碳氮化钛/粘胶纤维束集合体太阳能界面水蒸发器的制备及其性能

为提高太阳能光热转化效率,基于太阳能驱动的界面水蒸发原理,结合粘胶纤维的形貌和性能特点,通过在垂直排列的粘胶纤维束端面构筑碳氮化钛(MXene)作为光热转化层,制备MXene/粘胶纤维束集合体太阳能界面水蒸发器,并系统分析MXene涂层数、光照强度对太阳能界面水蒸发器蒸发性能及稳定性的影响。结果表明:粘胶纤维表面的沟槽结构及其集合体垂直排列形成的毛细孔为水传输提供了有利通道;纤维束集合体端面涂覆光热转换材料MXene和增加光照强度有利于提高器件的水蒸发性能,当MXene涂层数由1层增加至5层时,其蒸发速率和蒸发效率分别从0.78 kg/(m^(2)·h)和39.4%提高至1.47 kg/(m^(2)·h)和74.4%;随着光照强度的增大,太阳能界面水蒸发器的蒸发性能也随之大幅提高,当光照强度由1 kW/m^(2)增加到5 kW/m^(2)时,其蒸发速率由1.47 kg/(m^(2)·h)提高至6.45 kg/(m^(2)·h),蒸发效率由70.6%提高至82.4%;太阳能界面水蒸发器在2 kW/m^(2)的光照强度下使用144 h后,其蒸发速率和蒸发效率仍分别高达3.31 kg/(m^(2)·h)和82.1%,与初始值相比仅降低4.1%和3.5%,具有较好的稳定性能。

Effect of Temporal Resolution of NDVI on Potential Evapotranspiration Estimation and Hydrological Model Performance

Normalized difference vegetation index (NDVI) data, obtained from remote sensing information, are essential in the Shuttleworth-Wallace (S-W) model for estimation of evapotranspiration. In order to study the effect of temporal resolution of NDVI on potential evapotranspiration (PET) estimation and hydrological model performance, monthly and 10-day NDVI data set were used to estimate potential evapotranspiration from January 1985 to December 1987 in Huangnizhuang catchment, Anhui Province, China. The differences of the two calculation results were analyzed and used to drive the block-wise use of the TOPMODEL with the Muskingum-Cunge routing (BTOPMC) model to test the effect on model performance. The results show that both annual and monthly PETs estimated by 10-day NDVI are lower than those estimated by monthly NDVI. Annual PET from the vegetation root zone (PETr) lowers 9.77%-13.64% and monthly PETr lowers 3.28%-17.44% in the whole basin. PET from the vegetation interception (PETi) shows the same trend as PETr. In addition, temporal resolution of NDVI has more effect on PETr in summer and on PETi in winter. The correlation between PETr as estimated by 10-day NDVI and pan measurement (R2= 0.835) is better than that between monthly NDVI and pan measurement (R2 = 0.775). The two potential evapotranspiration estimates were used to drive the BTOPMC model and calibrate parameters, and model performance was found to be similar. In summary, the effect of temporal resolution of NDVI on potential evapotranspiration estimation is significant, but trivial on hydrological model performance.

Experimental study on the performance of a rotational supercavitating evaporator for desalination

Efforts have been made on experimental research of a supercavitation device for desalination, which is named rotational supercavitating evaporator （RSCE）. The RSCE is characterised by the simple construction and responsive capacity control, and only requires rough filtration of the source water for scaling- and fouling-free operations. The present study has been conducted for the water flow at temperature of around 22-30℃ and atmospheric pressure as the first step for investigation of the performance characteristics of RSCE. The multiply factor extremal experiments conducted with the Box-Wilson＇s method have revealed the salinity of the condensate, the temperature of steam inside the supercavity, and dependence of the shape of supercavity on the rate of steam extraction and rotation speed of impeller. The shape of impeller and the expected supercavitating effects it generates have been confirmed by experimental results at the rotation speed of 5430 rpm （round per minute）. The design of the steam extraction openings has been approved during the evacuation of steam. The experimental dependencies have been obtained in form of statistically valid regression equations, which can be used for engineering design of RSCE.

Characteristic of Local Boiling Heat Transfer of Ammonia and Ammonia/Water Binary Mixture on the Plate Type Evaporator

Power generation using small temperature difference such as ocean thermal energy conversion(OTEC)and discharged thermal energy conversion(DTEC)is expected to be the countermeasures against global warming problem.As ammonia and ammonia/water are used in evaporators for OTEC and DTEC as working fluids,the research of their local boiling heat transfer is important for improvement of the power generation efficiency.Measurements of local boiling heat transfer coefficients were performed for ammonia/water mixture(z=0.9-1)on a vertical flat plate heat exchanger in a range of mass flux(7.5-15 kg/m2s),heat flux(15-23 kW/m 2),and pressure(0.7-0.9 MPa).The result shows that in the case of ammonia/water mixture,the local heat transfer coefficients increase with an increase of mass flux and composition of ammonia,and decrease with an increase of heat flux.