Investigating the Influence of Helium Based Mixtures Composition on the Temperature Recovery Factor and Prandtl Number Values

The thermoacoustic prime mover (TAPM) is an attractive alternative to the conventional drive used in the pulse tube cryocoolers (PTCs), owing to no moving components, less wear and tear, less vibrations, simplicity in construction and use of environmentally friendly working fluids. In our objective to develop such a system, we have designed and developed twin standing wave TAPM. This paper presents the results of an experimental investigation using binary gas mixtures as working fluid. The gas mixtures of different working fluids, namely nitrogen, argon, and helium are used in the experimentation. The measurement shows that the performance of the twin standing wave TAPM improves as the working gas Prandtl number decreases. The operating frequency, pressure amplitude, temperature difference between the stack ends have been studied at different operating pressures and by varying gas mixture composition. However this needs optimization of binary gas mixture composition. The experimental studies show that for the best performance of TAPM, correct binary mixture of working fluids should be used. Among the binary mixtures the pressure amplitude is high when argon is used as the working fluid. However temperature difference across the stack is higher for argon. In view of this an optimal mixture of Helium 60% and Argon 40% can be chosen to obtain best performance of TAPM.

The results of 2-D numerical simulations of hypersonic flow of a single diatomic gas, e.g., Nitrogen and a binary inert mixture of two gases (which are constituents of air namely N2, O2, Ar) past a 2-D blunt body in rotational non-equilibrium from low to high Knudsen Numbers are obtained using the Wang-Chang Uhlenbeck equation [1] or the Generalized Boltzmann Equation (GBE) [2]. The computational framework available for the classical Boltzmann equation for a monoatomic gas with translational degrees of freedom [3] is extended by including the rotational degrees of freedom in the GBE. The general computational methodology for the solution of the GBE for a diatomic gas is similar to that for the classical Boltzmann equation except that the evaluation of the collision integral becomes significantly more complex due to the quantization of rotational energy levels. There are two main difficulties encountered in computation of high Mach number flows of diatomic gases with rotational degrees of freedom using the GBE: (1) a large velocity domain is needed for accurate numerical description of molecular velocity distribution function resulting in enormous computational effort in calculation of the collision integral and (2) about 50 to 70 energy levels are needed for accurate representation of the rotational spectrum of the gas. These two problems result in very large CPU and memory requirements for shock wave computations at high Mach numbers (> 6). We employ a two level Rotational-Translational (RT) relaxation model to address this problem [4]; as a result the efficiency of calculations increases by several orders of magnitude. For numerical solution of GBE for an inert binary gas mixture, the GBE is formulated in the impulse space. The gas mixtures may consist of both monatomic and diatomic gases with arbitrary constituents, concentrations, and mass ratios. The method is exercised for various concentration ratios, mass ratios, and density ratios to evaluate its ability to simulate a wide range of binary gas mixtures of monoatomic and diatomic gases. In particular, the method is applied to simulate two of the three primary constituents of air (N2, O2, Ar) in a binary mixture at 1:1 density ratio and air concentration ratio with gases in translational and rotational non-equilibrium. The results of GBE are compared with DSMC calculations; a reasonably good agreement is obtained. The solutions presented in this paper can also serve as validation test cases for other methods as well as an important building block in developing complex 3D simulations for shock waves in a mixture of multiple gases.

Molecular dynamics study on transport properties of supercritical working fluids: Literature review and case study

A numerical investigation of the boundary layer on a permeable wall in a supersonic gas flow is performed using a differential turbulence model. Temperature recovery factors are obtained for a series of Prandtl numbers and gas suction or injection in a wide range of the permeability factor from critical injection to asymptotic suction. With the example of air injection into a supersonic air flow, two methods for determining the temperature of a heat-insulated permeable wall are considered. The first is to solve the problem with a boundary condition of zero heat flux to the wall. The second is similar to an experimental method when the temperature of the gas injected at a section along the plate length becomes equal to the wall temperature. The heat-insulated wall temperatures and temperature recovery factors obtained by these two methods for injection below the critical one are close to each other. In case of critical injection, these two methods yield different results.

Exploration and Analysis of CO2 + Hydrocarbons Mixtures as Working Fluids for Trans-critical ORC

Over the past several years organic Rankine cycle (ORC) processes have become a promising technology for power production from low grade heat sources, such as solar, biomass, geothermal and waste heat. A key challenge in design is the selection of an appropriate working fluid. ORC systems that use single components as working fluids have two major shortcomings. First, in the majority of applications, the temperatures of the heat sink and source fluid vary during the heat transfer process, whereas working fluid evaporation and condensing is isothermal. As a consequence a pinch point is encountered in the evaporator and condenser giving rise to large temperature differences at one end of heat exchanger. This leads to irreversibility that in turn reduces process efficiency. A similar situation is also encountered in the condenser. A second shortcoming of the Rankine cycle is its lack of flexibility. For given operating conditions, a certain working fluid may be the optimum choice; however, as the operating conditions change another working fluid would become a more appropriate choice. The shortcomings result from a mismatch between thermodynamic properties of pure working fluids, the requirements imposed by the Rankine cycle and the particular application. In contrast, when working fluid mixtures are used instead of single component working fluids, improvements can be obtained in two ways: through the inherent properties of the mixture itself, and through cycle variations which become available with mixtures. The most obvious positive effect is decrease in exergy destruction, because occurrence of the temperature glide at phase change provides a good match of temperature profiles in condenser and evaporator. The paper presents detailed simulations analysis of organic Rankine cycle processes for energy conversion of low heat sources for various binary zeotropic mixtures. The rigorous and the most suitable thermodynamic models are applied in each mixture simulation. The paper explores the effect of mixture utilization on common ORC performance assessment criteria in order to demonstrate advantages of employing mixtures as working fluid as compared to pure fluids. In addition, several new criteria are developed in order to provide a new perspective on how ORC performance should be assessed from thermodynamic point of view.

Review of Filtered Rayleigh Scattering technique for mixing studies in supersonic air flow

On the use of noble gases and binary mixtures as reactor coolants and CBC working fluids

In this study, the quantitative discrimination of seven different types of binary volatile organic gas mixtures were realized by using a proposed structure which was combination of probabilistic neural networks (PNNs) and multilayer neural networks (MLNNs). At the first phase of the discrimination, the binary gas mixtures were classified using PNNs. For comparison, the MLNN structures were also used at this phase. And at the second phase, the MLNNs were processed for the quantitative identification of individual gas concentrations in their gas mixtures. A data set consisted of the steady state sensor responses from quartz crystal microbalance (QCM) type sensors was used for the training of the PNNs and MLNNs. The components in the binary mixture were quantified applying the sensor responses from the QCM sensor array as inputs to the combined neural network structures. The performance of the combined network structure was discussed based on the experimental results.

This research is concerned with the development of quantitative scientific descriptions of the thermodynamic and transport properties of supercritical and subcritical fluids and fluid mixtures. It is well known that the thermophysical properties of fluids and fluid mixtures exhibit singular behavior at critical points. Asymptotically close to critical points the thermophysical properties satisfy scaling laws with universal critical exponents and universal scaling functions. However, the range of validity of these asymptotic scaling laws is very small. It has now been well established that the range of temperatures and densities where various thermophysical properties are affected is quite large. The reason is that the correlation length associated with the critical fluctuations exceeds the short-range molecular interaction range in a sizeable part of the phase diagram of fluids and fluid mixtures. The paper discusses the research accomplishments of the following: Thermodynamic properties of one-component fluids; Thermodynamic properties of fluid mixtures; Transport properties of one-component fluids; and Transport properties of fluid mixtures.

Prediction accuracy of thermodynamic properties using PC-SAFT for high-temperature organic Rankine cycle with siloxanes

Improved correlations for working fluid properties prediction and their application in performance evaluation of sub-critical Organic Rankine Cycle

Towards working fluid properties and selection of Rankine cycle based waste heat recovery (WHR) systems for internal combustion engines – A fundamental analysis

Experiment of Non-equilibrium Condensation on Shock Tube Wall in Supersonic Flow behind both Incident and Reflected Shock Waves

The known methods of gas-dynamic temperature stratification are reviewed. Attention is concentrated on an analysis of the possibilities of the gas dynamic stratification method proposed by the author. The method is based on the difference between the equilibrium temperature of a thermally insulated wall in supersonic flow and the adiabatic stagnation temperature of the gas. Certain possible practical applications of the method to various types of energy-converting apparatus are considered. The basic trends of fundamental and applied research in the field of gas-dynamic temperature stratification are formulated.