Aqvsenti Miqashavidze

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 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

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 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 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

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

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