Coefficients of heat and mass transfer of current-technology sprinklers for process computations of cooling towers

Abstract

Analysis of formulas for computing coefficients of heat and mass transfer derived on the basis of results of laboratory tests of 22 sprinklers is used to show that the classification of sprinklers into film and drop ones can be based on a physically grounded parameter m, i.e., the exponent in the formula for the evaporation number K ev = A p ë m (or for the Merkel number Me = A x ë m ). A generalized formula describing the dependence of the coefficients of heat and mass transfer on the height of the sprinkler is derived, which makes it possible to determine the optimum sprinkler height in cooling tower design. The accuracy of the formulas for computing the coefficients is confirmed by a comparison of experimental and computed values of the temperature of cooled water in the cooling tower of the Novo-Ryazanskaya cogeneration plant.A sprinkler is an important component of a cooling tower, which determines the efficiency of cooling of the circulating water. The thermal efficiency of a sprinkler is primarily determined by the coefficients of heat and mass transfer. In order to evaluate the thermal efficiency of a cooling tower designers perform process computations, the accuracy of which depends on the quality of determination of these coefficients from data of laboratory tests.According to a contract between the RAO EÉS Rossii ("UPS of Russia") Company and the Vedeneev All-Russia Research Institute for Hydroengineering we have updated a test bench for determining the coefficients of heat and mass transfer and aerodynamic drag of sprinklers. At present, a great number of current-technology polymer sprinklers have been tested, their main characteristics determined, and recommendations given on their use [1]. In the present paper we will show that the formulas for computing the coefficients of heat and mass transfer used in [1] are physically grounded and ensure enough accuracy of process computations.In order to determine the coefficients of heat and mass transfer, the intensities of flow of water and air, the temperatures of hot and cooled water, the temperature and the relative humidity of air, and the barometric pressure are measured on a laboratory bench in every test. The equipment for measuring these quantities on the bench has passed metrological examination and the latter has proved the accuracy of the measurements. However, the accuracy of determination of individual quantities does not ensure the correctness and accuracy of the final result, i.e., of the values of the coefficients of heat and mass transfer, because the latter are computed with the help of a rather intricate mathematical method. The errors of measurement of some quantities have a complex and uncertain influence on the correctness and accuracy of the computed coefficients.The method developed at VNIIG determines the coefficients of heat and mass transfer by solving an inverse problem for systems of differential equations of heat and mass transfer in a sprinkler [2]. The sought-for coefficients in every test are such that the design temperature...

Cooling tower irrigator layout with allowances for non-uniformity of the airflow velocity field

“…The existence of large-scale nonuniformities of airflow in the cross-section of the irrigation space in cooling towers is discussed in [2,3,[5][6][7][8][9]. As a result of the studies on the model of a cooling tower with the irrigation area of 6500 m 2 , done in a scale of 1 : 65, we proved that the specific air consumption, taking into account the cooling tower's radius, varies from 0 in the center to 1.2 near the wall [5].…”

“…Furthermore, the ξ 1 > ξ 2 condition is met. The packing blocks are selected out of several known and produced ones [7][8][9]15] using the data of the velocity fields ( Fig. 1), equation (6), and the existing geometry characteristics of the industrial packing [7][8][9]15].…”

Forms for representation of thermal responses of evaporative cooling towers

“…1 is designed and constructed for the chimney cooling tower at the No. 1 Novo-Ryazanskaya TPP, and has been reported in [2]. In contrast to the nomogram cited in [1], and in addition to the sprinkler, additional cooling regions in the tower -a region of "rain" in the air-distribution space under the sprinkler, and a region of sprinkler flares from the pressurized water-distribution system -were defined more precisely in the design of the nomogram for the Novo-Ryazanskaya TPP.…”

“…As compared with the nomogram presented in [2], the following two additional families of curves are superposed on the nomogram of Fig. 1, and later in Fig.…”

“…From expression (2), the temperature of the cooled water t 2(1) = ¢ t 2 1 ( ) + ät 2(1) = 29°C. The temperature of the hot water t nom(1) = t 2(1) + Ät nom(1) = 29 + 7 = 36°C…”