Showing 8 results for Thermodynamics
L. Hassani, E. Safaei , F. Hakimian , S. Soufian,
Volume 9, Issue 3 (9-2018)
Abstract
Aims: The G-quadruplex structural motifs of DNA are considered a novel target for drug discovery. As potential compounds, small molecules that selectively target the G-quadruplex structures may be used for therapeutic purposes. The aim of this study was the thermodynamic investigation of copper porphyrazines and phthalocyanine interaction with human telomeric G-quadruplex DNA.
Materials and Methods: In the present experimental study, interaction of an anionic water-soluble phthalocyanine Cu(PcTs) and two cationic water-soluble tetrapyridinoporphyrazines, including [Cu(2,3-tmtppa)] 4+ and [Cu(3,4-tmtppa)]4+ complexes with human telomeric G-quadruplex DNA was thermodynamically investigated in different concentrations of Na+ and K+ cations, using fluorescence spectroscopy. The data were analyzed via the Stern-Volmer plot and the van't Hoff plot.
Findings: Fluorescent intercalator displacement indicated the displacement ability of the complexes with thiazole orange. Stern-Volmer plots of the porphyrazines exhibited a slight positive deviation from a straight line, suggesting both static and dynamic quenching. In addition, the quenching effect of the two porphyrazines was noticeably higher than the phthalocyanine, implying binding of Cu(PcTs) to both forms of the quadruplex was weaker compared to Cu(2,3-tmtppa) and Cu(3,4-tmtppa). Gibbs free energy (∆G) for binding was negative, implying that the interaction between the complexes and the G-quadruplex DNA was favorable thermodynamically.
Conclusion: The binding of copper porphyrazines to G-quadruplex DNA is stronger than copper phthalocyanine, and their binding is favorable thermodynamically. Porphyrazines have potential to be used as anti-cancer compounds and are suitable complexes for pharmaceutical studies.
Z. Solgi, Kh. Khalifeh , S. Hosseinkhani, B. Ranjbar ,
Volume 9, Issue 3 (9-2018)
Abstract
Aims: The probability of establishing electrostatic interactions due to the abundance of charged hydrophilic residues and especially arginine is considered the most important thermal stabilizing factor of thermophilic enzymes. The current study was conducted with the aim of comparing thermodynamic stability and kinetic refolding of Lampyris turkestanicus and some of its mutants.
Materials and Methods: In the present experimental thermal stability and the way of refolding Lampyris turkestanicus and 3 mutations, including ERR, ERR/I232R, ERR/Q35R/I182R/I232R were investigated by various spectroscopic techniques. In order to high expression of proteins, a single clone of each sample was selected and inoculated into 10ml of LB culture medium, containing Kanamycin at a concentration of 50μg/mg and incubated at 37°C with an ideal aeration for 12-15 hours. The culture medium was centrifuged for 5 minutes at 5000g at 4°C to provide the cellular contents of the bacteria. The results were obtained through spectroscopic methods of remote and near circular dichroism, intrinsic fluorescence, differential scanning calorimetry, and kinetics experiments, using fluorescence-stopped flow technique.
Findings: Along with the increase in the number of arginine residues at the protein level, the stability and structural compression of the mutated enzymes in comparison with the wild enzyme were increased and the thermograms obtained from differential scanning calorimetry showed a slight increase in Tm and calorimetric enthalpy of mutated proteins in comparison with wild protein.
Conclusion: The rate constant of refolding mutated enzymes has increased compared with the wild type. The improvement of thermodynamic and kinetic parameters results from the improvement of electrostatic interactions, which results in a higher degree of compression and structural density.
Volume 15, Issue 2 (4-2015)
Abstract
A differential thermal model for simulation of Stirling engines was presented. In the new model polytropic expansion/compression processes were substituted to traditional isothermal or adiabatic models of previous studies. In addition, the developed polytropic model was corrected for various loss mechanisms of real engines. In this regard, the effect of non-ideal operation as well as heat recovery in the regenerator was considered. In addition, non-ideal heat transfer of heater and cooler were implemented into the model. In pressure analysis and evaluating work produced or consumed in cylinders, the effect of finite speed motion of piston was considered based the concept of finite speed thermodynamics. Moreover, the effects of heat leakage in regenerator, leakage effect and shuttle effect were evaluated. Finally, new differential polytropic model were employed on a benchmark Stirling engine so-called GPU-3 and accuracy of models was validated through comparing with experimental results as well as previous models. As thermal performance of Stirling engines are significantly affected by thermohydraulic performance of regenerator in one hand and there are various thermohydraulic models for regenerator, three famous thermohydraulic models of regenerator was integrated into models and through comparison with experimental performance of GPU-3 engine, a more accurate thermohydraulic model was introduced.
Volume 15, Issue 7 (9-2015)
Abstract
The prediction of distillation zone is very important in steam turbine blades and steam nozzles. In identification of distillery with equilibrium method, as the steam flow contacts the two-phase dome, the second phase formes and flow properties will pass the distillery without any jumping, therefor after crossing the saturation curve, the droplet formation transpires, but in non-equilibrium method by a sudden increase in pressure, called “condensation shock” a discontinuity in the flow characteristics is seen and after crossing the saturation curve, the formation of droplets starts. In this paper, numerical analysis of a vapor-liquid two-phase transonic flow in a convergent-divergent nozzle with and without shock is investigated. Effects of stagnation temperature at nozzle inlet, viscosity and geometry is studied using thermodynamic equilibrium and non-equilibrium methods and results compared with experimental datas. Roe numerical method is used for vapor-liquid two-phase flow numerical solution. The main properties of the flow at the boundary of elements is extrapolated by MUSCL third order acuracy and time discretization is performed using Lax-Wendroff explicit two-step method of second order accuracy. It is observed that the results of non-equilibrium solution, has more correspondence to experimental results and Condensation starts earlier in the nozzle with further expansion rate. By increasing the temperature at nozzle inlet, the place at which condensation starts goes forward. Also in comparision with non-viscous flow, the shock location in viscous flow comes closed to the throat.
Volume 17, Issue 11 (1-2018)
Abstract
One of the most important achievements of the Carnot was creating a limit for heat engines; this limitation is a criterion for measuring and comparing the performance of heat engines. Classical thermodynamics studies completely the equilibrium and reversible processes but transfer phenomena effects have been ignored, while in the real irreversible process, there are finite time processes and finite size systems. On the other hand, the close relationship between thermodynamics, fluid mechanic and heat transfer has caused thermodynamics to move from theoretical analysis toward a comprehensive and real analysis. Another point is that all the practical processes are irreversible. This study analyzed the irreversible combined cycle in finite time thermodynamics. The combined cycle studied consists two endoreversible cycles and three thermal sources. The irreversibility has occurred between the subsystems and the thermal sources and sink on the system boundaries. By solving algebraic equations, obtained dimensionless total power and efficiency were calculated based on dimensionless variables. The MATLAB programming code is used to solve algebraic equations. Finally, it is obtained that the thermal efficiency and dimensionless total power functions of the heat sources temperature, working fluid temperature and thermal conductance. Also, the effects of each dimensionless variable were investigated to the proportion of dimensionless total power and efficiency. In this study, the parameter study has been used for improving the irreversible combined cycle in the finite time thermodynamics. In addition, Optimization results have shown that the maximum dimensionless total power and thermal efficiency associated with it are 0.086102 and 47.81%, respectively.
Volume 18, Issue 2 (4-2018)
Abstract
In this paper, performance analysis and optimization of a trigeneration system based on different thermodynamic criteria such as energy and exergy efficiency, power and dimensionless power have been investigated. The trigeneration system consists of three subsystems which including the solar subsystem, Kalina subsystem and lithium bromide-water absorption chiller subsystem. The proposed system uses solar energy generates power, cooling and domestic water heating. Power is introduced as a tool for understanding thermodynamic concepts of limited time. Dimensionless power is defined as the ratio of power to the product of total thermal conductivity and minimum temperature of the system. Dimensionless power can be used as a tool to understand the concepts of finite time thermodynamics. The exergy analysis has shown that the most exergy destruction is related to boiler. As a result, energy and exergy efficiencies, capital cost rates and dimensionless power are 17.77%, 18.82% and 9.63 dollars per hour, 0.01781 respectively. Sensitivity analysis has shown that increasing parameters such as ambient temperature, solar radiation, the dimensionless mass flow rate of the Kalina cycle, collector inlet temperature and pressure ratio of the Kalina cycle increase energy and exergy efficiencies. Also increasing pressure ratio the of Kalina Cycle, reducing the dimensionless mass flow rate of the Kalina cycle, the ambient temperature and collector inlet temperature has led to increased dimensional power. In addition, the optimization criteria such as energy efficiency, exergy efficiency, power and dimensional power have been compared. The results showed that power and dimensional power are the best thermodynamic optimization criteria.
Volume 18, Issue 5 (11-2018)
Abstract
The present study aimed to remove hexavalent chromium from aqueous solution by manganese ferrite nanoparticle. In this study, MnFe2O4 was prepared based on co-precipitation method. The adsorbent properties were determined using scanning electron microscopy (SEM), X-ray diffraction (XRD). In this research, the effects of pH (2, 5, 7, 9 and 11), contact time of 2 to 360 minutes and concentrations of 1 to 200 mg/l and temperature (283 to 328 K) for the removal of hexavalent chromium were investigated. The agitation parameter was kept constant for all experiments at 170 rpm. The results of nanoparticle synthesis showed that the nanoscale dimensions were less than 200 nm, and the shape of the spherical particles followed the cubic spinel structure. Moreover, the pH of zero point of the nanoparticle was 6.8. Kinetic studies showed that the removal of chromium followed the second-order kinetic model. Intrinsic particle diffusion model showed that single-particle intrusiveness was not present and absorption consists of two steps: first, pushing the absorbent layer onto the adsorbent surface and then penetrating the molecule inside the pores. It was found that the removal of chromium is followed the Langmuir model, and the maximum absorption capacity of the hexavallent-chrome is 34.84 mg/g. The resulting value of n=2.92 (Freundlich isotherm) indicates the chemical absorption of chromium on the adsorbent of hexavalent chromium. The highest adsorption rate occurred at 328 ° K. The amount of ΔG was negative and ΔH reacted positively. This is because that chromium-reacted manganese ferrite is chemically thermostable and spontaneous.
Volume 22, Issue 5 (4-2022)
Abstract
One of the problems in the experiment of breakup cryogenic liquid jet is the state of discharged cryogenic liquid jet from injector. In some applications, it is necessary jet to be in the sub-cooled condition. However, at atmospheric condition, the discharged cryogenic liquid jet becomes two-phase. In the present article, the methods for sub-cooling of the liquid nitrogen jet are investigated and a simple method to achieve this goal is used. With this method, which is based on holding at low pressure, a sub-cooled liquid nitrogen jet with a temperature of about 7 K lower than the saturation temperature was obtained. Then, the behavior of the liquid nitrogen jet at high pressure and atmospheric pressure is evaluated. High speed camera was used to observe the behavior of the jet. The speed of liquid jet is changed from 12 m/s to 34 m/s according to the Reynolds number from 90000 to 260000. When the liquid nitrogen jet is discharged into the environment under standard conditions, the jet becomes two-phase and expands. The larger the injector pressure difference, the greater the expansion of the jet; So that in the pressure difference of 6 and 13 bar, the diameter of the jet is 1.5 and 3.3 times the diameter of the injector, respectively. In the test speed range, under the conditions provided for the liquid and the environment, the breakup of the sub-cooled liquid jet leads to the production of very small droplets that are consistent with the expectation of such a liquid.
