Heat Capacity Difference Research Articles

Vaporization enthalpies of benzanthrone, 1-nitropyrene, and 4-methoxy-1-naphthonitrile: Prediction and experiment

Determination of the vaporization enthalpies of low-volatile organic compounds in the wide temperature range is a non-trivial experimental task. A number of predictive approaches were proposed to resolve this problem. Independent validation is necessary for the further development. In this work the saturated vapor pressures of 3 substituted polyaromatic compounds, 1-nitropyrene, benzanthrone, and 4-methoxy-1-naphthonitrile, were measured between 375 and 480 K using fast scanning calorimetry. From the measured vapor pressure – temperature dependences the vaporization enthalpies were derived. The experimental vaporization enthalpies were compared to the literature data and empirical approaches. The vaporization enthalpies of the studied compounds were calculated at 298.15 K from the molecular structure and then adjusted to the measurement temperatures, following two different schemes. The first is based on the approach employing a correlation between the difference of ideal gas phase and liquid heat capacities, on the one hand, and the vaporization enthalpy at 298.15 K, on the other hand, recently proposed by our group. The second is widely known Chickos et al. scheme. Consistence of the experimental, literature, and predicted data was critically analyzed.

Polymer informatics based on the quantitative structure-property relationship using a machine-learning framework for the physical properties of polymers in the ATHAS data bank

In polymer informatics based on the quantitative structure-property relationship (QSPR) through machine learning (ML), one of the key issues is how to utilize a high-quality database of polymer properties. The ATHAS data bank is one of the valuable databases of polymer-specific physical properties, including glass transition temperature (Tg) and heat capacity difference at Tg for fully amorphous polymers, equilibrium melting point and heat of fusion at 100% crystallinity, etc. Using the ATHAS data bank, QSPRs between fingerprints of repeating polymeric structural units and each physical property were obtained by ML. Two types of hidden-layer structures of artificial neural network (ANN) were examined as regression models, and their optimal hidden-layer structures were determined by the contour plots of root mean square error in each physical property. In both ANN structures, a good correlation was found between the registered values and the predicted ones, suggesting that the physical properties may be predicted from only the repeating polymeric structural units. Furthermore, the physical properties of poly(p-dioxanone), which are not yet registered in the ATHAS data bank, were predicted, indicating that the predicted properties agreed with the measured properties from literature within ± 25% in the practical temperature range. A new method for predicting heat capacity for polymers is proposed by combining ML and ATHAS analysis.

Effects of component proportions on multi-jet instant expansion of binary solutions under flash boiling conditions

Flash boiling injection can significantly promote spray atomization owing to rapid bubble growth and explosion. Nevertheless, the effects of component proportions on spray expansion of multi-component fuels still need more quantitative studies. In this work, a typical non-ideal binary solution (aqueous ethanol solution) was utilized as the injection fluid. The effects of ethanol proportion at varying injection temperatures and ambient pressures were tested in a constant volume vessel. Both increasing injection temperature and decreasing ambient pressure intensified the flashing instant expansion for all tested fluids. Instant expansion of pure water spray can be intensified by adding ethanol but adding ethanol into the aqueous ethanol solution induced an opposite behavior. Such phenomenon was caused by the combined effect of differences in heat capacity and proportions of evaporation components. Hence, superheat level was no longer a suitable index for evaluating the instant expansion between sprays with different component proportions. A new index ΔQ′ was proposed to quantify the expansion extent of binary solutions. A strong correlation was found between expansion extent and ΔQ′∙Pamb−0.75 over a wide condition range, indicating the superheated energy available for the first-vaporizable part of the solution is an important factor controlling the extent of instant expansion for binary solution spray.

Thermal stress, cooling-rate and fictive temperature of silicate melts

The unknown cooling-rate history of natural silicate melts can be investigated using differential scanning heat capacity measurements together with the limiting fictive temperature analysis calculation. There are a range of processes occurring during cooling and re-heating of natural samples which influence the calculation of the limiting fictive temperature and, therefore, the calculated cooling-rate of the sample. These processes occur at the extremes of slow cooling and fast quenching. The annealing of a sample at a temperature below the glass transition temperature upon cooling results in the subsequent determination of cooling-rates which are up to orders of magnitude too low. In contrast, the internal stresses associated with the faster cooling of obsidian in air result in an added exothermic signal in the heat capacity trace which results in an overestimation of cooling-rate. To calculate cooling-rate of glass using the fictive temperature method, it is necessary to create a calibration curve determined using known cooling- and heating-rates. The calculated unknown cooling-rate of the sample is affected by the magnitude of mismatch between the original cooling-rate and the laboratory heating-rate when using the matched cooling-/heating-rate method to derive a fictive temperature/cooling-rate calibration curve. Cooling-rates slower than the laboratory heating-rate will be overestimated, while cooling-rates faster than the laboratory heating-rate are underestimated. Each of these sources of error in the calculation of cooling-rate of glass materials—annealing, stress release and matched cooling/heating-rate calibration—can affect the calculated cooling-rate by factor of 10 or more.

An energy budget framework to understand mechanisms of land–ocean warming contrast induced by increasing greenhouse gases Part I: Near-equilibrium state

AbstractModeling studies have shown that surface air temperature (SAT) increase in response to an increase in the atmospheric CO2 concentration is larger over land than over ocean. This so-called land–ocean warming contrast, φ, defined as the land–mean SAT change divided by the ocean-mean SAT change, is a striking feature of global warming. Small heat capacity over land is unlikely the sole cause because the land-ocean warming contrast is found in the equilibrium state of CO2 doubling experiments.Several different mechanisms have been proposed to explain the land–ocean warming contrast, but the comprehensive understanding has not yet been obtained. In Part I of this study, we propose a framework to diagnose φ based on energy budgets at the top of atmosphere and for the atmosphere, which enables the decomposition of contributions from effective radiative forcing (ERF), climate feedback, heat capacity, and atmospheric energy transport anomaly to φ. Using this framework, we analyzed the SAT response to an abrupt CO2 quadrupling using 15 Coupled Model Intercomparison Project Phase 6 (CMIP6) Earth system models. In the near-equilibrium state (years 121-150), φ is 1.49 ± 0.11, which is primarily induced by the land–ocean difference in ERF and heat capacity. We found that contributions from ERF, feedback, and energy transport anomaly tend to cancel each other, leading to a small inter-model spread of φ compared to the large spread of individual components. In the equilibrium state without heat capacity contribution, ERF and energy transport anomaly are the major contributors to φ, which shows a weak negative correlation with the equilibrium climate sensitivity.

Comparison of isochoric and isobaric heat capacities of liquid organic non-electrolytes and their vaporization enthalpies

The present paper is devoted to the study of the relationship between the difference of isochoric heat capacities of liquid and ideal gas phase organic non-electrolytes and their vaporization enthalpy at 298.15 K. This investigation is intended to more deeply analyze the origin of the recent finding that the difference of isobaric heat capacities of organic compounds in liquid and ideal gas phase is in a linear correlation with the vaporization enthalpy. We showed that the difference of isobaric and isochoric heat capacities of liquid aromatic compounds is constant within 3 J·K−1·mol−1 and does not depend on the vaporization enthalpy. A direct proportionality between isochoric heat capacity change and the vaporization enthalpy was established for 84 compounds, which included not only aromatic liquids but other rigid and relatively inflexible molecules (root-mean-square deviation equaled 2.5 J·K−1·mol−1). The slope agreed with that of isobaric heat capacity change – vaporization enthalpy correlation. Statistical significance of the established relationship far exceeded correlations with other molecular size-related parameters, namely the heat capacities, molar volume, and molecular weight.

Thermodynamic Characteristics of Phenacetin in Solid State and Saturated Solutions in Several Neat and Binary Solvents.

The thermodynamic properties of phenacetin in solid state and in saturated conditions in neat and binary solvents were characterized based on differential scanning calorimetry and spectroscopic solubility measurements. The temperature-related heat capacity values measured for both the solid and melt states were provided and used for precise determination of the values for ideal solubility, fusion thermodynamic functions, and activity coefficients in the studied solutions. Factors affecting the accuracy of these values were discussed in terms of various models of specific heat capacity difference for phenacetin in crystal and super-cooled liquid states. It was concluded that different properties have varying sensitivity in relation to the accuracy of heat capacity values. The values of temperature-related excess solubility in aqueous binary mixtures were interpreted using the Jouyban–Acree solubility equation for aqueous binary mixtures of methanol, DMSO, DMF, 1,4-dioxane, and acetonitrile. All binary solvent systems studied exhibited strong positive non-ideal deviations from an algebraic rule of mixing. Additionally, an interesting co-solvency phenomenon was observed with phenacetin solubility in aqueous mixtures with acetonitrile or 1,4-dioxane. The remaining three solvents acted as strong co-solvents.

Temperature-Induced Structural Changes in the Liquid GaInSn Eutectic Alloy

The temperature-dependent structure and properties of a liquid GaInSn eutectic alloy have been investigated by using in situ high-energy X-ray diffraction, thermal expansion, and heat capacity measurements together with ab initio molecular dynamics simulations. It is found that below and above 550 K, the liquid exhibits differences in heat capacity, density, the first two peak positions of the structure factor and pair distribution function, partial coordination numbers, polyhedron connection, as well as Bader charge and Bader volume of In atoms. Both experimental and theoretical results obtained here clearly reveal a liquid-to-liquid crossover in the liquid GaInSn eutectic alloy at around 550 K, which mainly originates from the aggregation of In atoms upon cooling together with Sn atoms tending closer to In. The finding here deepens the understanding of the disorder-to-disorder transition in disordered materials.

Dynamic Modeling of the Reactive Side in Large-Scale Fluidized Bed Boilers

This work presents a dynamic model of the reactive side of large-scale fluidized bed (FB) boilers that describes the in-furnace transient operation of both bubbling and circulating FB boilers (BFB and CFB, respectively). The model solves the dynamic mass and energy balances accounting for the bulk solids, several gas species, and the fuel phase. The model uses semi-empirical expressions to describe the fluid dynamics, fuel conversion, and heat transfer to the furnace walls, as derived from units other than the studied ones. The model is validated against operational data from two different industrial units: an 80 MW CFB and a 130 MW BFB, both at steady-state and transient conditions. The validated model is used to analyze: (i) the performance of the reactive side of two FB boilers under off-design, steady-state conditions of operation; and (ii) the open-loop transient response when varying load or fuel moisture. The results underline the key role of heat capacity on the stabilization time. Within a given unit, the differences in heat capacity between the top and bottom of the furnace affect also the stabilization times, with the furnace top (lower heat capacity) being 1–3 times faster in the CFB unit and up to 10 times faster in the BFB unit. Due to the differences in gas velocity, the investigated boilers are found to stabilize more rapidly to input changes when running at full load than at partial load. Lastly, a variable ramping rate analysis shows that the inherent transient responses of the reactive side disappear when disturbances are introduced at (slower) rates, typical of industrial operation. Thus, the reactive side could be modeled as pseudo-static.

Relationship between the vaporization enthalpies of aromatic compounds and the difference between liquid and ideal gas heat capacities

Understanding connection between physicochemical parameters, molecular structure and heat capacity of liquids remains limited, especially for complex organic molecules. One of possible ways to resolve this problem is analysis of difference between the liquid and ideal gas heat capacities. This difference also defines the temperature dependence of vaporization enthalpy.This work is based on the assumption that the difference between the liquid and gas phase heat capacity is primarily related to intermolecular interactions in the liquid. As the measure of intermolecular interactions, the vaporization enthalpy at 298.15 K was considered. The relationship between the difference of liquid and gas phase heat capacities and the vaporization enthalpy was analyzed for a wide range of aromatic and heteroaromatic compounds. An excellent correlation was observed (residual standard deviation 3.7 J·K−1·mol−1, N = 99). This correlation appeared to be useful for estimation of the vaporization enthalpies of aromatic compounds at elevated temperatures solely from the value at 298.15 K. The calculated and literature vaporization enthalpies measured between 360 and 650 K of 80 compounds from 134 sources were compared. An average absolute deviation of 1.5 kJ·mol−1 was observed, being competitive with the experimental errors of vaporization enthalpy determination.

A non-equilibrium thermodynamic approach to symmetry breaking in cancer

This paper develops a non-equilibrium thermodynamics approach to oncogenesis, with a particular focus on ‘symmetry breaking’. The Onsager phenomenological coefficients are introduced to show the biophysical and thermophysical properties of cellular systems with differences between normal and cancerous cells. Seebeck- and Peltier-like effects are introduced to simplify the description of heat exchange and ion fluxes, in an effort to characterize the distinct role of the cellular electric membrane potential. Our result indicate that oncogenesis leads to changes in: (i) the thermophysical properties of the cell cytoplasm, caused by differences in density and heat capacity, (ii) the interactions with the micro-environment, (iii) geometrical characteristics, both in fractal dimensions and in shape symmetry, and (iv) the constitutive properties of membrane fluxes. This presents a unifying biophysics concept for such diverse characteristics, and it may yield new diagnostic and therapeutic opportunities.

Effect of Molar Mass Variation on a Flame Temperature and a Burning Rate

Difference in the molar masses of a combustible gas and its combustion products has a strong effect on a flame temperature and a burning rate. Instead of a molar mass difference, one may consider a heat capacity difference at a constant pressure. There are two heat sources in a combustion zone. One of them is chemical, and the other one is similar to heat release (heat absorption) during a first-order phase transition, but, depending on the process, it can be partially chemical. The higher the heat capacity of the fuel in comparison with the heat capacity of the combustion products, the higher the burning rate and the flame temperature. For the physical completeness of the issue under discussion, an ideal thermodynamic cycle is considered, and it is shown that Carnot’s formula should contain a correction factor that takes into account a change in heat capacity.

Land–sea breeze circulation structure on the west coast of the Yellow Sea, China: 中国黄海西岸海陆风循环结构研究

Land–sea breeze (LSB) is an atmospheric mesoscale circulation that occurs in the vicinity of the coast and is caused by uneven heating resulting from the difference in specific heat capacity between the sea and land surfaces. The circulation structure of LSB was quantitatively investigated with a Doppler wind lidar Windcube100s on the west coast of the Yellow Sea for the first time. The time of observation was 31 August to 28 September 2018. It was found that the height of LSB development was 700 m to 1300 m. The duration of conversion of LSB was between 6 h and 8 h. The biggest average horizontal sea-breeze wind speed at 425 m was 5.6 m s−1, and at 375 m it was 4.5 m s−1. During the conversion process from sea breeze to land breeze, the maximum wind shear exponent was 2.84 at 1300 m altitude. During the conversion process from land breeze to sea breeze, the maximum wind shear exponent was 1.28 at 700 m altitude. The differences in wind shear exponents between sea-breeze and land-breeze systems were between 0.2 and 3.6 at the same altitude. The maximum value of the wind shear exponent can reflect the height of LSB development.摘要陆海风是由于海陆表面之间的比热容不同而导致的昼夜热量分布差异, 从而在海岸附近引发的大气中尺度循环系统.本文利用多普勒风激光雷达Windcube100s首次对黄海西海岸的海陆风的循环结构进行了观测研究.在2018年8月31日至9月28日观测期间发现, 海陆风发展高度一般在700 m至1300 m.海陆风转化持续的时间为6小时至8小时.在425m高度, 海风水平风速出现最大值, 平均为 5.6 m s−1.陆风最大水平风速出现在370 m, 约为4.5 m s−1.最大风切变指数在1300m处, 为2.84;在陆风向海风转换过程中, 最大风切变指数在700m处, 为1.28.在同一高度上, 风切变指数在海风盛行和陆风盛行时的差值范围为0.2–3.6, 风切变能反映出海陆风的发展高度.

Vapor Pressures and Thermophysical Properties of 1-Heptanol, 1-Octanol, 1-Nonanol, and 1-Decanol: Data Reconciliation and PC-SAFT Modeling

Vapor pressures for liquid 1-heptanol (CAS RN: 111-70-6), 1-octanol (CAS RN: 111-87-5), 1-nonanol (CAS RN: 143-08-8), and 1-decanol (CAS RN: 112-30-1) were measured by a static method near ambient temperatures over an operating pressure range from 0.5 to 1270 Pa, thus complementing literature vapor pressure data obtained by ebulliometry at higher temperatures. Liquid heat capacities of 1-octanol, 1-nonanol, and 1-decanol were determined by Tian–Calvet calorimetry. Ideal-gas thermodynamic properties of 1-alkanols up to 1-heptanol were obtained by a combination of quantum chemistry and statistical mechanics and validated against available experimental data. Ideal-gas heat capacities and entropies for longer homologues were obtained by deriving a methylene increment due to having a too complex conformational shape for analogical treatment. The thermodynamic consistency of available data was validated by simultaneous correlation of selected vapor pressures, literature enthalpies of vaporization, and heat capacity differences between the ideal gaseous and the liquid phase. The results are represented by the Cox equation and compared with available literature data. Moreover, the results were used to examine the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state for its performance in describing vapor pressures, enthalpies of vaporization, residual liquid heat capacities, and liquid densities of neat 1-alkanols from 1-hexanol to 1-decanol. A new PC-SAFT parameter set for each of them was also regressed that improves the PC-SAFT performance for the studied properties in comparison to existing parameters published in the literature.

Hidden Conformational States and Strange Temperature Optima in Enzyme Catalysis.

The existence of temperature optima in enzyme catalysis that occur before protein melting sets in can be described by different types of kinetic models. Such optima cause distinctly curved Arrhenius plots and have, for example, been observed in several cold-adapted enzymes from psychrophilic species. The two main explanations proposed for this behavior either invoke conformational equilibria with inactive substrate-bound states or postulate differences in heat capacity between the reactant and transition states. Herein, we analyze the implications of the different types of kinetic models in terms of apparent activation enthalpies, entropies, and heat capacities, using the catalytic reaction of a cold-adapted α-amylase as a prototypic example. We show that the behavior of these thermodynamic activation parameters is fundamentally different between equilibrium and heat capacity models, and in the α-amylase case, computer simulations have shown the former model to be correct. A few other enzyme-catalyzed reactions are also discussed in this context.

Application of a sequential multi-solid-liquid equilibrium approach using PC-SAFT for accurate estimation of wax formation

Several existing thermodynamic models for Wax precipitation use cubic EOS and average properties for petroleum fractions. To improve predictions, this work introduces a thermodynamic model using a multi-solid framework in a sequential equilibrium calculation procedure. The PC-SAFT EOS is used to predict liquid phase properties. Binary interaction coefficients and difference of heat capacities between solid and liquid are adjusted to minimize the deviations caused by the employment of averaged relations for properties of hydrocarbon cuts. Three groups of oil samples are chosen for verification. First, the Wax precipitation data of three synthetic mixtures from Pauly et al. [1] are estimated, and the modeling results are compared to the predicted results of Dalirsefat and Feyzi [2] and Schou Pedersen et al. [3]. Also, two crude oil samples with Paraffin, Naphthene, and Aromatic (PNA) content from Pan et al. [4] are used for evaluation. Finally, the suggested model is used to calculate weight percent of precipitated Wax and Wax appearance temperature (WAT) of six crude oil samples from North Sea [3]. The calculated predictions of the suggested model are compared to the works of Schou Pedersen et al. [3], Lira‐Galeana et al. [5], and Bagherinia et al. [6]. The deviations for WATs and precipitation amounts from experimental data are lower compared to previous studies. The average absolute deviation for precipitated Wax weight of the North Sea samples is 0.19 in comparison to 0.61, 0.33, and 0.4 of Schou Pedersen et al. [3], Lira‐Galeana et al. [5], and Bagherinia et al. [6], respectively.

Heat Capacity Changes (ΔCp) for Interconversions between Differentially-Ordered DNA States within Physiological Temperature Domains: Implications for Biological Regulatory Switches.

Knowledge of differences in heat capacity changes (ΔCp) between biopolymer states provides essential information about the temperature dependence of the thermodynamic properties of these states, while also revealing insights into the nature of the forces that drive the formation of functional and dysfunctional biopolymer "order." In contrast to proteins, for nucleic acids there is a dearth of direct experimental determination of this information-rich parameter, a deficiency that compromises interpretations of the ever-increasing thermodynamic analyses of nucleic acid properties; particularly as they relate to differential nucleic acid (meta)stability states and their potential biological functions. Here we demonstrate that such heat capacity differences, in fact, exist not only between traditionally measured native to fully unfolded (assumed "random coil") DNA states, but also between competing order-to-order transformations. We illustrate the experimental approach by measuring the heat capacity change between "native"/ordered, sequence homologous, "isomeric" DNA states that differ in conformation but not sequence. Importantly, these heat capacity differences occur within biologically relevant temperature ranges. In short, we describe a new and general method to measure the value of such heat capacity differences anywhere in experimentally accessible conformational and temperature space; in this case, between two metastable bulge loop states, implicated in DNA expansion diseases, and their competing, fully paired, thermodynamically more stable duplex states. This measurement reveals a ΔCp of 61 ± 7 cal molbp -1 K -1. Such heat capacity differences between competing DNA "native" ensemble states must be considered when evaluating equilibria between different DNA "ordered" conformations, including the assessment of the differential stabilizing forces and potential biological functions of competing DNA "structured" motifs.

Prediction of the heat capacity of main-chain-type polymers below the glass transition temperature

This study predicts the absolute values of heat capacities from the molecular formula per monomer for main-chain-type polymers below the glass transition temperature. The frequencies of the skeletal and group-vibration modes are calculated using the Tarasov and Einstein equations, respectively, and the heat-capacity differences at constant pressure and constant volume are used to correct the predicted heat capacity. The contributes of skeletal vibrations to the heat capacity can be expressed by one- and three-dimensional Tarasov equations, and the contribution of group vibrations can be determined by summing the group-vibration heat capacities for functional groups and atoms constituting the monomer as obtained from the Einstein equation. The absolute value of the heat capacity is predicted from this combination of equations. The heat capacities of poly(4-methyl-1-pentene) are predicted within an error range of 8.0% from 90 to 180 K and ±2.0% from 180 to 300 K. The heat capacities of poly(vinyl benzoate) are within ±2.0% agreement from 190 to 350 K, while for poly(1,4-butylene adipate), the agreement is within ±2.0% from 80 to 200 K. This study predicted the absolute values of the heat capacities from the molecular formula per monomer for a main-chain-type polymer below the Tg. The calculations combined the Tarasov equation, the Einstein equation, and the (Cp − CV) correction term, accounting for the degrees of freedom of the monomer unit. The difference of predicted and experimental heat capacities of poly(4-methyl-1-pentene) was within 8.0% from 90 to 180 K and within ±2.0% agreement from 180 to 300 K. For poly(vinyl benzoate), the values were within ±2.0% from 190 to 350 K, and for poly(1,4-butylene adipate), they were within ±2.0% from 80 to 200 K. The predicted heat capacity was accurate, especially in the high-temperature region above 180 K.

Isobaric heat capacity prediction for HC, HFC, HFO and HCFO refrigerants in liquid phase

ABSTRACT In this work, it was found that the experimental heat capacity difference (cp-cv)exp has a linear relationship with the heat capacity difference calculated by using PR equation (cp-cv)PR. Based on this linear relationship, a predicted model of isobaric heat capacity for liquid refrigerants was presented. The accurate isobaric heat capacity of refrigerants in liquid phase can be obtained if the critical temperature, critical pressure, critical density, acentric factor and several experimental isobaric heat capacity data (at least two, more is better) are known. The proposed model was applied to 17 refrigerants (including HC, HFC, HFO and HCFO refrigerants) and a comparison was performed between the calculations by the proposed model and the experimental heat capacity data to validate the prediction. The results indicated the proposed method can represent the isobaric heat capacity of 17 refrigerants in liquid state with an average absolute deviation of 1.00%. The performance of this proposed method was then compared with that of other models (including Helmholtz equation, Peng-Robinson equation and a generalized corresponding state principle equation). It can be concluded that the proposed method generally shows better performance than other models. In addition, the proposed model reveals a good extrapolation ability in low temperature regions for refrigerants.

Speed of Sound and Derivative Properties of Ethyl Laurate from Rayleigh–Brillouin Light-Scattering Spectroscopy

The experimental speeds of sound combined with Brillouin frequency shifts of ethyl laurate at temperatures from 294.97 to 572.89 K along six isobaric lines from 0.1 to 10.0 MPa were measured by Rayleigh–Brillouin light-scattering spectroscopy. The expanded relative uncertainty in the reported speeds of sound in ethyl laurate is estimated to be 1.3% (coverage factor k = 2 with a confidence level of 0.95). Within the temperature limits of 303.15–383.15 K and at pressures up to 10.0 MPa, the derived thermoacoustic properties of ethyl laurate including density, specific isobaric heat capacity, isentropic compressibility, isobaric thermal expansivity, isothermal compressibility, the difference in isobaric and isochoric heat capacity, internal pressure, and intermolecular free length were studied. Because of the heavily updated data of density and the speed of sound in the literature, a modified Jacobson’s model for biodiesels was proposed over the temperature range from 293.15 to 343.15 K, which is able to calculate the intermolecular free length of ethyl laurate with higher accuracy compared with Jacobson’s model.