Theoretical investigation on the heating performance of a recuperative heat pump water heater using CO2/HCs with large temperature glides in cold regions

Considering the issues of environmental pollution and energy efficiency, heat pumps are gradually replacing traditional coal combustion for heating at low ambient temperatures. In this paper, eco-friendly CO2/HCs with large temperature glides are applied in a single-stage recuperative heat pump water heater. Its heating performance is theoretically investigated under the working condition of producing circulating hot water in typical winter of northern China, with medium temperature difference between supply/return water and large temperature difference between air inlet and water inlet. Due to its simple structure, low initial investment and high efficiency, its potential for producing circulating hot water is demonstrated. Exergy analyses are conducted to reveal the significant influence of the exergy losses of heat exchanger on system performance. For specified CO2/HC, optimal COP is obtained through global optimization of cycle pressures and mixture concentration. The heating performances of different CO2/HCs are compared, among which CO2/R600 and CO2/R600a behave better. Meanwhile, a typical vapor-injection cycle is used to demonstrate priorities on the heating performance of this recuperative cycle, in which the COP of recuperative cycle using CO2/R600 is more than 3.4% higher than that of the vapor-injection cycle. The results obtained in this paper provide a simple and efficient solution for producing circulating hot water at low ambient temperatures.

A case study on the impact of severe convective storms on the water vapor mixing ratio in the lower mid-latitude stratosphere observed in 2019 over Europe

Extreme convective events in the troposphere not only have immediate impacts on the surface, they can also influence the dynamics and composition of the lower stratosphere (LS). One major impact is the moistening of the LS by overshooting convection. This effect plays a crucial role in climate feedback as small changes of water vapor in the upper troposphere and lower stratosphere (UTLS) have a large impact on the radiation budget of the atmosphere. In this case study, we investigate water vapor injections into the LS by two consecutive convective events in the European mid-latitudes within the framework of the MOSES (Modular Observation Solutions for Earth Systems) measurement campaign during the early summer of 2019. Using balloon-borne instruments, rare measurements of the convective water vapor injection into the stratosphere were performed. The magnitude of the water vapor reached up to 12.1 ppmv with an estimated background value of 5 ppmv. Hence it is in the same order of magnitude as earlier reports of water vapor injection by convective overshooting above North America. However the overshooting took place in the extra-tropical stratosphere and has an impact on long-term water vapor mixing ratios in the stratosphere compared to the Monsoon-influenced region in North America. At the altitude of the measured injection, a sharp drop in a local ozone enhancement peak makes the observed composition of air very unique with high ozone up to 696 ppbv and high water vapor up to 12.1 ppmv. While ERA-Interim data does not show any signal of the convective overshoot, the measured values in the LS are underestimated by MLS satellite data and overestimated by ERA5 reanalysis data. Backward trajectories of the measured injected air masses reveal that the moistening of the LS took place several hours before the balloon launch. This is in good agreement with reanalyses and satellite data showing a strong change in the structure of isotherms, and a sudden and short-lived increase in potential vorticity at the altitude of the trajectory, as well as low cloud top brightness temperatures during the overshooting event.

Effect of Water Vapor Injection on the Performance and Emissions Characteristics of a Spark-Ignition Engine

The exhaust emissions from Internal Combustion Engines (ICE) are currently one of the main sources of air pollution. This research presented a method for improving the exhaust gases and the performance of a Spark-Ignition (SI) engine using a water vapor injection system and a Non-Thermal Plasma (NTP) system. These two systems were installed on the intake manifold to investigate their effects on the engine’s performance and the characteristics of exhaust emission using different air/fuel (A/F) ratios and engine speeds. The temperatures of the injected water were adjusted to 5 and 25 °C, using a thermoelectric cooler (TEC) temperature control device. The total hydrocarbons (HC), nitrogen oxide (NOx), and engine torque were measured at different A/F ratios and engine speeds. The results indicated that the adaptation of the water vapor injection system and NTP system increased the content of the combustibles and combustion-supporting substances while achieving better emissions and torque. According to the test results, while the engine torque under 25 °C water+NTP was raised to 7.29%, the HC under 25 °C water+NTP and the NOx under 25 °C water were reduced to 16.31% and 11.88%, respectively. In conclusion, the water vapor injection and the NTP systems installed on the intake manifold could significantly reduce air pollution and improve engine performance for a more sustainable environment.