Stirling Refrigerating Machine Modeling Using Schmidt and Finite Physical Dimensions Thermodynamic Models: A Comparison with Experiments

The purpose of the study is to show that two simple models that take into account only the irreversibility due to temperature difference in the heat exchangers and imperfect regeneration are able to indicate refrigerating machine behavior. In the present paper, the finite physical dimensions thermodynamics (FPDT) method and 0-D modeling using the Schmidt model with imperfect regeneration were applied in the study of a β type Stirling refrigeration machine.The 0-D modeling is improved by including the irreversibility caused by imperfect regeneration and the finite temperature difference between the gas and the heat exchangers wall. A flowchart of the Stirling refrigerator exergy balance is presented to show the internal and external irreversibilities. It is found that the irreversibility at the regenerator level is more important than that at the heat exchangers level. The energies exchanged by the working gas are expressed according to the practical parameters, necessary for the engineer during the entire project. The results of the two thermodynamic models are presented in comparison with the experimental results, which leads to validation of the proposed FPDT model for the functional and constructive parameters of the studied refrigerating machine.

Numerical Investigation on Heat Transfer Characteristics in Electronic Cavity of Downhole Measurement-While-Drilling System

In recent years, the number of deep wells and ultra-deep wells is increasing gradually, and the bottom hole temperature of many wells reaches more than 200 °C, which puts forward higher requirement for the downhole measurement-while-drilling system. In this paper, a new active cooling method is proposed to protect electronic components in the electronic cavity from high temperature. The circuit board is cooled by direct contact with the cold end of a custom split-Stirling refrigerator. According to the different heat loads, the electronic components can operate in the proper temperature range by adjusting the piston motion frequency and inflation pressure. At the same time, the electronic cavity is filled with thermal insulation material to induce heat leakage from the environment. The thermal resistance of solid insulation material, argon, and vacuum is studied, and the required effective cooling power is determined. When the thermal insulation material is vacuum, which is the best resistance medium when compared with solid insulation material and argon according to the research results, the effects of the structure size of circuit board and electronic cavity, material property and operational environment on the required effective cooling power and maximum temperature on the room temperature chamber wall of the split-Stirling refrigerator are discussed.

Computational Analysis of Cryogenic Stirling Refrigerator

In the present work, a system consisting of two combined cryocoolers is simulated with the use of Computational Fluid Dynamics (CFD) and ANSYS Fluent software. The cryocoolers operate with frequency of 1 Hz and at temperature below 1 K. Instead of a matrix containing a regenerator, each of the machines employs a recuperator. The two recuperators exchange heat with each other, combining thus the two machines into one system. The working gas of the cryocoolers is helium-3 (He-3), the properties of which are obtained by the available literature for cryogenic temperatures. The setup of the presented simulation is based on a one-dimensional (1D) analytical model. The model is used to describe conducted experiments, in which ideal He-3 is the working gas of a similar system of Stirling cryocoolers and superfluid helium-4 (He-4) can pass through the pistons (super leak). The simulations results, including the fluctuation of gas temperature in the machine’s spaces, pressure drop, work and heat exchanged are presented.

Thermodynamic Modelling of Superfluid Stirling Cryocoolers

The aim of this paper is to describe and thermodynamically model cryogenic Stirling refrigerators, using Helium in its different forms as the working medium. Helium has unique properties at cryogenic temperatures forming a superfluid. The cryogenic Stirling refrigerators with Helium at such low temperatures make use of the properties of this superfluid nature of Helium, thus they are referred to as Superfluid Stirling Refrigerators (SSR). To make use of these remarkable properties of superfluid helium a different version of Stirling refrigerator is used where superleaks are introduced in the pistons in order to let the superfluid part flow freely but constrain the normal fluid. This cooling procedure has an upper temperature limit as it is based on the superfluidity of helium, hence all the workings of this cycle must be well below the Lambda line. In addition, different models are needed and are used for the different isotopes of helium as their atomic spin nature is different and therefore their behavior at temperatures near absolute zero. In this study of SSR cryocoolers great care is being given towards the thermodynamic behavior of the entire system and working media, as well as different designs of the apparatus.