Long-Sheng Kuo

Effect of viscosity of base fluid on thermal conductivity of nanofluids

This study aims to investigate the effect of viscosity of the base fluid on the thermal conductivity of nanofluids in which Fe3O4 nanoparticles are suspended in the base fluid composed of diesel oil and polydimethylsiloxane. Viscosity of the base fluid is varied by changing the volumetric fractions between both fluids. The measured thermal conductivity of nanofluids gradually approaches the value predicted by the Maxwell equation by increasing the viscosity. It demonstrates that the viscosity of nanofluids does affect the thermal conductivity of nanofluids, and the Brownian motion of suspended particles could be an important factor that enhances the thermal conductivity of nanofluids.

Applications of Ferro-Nanofluid on a Micro-Transformer

An on-chip transformer with a ferrofluid magnetic core has been developed and tested. The transformer consists of solenoid-type coil and a magnetic core of ferrofluid, with the former fabricated by MEMS technology and the latter by a chemical co-precipitation method. The performance of the MEMS transformer with a ferrofluid magnetic core was measured and simulated with frequencies ranging from 100 kHz to 100 MHz. Experimental results reveal that the presence of the ferrofluid increases the inductance of coils and the coupling coefficient of transformer; however, it also increases the resistance owing to the lag between the external magnetic field and the magnetization of the material.

Thermal Conductivity of Nanofluid with Magnetic Nanoparticles

The thermal conductivities of Fe3O4 and Al2O3 nanofluids with the viscous base fluid composed by various fluids are investigated in this study. In order to change the viscosity of mixed fluid, the volumetric fractions between two fluids in the mixed fluid are varied. Measured values of thermal conductivity of nanofluids gradually approach the values predicted by Maxwell equation with increasing the viscosity. Our measured results demonstrate that Brownian motion of suspended magnetic particles could be an important factor that enhances the thermal conductivity of nanofluids, but it has little effect for suspended Al2O3 nanoparticles. It also indicates that the conduction part of prediction model can be obtained from Maxwell prediction.

Protein detection using a radio frequency biosensor with amplified gold nanoparticles

This study presents a device for protein detection using a low-pass radio frequency filter with gold nanoparticles (AuNPs). Self-assembled multilayer gold nanoparticles were immobilized on the sensing surface of the filter by sandwich immunoassay. The measured frequency of the filter ranges from 50MHzto30GHz. The multilayer gold nanoparticles result in a change of 3dB bandwidth of the low-pass filter. Results show that 1ng∕μl of RIgG solution can be detected after triple-layer AuNPs are completely formed. The change in 3dB bandwidth increases with the concentration of target protein. Therefore, this device has potential for protein quantification.

Influence of surface temperature and wettability on droplet evaporation

The evaporation characteristics of sessile water droplets on various wettability substrates (hydrophilic, hydrophobic, and mixed wettability surfaces) were experimentally investigated in this study. Placing droplets on a regulated superheated surface led to rapid vapor bubble formation. The droplet parameters, such as the contact angle and volume evolution over evaporation time, were experimentally measured. The results revealed that surface wettability plays a critical role not only in vapor bubble dynamics but also in evaporation.

Synthesis, characterizations and hydrophobicity of micro/nano scaled heptadecafluorononanoic acid decorated copper nanoparticle

Copper nanoparticle was synthesized in the presence of heptadecafluorononanoic acid by the conventional solution immersion method at room temperature from the copper plate, as a resource material. The bulk etching rate was calculated by the weight loss method. The pale green colored Cu-HDFN was characterized by Fourier transform infrared spectroscopy, UV-Visible spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and contact angle measurements and the results are critically analyzed.

Reversed boiling curve phenomenon on surfaces with interlaced wettability

We experimentally investigated the effects of contact angle difference of heterogeneous wettability surfaces on pool boiling. For surfaces exhibiting heterogeneous wettability, this study determined that the pool boiling curve experiences a superheat decrease in some regions before the system achieves the critical heat flux. In addition, oscillation of the vapor column and bubble transverse motions on the heterogeneous wettability coated surface were observed.

Real-time remote monitoring of temperature and humidity within a proton exchange membrane fuel cell using flexible sensors.

This study developed portable, non-invasive flexible humidity and temperature microsensors and an in situ wireless sensing system for a proton exchange membrane fuel cell (PEMFC). The system integrated three parts: a flexible capacitive humidity microsensor, a flexible resistive temperature microsensor, and a radio frequency (RF) module for signal transmission. The results show that the capacitive humidity microsensor has a high sensitivity of 0.83 pF%RH−1 and the resistive temperature microsensor also exhibits a high sensitivity of 2.94 × 10−3 °C−1. The established RF module transmits the signals from the two microsensors. The transmission distance can reach 4 m and the response time is less than 0.25 s. The performance measurements demonstrate that the maximum power density of the fuel cell with and without these microsensors are 14.76 mW·cm−2 and 15.90 mW·cm−2, with only 7.17% power loss.

Polymerase chain reaction with phase change as intrinsic thermal control

This research demonstrated that without any external temperature controller, the capillary convective polymerase chain reaction (ccPCR) powered by a candle can operate with the help of phase change. The candle ccPCR system productively amplified hepatitis B virus 122 base-pairs DNA fragment. The detection sensitivity can achieve at an initial DNA concentration to 5 copies per reaction. The results also show that the candle ccPCR system can operate functionally even the ambient temperature varies from 7 °C to 45 °C. These features imply that the candle ccPCR system can provide robust medical detection services.

Effects of Slip Boundary Conditions on Rayleigh-Bénard Convection

This work studied the Rayleigh-Benard convection under the first-order slip boundary conditions in both hydrodynamic and thermal fields. The variation principle was applied to find the critical Rayleigh number of instability. The exteneded relations of the critical Rayleigh number ( R c ) and the wavenumber ( a c ) under partially slip boundary conditions were derived. The numerical results showed that both R c and a c are decreasing with increasing the Knudsen number. The dependence of R c on the Knudsen number ( K ) shows that when K ≤10 −3 , the boundary can be considered as nonslip, while K ≥10, it can be considered as free boundaries. The maximum change rate occurs when the Knudsen number is around 0.1, indicating that the system would be affected significantly in that range.