Efficient Microgravity Heat and Mass Transfer with no Moving Parts
Science Principal Investigator: Peter Vorobieff, Professor, Mechanical Engineering, University of New Mexico
We propose to demonstrate an efficient, noncontact method of transporting heat in microgravity. This new method does not employ any moving parts and requires only a modest power supply to drive low-impedance Helmholtz coils. This method has been extensively tested on Earth and there is strong evidence that it should work even better in microgravity environments.
In Earth’s gravity field, heat and mass transfer in liquids occurs via convection, provided a destabilizing thermal gradient exists.
In the microgravity environments of space, artificial convection must be used, which is generally accomplished by driving the fluid with mechanical action, and that requires motors, other moving parts and seals, raising reliability and maintenance concerns. To address these concerns, much attention has been focused on non-contact methods of inducing fluid flow. Magnetic fields are the focus of many proposed techniques, because it is easy to generate fields having large energy densities over significant volumes. Recent discoveries reveal that dynamic magnetic fields of very modest strength (order of milliTesla) can create vigorous, organized flows in dilute magnetic particle suspensions.
We propose to show that these discoveries – isothermal magnetic advection (IMA) and vortex fluid formation with symmetry-breaking and rational fields – can create highly efficient heat/mass transfer in space applications. IMA occurs when a uniform biaxial magnetic field whose frequency ratio is a simple rational number (e.g. 1:2) is applied to a 1-2 vol.% suspension of magnetic particles (platelets) in fluid. The flow rate increases as the square of the field magnitude. With triaxial magnetic field, vortex flow can form in the fluid, producing strong mixing and heat and mass transfer in complex, confined geometries – and the flow direction can be controlled externally and with no moving parts.
We shall find if a high degree of control of fluid heat transfer can be achieved in microgravity with triaxial magnetic fields. These studies will employ an enclosed cell filled with water and seeded with a small volume fraction of magnetic platelets. Heat transfer will be quantified using off-the-shelf point diagnostics. One part of the cell will be heated. In the absence of natural or artificial convection, heat transfer will occur only through diffusion and radiation, so any local heating will lead to a quick temperature rise. In a strongly mixed fluid the rate of heating will be much slower.
The magnetic field will be comprised of two ac components and a small permanent field. Each ac component will require ~30 mW of power per milliliter of liquid at the 50 Gauss field that produced essentially maximum heat transfer on Earth. Each experiment would be less than 1 minute in duration, with the maximum power consumption not to exceed 30 W. We expect that in space the required field strength will be lower, since gravity-driven particle sedimentation will not occur. At 25 Gauss the power requirement would drop to ~7.5 mW/ml. Visualization of the flow patterns can further elucidate the physics of the flow. Results of microgravity and ground tests will be compared.
Our goal is to quantify control over heat/mass transfer as a function of the magnetic field parameters as an important first step to the implementation of this new technology in future space systems. The ISS is the perfect platform to explore the efficacy of this new approach in microgravity, where the ability to facilitate and control heat and mass transfer with no moving parts and very low power requirements may be indispensable.