HUNGARIAN JOURNAL OF INDUSTRIAL CHEMISTRY VESZPREM Vol. 30. pp. 1 - 5 (2002) WATER TEMPERATURE DISTRIBUTION IN A VERTICAL CROSS-SECTION OF A WET COUNTERFLOW COOLING TOWER D. SKOBALJ, Z. ZAVARG61 and L. JuHAsz1 (" Vujic-Valjevo", Alekse Dundica 61/1, 14000 Valjevo, YU 1Faculty of Technology, University of Novi Sad, Bul. Cara Lazara I, 21000 Novi Sad, YU) Received: November 29, 2000 The conventio_nal method of ~ooling tower calculation does not take into account heat exchange under the filL The basic reas~ns for this are: substantially less amount of heat is exchanged under the fill than in the fill and the definition of phys1cal model of heat transfer is rather complicated. Nevertheless, in the case of cooling tower of greater dimension this method of ~alcu~atio~ may give uncorrect results. There are very few authors who treat this problem by experiments: The results obtained m this work show that the heat exchange under the fill is significiant. Keywords: cooling tower, heat exchange, temperature distribution, counterflow Introduction In industrial and energetic plants, water is commonly used as cooling medium. Due to lack of industrial water, in most countries, there are in use only recirculated cooling systems. The main part of these systems are cooling towers in which water is cooled by atmospheric air. In the commonly used wet cooling tower the water and the air are in direct contact. There are several types of cooling towers depending on the air and water stream direction. One of the types is the counterflow cooling tower (Fig. I). The first theorethical formulation of water cooling in the counter cooling towers was given by Walker et al. [ 1]. According to this theory there are two independent coefficients: heat and mass transfer coeffi- cients. Merkel [2] was the ftrst who realized the conec- tion between these two phenomena. The amount of heat transferred from water to air, according to Merkel, is proportional to the difference in the enthalpy of the satu- rated air and the enthalpy of the humid air. Merkel [2] was the first who recognised the relation between these two processes. He gave the first appliciable formulation of differential equation of water cooling proces. Ac- cording to this formulation, the amount of heat transfer is proportional to the difference in enthalpy of the satu- rated air and the humid air in the main stream. In deter- mining the value of heat transfer it is sufficiant to use only one empirical coefficient; which includes both heat and mass transfer processes. The results of experimental investigation gave a certain deviation from the Merkel theory. According to some references this deviation is due to approximation in the Merkel equation [3] while in some others the Merkel theory is fully rejected [4]. There are also a great deal of engineering ·calculation procedures which are differing in a level of approxima- tion of the theory. The main reason for such great num- ber of procedures lies in the fact that simultaneous mo- mentum, heat and mass transfer in the cooling towers is one of the most complicated processes in the enginerring practice. Most of these procedures are based on the Merkel theory. Because of its simplicity and relatively satisfactory results, the Merkel theory is widely used and accepted in most well known international standards as a procedure for cooling tower performance calculation [5,6]. However, heat and mass transfer, according to this procedure, are taken into account only in the fill, while the space above and under the fill are neglected. The relatively high.price of the cooling tower fill demand the need to include the effect of water cooling in the zone under the fill. The experimental investigation shows that effect of cooling in the zone under the fill cannot be neglected. It enables to use less fill, keeping the same cooling intensity. 2 Fig. I Wet counterflow cooling tower Merkel theory The wellknown international standards (DIN, CTI) used in the Merkel formulation for counterflow cooling tower performance calculations, often called as standard pro- cedure [5,7]. The equation which describes heat and mass transfer according to Merkel is: madha =:= {J(has -ha)·dV (I) Setting air heat gain equal to water heat loss ma·dha =mw·dhw =mw· Cpw" dt {2) Combining with Eq.( 1) we have (3) The integral term in the above equation is known as Merkel number (4) The analytic solution of the integral (4) is not known. One way to solve it is to have an approximate analytic function between has and tw (linear or parabolic for ex- ample}. Another way is to solve the integral (4) numeri- cally. The left side of Eq.( 3} can be written in the fol- lowing form. connecting it with the fiB characteristics: (5) DISTRIBUTOR CS1 CS2 CS3 CS4 ~1 ~1 ta1 t41 . . . . ~2 ~ ~ t42 t,3 tn tu t.a . . . . ~4 ~ ta. t .. . . . . (s (s (. .t