Amos Ullmann

The piezoelectric valve-less pump—performance enhancement analysis

Abstract An analysis of the performance of a single chamber and a double chamber piezoelectric valve-less pumps is presented. The analysis will enhance the proper design of such pumps. Also presented is an analysis of the different combination modes possible for the operation of such pumps such as a series connection and a parallel connection. It is shown, that a series connection usually is advantageous to a parallel connection even for the purpose of increasing the flow rate (for fixed pressure difference). reserved.

Modeling of phase inversion phenomenon in two-phase pipe flows

Abstract Phase inversion in oil–water flow systems corresponds to the transitional boundary between oil-in-water dispersion and water-in-oil dispersion. In this study, the criterion of minimum of the system free energy is combined with a model for drop size in dense dispersions to predict the critical conditions for phase inversion. The model has been favorably compared with available data on the critical holdup for phase inversion. It also provides explanations of features of phase inversion phenomena in liquid–liquid pipe flows and in static mixers.

Efficiency and optimized dimensions of annular fins of different cross-section shapes

Abstract Increasing the heat dissipation of annular fins at a denned magnitude of mass is the problem considered in this paper. Four different cross-section shapes are examined—constant thickness, constant area for heat flow, triangular and parabolic fin shapes. The fin efficiency together with the optimized dimensions are presented, which enables the design of the best fin for any practical use.

The piezoelectric valve-less pump - improved dynamic model

The piezoelectric valve-less pump is an attractive device to be used as a micro pump for low flow rates. The pump converts the reciprocating motion of a diaphragm, activated by a piezoelectric disk, into a pumping action. Instead of conventional valves, which have moving parts, nozzle/diffuser elements that have a preferential flow direction are used to direct the flow from the inlet to the outlet. In this paper, an improved dynamic model for the simulation of valve-less piezoelectric pumps is presented. The model is capable of accurate simulation of the pump performance including the natural frequency, flow rate, and pressure drop. The model is utilized here to study the effect of the driving frequency and the inlet/outlet length and diameter of the leading pipes on the pump performance. Comparison with experiments shows good agreement with a minimal number of adjusting parameters.

A Piezoelectric Valve-Less Pump-Dynamic Model

A complete dynamic model for the simulation of the valve-less piezoelectric pump performance is presented, In this model the piezoelectric action is considered as a periodic force acting on a pumping membrane. The natural frequency of the pump is calculated as well as its performance as a function of the driving frequency, The effect of the deviation of the driving frequency from the natural frequency on the pump performances is clearly shown. Also, it is demonstrated that the effect of the liquid mass in the pump nozzles on the natural frequency of the system is very high owing to the high acceleration of the fluid in the nozzles. Comparison with experiments shows a very good agreement with a minimal number of adjusting parameters.

Multi-holdups in co-current stratified flow in inclined tubes

Abstract Maps of the multi-holdup regions in co-current and countercurrent flows are presented in terms of the controlling non-dimensional parameters. These maps clearly demonstrate the symmetrical relationship between upward and downward co-current inclined flows. The feasibility of obtaining multi-holdups in co-current up flow is validated experimentally using oil–water system. The multiple holdups are shown to be associated with hysteresis phenomenon. The introduction of the multi-holdup regions on flow-pattern maps of various gas–liquid and liquid–liquid systems, indicates that these regions correspond to operational conditions where stratified flow was experimentally observed. The significance of multi-holdups phenomena to transition from stratified flow to other bounding flow patterns is discussed.

Stratified laminar countercurrent flow of two liquid phases in inclined tubes

Abstract The effects of inclination on the characteristics of laminar countercurrent liquid–liquid flow are investigated both experimentally and theoretically. Experimental results show that with a slight off-vertical inclination the phases tend to segregate and the basic flow pattern in inclined tubes is stratified flow. Moreover, for fixed operational conditions, there exist two stable modes of stratified configuration that differ in the in situ holdup, velocity profiles and the pressure drop, and both may co-exist in the column. The application of the two-fluid and the two-plate models for the prediction of the characteristics of countercurrent flow is explored. Both models predict the existence of the two modes that have been observed in the column and their associated holdups. The TP model confirms the experimental finding that back flow (opposite to the feed direction) is an inherent characteristic of countercurrent flow and generally, is expected in the thicker layer. The findings of this study are applicable for improving the throughput of phase transition extraction columns.

Thermodynamic and hydrodynamic response of compressed air energy storage reservoirs: a review

Abstract Installation of large-scale compressed air energy storage (CAES) plants requires underground reservoirs capable of storing compressed air. In general, suitable reservoirs for CAES applications are either porous rock reservoirs or cavern reservoirs. Depending on the reservoir type, the cyclical action of air injection and subsequent withdrawal produces temperature and pressure fluctuations within the reservoir. An accurate prediction of these fluctuations is essential for the design of the reservoir and its associated turbomachinery. Being mutually dependent, the selection of the turbomachinery and reservoir characteristics must be conducted simultaneously to obtain an integrated cost-effective plant. The present review is intended to encompass the pertinent literature on the temperature and pressure variations within CAES reservoirs. The principal experimental and operational data sources are described, as well as important results of theoretical modeling efforts. Conclusions derived from those investigations and their relevance to CAES plant designs are discussed.

Fatigue characteristics of granular materials

Comminution and attrition are processes in which particles become broken or damaged. It occurs when a load higher than the particle strength is statically or dynamically applied. Breakage could also occur with lower loads that are applied repeatedly, a phenomenon that is known as fatigue. Fatigue is the real cause for the breakage of particles in many industrial systems such as grinding or transporting in pneumatic conveying pipelines. In this paper, experimental results of the fatigue behavior of an assembly of particles of several materials are analyzed. Fatigue curves of constant damage are presented for compression stress with the number of cycles.

Stability of stratified two-phase flows in horizontal channels

Linear stability of stratified two-phase flows in horizontal channels to arbitrary wavenumber disturbances is studied. The problem is reduced to Orr-Sommerfeld equations for the stream function disturbances, defined in each sublayer and coupled via boundary conditions that account also for possible interface deformation and capillary forces. Applying the Chebyshev collocation method, the equations and interface boundary conditions are reduced to the generalized eigenvalue problems solved by standard means of numerical linear algebra for the entire spectrum of eigenvalues and the associated eigenvectors. Some additional conclusions concerning the instability nature are derived from the most unstable perturbation patterns. The results are summarized in the form of stability maps showing the operational conditions at which a stratified-smooth flow pattern is stable. It is found that for gas-liquid and liquid-liquid systems, the stratified flow with a smooth interface is stable only in confined zone of relatively low flow rates, which is in agreement with experiments, but is not predicted by long-wave analysis. Depending on the flow conditions, the critical perturbations can originate mainly at the interface (so-called “interfacial modes of instability”) or in the bulk of one of the phases (i.e., “shear modes”). The present analysis revealed that there is no definite correlation between the type of instability and the perturbation wavelength.