Joule-Thomson Refrigerator Research Articles

An Identification of the Best Mixture Composition for the Joule-Thomson Refrigerator Operating at 90 K

An Identification of the Best Mixture Composition for the Joule-Thomson Refrigerator Operating at 90 K

A numerical model for boiling heat transfer coefficient of zeotropic mixtures

Zeotropic mixtures never have the same liquid and vapor composition in the liquid-vapor equilibrium. Also, the bubble and the dew point are separated; this gap is called glide temperature (Tglide). Those characteristics have made these mixtures suitable for cryogenics Joule-Thomson (JT) refrigeration cycles. Zeotropic mixtures as working fluid in JT cycles improve their performance in an order of magnitude. Optimization of JT cycles have earned substantial importance for cryogenics applications (e.g, gas liquefaction, cryosurgery probes, cooling of infrared sensors, cryopreservation, and biomedical samples). Heat exchangers design on those cycles is a critical point; consequently, heat transfer coefficient and pressure drop of two-phase zeotropic mixtures are relevant. In this work, it will be applied a methodology in order to calculate the local convective heat transfer coefficients based on the law of the wall approach for turbulent flows. The flow and heat transfer characteristics of zeotropic mixtures in a heated horizontal tube are investigated numerically. The temperature profile and heat transfer coefficient for zeotropic mixtures of different bulk compositions are analysed. The numerical model has been developed and locally applied in a fully developed, constant temperature wall, and two-phase annular flow in a duct. Numerical results have been obtained using this model taking into account continuity, momentum, and energy equations. Local heat transfer coefficient results are compared with available experimental data published by Barraza et al. (2016), and they have shown good agreement.

Experimental investigation on two-phase frictional pressure drop of zeotropic mixtures of R50/R170 in a horizontal tube

In recent years, due to the environmental issues, suitable substitutes are being searched to replace the traditional chlorinated refrigerants. With zero ozone depleting potential, low global warming potential and high thermodynamic performance, the hydrocarbons are suitable selections in refrigerators and heat pump systems. As hydrocarbons, R50 and R170 are also the important parts of the natural gas and often-used components in mixture refrigerants for the low-temperature Joule-Thomson refrigerator. As the flow characteristics play important parts in the design and optimization of the heat exchangers in refrigerators and air-conditioning systems, the two-phase frictional pressure drop should be well examined and analyzed. Although there are massive experimental studies on two-phase frictional pressure drop of hydrocarbons in horizontal tubes, the published experimental investigations for zeotropic mixtures of R50/R170 are rare. Therefore, it′s desirable to conduct an experimental investigation on two-phase frictional pressure drop of zeotropic mixtures of R50/R170 in a horizontal tube and find a suitable correlation. In this paper, two-phase frictional pressure drop of R50/R170 mixtures (0.27:0.73, 0.54:0.46 and 0.7:0.3 by mole) was studied experimentally in a horizontal tube with inner diameter of 4 mm. The tests were carried out at saturation pressures from 1.5 MPa to 2.5 MPa for mass fluxes from 99 kg m−2 s−1 to 255 kg m−2 s−1, vapor qualities from 0 to 0.9. The uncertainty for the pressure drop was 40 Pa and the uncertainties for the vapor quality with a 95% confidence interval were less than 11.74% under the employed operation conditions. The effects of mass flux, saturation pressure, vapor quality and concentration on two-phase frictional pressure drop were examined and analyzed. Some conclusions can be drawn that (1) the frictional pressure drops increase with the increasing mass flux and the impact becomes more obvious when the vapor quality increases; (2) the frictional pressure drops decrease with the increasing saturation pressure and the impact enhances when the vapor quality increases; (3) the frictional pressure drops increase with the increasing vapor quality and then change to be smooth even decline at high vapor qualities. And the effect of vapor quality enhances as the mass flux increases and the saturation pressure decreases; (4) the frictional pressure drops of pure R50 are lower than that of all R50/R170 mixtures and the frictional pressure drops of the initial concentration of R50/R170 mixtures at 0.27:0.73 are also lower than that of other two initial concentrations of R50/R170 mixtures. Their differences are not obvious at low vapor qualities, while the differences enhance when the mass flux and vapor quality increase as well as the saturation pressure decreases. The influence of concentration may be mainly related to the difference of the vapor densities. In addition, the experimental data were compared with twenty well-known frictional pressure drops correlations. The comparison results showed that the Friedel correlation showed the best agreement with a mean absolute relative deviation of 19.26% and 87.45% of points in the deviation bandwidth of ±30%.

Performance comparison of single-stage mixed-refrigerant Joule–Thomson cycle and pure-gas reverse Brayton cycle at fixed-temperatures from 80 to 180 K

Performance comparison of single-stage mixed-refrigerant Joule–Thomson refrigeration cycle (MJTR) and pure-gas reverse Brayton cycle (RBC) at fixed-temperatures from 80 to 180 K was made in this paper. The simulation was mainly conducted under nonideal conditions with extrinsic irreversibilities. Exergy efficiency and volumetric cooling capacity are two main evaluation parameters. Exergy loss distributions along the cycles were analyzed. Under ideal conditions, RBC achieved the highest exergy efficiency at all temperatures, but lower volumetric cooling capacity than MJTR at middle-high temperatures. Under nonideal conditions, both the exergy efficiency and volumetric cooling capacity of MJTR were obviously superior to RBC from 100 to 180 K, but inferior to RBC at 80 K. Two reasons account for the sharp performance degradation of MJTR: The high fraction of neon resulted in large entropy generation and exergy loss in throttling process. Larger recuperator duty and WLMTD lead to larger losses in the recuperator.

Investigation of ejector-equipped Joule–Thomson refrigerator operating below 77 K

The lowest attainable refrigeration temperature of a nitrogen based Joule–Thomson refrigerator is generally limited to 77 K since the compressor suction pressure is usually higher than atmospheric pressure. The Joule–Thomson process with an ejector is proposed to achieve a refrigeration temperature as low as 68 K by adjusting the evaporation pressure down to 28 kPa and boosting the return stream pressure up to 147 kPa. A one-dimensional numerical model is developed to predict the performance of the ejector at cryogenic temperature, and its accuracy is compared with experimental data. The analysis results show that the addition of the ejector in the Joule–Thomson refrigeration cycle increases up to 5 times the overall efficiency, where the maximum achievable COP and exergy efficiency are 0.0195 and 6.65%, respectively. Other featured advantages of the proposed Joule–Thomson refrigeration cycle with ejector are the simplicity of cycle, minimization of mechanical moving components, cost effectiveness, and high reliability compared to other cryogenic refrigeration methods using pumps or cold compressors in Joule–Thomson cycles.

Design of non-flammable mixed refrigerant Joule-Thomson refrigerator for precooling stage of high temperature superconducting power cable

A cryogenic Joule-Thomson (JT) refrigerator has many advantages for large industrial applications, including easy cooling power adjustability and high reliability because there are no moving parts at low temperature. In this paper, a single stage and a cascade type of non-flammable (NF) mixed refrigerant (MR) JT refrigerators have been proposed for the precooling process of a neon/nitrogen mixed refrigerant JT refrigerator. The neon/nitrogen MR JT refrigerator is used to maintain a subcooled state of liquid nitrogen coolant for an HTS (high temperature superconductor) cable.Both selected MRs for the 1st stage (low temperature cycle) of the cascade MR JT refrigerator and the single MR JT refrigerator are composed of Nitrogen (N2), Argon (Ar), Tetrafluoromethane (CF4, R14) and Octafluoropropane (C3F8, R218). R410A is selected as the refrigerant for the 2nd stage (high temperature cycle) of the cascade MR JT refrigerator, of which the cooling temperature is approximately 240K. A commercial software with Peng-Robinson equation of state (EOS) is utilized to design the non-flammable MR JT refrigerator. The optimal design is discussed with consideration for various parameters such as the temperature staging, the operating pressure of the compressor and the mass flow rate of the working fluid. The maximum coefficient of performance (COP) and Carnot efficiency of the cascade MR JT refrigerator are obtained as 0.216 and 40%, respectively at 105K. Exergy analysis is also carried out in this paper to reveal the irreversibility of the refrigeration cycle.

Steady-state thermodynamic simulation and structural design of the dephlegmator used in mixed-refrigerant Joule-Thomson refrigerators

Dephlegmators can be used to reduce the energy consumption and simplify the layout of the mixed-refrigerant Joule–Thomson (MRJT) cycle. Heat-exchange characteristics and refrigeration design are currently based on highly simplified assumptions. Synthesis methods to efficiently solve all design issues of dephlegmators in MRJT cycle are insufficient. No suitable separation module is available for the simultaneous heat and mass transfer processes in Aspen Plus because the module should be programmed and incorporated into Aspen Plus as a user-defined unit. In this paper, a systematic steady-state method was proposed for the detailed design of dephlegmators for gas mixture separation, considering the simulation and heat exchanger design simultaneously. The material balance, vapor–liquid equilibrium, mole fraction summation and heat balance (MESH) model was programmed in FORTRAN language. Good agreements and the feasibility of the MESH model were found. Deviations between the simulation results and patent data were all within 5%. The errors in the predicted temperatures of vapor and liquid products were less than 2% and 10%, respectively. Fine applicability and low energy consumption of the dephlegmator were addressed. The mole fraction of n-butane in the liquid phase had high recovery ratio of 90%. The dephlegmator decreased more than 30% of energy consumption compared with the traditional distillation tower under similar separation effects. In the structural design process, the dephlegmator was divided into certain segments by baffle plates on the basis of segmented calculation. The heat transfer coefficient, heat transfer area, pressure drop, and structural parameters of the dephlegmator were evaluated. A clear and comprehensive three-dimensional dephlegmator model was shown.

Visualization of the solid–liquid equilibria for non-flammable mixed refrigerants

Non-flammable mixed refrigerant (NF-MR) Joule Thomson (J–T) refrigerators have desirable characteristics and wide cooling temperature range compared to those of pure J–T refrigerators. However, the operating challenge due to freezing is a critical issue to realize this type of refrigerator. In this paper, the solid–liquid phase equilibria (i.e. freezing point) of the NF-MR which is composed of Argon (Ar), R14 (CF4), and R218 (C3F8), has been experimentally investigated by a visualized apparatus. The accuracy of the apparatus is experimentally verified with pure refrigerants and selected binary mixed refrigerants. Freezing points of the ternary NF-MRs have been measured with the molar compositions from 0.1 to 0.8 for each component. Each test result is simultaneously acquired by a camcorder for visual inspection and temperature measurement during a warming process. Experimental results reveal that the specific MR, with R14 molar composition higher than 0.4, can achieve remarkably low freezing temperature even below 77K. These unusual freezing point depression characteristics of the MR can be a useful information for designing a cryogenic MR J–T refrigerator to reach temperatures less than 77K.

Visual investigation of solid-liquid phase equilibria for nonflammable mixed refrigerant

Non-flammable mixed refrigerant (NF-MR) Joule Thomson (J-T) refrigerators have desirable characteristics and wide cooling temperature range compared to those of pure J-T refrigerators. However, the operating challenge due to freezing is a critical issue to construct this refrigerator. In this paper, the solid-liquid phase equilibria (i.e. freezing point) of the NF-MR which is composed of Argon, R14 (CF4), and R218 (C3F8), has been experimentally investigated by a visualized apparatus. Argon, R14 and R218 mixtures are selected to be effectively capable of reaching 100 K in the MR J-T refrigerator system. Freezing points of the mixtures have been measured with the molar compositions from 0.1 to 0.8 for each component. Each test result is simultaneously acquired by a camcorder for visual inspection and temperature measurement during a warming process. Experimental results show that the certain mole fraction of Argon, R14, and R218 mixture can achieve remarkably low freezing temperature even below 77 K. This unusual freezing point depression characteristic of the MR can be a useful information for designing a cryogenic MR J-T refrigerator to reach further down to 77 K.

Investigation on Cryogenic Refrigerator and Cooling Schemes for Long Distance HTS Cable

High-temperature superconducting (HTS) cable is one of the most prospective superconducting technologies for its low electric power transmission loss and high power density. One difficulty of practicing this technology is maintaining the HTS cable at a cryogenic temperature approximately at 70 K. The types of cryogenic refrigerators are briefly reviewed to apply in long-distance HTS cables. Recuperative-type refrigerators, such as Brayton and Joule-Thomson (JT) refrigerators, are more appropriate to satisfy the required high cooling power. The theoretical reliability of the newly proposed dual mixed refrigerant (DMR) JT refrigerator is analyzed. The cycle configuration of the DMR JT refrigerator is more complex than that of a Brayton refrigerator; however, the degradation of reliability was not significant. Furthermore, a remote operation apart from the compressor is possible in the JT refrigerator without moving components inside the cold box. This is the most desirable characteristic for long-distance HTS cable cooling. Finally, the advantage of using an oxygen and nitrogen mixture as the circulating coolant is discussed. The number of cooling stations can be reduced in a long-distance HTS cable by lowering the coolant feeding temperature.

Performance Investigation of Joule–Thomson Refrigeration System with Environment Friendly Refrigerant Mixtures

The importance on energy conservation has resulted in new efforts to develop more efficient refrigeration systems for achieving low temperature. The Joule-Thomson (J-T) concept has been widely used for achieving low temperature. The overall performance of the refrigeration system is governed by the selection of the mixture composition and heat exchanger used. Therefore, an attempt has been made to investigate the performance of the Joule–Thomson refrigeration system with the addition of a heat exchanger in between the condenser and the expansion device. In order to study the performance of the system experimentally, a Joule-Thomson refrigeration system experimental setup has been developed with mixture of R290/R600a (40/60, 50/50, 60/40 and 70/30 by weight) are used as environmental friendly refrigerant mixtures and experiments are conducted. The effect of evaporator temperature on the coefficient of performance, exergy efficiency and exergy destruction ratio of the J-T system are investigated. The Joule–Thomson refrigeration system with compact heat exchanger yields higher coefficient of performance by 10.45% and exergy efficiency obtained by 4.25%. Keywords: Coefficient of Performance, Exergy Destruction Ratio, Exergy Efficiency, Heat Exchanger, Joule–Thomson Refrigeration System

Investigation of two-phase heat transfer coefficients of argon–freon cryogenic mixed refrigerants

Mixed refrigerant Joule Thomson refrigerators are widely used in various kinds of cryogenic systems these days. Although heat transfer coefficient estimation for a multi-phase and multi-component fluid in the cryogenic temperature range is necessarily required in the heat exchanger design of mixed refrigerant Joule Thomson refrigerators, it has been rarely discussed so far. In this paper, condensation and evaporation heat transfer coefficients of argon–freon mixed refrigerant are measured in a microchannel heat exchanger. A Printed Circuit Heat Exchanger (PCHE) with 340μm hydraulic diameter has been developed as a compact microchannel heat exchanger and utilized in the experiment. Several two-phase heat transfer coefficient correlations are examined to discuss the experimental measurement results. The result of this paper shows that cryogenic two-phase mixed refrigerant heat transfer coefficients can be estimated by conventional two-phase heat transfer coefficient correlations.

Investigation of neon–nitrogen mixed refrigerant Joule–Thomson cryocooler operating below 70 K with precooling at 100 K

There has been two-stage mixed refrigerant (MR) Joule–Thomson (JT) refrigeration cycle suggested for cooling high temperature superconductor (HTS) electric power cable below 70K. As the continuation effort of realizing the actual system, we fabricated and tested a small scale neon and nitrogen MR JT cryocooler to investigate the refrigeration characteristics and performance. The compression system of the refrigeration circuit was accomplished by modifying commercially available air-conditioning rotary compressors. Compressors stably operated at the maximum compression ratio of 31 when the suction pressure was 77kPa. The achieved lowest temperature was 63.6K when the heating load was 35.9W. The measured Carnot efficiency of the present system was 6.5% which was lower than that of the designed goal of 17.4%. The low efficiency of compressor (34.5%), and the pressure drop at the compressor suction were the main reasons for this efficiency degradation. The feasibility and usefulness of neon and nitrogen MR JT refrigeration cycle was validated that the achieved minimum temperature was 63.6K even though the pressure after the expansion was maintained by 130kPa. The comparison between the measurement and calculation showed that each stream temperature of refrigeration cycle were predictable within 3% error by Peng–Robinson equation of state (EOS).

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.

Design of closed-loop nitrogen Joule-Thomson refrigeration cycle for 67 K with sub-atmospheric device

Closed-loop J-T (Joule-Thomson) refrigeration cycle is advantageous compared to common open loop <TEX>$N_2$</TEX> decompression system in terms of nitrogen consumption. In this study, two closed-loop pure <TEX>$N_2$</TEX> J-T refrigeration systems with sub-atmospheric device for cooling High Temperature Superconductor (HTS) power cable are investigated. J-T cooling systems include 2-stage compressor, 2-stage precooling cycle, J-T valve and a cold compressor or an auxiliary vacuum pump at the room temperature. The cold compressor and the vacuum pump are installed after the J-T valve to create sub-atmospheric condition. The temperature of 67 K is possible by lowering the pressure up to 24 kPa at the cold part. The optimized hydrocarbon mixed refrigerant (MR) J-T system is applied for precooling stage. The cold head of precooling MR J-T have the temperature from 120 K to 150 K. The various characteristics of cold compressor are invstigated and applied to design parameter of the cold compressor. The Carnot efficiency of cold compressor system is calculated as 16.7% and that of vacuum pump system as 16.4%. The efficiency difference between the cold compressor system and the vacuum pump system is due to difference of enthalpy change at cryogenic temperature, enthalpy change at room temperature and different work load at the pre-cooling cycle. The efficiency of neon-nitrogen MR J-T system is also presented for comparison with the sub-atmospheric devices. These systems have several pros and cons in comparison to typical MR J-T systems such as vacuum line maintainability, system's COP and etc. In this paper, the detailed design of the subcooled <TEX>$N_2$</TEX> J-T systems are examined and some practical issues of the sub-atmospheric devices are discussed.

Thermodynamic optimization analysis of a tube-in-tube helically coiled heat exchanger for Joule–Thomson refrigerators

In the present study, a novel optimization model is developed based on the available work loss minimization for tube-in-tube helically coiled heat exchangers. The present numerical model takes into account available work losses, i.e. irreversibilities, due to heat transfer and frictional pressure drops of heat exchangers. By employing the expression of Carnot cycle efficiency, the formula for calculating the available work loss resulting from the irreversible heat transfer process is obtained and then utilized in the computation of the total available work loss. In the case under study, the effects of main design parameters of the heat exchanger on the available work loss are discussed in detail and the optimal design parameters of the heat exchanger are also obtained under the specified condition. The model and results presented here for the optimization of tube-in-tube helically coiled heat exchangers may provide a helpful guidance for applying such heat exchangers in Joule–Thomson refrigerators.

Development of a −186 °C cryogenic preservation chamber based on a dual mixed-gases Joule–Thomson refrigeration cycle

First of all, a dual mixed-gases Joule–Thomson refrigeration system was designed, constructed and tested in this work. A minimum no-load temperature of −197.7 °C (about 75.5 K) was reached and about 110 W cooling capacities at −174 °C (about 99 K) was obtained with the mixed-gases refrigeration prototype. Secondly, a cryogenic chamber for biomaterials preservation was built and tested with the similar cycle configuration, which has reached the lowest temperature of −192 °C (about 81 K) with an effective preservation volume of 80 L. A relatively fast cooling-down rate for this cryogenic chamber was obtained. Specifically, it took 2.5 h to reach −180 °C, and about 5 h to reach −190 °C. The cryogenic chamber shows a good perspective as a substitute for traditionally used liquid nitrogen preservation vessels.

A compact sub-Kelvin ultrahigh vacuum scanning tunneling microscope with high energy resolution and high stability

We designed a scanning tunneling microscope working at sub-Kelvin temperatures in ultrahigh vacuum (UHV) in order to study the magnetic properties on the nanoscale. An entirely homebuilt three-stage cryostat is used to cool down the microscope head. The first stage is cooled with liquid nitrogen, the second stage with liquid (4)He. The third stage uses a closed-cycle Joule-Thomson refrigerator of a cooling power of 1 mW. A base temperature of 930 mK at the microscope head was achieved using expansion of (4)He, which can be reduced to ≈400 mK when using (3)He. The cryostat has a low liquid helium consumption of only 38 ml/h and standing times of up to 280 h. The fast cooling down of the samples (3 h) guarantees high sample throughput. Test experiments with a superconducting tip show a high energy resolution of 0.3 meV when performing scanning tunneling spectroscopy. The vertical stability of the tunnel junction is well below 1 pm (peak to peak) and the electric noise floor of tunneling current is about 6fA/√Hz. Atomic resolution with a tunneling current of 1 pA and 1 mV was achieved on Au(111). The lateral drift of the microscope at stable temperature is below 20 pm/h. A superconducting spilt-coil magnet allows to apply an out-of-plane magnetic field of up to 3 T at the sample surface. The flux vortices of a Nb(110) sample were clearly resolved in a map of differential conductance at 1.1 K and a magnetic field of 0.21 T. The setup is designed for in situ preparation of tip and samples under UHV condition.

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.

Design of high efficiency mixed refrigerant Joule–Thomson refrigerator for cooling HTS cable

The substitution of high temperature superconducting (HTS) cables for existing subterranean electric transmission lines is arising as a solution to continuously increasing electricity demand in urban areas. A cryogenic refrigeration system having the characteristics of high reliability, high efficiency, large cooling capacity, and low capital cost is essential to enable such a substitution. These requirements can be satisfied with a mixed refrigerant Joule–Thomson (MR JT) refrigerator. Unfortunately, usual MR JT refrigerators exhibit good performance at refrigeration temperatures above 80 K. A precooled neon–nitrogen MR JT refrigerator is proposed in this paper that can cool HTS cables at 70 K. The coefficient of performance (COP) of the proposed MR JT refrigerator is predicted to be 0.058 at 70 K (19.2% for exergy efficiency) with the optimized design variables. The COP can be improved further to 0.064 by enhancing the efficiency of the precooling cycle. The maximum achievable COP demonstrates the feasibility of MR JT refrigerator for cooling HTS cable.