Compact Refrigeration System For Electronics Cooling Based on a Novel Two-Phase Jet Impingement Heat Sink

The performance of a compact vapor compression cooling system equipped with a R-134a small-scale oil-free compressor and a novel heat sink that integrates, into a single unit, the evaporator and the expansion device was experimentally evaluated. The expansion device can be a single orifice or an array of orifices responsible for the generation of a high-speed two-phase jet impinging on a heated surface. A comparison between the performance of the proposed refrigeration system operating with single and multiple jets is presented and the influence of the following parameters is quantified: (i) thermal load applied on the heat sink, (ii) number of orifices and (iii) geometrical arrangement of the orifices (jets). The analysis is based on thermodynamic performance metrics (coefficient of performance, second-law efficiency and second-law ratio) and steady-state heat transfer parameters (surface temperature and heat transfer coefficient) associated with the impinging jet(s) for single and multiple orifice tests. The two-phase jet heat sink was capable of dissipating cooling loads of up to 160 W and 200 W from a 6.36-cm2 surface for single and multiple orifice configurations, respectively. For these cases, the temperature of the impingement surface was kept below 40ºC and the heat transfer coefficient reached values between 14,000 and 16,000 W/(m2K). The proposed compact vapor compression cooling solution can be further developed for specific applications in thermal management of power electronics for a variety of stationary and mobile systems

Zinc blende ZnS (001) surface structure investigated by XPS,LEED and DFT

The formation and stability of a sulfur-rich surface of the zinc blende ZnS (001) single crystal have been examined by x-ray photoemission spectroscopy (XPS), low-energy electron diffraction (LEED), and density-functional theory (DFT) calculations. LEED patterns obtained from ZnS (001) surface prepared in ultrahigh vacuum conditions are compatible to the formation of the ($1 \times 2$) reconstruction. Further XPS investigation is consistent with the conversion of the surface region into a sulfur-rich surface. DFT calculations support the S-richer ZnS surface hypothesis and the indirect notion of increasing in the conductivity of such a new structure.Comment: Article in submission process ; 25 pages, 3 figures. Supp.material available in the final versio