Development of energy and industrial cooling systems with natural draft which based on a new element base
Continuous growth in cooling water shortages and increase of environmental requirements through thermal pollution is closely linked with the problem of rational use of water resources and reducing water-intensive technologies. This necessitates the usage of modern energy technologies and their upgrading with help of existing cooling systems in a variety of industries.
The needs of buyers market of Ukraine in the new resource-air cooling systems can be effectively solved by the application of heat transfer surfaces with a new element base in the form of finned tubes of comfortable form of flowing. Such requirements are met by the proposed new surfaces of the bundles of flat oval tubes with an incomplete transverse fins that have no defects inherent in the known types of heat transfer surfaces of round steel and bimetallic finned tubes or steel oval tubes with planted or mechanically wrapped finning. New tubes combine a high degree of surface expansion, ideal thermal contact between the fins and tube, low aerodynamic drag and high manufacturability.
As part of the applied research there are designed and manufactured laboratory models and samples of flat oval tubes with an incomplete transversal fins by using relatively cheap technologies of automated contact welding of fins to flat oval tube
For the first time ever it is examined heat exchange of surface from tubes of comfortable form of flowing in conditions of forced, free convection and natural draft in a wide range of circumfluence velocities (0 - 20) m/s.
As the result of of experimental studies and numerical models there are constructed flow models of finned surface under free convection and natural draft under low circumfluence velocities. The structure of the flow in the near trail for finned tube and tube bearing surfaces and edges within boundary layers identified on the working surfaces of the field of flow separation.
There are received new systems of general relations for the calculation of heat transfer and aerodynamic drag in the conditions of low-velocity of tubes flow, that take into account the geometric characteristics of tubes and stepper characteristics of packages, free convection and natural draft. To change a parameter of fins from 0.2 to 0.65 it is proposed a new, more advanced and more accurate formula for calculating the efficiency ratio of the rectangular fin of flat oval tube.
To confirm the ideas applied in the design of flat oval tubes with an incomplete transverse fins on the basis of experimental data on heat transfer of bundles of these tubes and to verify the approach to the synthesis of results and reliability of the generalized empirical relationships for calculation of heat transfer coefficients and the efficiency coefficient of fins it was designed and manufactured layout of module of „dry” air cooler. On this module there were conducted laboratory thermal tests. Tests of coolant and experimental results of heat and aerodynamic characteristics of bundles of flat oval tubes with fins showed the competitiveness of such tubes when being used as the surface in heat exchange systems for „dry” cooling processed products, both in terms of forced convection, at low air circumfluence velocities and under free convection and natural draft.
According to the research there are created new methods of calculation of heat transfer and aerodynamic drag of surfaces of the flat oval tubes with an incomplete transverse fins intended for the „dry” systems of cooling of technological products. Created methods are based on empirical distributions dependencies and are designed for heat exchangers of "dry" cooling systems (type "gas-liquid"), which operate in a forced, free convection and natural draft.
Results of testing and heat aerodynamic calculations have shown that in case of use of flat oval tubes with an incomplete transverse fins it is possible to increase compactness, to reduce size and weight in comparison with existing conventional types of finned tubes which are used in "dry" cooling systems of various technological products (25-30)% due to the high heat transfer properties of the proposed tubes.