THEORETICAL INVESTIGATION OF HEAT PRODUCTION FEASIBILITY BY MEANS OF WIND MECHANICAL PLANTS

A widespread use of wind turbines can fully or partly provide energy for the consumers, but with due regards to certain investments and instability of energy generation. Technologies of using wind energy imply the conversion of the mechanical energy of a wind flow into the electrical or heat energy. The work is concerned with the estimation of the amount of heat in the process of heating liquid coolants and heat-transfer fluids when using wind mechanical plants. In the paper was made a numerical analysis of the temperature rise of the liquid which circulates in a closed loop of a gear-type pump, whose productivity is 3 l/m and which is driven by a wind turbine 5 kW of power capacity under a nominal wind speed of 7 m/s and under cycle duration of 2 s. The analysis showed that the temperature increased by 0.290 °К/s. If such wind speed is observed during one hour, the temperature of 100 kg of water will increase by 8.1°С. Heating of a heat-transfer fluid with a supply of mechanical energy to a working part can be achieved by a centrifugal fan. Assuming that the given process occurs without supplying and removing heat energy (it is adiabatic), for the capacity of 1.5 kW and under the revolution in a range of 1000….3000 r/m, the changes in temperature will range from 0.38 to 0.87 °К/s, but for the capacity of 7.5 kW and under 750 – 1500 r/m, the changes in temperature will range from 0.56 to 1.23 °К/s.

Flow instability in a volute-free centrifugal fan subjected to non-axisymmetric pre-swirl flow from upstream bended inflow tube

The characteristics of internal flow and performance of a centrifugal fan is greatly dependent on the inflow pattern. As the fan is subjected to incoming flow from an upstream tube, the size and geometry of the tube affect the three-dimensional motion of local flow and possibly degrades the aerodynamic performance of the fan. In this work, we performed a numerical investigation on the internal flow in a centrifugal fan subjected to incoming flow from an upstream bended inflow tube of various radii using the steady and unsteady Reynolds-averaged Navier-Stokes (RANS and URANS) simulation approaches. The effects of the non-axisymmetric pre-swirl flow generated due to the curvature of the bended inflow tube are demonstrated by analyzing the internal flow characteristics of the fan, including the spatial distributions and temporal variations of pressure field and streamlines, pressure fluctuations in the upstream tube, the inflow and outflow sections of the impeller, and the circumferential distributions of velocity and pressure in the impeller. The numerical results reveal that as the inflow tube is curved with larger curvature (smaller radius of the bended section), the pre-swirl inflow is strong and deteriorates the static pressure rise and static pressure efficiency of the centrifugal fan more remarkably, and the circumferential non-uniformity of pressure and velocity distributions appears inside of the channels of the fan. As the radius of the bended section increases, the instability of the internal flow gets more pronounced, as represented by the stronger pressure fluctuations at the inflow and outflow sections. The prediction capabilities of RANS and URANS approaches are also analyzed based on the numerical data and we found that the latter is more reliable in predicting the performance of the fan.

Blade shape optimization and internal-flow characteristics of the backward non-volute centrifugal fan

The work proposed the double parameter optimization method of the non-volute centrifugal fan’s blade profile based on the steepest descent method. Total-pressure efficiency improvement at the high-flow area was taken as an optimization objective. A method of applying the steepest descent method to modify the blade profile of backward centrifugal fan is proposed in this paper. The gradient descent direction was analyzed to design the blade profile and obtain the optimal blade profile at a high-flow rate. Besides, numerical simulations were carried out to analyze the aerodynamic performance and the internal flow characteristics of the centrifugal fan by the computational fluid dynamics method. Numerical results showed that the blade profile along the gradient descent was optimized to effectively increase the total pressure and the total pressure efficiency of the original model at the high-flow rate. The steepest descent method for local optimization could improve the fan blade design.

Materials Selection and Design Options Analysis for a Centrifugal Fan Impeller in a Horizontal Conveyor Dryer

Comparative strength analysis of two popular options of the radial centrifugal fan impeller design used in horizontal conveyor dryer for fine-grained raw materials is presented. Three types of materials for impeller manufacturing—ASTM A36 steel, Hardox 450 steel and aluminium alloy 6061-T6 are considered. The finite element method (FEM) has been used to investigate stresses and deformations of the impeller within the operational speed range. Analysis shows that the better design is the impeller made of Hardox 450 steel with a central disk. Although the maximum stress is slightly higher in the blades slot for central disk fitting for this design option, it has greatly reduced stresses in contact edges with two other disks (by 22–38%) and blades bending deformation (by 51%). For this design, the maximum operational rotation speed is 1135 min−1 according to the yield strength with a 15% safety factor, while for basic design, it is 1225 min−1. The rational choice of material depends on maximum value of the yield stress to density ratio as well as taking into account the operating conditions and required fan performance. Recommendations for manufacturing the centrifugal fan impeller related to chosen material are given.

CFD tool application in predicting the behavior of a centrifugal fan designed by one-dimensional theory

Computational fluid dynamics (CFD) is the most current technology in the fluid flow study. Experimental methods for predicting the turbomachinery performance involve greater time consumption and financial resources compared to the CFD approach. The purpose of this article is to present the analysis of CFD simulation results in a centrifugal fan. The impeller was calculated using the one-dimensional theory and the volute the principle of constant angular momentum. The ANSYS-CFX software was used for the simulation. The turbulence model adopted was the SST. The simulation provided the characteristic curves, the pressure and velocity distribution, and the static and total pressure values at impeller and volute exit. An analysis of the behavior of the pressure plots, and the loss and recovery of pressure in the volute was performed. The results indicated the characteristic curves, the pressure and velocity distribution were consistent with the turbomachinery theory. The pressure values showed the static pressure at volute exit was smaller than impeller exit for some flow rate. It caused the pressure recovery coefficient negative. This work indicated to be possible design a centrifugal fan applying the one-dimensional theory and optimize it with the CFD tool.

Evaluate the drying of food waste using cabinet dryer

Purpose In order to reduce leachate from food waste; a food waste dryer with a conventional tray was built, and drying of food waste was investigated. Methods Power of 2.7 kW was used as the heat source, and a centrifugal fan with an air volume of 1300 m3/h, 2800 rpm, and 110 pa was used. The experiments were performed at three temperatures of 50, 60, and 70°C and three air velocities of 1, 1.5, and 2 m/s with a thickness of 3 cm. A conventional tray was used for drying. The Drying kinetics, effective moisture diffusivity, activation energy, and dryer energy consumption during drying of food waste were obtained. Result The minimum drying process was occurred in temperature of 70°C and air velocity of 2 m/s at the 120 min, and the maximum drying process was happened in temperature of 50°C and air velocity of 1 m/s at the 890 min. The energy consumption of drying process had the lowest value at 70°C of temperature and 2 m/s of inlet air velocity. The highest energy consumption value was related to temperature of 50°C and velocity of 1m/s. Effective moisture diffusivity of waste food during the drying process was in the range of 2.74×10− 9-3.65×10− 8 m2/s. The values of energy of activation were determined between 21.596 and 64 KJ/mol. Conclusion Cabinet dryer with a conventional tray can be used for drying food waste in the shortest time with low energy consumption.

Optimization of Multi-Blade Centrifugal Fan Blade Design for Ventilation and Air-Conditioning System Based on Disturbance CST Function

The multi-blade centrifugal fan is commonly used in modern building ventilation and air-conditioning system. However, it does not readily satisfy the increasing demand for energy saving, high efficiency or noise reduction. Its performance is inherently limited by the geometrical structure of single circular arc blades. Q35-type multi-blade centrifugal fan studied as an example by combining the disturbance CST function to parameterize the blades. The optimization parameter change range is confirmed, and test samples are extracted before establishing an RBF proxy model. The NSGA-II algorithm is incorporated, and multi-objective optimization is performed with flow rate and total pressure efficiency as optimization goals. The results show that the fan performance is effectively improved. At the design working point, the air volume of the multi-blade centrifugal fan increases by 1.4 m³/min; at the same time, the total pressure efficiency increases by 3.1%, and the noise is reduced by 1.12 dB, applying the proposed design. The obtained higher fan efficiency can effectively improve performance of the whole ventilation and air-conditioning system. This novel optimization method also has relatively few parameters, which makes it potentially valuable for designing multi-wing centrifugal and other types of fans, providing a new idea for energy saving and emission reduction design of fan.