Thermo-hydraulic Performance Analyses And Design Study Of Indirect Dry Cooling System

Ambient winds seriously affect the thermo-hydraulic performances of indirect dry cooling system, so it is of use to study the wind effects on the thermo-hydraulic performances of various cooling deltas and sectors in the air-cooled heat exchanger and overall indirect dry cooling system. on the basis of indirect dry cooling system with vertically arranged heat exchanger bundles and horizontally arranged heat exchanger bundles respectively, the computational models of air-side fluid and heat flows coupled with the performance of the circulating water and exhaust steam are developed. The velocity, pressure and temperature fields of cooling air at various wind speeds are presented and the air mass flow rate,inlet air temperature as well as the heat rejection for each cooling delta, each sector are calculated, by which the outlet water temperature of the air-cooled heat exchanger and back pressure of turbine are obtained. The results show that:for the indirect dry cooling system with vertically arranged heat exchanger bundles, the cooling deltas suffer from different actions of ambient winds and the conspicuous dimensional characteristics of wind effects on the thermo-hydraulic performances of indirect dry cooling are presented. The performances of upwind cooling deltas are superior to those at the rear, and they are all better than the side ones. At high wind speeds,the side cooling deltas and sectors get improved in thermo-hydraulic performances to an extent as the wind speed increase, but the performances of the backward ones are deteriorated seriously due to the obstacle of high pressure converting from the strong ambient winds. There exists a critical wind speed, at which the air flow rate is lowest and the outlet water temperature of air-cooled heat exchanger reaches its maximum, the indirect dry cooling system performance is most deteriorated, resulting in an unfavorable turbine back pressure. for the indirect dry cooling system with horizontally arranged heat exchanger bundles, the wind effects on the thermo-hydraulic performances of indirect dry cooling system differ completely from those with vertically arranged air-cooled heat exchanger outside. The velocity and temperature fields present central symmetric characteristics for the heat exchanger bundles in the radial pattern of A-frames, however, the differences are observed for the heat exchanger bundles in the pattern of rectangular A-frames. The thermo-hydraulic performances of the upwind heat exchanger A-frames are most deteriorated by the adverse impacts of ambient winds, but they are improved for the downward ones, just similar to those of direct dry cooling system. As the wind speed increases, the mass flow rate and heat rejection of the downward A-frames increases, but they are reduced for the upwind ones. The outlet water temperature of the air-cooled heat exchanger and back pressure of turbine increase with increasing wind speed. Compared to the indirect dry cooling system with horizontally arranged heat exchanger bundles, the scale of the indirect dry cooling system with vertically arranged heat exchanger bundles is much small and it shows strong capacity of anti-wind.On the basis of the energy balance and heat transfer equations in the air-cooled heat exchanger and condenser, the design procedure of indirect dry cooling system with vertically arranged heat exchanger bundles is proposed, in which the outlet water temperature of air-cooled heat exchanger is used to validate the indirect dry cooling system design by comparing the inlet water temperature of condenser. The flow resistances for various parts of air-cooled heat exchanger and dry-cooling tower are obtained by means of numerical simulation, The correlation between the pressure loss and the face air velocity as well as geometric details are fitted., by which the air-cooled heat exchanger and dry-cooling tower can be basically confirmed. A case study of a typical indirect dry cooling system design shows that the flow resistance characteristics and design procedure for indirect dry cooling system are reliable and effective.