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Cryoablation is the most commonly used type of cryosurgery. Today, this treatment is insufficiently automated and therefore less accurate than alternative technologies that significantly limits and gradually reduces the scope of its application. However, from low temperature engineering point of view cryosurgery has the untapped potential of the improving its accuracy. In this paper three major methodological problems of cryosurgical equipment and procedure improving are considered: the impact on target isotherm location (1) of the soft biotissue moisture content solidification latent heat variation, (2) of the cryoprobe constructions and operating at maximum cooling power including the fluid cryogen features and the accuracy of boundary condition replacing a cryoprobe and (3) target isotherm fixation approach by modifying the cryoprobe operating mode. The numerical results showed that the target isotherm location depends insignificantly on different moisture content of soft biotissue, then it is not a limiting factor for cryoexposure prediction. Also numerical results showed that the theoretically minimum temperature of cryoprobe surface significantly overestimates their movement, this leads to a significant difference between the experimental and simulation results. The typical shape and movement of cryonecrosis isotherm at refined maximum cryoprobe cooling power for two typical constructions of cryoprobes and two cryogens are presented. The novel algorithm of modifying the cryoprobe operation mode for controlled precision cryosurgery is proposed and validated. All this complements the previously obtained data and shows the prospects for performing precision cryosurgery. The total average uncertainty of target isotherm location during the studied preliminary predicting stage of temperature field movement (virtual cryoablation) is estimated no more than ±0.41 mm. This information is expected to be useful for improving the quality of cryosurgery planning algorithms (e.g. for tumor treatment).

This paper presents a one-dimensional, steady-state, analytical and a two-dimensional, steady-state, numerical approach to describe heat transfer in the complex solid structure of a skin evaporator used in household refrigerators. Both models are based on a specific form of the energy equation (the heat diffusion equation), which is solved to obtain the temperature distributions and heat flows within the different parts of the structure. Heat transfer is limited by a number of thermal resistances, such as the inner plastic wall of the refrigerator, the aluminum plate, the foil, the tube of the evaporator, and the air gaps. The insulation that prevents heat flowing into the evaporator from the surroundings is also taken into consideration. A comparison of the models showed that the root-mean-square deviation of the calculated temperatures ranged from 0.34 K to 0.60 K and that the area-weighted discrepancy of the calculated heat flows was 4.6%. Experimental validation of the model showed that the calculated and measured evaporator capacities were within ±12%. This demonstrates that several simplifications to the analytical model can be made, so drastically reducing the complexity of modeling a skin evaporator's structure, while retaining sufficient accuracy. These simplifications include reducing the heat transfer to one-dimensional heat conduction in the individual parts of the structure, neglecting the heat flux through the aluminum–air-gap contact, and linearizing the aluminum foil.

This paper presents an analytical 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.

In this paper a computationally efficient steady state model for a typical refrigeration reciprocating compressor is proposed. The plenum cavity is modelled using the acoustic plane wave theory, while the compression process is modelled as a one-dimensional gas dynamics equation. Valve dynamic models, based on a single vibration mode approximation, are coupled with the gas dynamics equation and acoustic plenum models. The steady-state solution of the resultant coupled non-linear equations are posed as a boundary value problem and solved using Warner's algorithm. The Warner's algorithm applied to compressor simulation is shown to be computationally more efficient as compared to conventional techniques such as shooting methods. Comparisons are based on the number of iterations and time taken for convergence. Effect of operating conditions on the overall compressor performance is also investigated. ? 2002 Elsevier Science Ltd and IIR. All rights reserved.