INVESTIGATION OF HEAT TRANSFER RATE IN SMOOTH TURBULIZER PIPES

ABSTRACT

Heat exchangers play an important role in industrial thermal energy. They make up a large number of thermal power plants, which occupy large production areas and often exceed 50% of the total configuration value in the chemical, oil refining and several other industries, rather than in thermal energy. As a result, as rational use of fuel and energy resources, it is necessary to create new economic equipment to solve such pressing problems for industrial thermal energy, reduce its metal capacity and size, and increase its efficiency and reliability.

АННОТAЦИЯ

Теплообменники играют важную роль в промышленной тепловой энергетике. Они составляют большое количество тепловых электростанций, которые занимают большие производственные площади и часто превышают 50 % общей стоимости конфигурации в химической, нефтеперерабатывающей и ряде других отраслей промышленности, а не в теплоэнергетике. В результате в качестве рационального использования топливно-энергетических ресурсов необходимо создание нового экономичного оборудования для решения таких насущных задач промышленной теплоэнергетики, снижения его металлоемкости и габаритов, повышения эффективности и надежности.

Keywords: Shell pipe, thermal conductivity, base devices, industrial thermal energy, heat exchange equipment.

Ключевые слова: Кожух трубчатый, теплопроводность, базовые устройства, промышленная теплоэнергетика, теплообменное оборудование.

At present, the chemical industry and oil refineries of the Republic produce products by thermal means in the production process. Cooling or evaporation of the obtained products is carried out using heat exchangers. Today, enterprises have several types of heat exchangers and depending on the chemical composition and temperature of the product, heat exchangers are selected for the production process. Shell tube heat exchangers are also an optimal solution for condensing or evaporating high-temperature products [1, 14, 15].

Such devices are optimally efficient devices in the process of heat exchange and condensation of the required substances. There are several drawbacks to such devices, and to this day it has been one of the most pressing issues facing businesses. Elongation or compression of the inner tubes due to the high internal temperature in shell tube devices, and corrosion of the tubes due to their operation in a liquid medium occurs [11,13]. Among the heat exchangers used, there are two most common devices - shell tubes and plates. or the application of several depths, different shapes, holes, etc. [1,3,4,5,10,].

The versatility of the problem of accelerating convective heat exchange in pipes with smooth turbulizers means that there are many methods of calculating it. It is known that the acceleration of the heat exchange process depends on the amount of heat released from the surface of the moving pipe by the heat transfer agent and its hydraulic resistance. To date, many pipe profiles have been studied to accelerate the heat exchange process and certain results have been achieved. The complexity of the pipe profile leads to a slowing or partial disruption of the flow, but the increase in energy consumption expands the impact of constraints on the availability and technical acceptability of a particular heat carrier. Therefore, in industry, the application of the simple method of increasing the flow rate, which leads to the thinning of the flow boundary layer, but is associated with a rapid increase in hydrodynamic resistance, is limited [12-16].

A peculiar phenomenon called Reynolds resemblance occurs when smooth walls that do not have nebulizers on the surface are washed away by the flow. It establishes a direct relationship between heat exchange rate and surface friction. The relationship between the energy expended in the absorption of heat exchange surfaces in a more complex configuration than in a smooth wall and the rate of heat exchange achieved is more complex. For a long time, the Reynolds similarity has been a special type of constraint that sets a lower limit on the power required to drive a heat carrier to dissipate a certain amount of heat.

It was almost always assumed that any change in the physical environment due to random causes and leading to a violation of the similarity in the distribution of temperature and velocity would lead to a change in the direction of the ratio under consideration. The possibility of practical use of this or that method of accelerating heat exchange is determined by its technical convenience and feasibility. Data on this process are given in the works [1-6], which allow substantiating the methods of accelerating heat exchange.

Ducted pipes and ducts with a smooth inner side, designed as an inner ring turbulizer, have a high thermal efficiency [1; 2; 3]. In addition, according to AGShershevsky and other researchers, the main directions for accelerating the process of heat exchange are:

• increase the flow rate between pipes;
• maintaining its homogeneity;
• ensuring the maximum number of pipes that can be washed transversely by the working medium [4].

The most convenient ways to optimize the hydrodynamic regime in heat exchangers are:

• reduction of working fluid flow to laminar mode;
• use of artificial turbulization profiles;
• generating accelerated turbulent flow.

It is known that one of the main goals of improving heat exchange devices is to accelerate the heat exchange process. Naturally, the choice of acceleration method should be made taking into account the hydraulic resistance [5].

To date, the issues of heat transfer and hydraulic resistance for laminar and turbulent flow of fluids in pipes have been studied in-depth and in detail [6]. However, the effects of the fluid flow regime on heat exchange and pipe hydrodynamics have not been adequately studied.

Therefore, this research work is aimed at studying the effect of pipe profile on heat exchange and pipe hydrodynamics in heat exchange processes. Theoretical analysis of patents and literature sources has shown that discretely located annular or spiral grooved pipes, twisted pipes are the most optimal option in terms of hydraulic resistance and heat exchange rate. As can be seen from the graphs in Figures 1 and 2, the value of heat exchange intensity (Nu) increases for both smooth and complex profile pipes as the flow rate (Re) increases.

Figure 1. The dependence of the heat exchange rate on the flow regime in a pipe of size d/D = 0.94 (when n/D = 0.25; 0.35 and 0.44)

Figure 2. The dependence of the heat exchange rate on the flow regime in a pipe of size d/D = 0.88 (when n/D = 0.25; 0.35 and 0.44)

The experimental data obtained on heat exchange in a smooth pipe are almost consistent with the data of other well-known authors in the field of heat transfer. The results of the study on heat exchange in discretely placed outer surface smooth pipes in the range of position pitch n/D = 0.25-0.44 for pipes with dimensionless diameter d/D = 0.94 for turbulizers are shown in Figure 1. shown.

The analysis of the data shows that for pipes with n/D = 0.25 the Reynolds number is Re = 3500 when the heat transfer value is Nu = 790, at Re = 6300 Nu = 1025, and accordingly, at Re = 9800 Nu = 1280. As the flow rate increased from 3,500 to 9,800, the process intensity increased 1.63 times.

The results obtained for a smooth pipe are as follows: The Reynolds number at Re = 3500 is the value of the heat exchange rate for a pipe of n/D = 0.44 Nu = 600, and for a pipe of n/D = 0.25 Nu = 790, respectively. It can be seen that the decrease in the number of step values of the location of the ring turbulizers has a significant effect on the heat transfer process. In the first case, the heat exchange rate is 10–12% for n/D = 0.44 and 23–29%, respectively, for n/D = 0.25. Similar results were obtained for a pipe of d/D = 0.88 (Fig. 2), the only difference being that the numerical values of the acceleration of heat exchange are much higher. For n/D = 0.44, the smooth tube heat transfer rate was 26–28%, and for n/D = 0.25, it was 43–47%, respectively.

The bulge height or depth of the trench, in addition to the step of placing them, causes non-stationary swells and flows, as well as microcirculations of the flow, which does not lead to a significant increase in the hydrodynamic resistance of the channel and accelerates heat exchange.

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