Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: The valveless micropump holds great potential for the biomedical community in applications
such as drug delivery systems, blood glucose monitoring and many others. It is also a critical
component in many a lab-on-a-chip device, which in turn promises to improve our treatment
and diagnosis capabilities for diseases such as diabetes, tuberculosis, and HIV/AIDS.
The valveless micropump has attracted attention from researchers on the grounds of its
simple design, easy manufacturability and sensitive fluid handling characteristics, which are
all important in biomedical applications.
The pump consists of a pump chamber with a diffuser and nozzle on opposing sides of the
pump chamber. The flow into the diffuser and nozzle is induced by an oscillating piezoelectric
disc located on top of the pump chamber. The nozzle and diffuser rectify the flow in one
direction, due to different pressure loss coefficients.
The design process however is complex. In this study, we investigate the characteristics of
a diffuser / nozzle based micropump using detailed computational fluid dynamic (CFD) analyses.
Significant parameters are derived using the Buckingham-Pi theorem. In part based on
this, the respective shapes of the diffuser and of the nozzle of the micropump are selected for
numerical investigation. Hence the influence of the selected parameters on the flow rate of
the micropump is studied using three-dimensional transient CFD analyses. Velocity profiles
from the CFD simulations are also compared to the Jeffery-Hamel solution for flow in a wedge
shaped channel. Significant similarities exist between the data and the predicted Jeffery-Hamel
velocity profiles near the exit of the diffuser.
Three different diffuser geometries were simulated at three frequencies. The flow rate and
direction of flow are shown to be highly sensitive to inlet and outlet diffuser shapes, with the
absolute flow rate varying by as much as 200% for the geometrical perturbations studied. Entrance
losses at both the diffuser inlet and nozzle inlet appear to dominate the flow resistance
at extremely laminar flow conditions with the average Reynolds number of Reave ≈ 500.AFRIKAANSE OPSOMMING: Die kleplosemikropomp hou groot potensiaal in vir die biomediese gemeenskap in toepassings
soos medisyne dosering sisteme, bloed glukose monitering en baie ander. Dit is ook ’n
kritiese komponent in “lab-on-chip” sisteme, wat beloof om die behandeling en diagnose van
siektes soos suikersiekte, tuberkulose enMIV/VIGS te verbeter.
Die kleplose mikropomp het tot dusver die aandag van navorsers geniet as gevolg van sy
eenvoudige ontwerp, maklike vervaardiging en sensitiewe vloeistof hantering. Hierdie kenmerke
is krities inmenige biomediese toepassings.
Die pomp bestaan uit ’n pompkamer met ’n diffusor en ’n mondstuk aan teenoorstaande
kante van die pompkamer. Vloei in die diffusor en mondstuk in word geinduseer deur ’n ossillerende
piëso-elektiese skyf wat bo-op die pompkamer geleë is. Weens verskillende druk verlies
koëffisinëte van die diffusor en diemondstuk word die vloei in een rigting gerig.
Die ontwerp-proses is egter kompleks. In hierdie studie word die eienskappe van die diffusor
/mondstuk ondersoek deur gebruik temaak van gedetailleerde numeriese vloei-dinamiese
analises. Belangrike parameters word afgelei deur gebruik te maak van die Buckingham-Pi
teorema. Gedeeltelik gebaseer hierop word die onderskeidelike vorms van die diffusor en die
mondstuk van die mikropomp geselekteer vir numeriese ondersoek. Gevlolglik word die invloed
van die geselekteerde parameters op die vloei tempo van diemikropomp ondersoek deur
gebruik temaak van drie-dimensionele tyd afhanklike numeriese vloei-dinamiese analises. Snelheids
profiele van hierdie simulasiesword vergelykmet die Jeffrey-Hamel oplossing vir die vloei
in ’n wigvormige kanaal. Daar is oorwegende ooreenkomstighede tussen hierdie data en die
voorspelde Jeffrey-Hamel snelheids profiele veral by die uitgang van die diffusor.
Drie verskillende diffusor vorms is by drie frekwensies gesimuleer. Daar is bewys dat die
vloei tempo en vloeirigting baie sensitief is vir inlaat- en uitlaat diffusor vorms en dat die absolute
vloei tempo kan varieermet soveel as 200%vir die geometriese versteuringswat ondersoek
is. Inlaat verliese by beide die diffusor inlaat en die mondstuk inlaat, blyk om die vloei weerstand
te domineer waar die vloei uiters laminêr ismet ’n gemiddelde Reynolds getal van Regem
≈ 50
