scholarly journals Dynamics of Cross-Flow Heat Exchanger Tubes With Multiple Loose Supports

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Anwar Sadath ◽  
Harish N. Dixit ◽  
C. P. Vyasarayani
Keyword(s):  
Heat Exchanger ◽  
Flow Velocity ◽  
Galerkin Approximation ◽  
Cross Flow ◽  
Beam Equation ◽  
Critical Flow Velocity ◽  
Flow Heat ◽  
Delay Differential ◽  
The Impact ◽  
Loose Support

Dynamics of cross-flow heat exchanger tubes with two loose supports has been studied. An analytical model of a cantilever beam that includes time-delayed displacement term along with two restrained spring forces has been used to model the flexible tube. The model consists of one loose support placed at the free end of the tube and the other at the midspan of the tube. The critical fluid flow velocity at which the Hopf bifurcation occurs has been obtained after solving a free vibration problem. The beam equation is discretized to five second-order delay differential equations (DDEs) using Galerkin approximation and solved numerically. It has been found that for flow velocity less than the critical flow velocity, the system shows a positive damping leading to a stable response. Beyond the critical velocity, the system becomes unstable, but a further increase in the velocity leads to the formation of a positive damping which stabilizes the system at an amplified oscillatory state. For a sufficiently high flow velocity, the tube impacts on the loose supports and generates complex and chaotic vibrations. The impact loading on the loose support is modeled either as a cubic spring or a trilinear spring. The effect of spring constants and free-gap of the loose support on the dynamics of the tube has been studied.

Vibrations of a Simply Supported Cross Flow Heat Exchanger Tube With Axial Load and Loose Supports

2017 ◽  
Vol 12 (5) ◽  
Author(s):  
Anwar Sadath ◽  
V. Vinu ◽  
C. P. Vyasarayani
Keyword(s):  
Flow Velocity ◽  
Axial Load ◽  
Galerkin Approximation ◽  
Period Doubling ◽  
Critical Flow ◽  
Axial Loads ◽  
Critical Flow Velocity ◽  
Delay Differential ◽  
Loose Support ◽  
Flow Velocities

In this work, a mathematical model is developed for simulating the vibrations of a single flexible cylinder under crossflow. The flexible tube is subjected to an axial load and has loose supports. The equation governing the dynamics of the tube under the influence of fluid forces (modeled using quasi-steady approach) is a partial delay differential equation (PDDE). Using the Galerkin approximation, the PDDE is converted into a finite number of delay differential equations (DDE). The obtained DDEs are used to explore the nonlinear dynamics and stability characteristics of the system. Both analytical and numerical techniques were used for analyzing the problem. The results indicate that, with high axial loads and for flow velocities beyond certain critical values, the system can undergo flutter or buckling instability. Post-flutter instability, the amplitude of vibration grows until it impacts with the loose support. With a further increase in the flow velocity, through a series of period doubling bifurcations the tube motion becomes chaotic. The critical flow velocity is same with and without the loose support. However, the loose support introduces chaos. It was found that when the axial load is large, the linearized analysis overestimates the critical flow velocity. For certain high flow velocities, limit cycles exist for axial loads beyond the critical buckling load.

Fluid-Elastic Instability of Normal Square Tube Bundles in Two-Phase Cross Flow

2010 ◽  
Author(s):  
Woo Gun Sim ◽  
Mi Yeon Park
Keyword(s):  
Heat Exchanger ◽  
Flow Velocity ◽  
Dynamic Instability ◽  
Cross Flow ◽  
Elastic Instability ◽  
Two Phase ◽  
Critical Flow Velocity ◽  
Tube Heat Exchanger ◽  
Tube Bundles ◽  
Square Array

Some knowledge on damping and fluid-elastic instability is necessary to avoid flow-induced-vibration problems in shell and tube heat exchanger such as steam generator. Fluid-elastic instability is the most important vibration excitation mechanism for heat exchanger tube bundles subjected to the cross flow. Experiments have been performed to investigate fluid-elastic instability of normal square tube bundles, subjected to two-phase cross flow. The test section consists of cantilevered flexible cylinder(s) and rigid cylinders of normal square array. From a practical design point of view, fluid-elastic instability may be expressed simply in terms of dimensionless flow velocity and dimensionless mass-damping parameter. For dynamic instability of cylinder rows, added mass, damping and critical flow velocity are evaluated. The Fluid-elastic instability coefficient is calculated and then compared to existing results given for tube bundles in normal square array.

A Study of the Impact Dynamics of Loosely Supported Heat Exchanger Tubes

1989 ◽  
Vol 111 (4) ◽  
pp. 394-401 ◽  
Author(s):  
H. G. D. Goyder ◽  
C. E. Teh
Keyword(s):  
Heat Exchanger ◽  
Cross Flow ◽  
Excitation Level ◽  
Impact Dynamics ◽  
Heat Exchanger Tube ◽  
Wear Rates ◽  
Strongly Nonlinear ◽  
The Impact ◽  
Loose Support ◽  
Exchanger Tube

Heat exchanger tube bundles may be damaged by vibration induced from the cross flow. This damage generally occurs at the tube supports where the tube is only loosely supported. The loose support results in the tube motion being strongly nonlinear with very complicated dynamics. Some theoretical equations for the tube dynamics and wear rates are investigated by using dimensional analysis, physical modeling and numerical simulations. From the analysis of these equations, some simple formulas are developed which show the influence of excitation level and tube-to-support clearance on the tube response.

scholarly journals Numerical and experimental analysis of a tube-and-fin cross-flow heat exchanger with a controlled non-uniform inflow of gas

2021 ◽  
Vol 323 ◽  
pp. 00005
Author(s):  
Tomasz Bury ◽  
Małgorzata Hanuszkiewicz-Drapała
Keyword(s):  
Heat Exchanger ◽  
Water Temperature ◽  
Experimental Test ◽  
Experimental Analysis ◽  
Cross Flow ◽  
Ansys Fluent ◽  
Flow Rates ◽  
Air Inlet ◽  
Flow Heat ◽  
The Impact

The paper presents results of numerical and experimental analyses of a fin-and-tube air-water heat exchanger. The analysed device is a one-row heat exchanger with finned elliptical tubes. The aim of the analyses is to investigate the impact of a controlled non-uniform inflow of air on the heat exchanger performance. The heat exchanger was modelled numerically using the ANSYS Fluent program. The developed model was applied to simulate the heat exchanger operation in the conditions of the uniform inflow of air. Cases of an uncontrolled non-uniform inflow of gas were investigated experimentally, using a purpose-designed test station. On the experimental test station the effect of a controlled non-uniform air inflow was also achieved by placing appropriately shaped inserts in the air inlet duct, directing the air partially to the region of the water inlet header. By controlling the gas inflow, it was possible to significantly enhance the heat exchanger performance. The results of the multivariate numerical analyses conducted for the adopted parameters of the mediums (air and water volumetric flow rates and water temperature) show that the heat exchanger performance can be improved by up to almost 5% compared to a variant with a natural non-uniform air inflow taking place in the exchanger under consideration.

Heat and Mass Transfer to Air in a Cross Flow Heat Exchanger with Surface Deluge Cooling

2016 ◽  
Vol 24 (01) ◽  
pp. 1650002 ◽  
Author(s):  
Andrea Diani ◽  
Luisa Rossetto ◽  
Roberto Dall’Olio ◽  
Daniele De Zen ◽  
Filippo Masetto
Keyword(s):  
Heat Exchanger ◽  
Heat Flow ◽  
Flow Rate ◽  
Data Center ◽  
Heat Dissipation ◽  
Cross Flow ◽  
Critical Conditions ◽  
Heat Flow Rate ◽  
External Temperature ◽  
Flow Heat

Cross flow heat exchangers, when applied to cool data center rooms, use external air (process air) to cool the air stream coming from the data center room (primary air). However, an air–air heat exchanger is not enough to cope with extreme high heat loads in critical conditions (high external temperature). Therefore, water can be sprayed in the process air to increase the heat dissipation capability (wet mode). Water evaporates, and the heat flow rate is transferred to the process air as sensible and latent heat. This paper proposes an analytical approach to predict the behavior of a cross flow heat exchanger in wet mode. The theoretical results are then compared to experimental tests carried out on a real machine in wet mode conditions. Comparisons are given in terms of calculated versus experimental heat flow rate and evaporated water mass flow rate, showing a good match between theoretical and experimental values.

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