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Vol 27, No 1 (2018)
- Year: 2018
- Articles: 12
- URL: https://journal-vniispk.ru/1810-2328/issue/view/13141
Article
Numerical Simulation for Falling Film Flow Characteristics of Refrigerant on the Smooth and Structured Surfaces
Abstract
Flow characteristics of a liquid film flowing over a smooth surface and structured surface with the Reynolds number range from 10 to 1121 are studied. The mixture of R21 and R114 refrigerants is used as the test liquid. The 3D transient simulations are taken to capture the liquid film’s dynamic characteristics and spatial distribution. Effects of the inlet dimension, inlet flow rates, surface tension, and surface structuring on the wettability, average velocity, and film thickness are studied systematically. The obtained results show that surface tension is essential for an accurate simulation, while inlet width has no effect on the liquid film parameters in the steady-state flow regime. For low flow rates, wetting area and film thickness both are small, and a suggested range of Reynolds number is chosen to simulate further heat transfer in order to balance the film thickness and dry spots generation. It is shown that a ripple surface structure hinders the liquid film movement, reflected in a lower velocity and a larger film thickness compared to the smooth surface. Lateral movement of a liquid film can also be observed at the structured surface.
1-19
Numerical and Analytical Approaches to Modeling Critical Two-Phase Flow with Granular Layer
Abstract
Based on data obtained in the previous experimental study conducted by the authors, two approaches are proposed for analytical and numerical modeling of a critical two-phase flow in a pipe with a granular layer. An analytical approach is based on a polytrophic model, while a numerical approach was developed using a smoothed particle hydrodynamics method. A model of isenthalpic flow of vapor–water mixture in a fixed bed of solid particles is considered is this study. The mixture expansion process is considered to be polytropic. Similarly to the known problem of gas dynamics of a granular bed, an analytical relationship for calculation of a critical mass velocity was obtained. The results of the calculation based on the analytical and numerical models were compared with the experimental data and agreement between analytical and numerical data and the experiment was observed.
20-29
Experimental Investigation of the Enthalpy and Heat Capacity of Liquid Cesium
Abstract
The enthalpy of liquid cesium in the temperature range from 431 to 976 K was measured by a drop method on an isothermal calorimeter. The approximation equation of enthalpy was obtained and the isobaric heat capacity was determined. The estimated errors in the enthalpy and heat capacity data are 0.5% and 1.5%, respectively. The obtained results are compared with the literature data. The position of the minimum heat capacity of liquid cesium was clarified (733 K). Tables of recommended values of caloric properties in the investigated temperature range were developed.
30-35
Choice of Efficient Linear Scale and Generalized Description of Internal Heat Transfer Coefficient in Porous Structures
Abstract
The expedience of using the ratio of inertial β and viscous α hydraulic coefficients of a fluid flow in porous structures as the characteristic linear scale, when generalizing the experimental data on internal heat transfer in porous media, is shown. It is demonstrated that the correlation Nu = A · Pe, with both criteria based on β/α ratio, most efficiently describes the experimental data for a wide set of ordered and disordered porous structures, including sintered spheres, network materials, sintered felt and cellular foams of high porosity. The coefficient A depends on porosity and is equal to 0.004 for spheres, networks and felts, and 0.0004 for foams. For any specific case the values of α and β coefficients can be readily obtained from testing materials under consideration, control samples, or full-scale articles.
36-44
A Model of Heat and Mass Transfer in Gas Phase in Axial and Turbulent Dispersed Annular Flows
Abstract
The problem of simulation of heat and mass transfer in the gas phase of film devices in the regime of weak and strong phase interaction has been solved. The Deissler three-layer model of turbulent boundary layer was used. Expressions have been derived for calculating the average Nusselt and Sherwood numbers. Examples of calculations for various conditions of phase interaction and comparison with experimental data are shown.
45-50
Application of Passive Schemes for Pyroelectric Conversion of Low-Potential Heat
Abstract
The paper presents the results of experimental pyroelectric studies of PZT piezoceramics by the methods of open-circuit voltage and short-circuit current. Pyroresponses resulted from action of modulated laser radiation on a pyroelement. It is shown that using altering the temperature of even a single pyroelement by 8.5 K enables production of a maximum electricenergy output power of about 16 μW on a 10 MΩ resistor at an open-circuit voltage of ∼ 90 V and a short-circuit current of ∼ 0.18 μA. The presented research contributes to the development of pyrogenerators for conversion of thermal energy using commercially available piezo-ceramics.
51-57
The Influence of Inlet Disturbances on the Post-Stall Behaviors in Compression System
Abstract
The object of this paper is to provide a reliable tool to carry out the parametrical studies of post-stall behaviors in multistage axial compression systems. An adapted version of the 1.5D Euler equations with additional source terms is discretized with a finite volume method and are solved in time by a fourth-order Runge–Kutta scheme. The equations are discretized at mid-span both inside the blade rows and the non-bladed regions. The source terms express the blade-flow interactions and are estimated by calculating the velocity triangles for each blade row. Additional source terms are introduced to represent the effects of inlet disturbances on post-stall behaviors and the physical analysis is therefore proposed to explain the phenomenon.
58-71
Heat and Work of the Chemical Systems
72-81
A New Approach for Modeling of Industrial Adsorption Column
Abstract
A theoretical analysis of the effect of velocity radial nonuniformity on nonstationary gas-solid adsorption processes in the column apparatuses is presented. The average concentration model, where the radial velocity component in the gas phase is equal to zero (in cases of a constant velocity radial nonuniformity along the column height), is used in the cases of an axial modification of the radial nonuniformity of the axial velocity components in the gas phase. The use of experimental data, for average concentrations in the gas phase at the column end, for a concrete process (physical or chemical adsorption), permits obtaining the gas phase model parameters related with the radial nonuniformity of the velocity. These parameter values allow using the average concentration model for modeling different adsorption processes.
82-97
Single-Phase Convective Heat Transfer of Water and Aqua Ethylene Glycol Mixture in a Small-Diameter Tube
Abstract
A tailor-made convective heat transfer test facility is constructed to study the single-phase convective heat transfer of deionized water and 30 vol% and 60 vol% aqua–ethylene glycol in a stainless steel tube of 4 mm in inner diameter and 1 m in length. The heat flux is varied between 1 and 4 kW·m−2 and for mass flux ranging from 160 to 475 kg·m−2 s−1. The experiments were predominantly conducted only for laminar flow regime. Finally, the heat transfer coefficient is recorded and compared with the conventional theories. It is observed that the presence of ethylene glycol in water decreases the heat transfer coefficient by more than 50%, due to the decreased Reynolds number and thermal conductivity of the mixture.
98-105
MHD Three-Dimensional Flow of Viscoelastic Fluid with Convective Surface Boundary Condition
Abstract
This article reports the magnetohydrodynamic (MHD) three-dimensional flow of viscoelastic fluid over a stretching surface with heat transfer. Mathematical analysis is formulated using convective boundary conditions. Computations of dimensionless velocity and temperature fields are presented. The tabulated values show excellent agreement between present and previous limiting analysis. Graphical results show the impact of embedded parameters entering into the problem.
106-118
Loop Thermosyphon with Vapor Chamber Installation for Energy Thrift in a Chilli Oven
Abstract
This research presents a case study of applying a loop thermosyphon with a vapor chamber (LTVC) for a chilli oven (O/LTVC). The LTVC had a dimension evaporator chamber size of 200 mm × 200 mm ×75 mm (W×L×H) with a shape of eight-loops thermosyphon, the lengths of adiabatic and condenser sections were 824 mm and 800 mm, respectively. The air velocity was 1.5, 2.0 and 2.5 m/s with a air inlet operating temperature being 60, 70, and 80°C. The working fluid chosen for our study was distilled water with a filling ratio of 40% by chamber volume. The O/LTVC provided regular temperature distribution and a good thermal performance. The quality of color measurement and sensory of the chilli oven exceeded the manufacturing standard. The LPG consumption had a thrift of 0.3 $US/kg after drying of 280 kg chilli. Obviously, the O/OTCV has a good oven processing.
119-135