The influence of the surface structuring type on heat transfer in falling films of the refrigerant mixture

Abstract

The paper considers the influence of enhanced surfaces on heat transfer during evaporation and boiling of a falling laminar-wave liquid film. A mixture of R114/R21 refrigerants was used as a test fluid. The liquid film flowed on the outer surface of vertically-oriented cylinders. To intensify the evaporation process, the authors used the mesh coatings with variable mesh sizes, whereas the surfaces with variable characteristics of microstructure obtained by deformational cutting were used to enhance boiling. The report makes a conclusion about the studied types of structured surfaces, most effective for enhancement of heat transfer in different regimes. It is shown that the mesh coatings intensify heat transfer at evaporation twice as compared to a smooth surface; the microstructured coatings with partly-closed micropores obtained by deformational cutting allow fourfold heat transfer intensification at boiling.

Heat Transfer Enhancement on Multilayer Wire Mesh Coatings and Wire Mesh Coatings Combined with Other Surface Modifications—A Review

“…Volodin et al [21,22] presented similar results: up to twofold increase in the HTC for R114/R21 mixture films falling down vertical heated cylinders as compared with the smooth surface in the film evaporation mode with different wire diameters (0.4 to 0.7 mm), cell sizes (1.6 to 6 mm), and orientations of the mesh coatings. Figure 5b presents an example of mesh coating with mesh diagonally oriented relative to the flow.…”

“…Taking into account data from all the above works with mesh coatings on boiling of refrigerants, fluorocarbons, alcohols, etc. in a wide range of pressures, as well as subcooling of liquid, (see Table 3 [5,7,8,10,11,14,22,20,24,36]) will markedly extend the dependency shown in Fig. 25 of the maximum heat removed on the respective wall superheat values and demonstrate the possibility of using wire mesh coatings in various technical applications.…”

“…Enhancement of heat transfer in liquid films falling down heat-releasing surfaces with mesh or wire intensifiers was investigated in works [19][20][21][22]. This task relates to development of efficient evaporators for various industrial applications, including the transition from submersible evaporators to film ones, which are more economical in terms of consumption of working fluid and metal content of the structure.…”

“…In recent years, the interest in the research on heat transfer enhancement using wire mesh coatings kept growing [2,9,13,14,22,20,37,41,43,45,46]. The authors of the studies note the following main advantages of such coatings: availability of wire meshes with a wide range of characteristics, ease of application, durability, scaling possibilities (mesh coatings can easily be applied to both small and large heat transfer surfaces), as well as controllability of porous structure parameters.…”

“…To sum up, from about 1975 to the present, the number of publications on the intensification of heat mass transfer by means of wire mesh coatings for different applications, from heat tubes [18], vaporizers [19][20][21][22], and distillation columns [23] to refrigeration of miniature computer modules (IC chips) [7,10,24] and solar photovoltaic cells [2] is not very large, 3 yet it keeps growing. In these works, the mesh material and size, the number of mesh layers, and their mutual arrangement are varied or combination of mesh coating with other modification kinds is applied at various experimental conditions and methods of coating application.…”