Numerical and Experimental Studies of a Two-Stage Pulse Tube Cryocooler Working Around 20K

The absence of cold moving parts in pulse tube cryocoolers has allowed it to has advantages of low vibration, high reliability, and low cost, which can meet requirements of many high-temperature superconducting applications. However, Stirling type pulse tube cryocoolers working around 20 K are still not commerally aviable due to low efficiency and low power density. With Comprehensive consideration of higher specific power of whole system and performance in relative lower working temperature of 20K, this paper proposes a thermally coupled two stage co-axial pulse tube cryocooler to pursue several watts cooling power around 20K.At the first stage, an ultrahigh frequency operation of 100 Hz is utilized to precoo the second stage for seeking a higher power density. At the second stage, a relative lower frequency of around 30Hz is used for improving system efficiency. Firstly, a quasi-one-dimensional numeric model based on the thermoacoustic theory is used to optimize the operating and structure parameters and some simulation results are briefly introduced. The influences of different phase shifters such as doule-inlet and room temperature displacers are also also investigated numerically. Then, in the experiments, typically a lowest no-load temperature of 13 K has been obtained and the cooling power at 20K was 2 W with an input electric power of 500 W, which mean an efficiency of 5.6% of Carnot. The influences of different operating and structure parameters such as frequency, mean pressure and precooling temperature were also investigated numerically and experimentally

Experimental Investigation on a Linear-compressor Driven Travelling-wave Thermoacoustic Heat Pump

AbstractHeat pump system, offering economical alternatives in recovering waste heat from different sources for using in various industrial, commercial and residential applications, is considered to be a very environmentally-friendly heat and power transfer system. In this paper, to solve the problems of traditional vapour compression heat pump working in unconventional conditions, a novel TWTAHP (travelling-wave thermoacoustic heat pump) is presented to meet the requirement of working in ultra-low temperature. Base on the theoretical simulation and structure optimization, an experimental apparatus for preliminary test has been built, which is only one single independent unit from the whole loop of the TWTAHP system. The results show that the simulation and the testing results were agreeable as expected. Under the -20°C environment temperature and the 50°C heating temperature, we could obtain a maximal COPh (heating COP) of 2.1 and 260W heating capacity for one unit by consuming acoustic power less than 200W. Furthermore, a COPh above 3.0 could be achieved when the ambient temperature was raised to 0°C

Post-positioned gas spring enables ultra-high output power of hybrid thermoacoustic electric generators

High-capacity hybrid thermoacoustic electric generators (HTAEGs) are ideal in different small- and micro-scale energy systems, especially in space nuclear power systems. In this work, an HTAEG with a post-positioned gas spring is proposed. To demonstrate the superiority of the gas-spring-post-positioned design on high-capacity HTAEGs, an HTAEG prototype is modeled, built, and tested from the perspective of thermoacoustics accordingly. Experimental results demonstrate an output electric power of 15.0 kW. Furthermore, it could achieve the highest efficiency of 39.2% with an output electric power of 11.1 kW. Given that a 15-kW power output is an ultra-high level on a single-piston HTAEG of this type to date, and the achieved efficiency on the prototype is also encouraging, this work marks an important milestone in the development of high-capacity HTAEGs. It also demonstrates that the gas-spring-post-positioned design has significant advantages and enormous potential for application

Thermoacoustic heat pump utilizing medium/low-grade heat sources for domestic building heating

Thermoacoustic heat pumps are a promising heating technology that utilizes medium/low-grade heat to reduce reliance on electricity. This study proposes a single direct-coupled configuration for a thermoacoustic heat pump, aimed at minimizing system complexity and making it suitable for domestic applications. Numerical investigations were conducted under typical household heating conditions, including performance analysis, exergy loss evaluation, and axial distribution of key parameters. Results show that the proposed thermoacoustic heat pump achieves a heating capacity of 5.7 kW and a coefficient of performance of 1.4, with a heating temperature of 300 °C and a heat-sink temperature of 55 °C. A comparison with existing absorption heat pumps reveals favorable adaptability for large temperature lift applications. A case study conducted in Finland over an annual cycle analyzes the economic and environmental performance of the system, identifying two distinct modes based on the driving heat source: medium temperature (≥250 °C) and low temperature (<250 °C), both of which exhibit favorable heating performance. When the thermoacoustic heat pump is driven by waste heat, energy savings of 20.1 MWh/year, emission reductions of 4143 kgCO$_2$/year, and total environmental cost savings of 1629 €/year are obtained. These results demonstrate the potential of the proposed thermoacoustic heat pump as a cost-effective and environmentally friendly option for domestic building heating using medium/low-grade heat sources

Operating characteristics study of a dual-opposed free-piston Stirling generator

Dual-opposed Free-piston Stirling generators (dual-opposed FPSGs) offer advantages of reduced vibration and increased power density, making them promising candidates for space and distributed energy applications. So far, operational characteristics of the dual-opposed FPSG have yet to be completely understood. This study focuses on a 3 kW dual-opposed FPSG prototype designed to integrate heat pipes. Through computational fluid dynamics and thermoacoustic analysis, a novel hot end heat exchanger with evenly-distributed heat pipe bore was discovered to deliver 12 kW heating power with a gas–solid temperature difference of 21 K. Subsequently effort combined thermoacoustically-based calculations with experiments to investigate the impact of two electrical connection methods of linear alternators on FPSG performance. Experimental results validated the numerical model, showing heat-to-electricity efficiency deviations within 5 % under different electrical connection modes. The FPSG consistently achieved its rated power in both series and parallel connection modes, exhibiting a thermal-to-electric efficiency of 25.2 %. Notably, the series connection mode demonstrates superior sensitivity and consistency compared to parallel connection. Further experiments revealed that charge pressure, load resistance and external capacitance all exerts limited impact on the consistency, while external capacitance significantly influenced acoustic impedance. This resulted in an enhancement in both hot-end wall temperature and heat-to-electricity efficiency, while minimizing power piston displacement and damping temperature when resonating with the inductance

Numerical and Experimental Study of the Hydrostatic Pressure Correction in Gas Thermometry: A Case in the SPRIGT

Single-pressure refractive index gas thermometry (SPRIGT) is a new type of primary thermometry, which needs an extremely stable working pressure (stability &lt; 4 ppm). In practice, the pressure control system at room temperature is located above the cold resonator at 5 K to 25 K, and a long pressure tube is used to connect them, which entails a hydrostatic pressure correction (HPC). To this end, a three-dimensional (3D) Computational Fluid Dynamics (CFD) simulation model of the pressure tube has been developed and compared with experimental results. First, to verify the simulation results, the helium-4 gas pressure in the center of the resonator was measured using a determination of the refractive index by microwave resonance coupled with the knowledge of the temperature. Results of simulation and experiment showed good agreement. Thereafter, based on this CFD simulation, the non-linear temperature distribution in the vertical pressure tube and the uncertainty caused by this non-linear phenomenon were calculated. After this, the validity of the isothermal assumption to simplify the calculation of the HPC was verified. Finally, the effect of heating on the pressure was studied and its impact found to be negligible. To the best of our knowledge, this is the first time experimental and simulation results have been compared for the HPC. The results are expected to be more generally applicable to the accurate determination of pressure in cryostats

Development of a High Efficiency Pulse Tube Cryocooler Using Room Temperature Displacers for HTS Applications

The compact and high efficiency coolers working in the liquid nitrogen temperature region play an important role in HTS Applications. Stirling type pulse tube cooler servers as a promising candidate for cooling HTS devices for its advantages such as low vibration, high reliability and low cost due to absence of the moving parts in the cold head compared with traditional coolers. However, phase shift mechanisms used in a conventional pulse tube cryocooler need to dissipate expansion power at the ambient end of the pulse tube, which leads to a lower thermodynamic efficiency than that of a Stirling cryocooler. In order to improve the efficiency and obtain a reliable cryocooler system, this article presents a pulse tube cryocooler which uses room temperature displacers as the phase shifter, which aims at providing more than 10 W cooling power at 77 K. The cryocooler with a model number of TC4189 consists of linear compressor, coaxial pulse tube and two dual-opposed ambient displacers. High pressure ratio and high frequency operation are used to increase the power density. The whole system has a total mass of 4.3 kg. At an optimum working point, a lowest no-load temperature of 44 K has been obtained and the cooling power at 80K reaches 15 W with an input electric power of 240 W, which means an efficiency of 17.1% of Carnot. The influence of displacers operating and structural parameters were investigated through simulations and experiments