Numerical Investigation of Miniature Ejector Refrigeration System Embedded with a Capillary Pump Loop.

A miniature steam ejector refrigeration system embedded with a capillary pump loop can result in a compact design which can be used for electronics cooling. In this paper, computational fluid dynamics (CFD) is employed to investigate the effects of the area ratio of the ejector constant-area mixing section to the nozzle throat, the length of the constant-area section, and the nozzle exit position (NXP), on the performance of a miniature steam ejector. Results show that the performance of the miniature steam ejector is very sensitive to the area ratio of the constant-area mixing section to the nozzle. For the needs of practical application, the area ratio of the constant-area mixing section to the nozzle should be smaller than 16 when the temperature of the primary flow is 60 °C. The NXP plays an important role in the flow phenomena inside the miniature ejector. The critical back pressure is more sensitive to length of the constant-area mixing section than the entrainment ratio. Results of this investigation provided a good solution to the miniature steam ejector embedded with a capillary pump loop for electronics cooling application.

[White light upconversion luminescence and its mechanism of Yb3+/Ho3+/Tm3+ co-doped tellurite glass].

Yb3+ /Ho3+, Yb3+ /Tm3+ and Yb3+ /Ho3+ /Tm3+ co-doped tellurite glasses were prepared by melt-quenching method. Under the excitation of 980 nm laser, Yb3+ /Ho3+/Tm3+ co-doped glass sample shows strong blue, green and red emissions, corresponding to the transitions 1G4 --> 3H6 of Tm3+, 5F4 (5S2) --> 5 I8 of Ho3+, as well as 5F5 -->5 I8 of Ho3+ and 1G4 --> 3F4 of Tm3+ ions, respectively. It was found that the integrated emission intensity ratio of the red to green in Yb3+/Ho3+ /Tm3+ co-doped sample (3.95) is greater than that in Yb3+/Ho3+ co-doped sample (1.69) due to the cross-relaxation between Ho3+ and Tm3+ ions : 3H4 (Tm3+) + 5 I6 (Ho3+) -->3F4 (Tm3+) + 5F5 (Ho3+), and 3F4 (Tm3+ ) + 5 I8 (Ho3+) --> 3H6 (Tm3+) +5 I7 (Ho3+). When the pump power density is 8.2 W x cm(-2), the calculated color coordinates of Yb3+ /Ho3+ /Tm3+ co-doped sample are x = 0.345, y = 0.338, which is very close to the equal energy white light (x = 0.333, y = 0.333).