On Density Wave Instability Phenomena – Modelling and Experimental Investigation

Abstract

The heat transfer and analysis on laser beam, evaporator coils, shell-and-tube condenser, two phase flow, nanofluids, complex fluids, and on phase change are significant issues in a design of wide range of industrial processes and devices. This book includes 25 advanced and revised contributions, and it covers mainly (1) numerical modeling of heat transfer, (2) two phase flow, (3) nanofluids, and (4) phase change. The first section introduces numerical modeling of heat transfer on particles in binary gas-solid fluidization bed, solidification phenomena, thermal approaches to laser damage, and temperature and velocity distribution. The second section covers density wave instability phenomena, gas and spray-water quenching, spray cooling, wettability effect, liquid film thickness, and thermosyphon loop. The third section includes nanofluids for heat transfer, nanofluids in minichannels, potential and engineering strategies on nanofluids, and heat transfer at nanoscale. The forth section presents time-dependent melting and deformation processes of phase change material (PCM), thermal energy storage tanks using PCM, phase change in deep CO2 injector, and thermal storage device of solar hot water system. The advanced idea and information described here will be fruitful for the readers to find a sustainable solution in an industrialized society.

FY23 Report on Water NSTF Testing at Two-Phase Conditions: Off-normal Scenarios

“…DWOs are a typical dynamic instability that results from multiple regenerative feedbacks between the flow rate, vapor generation rate, and pressure drops in the boiling system [30]. Due to the difference in density between the single-phase and two-phase regions, delay of response can be triggered in the transient distribution of pressure drop along the boiling channel upon disturbance of inlet flow [45]. For certain combination of geometrical, operational, and boundary conditions, the disturbed single-phase and twophase pressure drops can be equal in magnitude but opposite in phase, causing sustained oscillations [30], [34].…”

Experimental and numerical study of the laminar flow in helically coiled pipes

“…2. In the sketch, two parallel tubes are included, since the same facility was adapted to study also two-phase instability phenomena in parallel tubes, as Density Wave Oscillations (DWOs) and Ledinegg instabilities (Papini et al, 2011(Papini et al, , 2014. For the measurement of the pressure drop, only one of the tubes was used, keeping closed the inlet valve of the second one (V2).…”

Experimental and theoretical studies on density wave instabilities in helically coiled tubes

“…According to classical DWO theory valid for straight tubes, the usual stability boundary shape is expected to show the so named ''L shape'' inclination, exhibited in general as the system pressure is reasonably low and the inlet loss coefficient is not too large [31]. Usually, an increase of the inlet subcooling is stabilizing at high subcooling and destabilising at low subcooling [17,18]. The stable region is on the left of the boundary, whereas the unstable region in on the right.…”

“…When considering thermal-hydraulic instabilities, Density Wave Oscillation (DWO) kind is frequently referred to. It is well known that DWOs are induced in a boiling system by the interaction between the single-phase and two-phase flow pressure drops, the inlet mass flow rate and the void fraction distribution [17,18]. Parallel channel boundary condition (commonly established in a steam generator tube bundle) is sufficient to maintain imposed the pressure drop across the channels, such to trigger the multiple feedback effects that are at the source of the instability inception.…”

“…In order to study the instability behaviour of a whole steam generator, made in principle by numerous parallel tubes working roughly with constant DP across, the experimental apparatus may be designed with just two parallel tubes connected by two headers. It is known [17][18][19] that, when two parallel channels are fed through a common plenum preceded by a common supply path, it is generally the heated channel alone, rather than the entire system, which reaches unstable conditions. Threshold conditions (mainly the limit power) obtained with a twin-channel system (the experimental facility) apply for the corresponding multi-channel system (the steam generator).…”