论果蔬冷库建筑的发展趋向

在分析国内果蔬冷库的发展概况并与国外对比的基础上,提出“果蔬冷库建筑发展趋向”的概念。     

Virial equation of state of helium, xenon, and helium-xenon mixtures from speed-of-sound and burnettPρT measurements

The virial equation of state was determined for helium, xenon, and helium-xenon mixtures for the pressure and temperature ranges 0.5 to 5 MPa and 210 to 400 K. Two independent experimental techniques were employed: BurnettPρT measurements and speed-of-sound measurements. The temperature-dependent second and third density virial coefficients for pure xenon and the second and third interaction density virial coefficients for helium-xenon mixtures were determined. The present density virial equations of state for xenon and helium-xenon mixtures reproduce the speed-of-sound data within 0.01% and thePρT data within 0.02% of the pressures. All the results for helium are consistent, within experimental errors, with recent ab initio calculations, confirming the accuracy of the experimental techniques.     

Experimental analysis of a pulse tube based new prototype for cells cryopreservation

Cells cryopreservation is crucial for the treatment of several diseases, but the survival rate of the cells is significantly affected by the cooling process. Currently, programmable freezers based on liquid nitrogen technology are usually adopted but these solutions may cause the death of the cells due to undesired crystallization, membrane damage or osmotic shock. In the recent years, pulse tube refrigerators have attracted a lot of interest in many applications because of their intrinsic characteristics. Despite more gradual, the cooling rate of a similar refrigerator needs to be carefully controlled to meet the desired requirements of cells cryopreservation. Therefore, at the premises of Sapienza University of Rome a pulse tube-based prototype has been designed for cells cryopreservation and an experimental tests campaign has been conducted to assess the performance of the system for the scope. A new control logic, able to adjust the supplied voltage to electric heaters for the conditioning of the temperature inside the stand tubes, has been implemented and different configurations evaluated with cooling rate varying in the range 0.5°C/min to 1.5°C/min. The analysis has shown that the proposed control logic is able to cool down the stem cells in all the investigated range with a maximum temperature difference between the mean temperature of the tubes and the theoretical temperature of −7.65°C for the configuration with copper plate and −4.09°C for the configuration with aluminium plate which represents a safe condition. On the contrary, the copper plate allows approximating better the real cooling curve with the theoretical one and achieving a lower temperature variance at cooling rates higher than 1.25°C/min. Although some further efforts are needed to tune the system up, the present work has demonstrated that a pulse tube refrigerator can be technically and commercially adopted as a viable solution for stem cells cryopreservation.     

Effect of component pressure drops in two-fluid pumpless continuous vapour absorption refrigerator

Miniaturisation of the vapour absorption refrigerator requires replacement of the solution pump by a heat operated bubble pump and air cooled condenser and absorber. The replacement necessitates the selection of working media restricted to vacuum operation, and the air cooling poses the problem of high pressure drops in the refrigerator. Thermodynamic analysis of the absorption refrigerator with such a suitable working medium is performed considering the pressure drops in the system as parameters. The analysis shows that the effect of the evaporator to absorber pressure drop on the system performance is more significant than that of the generator to condenser pressure drop, and it becomes more predominant at the low generator temperature normally encountered in solar operated systems.