The stress characteristics of plate-fin structures at the different operation parameters of LNG heat exchanger

In this paper, the stresses of plate-fin structures at the different operation parameters were analyzed in actual operation process of LNG plate-fin heat exchanger based on finite element method and thermal elastic theory. Stress characteristics of plate-fin structures were investigated at the different operation parameters of that. The results show that the structural failure of plate-fin structures is mainly induced by the maximum shear stress at the brazing filler metal layer between plate and fin while by the maximum normal stress in the region of brazed joint near the fin side. And a crack would initiate in brazed joint near the fin side. The maximum normal stress is also main factor to result in the structural failure of plate-fin structures at the different temperature difference (between Natural Gas (NG) and Mixture Refrigerant (MR)), MR temperature and NG pressure of LNG heat exchanger. At the same time, the peak stresses obviously increase as the temperature difference, MR temperature and NG pressure increase. These results will provide some constructive instructions in the safe operation of LNG plate-fin heat exchanger in a large-scale LNG cold-box.

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Fatigue Variability of Alloy 625 Thin-Tube Brazed Specimens

Metals ◽

10.3390/met11081162 ◽

2021 ◽

Vol 11 (8) ◽

pp. 1162

Author(s):

Seulbi Lee ◽

Hanjong Kim ◽

Seonghun Park ◽

Yoon Suk Choi

Keyword(s):

Fatigue Life ◽

Heat Exchanger ◽

Room Temperature ◽

Metal Layer ◽

Outer Diameter ◽

Multiple Crack ◽

Joint Failure ◽

Alloy 625 ◽

Thin Tube ◽

Brazed Joint

As an advanced heat exchanger for aero-turbine applications, a tubular-type heat exchanger was developed. To ensure the optimum performance of the heat exchanger, it is necessary to assess the structural integrity of the tubes, considering the assembly processes such as brazing. In this study, fatigue tests at room temperature and 1000 K were performed for 0.135 mm-thick alloy 625 tubes (outer diameter of 1.5 mm), which were brazed to the grip of the fatigue specimen. The variability in fatigue life was investigated by analyzing the locations of the fatigue failure, fracture surfaces, and microstructures of the brazed joint and tube. At room temperature, the specimens failed near the brazed joint for high σmax values, while both brazed joint failure and tube side failure were observed for low σmax values. The largest variability in fatigue life under the same test conditions was found when one specimen failed in the brazed joint, while the other specimen failed in the middle of the tube. The specimen with brazed joint failure showed multiple crack initiations circumferentially near the surface of the filler metal layer and growth of cracks in the tube, resulting in a short fatigue life. At 1000 K, all the specimens exhibited failure in the middle of the tube. In this case, the short-life specimen showed crack initiation and growth along the grains with large through thickness in addition to multiple crack initiations at the carbides inside the tube. The results suggest that the variability in the fatigue life of the alloy 625 thin-tube brazed specimen is affected by the presence of the brazed joint, as well as the spatial distribution of the grain size and carbides.

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Experimental Investigation of Lab-Scale, Heat Exchanger Prototypes Designed to Provide Refugia for Trout

ASME 2021 15th International Conference on Energy Sustainability ◽

10.1115/es2021-63934 ◽

2021 ◽

Author(s):

Rajib Uddin Rony ◽

Adam Gladen ◽

Sarah LaVallie ◽

Jeremy Kientz

Keyword(s):

Heat Exchanger ◽

Temperature Difference ◽

Large Scale ◽

Cold Water ◽

Cooling System ◽

Tube Bundle ◽

Small Scale ◽

Scaled Model ◽

Average Temperature ◽

Average Temperature Difference

Abstract In recent years Spring Creek in South Dakota, a popular fishing location, has been experiencing higher surface water temperatures, which negatively impact cold-water trout species. One potential solution is to provide localized refugia of colder water produced via active cooling. The present work focuses on the design and testing of a small-scale prototype heat exchanger, for such a cooling system. Various prototypes of the heat exchanger were tested in a 1/10th-scaled model of a section of the creek. A staggered, tube-bundle heat exchanger was used. The prototypes consisted of just the heat exchanger placed directly in the scaled-stream model and of the heat exchanger placed inside an enclosure with an aperture. The results show that, without the enclosure, the average temperature difference is 0.64 °C, with a corresponding heat transfer requirement of 1.63 kW/°C of cooling. However, with an enclosure, the average temperature difference is 1.95 °C, which required 0.59 kW/°C of cooling. Modifications to the enclosure decrease the average temperature difference but also decrease the standard deviation of the temperature difference. Thus, the cooling effect is more evenly spread throughout the water in the enclosure. This indicates that the enclosure design can be used to balance the requirements of obtaining a desired temperature difference with a relatively low spatial variation in that temperature difference. These results will be used to guide the design of the large-scale heat exchanger prototype.

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Some Observations on the Banding of Glacier Ice

Journal of Glaciology ◽

10.3189/002214355793702262 ◽

1955 ◽

Vol 2 (17) ◽

pp. 502-506 ◽

Cited By ~ 11

Author(s):

N. Untersteiner

Keyword(s):

Shear Stress ◽

Normal Stress ◽

Maximum Shear Stress ◽

Stress System ◽

Outward Appearance ◽

Glacier Tongue ◽

Maximum Normal Stress ◽

Glacier Ice

AbstractThe distribution of fine banding (foliation) on the surface of a flat glacier tongue was studied. The conclusions reached are that fine banding seems to be neither of sedimentary origin nor to be the representation of a straightforward stress system. In the present case, foliation seems to be connected with ice falls.Other bands definitely not belonging to the fine banding system were plotted irrespective of their outward appearance. Statistically, their preferred spacial directions correspond to the directions of either maximum shear stress or maximum normal stress (tension).

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Effect of Loading Frequency Ratio on Multiaxial Asynchronous Fatigue Failure of 30CrMnSiA Steel

Materials ◽

10.3390/ma14143968 ◽

2021 ◽

Vol 14 (14) ◽

pp. 3968

Author(s):

Tianqi Liu ◽

Xinxin Qi ◽

Xinhong Shi ◽

Limin Gao ◽

Tian Zhang ◽

...

Keyword(s):

Shear Stress ◽

Fatigue Life ◽

Normal Stress ◽

Frequency Ratio ◽

Prediction Models ◽

Maximum Shear Stress ◽

Fatigue Crack Initiation ◽

Loading Frequency ◽

Obvious Effect ◽

Maximum Normal Stress

Multiaxial asynchronous fatigue experiments were carried out on 30CrMnSiA steel to investigate the influence of frequency ratio on fatigue crack initiation and propagation. Test results show that the surface cracks initiate on the maximum shear stress amplitude planes with larger normal stress, propagate approximately tens of microns, and then propagate along the maximum normal stress planes. The frequency ratio has an obvious effect on the fatigue life. The variation of normal and shear stress amplitudes on the maximum normal stress plane induces the crack retardation, and results in that the crack growth length is longer for the constant amplitude loading than that for the asynchronous loading under the same fatigue life ratio. A few fatigue life prediction models were employed and compared. Results show that the fatigue life predicted by the model of Bannantine-Socie cycle counting method, section critical plane criterion and Palmgren-Miner’s cumulative damage rule were more applicable.

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A large scale heat exchanger with polygonally configurated heat pipeunits

10.2514/6.1978-393 ◽

1978 ◽

Cited By ~ 1

Author(s):

T. KOIZUMI ◽

S. FURUYA ◽

K. MATSUMOTO ◽

K. KARAWAWA

Keyword(s):

Heat Exchanger ◽

Large Scale

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Cohesive Zone Model for the Interface of Multiwalled Carbon Nanotubes and Copper: Molecular Dynamics Simulation

Journal of Nanotechnology in Engineering and Medicine ◽

10.1115/1.4029462 ◽

2014 ◽

Vol 5 (3) ◽

Cited By ~ 8

Author(s):

Ibrahim Awad ◽

Leila Ladani

Keyword(s):

Carbon Nanotubes ◽

Normal Stress ◽

Multiwalled Carbon Nanotubes ◽

Cohesive Zone ◽

Large Scale ◽

Cohesive Zone Model ◽

Dynamics Simulation ◽

Zone Model ◽

Multiwalled Carbon ◽

Significant Difference

Due to their superior mechanical and electrical properties, multiwalled carbon nanotubes (MWCNTs) have the potential to be used in many nano-/micro-electronic applications, e.g., through silicon vias (TSVs), interconnects, transistors, etc. In particular, use of MWCNT bundles inside annular cylinders of copper (Cu) as TSV is proposed in this study. However, the significant difference in scale makes it difficult to evaluate the interfacial mechanical integrity. Cohesive zone models (CZM) are typically used at large scale to determine the mechanical adherence at the interface. However, at molecular level, no routine technique is available. Molecular dynamic (MD) simulations is used to determine the stresses that are required to separate MWCNTs from a copper slab and generate normal stress–displacement curves for CZM. Only van der Waals (vdW) interaction is considered for MWCNT/Cu interface. A displacement controlled loading was applied in a direction perpendicular to MWCNT's axis in different cases with different number of walls and at different temperatures and CZM is obtained for each case. Furthermore, their effect on the CZM key parameters (normal cohesive strength (σmax) and the corresponding displacement (δn) has been studied. By increasing the number of the walls of the MWCNT, σmax was found to nonlinearly decrease. Displacement at maximum stress, δn, showed a nonlinear decrease as well with increasing the number of walls. Temperature effect on the stress–displacement curves was studied. When temperature was increased beyond 1 K, no relationship was found between the maximum normal stress and temperature. Likewise, the displacement at maximum load did not show any dependency to temperature.

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Analysis of the Thermal Stress at the Tubesheet in Floating-Head or U-Tube Heat Exchangers

Journal of Pressure Vessel Technology ◽

10.1115/1.4035827 ◽

2017 ◽

Vol 139 (2) ◽

Cited By ~ 1

Author(s):

Jiuyi Liu ◽

Caifu Qian ◽

Huifang Li

Keyword(s):

Thermal Stress ◽

Heat Exchanger ◽

Temperature Difference ◽

Heat Exchangers ◽

Influence Factors ◽

Area Ratio ◽

Shell Side ◽

Tube Heat Exchanger ◽

Numerical Tests ◽

Hole Area

Thermal stress is an important factor influencing the strength of a heat exchanger tubesheet. Some studies have indicated that, even in floating-head or U-tube heat exchangers, the thermal stress at the tubesheet is significant in magnitude. For exploring the value, distribution, and the influence factors of the thermal stress at the tubesheet of these kind heat exchangers, a tubesheet and triangle arranged tubes with the tube diameter of 25 mm were numerically analyzed. Specifically, the thermal stress at the tubesheet center is concentrated and analyzed with changing different parameters of the tubesheet, such as the temperature difference between tube-side and shell-side fluids, tubesheet diameter, thickness, and the tube-hole area ratio. It is found that the thermal stress of the tubesheet of floating-head or U-tube heat exchanger was comparable in magnitude with that produced by pressures, and the distribution of the thermal stress depends on the tube-hole area and the temperature inside the tubes. The thermal stress at the center of the tubesheet surface is high when tube-hole area ratio is very low. And with increasing the tube-hole area ratio, the stress first decreases rapidly and then increases linearly. A formula was numerically fitted for calculating the thermal stress at the tubesheet surface center which may be useful for the strength design of the tubesheet of floating-head or U-tube heat exchangers when considering the thermal stress. Numerical tests show that the fitted formula can meet the accuracy requirements for engineering applications.

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