Performance analysis of wave rotor based on response surface optimization method

An optimized wave rotor refrigerator (WRR) that can convert part of the expansion work into shaft work to improve the refrigeration performance is obtained by optimization method. Bézier curve is used to establish a two-dimensional simplified model, and response surface method and NLPQL optimization algorithm are used to search for the optimal wave rotor structure. The results show that the optimized wave rotor shape is rear back bending. Compared with original rotor, the isentropic expansion efficiency of the optimized rotor is higher under different pressure ratios and relative velocity, and changes more gently under different pressure ratios. Moreover, the expansion power of the optimized rotor is mainly converted into shaft powder, while the pressure energy and thermal energy increase at the hot end is relatively small. The pressure fluctuations on the inlet and outlet sides of the optimized rotor are smoother, and the compression waves that are constantly reflected during the low-temperature exhaust stage have a smaller intensity, which helps to improve the performance of WRR. The optimized rotor can significantly reduce the entropy production in the refrigeration process, especially the entropy production by velocity gradients. When the pressure ratio is 2.0 and relative velocity is 23 m/s, the isentropic expansion efficiency increases from 56.8% of the original rotor to 62.08% of the optimized rotor.

Entropic thermodynamics of nonlinear photonic chain networks

The convoluted nonlinear behaviors of heavily multimode photonic structures have been recently the focus of considerable attention. The sheer complexity associated with such multimode systems, allows them to display a host of phenomena that are otherwise impossible in few-mode settings. At the same time, however, it introduces a set of fundamental challenges in terms of comprehending and harnessing their response. Here, we develop an optical thermodynamic approach capable of describing the thermalization dynamics in large scale nonlinear photonic tight-binding networks. For this specific system, an optical Sackur-Tetrode equation is obtained that explicitly provides the optical temperature and chemical potential of the photon gas. Processes like isentropic expansion/compression, Joule expansion, as well as aspects associated with beam cleaning/cooling and thermal conduction effects in such chain networks are discussed. Our results can be used to describe in an effortless manner the exceedingly complex dynamics of highly multimoded nonlinear bosonic systems.

Comparison of conventional and heat balance based energy analyses of steam turbine

This paper presents a comparison of conventional and heat balance based energy analyses of steam turbine. Both analyses are compared by using measured operating parameters from low power steam turbine exploitation. The major disadvantage of conventional steam turbine energy analysis is that extracted energy flow streams are not equal in real (polytropic) and ideal (isentropic) expansion processes, while the heat balance based energy analysis successfully resolved mentioned problem. Heat balance based energy analysis require an increase of steam mass flow rates extracted from the turbine in ideal (isentropic) expansion process to ensure always the same energy flow streams to all steam consumers. Increase in steam mass flow rate extracted through each turbine extraction (heat balance based energy analysis) result with a decrease in energy power losses and with an increase in energy efficiency of whole turbine and all of its cylinders (when compared to conventional analysis). All of the obtained conclusions in this research are valid not only for the analyzed low power steam turbine, but also for any other steam turbine with steam extractions.

Acceleration Characteristics of Discrete Fragments Generated from Explosively-Driven Cylindrical Metal Shells

The acceleration characteristics of fragments generated from explosively-driven cylindrical shells are important issues in warhead design. However, there is as yet no reasonable theory for predicting the acceleration process of a specific metallic shell; existing approaches either ignore the effects of shell disintegration and the subsequent gas leakage on fragment acceleration or treat them in a simplified manner. In this paper, a theoretical model was established to study the acceleration of discrete fragments under the combined effect of shell disintegration and gas leakage. Firstly, an equation of motion was developed, where the acceleration of a cylindrical shell and the internal detonation gas was determined by the motive force impacting the inner surface of the metallic cylinder. To account for the force decrease induced by both the change in fragment area after the shell disintegrates and the subsequent drop in gas pressure due to gas leakage, the equation of motion was then associated with an equation for the locally isentropic expansion of the detonation gas and a modified gas-leakage equation. Finally, theoretical analysis was conducted by solving the associated differential equations. The proposed model showed good agreement with experimental data and numerical simulations, indicating that it was suitable for predicting the acceleration of discrete fragments generated from a disintegrated warhead shell. In addition, this study facilitated a better understanding of the complicated interaction between fragment acceleration and gas outflow.

Estimation of TNT equivalent of detonating explosive gas

The purpose of the study was to compare the genuine work of explosion of detonating gas and trinitrotoluene during their reaction in the form of detonation. The comparison was done in the framework of the concept of the strength of the explosives as the ability of their degradation products to perform work under isentropic expansion, starting from the initial state in which the products of instant explosion are located. The study introduces the calculation data using the gas equation for products of detonation of a detonating gas at different initial pressures, and the Johns-Wilkins-Lee (JWL) equation for trinitrotoluene. With a high-explosive effect characterized by a final pressure of the order of a tenth of a megapascal, in which the explosion products are still able to perform the required form of work, the relative TNT equivalent of detonating gas will rise from about 50% to 110% with an increase in the initial pressure of the gas charge from a normal value to one megapascal.

Thermodynamic Selection of the Optimal Working Fluid for Organic Rankine Cycles

A novel method proposed to choose the optimal working fluid—solely from the point of view of expansion route—for a given heat source and heat sink (characterized by a maximum and minimum temperature). The basis of this method is the novel classification of working fluids using the sequences of their characteristic points on temperature-entropy space. The most suitable existing working fluid can be selected, where an ideal adiabatic (isentropic) expansion step between a given upper and lower temperature is possible in a way, that the initial and final states are both saturated vapour states and the ideal (isentropic) expansion line runs in the superheated (dry) vapour region all along the expansion. Problems related to the presence of droplets or superheated dry steam in the final expansion state can be avoided or minimized by using the working fluid chosen with this method. Results obtained with real materials are compared with those gained with model (van der Waals) fluids; based on the results obtained with model fluids, erroneous experimental data-sets can be pinpointed. Since most of the known working fluids have optimal expansion routes at low temperatures, presently the method is most suitable to choose working fluids for cryogenic cycles, applied for example for heat recovery during LNG-regasification. Some of the materials, however, can be applied in ranges located at relatively higher temperatures, therefore the method can also be applied in some limited manner for the utilization of other low temperature heat sources (like geothermal or waste heat) as well.

About the operational determination of the state and parameters of flowing moist air

The presented paper deals with the solution of moist air parameters for the needs of aerodynamic research or design. From the thermodynamic theory of moist air, a p-t diagram of moist air is designed to allow the operative expression of the process and state of the moist air. Using this diagram, it is possible to illustratively describe the course of parameters at various state changes in moist air such as isentropic expansion and compression, isothermal expansion and compression, isobaric state change, isochoric state change, or general polytrophic state change. The initial state of moist air is determined by the pressure, temperature and moisture of the air. In the p-t diagram, the process is expressed by the applicable curve; the identification of the parameters in which the phase transformation occurs in moist air is significant. Uncertainty analysis is performed.