Rectangular Microchannel Research Articles

Applying position and time dependent nusselt number and friction factor into 1D model to improve regenerator design for solid-state caloric cooling cycles

Active caloric regenerative cycles have recently attracted much attention as a promising cooling technology that can potentially replace the vapor compression cycle based on its high efficiency and eco-friendly characteristics. The use of modeling is necessary in optimizing the active caloric regenerative cycle due to the system’s complex structure and numerous parameters that need to be taken into account. The cycle uses oscillatory flow to efficiently exchange heat between the caloric material and the heat transfer fluid and to generate a desired temperature gradient in the regenerator. When the oscillatory flow is used, hydrodynamically and thermally developing regions occur all over the regenerator when the direction of the fluid flow changes.To the best of the authors’ knowledge, no previous research has considered the oscillatory developing regions in a 1D model. Therefore, this study incorporated the developing regions generated by the oscillatory flow as well as the entrance developing regions into a regenerator model for the first time. Based on the modeling results, the influence of the oscillatory developing regions and the average Nusselt number increase with higher cycle frequency. Additionally, the new 1D model produces average Nusselt number similar to the 2D model with a maximum error of 4 %. Considering that the 2D model requires very high computational cost to solve the transient condition of the caloric cycle, the advanced 1D model can accurately assess the performance of the caloric cycle and provide a detailed analysis of heat transfer phenomena and fluid dynamics in the regenerator at modest computational cost.The parallel plate type, optimized using the new model, has a hydraulic diameter of 0.1 mm. However, maintaining such a small space between the plates can be challenging from an application standpoint. Therefore, this study proposes the use of a wide rectangular microchannel matrix as the regenerator. The rectangular microchannel matrix, with an aspect ratio of 30, produces a coefficient of performance of 5.65, which is comparable to the parallel plate matrix. Consequently, the wide rectangular microchannel matrix can achieve both high Nusselt number and structural stability simultaneously.

The Characterisation of Differential Pressure Based Flow Sensor in a Microfluidic Environment

Flows in a microfluidic environment differ in their flow parameter changes compared to macro flows and should be handled carefully. Recently microfluidic innovations have been drawn into much consideration in biomedical, chemical synthesis, and cooling industries. There exists a need for a flow rate sensor for measuring tiny fluid flows in developing microfluidic Lab-on-chip products, Organ-on-chip, and other products for biological, chemical, and other flow analysis. Working with microfluidic products mainly revolves around flow measurement. The control of these frameworks is just conceivable with sensors that estimate flow rate. In this work, we understand the dynamics of microfluidic flow and try to determine its influence on sensor behavior. The paper presents the construction of flow-sensing techniques for microflows. The design of the microchannel opted for the study is also discussed. A microfluidic flow rate sensing technique is put forward using the physical principle of fluid dynamics; based on pressure in a rectangular microchannel. For rectangular microchannel, the variation in pressure had an impact on the flow rate measurement of the microflow sensor.

Experimental test of rectangular microchannel printed circuit heat exchanger using supercritical carbon dioxide as working fluid

This study proposed a new type of printed circuit heat exchanger with rectangular microchannels and established a test platform with supercritical carbon dioxide as working fluid. The heat transfer and pressure drop of the test sample were tested, and the experiments considered inlet temperature ranges of 335.0–338.9 K and 316.1–339.1 K for the hot and cold sides, respectively. The results revealed that hot-side inlet temperature had the most significant effect on the heat transfer rate and thermal performance. With a 10.3% increase in the hot-side inlet temperature, the heat transfer rate increased by 89.0%, and the thermal performance decreased by 17.7%. The test sample effectiveness was most significantly affected by the cold-side inlet temperature, and it increased by 23.3% as the cold-side inlet temperature increased by 5.9%. The effectiveness increased to 0.96 with an increase in the cold-side inlet temperature to 339.1 K.

Optimised Electro-Osmotic Flow in Rectangular Microchannels with Smoothed Corners

Electro-osmotic flows are a means of circulating polar fluids through microchannels without resorting to mechanical pumping. The lack of moving parts, of noise and the ease of integration in silicon chips make them an interesting option for microchip cooling and miniaturized total analysis systems. This paper describes an optimization in terms of first- and second-law analysis of the cross-section of a microchannel subject to electro-osmotic flow. Starting from rectangular cross-sections of different aspect ratios, its corners are progressively smoothed and the resulting Poiseuille and Nusselt numbers computed. Performance evaluation criteria are then used to assess the change in, among others, heat transfer rate, temperature difference between wall and bulk fluid, and equivalent pumping power. The entropy number is also computed and the results commented. It is found that the latter criterion highlights a configuration of minimum entropy generation, whereas the trends of the heat transfer and temperature difference are opposite to that of the equivalent pumping power.

Electro-osmotic flow of Maxwell fluid induced by an alternating electric field in curved rectangular microchannels

The electro-osmotic flow of a Maxwell fluid in a rectangular curved microchannel driven by an external alternating electric field is numerically investigated in this work. Some flow field and stream function results are simulated using the spectral method. The combined effects of the Deborah number, angular frequency, curvature ratio, and aspect ratio on fluid flow behaviors are discussed in detail. The results show that the Deborah number retards the diffusion of the mainstream directional velocity from the boundaries to the central region. At the same time, it enhances the secondary flow within the cross section. An increase in angular frequency intensifies velocity oscillations (more peaks and troughs and larger axial velocity amplitudes) and promotes the generation and development of secondary flows. Decreasing the curvature ratio or increasing the aspect ratio will enhance the transverse momentum transport in the cross section and improve the secondary flow.

A hybrid microchannel heat sink with ultra-low pressure drop for hotspot thermal management

Hotspot with several orders of magnitude heat flux higher than the background areas has become a prominent issue in the thermal management of advanced electronics. In this study, a novel microchannel heat sink with ultra-low power consumption has been introduced for chip-level hotspot thermal management. The proposed IM-HM heat sink incorporates rectangular microchannels for the background zone and pin-fins for the hotspot region, configured with an upper inlet and two side outlets. Using maximum temperature, pressure drop, and temperature uniformity as key metrics, a comprehensive numerical analysis of the IM-HM heat sink at different Reynolds number were conducted based on computational fluid dynamics. Our results demonstrate that the IM-HM heat sink enhances local heat transfer capacity and exhibits better temperature uniformity compared to the traditional rectangular microchannel heat sinks. Moreover, incorporating entry chamfer and augmenting the microchannel height have been found to effectively mitigate pressure drop in microfluidic systems. Specifically, simulation results indicate that the pressure drop in the microchannel can be reduced by 63.4 and 72.3% by increasing the inlet chamfer angle and microchannel height to 500 and 1500, respectively. Notably, the optimized IM-HM heat sink yields over 98.4% savings in pumping power to achieve consistent maximum temperatures compared to traditional rectangular microchannel heat sinks, while also exhibiting smaller temperature gradient.

Boiling heat transfer of binary and ternary mixtures in multiple rectangular microchannels

In this study, the boiling heat transfer of binary and ternary refrigerant mixtures in a horizontal multiport tube with multiple rectangular microchannels was investigated. The influences of the mass velocity, vapor quality, and heat flux on the heat transfer were evaluated for near- and non-azeotropic mixtures of R410A, R32/CF3I, R32/R1123, R32/R1234yf, R1123/R32/R1234yf, and CO2/R32/R1234yf. The obtained results were compared with those of pure refrigerants R1234yf and R32. For R1234yf at low mass velocity, the flow patterns were estimated as intermittent (plug) and slug-annular flows with an extremely thin liquid film. The heat transfer coefficient decreased when the heat flux was increased because dry patch areas formed and expanded on the sides of the noncircular microchannel. The near-azeotropic mixtures with small temperature glides exhibited heat transfer characteristics similar to those of the pure refrigerant. Conversely, the heat transfer coefficients deteriorated slightly under lower mass velocities. The heat transfer coefficients of binary and ternary mixtures with larger temperature glides were significantly different from those of pure refrigerants and near-azeotropic mixtures; they decreased with decreasing mass velocity owing to mass diffusion resistance. The heat transfer coefficients of binary mixtures with large temperature glides decreased monotonically as the mass velocity decreased, and the heat transfer noticeably deteriorated at lower mass velocities. The heat transfer model was developed for rectangular microchannels by considering the heat transfer contributions of thin liquid film evaporation due to surface force, forced convection, and nucleate boiling. Moreover, this model considers the flow pattern of multiple microchannels, heat transfer degradations due to dry patches and mass diffusion resistance, and dryout incipience quality. The results of the present model agree well with the heat transfer coefficients, including those of binary and ternary mixtures, in the pre- and post-dryout regions with a mean percentage error of 3.1%.

Hydrodynamic influence on thermal management of flexible heatsink devices embedded with out-of-plane intricate microchannel design

This study examines the thermal management efficacy of a 3-D printed microfluidic heat sink device with an intricate microchannel design. The performance of the presented device was experimentally compared to device with contemporary rectangular microchannel for different base material compositions and flow parameters to further understand the complex heat transfer trade-off between heat conduction and convection. The study found that upon tuned with a relatively low flow rate of 10 μLmin−1, the heatsink device made from nanocomposite material, featuring an intricate 3D design, generates the lowest hotspot temperature due to uniform heat dissipation. However, when flow rate was increased to 120 μLmin−1, the phenomenon reverses and PDMS-based devices with intricate channel perform better compared to PDMS nanocomposite-based devices. There was concurrent occurrence of the aforementioned phenomena at various temperature settings of 338 K, 358 K, 373 K, and 388 K. Numerical simulation reveals that relatively high flow rates create vortices, which significantly alter the heat transfer characteristics of the devices. Along with its primary application of on-demand flexible electronic cooling, with optimal flow tuning, the applications of the proposed device can be further extended to the thermal management of batteries, industrial 3D-printer nozzle heads, and artificial organ cooling, etc.

Measuring flow-mediated protein drift across stationary supported lipid bilayers

Fluid flow near biological membranes influences cell functions such as development, motility, and environmental sensing. Flow can laterally transport extracellular membrane proteins located at the cell-fluid interface. To determine whether this transport contributes to flow signaling in cells, quantitative knowledge of the forces acting on membrane proteins is required. Here, we demonstrate a method for measuring flow-mediated lateral transport of lipid-anchored proteins. We rupture giant unilamellar vesicles to form discrete patches of supported membrane inside rectangular microchannels and then allow proteins to bind to the upper surface of the membrane. While applying flow, we observe the formation of protein concentration gradients that span the membrane patch. By observing how these gradients dynamically respond to changes in applied shear stress, we determine the flow mobility of the lipid-anchored protein. We use simplified model membranes and proteins to demonstrate our method’s sensitivity and reproducibility. Our intention was to design a quantitative, reliable method and analysis for protein mobility that we will use to compare flow transport for a variety of proteins, lipid anchors, and membranes in model systems and on living cells.

Experimental analysis on the heat transfer performance of gas-liquid Taylor flow in a square microchannel

The flow and heat transfer behaviors of gas–liquid Taylor flow in a 1 × 1 mm square microchannel are experimentally investigated in this paper, focusing on evaluating the slug length, void fraction β, and mixing velocity on the overall performance of Taylor flow in the microchannel. T-shaped junctions of varying widths were employed to control the slug length in the Taylor flow. The experimental results indicate that reducing the junction width can heighten the bubble generation frequency and shorten the bubble/slug length. This reduction in slug length can enhance the heat transfer performance of the Taylor flow in fixed cross-section microchannels, but the degree of enhancement is significantly influenced by the void fraction. When β = 0.5, reducing the slug length can significantly improve the heat transfer coefficient while maintaining a reasonable pressure drop increment, resulting in the best overall performance. The friction pressure drop increases significantly when β = 0.67, and the level of overall performance is low. When β = 0.33, the short slugs have little effect on the performance of Taylor flow, and the change of heat transfer and the friction coefficient is only within 3%. In general, increasing the mixing velocity can improve the overall performance of the Taylor flow. However, at a relatively low void fraction, the pressure drop increase outweighs the heat transfer coefficient, leading to a decline in overall performance. Finally, a correlation is proposed to predict the Nu number under Taylor flow in the three-sided heated rectangular microchannel, with an average error of 11.77%.

Accurate modeling of blood flow in a micro-channel as a non-homogeneous mixture using continuum approach-based diffusive flux model

This paper presents a continuum approach for the blood flow simulation, inside the micro-channel of the few micrometers characteristics dimension, within the context of the finite volume method on unstructured grids. The velocity and pressure fields, for the blood flow, are obtained here by solving the Navier–Stokes equations. A particle transport equation, based on the diffusive flux model, provides the hematocrit distribution (i.e., the red blood cells volume-fraction). The momentum conservation equation for a non-Newtonian fluid model is coupled with the particle transport equation through the constitutive blood viscosity model, and this blood viscosity is dependent on hematocrit and shear rate. The continuum approach for blood flow inside the micro-channel of the length scale of a few micrometers to a few hundred micrometers is expected to break down. Interestingly, the present approach provides meaningful insights into biophysics with less computational cost and shows a good match with the experiments and mesoscale simulation with a maximum average deviation of 11% even at the characteristic dimensions of 10–300 μm. A correlation is proposed for additional-local shear rate in terms of the hematocrit and the ratio of red blood cells diameter to the channel diameter, which helps us to demonstrate an increase in the accuracy and also eliminates the issues of unphysical hematocrit reported in the earlier studies available in the literature. The study is extended to provide new results inside a square and rectangular cross section micro-channels, under a range of inlet parameters.

Performance Analysis of a Phase Changing Material Based Thermocycler for Nucleic Acid Amplification

Abstract Modeling, simulation, and thermal performance analysis of a thermocycler for the continuous-flow polymerase chain reaction (CF-PCR), with a phase changing material (PCM)-laden annealing flow path, is presented. The incessant threat of microorganisms such as viruses, bacteria, and fungi has fostered effective, quick, and miniature detection devices in order to curtail the wide-spreading of infections. Microfluidics-based CF-PCR systems are compact and ideal for faster response. The thermal cycling process involves a sequential exposure of a given liquid sample to various temperature conditions when it is taken through the continuous-flow path. As a result, a prescribed periodic change of temperature suitable for deoxyribonucleic acid (DNA) amplification is achieved. A rapid temperature reduction and maintenance of isothermal conditions to facilitate the annealing phase of CF-PCR process by a PCM-assisted cooling is envisaged in the present study. Unsteady, two-dimensional, incompressible fluid flow, and internal convection heat transfer in a microchannel annealing path with melting of tetracosane (C24H50) boundary has been simulated using semi-implicit method for pressure linked equations-consistent (SIMPLEC) algorithm based finite volume solver. Solver validation is carried out against the experimental data on internal convection heat transfer in a rectangular microchannel. A detailed numerical study has been performed to assess the spatiotemporal heat transfer characteristics of internal convection in the microfluidic path when the flow triggers the melting of encapsulated PCM. A minimum sample flowrate with PCM encapsulation of less than 600 μm is found to be ideal for achieving desired thermal performance. The present study evidences the swift temperature reduction and management of isothermal conditions congenial for the annealing process in the CF-PCR system for various sample flowrates and PCM masses. The study offers valuable design input for the development of a microfluidic thermocycler for CF-PCR applications.

Influence of liquid height on pool boiling heat transfer over open rectangular microchannels

Open rectangular microchannels surface (ORMS) has been extensively studied in pool boiling heat transfer because of lower cost of fabrication, ease of application and better heat transfer performance. Researchers have examined liquid height effect on heat transfer performance at various heat fluxes for copper plain surface (CPS). However, few studies have revealed the underlying mechanisms of liquid height for ORMS. This study tested different liquid heights of 1 mm, 3 mm, 5 mm, 7 mm, 9 mm, 12 mm, 15 mm, 20 mm and 50 mm over both ORMS and CPS with deionized water at atmospheric pressure. Critical heat flux (CHF) and heat transfer coefficient (HTC) were determined and considered as functions of liquid height for each liquid level. For ORMS, three different HTC variation trends versus liquid height were evaluated. The results show that the distinction is primarily determined by heat flux, as follows: Type-I has critical liquid level, Type-II has both critical liquid level and optimum liquid level, and Type-III has optimum liquid level. Type-II, however, did not appear for CPS. This research also showed that ORMS and CPS have a critical liquid level of 5 mm, whereas ORMS may be able to achieve a higher heat flux in shallow liquid levels of 1 mm and 3 mm due to its improved liquid replenishment capability.

Influence of Bulk Volume Fraction on Shear‐Induced Diffusion Using the Multi‐Fluid Volume‐of‐Fluid Model

AbstractShear‐induced migration is the diffusion of particles in a direction normal to the flow of suspension. The particles migrate towards the low‐shear stress region from the higher‐shear stress region. In the kinetic theory of granular flow, the driving potential for the migration of particles is the difference in granular temperature, defined as the kinetic energy of particle fluctuations. The effect of bulk volume fraction on the particle migration in a dense suspension flow through a rectangular microchannel is analyzed. The multiphase simulation was conducted using the multi‐fluid volume‐of‐fluid and granular temperature model. The results show a blunted velocity profile, reduced peak velocity, and an increase in variation of local volume fraction with an increase in bulk volume fraction.

Flow thermohydraulic characterization of open diverging microchannel heat sink for high heat flux dissipation

The future fusion reactor puts forward higher demand for the heat dissipation capability of the divertor, which requires to withstand ultra-high heat flux of up to 20 MW/m2. Our previous study demonstrated that microchannel cooling technology is a promising strategy to remove high heat loads on the target plate of the divertor. However, the high pressure drop of the straight rectangular microchannel limits its practical implementation. In this study, we propose an open diverging microchannel heat sink (ODMHS) to reduce the pressure drop under high heat flux and high flow rate conditions. The effects of the width and height of expanding channel on the heat transfer performance and pressure drop were first studied numerically. The results indicated that expanding channel width resulted in a reduction of heat transfer coefficient, whereas the expansion of the channel height led to the enhancement of heat transfer performance. Regardless of the divergence of channel width or height, the enlargement of the channel dimension can effectively reduce the pumping power. Subsequently, experimental tests were carried out in ODMHS with a width ratio and a height ratio of 1.33 and 1.30, respectively. The results demonstrated that the ODMHS can withstand heat flux of up to 15.6 MW/m2 at 3 L/min. This study provides important insights for high heat flux dissipation on the target plate of the divertor by rational design of microchannel structures.

Transient heat transfer and electro-osmotic flow of Carreau–Yasuda non-Newtonian fluid through a rectangular microchannel

PurposeThe purpose of this study is to investigate heat transfer and electrokinetic non-Newtonian flow in a rectangular microchannel in the developed and transient states.Design/methodology/approachThe Carreau–Yasuda model was considered to capture the non-Newtonian behavior of the fluid. The dimensionless forms of governing equations, including the continuity equation for the Carreau–Yasuda fluid, are numerically solved by considering the volumetric force term of electric current (DC).FindingsThe impact of pertinent parameters such as electrokinetic diameter (R), Brinkman number and Peclet number is examined graphically. It is observed that for increasing R, the bulk velocity decreases. The velocity of the bulk fluid reaches from the minimum to the maximum state across the microchannel over time. At the electrokinetic diameter of 400, the maximum velocity was obtained. Temperature graphs are plotted with changes in the various Brinkman number (0.1 < r < 0.7) at different times, and local Nusselt are compared against changes in the Peclet number (0.1 < ℘e < 0.5). The results of this study show that by increasing the Brinkman number from 0.25 to 0.7, the temperature along the microchannel doubles. It was observed that increasing the Peclet number from 0.3 to 0.5 leads to 200% increment of the Nusselt number along the microchannel in some areas along the microchannel. The maximum temperature occurs at Brinkman number of 0.7 and the maximum value of the local Nusselt number is related to Peclet number 0.5. Over time in the transient mode, the Nusselt number also decreases along the microchannel. By the increasing of time, the temperature increases at given value of Brinkman, which is insignificant at Brinkman number of 0.1. The simulation results have been verified by Newtonian and non-Newtonian flows with adequate accuracy.Originality/valueThis study contributes to discovering the effects of transient flow of electroosmotic flow for non-Newtonian Carreau–Yasuda fluid and transient heat transfer through rectangular microchannel. To the authors’ knowledge, the said investigation is yet not available in existing literature.

Numerical study of different micro-channel structures on fluid flow and heat transfer performance

This research mainly proposed three new types of micro-channel heat sink structures. Numerical simulations and simulation calculations were carried out on the heat sink structure. The three groups of inlet flow rates were used as the main variables to analyse the three new types of heat sinks, model flow characteristics and heat transfer performance. In addition, it was compared with the traditional rectangular micro-channel heat sink (RT-MCHS). Based on and compared with RT-MCHS, three new microchannel heat sinks, reverse concave microchannel heat sink (RC-MCHS), co-directional concave microchannel heat sink (CC-MCHS) and convex reverse concave microchannel heat sink (CRC-MCHS), were designed and studied numerically. The comparative analysis of MCHS design performance includes fluid flow characteristics, fluid heat transfer performance and heat transfer efficiency. The effects of inlet velocity on the Darcy friction coefficient, pressure drop, Nusselt number, average outlet temperatures and efficiency factors were studied numerically as inlet velocity from 1 m·s-1 to 5 m·s-1. The results show that the optimal strategy in the new design is the CRC-MCHS, which can hinder the flow of fluid and enable sufficient heat exchange between the liquid and the substrate. In addition, at the optimal inlet flow rate of 3 m·s-1, the outlet water temperature of CC-MCHS is the lowest, indicating the heat transfer performance of the electronic components is the best.

Numerical Investigation of Flow Patterns and Plug Hydrodynamics in a 3D T-junction Microchannel

A three-dimensional (3D) numerical simulation of a two-phase flow liquid/liquid is performed in a rectangular microchannel with a T-junction. The volume of fluid (VOF) method was used under ANSYS Fluent to capture the interface between the two phases. The dynamic mesh adaptation technique together with the assumption of symmetry plane helps us to reduce the computational cost. The study focuses on the flow patterns and hydrodynamics of plugs. So, the influence of the flow rate ratio $$q$$ , the capillary number $$Ca$$ , and the viscosity ratio on the liquid film, the plug/droplet shape, and velocity are examined here. Particularly, the plug/droplet lengths predicted by the simulation show good agreement with the experimental and correlation available in the literature. The results revealed six distinct flow patterns by dispersing water in a continuous phase of silicone oil. By decreasing the flow rate ratio as well as the viscosity ratio, the liquid film thickness increases in the corners and side planes. In turn, this greatly impacts the liquid film velocity and the plug velocity. Furthermore, capillary number (based on two-phase flow velocity) is also shown to have a greater impact than viscosity ratio and flow rate ratio on plug shape, with the curvature radii of the tail always larger than the front one.

Hydrothermal performance analysis of microchannel heat sink with embedded module with ribs and pin-fins

A new microchannel heat sink with embedded modules with ribs and pin-fins is proposed as an effective solution to realize microchannel heat dissipation within low-temperature co-fired ceramic substrates. Enhance heat dissipation with the following strategies: 1. microchannel cooling within the low-temperature co-fired ceramic substrate to shorten the heat transfer path; 2. embedding embedded modules in the substrate to reduce the overall thermal resistance; 3. creating ribs and pin-fins on the embedded modules to enhance convective heat transfer. The impacts of relative rib height, relative pin-fin height, and relative number of auxiliary channels on the heat transfer performance, temperature uniformity, and pressure drop were investigated. The performance of the proposed design has been compared to the performance of similar designs like straight rectangular microchannels, microchannels with pin-fins embedded modules, and microchannels with ribs embedded modules. Under the condition of Reynolds number 458, the heat transfer performance is improved by 63.91%, the temperature uniformity is improved by 67.65% and the pressure drop is increased by only 10.24%. The heat transfer performance of the microchannel heat sink with embedded modules with ribs and pin-fins can be effectively improved by adjusting the height of the pin-fins and the ribs height on the embedded module.

Numerical Study About Nanofluids of Spherical and Tube-Shaped TiO2 Nanomaterials on the Thermal Performance and Entropy Generation of Different Cross-Section Microchannel Heat Sinks

We numerically evaluated the thermal performance of microchannel heat sinks, considering rectangular, hexagonal, and circular cross-sections. Moreover, as a passive heat transfer augmentation technique, dimples were added to improve the rectangular microchannel heat sinks. These simulations use nanofluids based on TiO2 nanoparticles or nanotubes dispersed in bidistilled water as working fluids. The mathematical model considered variable thermophysical properties of the nanofluids; for this purpose, polynomial fittings correlate the dependence of the thermophysical properties on the temperature. We considered a heat flux of q″ = 50 W/cm2 at the microchannel’s lower surface as a boundary condition along with laminar flow conditions. The numerical simulations allowed the Nusselt numbers and entropy generation calculation, which were the basis for the thermal performance calculation. Regarding the effect of TiO2 nanoparticles shape, spherical TiO2 nanoparticles based nanofluids using rectangular microchannels improve the Nusselt number. Moreover, the frictional entropy decreases with nanofluids based on TiO2 nanotubes, but the thermal entropy decreases with nanofluids based on TiO2 nanotubes. Incorporating dimples in the rectangular microchannel enhances the Nusselt numbers and lowers the entropy generation. Considering the Reynolds number range and from the perspective of Nusselt number and entropy generation, we concluded that the microchannels must be operated at a high Reynolds number to improve the microchannel heat sinks thermal performance.