Investigations On Liquid Flow, Heat Transfer Characteristics In Microscale And Its Applications

Due to the promising applications of microfluidic devices in fields such as high efficient heat and mass transfer processes, production of high added value products etc, the investigations on liquid flow and heat transfer characteristics in microscale are receiving more and more attentions. Questions such as whether the conventional scale theory are still valid in microscale, factors that are negligible in conventional scale will have effect on the liquid flow and heat transfer characteristics in microscale or not should be analyzed and discussed. In this paper, experiments of different liquids’ (water, [C2mim][EtSO4] aqueous solutions and NaNO3 aqueous solutions) flow processes in microscale were performed, simulations of ionic liquid solutions’flow and heat transfer processes in microscale were carried out using COMSOL Multiphysics, the characteristics of using microfluidic device to synthesize mPEG-PLGA nanoparticles were studied. The main contents are as follows:1. The liquid flow characteristics of water in 3 different material tubes (SS, PEEK and FS) with diameters in the range 44.5-1011μm, roughness (relative roughness) in the range 0.1-5.2 μm (0.02-4.32%) were studied and 2502 data points over a Reynolds number range 29-11644 were obtained. A parameter a was proposed to describe the deviation between microscale (1-1000 μm) and conventional scale (≥1000μ). Based on the characteristic parameter, a correlation was proposed to calculate the critical Reynolds number for microscale (AAD 1.9%), and a modified Moody equation was proposed to calculate the friction factor in turbulent region for microscale (AAD 2.4%).2. The liquid flow characteristics of 10-2、10-4、10-6 mol-L-1 [C2mim][EtSO4] aqueous solutions and NaNO3 aqueous solutions in PEEK microtubes (smooth) with diameters in the range 44.5-102.5μ∴m were studied. The experimental results indicate that the electroviscous effect in microtubes with diameter larger than 44.5 μm is negligible and there is no difference between ionic liquid aqueous solution and sodium nitrate aqueous solution’s flow characteristics. Furthermore, COMSOL Multiphysics was used to simulate the influence of diameter (1-100μm) and concentration (10-2、10-4、10-6 mol-L-1) on electroviscous effect during flow process. It is found that when the concentration decreases to 10-6 mol-L-1 and diameter equals or less than 10 μm, the influence of electroviscous effect on flow characteristics is larger than 5% and the electroviscous effect is significant.3. The thermal conductivities of [C2mim][EtSO4] and its mixtures were measured and a correlation was proposed to predict the thermal conductivity under different temperatures and concentrations based on the second-order Scheffe polynomial. A topological index method was proposed to estimate the thermal conductivity of ionic liquids. COMSOL Multiphysics was used to simulate the influence of diameter (1-100 μm) and concentration (10’2、10-4、10-6 mol-L-1) on electroviscous effect during heat transfer process. It is found that when the concentration decreases to 10-6 mol-L-1 and diameter equals or less than 5 μm, the influence of electroviscous effect on heat transfer characteristics is larger than 5% and the electroviscous effect is significant.4. A PDMS microfluidic device was made using photolithography method. mPEG-PLGA nanoparticles with diameters in the range 19-129 nm were obtained, by controlling the flow ratio, mPEG-PLGA molecular weight and concentration, in the microfluidic device under stable laminar flow region. It is found that microfluidic method can be used to precisely control the nanoparticle size, also, the properties of nanoparticles synthesized by microfluidic method such as PDI are better than the nanoparticles synthesized by traditional method. Ibuprofen and curcumin were used to synthesize drug-loaded mPEG-PLGA nanoparticles, also by microfluidic method, and satisfying drug loading, encapsulation efficiency and in vitro drug release kinetics were obtained.