Enhanced heat transfer in rectangular duct with punched winglets

Thermal performance of a heat exchanger duct with punched winglets(PWs)mounted on the upper duct wall has been examined for Reynolds number(Re)ranging from 4100 to 25,500.In the present experiment,two types of PWs:punched delta-and elliptical-winglets(P-DW and P-EW)with four punched-hole sizes were tested at a fixed attack angle,optimal relative pitch and height.Also,data of solid delta-and elliptical-winglets(DW and EW)were included for comparison.The investigation has shown that the P-DW yields higher thermal-performance enhancement factor(η)than the P-EW.Although the solid DW and EW with no punch have the highest heat transfer and friction loss,the PWs yield betterηthan the solid ones.For PWs,the P-DW with smaller hole size has the peak heat transfer and friction loss around 5.7 and 40 times over the smooth duct,respectively but the optimumηof 2.17 is seen for the one with a certain hole size.The PWs provideηat about 5%–8%above the solid winglets.

Review of System Strength and Inertia Requirements for the National Electricity Market of Australia

Synchronous generators(SGs)are still making major contributions to the re-stabilization of a power system following voltage/frequency disturbances,attributed to their inherent capability of providing system strength and inertia.However,SGs powered by fossil fuels are operating to a lesser extent and scheduled for decommissioning in the National Electricity Market(NEM)of Australia due to the accelerating increase of low bidding priced asynchronous generation of wind and solar,which leads to the reduction and even in some cases,a shortage of system strength and inertia.This paper comprehensively reviews the requirements of system strength and inertia in the NEM from an operational security perspective.Australia is the first country that established the regulation rules of system strength and inertia to accommodate issues of an emerging high penetration level of non-synchronous renewable generation.