Philippe Nika

Comparison of two models of a double inlet miniature pulse tube refrigerator: Part A thermodynamics

The cooling of electronic components is of great interest to improve their capabilities, especially for CMOS components or infrared sensors. The purpose of this paper is to present the design and the optimization of a miniature double inlet pulse tube refrigerator (DIPTR) dedicated to such applications. Special precautions have to be considered in modeling the global functioning of small scale DIPTR systems and also in estimating the net cooling power. In fact, thermal gradients are greater than those observed in normal scale systems, and moreover, because of the small dimensions of ducts (diameter), the pulse tube cannot be assumed to be adiabatic. Hence thermal heat conduction phenomena must be considered. Besides dead volumes introduced by junctions and capillaries cannot be neglected any more in front of the volume of the gas tube itself. The hydrodynamic and thermal behaviors of the cooler are predicted by means of two different approaches: a classical thermodynamic model and a model based on an electrical analogy. The results of these analysis are tested and criticized by comparing them with experimental data obtained on a small commercial pulse tube refrigerator.

Comparison of two models of a double inlet miniature pulse tube refrigerator: Part B electrical analogy

The design of a double inlet pulse tube refrigerator is investigated by means of an analogy with an electric circuit. The results obtained are compared with both those of the thermodynamic model (Part A) and experiments. The basic formulation of equivalent electronic components is discussed and a few improvements are proposed for adjusting the theoretical expressions of the electric impedance concerning the capillaries and the regenerator. Then additional effects such as pressure drops due to geometrical singularities are taken into account considering the different internal flow regimes that may occur. Besides a simplified formulation for the regenerator efficiency is deduced from considerations on its harmonic functioning. In this analysis, the emphasis concerns principally the design of miniature cryocoolers dedicated to electronic applications. Those models are applied to a commercial miniature refrigerator. A discussion of their relevance is achieved and a few suggestions on the refrigerator design are proposed in order to improve the cooling production.

An integrated pulse tube refrigeration device with micro exchangers: design and experiments

The cooling of electronic components is of great interest to improve their capabilities, especially for CMOS components. The purpose of this paper is to present the principle and the design of a micro cooler dedicated to such application. The originality of the approach concerns both the use of a thermodynamic system and the use of a micro-fabrication technology entirely compatible with the small scale of the component. The cooling function is assumed by a pulsed gas in a small canal (pulse tube) made of glass and of silicon. Specific micro heat exchangers, also made of silicon, have been designed from the results of a study concerning both the pressure drop and the transitory thermal response. The actual micro-cooler performances are estimated in an experimental way by means of temperature and pressure measurements.

MINIATURE PULSE TUBE FOR THE COOLING OF ELECTRONIC DEVICES: FUNCTIONING PRINCIPLES AND PRACTICAL MODELING

The miniaturization of refrigerating systems represents a very current scientific and technical challenge to improve the performances of numerous electronic components. This work presents a global approach to the problem and suggests studying the cooling by means of small channels filled with an oscillating gas: the double inlet pulse tube refrigerator (DIPTR). A great level of miniaturization based on the technology of carving silicon is exposed. This study proposes to apply an electric analogy for modeling both hydrodynamic and thermal phenomena. Considering the complexity of the theoretical problem including mechanical, thermal, thermodynamical, and acoustic considerations, the authors take care to summarize the main governing equations in a particular form so any scientific engineer could understand the DIPTR principle.

Effets thermoacoustiques dans un régénérateur cylindrique contenant un empilement de billes

Resume La theorie de la thermoacoustique lineaire est appliquee a letude dun regenerateur de machine Stirling ou de Tube a Gaz Pulse constitue par un empilement de billes contenues dans une enveloppe cylindrique. Les expressions des differentes amplitudes, pression, vitesse, temperature sont calculees, et en consequence des resultats, la constante de temps complexe ainsi que le schema thermoacoustique equivalent du regenerateur sont introduits. Lexpression du flux total axial denergie est ensuite demontree et les roles de la constante de temps et des diverses impedances sont commentes. Les variations axiales de ce flux denergie, qui correspondent aux echanges denergie avec lexterieur sont exprimees en fonction des differents phenomenes thermoacoustiques : relaxation thermique de lenergie acoustique, effet de la viscosite, sources/puits thermoacoustiques. Les resultats theoriques sont employes pour discuter le profil des temperatures le long du regenerateur en regime pulse.