Hydrodynamic Effects on Particle Deposition in Microchannel Flows at Elevated Temperatures

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Zhibin Yan ◽  
Xiaoyang Huang ◽  
Chun Yang
Keyword(s):  
Reynolds Number ◽  
Steady Flow ◽  
Deposition Rate ◽  
Pulsatile Flow ◽  
Heat Exchangers ◽  
Particle Deposition ◽  
Elevated Temperatures ◽  
Solution Temperature ◽  
Particulate Fouling ◽  
Hydrodynamic Effects

Particulate fouling and particle deposition at elevated temperature are crucial issues in microchannel heat exchangers. In this work, a microfluidic system was designed to examine the hydrodynamic effects on the deposition of microparticles in a microchannel flow, which simulate particle deposits in microscale heat exchangers. The deposition rates of microparticles were measured in two typical types of flow, a steady flow and a pulsatile flow. Under a given elevated solution temperature and electrolyte concentration of the particle dispersion in the tested flow rate range, the dimensionless particle deposition rate (Sherwood number) was found to decrease with the Reynolds number of the steady flow and reach a plateau for the Reynolds number beyond 0.091. Based on the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, a mass transport model was developed with considering temperature dependence of the particle deposition at elevated temperatures. The modeling results can reasonably capture our experimental observations. Moreover, the experimental results of the pulsatile flow revealed that the particle deposition rate in the microchannel can be mitigated by increasing the frequency of pulsation within a low-frequency region. Our findings are expected to provide a better understanding of thermally driven particulate fouling as well as to provide useful information for design and operation of microchannel heat exchangers.

Particulate Fouling and Mitigation Approach in Microchannel Heat Exchanger

2016 ◽  
Author(s):  
Zhibin Yan ◽  
Xiaoyang Huang ◽  
Chun Yang
Keyword(s):  
Deposition Rate ◽  
Heat Exchangers ◽  
Low Frequency ◽  
Microfluidic System ◽  
Solution Temperature ◽  
Working Fluid ◽  
Constant Flow Rate ◽  
Particulate Fouling ◽  
Microchannel Heat Exchanger ◽  
Micro Particles

Particulate fouling at elevated temperature is a crucial issue for microchannel heat exchangers. In this work, a microfluidic system is designed to experimentally study on the deposition of micro-particles suspended in microchannels, which simulates the working fluid in microscale heat exchangers. We have directly measured the deposition rate of microparticles and found that the number density of deposited particles was monotonically increased with solution temperature when constant flow rate of samples was maintained. Moreover, our results show that pulsatile flow, which was generated by a piezoelectric unit, could mitigate the particulate fouling in microchannels, and the deposition rate was decreased with increasing the frequency of pulsation within a low frequency region. Our findings are expected to gain better understanding of thermally driven particulate fouling as well as provide useful information for design and fabrication of microchannel heat exchangers.

Investigation of Fouling and Its Mitigation in Silicon Microchannels

2008 ◽  
Author(s):  
Jeffrey L. Perry ◽  
Satish G. Kandlikar
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Fibrous Material ◽  
Particle Deposition ◽  
Particle Dispersion ◽  
Secondary Effect ◽  
Primary Reason ◽  
Pressure Drops ◽  
Particulate Fouling ◽  
Microchannel Device

Particulate fouling studies with 4.0-μm silica and 1.25-μm alumina dispersions in water were performed in rectangular, silicon microchannels having a hydraulic diameter of 225 μm with a Reynolds number of 17. Data show the absence of particle deposition within the microchannels. The primary reason for this is the relatively high wall shear stress at the microchannel walls of 2.3 Pa compared to conventional size passageways. In contrast, the headers for the microchannels are quite susceptible to particulate fouling under the same conditions. This is because the shear stress in the header region is lower. Moreover, there is a secondary effect in particulate fouling when fibrous elements exist within the particle dispersion. The fouling behavior due to fibrous material is quite different. In fact, the presence of fibers is extremely detrimental to pressure drops within a microchannel device.

A Comparison of Steady and Pulsatile Flow in Symmetrically Branched Tubes

1982 ◽  
Vol 104 (1) ◽  
pp. 66-68 ◽  
Author(s):  
F. J. Walburn ◽  
P. D. Stein
Keyword(s):  
Reynolds Number ◽  
Secondary Flow ◽  
Steady Flow ◽  
Pulsatile Flow ◽  
Area Ratio ◽  
Secondary Velocity

The purpose of this study was to compare the characteristics of flow in the region of symmetrical bifurcations having branch-to-trunk area ratios of 0.4, 0.8 and 1.2 during steady and pulsatile flow. Flow was visualized with neutrally bouyant particles. Secondary flow was not observed in the branches during either steady or pulsatile flow when the branch-to-trunk area ratio was 0.4. Secondary velocity patterns were not observed in the branches with branch-to-trunk area ratios of 0.8 and 1.2 during pulsatile flow, although they were observed during steady flow. It may be inaccurate, therefore, to characterize pulsatile flow at an instantaneous Reynolds number on the basis of steady flow at the same Reynolds number.

Flow Structures at the Proximal Side-to-End Anastomosis. Influence of Geometry and Flow Division

1995 ◽  
Vol 117 (2) ◽  
pp. 224-236 ◽  
Author(s):  
P. E. Hughes ◽  
T. V. How
Keyword(s):  
Reynolds Number ◽  
Steady Flow ◽  
Pulsatile Flow ◽  
Critical Reynolds Number ◽  
Flow Patterns ◽  
Time Dependent ◽  
Flow Structures ◽  
Proximal Side ◽  
Flow Division ◽  
Distal Artery

Flow structures were visualized in transparent polyurethane models of proximal side-to-end vascular anastomoses, using planar illumination of suspended tracer particles. Both the effects of geometry and flow division were determined under steady and pulsatile flow conditions, for anastomosis angles of 15, 30, and 45 degrees. The flow patterns were highly three-dimensional and were characterized by a series of vortices in the fully occluded distal artery and two helical vortices aligned with the axis of the graft. In steady flow, above a critical Reynolds number, the flow changed from a laminar regime to one displaying time-dependent behavior. In particular, significant fluctuating velocity components were observed in the distal artery and particles were shed periodically from the occluded artery into the graft. Pairs of asymmetric flow patterns were also observed in the graft, before the onset of the time-dependent flow regime. The critical Reynolds number ranged from 427 to 473 and appeared to be independent of anastomosis angle. The presence of a patent distal artery had a significant effect on the overall flow pattern and led to the formation of a large recirculation region at the toe of the anastomosis. The main structures observed in steady flow, such as vortices in the distal artery and helical flow in the graft, were also seen during the pulsatile cycle. However, the secondary flow components in the graft were more pronounced in pulsatile flow particularly during deceleration of the flow waveform. At higher mean Reynolds numbers, there was also a greater mixing between fluid in the occluded arterial section and that in the graft.

MUELLER ALLOY 7060

Alloy Digest ◽  
1985 ◽  
Vol 34 (10) ◽  
Keyword(s):  
Heat Exchangers ◽  
Cold Working ◽  
Elevated Temperatures ◽  
Salt Water ◽  
Iron Alloy ◽  
Heat Treating ◽  
Good Resistance ◽  
Nickel Iron ◽  
Water Heaters ◽  
Nickel Iron Alloy

Abstract MUELLER Alloy 7060 is a copper-nickel-iron alloy. It has good strength at moderately elevated temperatures and can be fabricated by both hot and cold-working procedures. It contains nominally 11/4 iron to increase its resistance to corrosion and erosion. It has good resistance to corrosion by salt water and is used in marine service. It is used widely for condenser tubes, distiller tubes, heat exchangers, evaporators and water heaters for domestic service. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: Cu-501. Producer or source: Mueller Brass Company.

COPPER ALLOY No. C70400

Alloy Digest ◽  
1985 ◽  
Vol 34 (9) ◽  
Keyword(s):  
Corrosion Resistance ◽  
High Velocity ◽  
Heat Exchangers ◽  
Copper Alloy ◽  
Cold Working ◽  
Elevated Temperatures ◽  
Salt Water ◽  
Heat Treating ◽  
Nickel Copper ◽  
Resistance To Stress

Abstract Copper Alloy No. C70400 is a 5.5% nickel-copper alloy characterized by resistance to corrosion by high-velocity seawater, resistance to stress-corrosion cracking, and retention of strength at moderately elevated temperatures. It responds well to both hot and cold-working operations. Among its many uses are springs, switches, heat exchangers, salt-water piping and relays. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, machining, joining, and surface treatment. Filing Code: Cu-500. Producer or source: Copper and copper alloy mills.

EASTERN STAINLESS TYPE 309S

Alloy Digest ◽  
1984 ◽  
Vol 33 (3) ◽  
Keyword(s):  
Stainless Steel ◽  
Heat Exchangers ◽  
Elevated Temperatures ◽  
Heat Treating ◽  
Scaling Up ◽  
Oil Refining ◽  
Steel Company ◽  
High Alloy ◽  
Creep Properties ◽  
Refining Equipment

Abstract EASTERN STAINLESS TYPE 309S is a heat-resisting grade of stainless steel. Because of its high alloy content, it resists scaling up to 2000 F. It also has good tensile and creep properties and elevated temperatures. Type 309S has good ductility and malleability; therefore, difficult shapes and structures can be fabricated easily and it can be machined readily. It can be welded easily and gives strong, ductile welds. Some of its many applications are annealing boxes, boiler baffles, dryers, furnace parts, heat exchangers and oil-refining equipment. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties as well as creep. It also includes information on high temperature performance and corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: SS-441. Producer or source: Eastern Stainless Steel Company.

Aqueous acid-aided corrosion products removal from the surface of the brass elements of heat exchangers

2019 ◽  
pp. 110-115
Author(s):  
L. M. Mironovich ◽  
A. Yu. Eliseev ◽  
A. Yu. Eliseeva
Keyword(s):  
Heat Exchangers ◽  
Solution Temperature ◽  
Cleaning Process ◽  
Complex Effect ◽  
Aqueous Acid ◽  
Surface Configuration ◽  
Additional Input ◽  
Heat Exchange Equipment ◽  
Working Solution ◽  
Strong Acids

The paper studies complex effect of various factors on the process of cleaning brass brand L-68, used for the manufacture of heat exchange equipment. It has been established that acids of various strengths can be used as working solutions. The speed of the cleaning process depends on the nature of the acid and its initial concentration. For strong acids, a working solution with low concentration is recommended, followed by an increase in their concentration during the cleaning process. Additional input of oxygen into the system and an increase of the working solution temperature increase the cleaning rate of brass. The cleaning process proceeds without significant changes in the surface configuration, and, consequently, the expenditure of metal.

scholarly journals Net-exergetic, hydraulic and thermal optimization of coaxial heat exchangers using fixed flow conditions instead of fixed flow rates

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Tobias Blanke ◽  
Markus Hagenkamp ◽  
Bernd Döring ◽  
Joachim Göttsche ◽  
Vitali Reger ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Mass Flow ◽  
Flow Rate ◽  
Heat Exchangers ◽  
Circular Ring ◽  
Flow Conditions ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Pipe Radius

AbstractPrevious studies optimized the dimensions of coaxial heat exchangers using constant mass flow rates as a boundary condition. They show a thermal optimal circular ring width of nearly zero. Hydraulically optimal is an inner to outer pipe radius ratio of 0.65 for turbulent and 0.68 for laminar flow types. In contrast, in this study, flow conditions in the circular ring are kept constant (a set of fixed Reynolds numbers) during optimization. This approach ensures fixed flow conditions and prevents inappropriately high or low mass flow rates. The optimization is carried out for three objectives: Maximum energy gain, minimum hydraulic effort and eventually optimum net-exergy balance. The optimization changes the inner pipe radius and mass flow rate but not the Reynolds number of the circular ring. The thermal calculations base on Hellström’s borehole resistance and the hydraulic optimization on individually calculated linear loss of head coefficients. Increasing the inner pipe radius results in decreased hydraulic losses in the inner pipe but increased losses in the circular ring. The net-exergy difference is a key performance indicator and combines thermal and hydraulic calculations. It is the difference between thermal exergy flux and hydraulic effort. The Reynolds number in the circular ring is instead of the mass flow rate constant during all optimizations. The result from a thermal perspective is an optimal width of the circular ring of nearly zero. The hydraulically optimal inner pipe radius is 54% of the outer pipe radius for laminar flow and 60% for turbulent flow scenarios. Net-exergetic optimization shows a predominant influence of hydraulic losses, especially for small temperature gains. The exact result depends on the earth’s thermal properties and the flow type. Conclusively, coaxial geothermal probes’ design should focus on the hydraulic optimum and take the thermal optimum as a secondary criterion due to the dominating hydraulics.

Reducing Particle Deposition in Air-Cooled Heat Exchangers

1992 ◽  
Vol 13 (2) ◽  
pp. 81-87 ◽  
Author(s):  
G. ZHANG ◽  
T. R. BOTT ◽  
C. R. BEMROSE
Keyword(s):  
Heat Exchangers ◽  
Particle Deposition
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