Caracterización experimental y modelización del binomio sistema de distribución-separador de gotas en torres de refrigeración

  1. RUIZ RAMÍREZ, JAVIER
Supervised by:
  1. Manuel Lucas Miralles Director
  2. Antonio Sánchez Káiser Co-director

Defence university: Universidad Politécnica de Cartagena

Fecha de defensa: 04 July 2014

Committee:
  1. José Manuel Pinazo Ojer Chair
  2. Blas Zamora Parra Secretary
  3. Pedro Juan Martínez Beltrán Committee member
Department:
  1. Ingeniería Térmica y Fluidos

Type: Thesis

Abstract

Cooling tower emissions are harmful for several reasons, but mainly due to human health hazards (i.e. Legionella outbreaks). Despite the higher performance of this kind of devices, because of the lower condensating pressure level originated by water-cooled systems, many local governments are limiting or banning these systems as they have been listed as potential sources of contamination. The cooling tower level of emissions as well as its thermal performance depend mostly on the operating conditions and its elements (the couple of elements water distribution system and drift eliminator, also known as binomial, and the fill). The present Doctoral Thesis presents a detailed study on the influence of the binomial water distribution system-drift eliminator and the operating conditions on cooling tower thermal performance and emissions. The dispersion of the emissions is also studied. A broad experimental study has been undertaken. Experiments related to thermal performance, emissions and dispersion in an urban areas have been carried out in the cooling tower experimental facility. A weather mast has been used to characterize ambient conditions. To achieve a higher knowledge of the flow inside the tower, a numerical model of the drift eliminators has been developed. Numerical results have been compared to those observed in the experiments carried out in the experimental drop-pressure tunnel. Cooling tower thermal behavior as a function of the binomial and the operating conditions has led to differences about 20% between distribution systems for the eliminators tested. Dimensionless correlations for all the tested geometries have been proposed. These correlations have been validated through experimental results with about 1% differences. The energy consumption of the system has been evaluated through the calculation of the outlet water temperature, which can be 1ºC lower on average depending on the distribution system. The influence of the binomial and the operating conditions on cooling tower emission has been carried out using the sensitive paper method. One of the most relevant contributions to the methodology is the developed automatic classifier which allows to discern between the stains coming from real drops. The number and shape of exiting droplets have been calculated for each combination tested. The lowest level of emissions, 0, 00009%, has been observed for the combination honeycomb-type drift eliminator and the gravity distribution system. Results are discussed according to international standars. According to the limits, a review of these standars is proposed because today technologies can guarantee lower drift rates. The experimental collection efficiency for the tested eliminators has found to be an important result. Cooling tower emission study is completed with the experimental determination of the downwind deposition. The sensitive paper method is also used for experimentally investigating drift deposition in urban areas for eight tests. The influence of ambient conditions on cooling tower drift deposition has been investigated. Decreasing patterns of deposition have been found when increasing the distance from the tower and the wind velocity. The test zone also affects the results (70% differences depending on the wind velocity). To complete experimental results, a numerical model for the lath-type eliminators has been developed. This model has been compared to the experimental results derived in this document and those available in the literature (numerical). It is has been investigated the difference between closing the systems of fundamental equations using RANS and LES approaches. The LES model does not improve results comparing them with the results obtained with RANS models. However, the need of modeling the water film formed in the eliminators has been highlighted. The accomplishment of this information provides a deep knowledge on the influence of the binomial water distributions system-eliminator and the operating conditions on cooling tower performance. This methodology provides with the necessary knowledge to improve future designs and to ensure better operating conditions, always reaching a compromise between the energy consumption (thermal behavior, pressure losses) and emissions (drift and PM10).