Tengiz Magrakvelidze

The article presents the results of an experimental study to determine the effect of two-dimensional, pyramidal and combined roughness on heat transfer when a water film flows down the outer surface of a vertical pipe. A two-dimensional roughness was created by winding a wire around a pipe. The pyramidal roughness was created by cutting the left and right screws on the pipe, as a result of which the pipe surface was covered with densely spaced truncated pyramids of height - k. The combined roughness was created by a combination of the above two types with different heights - h and relative step - s/h of two-dimensional roughness. Three regimes of manifestation of the effect of roughness on the intensity of heat transfer were identified: 1. Regime without manifestation of the effect, 2. Regime with partial manifestation of the effect and 3. Regime of full manifestation of the effect of roughness on heat transfer. It was experimentally established that the maximum increase in the heat transfer intensity (more than 3.5-times) is achieved in the case of using a combined roughness with geometric parameters: k=0.25mm, h =0.7mm, s/h =10. It was also found that the effect of the combined roughness (pyramidal + spiral) on heat transfer in the entire range of the Reynolds number investigated by us is higher than the effect of both two-dimensional and pyramidal roughness.

It has been experimentally established that the creation of two-dimensional roughness on the heat-transfer surface causes a significant increase in the intensity of heat transfer into a film flowing down the surface of a vertical pipe. The highest effect is achieved with the ratio of the step between the roughness elements to their height s/h=10.

The article mentions the need for a sharp increase in electricity generation in Georgia. Based on the optimized task, taking into account the expected dynamics of electricity development trends in the world, technological advances and capital expenditures, it is concluded that in the first stage the main focus should be on the so-called traditional energy resources, and later on solar and wind energy resources

It is shown that the current level of electric power generation and consumption is completely insufficient for the normal development of the country. Opinions are expressed on the need for a sharp increase in electric power generation and on some issues of overcoming the existing resistances to the construction of new power plants

The article presents the results of an experimental study of the effect of artificial roughness on heat transfer in an apparatus with a stirrer. It has been established that the creation of roughness on one branch of a heat-releasing coil (annular pipe) immersed in an apparatus with a stirrer in the case of distilled water causes an increase in the intensity of heat transfer by about two times. It has also been found that the roughness of the vessel surface causes an increase in torque (M) and, accordingly, in power factor (KN) by less than two times. Along with this, it is shown that the installation of baffles 20 mm wide in the vessel leads to an increase of M and KN by more than three times

The article analyzes the works devoted to the issues of hydrodynamics and heat transfer at flowing around rough surfaces with a turbulent flow both in channels and in apparatus with a stirrer. The main focus is on the important results obtained by Georgian scientists. In particular, I. Nikuradze's classical experiments and the results obtained by V. Gomelauri and his students. The unpublished results obtained by the authors are also presented

In the article discusses the development trends of electric power in the world. Appropriate data are presented and analyzed. It is shown that for the economically sustainable development of Georgia it is necessary to reach the level of annual electric power production in the coming decades to 40-45 billion kw/h.

The results of the experimental study of the heat transfer of ring-shaped smooth and rough tubes in the apparatus with a stirrer are presented. Distilled water and transformer oil were used as a coolant in the experiments. It has been established that the formation of roughness on the surface of the heat exchanger causes a significant increase in the intensity of heat transfer in the regime of full manifestation of the roughness effect

The article presents the results of experiments to determine the local heat transfer coefficients of smooth and rough surfaces under conditions of deposit formation. The experimental section of the installation was a vertically located annular channel with an internal heated pipe. The roughness was created by winding a thin wire around the inner tube. Tap water with a hardness of 3.6 mg-eq/l was used as a heat carrier. The water in the annular channel moved from bottom to top. The local heat transfer coefficient was determined in three places of the heat transfer tube: at the beginning, in the middle and at the end. The intensity of deposit formation was determined by the decrease in the heat transfer coefficient over time. It has been established that the creation of a two-dimensional roughness on the heating surface causes a significant decrease in the intensity of deposit formation. At the same time, in the case of a smooth heat-releasing pipe, the deposited thickness, as expected, increases downstream, and in the case of a rough surface with optimal geometric parameters, the reverse picture is observed. For a qualitative explanation of this phenomenon, a physical model of the process is proposed

The article notes that, at processing experimental data, the choice of the mixer diameter as the determining size - d does not make it possible to generalize the experimental data for different values ​​of the height and number of blades, as well as the deviation of the blades from the vertical position. It is proposed that the equivalent diameter of the stirrer can be taken as the determining dimension. Processing of experimental data using the equivalent stirrer diameter gives satisfactory results

The results of an experimental study of the process of convective and boiling heat transfer in the vessel with stirrer for smooth and rough ring-shaped pipes are presented. Experimentally was found three regimes of the influence of artificial roughness on the convective heat transfer: 1. regime, where roughness has no influence on heat transfer; 2. regime of partial influence of roughness on heat transfer; 3. fully developed roughness effect regime. It was established that creation of two-dimensional artificial roughness on the heated surface causes the essential (~90%) intensification of convective heat transfer in case of fully developed roughness effect regime. The similitude equation for calculating convective heat transfer coefficient, which generalizes well experimental data both for the smooth and the rough surfaces is proposed. In case of boiling the influence of roughness appears on the initial stage of boiling and in case of fully developed nucleate boiling there was no intensification of heat transfer

The results of an experimental study of the process of convective and boiling heat transfer in the vessel with stirrer for smooth and rough ring-shaped pipes are presented. It is established that creation of two-dimensional artificial roughness on the heated surface causes the essential (~100%) intensification of convective heat transfer. In case of boiling the influence of roughness appears on the initial stage of boiling and in case of fully developed nucleate boiling there was no intensification of heat transfer. The similitude equation for calculating convective heat transfer coefficient, which generalizes well experimental data both for the smooth and the rough surfaces is proposed

The results of an experimental study of the process of convective heat transfer in the apparatus with mixer for the smooth and rough ring-shaped pipes are presented. It is established that the creation of two-dimensional artificial roughness on the heated surface causes the essential (~100%) intensification of heat transfer for both the normal and crisis regimes of mixing. The similitude equation for calculating heat transfer coefficient, which generalizes well experimental data both for the smooth and the rough surfaces, is proposed. Considerations, satisfactorily explaining some special features of the process of the heat transfer of rough surfaces in the apparatus with mixer are given.

The results of an experimental study to determine the intensity of deposit formation on smooth and rough heat transfer surfaces are presented. In the experiments, network water with a hardness of 3.5 mg.eq./L was used as a coolant. It was found that the two-dimensional roughness with the ratio of the step between the roughness elements –s to their height –h equal to 12.5, causes a significant decrease in the intensity of deposit formation. At other values ​​of s/h, the effect of roughness decreases. The surface with holes also turned out to be less effective. In the case of a smooth surface, the thickness of the deposits increases downstream, and in the case of a rough surface (s/h=12.5), the opposite pattern takes place

The article provides data on both traditional and so-called non-traditional renewable energy recourses. Some issues of the country energy security are discussed. A mathematical model of the Georgian electric power system has been developed, on the basis of these model the task of proper optimization has been solved. Based on the solution, it is shown that Georgia can satisfy the demand for electric power at the level of 45 billion kWh/year using its own energy resources

The report contains an analytical review of studies devoted to the problems of hydrodynamics and heat transfer in a turbulent flow around rough surfaces. Along with studies carried out in the world, the works of Georgian scientists are analyzed in more detail, in which, in the author's opinion, important results, including those that have not yet been published, have been obtained that deserve the interest of the scientific community. Attention is focused on problems that have not found a satisfactory solution to date

It has been established that the roughness of the heating surface causes a significant decrease in the intensity of deposit formation. It is shown that among the studied surfaces, the most effective is the surface with two-dimensional roughness, the ratio of the step between the roughness elements-s to their height-h, equal to 12.5

The report presents the results of an experimental study of heat transfer from smooth and rough annular tubes during nucleate boiling in an apparatus with a stirrer under the conditions of placing the stirrer at different levels from the heat transfer tube

The latest data on the theoretical, technical and economic potentials of the main rivers of Georgia are analyzed. It is shown that due to the increase in the price of organic fuels, the urgency of the development and use of Georgia's hydropower potential, including small hydropower potential, is increasing. Solving the problem of appropriate optimization of the mathematical model of the electric power system of Georgia, it is shown that the role of small HPPs in the conditions of rising prices for organic fuel can become quite important.

The data of an experimental study are presented, according to which the creation of a two-dimensional roughness on the heat-releasing surface causes a significant decrease in the intensity of deposit formation. The optimal geometric parameters of two-dimensional roughness are established. It is shown that the heat-transfer surface with dimples is less effective than the surface with two-dimensional roughness in terms of reducing the intensity of deposit formation. It has also been established that on surfaces with two-dimensional roughness, in contrast to smooth surfaces, the process of deposit formation is most intense in the initial section of the heat-transfer pipe and decreases downstream

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