An analytical equation of state for refrigerants

The liquid density of halogenated hydrocarbons has been calculated using an analytical equation of state. The temperature-dependent parameters of the equation of state have been calculated using our previous corresponding-states correlation based on the normal boiling point constants. In this work, it is shown that the equation of state for halogenated paraffins could be expressed in terms of the minimum input information, namely the normal boiling point temperature and the liquid density at the normal boiling point. The equation of state has been employed to calculate the liquid density of a great number of refrigerants both at saturation and compressed states, over a wide range of temperatures and pressures. A comparison of the predicted results with experimental data shows that the agreement is quite good.     

Sphericity error evaluation: theoretical derivation and algorithm development

Several methods for the evaluation of sphericity error exist. The Minimum Radial Separation (MRS) spheres method is a method that has been studied by several researchers. In the MRS criterion, two concentric spheres at minimum radial separation must be found such that they contain all points on the actual spherical surface. The existing procedures for finding MRS spheres are either too complex and time consuming or do not provide an optimal solution to the sphericity error evaluation problem. In this paper, mathematical optimization concepts are utilized to develop a theory and an algorithm for the evaluation of sphericity error based on MRS criterion. Results indicate that the algorithm is fast and accurate in providing optimal solution to the sphericity error evaluation problem.     

Simple method to calculate explosion temperature of ideal and non-ideal energetic compounds

ABSTRACT

The explosion (detonation) temperature of organic compounds containing energetic groups can be related to the study of the kinetics of chemical reactions in the reaction zone as well as the thermodynamic state of the detonation products. It can be predicted by a simple approach for ideal and less ideal energetic compounds as well as non-ideal composite explosives containing aluminum (Al) or ammonium nitrate (AN). A general correlation is introduced for calculation of the explosion temperature from the heat of detonation where it can be corrected for AN and liquid organic energetic compounds. For ideal and less ideal energetic compounds, the predicted results are compared with the outputs of complex thermochemical/hydrodynamic computer codes using two appropriate equations of state (BKWR-EOS and BKWS-EOS). The values of mean absolute percentage error (MAPE) in the explosion temperature for ideal and less ideal organic energetic compounds are 5.4, 5.5 and 12.5 for the new method, BKWS-EOS, and BKWR-EOS, respectively. The new method shows good agreement for non-ideal energetic compounds with respect to the outputs of BKWS-EOS using partial equilibrium where it provides good predictions for detonation performance.     

Effect of reactive diluent on gas separation behavior of photocurable acrylated polyurethane composite membranes

In this study, the effects of the type and content of reactive diluents on the permeation/separation of carbon dioxide/nitrogen (CO₂/N₂) through acrylate-terminated polyurethane (APU)-acrylate/acrylic diluent (APUA) composite membranes was investigated. A series of APUs based on poly(ethylene glycol) (PEG)-1000 g mol⁻¹, toluene diisocyanate, and 2-hydroxyethyl methacrylate was synthesized and then diluted with several reactive diluents. The results obtained from differential scanning calorimetry (DSC) and Fourier transform infrared analyses showed that the microphase interference of hard and soft segments increased with increasing reactive diluent content. Furthermore, with increasing alkene double bond of reactive diluents, the degree of phase separation increased, which might be due to the higher gel content of APUAs. APUAs were used as top selective layer on PS/PSF as the support layer to obtain composite membrane. Field emission scanning electron microscopy micrographs revealed that APUAs penetrated into the support layer, leading to strong interfacial adhesion between APUA and support layers. The gas permeation experiments indicated that the gas permeability decreased, while the CO₂/N₂ selectivity increased with increasing reactive diluent content due to the enhancement of crosslinking density of APUAs. Moreover, the reactive diluent with high polarity, for example, acrylonitrile monomer, exhibited higher CO₂/N₂ selectivity due to the improvement in solubility of CO₂ in APUA, while the permeability was retained compared with other reactive diluents. The thickness of APUA selective layer exhibited expectedly opposite effect on permeability and selectivity; however, the increment in selectivity is higher than the reduction in permeability when the thickness decreased from 50 to 10 μm. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48293.     

Maximum natural frequencies of polymer composite micro-beams by optimum distribution of carbon nanotubes

Optimum distribution of multi-walled carbon nanotubes (MWCNTs) within a polymer composite micro-beam is sought to achieve its highest natural frequencies given a weight percent (wt.%) of MWCNTs. To this end, the micro-beam is divided into ten segments which are perfectly bonded to their neighbors. Each segment is made of low-viscosity, thermosetting polyester epoxy/amine resin LY-5052 and is reinforced by MWCNTs. A computer program, written in the Python programming language, is compiled with ABAQUS to generate a three-dimensional (3D) finite element (FE) model of the micro-beam and subsequently to evaluate an optimum CNT distribution under various vibration modes and boundary conditions. The influence of uniform and optimum MWCNT distributions on the natural frequencies, mode shapes and equivalent stiffness of the micro-beams is investigated and the results are compared with those of the pure polymer micro-beam. Subsequently, after acquiring the optimum distribution of the MWCNTs, two new CNT dispersion functions are proposed for maximizing fundamental frequencies of the clamped-free and clamped–clamped micro-beams. The results of the FE analysis reveal that the optimal reinforcement distribution pattern significantly depends on vibration mode shapes, particularly the micro-beam curvature under each mode. It is observed that fundamental frequencies of clamped-free, clamped-guided and clamped–clamped micro-beams are enhanced up to 15.9%, 13.1% and 12.6%, respectively, by choosing optimum MWCNT distribution profiles along the micro-beam length.     

Combined heat and power economic dispatch by mesh adaptive direct search algorithm

The optimal utilization of multiple combined heat and power (CHP) systems is a complex problem. Therefore, efficient methods are required to solve it. In this paper, a recent optimization technique, namely mesh adaptive direct search (MADS) is implemented to solve the combined heat and power economic dispatch (CHPED) problem with bounded feasible operating region. Three test cases taken from the literature are used to evaluate the exploring ability of MADS. Latin hypercube sampling (LHS), particle swarm optimization (PSO) and design and analysis of computer experiments (DACE) surrogate algorithms are used as powerful SEARCH strategies in the MADS algorithm to improve its effectiveness. The numerical results demonstrate that the utilized MADS–LHS, MADS–PSO, MADS–DACE algorithms have acceptable performance when applied to the CHPED problems. The results obtained using the MADS–DACE algorithm are considerably better than or as well as the best known solutions reported previously in the literature. In addition to the superior performance, MADS–DACE provides significant savings of computational effort.     

An automatic phase error compensating multiphase LC oscillator: analysis and design

In this work a self phase error compensating multiphase LC oscillator is proposed. Mismatches in LC tanks are considered as the main source of phase errors. Considering this, an analytical approach is proposed to find a relationship between phase errors and their corresponding coupling factors as a necessary condition for phase error cancellation then a self compensating circuit is proposed accordingly. The compensation circuit first detects the phase errors then employs them in a current tuner to change each stage coupling factor to reduce phase errors. The building blocks of the proposed circuit are investigated and the transistor level implementation of each one is presented afterwards. The theoretical results are evaluated and confirmed through simulations using ADS software in 0.18 μm CMOS technology. Simulation results show that not only phase errors are reduced with respect to the previous methods but also this procedure does not impose any further power consumption and phase noise to the circuit.