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Micromachines
Special Issues
Heat and Mass Transfer in Microchannels
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Heat and Mass Transfer in Microchannels

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "E：Engineering and Technology".

Deadline for manuscript submissions: closed (31 August 2022) | Viewed by 28042
Submit your paper and select the Journal “Micromachines” and the Special Issue “Heat and Mass Transfer in Microchannels” via: https://susy.mdpi.com/user/manuscripts/upload?journal=micronachines. Please contact the guest editor or the journal editor ([email protected]) for any queries.

Special Issue Editors

Dr. Xin Xiao

E-Mail Website
Guest Editor
College of Environmental Science and Engineering, Donghua University, Shanghai 201620, China
Interests: building energy storage; thermal management
Special Issues, Collections and Topics in MDPI journals
Dr. Xuan Zhang

E-Mail Website
Guest Editor
Department of Energy and Power Engineering, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China
Interests: icing; condensation; phase change heat transfer and flow; droplet dynamics; surface and interface science; micro-/nano-scale heat and mass transfer
Special Issues, Collections and Topics in MDPI journals
Dr. Long Zhang

E-Mail Website
Guest Editor
Department of Energy and Power Engineering, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China
Interests: frosting mechanism and characteristics on cold surfaces; defrosting performances for air source heat pumps; energy efficiency; advanced heat pump technologies
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The miniaturization of components in mechanical and electronic equipment and systems is becoming increasingly popular in recent decades. Heat and mass transfer processes, usually accompanied by multiphase flow, are crucial for the normal operation of such micro/nano equipment and systems and thus attract a great amount of attention. Great effort has been devoted to deepening our understanding of the complex heat and mass transfer processes and advancing the development of related applications in microchannels. For example, phase change (e.g., boiling and condensation), nanofluids, and micro-/nano-structured surfaces are applied to enhance heat transfer and achieve a potentially higher critical heat flux. The aim of this Special Issue of Micromachines, “Heat and Mass Transfer in Microchannels”, is to present recent advances in heat and mass transfer in microchannels, including but not limited to the associated theoretical analyses, experimental measurements, numerical simulations, and practical applications.

Dr. Xin Xiao
Dr. Xuan Zhang
Dr. Long Zhang
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • heat and mass transfer
  • micro-/nano-fluids
  • enhanced heat transfer
  • phase change (boiling, evaporation, condensation, frosting, icing, etc.)
  • multiphase flow (gas–liquid, bubble, etc.)
  • heat exchanger
  • MEMS (micro-electromechanical system)

Published Papers (17 papers)

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Research

15 pages, 6660 KiB  
Article
Influence of Marangoni Effect on Heat and Mass Transfer during Evaporation of Sessile Microdroplets
by Haiting Liu and Jiewen Deng
Micromachines 2022, 13(11), 1968; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13111968 - 13 Nov 2022
Cited by 4 | Viewed by 2296
Abstract
Evaporative cooling is an important method for controlling the temperature of micro devices, and heat and mass transfer from the microdroplets in the evaporation process directly affect the cooling performance. In order to study the droplet heat and mass transfer law in the [...] Read more.
Evaporative cooling is an important method for controlling the temperature of micro devices, and heat and mass transfer from the microdroplets in the evaporation process directly affect the cooling performance. In order to study the droplet heat and mass transfer law in the droplet evaporation process, this paper builds a coupled thermal mass model of droplet evaporation and tests the accuracy of the numerical model through theoretical results. In order to study the influence of the Marangoni effect on the droplet evaporation process and the effects of different initial droplet radius and ambient temperature on the temperature and flow, fields within the droplet are compared. From this result, it can be seen that the droplet volume is 20 μL, and the maximum flow velocity in the droplet is 0.34 mm/s, without taking into account the Marangoni effect. When the Marangoni effect is taken into account, the maximum flow velocity increases by almost 100 times. The Marangoni effect can cause the convection in the droplet to change direction, and the formation of the Marangoni flow may affect the temperature distribution within the droplet, thereby increasing the evaporation efficiency by 2.5%. The evaporation process will increase the velocity of the air close to the surface of the liquid, but the increase in air velocity close to the liquid surface is not sufficient to reinforce evaporation. There is a non-linear relationship between increasing ambient temperature and increasing evaporation efficiency. For every 5 °C increase in ambient temperature, the maximum increase in the rate of evaporation is approximately 22.7%. Full article
(This article belongs to the Special Issue Heat and Mass Transfer in Microchannels)
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16 pages, 8682 KiB  
Article
Investigation of Needle Motion Profile Effect on Diesel Spray in Near-Nozzle Field
by Ya Gao, Weidi Huang, Raditya Hendra Pratama, Huifeng Gong and Jin Wang
Micromachines 2022, 13(11), 1944; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13111944 - 10 Nov 2022
Cited by 2 | Viewed by 1332
Abstract
A variety of needle-motion profiles are used in diesel injectors. However, it is unclear what the underlying mechanism is to determine the needle-motion profiles and how they affect the spray dynamics. It has been of significant interest to examine how the spray dynamics [...] Read more.
A variety of needle-motion profiles are used in diesel injectors. However, it is unclear what the underlying mechanism is to determine the needle-motion profiles and how they affect the spray dynamics. It has been of significant interest to examine how the spray dynamics will change if only altering the needle valve opening speed or closing speed while all other parameters are kept the same. The different needle-motion profiles were obtained using a piezo nozzle (Nozzle #P) and a solenoid nozzle (Nozzle #S), which have identical nozzle geometry. By utilizing the X-ray imaging technique, it was observed that the average needle valve speed of Nozzle #P was 51% higher at the opening stage but 17% lower at the closing stage than Nozzle #S. When the needle valve lift is low (approximately 200 μm), the needle valve opening speed has a crucial effect on spray dynamics. The faster needle valve opening of Nozzle #P results in a 42% larger spray spreading angle and 34% lower spray velocity at the downstream field. The spray dynamics may be controllable by properly designing the needle-motion profiles in the scenarios of the low needle lifts. However, when the needle valve is sufficiently open (approximately over 200 μm), almost identical spray characteristics were observed regardless of the needle-motion profiles. Full article
(This article belongs to the Special Issue Heat and Mass Transfer in Microchannels)
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20 pages, 8109 KiB  
Article
Localized Characteristics of the First Three Typical Condensation Frosting Stages in the Edge Region of a Horizontal Cold Plate
by Long Zhang, Mengjie Song, Christopher Yu Hang Chao, Chaobin Dang and Jun Shen
Micromachines 2022, 13(11), 1906; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13111906 - 04 Nov 2022
Cited by 10 | Viewed by 1262
Abstract
Condensation frosting usually causes a negative influence on heat exchangers employed in engineering fields. As the relationships among the first three typical condensation frosting stages in the edge regions of cold plates are still unclear, an experimental study on the localized condensation frosting [...] Read more.
Condensation frosting usually causes a negative influence on heat exchangers employed in engineering fields. As the relationships among the first three typical condensation frosting stages in the edge regions of cold plates are still unclear, an experimental study on the localized condensation frosting characteristics in the edge region of a cold plate was conducted. The edge effects on the water droplet condensation (WDC), water droplet frozen (WDF) and frost layer growth characteristics were quantitatively investigated. The results showed that the number of droplets coalescing in the edge-affected regions was around 50% greater than in the unaffected regions. At the end of the WDC stages, the area-average equivalent contact diameter and coverage area ratio of water droplets in the edge-affected regions were 2.69 times and 11.6% greater than those in the unaffected regions under natural convection, and the corresponding values were 2.24 times and 9.9% under forced convection. Compared with the unaffected regions, the WDF stage duration in the edge-affected regions decreased by 63.6% and 95.3% under natural and forced convection, respectively. Additionally, plate-type and feather-type frost crystals were, respectively, observed in natural and forced convection. The results of this study can help in the better understanding of the condensation frosting mechanism on a cold plate, which provides guidelines for optimizing the design of heat exchanger structures and system control strategies facing frosting problems. Full article
(This article belongs to the Special Issue Heat and Mass Transfer in Microchannels)
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13 pages, 5960 KiB  
Article
Replenishment of the Gas in a Hydrophobically-Structured Surface by Mass Transfer at the Liquid-Gas Interface for Improving the Stability of Entrapped Gas
by Bao Wang, Caihua Wang, Ding Weng, Marisa Lazarus, Dayun Yan and Xiaoyan Liu
Micromachines 2022, 13(11), 1893; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13111893 - 02 Nov 2022
Viewed by 1036
Abstract
The underwater nonwetted state on a superhydrophobic surface is hardly maintained in flowing water because the entrapped gas dissolves into the water or is carried off by flow. Therefore, a source gas is necessary to maintain a superhydrophobic state for its applications under [...] Read more.
The underwater nonwetted state on a superhydrophobic surface is hardly maintained in flowing water because the entrapped gas dissolves into the water or is carried off by flow. Therefore, a source gas is necessary to maintain a superhydrophobic state for its applications under realistic conditions. As detailed in this paper, based on the gas entrapped on a hydrophobic structured surface, the gas regeneration was experimentally achieved to replenish the losses of gas carried off by the flowing and reduced through dissolution. Furthermore, the mechanism of mass transfer at the liquid-gas interface was investigated by simulation. The results indicated that water molecules at a liquid-gas interface should escape to entrapped gas when water content didn’t reach saturation. This phenomenon could be due to the evaporation at the liquid-gas interface. With the increasing water content in the entrapped gas, the evaporation rate at the liquid-gas interface descended gradually. Under the action of flowing, the substances containing high concentrations of water molecule was washed away at the liquid-gas interface. Therefore, the low concentration of the water molecule at the liquid-gas interface was created. As a result, the equilibrium of water and gas at the liquid-gad interface was broken, and the evaporation continued to replenish the lost gas. Overall, the presented results in this study could be considered a promising candidate for replenishing the lost gas in hydrophobic structured surfaces by mass transfer at the liquid-gas interface. Full article
(This article belongs to the Special Issue Heat and Mass Transfer in Microchannels)
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15 pages, 3310 KiB  
Article
Nonlinear Thermal Diffusion and Radiative Stagnation Point Flow of Nanofluid with Viscous Dissipation and Slip Constrains: Keller Box Framework Applications to Micromachines
by Omar T. Bafakeeh, Bilal Ahmad, Skeena Noor, Tasawar Abbas, Sami Ullah Khan, Muhammad Ijaz Khan, Samia Elattar, Sayed M. Eldin, Mowffaq Oreijah and Kamel Guedri
Micromachines 2022, 13(11), 1839; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13111839 - 27 Oct 2022
Cited by 11 | Viewed by 1193
Abstract
The radiated flow of magnetized viscous fluid subject to the viscous dissipation phenomenon is numerically studied. The radiative phenomenon is addressed with nonlinear relations. Further, analysis is performed by using the slip effects and convective thermal flow constraints. The transformed problem is numerically [...] Read more.
The radiated flow of magnetized viscous fluid subject to the viscous dissipation phenomenon is numerically studied. The radiative phenomenon is addressed with nonlinear relations. Further, analysis is performed by using the slip effects and convective thermal flow constraints. The transformed problem is numerically evaluated using the Keller Box method. The physical parameter effects, such as the magnetic parameter for the velocity profile, Prandtl number, Brownian motion parameter and Biot number for the energy profile and Lewis number, and the thermophoresis parameter for the concentration profile are discussed. The obtained results suggest applications in enhancing the heat transfer phenomenon, thermal system, energy generation, heat transmission devices, power generation, chemical reactions, etc. Full article
(This article belongs to the Special Issue Heat and Mass Transfer in Microchannels)
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13 pages, 6880 KiB  
Article
The Effect of Fin Shape on the Heat Transfer and the Solution Time of a Microchannel Evaporator in a CO2 Air Conditioning System—A Numerical Investigation
by Tronghieu Nguyen and Thanhtrung Dang
Micromachines 2022, 13(10), 1648; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13101648 - 30 Sep 2022
Cited by 2 | Viewed by 1580
Abstract
Numerical simulations on the fin shape of a microchannel evaporator in a CO2 air conditioning system were performed at the inlet evaporative temperature of 10 °C and the vapor quality of 0.61. Two types of fin shapes were dealt with: the straight [...] Read more.
Numerical simulations on the fin shape of a microchannel evaporator in a CO2 air conditioning system were performed at the inlet evaporative temperature of 10 °C and the vapor quality of 0.61. Two types of fin shapes were dealt with: the straight fins and V-fins. The numerical results were verified by the experimental data. For the system under consideration and for the same heat transfer area and the heat transfer coefficient for the air side in the microchannel evaporator, the effect of the fin shape on the heat transfer was not different; however, the solution time and the physical memory for the straight fins were 1.3 and 1.45 times compared with the V-fins, respectively. Therefore, the V-fin shape should be used for numerical simulation to compare it with the straight fin shape. In this study, the evaporation of the refrigerant in the microchannel evaporator took place in four passes. The normal heat flux from the air through the fins and tubes was almost reached at 1550 W/m2 at the evaporative temperature of 10 °C. The results obtained from the experimental data were in good agreement with those obtained from the numerical results, with a deviation of less than 10%. Full article
(This article belongs to the Special Issue Heat and Mass Transfer in Microchannels)
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21 pages, 5299 KiB  
Article
Thermal Conductivity Measurement of Flexible Composite Phase-Change Materials Based on the Steady-State Method
by Ze Feng and Xin Xiao
Micromachines 2022, 13(10), 1582; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13101582 - 23 Sep 2022
Viewed by 1359
Abstract
Phase-change materials (PCMs) are widely used in energy storage and thermal management due to the large latent heat in the phase-change process. As one of the most significantly thermophysical properties of PCMs, the thermal conductivity has been extensively studied. Great attention has been [...] Read more.
Phase-change materials (PCMs) are widely used in energy storage and thermal management due to the large latent heat in the phase-change process. As one of the most significantly thermophysical properties of PCMs, the thermal conductivity has been extensively studied. Great attention has been paid to improving the thermal conductivities of PCMs; however, the studies on the thermal conductivities of flexible PCMs are relatively inadequate. In this study, polyethylene glycol 1500 (PEG1500) was used as the base PCM, and expanded graphite (EG) and styrene–butadiene–styrene (SBS) were added to improve the thermal conductivity and flexibility of pure PCMs, respectively. A steady-state experimental test rig was built and verified with the measurement of the thermal conductivity of stainless steel and deionized water, and then the thermal conductivities of PCMs at different phases and qualitative temperatures were measured extensively. Compared to the PEG1500 with 5 wt.% EG, the addition of SBS sharply reduces the thermal conductivity, which is only 0.362 W/(m·K) at 12.5 °C when the addition ratio is 50%. This is approximately a 69% reduction compared with the composite PCMs without SBS. Furthermore, the theoretical thermal conductivities of the composite PCMs were calculated with six theoretical models of multiphase systems. The majority of the models provide a good prediction of thermal conductivities of composite PCM with high SBS concentration, while the average deviation of Agari-Uno model is only 20.5% with different SBS concentration and relatively agrees well with the experimental results. Full article
(This article belongs to the Special Issue Heat and Mass Transfer in Microchannels)
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20 pages, 5731 KiB  
Article
Significance of Convection and Internal Heat Generation on the Thermal Distribution of a Porous Dovetail Fin with Radiative Heat Transfer by Spectral Collocation Method
by G. Sowmya, Maha M. A. Lashin, M. Ijaz Khan, R. S. Varun Kumar, K. C. Jagadeesha, B. C. Prasannakumara, Kamel Guedri, Omar T Bafakeeh, El Sayed Mohamed Tag-ElDin and Ahmed M. Galal
Micromachines 2022, 13(8), 1336; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13081336 - 17 Aug 2022
Cited by 14 | Viewed by 1615
Abstract
A variety of methodologies have been used to explore heat transport enhancement, and the fin approach to inspect heat transfer characteristics is one such effective method. In a broad range of industrial applications, including heat exchangers and microchannel heat sinks, fins are often [...] Read more.
A variety of methodologies have been used to explore heat transport enhancement, and the fin approach to inspect heat transfer characteristics is one such effective method. In a broad range of industrial applications, including heat exchangers and microchannel heat sinks, fins are often employed to improve heat transfer. Encouraged by this feature, the present research is concerned with the temperature distribution caused by convective and radiative mechanisms in an internal heat-generating porous longitudinal dovetail fin (DF). The Darcy formulation is considered for analyzing the velocity of the fluid passing through the fin, and the Rosseland approximation determines the radiation heat flux. The heat transfer problem of an inverted trapezoidal (dovetail) fin is governed by a second-order ordinary differential equation (ODE), and to simplify it to a dimensionless form, nondimensional terms are utilized. The generated ODE is numerically solved using the spectral collocation method (SCM) via a local linearization approach. The effect of different physical attributes on the dimensionless thermal field and heat flux is graphically illustrated. As a result, the temperature in the dovetail fin transmits in a decreasing manner for growing values of the porosity parameter. For elevated values of heat generation and the radiation-conduction parameter, the thermal profile of the fin displays increasing behavior, whereas an increment in the convection-conduction parameter downsizes the thermal dispersal. It is found that the SCM technique is very effective and more conveniently handles the nonlinear heat transfer equation. Furthermore, the temperature field results from the SCM-based solution are in very close accordance with the outcomes published in the literature. Full article
(This article belongs to the Special Issue Heat and Mass Transfer in Microchannels)
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18 pages, 7707 KiB  
Article
Study of New Mini-Channel Trans-Critical CO2 Heat Pump Gas Cooler
by Jiawei Jiang, Shiqiang Liang, Can Ji, Longyan Wang and Chaohong Guo
Micromachines 2022, 13(8), 1206; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13081206 - 29 Jul 2022
Cited by 4 | Viewed by 1375
Abstract
A gas cooler is one of the important parts of a carbon dioxide (CO2) heat pump water heater, and it must meet the needs of not only pressurization but also heat transfer. It is important to study gas coolers. In this [...] Read more.
A gas cooler is one of the important parts of a carbon dioxide (CO2) heat pump water heater, and it must meet the needs of not only pressurization but also heat transfer. It is important to study gas coolers. In this paper, a heat exchanger with a spiral channel is studied. ANSYS CFX software was used to analyze the flow and heat transfer characteristics of the heat exchanger (single-plate model). The influences of the cooling pressure of CO2, the mass flux of CO2, the mass flux of water and the channel radius of CO2 are discussed. In this paper, the results show that the cooling pressure of CO2, the mass flux of CO2 and the channel radius of CO2 all have a large influence on the local heat transfer coefficient: with an increase in the cooling pressure of CO2, the peak value of the heat transfer coefficient of CO2 decreases and the average heat transfer coefficient decreases; with an increase in the mass flux of CO2, the peak value of the heat transfer coefficient of CO2 increases and the average heat transfer coefficient increases; and with a decrease in the channel radius of CO2, the peak value of the heat transfer coefficient of CO2 increases. The water mass flux has only a slight effect on heat transfer, and the lower cooling pressure of CO2 corresponds to a higher peak heat transfer coefficient, which can reach 27.5 kW∙m−2∙K−1 at 9 MPa. Full article
(This article belongs to the Special Issue Heat and Mass Transfer in Microchannels)
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22 pages, 6260 KiB  
Article
Considerations for the Maximum Heat Load and Its Influence on Temperature Variation of the Evaporator in Flat MHPs in Transient Regimes
by Ioan Mihai, Cornel Suciu and Claudiu Marian Picus
Micromachines 2022, 13(6), 979; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13060979 - 20 Jun 2022
Cited by 2 | Viewed by 1749
Abstract
The present paper describes a series of considerations for the occurrence of capillary boundaries in flat micro heat pipes (flat MHPs) and the conditions required for their stable operation in relation to the working circumstances and to the type of liquids inside the [...] Read more.
The present paper describes a series of considerations for the occurrence of capillary boundaries in flat micro heat pipes (flat MHPs) and the conditions required for their stable operation in relation to the working circumstances and to the type of liquids inside the pipes. Particularities of heat transfer in a flat MHP are analyzed for situations of either excessive or deficient working liquid. Depending on the physical properties of the working liquids (acetone, methanol and distilled water), the maximum rate of heat flow that can be applied to a flat MHP is determined analytically. The calculus is made with the assumption that constant vaporization of the liquid is ensured in the flat MHP’s evaporator, with no overheating. The considered analytical models allow for the evaluation of the liquid film thickness and the mass flow corresponding to the vaporization region. The temperature difference between the inner and outer walls of a flat MHP is found in the case of a transient regime and a variable thermal flow is applied in the evaporation region. The interior of flat MHPs was modeled in MATLAB using an FTCS (Forward-Time Central-Space) method, which is a finite difference method used for numerically solving the heat equation. Full article
(This article belongs to the Special Issue Heat and Mass Transfer in Microchannels)
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18 pages, 9385 KiB  
Article
Numerical Investigation of Special Heat Transfer Phenomenon in Wire-Wrapped Fuel Rod of SFR
by Xuefeng Tan, Bing Wang, Yun Guo and Miao Hu
Micromachines 2022, 13(6), 935; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13060935 - 11 Jun 2022
Cited by 1 | Viewed by 1690
Abstract
Sodium-cooled reactors (SFR) have always been recognized as one of the most promising candidates for the fourth-generation nuclear systems as announced by the Generation-IV International Forum. In the design of SFR, helical wire-wrapped rod is applied to stabilize the structure of the rod [...] Read more.
Sodium-cooled reactors (SFR) have always been recognized as one of the most promising candidates for the fourth-generation nuclear systems as announced by the Generation-IV International Forum. In the design of SFR, helical wire-wrapped rod is applied to stabilize the structure of the rod bundle and enhance coolant mixing. Although there has been considerable research on SFR in computational fluid dynamics (CFD), the phenomenon of heat transfer has rarely been paid attention to. This article discovered that there exists reversed heat flux from coolant to wrapped wire, which is contrary to our usual understanding. This phenomenon has not been reported in previous CFD calculations. Hence, a solid heat conduction model is proposed to prove this phenomenon and analyze the heat transfer process. The simulation results show that the wrapping wire embedding depth, the shape of the calculation domain and the physical properties of all components have great influence on the magnitude of the reversed heat flux. The present findings will have strong influence on the temperature field and maximum value of the fuel rod as well as profound reference value for future flow calculation, especially in grid generation and treatment of the junction between the winding wire and fuel rod. Full article
(This article belongs to the Special Issue Heat and Mass Transfer in Microchannels)
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20 pages, 9460 KiB  
Article
Particularities of R134a Refrigerant Temperature Variations in a Transient Convective Regime during Vaporization in Rectangular Microchannels
by Ioan Mihai, Cornel Suciu and Claudiu Marian Picus
Micromachines 2022, 13(5), 767; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13050767 - 13 May 2022
Cited by 1 | Viewed by 1475
Abstract
An analysis of the R134a (tetrafluoroetane) coolant’s non-stationary behavior in rectangular microchannels was conducted with the help of a newly proposed miniature refrigerating machine of our own design and construction. The experimental device incorporated, on the same plate, a condenser, a lamination tube [...] Read more.
An analysis of the R134a (tetrafluoroetane) coolant’s non-stationary behavior in rectangular microchannels was conducted with the help of a newly proposed miniature refrigerating machine of our own design and construction. The experimental device incorporated, on the same plate, a condenser, a lamination tube and a vaporizer, all of which integrated rectangular microchannels. The size of the rectangular microchannels was determined by laser profilometry. R-134a coolant vapors were pressurized using a small ASPEN rotary compressor. Using the variable soft spheres (VSS) model, the mean free path, Knudsen and Reynolds numbers, as well as the dimensionless velocity profile can be assessed analytically. In order to determine the average dimensionless temperature drop in the vaporizer’s rectangular microchannels, in non-stationary regime, an analytical solution for incompressible flow with slip at the walls, fully developed flow and laminar regime was used, by aid of an integral transform approach. In the experimental study, the transitional distribution of temperature was tracked while modifying the R134a flow through the rectangular microchannels. Coolant flow was then maintained at a constant, while the amount of heat absorbed by the vaporizer was varied using multiple electric resistors. A comparative analysis of the analytical and experimental values was conducted. Full article
(This article belongs to the Special Issue Heat and Mass Transfer in Microchannels)
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13 pages, 2023 KiB  
Article
Particle Deposition in the Vicinity of Multiple Film Cooling Holes
by Yubo Peng, Guoqiang Xu, Xiang Luo, Jian He and Dongdong Liu
Micromachines 2022, 13(4), 523; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13040523 - 26 Mar 2022
Viewed by 1379
Abstract
Particle deposition on film cooling surface is an engineering issue that degrades the thermal protection of turbine blade. Here, we present a combined experimental and numerical investigation on the particle deposition in the vicinity of multiple film cooling holes to reveal the effect [...] Read more.
Particle deposition on film cooling surface is an engineering issue that degrades the thermal protection of turbine blade. Here, we present a combined experimental and numerical investigation on the particle deposition in the vicinity of multiple film cooling holes to reveal the effect of interactions between cooling outflows on particle deposition. The numerical simulation of film cooling with a group of three rows of straight film cooling holes is conducted and validated by experimental data with blowing ratios ranging from 0 to 0.08. Wax particles with size range from 5 to 40 μm are added in the heated mainstream to simulate the particle deposition in the experiment. The simulation results show the decrease of particle deposition with blowing ratio and various deposition characteristics in different regions of the surface. The flow fields from numerical results are analyzed in detail to illustrate deposition mechanism of the particles in different regions under the interactions of cooling outflows. The cooling air from the holes in the first row reduces the particle concentration near the wall but causes particle deposition in or between the tail regions by the generated flow disturbance. The cooling air from the latter hole separates the diluted flow in the upstream from the wall, and creates a tail region without particle deposition. This revealed particle deposition characteristics under the effect of outflows interaction can benefit the understanding of particle deposition in engineering applications, where multi-row of cooling holes are utilized. Full article
(This article belongs to the Special Issue Heat and Mass Transfer in Microchannels)
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11 pages, 848 KiB  
Article
Experimental Investigation on the Transpiration Cooling Characteristics of Sintered Wire Mesh in Plain Weave
by Yubo Peng, Guoqiang Xu, Xiang Luo, Jian He and Dongdong Liu
Micromachines 2022, 13(3), 450; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13030450 - 16 Mar 2022
Cited by 3 | Viewed by 1624
Abstract
We experimentally investigate the transpiration cooling characteristics of a porous material, sintered wire mesh. Three samples with different porosities in a plain weave structure are tested with various blowing ratios in an open-loop wind tunnel with a heated mainstream flow. The temperature on [...] Read more.
We experimentally investigate the transpiration cooling characteristics of a porous material, sintered wire mesh. Three samples with different porosities in a plain weave structure are tested with various blowing ratios in an open-loop wind tunnel with a heated mainstream flow. The temperature on the surface of the porous material is measured by an infrared camera to obtain the cooling efficiency. The measurements reveal nonuniform distributions of the surface temperature and the cooling efficiency in both the flow direction and the transverse direction. The averaged cooling efficiency on the surface first decreases and then increases with the blowing ratio, but increases and then decreases with the porosity of the material. The internal cooling by forced convection and its combination with the external film cooling from the transpiration cooling are considered to be attributed to those two cooling characteristics, respectively. Finally, we propose a modified blowing ratio to collapse the minima of the blowing ratio for all tested samples, providing an universal transition for the decreasing and increasing branches for all tested samples in the relation between averaged cooling efficiency and blowing ratio. Full article
(This article belongs to the Special Issue Heat and Mass Transfer in Microchannels)
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24 pages, 6614 KiB  
Article
Entropy Generation Analysis of Peristaltic Flow of Nanomaterial in a Rotating Medium through Generalized Complaint Walls of Micro-Channel with Radiation and Heat Flux Effects
by Aamir Ali, Mehak Sajid, Hafiz Junaid Anjum, Muhammad Awais, Kottakkaran Sooppy Nisar and C. Ahamed Saleel
Micromachines 2022, 13(3), 375; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13030375 - 26 Feb 2022
Cited by 14 | Viewed by 1509
Abstract
This study discusses entropy generation analysis for a peristaltic flow in a rotating medium with generalized complaint walls. The goal of the current analysis is to understand the fluid flow phenomena particular to micro devices. Nano materials with a size less than 100 [...] Read more.
This study discusses entropy generation analysis for a peristaltic flow in a rotating medium with generalized complaint walls. The goal of the current analysis is to understand the fluid flow phenomena particular to micro devices. Nano materials with a size less than 100 nm have applications in micro heat exchangers to cool electronic circuits, blood analyzers, biological cell separations, etc. For this study, we considered the effects of radiation, viscous dissipation and heat flux on the flow of nanomaterial inside a cylindrical micro-channel. To investigate the slip effects on the flow, the second order slip condition for axial velocity, the first order slip condition for secondary velocity and the thermal slip conditions were used. The flow was governed by partial differential equations (PDE’s), which were turned into a system of coupled ordinary differential equations (ODE’s) that were highly non-linear and numerically solved using the NDSolve command in Mathematica. The impacts of different involved parameters on the flow field were investigated with the aid of graphical illustrations. Entropy generation and the Bejan number were given special attention, and it was found that they decreased as the Hartman number, rotation, and radiation parameters increased. Full article
(This article belongs to the Special Issue Heat and Mass Transfer in Microchannels)
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13 pages, 4785 KiB  
Article
Investigation of the Dynamics of Cavitation Bubbles in a Microfluidic Channel with Actuations
by Xiaopeng Shang and Xiaoyang Huang
Micromachines 2022, 13(2), 203; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13020203 - 28 Jan 2022
Cited by 3 | Viewed by 1844
Abstract
This work presents experimental and numerical studies on the dynamics of cavitation bubbles in a nozzle-shaped microfluidic channel with PZT (lead-zirconate-titanate) actuations. It is found that a cloud of bubbles can be generated near the center of the microfluidic channel when the actuation [...] Read more.
This work presents experimental and numerical studies on the dynamics of cavitation bubbles in a nozzle-shaped microfluidic channel with PZT (lead-zirconate-titanate) actuations. It is found that a cloud of bubbles can be generated near the center of the microfluidic channel when the actuation voltage is larger than a threshold at 1 kHz. After being generated, the bubbles under actuations oscillate radially with violent expansion and compression, and simultaneously translate upstream towards the opening of the nozzle. Along with radial oscillation and translation, the bubbles undergo frequent and drastic coalescence and breakup, leading to vigorous churning of surrounding liquids. The pressure variation and distribution in the microchannel are calculated by numerical simulation in Ansys Fluent, and results show that there is a low-pressure zone inside the microfluidic channel within each cycle of the actuation period, which is responsible for bubble generation observed in the experiments. The method of bubble generation in this study is novel and can be applied for the enhancement of heat and mass transfer in microfluidic operations. Full article
(This article belongs to the Special Issue Heat and Mass Transfer in Microchannels)
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23 pages, 5984 KiB  
Article
Flow and Heat Transfer Performances of Liquid Metal Based Microchannel Heat Sinks under High Temperature Conditions
by Tao Wu, Lizhi Wang, Yicun Tang, Chao Yin and Xiankai Li
Micromachines 2022, 13(1), 95; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13010095 - 08 Jan 2022
Cited by 13 | Viewed by 2186
Abstract
Developments in applications such as rocket nozzles, miniature nuclear reactors and solar thermal generation pose high-density heat dissipation challenges. In these applications, a large amount heat must be removed in a limited space under high temperature. In order to handle this kind of [...] Read more.
Developments in applications such as rocket nozzles, miniature nuclear reactors and solar thermal generation pose high-density heat dissipation challenges. In these applications, a large amount heat must be removed in a limited space under high temperature. In order to handle this kind of cooling problem, this paper proposes liquid metal-based microchannel heat sinks. Using a numerical method, the flow and heat transfer performances of liquid metal-based heat sinks with different working fluid types, diverse microchannel cross-section shapes and various inlet velocities were studied. By solving the 3-D steady and conjugate heat transfer model, we found that among all the investigated cases, lithium and circle were the most appropriate choices for the working fluid and microchannel cross-section shape, respectively. Moreover, inlet velocity had a great influence on the flow and heat transfer performances. From 1 m/s to 9 m/s, the pressure drop increased as much as 65 times, and the heat transfer coefficient was enhanced by about 74.35%. Full article
(This article belongs to the Special Issue Heat and Mass Transfer in Microchannels)
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