Plain Microchannel Research Articles

Enhanced single-phase and flow boiling heat transfer performance in saw-tooth copper microchannels with high L/Dh ratio

Owing to its potential of high heat dissipation capability, flow boiling in copper microchannels is one of the most effective cooling techniques for high power density thermal components. Normally, it is difficult to substantially enhance the HTC and CHF in high L/Dh (channel length relative to hydraulic diameter) microchannels due to bubble confinement and boiling crisis. To date, various functional geometries and surface modifications have been extensively studied to enhance flow boiling performances. In this study, the effect of extensive two-phase mixing in the entire channel length on flow boiling performance is investigated in this saw-tooth copper microchannel with L/Dh ratio up to 75 on DI-water ranging from 50 to 300 kgm-2s−1. The results show that HTC and CHF are dramatically enhanced owing to the intensified two-phase mixing and continuous interruption of thermal boundary layers. For example, CHF and HTC are up to 280 Wcm−2 and 141.8 kWm-2K−1, respectively, at G = 300 kgm-2s−1. These enhancements are ∼ 87% and ∼ 110.7%, respectively, compared to that of plain microchannel. Furthermore, a correlation of CHF is developed to predict CHF.

A comprehensive analysis of a rectangular microchannel heat sink furnished with a circular perforated cylindrical pinfin

In this study, a simulation has been performed to investigate the effect of circular perforated pinfins on the performance of microchannel heat sink by varying the number of holes and their locations on the pinfins. A total of ten configurations are considered in this work including a plain microchannel (without pinfin) and a solid pinfin case. The study was conducted on a single-phase flow using deionized water as coolant and the Reynolds numbers range from 150 to 350 when a constant heat flux of 100W/cm2 has been applied at the heated base wall of a heat sink. The results obtained indicate that the location, as well as the number of perforations, affects the heat transfer capacity and pressure drop that occurs in the microchannel. However, the outcomes of the present analysis contradict the findings for thermal airflows when identical cases have been applied to the micro heatsink. According to the present analysis case 1 (perforation at the underside of the pinfin) has the maximum Nusselt number followed by case 2 (perforation at the mid of the pinfin) and case 3 (perforation at the topside of the pinfin) whereas the minimum pressure drop is achieved by case 8 (four equidistant perforations) among pinfin configurations. The highest performance factor is achieved by case 1 at a low Reynolds number while case 6 (perforation at the underside and topside) performs best at a higher Reynolds number.

Investigation on the thermohydraulic performance and entropy-generation of novel butterfly-wing vortex generator in a rectangular microchannel

• A new butterfly-wing vortex generator is introduced on the bottom wall of microchannel. • Thermohydraulic performance and entropy-generation in microchannel are investigated. • The maximum Pf of 1.23 and minimum N s , a of 0.84 are obtained . • The proposed microchannel is advantageous according 1 st & 2 nd law of thermodynamics. In the present study, a 3D numerical analysis is carried out to understand the effect of the butterfly-wing vortex generator on the thermohydraulic performance and entropy-generation in a rectangular microchannel. To validate the numerical model, experiments are carried out in the plain microchannel of width ( W ) = 1 mm, height ( H ) = 0.63 mm, and length ( L ) = 50 mm. Further, the simulation is extended to study the effect of several geometric parameters of the butterfly-wing vortex generator, i.e., height ( h ) = 0.05, 0.1 & 0.2 mm, bigger width ( w ) = 0.24, 0.36 & 0.48 mm, smaller width ( b ) = 0.12, 0.18 & 0.24 mm, length ( l ) = 1, 2 & 3 mm, and number of wings ( n ) = 5, 8 & 11 with varying Reynolds number ( R e ) in the range of 142 to 945. Thus, a total of tweleve different combination of microchannel are formed by varying the geometric parameters of the butterfly-wing to carry out the parametric study. The simulation results reveal that the presence of the butterfly-wing vortex generator enhances the convective heat transfer rate (10-26)% with an increase in pressure drop (3-14)%, and reduces the total entropy-generation (3-16)% when compared to a plain microchannel. It is also found that with an increase in h, n, and w, the friction factor ( f ) increases (7-13)%, (3-8)% and (1-9)%, respectively,while the average Nusselt number ( Nu avg ) increases (4-11)%, (4-9)%, and (5-12)%, respectively, by increasing Re value from 142 to 945. However, the l has no significant effect on f and Nu avg . A decreasing trend of Nu avg is seen for increasing b, whereas f does not vary significantly with b . The total entropy generation ( S G ) decreasing with the increase in h , n , and w and remain invariant for b and l . For the studied geometric parameters and Re values, the maximum increase in performance of 23% and a maximum reduction in total entropy-generation of 16% are obtained for the microchannel with butterfly-wing of w = 0.48 mm, b = 0.24 mm, l = 3 mm, h = 0.1 mm, n = 5 at Re = 945.

Effect of undercut slots on the overall performance of microchannel heatsink

In the current study, a numerical analysis has been performed to examine the performance characteristics of the slotted microchannel heat sink. Twelve equidistant slots are entrenched at the base wall of the channel. Four different shapes of slots are considered in this study. They are rectangular (case 1), trapezoidal (case 2), V (case 3) and curved shaped (case 4). Numerical simulations have been performed for these cases with Reynold’s number ranging between 150 to 350 with a constant heat flux of 100 W/cm2 and the results are compared with the plain channel. It is observed that cases 1 and 2 have higher overall thermal performance than the plain channel in which case 2 outperforms case 1 whereas the performance of cases 3 and 4 are lower than the plain microchannel. It is suggested from the analysis that the plain microchannel may be replaced by a trapezoidal shape slotted microchannel in further studies.

Analysis of heat transfer and fluid flow in a microchannel heat sink with sidewall dimples and fillet profile

The performance of microchannel with sidewall dimples and fillet profile in the bottom surface is investigated. Two dimple sizes of (0.5 mm and 1 mm) are systematically clustered along the channels with and without fillet are considered. The laminar flow regime is assumed with Reynolds numbers ranging from 200 to 1200. The results show that the dimples and fillet profile have a significant effect on the thermal performance of microchannel. The Nusselt number of the microchannels with 1 mm dimples is 20% higher than the plain microchannel. However, an increase in pressure drop of 10% was obtained. In addition, the fillet profile impacts the thermal performance of microchannels without pressure drop penalty increase. Combining both dimples and fillet profile causes a significant enhancement in the thermal performance. Nusselt number of microchannels heat sink with 1 mm dimple size and fillet profile is 60% higher compared to the plain microchannel.

Enhanced heat transfer coefficient of flow boiling in microchannels through expansion areas

Flow boiling in microchannels is a promising technique to achieve large cooling rates and high heat transfer coefficients for electronic cooling. This work reports an effective approach to enhance flow boiling heat transfer in microchannels through expansion areas. Flow boiling experiments were conducted on plain microchannels and microchannels with single and three expansion areas for comparison. Experimental results show that the flow boiling heat transfer coefficient can be effectively enhanced by up to 43.3% through adding three expansion areas in microchannels, while the pressure drop variation is within 3 kPa. Expansion areas significantly reduce the inlet temperature fluctuation, indicating the suppression of flow boiling instability in microchannels. As disclosed by the visualization of flow patterns, the improved heat transfer coefficient can be attributed to the enhanced bubble nucleation and formation of a nonuniform liquid layer near the corners of expansion areas.

Eulerian-Lagrangian investigation of nanoparticle migration in the heat sink by considering different block shape effects

In this study, the Eulerian-Lagrangian method is employed to inspect the impact of nanoparticle migration on the hydrothermal and entropy generation features of Fe3O4–water nanofluid in a ribbed-blocked microchannel with two different arrangements. The results are compared with those of the plain microchannel at different volumes of flow rate and nanoparticle concentration. It was found that the nanoparticle migration results in an increase in the pressure drop, friction factor, heat transfer coefficient, overall hydrothermal performance of nanofluid as well as the thermal and frictional entropy generations. In addition, it was depicted that the increase of mass flow rate is associated with the rise of pressure drop, heat transfer coefficient and frictional entropy generation and the decrease of friction factor and thermal entropy generation. Moreover, the augmentation of nanoparticle volume fraction was associated with increasing pressure drop, friction factor, and heat transfer coefficient and the decrease of thermal entropy generation. Finally, it was found that for all the examined cases, the overall hydrothermal performance of the Fe3O4-water nanofluid is better than the pure water.

Thermal performance evaluation of a microchannel with different porous media insert configurations

PurposeThis paper aims to numerically investigate the thermal performance evaluation of a microchannel with different porous media insert configurations.Design/methodology/approachHeat transfer and pressure drop of fluid flow through a three-dimensional (3D) microchannel with different partially and filled porous media insert configurations are investigated numerically. The number of divisions and positions of porous material inside the microchannel for 12 different arrangements are considered. A control volume method is used for single-phase laminar flow with the Darcy–Forchheimer model used for the porous media. The geometry of the problem consists of a microchannel with a rectangular cross-section of 0.4 mm × 0.2 mm and length 20 mm, with a stainless steel porous material insert with a porosity coefficient of ε = 0.32 and a Darcy number of Da = 2.7 × 10−4.FindingsNumerical results show that when the transverse arrangement is used, as the number of partitions increases, the thermal performance is improved and the heat transfer increases up to 300% compared to that of the plain microchannel. Comparing the obtained results from the microchannels with transverse and longitudinal configurations, at low Reynolds numbers, the transverse arrangement of porous blocks and at high Reynold numbers, the longitudinal arrangement present the best thermal performance which is virtually four times higher compared to the obtained Nu numbers from the plain microchannel. The results show that as the volume of porous material is constant in the cases with various transverse porous blocks, the pressure drop is not changed in these cases. Also, the highest thermal performance ratio is when the porous material is placed along the walls in a longitudinal direction.Originality/valueTo the best knowledge of the authors, in the previous research, the effect of the arrangement and location of the porous medium in the transverse and longitudinal direction in the microchannel and their effect in different states on the behavior of flow and heat transfer has not been numerically investigated. In this study, the porous media configuration and its placement in a 3D microchannel were numerically studied. The effect of porous material layout and configurations in different longitudinal and transverse directions on the pressure drop, heat transfer and thermal performance in the 3D microchannel is investigated numerically.

Effect of shape and arrangement of micro-structures in a microchannel heat sink on the thermo-hydraulic performance

In the present article, micro-pillars and micro-blind holes has been introduced inside the microchannel heat sink (MCHS) to enhance the heat transfer coefficient and reduce the interface temperature as well as pumping power. Optimization of these micro-structures (shape and arrangements) has been performed by three computational analyses in Ansys 19.3. A microchannel of dimension 0.4 mm×0.4 mm×50 mm has been considered in this study with water as a working fluid. The three analyses are as follows- (i) selection of blind hole, (ii) selection of optimized position using selected blind hole from the first analysis, and (iii) selection of optimized pillar cross section using selected arrangement. The heat transfer coefficient, pressure drop, interface temperature, temperature gradient, and overall thermal performance of all the nineteen cases has been compared with same parameters of a plain channel for a range of Reynolds number 500 to 1000. The overall performance of the MCHS with circular blind hole has been found to be 5% higher than the plain channel the best among the selected cross sections. The optimized positions of pillars and blind holes are suggested from the second analyses. The heat transfer coefficient of the MCHS with suggested arrangement has been estimated 1.61 to 1.7 times of the same of a plain microchannel for the same range of Reynolds number. Whereas, the thermo-hydraulic performance of the same is increased by 12.4% to 16.5%. From the third analysis, the best thermo-hydraulic performance (14.8% to 19.4% higher than the plain channel) has been identified for the MCHS with elliptical pillars. A detail thermo-hydraulic analysis has been performed to support these facts.

Effect of outlet plenum design on flow boiling heat transfer in microchannel heat sinks

Instabilities during flow boiling in microchannel lead to fluctuations in temperature, pressure, mass flux. It is well known that the instabilities can be suppressed by effective extraction of the accumulated vapor away from the outlet plenum. Here we investigate the effect of outlet plenum volume on instabilities during flow boiling in a heat sink comprising of fourteen parallel microchannels within a footprint area of 1 × 1 cm2. Plain and nanostructured microchannel surfaces are investigated with two outlet plenum designs including the one with same volume (baseline case) as the inlet plenum and another one with eight times the volume of the inlet plenum. An eight-fold increase in the outlet plenum volume facilitates a significant reduction in amplitude of fluctuations of surface temperature from 6.6 to 2.8 °C at heat flux of 137 W/cm2 and mass flux of 500 kg/m2s. Efficient vapor removal due to the increase in the manifold volume also lowers the pressure drop, thereby allowing maximum reduction in surface temperature of 4.8 °C and 3 °C for mass flux of 250 and 500 kg/m2s, respectively, compared to that of the baseline case. The enhancement in heat transfer by implementing nanostructured surface with larger outlet plenum volume is marginal with a temperature reduction of about 0.5 °C in comparison to that with plain microchannel with similar outlet plenum volume. Overall, it is shown that the performance improvement obtained with simple outlet plenum design modifications can be comparable or better in comparison to the enhancement due to complex surface modification strategies.

Computational analysis of the thermal performance of rarefied air flow in V‐shaped microchannels

AbstractIn this study, a computational fluid analysis of a slip flow developing thermally and hydrodynamically in a triangular microchannel has been considered. The wall of the channel is preserved at a fixed temperature. Temperature jump and velocity slip boundary conditions are imposed on the surfaces. The microchannel is constructed from seven triangular‐shaped channels and the angle of the microchannel (θ) is varied from 0° to 40°. Simulations are carried out for , and the air is used as a working fluid with variable physical properties. The simulation results show that the triangular microchannel can improve heat transfer as compared with plain microchannels. An optimal θ of 20° is found to provide the best heat transfer at moderate frictional losses. Finally, correlations for the average Nusselt number and the average friction coefficient among all parameters are proposed as follows: , .

Fluid flow and heat transfer in microchannel with porous bio-inspired roughness

A numerical simulation is conducted to investigate the hydrothermal performance of microchannel modified with bio-inspired fish scale type roughness structures on the hot bottom surface. The fish scale geometry and permeability of it are varied along with fluid velocity to analyze the effect of these parameters on the heat transfer, pressure drop, and overall performance of the microchannel. The present result indicates that the modified bio-inspired microchannel can enhance significant heat transfer rate than a plain microchannel. It is observed that fish scale geometry, permeability, and Reynolds number has a substantial effect on the hydrothermal performance and the maximum heat transfer can be achieved by solid fish scale type roughness with a considerable pressure drop. However, the pressure drop can be reduced through porous fish scale with a minimal reduction in heat transfer. A maximum heat transfer enhancement of 78.8% and 78.1% is observed for the solid and porous fish scale of Darcy number 10−5, respectively. Besides, a maximum enhancement in friction factor of 48.5% and 37.8% is observed for the solid and porous fish scale of Darcy number 10−5, respectively. Thus, the trade-off between heat transfer and pressure drop is found best in porous fish scale than a solid fish scale microchannel considered in the present study. The maximum overall performance value for every considered case in this study is found as 1.60 for porous fish scales, and 1.56 for the solid fish scale microchannel.

Combined effect of inlet restrictor and nanostructure on two-phase flow performance of parallel microchannel heat sinks

In this study, the combined effect of nanostructure and inlet restrictor on reducing the instabilities during flow boiling in parallel microchannel heat sinks is investigated experimentally. Four types of microchannel heat sinks are considered; plain microchannel, microchannel with inlet restrictor, nanostructured microchannel, and nanostructured microchannel with inlet restrictor. Different flow regimes such as bubbly flow, slug flow, annular flow, and partial dry out are observed with the variation in applied heat flux and mass flux. The fluctuations in pressure, temperature, and mass flux are characterised in each regime. It is found that the fluctuations increase with power input, which is primarily due to backflow of vapour in the upstream direction of flow. The microchannel with inlet restrictor is more effective in reducing fluctuations and result in less surface temperature compared to the baseline case of plain microchannel without restrictor at the same mass flux. Moreover, if the nanostructured surface is added to the plain microchannel with inlet restrictor, the effectiveness in reducing fluctuations increases at higher heat flux and also produces less surface temperature compared to other types of microchannels.

Exergy analysis of microchannel heat exchangers

This study investigates the exergetic efficiencies of four plain microchannel heat exchangers under single-phase and two-phase flow conditions using de-ionised water as the working fluid. The friction factor and heat transfer coefficient data of microchannels are obtained using experimental studies from the literature. The exergetic efficiencies of microchannels are compared to reveal the effect of different geometrical parameters. The results showed that the microchannel aspect ratio is an insignificant parameter on the exergetic efficiency for single-phase flow conditions. However, the exergetic efficiency increased around 90% with the decreasing of the microchannel aspect ratio in two-phase tests. On the other hand, the microchannel heat exchanger having shorter heated length exhibited about 10% and 90% improved exergetic efficiency both in single-phase and two-phase regimes respectively. Moreover, the thermo-economic analysis has been performed in two-phase conditions to propose design guidelines for microchannel heat exchangers from the exergy and thermo-economic performance perspectives.

Experimental and numerical investigations of fluid flow and heat transfer in a bioinspired surface enriched microchannel

In this paper, experimental and numerical studies of fluid flow and heat transfer characteristics of novel fish scale bioinspired structures on the bottom surface of microchannel to enhance heat transfer are presented. Deionized water is selected as the working fluid. A three-dimensional numerical model is developed to analyse conjugate heat transfer in the microchannel, and the model is validated with the experimental results obtained from a copper microchannel of hydraulic diameter of 193.5 μm and length of 20 mm for three different Reynolds numbers and a constant bottom heat flux of 50 W/cm2. Further the numerical model is extended to study the effect of several geometrical parameters on the thermohydraulic performance of microchannel. It is found that the bioinspired surface can enhance the convective heat transfer compared to the plain microchannel, whereas the pressure drop is found less for fish scale structure with dimensionless inclination height of 0.026. The friction factor for the fish scale inclination height of 0.026 reduces by maximum 5% and the Nusselt number increases by maximum 14% as compared to those quantities for the plain microchannel. Further increment in the inclination height increases the heat transfer rate and friction factor than the plain microchannel. The maximum value of the performance evaluation criteria is found as 1.75 at inclination height of 0.26 and Re = 1050. Correlations of Nusselt number and Poiseullie number are developed for this type of microchannel.

Single phase laminar fluid flow and heat transfer in microchannel with cylindrical and parallelepiped micro-fins

In this paper, the fluid flow and heat transfer characteristics of water as coolant in cylindrical and parallelepiped micro-finned rectangular microchannels are investigated. Experiments are performed on a copper plain microchannel with six parallel channels of dimensions 350 (width) × 605 (depth) μm for Reynolds number in the range of 67 to 153 and four different heat inputs. Experimental results are used to validate the numerical model, which is extended to analyze the effects of diameter of cylindrical and length and width of parallelepiped micro-fins on the overall performance of microchannel using non-dimensional parameters, such as Poiseuille number, Nusselt number and performance evaluation criteria. It is found that the enhancement in heat transfer is higher than that of pressure drop. Smaller diameter cylindrical fin performs better than the plain channel, when the performance is evaluated considering both heat transfer and pressure drop in channels. Correlations are developed for Poiseuille number and Nusselt number for cylindrical and parallelepiped micro-finned rectangular channels, which can be used to design microchannel with extended surface for thermal management of electronic devices.

EXERGO-ECONOMIC ANALYSIS OF MICROCHANNELS IN SINGLE-PHASE FLOW

With the increase of energy demand, many researchers tried to develop scientific approaches in order to design more efficient and environmentally friendly energy systems. Exergo-economic (thermoeconomic) analysis of a system or device is an efficient tool for evaluating the system in terms of the thermodynamic and economic aspects. In this parametric study, exergo-economic analysis of rectangular copper plain microchannels under single-phase flow conditions were investigated using de-ionised water. The exergo-economic performance was evaluated based on the relative cost difference and unit cost per product exergy tools. The channel aspect ratio effect on the unit cost per product exergy and relative cost difference was examined using three microchannel test sections with the same channel hydraulic diameter (Dh = 0.56 mm) and length (L = 62 mm) but different aspect ratios (β = 0.5, 2.56 and 4.94) under single-phase flow conditions. The results showed that the exergo-economic performances of the three microchannel test sections decreased as the net heat input increased over the experimental range. Moreover, the exergo-economic performance of test section 2 (β = 4.94) was found to be greater than the exergo-economic performances of test sections 1 and 3 (β = 0.5 and 2.56) at fixed flow rate and fixed net heat input case.

Flow boiling of HFE-7100 in silicon microchannels integrated with multiple micro-nozzles and reentry micro-cavities

Flow boiling of dielectric fluids in microchannels is one of the most desirable cooling solutions for high power electronics. However, the flow boiling of dielectric fluids is hindered by their unfavorable thermophysical properties. Specifically, without precooling dielectric fluids, it is challenging to promote critical heat flux (CHF) due to its high vapor density, low surface tension and the resulted superior wettability. In this study, each side wall of a five-parallel silicon microchannel array was structured with an array of microscale reentry cavities and four micronozzles bypassed by an auxiliary channel. The present microchannel configuration aims to significantly enhance CHF of HFE-7100 flow boiling by improving global liquid supply using auxiliary channels and micrononozzles as well as by sustaining liquid film using capillarity induced by reentry cavity array. Equally important, these structures can promote nucleate boiling at low heat flux, generate intense mixing, and promote thin film evaporation at high heat flux, resulting in high flow boiling heat transfer rate. Flow boiling of HFE-7100 in the present microchannel configuration is characterized with mass flux ranging from 231 kg/m2 s to 1155 kg/m2 s. The effective two-phase heat transfer coefficients (HTCs) are ranging from 6 kW/m2 K to 117 kW/m2 K. Compared to the four-nozzle plain-wall microchannels, for example, the effective HTC and CHF can be substantially enhanced up to 208% and 37%, respectively, without escalating pressure drop at a mass flux of 462 kg/m2 s. Compared to plain microchannels with inlet restrictors, CHF is considerably enhanced up to 70% with a reduction of pressure drop ∼82% at a mass flux of 1155 kg/m2 s. Significantly reduced pressure drop is achieved by integrating bypass and the enhanced confined bubble removal. A peak CHF value of 216 W/cm2 is achieved at mass flux of 2772 kg/m2 s in the present microchannel configuration with inlet temperature at room temperature.

Flow Patterns During Flow Boiling Instability in Silicon-Based Pin-Fin Microchannels

In this paper, the flow patterns during water flow boiling instability in pin-fin microchannels were experimentally studied. Three types of pin-fin arrays (in-line/circular pin-fins, staggered/circular pin-fins, and staggered/square pin-fins) were used in the study. The flow instability started to occur as the outlet water reached the saturation temperature. Before the unstable boiling, a wider range of stable boiling existed in the pin-fin microchannels compared to that in the plain microchannels. Two flow instability modes for the temperature and pressure oscillations, which were long-period/large-amplitude mode and short-period/small-amplitude mode, were identified. The temperature variation during the oscillation period of the long-period/large-amplitude mode can be divided into two stages: increasing stage and decreasing stage. In the increasing stage, bubbly flow, vapor-slug flow, stratified flow, and wispy flow occurred sequentially with time for the in-line pin-fin microchannels; liquid single-phase flow, aforementioned four kinds of two-phase flow patterns, and vapor single-phase flow occurred sequentially with time for the staggered pin-fin microchannel. The flow pattern transitions in the decreasing stage were the inverse of those in the increasing stage for both in-line and staggered pin-fin microchannels. For the short-period/small-amplitude oscillation mode, only the wispy flow occurred. With the increase of heat flux, the wispy flow and the vapor single-phase flow occupied more and more time ratio during an oscillation period in the in-line and staggered pin-fin microchannels.

A Spring in Performance: Silica Nanosprings Boost Enzyme Immobilization in Microfluidic Channels.

Enzyme microreactors are important tools of miniaturized analytics and have promising applications in continuous biomanufacturing. A fundamental problem of their design is that plain microchannels without extensive static internals, or packings, offer limited exposed surface area for immobilizing the enzyme. To boost the immobilization in a manner broadly applicable to enzymes, we coated borosilicate microchannels with silica nanosprings and attached the enzyme, sucrose phosphorylase, via a silica-binding module genetically fused to it. We showed with confocal fluorescence microscopy that the enzyme was able to penetrate the ∼70 μm-thick nanospring layer and became distributed uniformly in it. Compared with the plain surface, the activity of immobilized enzyme was enhanced 4.5-fold upon surface coating with nanosprings and further increased up to 10-fold by modifying the surface of the nanosprings with sulfonate groups. Operational stability during continuous-flow biocatalytic synthesis of α-glucose 1-phosphate was improved by a factor of 11 when the microreactor coated with nanosprings was used. More than 85% of the initial conversion rate was retained after 840 reactor cycles performed with a single loading of enzyme. By varying the substrate flow rate, the microreactor performance was conveniently switched between steady states of quantitative product yield (50 mM) and optimum productivity (19 mM min-1) at a lower product yield of 40%. Surface coating with silica nanosprings thus extends the possibilities for enzyme immobilization in microchannels. It effectively boosts the biocatalytic function of a microstructured reactor limited otherwise by the solid surface available for immobilizing the enzyme.