Heat Transfer Engineering, 24(3):1–10, 2003 Copyright C  2003 Taylor & Francis 0145–7632/03 $12.00 + .00 DOI: 10.1080/01457630390149224 Energy and Mass Transfer Phenomena in Natural Draft Cooling Towers B. ˇ SIROK and B. BLAGOJEVI ˇ C Faculty of Mechanical Engineering, Aˇ skerˇ ceva 6, 1000 Ljubljana, Slovenia M. NOVAK, M. HO ˇ CEVAR, andF. JERE Turboinstitut, Rovˇ snikova 7, 1000 Ljubljana, Slovenia In this paper, the development of natural draft cooling towers diagnostics is presented. Diagnostic method is based on measurements of velocity and temperature ﬁelds of the airﬂow in the entire surface area of cooling tower and the raised phenomenological model of heat and mass transfer in a selected reference vertical segment of cooling tower. Velocity and temperature ﬁelds of the airﬂow were measured with the aid of a remote control mobile robot unit that was developed to enable measurements in an arbitrary measurement point above the spray zones over the entire cooling tower area. Topological structures of the humid air velocity proﬁles and temperature proﬁles above the spray zones were obtained at constant integral parameters of a power plant. Measurement results of temperature and mass ﬂow characteristics of the air and water ﬂows in a selected reference vertical segment of cooling tower are presented in the form of phenomenological dependence. Phenomenological dependence links local cooling tower efﬁciency, geometrical characteristics of spray elements, and air and water ﬂow rates. In the concluding part, both methods are applied together on a selected segment of cooling tower, and local and integral cooling tower efﬁciency can be determined. INTRODUCTION In large thermo-energetic systems, the circulating- 5 10 15 water system supplies cooling water to the turbine con- 20 densers and thus acts as the instrument by which heat is 25 efﬁciently extracted from the steam cycle to the environ- The research reported in this manuscript is supported by the Commission of the European Communities DG XII Science, Research, and Development, under the EU Copernicus Project: “Optimising cooling tower efﬁciency by advanced measuring and analysis (OCTEBAMA)”, Contract No. ERB IC15 CT98 0514. Address correspondence to Dr. Matej Novak, Turboinstitut, Rovˇ snikova 7, 1000 Ljubljana, Slovenia. E-mail: matej.novak@turboinstitut.si ment. However, the thermal-discharge rules set limits to its operation. Its performance is vital for the efﬁciency of the thermo-energetic system because a condenser operating at the lowest possible temperature results in maximum turbine work output and overall cycle efﬁ- 30 ciency via a minimum heat extraction. Hence, a good heat extraction system makes its own job easier; i.e., it is called upon to extract less heat, is smaller, and requires less cooling water. The heat extracted by the circulating- water system is larger than that converted to useful work 35 by the steam cycle. In currently operating systems, new and old, the heat extracted varies from 1.5 to 3 times the useful work output of these systems. This is given by 1