Introduction.
In the industry are widespread thermal processes - heating and cooling of liquids and gases and the condensation of the vapors that are carried out in heat exchangers. Heat exchangers or just heat exchangers are used in virtually all industries. Their main task is to provide temperature control of technological processes.
Currently, all heat exchangers are divided into groups defined by the following criteria: destination (heaters, evaporators and boilers, coolers, condensers and so on.), In a work schedule, in terms of design and so on. Refrigerators Capacitors are used for cooling or condensing vapor stream with special refrigerants (water, air, propane, methyl chloride, freons, etc. d.).
The surface heat exchangers can be divided into the following types of design features:
- shell and tube heat exchangers (hard type, a compensator lens on the body, with a floating head, with a U-shaped tubes);
- heat exchangers type "pipe in pipe";
- with the vapor space heaters (reboilers);
- air cooled condensers.
Shell and tube heat exchangers are currently the most widespread, according to some sources, they make up 80% of the heat exchange equipment. The main part of such a heat exchanger tube bundle is enshrined in the tube sheets. The tubes are placed in the tube bundle in a staggered or apex of the triangle. One teploobmenivayuschihsya media moves through the tubes, while the other - in the case between trubkami.Kozhuhotrubchatye exchangers currently most widespread, according to some reports they make up 80% of the total heat exchange apparatus. The main part of such a heat exchanger tube bundle is enshrined in the tube sheets. The tubes are placed in the tube bundle in a staggered or apex of the triangle. One teploobmenivayuschihsya media moves through the tubes, while the other - between the tubes inside the shell.
Main study material
Analysis of recent publications and information posted on the websites of manufacturers of boilers of low power (VKMM), led to the conclusion that modern boiler technology small and medium thermal power developed in the following areas: increasing energy efficiency by reducing heat loss and more full use of the energy potential of the fuel; reduction in the size of the boiler unit due to the intensification of the process of fuel combustion; intensification of heat transfer in the combustion chamber and on the heating surfaces; reduction of polluting gas emissions (CO, NOx, SOx); improving the reliability of the boiler.
Today, aware of the various methods of heat transfer in the convective cell boilers: the use of perforated surfaces, multilayer convective surfaces, fins, and inserts of various configurations.
Heat exchangers are widely used in many areas of economic activity, the aerospace, power generation, chemical, petrochemical, food processing, refrigeration and cryogenic engineering, heating systems, hot water supply, air-conditioning, different heat engines. With the increasing power density devices, the increased requirements for possible regulatory regimes systems quite important is the question of studying the possible enhancement of heat transfer processes.
Through the enhancement of heat transfer increases the amount of heat transferred through the unit heat transfer surface and consequently, reduced weight and overall dimensions of the heat exchanger; It achieved a more favorable ratio between the transmitted amount of heat and power consumed for pumping coolants. The high technical quality of the intensified heat transfer equipment improves the general characteristics of power technology units. Selecting intensifier - an important stage design of heat transfer equipment.
Selecting intensifier - an important stage design of heat transfer equipment.
The use of wire intensifiers is one of the best ways of heat transfer, combining maximum performance and efficiency.
The main objectives is to increase energy efficiency in the whole system of generation and transport of thermal energy and thermal energy distribution system.
The intensification of heat transfer, which is used to increase the specific heat flux, always accompanied by an increase of pressure loss. To date, to assess the effectiveness of a particular method of heat transfer using multiple criteria that include both thermal and hydrodynamic characteristics of the flow.
And vinzhenernoy practice, in addition to these criteria no less important are the weight and size of the boiler and fuel efficiency. All these parameters have to be systematically taken into account, not only in a separate step (creation, operation), and during the entire life cycle of the task kotla.Dlya fuel economy (at constant power and the geometrical dimensions of the boiler fuel consumption compared with the intensification of the boiler and the boiler heat exchange with smooth pipe surface) criterion of efficiency of heat transfer enhancer may be written in the form
In order to increase the heat transfer can be used a variety of methods: the use of turbulence-inserts, ultrasound, pressure pulsation and vibration heat transfer surfaces, apply various methods of fins inside the tubes
The criterion for reducing the weight and size characteristics of the problem at a constant flow rate of fuel and power, shown in the form:
Where V - volume of convective bundle, Q - thermal capacity of the boiler efficiency enhancer kVt.Kriteriem heat to the selected fraction of reducing the environmental impact throughout the life cycle of the heat exchanger by the use of heat exchange intensifiers.
Conclusions
analyzes modern trends of development of low-power boiler technology. The modern methods of heat transfer in hot water boilers of small capacity. Based on original research and analysis work of the authors proposed to calculate the heat transfer in the channels Smooth pipe boilers adjusted for the intensity of heat exchange in the initial portion of the hydrodynamic flow stabilization. It is shown that the use of plates of different configuration significantly improves the heat-engineering parameters of the boiler.
References
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