Faculty and Staff
Research of Dr. Richard Long, P.E.
My research focus is dynamic modeling linking nano, micro, meso, and macro-scale phenomena. Two current areas are: multiphase flow and continuum mechanics in tissue engineering.
Modeling Inertial Migration:
Inertial migration of micro particles can be exploited to concentrate those particles in fluids. This technique was first noted as the Segre-Silverberg Effect in 1963 in blood flow. It was exploited at NMSU to concentrate and separate algae cells from water. Analytical modeling is only possible at creeping flow. Real separations are only possible in laminar flow in tubes at Reynolds numbers that are laminar, but at well above the creeping flow range. Dimensional analysis and order arguments can be used to develop model equations for the equilibrium position of micro particles as a function of Reynolds number.
Modeling of Metal Ion and Organics Separations by Means of Emulsion and Hollow Fiber MembraneTtechniques:
Emulsion liquid membrane technology can be used to separate metal ions and organics from water. The modeling of this process is challenging because kinetics and transport mechanisms must be coupled together through a moving boundary condition. A finite element techique can be employed numerically to compute an excellent result. A perturbation method is suitable in some cases. An external aqueous, organic membrane, and internal aqueous phase (wow) are employed in the experimental work. Recovery of the membrane phase is key to the economics of such processes.
Hollow fiber membrane technology can be used to separate both metal ions and organics from aqueous solutions. The shell side mass transfer coefficient is difficult to compute quantitatively because the filaments of the fiber bundle are packed randomly in the shell. A computational technique known as Voronoi tessellation was used to model and compute the mass transfer coefficient. This technique was developed from topology. This is a revolutionary method for quantiatively computing the shell side mass transfer coefficient.
Modeling Dispersion of Contaminants in the Atmosphere:
Gaussian puff and plume models are used to model dispersion of contaminants in the atmosphere. The advection/diffusion equation can be solved by special techniques characterizing the turbulence of the atmosphere in particularly efficient ways.
Modeling of Transport and Adsorption of Metal Ion Components in Bandelier Tuff:
Solution of the transient form of the advection/diffusion equation by combining the Laplace Transform Technique with the variation of parameters technique under special boundary conditions in this case shows that colloid transport is necessary to explain the large transport distances observed.
Modeling Mass Transfer In Laminar Rippling Flow:
Rippling flow can enhance film mass transfer by 200-300%. In this case rising film mass transfer is used to make possible a novel bioreactor.
Modeling Liquid-liquid dispersion in a tee junction, a co-current jet, and a static mixer:
Liquid-liquid dispersion occurrs by interaction of liquid drops with the turbulence field of the continuous fluid. Modeling of these phenomena can be challenging because the interactions of the fields are highly non-linear. Experiments done at NMSU showed that interaction of the time scales of breakage, coalescence, and residence time dictate the limits of possible droplet size. This requires that models of droplet size as a function Weber and Reynolds numbers be modified to account for the time scale effects. This is crucial because the relation between mass transfer and kinetics is dictated by the droplet size that can occur. Static mixer experiments at LANL showed that transients in the mixer can be computed by application of an interfacial energy balance. This interfacial energy balance has a source term related to the mechanical energy balance of the continuous phase.
Mechanochemical Energy Transduction In Muscle Contraction:
Muscle is a living biomaterial. All materials must have some type of constitutive equations to relate the dynamic to kinematic variables. There is a complex relation between the biochemistry and the mechanics that has to be sorted out in this case. There are some controversies surrounding the proper way to link these variables together. The models developed at NMSU are based on a ratchet mechanism at the nano scale (< 20nm). Macroscale responses under both the steady state and transient conditions can be computed very accurately by these models.