Combining Microstructured Surface and Mesh Covering for Heat Transfer Enhancement in Falling Films of Refrigerant Mixture

The article presents the experimental results of combining a basic microstructure with partly closed pores and a mesh covering for heat transfer enhancement at the film flow of a refrigerant mixture. To reveal the effect of the combined structure, heat transfer on a microstructured surface without a covering as well as on a smooth surface with a mesh covering only has been studied. All experimental series were carried out using a binary mixture of R114 and R21 refrigerants. The mixture film flowed down the outer surface of a vertical cylinder in the undeveloped turbulence regime, when the film Reynolds number varied from 400 to 1300. It is shown that a microstructured surface with a fin pitch of 200 μm, fin height of 220 μm, and longitudinal knurling pitch of 160 μm, created by deformational cutting, demonstrates significant heat transfer enhancement: up to four times as compared to a smooth surface. However, adding a mesh covering with an aperture of 220 μm and a wire diameter of 100 μm reduces the intensification. The mesh covering overlaid on a smooth surface also does not provide heat transfer enhancement as compared to the smooth surface itself. The absence or even deterioration of heat transfer enhancement on surfaces with mesh covering can be primarily associated with the low thermal conductivity of the mesh material and shortcomings of the applied method of mesh mounting. The possibility of deteriorating vapor removal due to the incorrect selection of mesh covering parameters was also analyzed. The heat transfer coefficient values obtained for basic microstructured surfaces were compared with the dependencies available in the literature for predicting pool boiling heat transfer on microfinned surfaces

Regimes of falling liquid film flowing over the vertical cylinder at contact angles up to 90° and Reynold number 50

The paper presents 3D numerical modeling of spreading dynamics of R21 (mol. fraction: 0.9) and R114 refrigerant mixture film. We considered an outer flow along a round vertical cylinder at Reynolds numbers of 50 and contact angles of 10°, 30°, 50°, 70° and 90°. The simulation was performed in OpenFOAM software on the basis of the volume of fluid (VOF) method. We obtained that the contact angle has a key effect on the wetted area due to the change of liquid spreading modes over the cylinder. At that, we distinguished the following flow modes: the stable jet mode, the cascade jet mode, the jet-droplet mode and the drying mode. These modes are similar ones for horizontal tubes. In some flow modes over the vertical cylinder, we demonstrated the existence of the back liquid flow between jets, directed against gravity

Studying the process of freons mixture separation on a structured packing Sultzer 500X

Structured packings are widely used in distillation columns to separate various types of mixtures. These packings have an ordered structure, which ensures more uniform conditions for interaction of counter-current flows of liquid and vapor than in the random packings and have a small hydraulic resistance. Nevertheless, in columns with a diameter of more than 0.5 m, formation of large-scale non-uniformity in distribution of liquid and vapor flow parameters over the packing cross-section is observed. In this work, experimental data on formation of large-scale non-uniformity in the temperature field over the cross-section of the Sulzer 500X packing, as well as on the efficiency of mixture separation and the pressure drop across the packing were obtained. The experiments were carried out with separation of R114/R21 freon mixture on a 10-layer structured packing Sulzer 500X with a diameter of 0.6 m and a height of 2.2 m. Experimental data were compared with the results obtained earlier for a structured packing Mellapack 350.Y with a diameter of 0.9 m and a height of 2.1 m. The presented experimental data will be used to construct and verify a new model of mass transfer and efficiency of mixture separation in the large-scale distillation packed columns

Effect of the structured packing height on efficiency of freons mixture separation in a large-scale model of distillation column

Results of experimental studies of heat-and-mass transfer and hydrodynamic processes at distillation on a regular packing are presented. The mixture of freons R114–R21 at the pressure of 0.3 MPa was used as a working mixture. The mixture was separated on the Mellapak 350Y structured packing with the diameter of 0.9 m under the conditions of complete reflux (L/V = 1) at different packing heights. A specially designed liquid distributor with a possibility to change the density and pattern of drip points was used to irrigate the packing. The experimental data on the efficiency of mixture separation (height of transfer unit HTU) and distribution of the local flow rate density over the column cross-section were compared. It is shown that an increase in the height of the structured packing from 2.1 m to 4.0 m leads to a significant decrease in the efficiency of mixture separation in the distillation column

Effect of the structured packing height on efficiency of freons mixture separation in a large-scale model of distillation column

Results of experimental studies of heat-and-mass transfer and hydrodynamic processes at distillation on a regular packing are presented. The mixture of freons R114–R21 at the pressure of 0.3 MPa was used as a working mixture. The mixture was separated on the Mellapak 350Y structured packing with the diameter of 0.9 m under the conditions of complete reflux (L/V = 1) at different packing heights. A specially designed liquid distributor with a possibility to change the density and pattern of drip points was used to irrigate the packing. The experimental data on the efficiency of mixture separation (height of transfer unit HTU) and distribution of the local flow rate density over the column cross-section were compared. It is shown that an increase in the height of the structured packing from 2.1 m to 4.0 m leads to a significant decrease in the efficiency of mixture separation in the distillation column