scholarly journals Study on the Effect of Oval Tubes on Airflow Turbulence Characteristics in Wind Tunnel

2020 ◽  
Vol 38 (2) ◽  
pp. 303-308
Author(s):  
Bo Zhao ◽  
Cheng Fu ◽  
Haitao Pei ◽  
Daxiong Liao ◽  
Bo Zhu
Keyword(s):  
Heat Exchanger ◽  
Wind Tunnel ◽  
Turbulence Intensity ◽  
Flow Direction ◽  
Structural Parameters ◽  
Simulation Method ◽  
Experimental Result ◽  
Turbulence Characteristics ◽  
Tube Heat Exchanger ◽  
Inflow Conditions

The flow Turbulence characteristics of finned oval tube heat exchanger used in wind tunnel were studied by using numerical simulation method. Firstly, the reliability of the numerical method was verified by the experimental results. And then the research was focused on the comparative analysis of the characteristics of turbulent flow downstream of heat exchanger under different inflow conditions, and the influence of the tubes number and fins spacing on the airflow turbulence and the flow field distribution downstream of heat exchanger were obtained too. The results indicate that oval tubes have a significant effect for improving the flow quality when incoming flow is inhomogeneous, and the velocity distribution behind heat exchanger tends to become uniform. Inflow conditions have a slight effect on the turbulence intensity behind heat exchanger, which mainly depends on the structural parameters of heat transfer tubes. The turbulence intensity decays very quickly in the flow direction. The value is reduced to 7.5% at the cross section 600 mm downstream of the heat exchanger inlet, which agrees well with the experimental result.

scholarly journals Blind test comparison of the performance and wake flow between two in-line wind turbines exposed to different atmospheric inflow conditions

2016 ◽  
Author(s):  
Jan Bartl ◽  
Lars Sætran
Keyword(s):  
Wind Tunnel ◽  
Wind Turbines ◽  
Turbulence Intensity ◽  
Wake Flow ◽  
Detached Eddy Simulation ◽  
Mean Velocity ◽  
Blind Test ◽  
The Mean ◽  
Inlet Conditions ◽  
Inflow Conditions

Abstract. This is a summary of the results of the fourth Blind test workshop which was held in Trondheim in October 2015. Herein, computational predictions on the performance of two in-line model wind turbines as well as the mean and turbulent wake flow are compared to experimental data measured at NTNU's wind tunnel. A detailed description of the model geometry, the wind tunnel boundary conditions and the test case specifications was published before the workshop. Expert groups within Computational Fluid Dynamics (CFD) were invited to submit predictions on wind turbine performance and wake flow without knowing the experimental results at the outset. The focus of this blind test comparison is to examine the model turbines' performance and wake development up until 9 rotor diameters downstream at three different atmospheric inflow conditions. Besides a spatially uniform inflow field of very low turbulence intensity (TI = 0.23 %) as well as high turbulence intensity (TI = 10.0 %), the turbines are exposed to a grid-generated atmospheric shear flow (TI = 10.1 %). Five different research groups contributed with their predictions using a variety of simulation models, ranging from fully resolved Reynolds Averaged Navier Stokes (RANS) models to Large Eddy Simulations (LES). For the three inlet conditions the power and the thrust force of the upstream turbine is predicted fairly well by most models, while the predictions of the downstream turbine's performance show a significantly higher scatter. Comparing the mean velocity profiles in the wake, most models approximate the mean velocity deficit level sufficiently well. However, larger variations between the models for higher downstream positions are observed. The prediction of the turbulence kinetic energy in the wake is observed to be very challenging. Both the LES model and the IDDES (Improved Delayed Detached Eddy Simulation) model, however, are consistently managing to provide fairly accurate predictions of the wake turbulence.

Characteristics of Inclined Fin-Tube Heat Exchanger for Compact Air Conditioner

2002 ◽  
Author(s):  
Haruaki Kanematsu ◽  
Kazuhiko Murakami
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
High Performance ◽  
Flow Direction ◽  
Numerical Approach ◽  
Air Conditioner ◽  
Large Space ◽  
Tube Heat Exchanger ◽  
Fin Tube ◽  
Inclined Angle

For saving space at an office or a clean room, it is needed to reduce the space of an air conditioner. It is effective to miniaturize a heat exchanger because it occupies the large space in the air conditioner. Three types of a heat exchanger that are an in-line tube and cut fins type, a staggered tube and cut fins type and a staggered tube and uncut fins type were investigated as four inclined angle tests of 0, 45, 60 and 80 degrees in a heat wind tunnel. The coefficients of flow friction and heat transfer rates were obtained from these experiments, and the characteristics of inclined heat exchanger were clarified by effects of tube arrangements, fin types and inclined angles against flow direction. As a numerical approach, two-dimensional steady models were applied on the staggered tube and the in-line tube by using BFC (Boundary-Fitted Coordinate Method); BFC is available to make grids for any install angle of the heat exchanger. The results of the numerical analysis visualized flow patterns and heat transfer in these heat exchangers. In case of 80-degrees angle, the flow makes dead area in a part of the heat exchanger, and it causes reducing performance of the heat exchanger. These results are available for improve a compact high performance heat exchanger.

Sensitivity Analysis for Shell-and-Tube Heat Exchangers Based on Entropy Production

2012 ◽  
Vol 516-517 ◽  
pp. 419-424
Author(s):  
Guo Rong Zhu ◽  
Xiao Hua Wang ◽  
Hong Biao Huang ◽  
Hu Chen
Keyword(s):  
Heat Transfer ◽  
Sensitivity Analysis ◽  
Heat Exchanger ◽  
Heat Exchange ◽  
Entropy Production ◽  
Heat Exchangers ◽  
Structural Parameters ◽  
Flow Process ◽  
Tube Heat Exchanger ◽  
Shell And Tube

In this article, sensitivity analysis was performed using bidirectional single method with shell-and-tube heat exchanger as the basis and the entropy production in the working process of heat exchanger as target, to explore the optimizing direction for heat exchangers with the objective to reduce entropy production. First, the differential element analysis method was used in a case study of the entropy production of the heat transfer process - including the three heat transfer processes of convective heat exchange inside and outside the pipes and heat conduction across the pipe wall and the flow process - the fluid flowing process inside and outside the pipes, and the typical process parameter - dimensionless inlet heat exchange temperature difference, operation parameter - fluid flow rate inside the pipe and structural parameters - the heat transfer pipe inner diameter and length were used as characteristic parameters, to obtain the sensitivity coefficients under the conditions of the example, being respectively 0.95, 0.3, 0.3 and 0.38. The study in this article can provide some support to the energy efficiency evaluation of heat exchangers.

scholarly journals Investigation of a Portable Wind Tunnel for Energy Harvesting

Aerospace ◽  
2021 ◽  
Vol 8 (12) ◽  
pp. 386
Author(s):  
Haigang Tian ◽  
Tianyi Hao ◽  
Chao Liu ◽  
Han Cao ◽  
Xiaobiao Shan
Keyword(s):  
Wind Tunnel ◽  
Energy Harvesting ◽  
Turbulence Intensity ◽  
Structural Parameters ◽  
Manufacturing Cost ◽  
Airflow Velocity ◽  
Large Space ◽  
Low Speed ◽  
Piezoelectric Energy ◽  
Distribution Uniformity

Current wind tunnels possess a large space volume and high manufacturing cost, which are not suitable for investigating micro energy harvesters. This paper aims to design and fabricate a small, portable and low-speed wind tunnel for energy harvesting. A wind tunnel structure was first designed, a finite element analyses is then utilized to obtain the airflow velocity and turbulence intensity at the testing section, and the influence of the structural parameters of the wind tunnel on the flow field performance is finally investigated to achieve better performance. An experimental prototype of the wind tunnel was fabricated to verify the simulation results. Results demonstrated that the distribution uniformity and average turbulence intensity at the test section decrease first and then increase with the increase of both the diffuser and contraction lengths. The rectifying and damping effect of the honeycomb increase with increasing porosity and thickness. When the diffuser and contraction lengths are 850 mm and 480 mm, respectively, a better distribution uniformity and a lower turbulence intensity can be achieved. Experimental results were in good agreement with the simulation values. The maximum airflow velocity can reach up to 24.74 m/s, and the minimum error was only 1.23%. The designed wind tunnel achieved low-speed, small, portable and stable functions. This work provides an important guidance for further investigating the piezoelectric energy harvesting.

scholarly journals Blind test comparison of the performance and wake flow between two in-line wind turbines exposed to different turbulent inflow conditions

2017 ◽  
Vol 2 (1) ◽  
pp. 55-76 ◽  
Author(s):  
Jan Bartl ◽  
Lars Sætran
Keyword(s):  
Wind Tunnel ◽  
Wind Turbines ◽  
Turbulence Intensity ◽  
Wake Flow ◽  
Turbulent Shear ◽  
Mean Velocity ◽  
Blind Test ◽  
Turbulent Inflow ◽  
The Mean ◽  
Inflow Conditions

Abstract. This is a summary of the results of the fourth blind test workshop that was held in Trondheim in October 2015. Herein, computational predictions on the performance of two in-line model wind turbines as well as the mean and turbulent wake flow are compared to experimental data measured at the wind tunnel of the Norwegian University of Science and Technology (NTNU). A detailed description of the model geometry, the wind tunnel boundary conditions and the test case specifications was published before the workshop. Expert groups within computational fluid dynamics (CFD) were invited to submit predictions on wind turbine performance and wake flow without knowing the experimental results at the outset. The focus of this blind test comparison is to examine the model turbines' performance and wake development with nine rotor diameters downstream at three different turbulent inflow conditions. Aside from a spatially uniform inflow field of very low-turbulence intensity (TI = 0.23 %) and high-turbulence intensity (TI = 10.0 %), the turbines are exposed to a grid-generated highly turbulent shear flow (TI = 10.1 %).Five different research groups contributed their predictions using a variety of simulation models, ranging from fully resolved Reynolds-averaged Navier–Stokes (RANS) models to large eddy simulations (LESs). For the three inlet conditions, the power and the thrust force of the upstream turbine is predicted fairly well by most models, while the predictions of the downstream turbine's performance show a significantly higher scatter. Comparing the mean velocity profiles in the wake, most models approximate the mean velocity deficit level sufficiently well. However, larger variations between the models for higher downstream positions are observed. Prediction of the turbulence kinetic energy in the wake is observed to be very challenging. Both the LES model and the IDDES (improved delayed detached eddy simulation) model, however, consistently manage to provide fairly accurate predictions of the wake turbulence.

Application of Nanofluids in a Shell-and-Tube Heat Exchanger

2013 ◽  
Author(s):  
Jonathan Cox ◽  
Anoop Kanjirakat ◽  
Reza Sadr
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Exchangers ◽  
Nano Particles ◽  
Experimental Result ◽  
Tube Heat Exchanger ◽  
Shell And Tube

Innovations in the field of nanotechnology have potential to improve industrial productivity and performance. One promising applications of this emerging technology is using nanofluids with enhanced thermal properties. Nanofluids, engineered colloidal suspensions consisting of nano-sized particles (less than 100nm) dispersed in a basefluid, have shown potential as industrial cooling fluids due to the enhanced heat transfer characteristics. Experiments are conducted to compare the overall heat transfer coefficient and pressure drop of water vs. nanofluids in a laboratory scale industrial type shell and tube heat exchanger. Three mass particle concentrations, 2%, 4% and 6%, of SiO2-water nanofluids are formulated by dispersing 20 nm diameter nano particles in desalinated water. Nanofluid and tap water are then circulated in the cold and hot loops, respectively, of the heat exchanger to avoid direct particle deposition on heater surfaces. Interestingly, experimental result show both augmentation and deterioration of heat transfer coefficient for nanofluids depending on the flow rate through the heat exchangers. This trend is consistent with an earlier reported observation for heat transfer in micro channels. This trend may be explained by the counter effect of the changes in thermo-physical properties of fluids together with the fouling on the heat exchanger surfaces. The measured pressure drop in the nanofluids flow shows an increase when compared to that of basefluid that could limit the use of nanofluids in heat exchangers for industrial application.

The Numerical Simulation of Iced Conductor and Research of Influencing Factors

2015 ◽  
Vol 734 ◽  
pp. 748-752
Author(s):  
Le Gao ◽  
Ji Cai Hu
Keyword(s):  
Numerical Simulation ◽  
Wind Tunnel ◽  
Influencing Factors ◽  
Turbulence Intensity ◽  
Simulation Method ◽  
Aerodynamic Characteristics ◽  
Key Factors ◽  
Wind Tunnel Tests ◽  
Aerodynamic Parameters ◽  
Micro Topography

In order to study the influence of some key factors such as the turbulence intensity related to micro topography and the diameter of conductor to the aerodynamic characteristics of iced conductor , the model is built based on the characteristic of iced conductor with crescent type ,to simulate the aerodynamic parameters for it and compare with the wind tunnel tests .The results show that we can make supplement reference to the wind tunnel tests through the numerical simulation method. Besides , we adjust the model and make research for the influence of diameter of conductor. The aerodynamic parameters we get can provide some reference to the research of galloping conductor.

Flow field simulation and stress analysis of a shell-tube heat exchanger with spiral bend tubes

2020 ◽  
pp. 2150100
Author(s):  
Binbin Qiu ◽  
Bowen Du ◽  
Yanna Li ◽  
Qingchuan Yang ◽  
Weixiong Chen ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Thermal Stress ◽  
Heat Exchanger ◽  
Flow Field ◽  
Flow Direction ◽  
Straight Tube ◽  
Pressure Drops ◽  
Tube Heat Exchanger ◽  
Porous Media Model ◽  
Experimental Values

The porous media model was improved to simulate the flow field of a shell-tube heat exchanger with spiral bend tubes. The improved porous medium model can be used to control the fluid flow direction. On the tube side, the streamline was along the spiral bend tubes. The fluid velocities and pressure drops on the tube and shell sides agree well with the experimental values. The fluid flow on the shell side is little affected by the spiral bend structure. The thermal stress of the spiral bend tubes was analyzed. The thermal stress of the spiral bend tubes is much smaller than the thermal stress of the straight tube. The thermal stress at the bend part decreases with the increase of bending angles.

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