Miniature-scale diaphragm compressor for electronics cooling

Vapor compression refrigeration is one of the more promising alternatives to conventional electronics cooling techniques, especially at high ambient temperature. For the use of refrigeration in electronics cooling, a miniature-scale, low cost, and reliable refrigerant compressor is needed. An electrostatically actuated diaphragm compressor is a promising concept for this application. The compressor consists of a flexible circular diaphragm clamped at its circumference inside a conformal chamber. The membrane and the chamber surfaces are coated with metallic electrodes. A potential difference applied between the diaphragm and the chamber pulls the diaphragm towards the chamber surface progressively from the outer circumference towards the center. This zipping actuation reduces the volume available to the refrigerant gas, thereby increasing its pressure. A segmentation technique is proposed for analysis of the compressor by which the domain is divided into multiple segments for each of which the forces acting on the diaphragm are estimated. The pull-down voltage to completely zip each individual segment is thus obtained. The required voltage for obtaining a specific pressure rise in the chamber can thus be determined. Predictions from the model compare well with other simulation results from the literature, as well as to experimental measurements of the diaphragm displacement and chamber pressure rise in a custom-built setup. A dynamic compressor model is also developed in which the dynamic forces induced due to the finite-time deflection of the diaphragm are taken into consideration using the segmentation approach developed in the quasi-static model. Results from the analytical model compare favorably with those from a detailed numerical simulation as well as with experimental measurements available in the literature. A finite element quasi-static model is also developed for further validation of the analytical model. Based on the simulation model predictions, the design of the diaphragm compressor is optimized for the maximum performance. Since the desired cooling performance is not possible with a single compressor unit, a 3-D array for boosting the pressure rise and the volume flow rate is proposed. Finally, suggested future work on diaphragm compressors is outlined

Dynamic Analysis of an Electrostatic Compressor

This paper presents ananalytical approach for modeling the transient dynamic forces in a diaphragm compressor which operates under the action of an electrostatically actuated diaphragm. An experimentally validated, quasi-static model for a diaphragm compressor for electronics cooling was previously developed in which dynamic effects were neglected. In the new model, the dynamic forces induced due to the finite time necessary for deflection of the diaphragm are taken into consideration using the segmentation approach developed earlier. Results from the analytical model compare favorably with those from a detailed numerical simulation as well as with experimental measurements available in the literature. The analytical dynamic model is applied to two different pumping devices to illustrate the effects of the dynamic forces on the overall performance of the device. The effect of pumping frequency of the device on the operating voltage is also explored

Analytical Model for an Electrostatically Actuated Miniature Diaphragm Compressor

This paper presents a new analytical approach for quasi-static modeling of an electrostatically actuated diaphragm compressor that could be employed in a miniature scale refrigeration system. The compressor consists of a flexible circular diaphragm clamped at its circumference. A conformal chamber encloses the diaphragm completely. The membrane and the chamber surfaces are coated with metallic electrodes. A potential difference applied between the diaphragm and the chamber pulls the diaphragm toward the chamber surface progressively from the outer circumference toward the center. This zipping actuation reduces the volume available to the refrigerant gas, thereby increasing its pressure. A segmentation technique is proposed for analysis of the compressor by which the domain is divided into multiple segments for each of which the forces acting on the diaphragm are estimated. The pull-down voltage to completely zip each individual segment is thus obtained. The required voltage for obtaining a specific pressure rise in the chamber can thus be determined. Predictions from the model compare well with other simulation results from the literature, as well as to experimental measurements of the diaphragm displacement and chamber pressure rise in a custom-built setup

Simplification and Validation of a Spectral-Tensor Model for Turbulence Including Atmospheric Stability

A spectral-tensor model of non-neutral, atmospheric-boundary-layer turbulence is evaluated using Eulerian statistics from single-point measurements of the wind speed and temperature at heights up to 100 m, assuming constant vertical gradients of mean wind speed and temperature. The model has been previously described in terms of the dissipation rate epsilon, the length scale of energy-containing eddies L, a turbulence anisotropy parameter Gamma, the Richardson number Ri, and the normalized rate of destruction of temperature variance eta(theta) equivalent to epsilon(theta)/epsilon. Here, the latter two parameters are collapsed into a single atmospheric stability parameter z/L usingMonin-Obukhov similarity theory, where z is the height above the Earth's surface, and L is the Obukhov length corresponding to {Ri ,eta(theta)}. Model outputs of the one-dimensional velocity spectra, as well as cospectra of the streamwise and/or vertical velocity components, and/or temperature, and cross-spectra for the spatial separation of all three velocity components and temperature, are compared with measurements. As a function of the four model parameters, spectra and cospectra are reproduced quite well, but horizontal temperature fluxes are slightly underestimated in stable conditions. In moderately unstable stratification, our model reproduces spectra only up to a scale similar to 1 km. The model also overestimates coherences for vertical separations, but is less severe in unstable than in stable cases