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Detailed experimental data are presented on the n-heptane isobaric heat capacity obtained by a modernized adiabatic running calorimeter with the calorimetric measurement of the flow rate in the liquid, gaseous, and supercritical domains, within a temperature range of 300-620 K and a pressure range of 0.5-60 MPa. A thorough consideration of errors made it possible to obtain an error of 0.4% within a wide range of the state parameters. According to the experimental data on the heat capacity, using the known thermodynamics relations, the tables of the n-heptane enthalpy, entropy, and Gibbs energy were calculated (estimated against the accuracy) on the basis of the reliable state equations and the available literature data. The obtained results can be applied directly in the design of chemical processes and the processes in the bedded systems of the hydrocarbon deposits and for development and testing of the equations of state and the methods of the thermodynamic similarity. [ABSTRACT FROM AUTHOR]

In this study, simulation and optimization of ammonia synthesis reactor based on the implemented cooling methods was presented in three cases: internal direct cooling reactor (IDCR), adiabatic quench cooling reactor (AQCR), and adiabatic indirect cooling reactor (AICR). A one-dimensional pseudo-homogeneous model was developed to investigate the effect of various parameters on maximum N 2 conversion at the outlet of IDCR, 2-bed AQCR and 2-bed AICR. Differential evolution algorithm was applied to optimize three types of ammonia synthesis reactor, considering N 2 conversion as the main objective. A comparison between IDCR, 2/3/4-bed AQCR and 2/3/4-bed AICR was carried out under the optimal operating conditions by considering the same catalyst volume, operating pressure and feed mass flow rate for all three types of reactor. The optimization results show that a maximum conversion of 0.26 was achieved in 3-bed AQCR, in which the temperature of feed gas to the first bed was 635 K, dimensionless lengths of each bed were 0.13, 0.25 and 0.62, and fractions of total feed flow rate quenching from the first to end bed were 0.2, 0.26 and 0.54, respectively. The optimum value of N 2 conversion was found 0.3 in IDCR at the gas temperature to the cooling tube of 495 K. In 3-bed AICR, the highest conversion of 0.3 was determined at temperature of inlet gas to each bed, 696 K, and dimensionless length of each bed, 0.33. Generally, IDCR, 3-bed AICR and 3-bed AQCR were suggested as ammonia synthesis reactor configurations from the most favorable to the least favorable. [ABSTRACT FROM AUTHOR]

A zero-dimensional spark ignition engine model was used to conduct a systematic study of combustion dynamics at the top dead center (TDC) position of a 5.734 liter, V8 spark-ignition engine. The model captures all the experimentally observed essential features concerning combustion at the TDC. The combustion dynamics at compression ratios, rc = 9.5, 10.5, 11.5 and 15.5 and fuel-air equivalence ratio, ϕ = 1.0 were investigated with the numerical model. The results show that for rc = 15.5, the fueloxidizer charge was consumed almost instantaneously. Furthermore, the data shows that it took about 153.0, 52.6, 21.0 and 1.43 ms at compression ratios, rc of 9.5, 10.5, 11.5 and 15.5 respectively for the in-cylinder combustion dynamics to reach a value T* = 1.0. In the last 0.01 ms, for all compression ratios, the rate of change of pressure, dp/dt lies in the range 108 < dp/dt < 1014 Pa/s while the corresponding temperature varies from 2230 ≤ T ≤ 2700 K. The study also shows that as the compression ratio increases both the adiabatic flame temperature and heat of combustion at the top dead center increases monotonically as well. [ABSTRACT FROM AUTHOR]

An adjoint-response surface method is developed to provide efficient surrogate model in a parametrized design space for aerodynamic optimization of turbomachinery blades. Our goal is to improve the adiabatic efficiency or equivalently reduce the entropy generation through blade row with a mass flow rate constraint. Firstly, an aerodynamic sensitivity analysis is conducted with a viscous adjoint method to find the suitable number of control points on the suction surface of the transonic NASA rotor 67. Then quadratic polynomial (QP) based response surfaces of 4, 6 and 8 parameters are examined to validate the advantages of the gradient-enhanced model. In the following 24-parameter aerodynamic design optimization case, a steepest descent optimization (SDO) based on adjoint gradient is conducted, then QP based response surface model is constructed using both the values of cost function and its adjoint gradients with respect to geometry control parameters. We present the geometric features, overall aerodynamic improvements and flow details of optimal designs given by SDO and gradient-enhanced response surface model (GERSM). The effects of blade reshaping on shock system, tip clearance flow and flow separation at hub are examined. Also, off-design performances are analyzed regarding both adiabatic efficiency and stall margin. [ABSTRACT FROM AUTHOR]

Adiabatic potential energy curves of the 28 low-lying doublet and quartet electronic states in the representation 2s+1Λ(±) of the zinc monofluoride molecule are investigated using the complete active space self-consistent field (CASSCF) with multi-reference configuration interaction (MRCI) method including single and double excitations with the Davidson correction (+Q). The internuclear distance Re, the harmonic frequency ωe, the static and transition dipole moment μ, the rotational constant Be, and the electronic transition energy with respect to the ground state Te are calculated for the bound states. The transition dipole moment between some doublet states is used to determine the Einstein spontaneous A21 and induced emission coefficients, as well as the spontaneous radiative lifetime τspon, emission wavelength λ21, and oscillator strength f21. The ground state ionicity qionicity and equilibrium dissociation energy DE,e are also computed. The comparison between the values of the present work and those available in the literature for several electronic states shows very good agreement. Twenty-three new electronic states have been studied in the present work for the first time. [ABSTRACT FROM AUTHOR]

The difference between quantum isoenergetic process and quantum isothermal process comes from the violation of the law of equipartition of energy in the quantum regime. To reveal an important physical meaning of this fact, here we study a special type of quantum heat engine consisting of three processes: isoenergetic, isothermal and adiabatic processes. Therefore, this engine works between the energy and heat baths. Combining two engines of this kind, it is possible to realize the quantum Carnot engine. Furthermore, considering finite velocity of change of the potential shape, here an infinite square well with moving walls, the power output of the engine is discussed. It is found that the efficiency and power output are both closely dependent on the initial and final states of the quantum isothermal process. The performance of the engine cycle is shown to be optimized by control of the occupation probability of the ground state, which is determined by the temperature and the potential width. The relation between the efficiency and power output is also discussed. [ABSTRACT FROM AUTHOR]

The finite-time operation of a quantum heat engine that uses a single particle as a working medium generally increases the output power at the expense of inducing friction that lowers the cycle efficiency. We propose to scale up a quantum heat engine utilizing a many-particle working medium in combination with the use of shortcuts to adiabaticity to boost the nonadiabatic performance by eliminating quantum friction and reducing the cycle time. To this end, we first analyze the finite-time thermodynamics of a quantum Otto cycle implemented with a quantum fluid confined in a time-dependent harmonic trap. We show that nonadiabatic effects can be controlled and tailored to match the adiabatic performance using a variety of shortcuts to adiabaticity. As a result, the nonadiabatic dynamics of the scaled-up many-particle quantum heat engine exhibits no friction, and the cycle can be run at maximum efficiency with a tunable output power. We demonstrate our results with a working medium consisting of particles with inverse-square pairwise interactions that includes non-interacting and hard-core bosons as limiting cases. [ABSTRACT FROM AUTHOR]

The performance, emission and combustion characteristics of a diesel engine are investigated using two methyl esters: One obtained from cotton seed oil and other from neem kernel oil. These two oils are transesterified using methanol and alkaline catalyst to produce the cotton seed oil methyl ester (CSOME) and neem kernel oil methyl ester (NKOME) respectively. These biodiesels are used as alternative fuels in low heat rejection engine (LHR), in which the combustion chamber temperature is increased by thermal barrier coating on piston face. Experimental investigations are conducted with CSOME and NKOME in a single cylinder, four stroke, direct injection LHR engine. It is found that, at peak load the brake thermal efficiency is lower by 5.91% and 7.07% and BSFC is higher by 28.57% and 10.71% for CSOME and NKOME in LHR engine, respectively when compared with conventional diesel fuel used in normal engine. It is also seen that there is an increase in NO x emission in LHR engine along with slight increase in CO, smoke and HC emissions. From the combustion characteristics, it is found that the values of cylinder pressure for CSOME and NKOME in LHR engine are near to the diesel fuel in normal engine. [ABSTRACT FROM AUTHOR]

The assumptions of second order Stirling engine models were reviewed. An ideal adiabatic plus simple heat exchanger model was developed. The model included the external components such as the fan, combustor, and preheater. The external heat transfer to the engine heater was modeled using a log-mean-temperature difference for a constant tube surface temperature. The performance of the model of the external components compared reasonably well to experimental data. The performance of the complete engine model was also compared to experimental data of the GPU-3. By adjusting the flow dissipation to better account for unsteady flow conditions and compressibility effects, the complete engine model was able to predict engine power and brake specific fuel consumption to within ±14% over a wide range of engine speeds and mean pressures. This analysis and others suggest that second order models of Stirling engines need to account for the gradient of the divergence of velocity term in the compressible momentum equation if the mean engine pressure is low enough (less than 3.0 MPa) and the engine speed is high enough (above 30 Hz). [ABSTRACT FROM AUTHOR]

Current induced forces are not only related with the discrete nature of electrons but also with its quantum character. It is natural then to wonder about the effect of decoherence. Here, we develop the theory of current induced forces including dephasing processes and we apply it to study adiabatic quantum motors (AQMs). The theory is based on Büttiker's fictitious probe model, which here is reformulated for this particular case. We prove that it accomplishes the fluctuation-dissipation theorem. We also show that, in spite of decoherence, the total work performed by the current induced forces remains equal to the pumped charge per cycle times the voltage. We find that decoherence affects not only the current induced forces of the system but also its intrinsic friction and noise, modifying in a nontrivial way the efficiency of AQMs. We apply the theory to study an AQM inspired by a classical peristaltic pump where we surprisingly find that decoherence can play a crucial role by triggering its operation. Our results can help to understand how environmentally induced dephasing affects the quantum behavior of nanomechanical devices. [ABSTRACT FROM AUTHOR]