This present study employs comprehensive wavelet analysis to investigate pressure drop signals during subcooled flow boiling within a straight-through microchannel heat sink (MCHS). The research proposes the use of a flow restrictor (FR) to address the flow boiling instability, exploring its impact across a broad range of heat fluxes (15–80 W/cm²) and mass fluxes (320 and 520 kg/(m²·s)) in a high aspect ratio configuration with 44 parallel micro-channels (230 μm in width, 500 μm in height) utilizing degassed DI water as the coolant. The decomposed pressure signals reveal the contribution of various frequency components to the overall system dynamics, aiding in identifying dominant frequencies associated with flow boiling phenomena. The study demonstrates the effectiveness of the flow restrictor in mitigating flow boiling instability and enhancing heat transfer efficiency. The analysis of pressure drop fluctuations showcases the altered power spectrum behaviour and improved stability with the use of flow restrictor. The results present detailed power magnitude and dominant frequency ranges for different mass and heat fluxes, offering essential information for optimizing the heat transfer processes in the MCHS.

Interfacial behaviour of stratified and wavy-stratified flow is analysed in terms of measured velocity signals in liquid phase using Laser Doppler Velocimetry. Measurement of liquid height (interface level) is achieved using Laser Doppler Velocimetry synchronized with a computerised 3-dimensional traverse system. The precision obtained in measurement of air sheared interface level (liquid height) in this approach is 0.032±0.01 mm. First part of this paper deals with influence of gas and liquid superficial Reynolds numbers on the liquid height for stratified and wavy-stratified flow. With increase in liquid depth, waves are initiated at the gas-liquid interface which is precursor to slug formation. A critical liquid height for onset of slug formation is obtained in this part. The second part deals with the measurement of fluctuations occurring near to the air-sheared interface. These fluctuations are recorded in terms of local velocity of liquid phase and have been used to characterize the behaviour of air-water interface for stratified and wavy-stratified flow. Furthermore, influence of gas and liquid flow rates on local liquid velocity for different stratified and wavy-stratified flow conditions is analysed by plotting the axial velocity profiles in radial direction.