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Abstract This paper investigated the cooling performance of a high-efficiency dew-point evaporative cooler with optimised air and water flow arrangement using the combined experimental and numerical simulation method. The experimental results showed that the wet-bulb efficiency of the dew-point evaporative cooler was increased by 29.3% and COP was increased by 34.6%, compared to the existing commercial dew point air cooler of the same capacity. An improved two-dimensional, multi-factor engaged numerical model which can scale up and optimize the size and capacity of the cooler was developed. The numerical predictions agreed well with the experimental results, indicating that the cooling rate of the dew-point evaporative cooler is influenced by the dew-point evaporative cooler structure. The cooling efficiency of the dew-point evaporative cooler with corrugated plates is more than 10% higher than with flat plates and the cooling efficiency of the dew-point evaporative cooler with the actual flow arrangement is only 62%–67% that of a dew-point evaporative cooler with an ideal counter-flow arrangement. The cooling efficiency can be improved by increasing the channel length and the air entrance length, and decreasing the channel width and channel gap within a reasonable range.

Abstract This paper investigated the cooling performance of a high-efficiency dew-point evaporative cooler with optimised air and water flow arrangement using the combined experimental and numerical simulation method. The experimental results showed that the wet-bulb efficiency of the dew-point evaporative cooler was increased by 29.3% and COP was increased by 34.6%, compared to the existing commercial dew point air cooler of the same capacity. An improved two-dimensional, multi-factor engaged numerical model which can scale up and optimize the size and capacity of the cooler was developed. The numerical predictions agreed well with the experimental results, indicating that the cooling rate of the dew-point evaporative cooler is influenced by the dew-point evaporative cooler structure. The cooling efficiency of the dew-point evaporative cooler with corrugated plates is more than 10% higher than with flat plates and the cooling efficiency of the dew-point evaporative cooler with the actual flow arrangement is only 62%–67% that of a dew-point evaporative cooler with an ideal counter-flow arrangement. The cooling efficiency can be improved by increasing the channel length and the air entrance length, and decreasing the channel width and channel gap within a reasonable range.

Low-temperature preheating, fast charging, and vehicle-to-grid (V2G) capabilities are important factors for the further development of electric vehicles (EVs). However, for conventional two-stage chargers, the EV charging/discharging instructions and grid instructions cannot be addressed simultaneously for specific requirements, pulse heating and variable-current charging can cause high-frequency power fluctuations at the grid side. Therefore, it is necessary to design a bidirectional grid-friendly charger for EVs operated under pulse-current heating and variable-current charging. The DC bus, which serves as the medium connecting the bidirectional DC–DC and bidirectional DC–AC, typically employs capacitors. This paper analyzes the reasons why the use of capacitors in the DC bus cannot satisfy the grid and EV requirements, and it proposes a new DC bus configuration that utilizes energy storage batteries instead of capacitors. Due to the voltage-source characteristics of the energy storage batteries, EV instructions and grid instructions can be flexibly and smoothly scheduled by using phase-shift control and adaptive virtual synchronous generator (VSG) control, respectively. In addition, the stability of the control strategy is demonstrated using small signal modeling. Finally, typical operating conditions (such as EV pulse preheating, fast charging with variable current, and grid peak shaving and valley filling) are selected for validation. The results show that in the proposed charger, the grid scheduling instructions and EV charging/discharging instructions do not interfere with each other, and different commands between EVs also do not interfere with each other under a charging pile with dual guns. Without affecting the requirements of EVs, the grid can change the proportion of energy supply based on actual scenarios and can also obtain energy from either EVs or energy storage batteries. For the novel charger, the pulse modulation time for EVs consistently achieves a steady state within 0.1 s; thus, the pulse modulation speed is as much as two times faster than that of conventional chargers with identical parameters.

Low-temperature preheating, fast charging, and vehicle-to-grid (V2G) capabilities are important factors for the further development of electric vehicles (EVs). However, for conventional two-stage chargers, the EV charging/discharging instructions and grid instructions cannot be addressed simultaneously for specific requirements, pulse heating and variable-current charging can cause high-frequency power fluctuations at the grid side. Therefore, it is necessary to design a bidirectional grid-friendly charger for EVs operated under pulse-current heating and variable-current charging. The DC bus, which serves as the medium connecting the bidirectional DC–DC and bidirectional DC–AC, typically employs capacitors. This paper analyzes the reasons why the use of capacitors in the DC bus cannot satisfy the grid and EV requirements, and it proposes a new DC bus configuration that utilizes energy storage batteries instead of capacitors. Due to the voltage-source characteristics of the energy storage batteries, EV instructions and grid instructions can be flexibly and smoothly scheduled by using phase-shift control and adaptive virtual synchronous generator (VSG) control, respectively. In addition, the stability of the control strategy is demonstrated using small signal modeling. Finally, typical operating conditions (such as EV pulse preheating, fast charging with variable current, and grid peak shaving and valley filling) are selected for validation. The results show that in the proposed charger, the grid scheduling instructions and EV charging/discharging instructions do not interfere with each other, and different commands between EVs also do not interfere with each other under a charging pile with dual guns. Without affecting the requirements of EVs, the grid can change the proportion of energy supply based on actual scenarios and can also obtain energy from either EVs or energy storage batteries. For the novel charger, the pulse modulation time for EVs consistently achieves a steady state within 0.1 s; thus, the pulse modulation speed is as much as two times faster than that of conventional chargers with identical parameters.

The removal of natural organic matter (NOM) in term of CODMn by up-flow biologically activated carbon filter (UBACF) and down-flow biologically activated carbon filter (DBACF) was investigated in a pilot-scale test. The impacts of the molecular weight distribution of NOM on its degradation by the UBACF and DBACF were evaluated. The relationship between biodegradation and the microbial properties in the UBACF and DBACF were approached as well. The feed water of the UBACF and DBACF were pumped from the effluent of the rapid sand filtration (RSF) of Chengnan Drinking Water Treatment Plant (CDWTP), Huaian, Jiangsu Province, China. When the adsorption was the dominant mechanism of NOM removal at the initial stage of operation, the CODMn removal efficiency by the UBACF was lower than the DBACF. However, with the microbes gradually accumulated and biofilm formed, the removal of CODMn by the UBACF increased correspondingly to 25.3%, at the steady-state operation and was approximately 10% higher than that by the DBACF. Heterotrophy plate count (HPC) in the finished water of the UBACF was observed 30% higher than that of the DBACF. The UBACF effluent had higher concentration of detached bacteria whereas the DBACF harbored more attached biomass. The highest attached biomass concentration of the UBACF was found in the middle of the GAC bed. On the contrary, the highest attached biomass concentration of the DBACF was found on the top of the GAC bed. Furthermore, a total of 9479 reads by pyrosequencing was obtained from samples of the UBACF and DBACF effluents. The UBACF effluent had a more diverse microbial community and more even distribution of species than the DBACF effluent did. Alphaproteobacteria and Betaproteobacteria were the dominant groups in the finished water of the UBACF and DBACF. The higher organic matter removal by the UBACF was attributed to the presence of its higher biologically activity.

The removal of natural organic matter (NOM) in term of CODMn by up-flow biologically activated carbon filter (UBACF) and down-flow biologically activated carbon filter (DBACF) was investigated in a pilot-scale test. The impacts of the molecular weight distribution of NOM on its degradation by the UBACF and DBACF were evaluated. The relationship between biodegradation and the microbial properties in the UBACF and DBACF were approached as well. The feed water of the UBACF and DBACF were pumped from the effluent of the rapid sand filtration (RSF) of Chengnan Drinking Water Treatment Plant (CDWTP), Huaian, Jiangsu Province, China. When the adsorption was the dominant mechanism of NOM removal at the initial stage of operation, the CODMn removal efficiency by the UBACF was lower than the DBACF. However, with the microbes gradually accumulated and biofilm formed, the removal of CODMn by the UBACF increased correspondingly to 25.3%, at the steady-state operation and was approximately 10% higher than that by the DBACF. Heterotrophy plate count (HPC) in the finished water of the UBACF was observed 30% higher than that of the DBACF. The UBACF effluent had higher concentration of detached bacteria whereas the DBACF harbored more attached biomass. The highest attached biomass concentration of the UBACF was found in the middle of the GAC bed. On the contrary, the highest attached biomass concentration of the DBACF was found on the top of the GAC bed. Furthermore, a total of 9479 reads by pyrosequencing was obtained from samples of the UBACF and DBACF effluents. The UBACF effluent had a more diverse microbial community and more even distribution of species than the DBACF effluent did. Alphaproteobacteria and Betaproteobacteria were the dominant groups in the finished water of the UBACF and DBACF. The higher organic matter removal by the UBACF was attributed to the presence of its higher biologically activity.

Wind farms (WFs) controlled with conventional vector control (VC) algorithms cannot be directly integrated to the power grid through line commutated rectifier (LCR)-based high voltage direct current (HVDC) transmission due to the lack of voltage support at its sending-end bus. This paper proposes a novel coordinated control scheme for WFs with LCC-HVDC integration. The scheme comprises two key sub-control loops, referred to as the reactive power-based frequency (Q-f) control loop and the active power-based voltage (P-V) control loop, respectively. The Q-f control, applied to the voltage sources inverters in the WFs, maintains the system frequency and compensates the reactive power for the LCR of HVDC, whereas the P-V control, applied to the LCR, maintains the sending-end bus voltage and achieves the active power balance of the system. Phase-plane analysis and small-signal analysis are performed to evaluate the stability of the system and facilitate the controller parameter design. Simulations performed on PSCAD/EMTDC verify the proposed control scheme.