile combustion process modeling in a gaseous phase. Findings – Applying the air- to oxy-combustion technology the temperature in the combustion chamber, decreased for investigated oxidizer compositions. This was caused by the higher heat capacity of flue gases which also influences on the level of the heat flux at the boiler walls. Simulations shows that increasing the O2 concentration to 30 percent of volume base in the oxidizer mixture provided the similar combustion conditions as those for the conventional air firing. Moreover, the evaluated results give a good overview of differences between approaches used for complex swirl burners simulations. Practical implications – Nowadays, the numerical techniques such as computational fluid dynamic (CFD) can be seen as an useful engineering tool for design and processes optimization purposes. The application of the CFD gives a possibility to predict the combustion phenomena in a large industrial PC boiler and investigate the impact of changing the combustion technology from a conventional air firing to oxy-fuel combustion. Originality/value – This paper gives good overview on existing technique, approaches used for modeling PC boiler equipped with complex swirl burners. Additionally, the novelty of this work is application of the heat exchanger model for predicting heat loses in convective section of the boiler. This usually is not taken into account during simulations. The reader can also find basic concept of oxy-combustion technology, and their impact on boiler working conditions.

Ideal Gas Heat Capacity Derived from Speed of Sound Measurements in the Gaseous Phase for trans-1,3,3,3-Tetrafluoropropene

trans-1,3,3,3-Tetrafluoropropene (HFO-1234ze(E)) is considered as an alternative refrigerant in automobile air conditioning applications because of its low global warming potential. For the purpose of evaluation of thermophysical properties of HFO-1234ze(E), the speed of sound was measured in the dilute gas region in order to derive heat capacities in the ideal gas state. The speed of sound was obtained from measurements of acoustic resonance frequencies of radial modes in a spherical resonator filled with sample gas. Taking some perturbation effects into account, the speed of sound was determined with a relative uncertainty of 0.01 %. The speed of sound data were fitted to the acoustic virial equation. By extrapolating the speed of sound data on each isotherm to zero pressure, the ideal gas heat capacities at constant pressure were determined with a relative uncertainty of 0.1 %. The isobaric ideal gas heat capacities were represented by a third-order polynomial function in temperature.

Thermophysical characterization of N-methyl-2-hydroxyethylammonium carboxilate ionic liquids

The thermophysical properties including density, heat capacity, thermal stability and phase behaviour of protic ionic liquids based on the N-methyl-2-hydroxyethylammonium cation, [C2OHC1NH2]+, with the carboxylate anions (propionate, [C2COO]−, butyrate, [C3COO]−, and pentanoate, [C4COO]−) are reported and used to evaluate structure-property relationships. The density was measured over the temperature and pressure ranges, T=(298.15 to 358.15)K and p=(0.1 to 25)MPa, respectively, with an estimated uncertainty of ±0.5kg·m−3. The pressure dependency of the density for these ionic liquids (ILs) is here presented for the first time and was correlated using the Goharshadi–Morsali–Abbaspour (GMA) equation of state, from which the isothermal compressibility, thermal expansivity, thermal pressure, and internal pressure were calculated. The experimental PVT data of the protic ILs were predicted by the methods of Gardas and Coutinho (GC), and Paduszyńki and Domańska (PD). The thermal stability was assessed by high resolution modulated thermogravimetric analysis within the range T=(303 to 873)K. The heat capacity was measured in the temperature range T=(286.15 to 335.15)K by modulated differential scanning calorimetry with an uncertainty in the range (1 to 5)J·K−1·mol−1. The Joback method for the prediction of ideal gas heat capacities was extended to the ILs and the corresponding states principle was employed to the subsequent calculation of liquid heat capacity based on critical properties predicted using the modified Lydersen–Joback–Reid method. The Valderrama’s mass connectivity index method was also used for liquid heat capacity predictions. This series of N-methyl-2-hydroxyethylammonium was used to establish the effect of the anion alkyl chain length on the ionic liquid properties.

Heat Transfer Characteristics of O<sub>2</sub>/CO<sub>2</sub> Pulverized Coal Boiler Furnace

Global warming is currently one of the most serious environmental challenges in the world. The increase of CO2 in the atmosphere is a dominating factor to global warming .O2 / CO2 combustion technology is a new generation of clean coal power generation technology[1],it can directly capture high concentration of CO2 and make the pollutant resource ,so it is one of the most promising feasible technical to reduce CO2 emissions [2]. Compared with conventional pulverized coal combustion boiler, O2 / CO2 combustion technology can be used to produce a CO2 rich flue gas stream. So physical parameters had a very big change, such as flue gas heat capacity, motion viscosity, prandtl number and so on. Thus they affect the heat transfer characteristics [3] inside the furnace.In order to study the heat transfer characteristics of the furnace; this paper established a dynamic mathematical model for the radiation heat transfer progress of the furnace and adequate for control system design.

Predictive correlations for ideal gas heat capacities of pure hydrocarbons and petroleum fractions

The development of continuous predictive correlations for the temperature dependence of the ideal gas heat capacity for hydrocarbons and substituted hydrocarbons valid over a wide range of elemental compositions (CHNOS), molecular structures, and temperatures (298.15–1500K) is reported. The correlations are functions of temperature, elemental composition, and 10 (naphthenic hydrocarbons) or 12 (aromatic and aliphatic hydrocarbons) universal coefficients. There are no compound specific coefficients. The variables are absolute temperature and a similarity variable, which possesses a value proportional to the number of atoms in a molecule, irrespective of their nature, divided by molecular mass. Different data sets obtained from the NIST TRC Ideal Gas Database 88 were used to evaluate parameters, and to test the predictive nature of the correlations. Detailed comparisons between predicted ideal gas heat capacities (cpg0) obtained in this work and values obtained using four Lee–Kesler correlations, and the Harrison–Seaton correlation are presented. The present correlations are shown to be preferred over these other options on the basis of accuracy and range of application for general-purpose calculations, unless the fluid assignment (naphthenic vs. aromatic/aliphatic) is unknown and cpg0 values are only required at set temperatures available for the Harrison–Seaton correlation. In this latter case, the Harrison–Seaton correlation is preferred. For large molecules, the universal correlations presented in this work approach the accuracy of the benchmark Benson method. The universal correlations are well suited for the determination of ideal gas heat capacities of large and complex molecules or mixtures, where more precise structure–property group contribution correlations are difficult to apply or are inapplicable because groups present are not defined in the correlations or are unknown.

Selectively combusting CO in the presence of propylene

Acrylic acid plant capacity can be increased by 30% by substituting propane for nitrogen (in air) thereby increasing the overall gas heat capacity. To minimize propane purge rates, the effluent is recycled but the CO in the recycle stream must be oxidized to avoid poisoning the catalyst. We studied the kinetics of CO combustion in a micro-fluidized bed with a catalyst inventory of 1g and a 4cm ID reactor charged with 5g of catalyst – Pd/zeolite – and 145g of inert. Experiments were run at temperatures between 90 and 240°C and at 1 and 3.2 bara. At temperatures below 140°C propylene conversion was less than 30% while CO conversion approached 90% at gas hourly space velocities near 10,000h−1. A first order kinetic model characterized the data over the whole range of conditions in which conversion was varied between 2% and 99+%. The rate constant for CO conversion was equal to 0.75s−1 whereas it equaled 0.04s−1 for propylene oxidation; the activation energy for CO oxidation was 95kJmol−1K−1 whereas it was 140kJmol−1K−1 for propylene.