Environmental Conditions of Barchan Dune and Barchan Chain-A Case Study from the Hexi Desert Area of Gansu

[Objective] The paper was to discuss why the top of tall barchan dunes and barchan chains widespread in single prevailing wind area had not been leveled by wind erosion. [Method] Based on the preliminary survey of distribution status,the morphological characteristics and environmental conditions of barchan dunes and barchan chains in Hexi desert area of Gansu were investigated in details. The significance of difference between samples and significance of correlation between indicators were examined via variance test. [Result] Barchan dunes and barchan chains in Hexi desert area of Gansu distributed at the leeward direction of desert fringe,generally in patch distribution. The distribution area was gravelly beach or cohesive gravel beach,with broader dune slack; winds in distribution area of barchan dunes and barchan chains blew obviously from one direction,while winds at other directions were light or occasionally strong but with low frequency;the barchan dune in the desert fringe of Hexi desert area of Gansu was relatively tall,while barchan chain was even more taller and larger. Coincidence or separation of the dune peak and the sand ridge might be related to distribution frequency of dominant prevailing wind or wind at opposite direction and the observation seasons.[Conclusion]Studying top stability of barchan dune has an important academic value in revealing blowing sand movement rule at desert fringe,invasion of sand flow,and expansion of desert.

Influences of Lateral Double-Layered Deflectors on Cooling Performance of Air-Cooled Condenser

The cooling performance of air-cooled condenser(ACC)is susceptible to adverse impacts of ambient winds.In this work,three kinds of lateral double-layered deflectors installed under the ACC platform are proposed to weaken the unfavorable effects of cross winds.Through CFD simulation methods,the main parameters of thermo-flow performances of a 2×660 MW direct dry cooling system are obtained,by which it can be concluded that the deflectors can effectively reduce the inlet air temperatures while enhance the mass flow rates of upwind fans due to the guiding effect,especially at high wind speeds,while the improvement of cooling capacity of ACCs in the 0°wind direction is weak.The inclined-vertical deflectors are superior to others in performance improvement of ACCs for all cases,which can reduce the turbine back pressure by 12.15%when the wind speed is 12 m/s,so they can be applied to the performance enhancement of ACCs under windy conditions in practical engineering.