An Improved Design of Threaded Closures for Screw Plug (Breech Lock) Heat Exchangers

2016 ◽  
Author(s):  
Haresh K. Sippy ◽  
Dipak K. Chandiramani
Keyword(s):  
Thermal Expansion ◽  
Heat Exchangers ◽  
Tube Bundle ◽  
Pressure Vessels ◽  
Typical Application ◽  
Heat Transfer Efficiency ◽  
Shrink Fitting ◽  
Shell And Tube ◽  
Improved Design ◽  
Screw Threads

Threaded closures for pressure vessels have been in use for decades. Much work has been done to develop convenient, safe and economical threaded closures. Threaded closures are used when there is a need for opening the vessel either for maintenance or as part of its operation. Heat Exchangers are a typical application where there is a need for opening the vessel and cleaning the tubes at regular intervals to maintain the heat transfer efficiency. These are known as Breech Lock or Screw Plug Exchangers. These are basically U-tube exchangers. The channel side operates at high temperature and pressure and it has a threaded end closure. In some designs, the shell side may also be at high pressure. The tube bundle is removable without having to dismantle the channel or disconnect the nozzles from the pipeline. Thus screw plug exchangers help to reduce fabrication cost and reduce time for in-service maintenance. The major problem encountered with the use of such end closures are 1) Jamming of the threaded plug, due to deformation of the channel barrel. Thus the opening of the end closure by unscrewing becomes a difficult task. With the increase in operating temperatures and pressures, the problems become more severe, due to which, users are not inclined to use these type of end closures. A study was undertaken to assess the reasons for bulging of the end of the channel which caused jamming of the screw threads and also for leakage through the gasket. By shrink fitting a ring over the end of the channel, the deformation was reduced, enabling easy opening of the cover. 2) The leakage through the gasket between the shell and tubesheet, causing the intermixing of shell and tube-side fluids. This on analysing was found that the additional forces were acting on the gasket due to thermal expansion of the internals. This led to changing to a gasket that could withstand the forces and pressure. Leakage through the gasket was prevented by analysing the additional forces acting on the gasket due to thermal expansion of the internals and changing to a gasket that could withstand the forces and pressure.

Design of Threaded Closures for High Pressure Screw Plug Heat Exchangers Designed to ASME Section VIII Div. 2

2017 ◽  
Author(s):  
Haresh K. Sippy ◽  
Dipak K. Chandiramani
Keyword(s):  
High Pressure ◽  
Heat Exchangers ◽  
Pressure Vessels ◽  
Typical Application ◽  
High Pressure And Temperature ◽  
Heat Transfer Efficiency ◽  
Allowable Stresses ◽  
Section Viii ◽  
Screw Threads ◽  
Good Access

Threaded closures for pressure vessels have been in use for decades. Much work has been done to develop safe threaded closures. Threaded closures are very advantageous when there is a need for opening the vessel at intervals for maintenance purposes. Heat Exchangers are a typical application where there is a need for opening the vessel to get good access to the inside and outside of the tubes for mechanical cleaning, thus maintaining heat transfer efficiency. These are known as Screw Plug Heat Exchangers and are basically U-tube heat exchangers. The tube side normally operates at high pressure and temperature and is closed by a threaded end closure. Two problems are often encountered in screw plug heat exchangers. These are: 1. Leakage through the gasket at the tubesheet causing intermixing of shell side and tube side fluids, which is unacceptable 2. Jamming of the threaded plug due to deformation of channel barrel In an earlier paper (PVP2016-63137) these problems were studied for a vessel designed to ASME Section VIII Div. 1. It was found that leakage through the tubesheet gasket could be eliminated by changing the gasket to a grooved metal gasket with covering layers as defined in ASME B16.20. Preventing leakage from the tubesheet gasket is extremely necessary to get the ultra-low sulphur requirements for clean fuel. In the work reported in this paper, a procedure for obtaining leak-free performance on a vessel designed to ASME Section VIII Div. 2 was developed and verified using a prototype. Code formulae for calculation of thickness of various parts normally consider only the need to limit the component stress to be within allowable limits defined in the Code. Allowable stresses for Section VIII Div. 2 construction may be about 18 % higher than the allowable stress for Section VIII Div. 1 construction at design temperature, thereby allowing thinner sections for the same design conditions. As the thinner sections would deform more, the likelihood of jamming of the end cover could be more severe in ASME Section VIII Div. 2 constructions. Hence this study was additionally undertaken to verify the adequacy of the earlier proposed design methodology, i.e., use of an additional steel ring shrunk fit to the end of the channel to prevent flaring of the channel and jamming of screw threads, for Section VIII Div. 2 constructions.

On Thermal Expansion Induced Stresses in U-Bends of Shell-and-Tube Heat Exchangers

1979 ◽  
Vol 101 (4) ◽  
pp. 634-639 ◽  
Author(s):  
Krishna P. Singh ◽  
Maurice Holtz
Keyword(s):  
Thermal Expansion ◽  
Heat Exchangers ◽  
Structural Characteristics ◽  
Design Tool ◽  
Design Variables ◽  
Depth Study ◽  
Shell And Tube ◽  
Induced Stresses ◽  
Critical Regions ◽  
Effective Design

An analytical method is herein developed to evaluate the stress field in the critical regions of a U-tube subject to differential thermal expansion. The solution is intended to be used as a design tool to conveniently study the variation of geometric parameters on the U-tube stress distribution. Those design variables which have significant effects on the structural characteristics of the U-tube are identified by an in-depth study of a typical example problem. Some effective design remedies are also discussed.

A numerical study of heat transfer in the in-line tube bundle under pulsating fluid flow conditions

Vestnik IGEU ◽  
2019 ◽  
pp. 12-21
Author(s):  
A.I. Khaibullina ◽  
A.R. Khairullin
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Numerical Study ◽  
Tube Bundle ◽  
Cross Flow ◽  
Pulsating Flow ◽  
Operating Parameters ◽  
Flow Conditions ◽  
Study Results ◽  
Shell And Tube

Shell-and-tube heat exchangers are widely used in different industries. Even a small increase in the efficien-cy of shell-and-tube heat exchangers can lead to significant energy savings. One of the ways to improve the efficiency of shell-and-tube heat exchangers is the use of pulsating flows for the enhancement of heat ex-change. Despite the fact that heat transfer in the tube bundle cross flow in steady-state conditions has been studied quite well, there is limited data on heat transfer in pulsating flow, which means that the problem of finding regularities of heat transfer with pulsating flows in tube bundles is still important. The work employs the incompressible Reynolds averaged Naviere-Stokes (URANS) equations and the continuity equation. Heat transfer is described by the convective heat transfer (Fourier-Kirchhoff) equation. The calculations are performed using Ansys Fluent. A numerical study has been conducted of the effects of forced asymmet-rical pulsating flow on heat exchange in in-line tube bundle cross-flow conditions. In the numerical experi-ment the Reynolds number Re ranged from 1000 to 2000, the relative pulsating amplitude A/D – from 1 to 2, the Strouhal number Sh – from 0,77 to 1,51, the Prandtl number and the duty cycle had fixed values: Pr = 7,2,  = 0,25. The relative transverse and longitudinal pitch was s1,2/D = 1,3. It has been found that pulsating flows lead to the enhancement of heat transfer in the whole range of the studied operating parameters. An increase in A/D and Sh leads to bigger Nusselt number Nu. An increase in the Re number leads to a de-crease in the Nu ratio in pulsating and steady flow conditions. The general correlation obtained based on the numerical study results can be used to predict heat transfer in a pulsating flow in the range of the studied geometric and operating parameters. More research is needed to predict heat transfer in a wider range of operating parameters and with other tube bundle configurations.

Numerical Analytic Approach to a Calculation of a Thermal Stress State of Shell and Tube Heat Exchangers

2013 ◽  
Author(s):  
Igor Laskin ◽  
Boris Volfson
Keyword(s):  
Numerical Modeling ◽  
Heat Exchangers ◽  
Analytic Solution ◽  
Tube Bundle ◽  
Shell Elements ◽  
Analytic Methods ◽  
Distribution Calculation ◽  
Element Simulation ◽  
Shell And Tube ◽  
Comparison Of The Results

Nowadays, a stress calculation of shell and tube heat exchangers’ elements is based either on analytic methods described in ASME, TEMA, EN, GOST and other standards or on numerical modeling using FEA. The main disadvantage of the analytic methods is that they can be applied only to certain apparatuses’ designs and it is very difficult or even impossible to use them with non-typical constructions. Otherwise, such a calculation is easy to perform with modeling by FEA. However, a direct finite element simulation of several thousands of tubes, which can be designed in one heat exchanger, makes the task very time-consuming and the resulting model very big and computation-intensive. This paper examines a typical model, which includes 3.5 million nodes and more than 3 million elements. We offer a numerical analytic solution of this task, which consists in modeling of a tube bundle by an orthotropic continuum with equivalent properties. The comparison of the results of a temperature distribution calculation and the stress-strain distribution calculation using direct numerical modeling of the tubes in the tube bundle by shell elements from one hand, and of the suggested numerical analytic solution from another, shows that these results do match closely enough to practice.

scholarly journals Numerical Investigation on Effect of Thermal Expansion Joint in a Tube Holder Insulating Section in Shell and Tube Heat Exchanger

2021 ◽  
Vol 4 (2) ◽  
pp. 14-20
Author(s):  
Amirhossein Khayyami nejad ◽  
Hadi Amirshaghaghi ◽  
Navid P.Khabazi ◽  
Pourya Shadkami Ahvazi
Keyword(s):  
Thermal Expansion ◽  
Heat Exchangers ◽  
Thermal Stresses ◽  
Applied Pressure ◽  
The Finite Element Method ◽  
Expansion Joint ◽  
Ansys Software ◽  
Expansion Joints ◽  
Tube Heat Exchanger ◽  
Shell And Tube

As shell and tube heat exchangers become more widely used, their challenges are becoming more and more important. In some of these heat exchangers, an insulating section is used to reduce thermal stresses on the tube holder section. In this study, the effect of the presence and absence of expansion joints in this insulation section has been investigated. For this purpose, the desired section with and without expansion joint has been analyzed using the finite element method (FEM) in ANSYS software. Based on the results, it was found that the thermal expansion joint reduces thermal deformation and significantly reduces the rate of stresses in the mentioned section, which increases the life of the tube holder section. Also, the presence of expansion joints reduces the applied pressure to the insulation tape around the tube holder section, which increases the life of the insulation tape around the insulation section.

Shellside Waterflow-Induced Tube Vibration in Heat Exchanger Configurations With Tube Pitch-to-Diameter Ratio of 1.42

1989 ◽  
Vol 111 (4) ◽  
pp. 441-449 ◽  
Author(s):  
H. Halle ◽  
J. M. Chenoweth ◽  
M. W. Wambsganss
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Tube Bundle ◽  
Diameter Ratio ◽  
Design Parameters ◽  
Comprehensive Investigation ◽  
Flow Area ◽  
Shell And Tube ◽  
Vibration Coupling ◽  
Tube Pitch

The pitch-to-diameter ratio (P/D) of the tube layout in shell-and-tube heat exchangers is one of the major parameters with which the designer may control heat transfer and pressure drop and facilitate mechanical cleaning. As part of a comprehensive investigation of waterflow-induced tube vibration in an industrial-size research heat exchanger, various configurations characterized by different design parameters, including P/D ratio, had been investigated. To provide a comparison with previous data obtained with P/D = 1.25, this paper presents the results of a study of eight different tube bundle configurations with P/D = 1.42. Four equilaterally spaced tube layout patterns and two baffle edge orientations were investigated. The results indicate that the greater flow area of the P/D = 1.42 configuration increases flow penetration into the bundle, reduces the tube-to-tube vibration coupling and generally provides less well-defined, even though sometimes improved, fluidelastic instability thresholds.

An Experimental Study of Shell-and-Tube Heat Exchangers With Continuous Helical Baffles

2007 ◽  
Vol 129 (10) ◽  
pp. 1425-1431 ◽  
Author(s):  
B. Peng ◽  
Q. W. Wang ◽  
C. Zhang ◽  
G. N. Xie ◽  
L. Q. Luo ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Exchangers ◽  
Tube Bundle ◽  
Shell Side ◽  
Helical Baffle ◽  
Shell And Tube

Two shell-and-tube heat exchangers (STHXs) using continuous helical baffles instead of segmental baffles used in conventional STHXs were proposed, designed, and tested in this study. The two proposed STHXs have the same tube bundle but different shell configurations. The flow pattern in the shell side of the heat exchanger with continuous helical baffles was forced to be rotational and helical due to the geometry of the continuous helical baffles, which results in a significant increase in heat transfer coefficient per unit pressure drop in the heat exchanger. Properly designed continuous helical baffles can reduce fouling in the shell side and prevent the flow-induced vibration as well. The performance of the proposed STHXs was studied experimentally in this work. The heat transfer coefficient and pressure drop in the new STHXs were compared with those in the STHX with segmental baffles. The results indicate that the use of continuous helical baffles results in nearly 10% increase in heat transfer coefficient compared with that of conventional segmental baffles for the same shell-side pressure drop. Based on the experimental data, the nondimensional correlations for heat transfer coefficient and pressure drop were developed for the proposed continuous helical baffle heat exchangers with different shell configurations, which might be useful for industrial applications and further study of continuous helical baffle heat exchangers. This paper also presents a simple and feasible method to fabricate continuous helical baffles used for STHXs.

Vibration of Tube Bundles Subjected to Two-Phase Cross-Flow

1985 ◽  
Vol 107 (4) ◽  
pp. 335-343 ◽  
Author(s):  
M. J. Pettigrew ◽  
J. H. Tromp ◽  
J. Mastorakos
Keyword(s):  
Heat Exchangers ◽  
Tube Bundle ◽  
Cross Flow ◽  
Elastic Instability ◽  
Steam Generators ◽  
Two Phase ◽  
Vibration Excitation ◽  
Mass Fluxes ◽  
Excitation Mechanisms ◽  
Shell And Tube

Two-phase cross-flow exists in many shell-and-tube heat exchangers such as condensers, reboilers and nuclear steam generators. Thus we are conducting a comprehensive program to study tube bundle vibrations subjected to two-phase cross-flow. This paper presents the results of experiments on a normal-triangular and a normal-square tube bundle, both of p/d = 1.47. The bundles were subjected to air-water mixtures to simulate realistic vapor qualities and mass fluxes. Vibration excitation mechanisms were deduced from vibration response measurements. Results on damping, hydrodynamic mass, fluid-elastic instability and random turbulence excitation in two-phase cross-flow are presented.

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