Magnetohydrodynamic pumping in nuclear magnetic resonance environments

Abstract

We present a DC magnetohydrodynamic (MHD) pump as component of a nuclear magnetic resonance (NMR) microfluidic chip. This is the first time that MHD pumping in an NMR environment was observed and demonstrated. This chip generates a maximum flow rate of 1.5 L min −1 (2.8 mm s −1 in the microchannel) for an applied voltage of 19 V with only 38 mW of power consumption in a 7 T superconductive magnet. We developed a simple method of flow rate measurement inside the bulky NMR magnet by monitoring the displacement of a liquid-liquid interface of two immiscible liquids in an off-chip capillary. We compared and validated this flow measurement technique with another established technique for microfluidics based on the displacement of microbeads. This allowed us to characterize and compare the flow rate generated by the micropump on top of a permanent magnet (B 1 = 0.33 T) with the superconductive magnet (B 0 = 7.05 T). We observed a 21-fold increase in flow rate corresponding to the ratio of the magnetic field intensities (B 0 /B 1 = 21) in accordance with the theoretical flow dependence on the magnetic field intensity. The final aim is to integrate MHD pumps together with planar coils in a microfluidic system for NMR analysis. The high performance of MHD pumps at relatively low flow rates is seen as an asset for NMR and MRI applications.

Recent advances in microscale pumping technologies: a review and evaluation

“…MHD pumps with the highest body force are obtained when the current density, magnetic field intensity and electrode length are maximized (by minimizing the cross-sectional area). In an NMR environment, this pump by Homsy et al (2007) was shown to perform the best as compared to other MHD pumps under such operating conditions but the superconductive magnet used was several feet high.…”

“…For laminar flow, the maximum flow rate can be obtained by ( Several MHD pumps in the literature were compared against a recent MHD pump designed for use in a nuclear magnetic resonance (NMR) environment by Homsy et al (2007).…”

Micro-magnetofluidics: interactions between magnetism and fluid flow on the microscale

“…The electric field is applied through a small gap connecting the reservoirs with electrodes and the flow channel. To increase the flow rate, Homsy et al (2007) used a strong magnet of 7 Tesla. A linear relationship between the flow rate and the applied voltage was found.…”

Magneto-hydrodynamics based microfluidics

“…The application of MHD to weakly conductive electrolyte solutions is somewhat more complicated due to electrodes' electrochemistry. Recently, various MHD-based microfluidic devices including micro-pumps (Jang and Lee, 2000; Lemoff and Lee, 2000; Huang et al, 2000; Bau, 2001; Zhong et al, 2002; Bau et al, 2002, 2003; Sawaya et al, 2002; West et al, 2002, 2003; Ghaddar and Sawaya, 2003; Bao and Harrison, 2003a, 2003b; Eijkel et al, 2004; Wang et al, 2004; Arumugam et al, 2004, 2006; Qian and Bau, 2005b; Homsy et al, 2005, 2007; Affanni and Chiorboli, 2006; Aguilar et al, 2006; Kabbani et al, 2007; Patel and Kassegne, 2007; Duwairi and Abdullah, 2007; Ho, 2007), stirrers (Bau et al, 2001; Yi et al, 2002; Qian et al, 2002; Gleeson and West, 2002; Xiang and Bau, 2003; Gleeson et al, 2004; Qian and Bau, 2005a), networks (Bau et al, 2002, 2003), heat exchangers (Sviridov et al, 2003; Singhal et al, 2004; Duwairi and Abdullah, 2007), and analytical and biomedical devices (Leventis and Gao, 2001; West et al, 2002, 2003; Bao and Harrison, 2003a; Lemoff and Lee, 2003; Eijkel et al, 2004; Clark and Fritsch, 2004; Homsy et al, 2007; Gao et al, 2007; Panta et al, 2008) operating under either DC or AC electric fields have been designed, modeled, constructed, and tested. The DC operation is often adversely impacted by the electrodes' electrochemistry leading to bubble formation and electrode corrosion.…”