MicroCooler

The Microcooler project is a collaborative effort between the Low-temperature division and the Micromechanical Transducers group at the University of Twente. This research is directed towards the development of miniaturized cooler employing MEMS technologies. The dimensions of the cold stage will be of the order of few millimeters with a net cooling power of 1 milliwatt. Fig 1. is the schematic of such a cooler.

Fig 1. Schematic picture of an electronic chip that is directly mounted to the cold top of a cryocooler.(Phd Thesis- Johannes Burger)

Two types of thermodynamic cooling cycles are investigated:

1.

Recuperative cycle.

2.

Regenerative cycle.

At the Micromechanics group we investigate the second type.

Introduction to Regenerative Cooling Cycles

There are four major classes of regenerative cycles: Stirling, Gifford-McMahon (GM), Vuillemier (VM) and Pulse-tube (PT). In all these cycles, cooling is obtained by allowing the gas to expand and thereby taking heat from the surroundings. The regenerator located in between the hot and the cold sides of the system acts as a thermal mass to temporarily store the heat. Fig 2 is the schematic of the regenerator. Gas flows in and out periodically from its both ends.

Fig 2. Schematic of the Regenerator.

Fig 3. Schematic of a typical regenerative cycle.

Fig 3 is the schematic of a general regenerative type cooler, the working principle can be summarized as follows: The gas is isothermally compressed rejecting heat to the surroundings. Subsequently it moves through the regenerator where the gas is cooled to the low temperature by delivering heat to the heat capacity of the regenerator. The gas is made to isothermally expand in the expander space thereby taking heat from the surroundings. In the final step the gas moves back to the compression space through the regenerator, taking heat in the process (which was earlier exchanged with the regenerator).

Assignments

Conglomeration of Micromechanics, Fluid Mechanics, Heat transfer and Thermodynamics is truly a scientific project with lot of things to investigate. We can propose a project that will suit your interest. Listed below are some assignments for guidelines. If you are interested or have any queries feel free to write to me or drop in my room.

Topics

1.

Micro-compressor

Micro-compressor required for the regenerative cycle is an oscillating pressure wave generator. The compressor should be able to produce pressure ratio of ~ 1.2 at an absolute pressure ranging between 10-20 bar. There are a number of dynamic requirements for the compressor, like the resonance frequency of the system and overall integration with the cooler. More information will be provided on request.

2.

Design, fabrication and characterization of Displacer and Regenerator.

In a regenerative cycle there are two oscillating components, out of phase by 90 degrees. One of them is the compressor. The second component is a displacing regenerator. Short description about regenerator is given above. The idea is to have an oscillating regenerator. Challenges exist in thermally isolating the matrix and providing an oscillating structure. More information will be provided on request.

3.

Designing the Cryogenic Microcooler Experimental Setup

Packaging of microsystems is an important subject in MEMS. The systems we are considering are at high pressure and should have vacuum tight environment. In this task we will investigate various packaging means, design and build the experimental setup and finally characterize the devices. A lot of work has already been done in building the experimental setup and hence it will serve as a good learning tool and quick start for your thesis. More information will be provided on request.

Contact

Srinivas Vanapalli (Srini) s.vanapalli @ utwente.nl T505 2787

Other Members in the project

Pieter Lerou Theo Veenstra Gunter Venhorst

Harry Holland Johannes Burger

Henri Jansen Marcel Ter Brake