Том 23, № 1 (2016)

The results of study of evaporation of water droplets and NaCl salt solution from a solid substrate made of anodized aluminum are presented in this paper. The experiment provides the parameters describing the droplet profile: contact spot diameter, contact angle, and droplet height. The specific rate of evaporation was calculated from the experimental data. The water droplets or brine droplets with concentration up to 9.1 % demonstrate evaporation with the pinning mode for the contact line. When the salt concentration in the brine is taken up to 16.7 %, the droplet spreading mode was observed. Two stages of droplet evaporation are distinguished as a function of phase transition rate.

The aim of this study is to investigate the effect of mass flow rate on film cooling effectiveness and heat transfer over a gas turbine rotor blade with three staggered rows of shower-head holes which are inclined at 30° to the spanwise direction, and are normal to the streamwise direction on the blade. To improve film cooling effectiveness, the standard cylindrical holes, located on the leading edge region, are replaced with the converging slot holes (console). The ANSYS CFX has been used for this computational simulation. The turbulence is approximated by a k-ε model. Detailed film effectiveness distributions are presented for different mass flow rate. The numerical results are compared with experimental data.

A possible influence of the deflection of control surfaces on the aerodynamics of an axisymmetric slender configuration at supersonic flow speeds is considered. A classical configuration consisting from the fuselage in the form of a body of revolution and having cross frontal fins and six-blade trailing stabilizers is considered as the investigation object. The physical flow pattern at the deflection of horizontal fin consoles is investigated and the estimates are obtained for the influence of this deflection on both the characteristics of elements (the body and stabilizers) as well as on the integral aerodynamic characteristics of the entire configuration. Numerical computations of the flow have been done at the freestream Mach number М = 3 in the range of attack angles α = 0−10° and the angles of the control surfaces deflection δ_cs = ±5° on the basis of the averaged Navier−Stokes equations and the SST k-ω turbulence model.

This article presents an investigation on heat transfer enhancement in a round tube inserted with a helically twisted tape. The effects of a helically twisted tape with alternate axis (HTT-A) on heat transfer, friction factor, and thermal performance factor behaviours are reported for the turbulent regime. HTT-A geometries are tape pitch to tube diameter, P/D = 1.0, 1.5, and 2.0; alternate length to pitch length, l/P = 1.0, 1.5, and 2.0; twisted length to tape width, y/W = 3.0; and tape width to tube diameter, w/D = 0.2. The experiment has been performed by varying the volumetric air flow rate in order to adjust Reynolds number ranging from 6 000 to 20 000. The wall of the testing tube is uniformly heated as a constant heat flux while the tests are covered with thermal insulations to reduce heat loss to surroundings. Thermal performance is evaluated by comparing the present experimental results with the results of the modified HTT-A and also those obtained from previous study (conventional helically twisted tape, HTT). The thermal performance of tested tube with HTT-A is evaluated to obtain the degree of heat transfer enhancement and friction factor induced by HTT-A with respect to the plain tube under the same test conditions. Evenly, it is interesting to observe that the tube with HTT-A consistently possesses higher heat transfer and thermal performance factor than those with the HTT around 14.1% and 1.9%, respectively. The HTT-A with the smaller pitch ratio and adjacent twist length provides higher heat transfer rate and friction factor than the one with larger pitch ratio and alternate length as a result of a larger contact surface area, stronger swirl intensity and, thus, better fluid mixing near the tube wall. In the range determined, the tubes with the largest pitch ratio (P/D = 2.0) and smallest alternate length (l/P = 1.0) give the highest thermal performance factor at around 1.35. In addition, the empirical correlations of the Nusselt number, friction factor, and thermal performance factor are also described.

The paper presents an investigation of the influence of thermophoresis on MHD mixed convective heat and mass transfer of a viscous, incompressible and electrically conducting fluid along a vertical flat plate with radiation effects. The plate is permeable and embedded in a porous medium. To describe the deviation from the Darcy model the Forchheimer flow model is used. The Rosseland approximation is used to describe the radiative heat flux in the energy equation. The governing partial differential equations are transformed into a system of ordinary differential equations using similarity transformation. The nonlinear ordinary differential equations are linearized by using quasilinearization technique and then solved numerically by using implicit finite difference scheme. The numerical results are analyzed for the effects of various physical parameters such as magnetic parameter Ha, mixed convection parameter Ra_d /Pe_d, Reynolds number Red, radiation parameter R, thermophoretic parameter τ, Prandtl number Pr, and Schmidt number Sc. The heat transfer coefficient is also tabulated for different values of physical parameters.

Plasma technology was developed to create protective-decorative coatings on the wood surfaces. Experimental investigation on applying the protective coating using the low-temperature plasma energy as well as studies of the distribution of temperature fields over the section of the treated workpiece have been carried out, and the calculated results have been compared with the experimental data.

The effect of parameters of the multi-ring Couette system with counter rotating coaxial cylinders on the process of thermal energy release in a viscous liquid filling this system is considered with regard to the problem of determining the possibility of creating the high-performance wind heat generator. The multi-cylinder rotor design allows directly conversion of the mechanical power of a device consisting of two “rotor” wind turbines with a common axis normal to the air flow into the thermal energy in a wide range of rotational speed of the cylinders. Experimental results on the measurement of thermal power released in the pilot heat generator at different relative angular speeds of cylinder rotation are presented.