Numerical Simulation for Falling Film Thickness around Horizontal Tube in MVC and MED Evaporators

Falling film on horizontal tube evaporators, of both Mechanical Vapor Compression (MVC) and the Multi-Effect Distillation (MED) desalination systems, plays an important role in the heat and mass transfer (evaporation) and accordingly the systems productivity. Falling film thickness is mainly influenced by the intertube space, circumferential angle and the film’s Reynolds number. This paper presents two-dimensional numerical study of falling film thickness around horizontal tube in MVC and MED evaporators. The study is based on computational fluid dynamics (CFD) using volume of fraction (VOF) as a multi-phase technique in ANSYS Fluent. The numerical model is developed in order to study the heat and mass transfer charactristics, the liquid falling film behaviour and thickness distribution around circular horizontal. Four CFD study cases are developed to simulate the falling film behaviour at circumferential angle range from 150 to 1650 with inter-tube spacing of 10 mm, 16 mm, 33 mm and 40 mm and for constant value of flow rate and at the same surrounding conditions. Simulations are conducted using a domain of only two tubes with 20 mm outer diameter.The results from the numerical models are compared with the published experimental correlations, showing a comparatively reasonable agreement. In addition, a parametric study is carried out to illustrate the effect of flow Reyonlds number (Re) and intertube space on the average circumferential film thickness and heat transfer rates.

Systematic Investigations of Annealing and Functionalization of Carbon Nanotube Yarns

Carbon nanotube yarns (CNY) are a novel carbonaceous material and have received a great deal of interest since the beginning of the 21st century. CNY are of particular interest due to their useful heat conducting, electrical conducting, and mechanical properties. The electrical conductivity of carbon nanotube yarns can also be influenced by functionalization and annealing. A systematical study of this post synthetic treatment will assist in understanding what factors influences the conductivity of these materials. In this investigation, it is shown that the electrical conductivity can be increased by a factor of 2 and 5.5 through functionalization with acids and high temperature annealing respectively. The scale of the enhancement is dependent on the reducing of intertube space in case of functionalization. For annealing, not only is the highly graphitic structure of the carbon nanotubes (CNT) important, but it is also shown to influence the residual amorphous carbon in the structure. The promising results of this study can help to utilize CNY as a replacement for common materials in the field of electrical wiring.

Static calculations of the pipeline under sanitation by means of “pipe-in-pipe” method

In recent years, methods of trenchless pipe reconstruction have become widely used in Russia. Once the polymer pipe pulled into the existing pipeline, the necessity of filling the intertube space with a mortar is solved. Due to the lack of clear recommendations on the implementation of the filling, builders often perform these works by trial and error. This requires special research. The article deals with an analysis of standards in this area, There is an example of a static strength calculation.

Dynamics of capillary infiltration of liquids into a highly aligned multi-walled carbon nanotube film

The physical compatibility of a highly aligned carbon nanotube (HACNT) film with liquids was established using a fast and convenient experimental protocol. Two parameters were found to be decisive for the infiltration process. For a given density of nanotube packing, the thermodynamics of the infiltration process (wettability) were described by the contact angle between the nanotube wall and a liquid meniscus (θ). Once the wettability criterion (θ < 90°) was met, the HACNT film (of free volume equal to 91%) was penetrated gradually by the liquid in a rate that can be linearly correlated to dynamic viscosity of the liquid (η). The experimental results follow the classical theory of capillarity for a steady process (Lucas–Washburn law), where the nanoscale capillary force, here supported by gravity, is compensated by viscous drag. This most general theory of capillarity can be applied in a prediction of both wettability of HACNT films and the dynamics of capillary rise in the intertube space in various technological applications.