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The attainment and maintenance of a low temperature environment is essential for aerospace cryogenic detectors to achieve their required performance. Developing cryocoolers with features of high efficiency, compact structure, and long lifetime is the main challenge for cryogenic detector cooling. In this paper, a high efficiency thermally-coupled two-stage Stirling type pulse tube cryocooler working at 35 K for HgCdTe long wave infrared detector cooling is designed and tested. The thermally-coupled type avoids gas distribution at cold side which minimizes the inter-stage influence. The whole cryocooler is driven by one linear compressor which enables compact structure. The influence of operation frequency and mean pressure is studied by numerical calculation and experiments to determine the optimum operation condition. Acoustic impedance characteristics of both stages and the whole cold finger are also analyzed by comparing performance of cryocooler with different frequency, mean pressure and structure dimensions. The distributions of acoustic power and phase angle are presented to study the relation between impedance characteristic and the cooling performance. Impedance match between compressor and cold finger is also discussed by analyzing the efficiency of the linear compressor and the performance of cryocooler with different pulse tubes. Under optimum impedance match and operation condition of a working frequency of 39.2 Hz and a mean pressure of 2.45 MPa, the cryocooler provides a cooling power of 1 W at 35.1 K with an input electrical power of 150 W, which indicates a relative Carnot efficiency of 5%. This is a rather high efficiency for developed Stirling type multi-stage pulse tube cryocooler working at 35 K with only inertance tubes as phase shifter. The development of this cryocooler lays a solid base for the further optimization to realize a competitive candidate for aerospace cooling requirements.

A new axisymmetric CFD model capable of describing pumping loss is proposed for free piston Stirling engine (FPSE). Inclusion of clearance seals, bounce space, heater, cooler and regenerator in a single model is the unique strength of this work. For transient simulation of engine, dynamic mesh was utilized for catering needs of moving boundaries. The model was validated with 12.5 kW component test power converter (CTPC) and successfully predicted indicated power, efficiency, pressure amplitude, pressure drop, and gas temperature in expansion and compression space at different piston amplitudes with 6% maximum deviation. The results showed that the heat exchange at heater and cooler was minimized at each flow reversal and was strongly influenced by oscillating gas flow rate. The results also present optimum displacer and piston seal clearance at different charge pressure and operating frequencies. The displacer seal clearance could be increased up to 125μm without compromising power: however, engine output was severely affected with increasing piston seal gap.

Due to the excellent heat transfer performance and low pressure drop, the parallel-plate regenerator (PPR) is very suitable for use in Stirling engines. At present, researches on the application of...

Water dispensers are currently one of the essential home items. The international marketplace for water dispensers uses a vapour compression refrigeration cycle, which spends a large amount of energy and uses environmentally harmful refrigerants. In the present work, a numerical and experimental investigation for obtaining hot and cold drinking water using the Stirling cycle is characterized by saving energy, being environment-friendly, rapidly reaching the required cooling or heating loads, and having the highest possible performance. The present work uses a tubular heat exchanger as both a cold and a hot heat exchanger. According to Schmidt's analysis, the optimal water dispenser dimensions is calculated and experimentally confirmed for higher cooling/heating loads. The experimental and numerical results concluded that the machine speed increases the cooling/ heating load at various charged pressure. Also, the increase in the charged mass improves the cooling/heating load. The water dispenser can produce about 3 kW of cooling load and about 7 kW of heating load at 4 bars of charged pressure and 1200 rpm.

This study aims to present a novel tri-generation plant consisting of a molten carbonate fuel cell (MCFC) unit coupled with a Stirling engine (SE), a heat recovery steam generator (HRSG), and two types of absorption refrigeration cycles (ARCs), i.e., Generator Absorber eXchanger (GAX) and Vapour Absorption Refrigeration (VAR). The proposed system is evaluated from energy, exergy, as well as environmental impact (3E) points of view. To carry out the parametric study, three sub-models are also introduced for the whole system. The sub-model (1) investigates the solo MCFC with the new configuration. In the sub-model (2), the SE and HRSG are added to boost the power generation and overall system efficiency through employing the heat wasted in the sub-model (1). In the last sub-model, for cooling purposes, the surplus heat of MCFC is reutilized using an absorption refrigeration cycle. Besides, to make a comparative study between GAX and VAR systems, the sub-model (3) is classified into two different schemes: (a) with a VAR cycle, and (b) with a GAX cycle. The results reveal that the exergy efficiency and CO2 emissions of the sub-models (1), (2), and (3) are 48.04%, 51.24%, 52.35% (VAR cycle), 52.12% (GAX cycle), 0.388 t/MWh, 0.364 t/MWh, 0.357 t/MWh (VAR cycle), and 0.358 t/MWh (GAX cycle), respectively. Either with GAX or VAR cycle, the proposed system indicates an acceptable standard of functionality in thermodynamic and environmental perspectives.

As one of the key component in the pulse tube cryocooler (PTC), a regenerator needs to reduce losses for performance improvement. Thus, a good regenerator material should have large volumetric specific heat capacity and heat exchange area with small flow resistance. At present, high-mesh stainless steel screen and magnetic materials such as Er3Ni are commonly used as regenerator materials in the low temperature range. However, with the cooling temperature decreasing to lower than about 20K, the volumetric specific heat capacity of stainless steel decreases significantly, increasing the irreversible heat transfer losses of the regenerator. This paper proposes a new regenerator material which coats a magnetic material (Er) with high volumetric heat capacity at low temperature on the surface of stainless steel screen. The two-stage Stirling type pulse tube cryocooler (SPTC) with Er-plated screen filled in the cold end of the second-stage regenerator is investigated. The cooling performance of the SPTC filling with stainless steel screen and Er-plated screen is compared numerically and experimentally. A no-load temperature of 14.95 K can be obtained with an electric power of 303 W when Er-plated screen is used. The relative Carnot efficiency (rCOP) of the cryocooler with Er-plated screen at 20K is 3.32 %, which is higher than with stainless steel screen. Another interesting phenomenon found in the research is that the rCOP of the SPTC with Er-plated screen reverses to be lower than with stainless steel screen when the temperature exceeds 30 K.

In some applications, the cool-down speed obtainable with a cryocooler is important besides the high efficiency at the working temperature. Because of the difference in configurations, the design and the control strategies for various cryocoolers may be different. This work numerically studies the cool-down characteristics of a Stirling-type pulse tube cryocooler (PTC), which uses inertance tube and reservoir as the phase shifter and work at the temperature region of liquid nitrogen. The cryocooler is predicted to provide a nominal cooling power of 18.7 W at 77 K. Three cool-down strategies, namely, cool-down with constant voltage at 66 Hz, cool-down with constant piston displacement by tuning the voltage at 66 Hz, and cool-down with constant piston displacement by tuning voltage and frequency simultaneously during the cool-down process, are investigated. The corresponding calculated cool-down time from the ambient temperature to 77 K of these strategies are 340, 275, and 260 s, respectively. Using the third strategy, the cool-down time can be reduced by 23%.

Background and Objectives: The bidirectional impulse turbine can be used to generate electricity from the energy of sea waves or to convert acoustic energy into electrical energy in thermoacoustic generators. Materials and Methods: In this paper, an experimental study of the characteristics of a bidirectional turbine in a constant gas flow was carried out. The experiments were carried out with a fixed and freely rotating turbine rotor. The outer diameter of the turbine blades is 44 mm. The average gas velocity at the turbine inlet was measured using a Venturi tube and an anemometer. Measurements were made for the dependence of the pressure drop across the nozzles and the turbine rotor on the cross-sectional mean gas velocity at the turbine inlet. Results: It is shown that with an increase in the rotor speed, the pressure drop across the inlet nozzle apparatus decreases, while on the rotor and the outlet nozzle apparatus it increases. The proportion of the parasitic pressure drop at the outlet nozzle apparatus in the pressure drop across the entire turbine increases with an increase in the rotor speed. At a rotor speed of 7000 rpm, the parasitic pressure drop was 15% of the pressure drop across the entire turbine. It was shown that in a constant gas flow, the investigated turbine has a degree of reaction from 0.61 to 0.84.

The Stirling cycle is regarded as one alternative to the compressive cooling cycle. The current study examines the performance of a beta Stirling refrigerator with a cylinder with different bores. Bores differ in terms of the diameters of the compression and expansion cylinder. The refrigerator comprises a twin shell and tube condenser, and evaporator. The evaporator and condenser tubes show an elliptical cross-section. The elliptical ratios in the evaporator and condenser (1, 0.75, 0.50, 0.25, 0.20) with a fixed cross-section area are compared. A wire mesh regenerator uses as the regenerator. The selection of the working fluid is helium. The current work prepares a spreadsheet program to overcome the reversed Stirling refrigeration cycle. The suitable dimensions of the refrigerator to obtain a high cooling load are determined. The results recommended that using tubes with elliptical cross-sections in both evaporator and condenser enhances the COP of the refrigerator by about 33% (COP = 1.3). Also, using tubes having elliptical cross-sections in both evaporator and condenser enhances the cooling load of the refrigerator by about 24% at a 0.2 elliptical ratio. Furthermore, the use of different bores of refrigerator cylinder increases the cooling load of the refrigerator by about 25% when the expansion to compression bore ratio is 1.5. Additionally, the use of different bores of refrigerator cylinder increases the COP of the refrigerator by about 40%, especially at low pressures at expansion to compression bore ratio of 2.0. The proposed refrigerator can achieve a cooling capacity of 450 W at COP = 0.9 under a charged pressure of 5 bar. Comparing the current work and earlier studies shows that the proposed refrigerator achieves a 60% improvement in cooling load at the same pressure.

The Free-Piston Stirling engine (FPSE) is of interest for many research in aerospace due to its advantages of long operating life, higher efficiency, and zero maintenance. In this study, a 1-kW FPSE was proposed by analyzing the requirements of Space Reactor Power Systems (SRPS), of which performance was evaluated by developing a code through the Simple Analysis Method. The results of SAM showed that the critical parameters of FPSE could satisfy the designed requirements. The heater of the FPSE was designed with the copper rectangular fins to enhance heat transfer, and the parametric study of the heater was performed with Computational Fluid Dynamics (CFD) software STAR-CCM+. The Performance Evaluation Criteria (PEC) was used to evaluate the heat transfer enhancement of the fins in the heater. The numerical results of the CFD program showed that pressure drop and Nusselt number ratio had a linear growth with the height of fins, and PEC number decreased as the height of fins increased, and the optimum height of the fin was set as 4 mm according to the minimum heat exchange surface area. This paper can provide theoretical supports for the design and numerical analysis of an FPSE for SRPSs.

This study involves performance examination of an alpha-type novel Stirling engine and performance comparison with a V-type alpha engine. The novel engine displays very different features from the conventional V-type alpha engine. In the conventional engine, the work calculated with nodal analysis (real work) is lesser than isothermal work. In the novel engine, however, the real work becomes larger than the isothermal work if the heat transfer in compression and expansion cylinders is poor. If performances of engines are compared for equal amount of working fluid mass, the real work of the novel engine is always larger than the real work of the conventional V-type alpha engine. If performance comparison is made for equal amount of charging pressure of the working fluid, the difference of works of engines becomes multiple. The thermal efficiency of the novel engine is also greater. At relatively lower speeds and lower charging pressures of the engine, the efficiency difference between novel engine and conventional engine becomes more than 25%. The mean gas pressure in the novel engine is about 40% lesser than that in the conventional engine. All of the properties of the novel engine were found to be advantageous except flow losses.

Background and Objectives: The traveling wave thermoacoustic engine is a variation of the Stirling engine family. With an increase in the number of stages of a traveling wave thermoacoustic engine from one to four, an improvement in the characteristics of the acoustic wave in the regenerator zone is observed, the temperature difference between the heat exchangers required to start the engine decreases, and theefficiency increases. For this reason, it is important to study the patterns of changes in engine characteristics with a further increase in the number of stages. The aim of the work was to study the influence of the number of stages on the characteristics of the acoustic wave in the engine. Materials and Methods: A numerical calculation of eight models of engines with the number of stages from three to ten was carried out in the Delta EC program. The working gas is argon under a pressure of 1.5 MPa, the diameter of the heat exchangers is 160 mm, the diameter of the acoustic resonator is 41.2 mm, the length of the looped engine resonator for all models was 8 meters. The stages in all engines were structurally the same. In the course of the calculations, the number of stages and the number of acoustic loads changed, while maintaining the same total length of the hull-resonator. For each of the eight models studied, the acoustic load was optimized to achieve the maximum engine efficiency. Conclusion: It was shown that with an increase in the number of stages from three to ten, there is a gradual increase in the phase difference between the pressure and velocity oscillations, that is, the wave approaches the parameters of a standing wave in the entire cavity of the resonator. In this case, the maximum acoustic load power and efficiency were observed when the number of stages was equal to five. With an increase in the number of stages from five to ten, the power of each individual stage decreased by 15.8%, and the efficiency decreased by 8%.

The displacer-type pulse tube refrigerator is a kind of Stirling-type pulse tube refrigerator with work recovery. It uses a displacer as a phase shifter and has the advantages of high efficiency an...

Stirling / pulse tube hybrid refrigerator (SPR) has attractive prospects due to its high reliability, high efficiency and compactness around 30 K. As the typical characteristics of the SPR, the inter-stage cooling capacity allocation characteristics allows the refrigerator to shift cooling capacity of both stages by adjusting the movement of the displacer, which enables the SPR to meet the demand of time-varying heat loads at different cooling temperatures and makes it a competitive choice in complicated space applications. In this paper, a SPR designed by our lab is adopted to study the typical characteristics. A one-dimensional thermoacoustics-based numerical model is adopted to optimize the structure parameters and the operating parameters. The cooling capacities, relative Carnot efficiencies at different displacer phases are given. The axial distributions of gas temperature and wall temperature in SPR are drawn. In addition, axial distributions of pressure amplitude, phase difference between volume flow and pressure wave and acoustic power are presented and compared. Experimental results operating at different mean pressures and frequencies are given. Compared the experimental results with the corresponding simulation results, a good consistency is revealed. The experimental results show that the SPR can obtain cooling capacities of 8.8 W at 80 K plus 0.81 W at 30 K with an input electric power of 245 W, which indicates an overall relative Carnot efficiency of 12.85%.

The free-piston Stirling engine (FPSE) has been widely used in aerospace owing to its advantages of high efficiency, high reliability, and self-starting ability. In this paper, a 20-kW FPSE is proposed by analyzing the requirements of space nuclear power reactor. A code was developed based on an improved simple analysis method to evaluate the performance of the proposed FPSE. The code is benchmarked with experimental data, and the maximum relative error of the output power is 17.1%. Numerical results show that the output power is 21 kW, which satisfies the design requirements. The results show that: a) reducing the pressure shell’s thickness can improve the output power significantly; b) the system efficiency increases with the wire porosity, while the growth of system efficiency decreases when the porosity is higher than 80%, and system efficiency exhibits a linear relationship with the temperatures of the cold and hot sides; c) the system efficiency increases with the compression ratio; the compression ratio increases by 16.7% while the system efficiency increases by 42%. This study can provide valuable theoretical support for the design and analysis of FPSEs for space nuclear power reactors.

In this work, the elbow bend heat exchangers were suggested to be used as a heater and a cooler in an alpha type Stirling engine. Elbow bend heat exchanger is a bank of tubes arranged in a quadrant either in line or staggered with different normal and parallel pitches. Eight of the suggested heat exchangers of different dimensions were tested experimentally for steady flow (in a previous research by the same authors). The experimental results were correlated for heat transfer and pressure drop. In the present research, two parallel pistons on a common crankshaft alpha Stirling engine were designed to use elbow bend heat exchangers as a heater and a cooler. The heating fluid flows inside the tubes of the heater, the coolant flows inside the cooler tubes, while the gas circuit fluid (working fluid) flows past the tubes in both of them. A computer program was prepared to analyze the working fluid cycle in the vision of Schmidt theory and it was solved numerically by the program. After that the effect of heat transfer and pressure drop were taken into consideration. Upon calculations, the most suitable values of each of the stroke/bore ratio, the crank phase angle between the hot and cold pistons and the speed range were found out for nitrogen as a working fluid. In a comparison between the proposed engine and practical ones by the literature, it was found that the proposed engine delivers higher power per unit swept volume per unit temperature difference between the heat source and sink in addition to higher values of the efficiency.

Fuel cells are chemical energy converted to electric energy, which is today a new technology in energy production. Among the existing fuel cells, solid fuel oxide cells have a high potential for use in synthetic and combined production systems due to their high temperature (700–1000°C). The solid oxide fuel cell (SOFC) output acts as a high-temperature source, which can be used for heat engines such as the Stirling engine as a high-temperature heat source. A hybrid system including solid oxide fuel cell and Stirling engine and reverse osmosis desalinating is a cogeneration plant. This system includes two parts for power generation; the first part is power generated in the SOFC, and the second part is that with use of heat rejection of solid oxide fuel cell to generate power in the Stirling engine. Also, due to the water critical situation in the world and the need for freshwater, it is very common to use desalination systems. In this study, important goals such as power density and exergy destruction, and exergy efficiency, have been investigated. In general, the performance of the hybrid system has been investigated. Firstly, a thermodynamic analysis for all components of the system and then multi-objective optimization performed for several objective functions include exergy destruction density, exergy efficiency, fuel cell power and freshwater production rate. The present optimization is performed for two overall purposes; the first purpose is to improve fuel cell output power, exergy efficiency and exergy destruction density, and the second purpose is to improve the exergy efficiency, the amount of freshwater production and exergy destruction density. In this optimization, three robust decision-making methods TOPSIS, LINMAP and FUZZY are used. Two scenarios are presented; the first scenario is covering power, exergy efficiency and exergy destruction density. The output power and exergy efficiency, and exergy destruction density, have optimum values in the TOPSIS method’s results. The values are 939.393 (kW), 0.838 and 1139.85 (w/m2) respectively. In the second scenario that includes the freshwater production rate, the exergy destruction density and exergy efficiency, three objective functions are at their peak in the FUZZY results, which are 5.697 (kg/s), 7561.192 (w/m2) and 0.7421 respectively.

The respective performances of hypothetical Stirling engine and Stirling cooler in Vuilleumier machines are usually unclear. In this paper, a method of alternate combination of adiabatic sub-model with considering the losses and isothermal sub-model without considering the losses was proposed. The engine's work output is obtained by combining adiabatic engine and isothermal cooler, while the cooler's work input is obtained by combining adiabatic cooler and isothermal engine. Then, engine's thermal efficiency and cooler's coefficient of performance (COP) were obtained. The relative Carnot efficiency of hypothetical engine was 45%–57% at conditions of 550 °C hot temperature and 50 °C–70 °C warm temperature. The relative Carnot efficiency of hypothetical cooler was 44%–51% at conditions of −20 °C~10 °C cold temperature and 50 °C~70 °C warm temperature. In addition, a comparison of Vuilleumier machines’ COP based on a complete adiabatic model and the hybrid model was made. The ratio of COPV,hybrid over COPV,adia was in the range of 0.9~0.94. It indicated that the respective thermal efficiency and COPcooler in the hybrid model could approach to those in a complete adiabatic model.

We propose a novel cooling and power cogeneration system based on duplex free-piston thermoacoustic-Stirling cycles and an oscillating linear alternator. In such a cogeneration system, a free-piston Stirling heat engine produces acoustic power via the thermoacoustic power cycle, and a free-piston Stirling refrigerator produces cooling power via the thermoacoustic refrigeration cycle; an oscillating linear alternator is used to couple the free-piston heat engine and refrigerator and simultaneously produces electricity. The configuration and operating principles of the cogeneration system are described along with the thermoacoustic energy transformations and transmission mechanisms. An experimental prototype system was designed, built and successfully operated for the first time. In the preliminary experiments, thermoacoustic oscillation startup typically occurred at heating temperatures around 50 to 60 °C, and a cooling power of about 230 W at -20 °C and an electrical power of more than 6 W were obtained at a heating temperature below 190 °C. The alternator-coupled system has potential applications in heat-driven cogeneration systems for low-grade waste heat recovery and solar energy utilization.

A typical scheme of a biomass fueled micro-CHP unit with a Stirling engine, including a combustion chamber, a Stirling Engine, a recuperator and water heater, is considered. A brief overview of the main biomass combustion methods used in this installation is made. Thermophysical analysis was carried out on the basis of solving a system of equations: the reaction equation for wood biomass combustion, the equations of both the general heat balance and the heat balance of parts of CHP unit, as well as the equation of energy conservation at flows mixing in the combustion chamber, taken into account the heat input and losses. The relationship for calculating the theoretical temperature in the combustion chamber and heat flux in the recuperatoris obtained. The last equation is obtained in dimensionless form. The theoretical temperature in the combustion chamber and the heat flux in the recuperator have been calculated, the influence of the main factors has been analyzed - the efficiency of heat exchange in the recuperator, the share of the total air flow passing through the recuperator, the excess air ratio, dimensionless heat losses and heat flux on the hot heat exchanger of the Stirling engine. It is shown that the temperature in the combustion chamber decreases with a decrease in the efficiency of the recuperator and with an increase in the excess air ratio. A significant influence of heat losses in the combustion chamber on the heat flux in therecuperatorwas found. Under certain conditions (high heat losses and high heat exchange on the hot heat exchanger of the Stirling engine), the recuperator is not neededatall. It is also shown that the share of the total air flow passing through the recuperator has a significant effect on the heat flux in the recuperator. Thus, when the air flow passing through the recuperator is reduced by 2 times, the heat flow is reduced by 5 times. Therefore, it is necessary to minimize the air flow bypassing the recuperator. As a result of thermophysical analysis, the optimal value of the excess air ratio was obtained, which is 1.7 ... 1.8.

In this study, the combined thermodynamic and dynamic model of a new concept of gamma type free-piston Stirling engine is conducted. The engine consists of two identical displacer cylinders, a power cylinder, a linear alternator, and three-cushion pistons. Two displacer cylinders are symmetrically positioned on each side of the power cylinder for minimizing the rotational vibrations. Hydrogen is used as the working gas and the effect of gas temperature on the specific heat capacity is considered. The analysis carried out in this study involves the prediction of the thermodynamic-dynamic performance characteristics of the engine. In the thermodynamic section of the analysis, the working space of the engine is divided into 31 nodal volumes and the gas pressures in nodal volumes are assumed to be equal to each other. The conservation of mass and energy equations is obtained for each nodal volume. Instantaneous gas temperatures of nodal volumes are calculated by the first law of thermodynamics given for the unsteady open systems. The dynamic section of the analysis involves the motion equations of displacer, power and cushion pistons. The motion equations are derived using the Newton method. In the calculations done for variable specific heat capacity, it has been determined that there is 1% cyclic work reduction compared to the constant heat capacity. It is estimated that the maximum effective power that can be produced by the linear alternator will be around 1.6 kW. The working frequency range of the proposed engine is found to be suitable to generate electrical power.

Numerical simulations were carried out to study the heat transfer and friction characteristics for Stirling engine heater tubes with three-dimensional internal extended micro-rib. During the numeri...

This paper aims to analyze the thermodynamic performance of a gas turbine–Stirling engine hybrid system with series and parallel configurations. The proposed hybrid systems include two separate cycles. In the first configuration, a gas turbine is combined with two Stirling engines in series formation, and in the second configuration, this combination is implemented in parallel formation. By conducting a parametric study of the introduced hybrid systems, the effects of the compressor pressure ratio, temperature of turbine inlet gases, type of fluid used in the Stirling engine, number of heater tubes, number of meshes and the matrix porosity of regenerator on the hybrid system’s efficiency and power output are investigated. The findings indicate that by raising the compressor pressure ratio and turbine inlet gas temperature, the system’s efficiency and power generation capacity are increased more in the parallel configuration than in the series configuration. Based on the results of comparison, the power generated by the hybrid system in parallel configuration and series configuration is 2.18 times and 1.8 times the power generated by a simple gas turbine cycle, respectively. The obtained results reveal that the electrical efficiency of the hybrid system in parallel configuration and series configuration is 56% and 49%, respectively, while the efficiency of a gas turbine hybrid system with just one Stirling engine is 42% and that of a simple gas turbine cycle is 30%.

For future space transportation and planetary exploration mission power applications, NASA Glenn Research Center (GRC) is currently developing a small-scale nuclear fission system (i.e. Kilopower system), which has an operable range of 1 to 10 kWe and a design life of 8 to 15 years. The thermal management system of Kilopower system involves two types of heat pipes: high temperature alkali metal heat pipes that are used to transport thermal energy from the nuclear reactor to the Stirling convertors hot end and titanium water heat pipes that are used to remove the waste heat from the convertors cold end and transport it to the radiators for ultimate rejection. This paper presents the development of the titanium water heat pipes, which are featured with a special wick structure design: it has bi-porous screened evaporator and screen-groove hybrid wick in the adiabatic and condenser sections. This will allow the heat pipe to (1) operate in space with zero gravity (2) operate on planetary surface with gravity-aided orientation (3) be tested on ground with slight adverse gravity orientation and (4) to startup smoothly after being frozen. Under a research and development program, several freeze/thaw tolerant heat pipes were designed, fabricated and experimentally validated. Later, various heat pipe radiators were developed and tested in a thermal vacuum chamber (TVC). Test results successfully demonstrated that the titanium heat pipes with radiator attached are able to transfer the required power at the working temperature of 400 K under space-like testing conditions with a thermal resistance of 0.019 °C/W while the total heat pipe radiator weight is less than 0.73 kg.

A novel single phase tubular permanent magnet linear generator (TPMLG) for Stirling engines is proposed in this paper. It has an outer-stator, an inner-stator, a mover and a bread type winding which has no cutting. The mover consists of four ring-shaped permanent magnets, all of which are polarized radially. The polarization direction of the outer two permanent magnets is opposite to that of the inner two to form more magnetic circuits and achieve higher power generation density. The polarized directions of the two adjacent permanent magnets of both the outside and inside are opposite. The structure, dimensional parameters and operation characteristics of the generator are illustrated in detail. One of the structural advantages of this generator is that it is easy to control. The 3-D finite element (FE) model of proposed TPMLG is established. The model and its boundary conditions are presented and explained in detail. Through the FE model, its electromagnetic analysis is carried out. The performance of this generator under reciprocating frequency 75 Hz is investigated and analyzed. The simulation results show that the generator has the advantages of high power density.

DC flow may exist in a pulse tube cryocooler if a closed loop is formed by double inlet, etc. It has been found that, given the right amount and the right direction, DC flow may be favorable to the cooling performance of a PTC working at liquid hydrogen temperature and liquid helium temperature with Stirling type or G-M type PTC. In case of Vuilleumier type PTC, which is driven by a thermal compressor, none has been studied. In this paper, the effects of DC flow on a Vuilleumier type PTC working around 10 K have been studied through numerical analysis. In the simulation, the software SAGE is utilized to study the DC flow with a double-inlet module capable of adjusting the DC flow rate. The dependence of performance for thermal compressor on DC flow was firstly investigated. Then the influence of DC flow on the cooling performance was studied, including the cold end enthalpy, cooling capacity, expansion efficiency for pulse tube, etc. Main factors affecting the pulse tube expansion efficiency was distinguished. Finally, the operating parameters effects on cooling performance with varying DC flow rate were carried out. It is found that certain amount of DC flow is beneficial to the system performance with the optimum ratio between DC flow rate and AC flow rate amplitude lying within the approximate range from 0.05% to 0.08%.

Stirling type pulse tube cryocoolers (SPTCs) usually require multi-stage configuration for working below liquid hydrogen temperatures but their cooling efficiency is still poor at present. One of the main reasons is that their high-temperature part regenerators consume large amount of input pV power as isothermal components with large temperature drop. Theoretically, when there is a surplus cold source such as LN2 or LNG for precooling, the high-temperature part regenerator can be replaced by an empty tube with little pV power drop, which will increase the efficiency of the SPTC while recovering cold energy. In this paper, the SPTC with a precooled transmission tube instead of high-temperature part regenerator is proposed and studied. The hot end of the transmission tube was linked to the room-temperature compressor at ~300 K, while its cold end was connecting to the low-temperature part regenerator precooled to ~ 80 K by LN2. The heat transfer and pV power losses in the precooled transmission tubes under different sizes were calculated and analyzed. Experiments were carried out to verify the feasibility of the precooled transmission tube in a SPTC. Results show that the SPTC can work well with the precooled transmission tube. A no-load refrigeration temperature of 17.7 K and cooling capacity of 1.74 W at 25 K are obtained with a total input pV power of about 52.9 W. The hot end heat exchanger of the precooled transmission tube is found to be necessary for quickly stabilizing the cold end cooling temperature.

The performance of an actual free piston free displacer (FPFD) Stirling miniature cryocooler has been simulated based on the parameters affecting the performance of the cryocooler. The processes of compression and expansion in the cryocooler have been assumed to be polytropic with variable ratio of specific heats for the working fluid, i.e., helium. The effect of design parameters like piston spring stiffness, displacer spring stiffness, mass of the piston, displacer mass and frequency of operation on the cooling power of the cryocooler has been calculated. The parameters thus obtained with polytropic processes have been compared with the parameters obtained by assuming the compression and expansion processes to be isothermal. The amplitude of the piston and the displacer is not constant in the case of free piston free displacer cryocooler with linear motors. Linear motor drives have been used for eliminating the side forces on the cylinder walls and wear and tear of the reciprocating parts of the cryocoolers giving them a very long life. A computer program named CRYOJIN which was developed for the isothermal case has been modified for analyzing the real-time performance of the cryocooler for polytropic processes. The physical dimensions of Philips 1 W FPFD cryocooler have been taken for study and comparison.

International audience; LiteBIRD is a JAXA-led L-Class mission aimed at the study of B-mode polarization of the cosmic microwave background. Measurements on 15 bandwidth from 34 to 448 GHz are made on two instruments, low-frequency telescope and medium- and high-frequency telescope. To reach the desired sensitivities, more than 4500 transition edge sensors detectors, used on both instruments, will be continuously cooled to 100 mK. The cryogenic design based on shield cooling and mechanical coolers is presented in this paper. Shield cooling will be done with passive cooling and 15 K pulse tube coolers. A single cryogenic chain will cool both instruments. A 4 K stage is cooled by a $^{4}$He Joule–Thomson cooler from Japanese Aerospace Exploration Agency, pre-cooled by Stirling coolers. Multistage adiabatic demagnetization refrigerator will be optimized to provide continuous cooling at 1.75 K, 300 mK and 100 mK with 2.2 µW of cooling power on the latter stage. Seven ADR stages provided by NASA (USA) and CEA (France) are required. Details on the thermal design, preliminary sizing and expected performance are presented.

Regenerative cryocoolers with large cooling capacity at 30 K have a promising prospect in the fields of superconducting technology and gas liquefaction. Compared with other types of cryocoolers, Stirling cryocoolers have the advantages of high cooling capacity, high efficiency, fast cool-down process and compact configuration. A two-stage Stirling cryocooler with large cooling capacity driven by the crank-rod mechanism is developed based on the Sage simulation results, and the preliminary experimental results are presented. Firstly, the pressure characteristics under different working conditions are investigated. The amplitude of the pressure and the pressure ratio at the compression chamber increases as the charging pressure increases. Increasing the refrigeration temperature of the second stage results in the decrease of the pressure amplitude, and the decreasing rate increases as the heat load on the first stage increases. Then, the performance of the ambient heat exchanger is studied. As the charging pressure increases from 2.2 to 2.6 MPa, the heat rejected from the ambient heat exchanger increases from 7.57 to 9.19 kW when there are no heat loads at the two stages of the cryocooler. The heat rejected from the ambient heat exchanger increases by 400 W with every increase of 0.1 MPa of charging pressure. With the increase of the refrigeration temperature of the second stage, the heat rejected from the ambient heat exchanger decreases, and the decreasing rate increases as the heat load on the first stage increases. Furthermore, the influence of the variation of the charging pressure and heat loads at the two stages on the cooling performance is introduced. The temperature of the second-stage cold end heat exchanger drops to 30 K at a nearly constant cooling rate after the startup of the cryocooler. As the charging pressure increases from 2.2 to 2.6 MPa, the cooling rate increases from 16.59 to 19.46 K/min, and the cooling rate increases by about 0.72 K/min for every increase in pressure of 0.1 MPa. Under the charging pressure of 2.6 MPa, the second stage of the cryocooler reaches a no-load refrigeration temperature of 19.83 K, while the temperature of the first stage is 71.2 K. The no-load refrigeration temperature has a weak relationship with the charging pressure. As the charging pressure increases, the increasing rate of cooling capacity and COP with the refrigeration temperature increases. The cryocooler is capable of providing 110 W cooling power at 30 K with a relative Carnot efficiency of 10.96%. This is the best result ever reported in China. What is more, it is found that the cooling power at the two stages has little influence on the cooling performance of each other, which means the cooling power from the first stage can be applied in the pre-cooling process with little influence on the second stage. These results lay a solid foundation for future applications and performance improvement of the cryocooler.

Vuilleumier machines are a promising technology for heating. Respective performances of Vuilleumier’s engine and cooler are generally unclear. In Stirling machines, performances can be determined based on PV power flow and heat flow methods. In this work, respective performances based on two methods in current Vuilleumier models were investigated. It was found that PV power flow and heat flow methods in current Vuilleumier models were ineffective for analysis of respective performances due to there being no piston as a boundary between Vuilleumier’s engine and cooler. Then, a virtual piston was assumed, and a virtual piston based Vuilleumier model (VPBVM) was developed. The relative Carnot efficiencies of the obtained engine and cooler were 53~64% and 43~49%, respectively, at conditions of 550 °C hot temperature, 50~70 °C warm temperature, and −20~10 °C cold temperature. The results indicated that respective performances obtained in VPBVM were reasonable. Moreover, the engine’s compression ratios could be obtained in VPBVM and were 1.2~1.24. Thus, VPBVM could be effective for the analysis of the Vuilleumier machine’s engine and cooler.

By developing our proper CFD code under Fortran, the performances of a Stirling engine are studied in unsteady laminar regime and closely linked to the properties of its regenerator. However, it is responsible about the maximum part of losses in the Stirling engine. These losses depend on geometric and physical properties of the material constituting the regenerator. Thus, finding the suitable regenerator material that generates the greatest heat exchange and the lowest pressure drop is a good solution to reduce sources of irreversibility and ameliorate the global performances of the Stirling engine. The aim of this paper is to describe oxillatory flow and heat transfer inside porous regenerator materials and to determine the most suitable regenerator material. Brinkman-Forchheimer-Lapwood extended Darcy model is assumed to simulate momentum transfer within the porous regenerator. And the oscillatory flow is described by the Navier-Stockes compressible equations. The local thermal equilibrium of the gas and the matrix is taken into account for the modelling of the porous regenerator. The governing equations with the appropriate boundary conditions are solved by the control volume based finite element method (CVFEM). A numerical code on the software Fortran is elaborated to evaluate flow and heat transfer characteristics inside regenerator. Results showed that the fluid flow and heat transfer between the compression and expansion phases were varied significantly. It was shown that the superior comprehensive performance of the regenerator makes it possible to improve the performance of Stirling engines.

This study examined the influence of an in-line phase-adjuster on the energy conversion efficiency of a thermoacoustic Stirling heat engine (TASHE). The numerical and experimental investigations were performed. An acoustic field in the system can be adjusted using the phase-adjuster. Therefore, the thermoacoustic engine could maintain high-level performance at all operating conditions. The engine is composed of a torus section where core components were located, and a long resonator pipe. The phase-adjuster or the telescopic in-line piston was set up at the tail of the resonance tube. The TASHE was modeled by employing DeltaEC to search the optimal configurations of the prototype. Due to the variations of acoustic loads or operating conditions from the design criteria, the engine absolutely cannot maintain maximum efficiency. The proposed phase-adjuster could bring back its maximum efficiency by re-matching the acoustic impedance in the regenerator. The TASHE was designed to operate with compressed air at 9 bar. In the experiments, the self-excited temperature of the engine was around 480 °C, and the steady-state temperature was about 397 °C. The TASHE can provide an acoustic power of up to 40 W. The thermo-to-acoustic efficiency of 12.03% related to 22.56% of the theoretical Carnot efficiency was achieved. There was a reasonably good agreement between the measured and DeltaEC simulation results. This can reflect on the preciseness of the proposed model. Furthermore, the function of the phase-adjuster in tuning the acoustic impedance was also demonstrated experimentally. In case of the TASHE being operated under the off-design conditions, i.e., due to pressure leak or heat losses, these scenarios would drop the efficiency of the system. The research presented in this study can confirm that the phase-adjuster is the component applied to tune the acoustic field in the regenerator accurately with minimum changes in the system. It could help to improve the efficiency of such consequences.

This research studies the double-acting four-cylinder α-type Stirling engine. A numerical model is developed by combining the thermodynamic model and dynamic model to study the engine performance. The pressure values of the working zone calculated using the thermodynamic model are taken into the dynamic model to calculate the forces acting on the mechanism. Then, the dynamic model further calculates the displacement, velocity, and acceleration of the mechanism link to provide the pistons’ displacements for the thermodynamic model. The model is also validated using experimental data obtained from testing an engine prototype. Under a heating temperature of 1000 K, cooling temperature of 315 K, charged pressure of 10 bar, and loading torque of 0.33 Nm, the engine is capable of achieving a shaft power of 26.0 W at 754 rpm. In addition, the thermal properties and the transient behavior of the engine can be further simulated using the validated numerical model.

In general, the circular lamination is used in tradition linear machine, several voids are produced in outside stators which decrease the core utilization and flux density in air gap. To address this problem, a double-stator tubular linear oscillator based on hybrid laminated structure (HL-DSTLO) is proposed. The HL-DSTLO is constituted of two stators and a permanent magnets mover. The teeth and yoke of the outer stator lamination in a separated formation, and the teeth is separated in direction of axial and circular to laminate, meanwhile, circular split lamination method is applied in the inner stator. The paper forces on the main electromagnetic features of the HL-DSTLO. The operation principle based on the flux path analysis is presented, and the influence of structural parameters on the electromagnetic properties are discussed by using finite-element method. Finally, the experimental result was analysed to confirm the prediction of the FEA.

Energy demand increment besides the reduction of fossil fuel resources from one side, and climate issues concerning the conventional power production methods from another side lead humanity to more efficient and cleaner power production methods. One of these methods is polygeneration microgrids based on a renewable energy source. In the present study, a combined cycle of a Free Piston Stirling Engine with a Permanent Magnet Linear Synchronous Machine was proposed as a new heat recovery option for the high-quality thermal energy of an Internal Reforming Solid Oxide Fuel Cell as electricity. Then, a Double Effect Absorption Chiller and a heat exchanger were used to recover the rest of the heat as cooling and hot water, respectively. After modeling and validating all the systems, they were combined. The results of the combined system showed 31.7% (or 40% by including cooling production of Double Effect Absorption Chiller instead of its heat consumption for efficiency calculation) of total efficiency improvement compared to the standalone Internal Reforming Solid Oxide Fuel Cell. Furthermore, the electrical efficiency of the system was improved by 14.1%.

A new integrated combined cooling, heating and power system which includes a solid oxide fuel cell, Stirling engine, steam turbine, linear Fresnel solar field and double effect absorption chiller is introduced and investigated from energy, exergy and thermodynamic viewpoints. In this process, produced electrical power by the fuel cell and steam turbines is 6971.8 kW. Stirling engine uses fuel cell waste heat and produces 656 kW power. In addition, absorption chiller is driven by waste heat of the Stirling engine and generates 2118.8 kW of cooling load. Linear Fresnel solar field produces 961.7 kW of thermal power as a heat exchanger. The results indicate that, electrical, energy and exergy efficiencies and total exergy destruction of the proposed system are 49.7%, 67.5%, 55.6% and 12560 kW, respectively. Finally, sensitivity analysis to investigate effect of the different parameters such as flow rate of inputs, outlet pressure of the components and temperature changes of the solar system on the hybrid system performance is also done.

The paper presents a Computational Fluid Dynamics (CFD) model of the cold alpha-type Stirling engine. The developed mathematical model comprises of Unsteady Reynolds Averaged Navier-Stokes (URANS) set of equations, i.e. continuity, momentum and energy equations. Moreover, the developed mathematical model comprises a non-equilibrium description of the regenerator, by the introduction of the energy conservation equation for the regenerator matrix. It was implemented in the framework of commercial CFD software ANSYS Fluent. The work presents an in-depth analysis of the influence of the numerical mesh and applied turbulence model on the obtained results. The model was used to analyse the influence of the regenerator on the performance of the cold Stirling engine at different operating conditions. It appeared that on an average application of the regenerator increased the engine specific work by 10 J/kg and this increase is significantly higher at a high rotational speed of the engine. At the same time, the engine efficiency averagely was increased by 10 percent points and again this increase was significantly higher at higher rotational speeds of the engine. Especially, the influence of the heat source and sink temperatures on the engine operation were analysed. It appears that the lower are temperatures of a heat source and sink the more pronounced is the presence of the regenerator in the engine. Finally, the influence of the elementary parameters: particle diameter and porosity of the solid matrix which constitute the regenerator filling was investigated. It was shown that for the analysed engine the optimal value of the regenerator packing porosity equals about 0.72 it results in the specific area of the regenerator equal around 1675 m2/m3. Obtained results can be used to analyse the possibility of application of Stirling engines to recover low-temperature exergy of regasified Liquified Natural Gas (LNG), which for small regasification units can be alternative for commonly utilised Ambient Air Vaporizers (AAV) and it aside for regasification of LNG it could produce electric energy.

The regenerator used in Stirling cryocoolers is the crucial component, which has a flow conduit through the porous matrix material. Various parameters affect the performance of the regenerator, of ...

In this study, a numerical and experimental investigation was carried out to research the effect of three types of working fluids (i.e., helium, nitrogen and argon) on the performance of a thermoacoustic Stirling engine. To predict and analyze thermoacoustic conversion capacity of the engine, a wide range of critical parameters (e.g. onset temperature, working frequency and pressure oscillations) were selected as analysis parameters. According to the results, a relatively optimum value of mean pressure (0.7–1.0 MPa) appears when the thermoacoustic engine is filled with helium. Compared to other working fluids (i.e, nitrogen and argon), the engine could work (onset temperature below 500 °C) in a relatively high mean pressure range (0.4–2.6 MPa) when using helium. Furthermore, working frequency of helium was found to be nearly three times that of the other two gases regardless of operating conditions. Moreover, when using nitrogen and argon as working gases, the pressure amplitude of thermoacoustic engine was significant under the condition of the same mean pressure. The findings in this study are helpful to improve the practicability of thermoacoustic engine.