Nitrogen-hydrocarbon Mixtures Research Articles

An analytical method for ensuring the optimal circulating composition of the multicomponent refrigerant mixture in a steady-state operation mode of the Joule-Thomson refrigerator operating with mixtures

Single and multi-stage Joule-Thompson refrigerators operating with natural nitrogen-hydrocarbon mixtures are marketable for creating refrigeration equipment for freezing and cryopreservation of biomedical materials, liquefaction of certain gases, high-temperature superconductors cooling, conducting climate tests without using cryogenic liquids. One of the main objectives of the development of such refrigerators is to determine the optimal weight of mixed-refrigerant charge with the known geometry of the refrigeration circuit and to ensure the optimal “circulating” composition in the steady-state mode. This article proposes an analytical method for solving this problem and presents the experimental results. The accuracy of the method is determined by the validity of calculating thermodynamic properties of the mixed refrigerants forming solutions with limited solubility in the liquid phase and by taking into account the shift of the “circulating” working body composition relative to the “charge” composition in the steady-state mode due to structural specifics of real refrigerators. The application of the method will allow reducing the time and cost of experimental development of new refrigeration equipment.

Estimation of performance of a J-T refrigerators operating with nitrogen-hydrocarbon mixtures and a coiled tubes-in-tube heat exchanger

The exergy efficiency of Joule-Thomson (J-T) refrigerators operating with mixtures (MRC systems) strongly depends on the choice of refrigerant mixture and the performance of the heat exchanger used. Helically coiled, multiple tubes-in-tube heat exchangers with an effectiveness of over 96% are widely used in these types of systems. All the current studies focus only on the different heat transfer correlations and the uncertainty in predicting performance of the heat exchanger alone. The main focus of this work is to estimate the uncertainty in cooling capacity when the homogenous model is used by comparing the theoretical and experimental studies. The comparisons have been extended to some two-phase models present in the literature as well.Experiments have been carried out on a J-T refrigerator at a fixed heat load of 10 W with different nitrogen-hydrocarbon mixtures in the evaporator temperature range of 100–120 K. Different heat transfer models have been used to predict the temperature profiles as well as the cooling capacity of the refrigerator. The results show that the homogenous two-phase flow model is probably the most suitable model for rating the cooling capacity of a J-T refrigerator operating with nitrogen-hydrocarbon mixtures.

Prediction of vapour-liquid and vapour-liquid-liquid equilibria of nitrogen-hydrocarbon mixtures used in J-T refrigerators

Nitrogen-hydrocarbon mixtures are widely used as refrigerants in J-T refrigerators operating with mixtures, as well as in natural gas liquefiers. The Peng-Robinson equation of state has traditionally been used to simulate the above cryogenic process. Multi parameter Helmholtz energy equations are now preferred for determining the properties of natural gas. They have, however, been used only to predict vapour-liquid equilibria, and not vapour-liquid-liquid equilibria that can occur in mixtures used in cryogenic mixed refrigerant processes. In this paper the vapour-liquid equilibrium of binary mixtures of nitrogen-methane, nitrogen-ethane, nitrogen-propane, nitrogen-isobutane and three component mixtures of nitrogen-methane-ethane and nitrogen-methane-propane have been studied with the Peng-Robinson and the Helmholtz energy equations of state of NIST REFPROP and compared with experimental data available in the literature.

Studies on capillary tube expansion device used in J-T refrigerators operating with nitrogen-hydrocarbon mixtures

Capillary tube expansion devices are used extensively in small closed cycle J-T refrigerators operating with refrigerant mixtures due to its low cost and the absence of any moving parts. It is possible for J-T refrigerators operating with mixtures that the velocity of refrigerant mixture at capillary tube outlet reaches a value where it equals the speed of sound at certain conditions. The variation of the speed of sound of nitrogen-hydrocarbon mixtures used in J-T refrigerators has been studied in two phase (vapour-liquid) and three-phase (Vapour-liquid-liquid) region as a function of temperature and pressure in this work. Also the conditions under which choking occurs in practical J-T refrigerators is investigated.

Performance Analysis of Joule-Thomson Cooler Supplied with Gas Mixtures

Joule-Thomson (J-T) cryo-coolers working in closed cycles and supplied with gas mixtures are the subject of intensive research in different laboratories. The replacement of pure nitrogen by nitrogen-hydrocarbon mixtures allows to improve both thermodynamic parameters and economy of the refrigerators. It is possible to avoid high pressures in the heat exchanger and to use standard refrigeration compressor instead of gas bottles or high-pressure oil free compressor. Closed cycle and mixture filled Joule-Thomson cryogenic refrigerator providing 10-20 W of cooling power at temperature range 90-100 K has been designed and manufactured. Thermodynamic analysis including the optimization of the cryo-cooler mixture has been performed with ASPEN HYSYS software. The paper describes the design of the cryo-cooler and provides thermodynamic analysis of the system. The test results are presented and discussed.

Description and validation of the Little correlation for boiling zeotropic mixtures in horizontal tubes from cryogenic to room temperature

The use of mixed gas working fluids has become common in Joule-Thomson (JT) type cryocoolers for a variety of applications operating in temperatures ranging from 80 to 230 K. The thermal efficiency of mixed gas JT cryocoolers is dependent on the optimization of the gas mixture composition. Most optimization methodologies focus on thermodynamic criteria of the cycle because there are very little data or theory currently available regarding the heat transfer coefficients associated with these multi-component mixtures in two-phase regimes at cryogenic temperatures. A generally accepted correlation to predict the local heat transfer coefficient (htc) for mixtures during the boiling process does not exist. Little [1] proposed a correlation to be used on horizontal tubes that shows good agreement with Nellis et al. [2] experimental data of nitrogen-hydrocarbon mixtures. However, it is not clearly shown how the correlation is obtained and how it should be applied. This paper provides a more complete description of the Little correlation and also expands its validation using the experimental data provided by Barraza [3]. The new experimental data include measurements of the local heat transfer coefficient for mixtures comprising 2 component (binary) up to 5 components in the temperature range between 100 K and room temperature. These mixtures are formed from nitrogen-hydrocarbon and argon-fluorocarbon mixtures and evaporate in horizontal tubes with diameters from 0.5 to 3.0 mm for different heat flux, mass flux, evaporating pressure, and composition.

Studies on the performance of a small reciprocating compressor with different nitrogen–hydrocarbon mixtures

The performance of Joule–Thomson refrigerators operating with mixed refrigerants depends on the composition of mixtures as well as the hardware employed. The role of mixture composition on the overall performance of the system has been well addressed in the open literature. What is not well known is the role of mixture composition on the performance of individual components such as the compressor, heat exchanger, etc. The adiabatic efficiency of a single stage Joule–Thomson refrigerator compressor was measured with thirty different nitrogen–hydrocarbon and neon–nitrogen–hydrocarbon mixtures. Our results show that the adiabatic efficiency of the compressor is independent of the mixture composition in the range of pressure ratios tested.

Effect of mixture composition and hardware on the performance of a single stage JT refrigerator

The specific refrigeration effect that can be obtained in a single stage mixed refrigerant Joule–Thomson refrigerator is strongly dependent on the composition of mixture used. Comprehensive methods have been developed over the last two decades to determine the mixture composition that results in the highest exergy efficiency or the refrigeration produced. However, what is not well known is the relationship between the mixture composition and the hardware, which ultimately decides the performance of the refrigerator. Experiments were conducted with seven different nitrogen–hydrocarbon mixtures in a single stage JT refrigerator to understand the effect of both composition and hardware on the performance of the refrigerator, the results of which are presented in this paper.

Long time mass fraction statistics in stationary compressible isotropic turbulence at supercritical pressure

Direct numerical simulations are used to investigate the “long time” distribution of mass fraction fluctuations in stationary compressible isotropic turbulent binary nitrogen–hydrocarbon mixtures under supercritical pressure conditions. The governing equations are the compressible Navier–Stokes equations together with the cubic Peng–Robinson real gas state equation, and generalized heat and mass diffusion derived from nonequilibrium thermodynamics. A highly efficient procedure is presented which allows for the solution of all thermodynamic quantities without iterations or interpolation tables. The simulations consider equal mass binary mixtures of various combinations of nitrogen, heptane, dodecane, and 3-methylhexane, having molecular weight ratios in the range 1⩽MB/MA⩽6.08. It is shown that temperature and pressure-gradient-induced Soret mass diffusion results in statistically stationary mass fraction distributions at long times. The results reveal that the mass diffusion term due to the pressure gradient acts as a production mechanism in the Favre averaged scalar variance transport equation, and is balanced by Fickian dissipation to produce the stationary states. The resulting scalar probability density function is characterized by a larger than Gaussian flatness factor, and is asymmetric due to the mass fraction dependence of the partial molar volume. The stationary scalar variance amplitude increases both with increasing turbulence Mach number and molecular weight ratio of the species, but is inversely related to the turbulence Reynolds number. The scalar energy spectra exhibit peak values at wave numbers corresponding to the peak in the velocity dissipation spectra.

Start-up and operating characteristics of a refrigerator operating on nitrogen-hydrocarbon mixtures with isothermal heat load

Start-up and operating characteristics of a refrigerator operating on nitrogen-hydrocarbon mixtures with isothermal heat load