D.G. Kröger

Solar Chimney Power Plant Performance

This paper evaluates the performance of a large-scale solar chimney power plant. The study considers the performance of a particular reference plant under specified meteorological conditions at a reference location in South Africa. A computer simulation program is employed to solve the governing conservation and draught equations simultaneously. Newly developed convective heat transfer and momentum equations are included in the numerical model and multiple simulations are performed. Results indicate 24 hr plant power production, while illustrating considerable daily and seasonal power output variations. It is shown that plant power production is a function of the collector roof shape and inlet height.

The effect of the heat exchanger arrangement and wind-break walls on the performance of natural draft dry-cooling towers subjected to cross-winds

Abstract In most full scale dry-cooling towers rectangular heat exchanger bundles are arranged either vertically around the circumference of the tower or horizontally in the inlet cross-section of the tower. A numerical procedure is used in the present paper to investigate the influence of the particular arrangement on the performance of a tower in windy conditions with the results being verified by full scale and experimental measurements. Practical suggestions concerning the arrangement of the heat exchangers and wind-break walls are made which may lead to significant reductions in the adverse effect of cross-winds on the performance of dry-cooling towers.

Loss Coefficient Correlation for Wet-Cooling Tower Fills

Loss coefficient correlations given in the literature for wet-cooling tower fills are relatively simple and generally do not represent the pressure drop accurately over a wide range of operational conditions. A new form of empirical equation is proposed that correlates fill loss coefficient data more effectively when compared to other forms of empirical equations commonly found in the literature.

The influence of wind on the performance of forced draught air-cooled heat exchangers

Abstract The influence of wind on fan performance and recirculation in a forced draught air-cooled heat exchanger (ACHE) bank is investigated numerically. Winds blowing across and parallel to the longitudinal axis (long axis) of an ACHE bank are considered. It is found that cross winds significantly reduce the air volume flow rate that is delivered by the up-wind fans, while winds along the longitudinal axis cause increased hot plume air recirculation along the sides of the ACHE bank.

Effect of wind on performance of a dry-cooling tower

Abstract The influence of cross-winds on the performance of a natural draft dry-cooling tower is investigated by means of full scale measurements. By monitoring all the relevant independent variables, the results of these measurements allow direct comparison with the wind effect predicted by a numerical procedure employing the PHOENICS code. It is shown that results obtained on full scale towers can be successfully reproduced provided that the effects of all tower components are included in the analysis. In practical cooling towers rectangular heat exchanger bundles are arranged either vertically around the circumference of the tower or in the horizontal inlet cross-section of the tower and the wind is found to be dependent on the particular layout.

Performance Trends of an Air-Cooled Steam Condenser Under Windy Conditions

Air-cooled steam condensers (ACSCs) are increasingly employed to reject heat in modern power plants. Unfortunately, these cooling systems become less effective under windy conditions and when ambient temperatures are high. A better understanding of the fundamental air flow patterns about and through such ACSCs is essential if their performance is to be improved under these conditions. The present numerical study models the air flow field about and through a particular ACSC. The performance of the fans is modeled with the aid of a novel numerical approach known as the “actuator disc model.” Distorted air flow patterns that significantly reduce fan performance in certain areas and recirculatory flows that entrain hot plume air are found to be the reasons for poor ACSC performance. It is found that the reduction in fan performance is the main reason for the poor ACSC performance while recirculation of hot plume air only reduces performance by a small amount.

Plenum chamber flow losses in forced draught air-cooled heat exchangers

The primary objective of this experimental investigation is to determine the influence that different fan and heat exchanger characteristics as well as the plenum chamber geometry have on the flow losses in the plenum chamber of a forced draught air-cooled heat exchanger (ACHE). The effect of air flow maldistribution on the heat exchanger thermal performance is also investigated. A series of model tests are conducted employing different fans and heat exchangers. It is found that there is a critical minimum distance between the outlet of the fan and the heat exchanger. The heat exchanger loss coefficient and its inlet geometry have a relatively strong influence on plenum losses as well as on the air velocity distribution at the outlet of the heat exchanger. Other variables, including the position of the fan in the fan casing, fan-to-heat exchanger area ratio and fan characteristics, have a lesser effect on plenum performance. A plenum chamber recovery coefficient is defined and expressed in terms of measured parameters. This coefficient can be employed in the design of practical ACHEs. It is further found that air flow maldistribution only has a small influence on the heat exchanger thermal performance.

Effect of inlet flow distortions on fan performance in forced draught air-cooled heat exchangers

Abstract Forced flow air-cooled heat exchangers (ACHEs) as found in the petro-chemical, process and power industries use fans arranged in single or multiple fan rows to force air over finned tube bundles. Any flow disturvances or distortions experienced at the inlets of these fans tend to reduce the effectiveness of the ACHE. The reduction of the air flow rate through ACHE models having different numbers of fan rows is investigated experimentally. By varying the distance between the fan platform and the ground level, significant changes in air flow rate are observed and the results are correlated by an empirical relation which can be applied to the design of ACHEs. Fans along the edge of an ACHE are most affected by the distorted inlet air flow pattern. Furthermore, the influence of a walkway along the edge of the fan platform on the air flow rate through an ACHE is also investigated.

Performance evaluation of dry-cooling systems for power plant applications

The performance evaluation of dry-cooling systems rely heavily on the ability to model the physical phenomena of the system. A sophisticated equation-based model, consisting of the conservation equations (energy, mass, momentum) and engineering design relations, is presented to model the dry-cooling systems performance for power plant applications. The implementation of this model gives rise to practical and reliable design methods and system performance evaluation throughout its entire operating life. Small modifications, as well as improved and reliable design practices, may result in major savings in capital and running costs over the operating life of these often large and costly plants.

Flow distortions at the fan inlet of forced-draught air-cooled heat exchangers

The effect of inlet flow distortions on fan performance in forced-draught air-cooled heat exchangers (ACHEs) is investigated numerically and experimentally. By varying the distance between the ACHE fan platform and the ground level, significant changes in air volume flow rate are observed. Three different fan inlet shrouds are considered and recommendations towards designing and evaluating the performance of an ACHE are made. The effect of different lengths of a cylindrical fan inlet shroud, as well as the effect of cylindrical sections as part of a conical and a bell-mouth inlet shroud, is also investigated. The results show that a critical length for both the cylindrical inlet shroud and the cylindrical sections of the conical and bell-mouth inlet shrouds can be obtained for optimal fan performance.