Pressure Drop in Solar Power Plant Chimneys

Abstract

The paper investigates flow through a representative tall solar chimney with internal bracing wheels. It presents experimental data measured in a 0.63-m-dia model chimney with and without seven bracing wheels. The bracing wheels each had a rim protruding into the chimney and 12 spokes, each spoke consisting of a pair of rectangular section bars. The investigation determined coefficients of wall friction, bracing wheel loss, and exit kinetic energy in a model chimney, for both ideal non-swirling uniform flow and for swirling distorted flow. A fan at one end of the chimney model either sucked or blew the flow through it. The flow entering the chimney through the fan and its diffuser simulated the flow leaving the turbine at the bottom of the chimney. The swirling distorted flow increased the total pressure drop by about 28%, representing 4.7% of the turbine pressure drop. The pressure drop across the bracing wheels exceeded the frictional pressure drop by far. Designers of tall, thin-walled chimneys should take care to minimize the number of bracing wheels, reduce their rim width as much as possible, and investigate the feasibility of streamlining their spoke sections. If at all structurally possible, the top bracing wheel should be far enough from the chimney exit to allow the spoke wakes to decay and the separated flow to re-attach to the chimney wall downstream of the rims before the flow leaves the chimney, to reduce the exit kinetic energy loss.