Search

Changing the working conditions of an industrial heat pump can cause a mismatch of the inner and outer pressure ratios of the twin-screw compressor. Over-compression and under-compression increase the compressor power consumption and decrease the heat-pump’s coefficient of performance (COP). Injecting refrigerant vapor into the compression chamber would increase the inner-pressure ratio and avoid under-compression. An experimental study was conducted with different injection pressures when the condenser outlet’s water temperature reached 90 ℃. The results show that the optimal injection pressure causes the COP and adiabatic efficiency to peak at the same time. This result shows that the vapor injection changes the compression process to a quasi-polytropic compression process. Adjusting the compressor’s inner-pressure ratio by changing the refrigerant-injection pressure is feasible.

Highly sensitive silicon-based nano-structure photodetectors have attracted tremendous attention in night vision imaging. However, most reported photodetectors suffer from large dark current, low detectivity and narrow operating waveband, which greatly limit their application in low-light and broadband detection. Herein, an NN+/MS double junction enhanced photodetector based on silicon nanowire (SiNW) arrays wrapped by silver nanoparticles has been fabricated. The light confinement effect and photogain in the SiNW arrays ensure high sensitivity to weak light, and the built-in electric field formed NN+ junction effectively accelerates carrier separation and suppresses dark currents. Meanwhile, plasmonic hot electrons generated in Ag nanoparticles after excitation could be emitted over MS junctions to achieve superior response currents and obvious sensitivity to near-infrared illumination. As a result, the double junction photodetector exhibits an ultrabroad spectral response ranging from 254 nm to 2200 nm in the self-driven operation mode, which not only enables a peak responsivity of 2.2 × 103 mA W−1, an outstanding specific detectivity up to 5.1 × 1014 cm Hz1/2 W−1 and an ultralow dark current density of 6 × 10−11 A cm−2, which are exceedingly better than those of the existing silicon-based devices, but also endows it with a rapid response speed with a rise/fall time of 25/62 μs at 980 nm. More importantly, the device shows a high low-light sensitivity to starlight irradiation (1.4 × 10−3 lux) due to photogain and sharp imaging capability under low-light conditions. This work provides a potential strategy for fabricating high sensitivity and broadband photodetectors for night vision imaging. [ABSTRACT FROM AUTHOR]