Session: 04-04: Nano/Microscale Boiling and Condensation Heat Transfer

Paper Number: 133026

133026 - Frequency Analysis of Pressure Drop Oscillations in Subcooled Flow Boiling through Microchannel Heat Sink 

Abstract: 

In spite of the impressive heat extraction capabilities demonstrated by flow boiling in microchannel heat sinks, its practical implementation in micro-scale cooling faces a substantial challenge. This challenge arises from the occurrence of flow boiling instabilities within the small passages of microchannels, leading to a notable decrease in the overall performance of the microchannel heat sink (MCHS). The rapid generation and growth of vapor bubbles at a high rate impede the confined flow passage within the microchannel, leading to a substantial increase in flow resistance. This phenomenon results in periodic alterations in flow patterns and inefficient release of vapor, ultimately causing backflow. These consequences manifest as a prolonged dryout period and a reduced overall heat transfer coefficient in the MCHS. Furthermore, the periodic changes in flow boiling patterns and oscillations in mass flow significantly impact the temporal variation in pressure drop. Analyzing the pattern of temporal pressure drop oscillations during flow boiling becomes crucial in identifying the predominant flow boiling regime. Therefore, conducting a thorough investigation into the frequency distribution and amplitude of pressure drop oscillation is essential for a comprehensive understanding of the challenges posed by flow boiling instability in micro-scale cooling systems.

The study presents frequency analysis of pressure drop oscillations in subcooled flow boiling through a MCHS. The analysis employs the Welch power spectrum method to estimate the dominant frequency, providing insights into the dynamic behavior of the flow oscillation. The Welch Power Spectrum method addresses its limitation related to spectral leakage by incorporating windowing, leading to more accurate and reliable spectral analysis, especially in scenarios involving non-stationary signals or noisy data. To control the backflow during flow boiling, a single disc spring loaded flow restrictor is incorporated before the inlet plenum of the MCHS. The impact of flow restrictor on pressure drop oscillations is comprehensively examined using Welch power spectrum across varying heat fluxes (30 W/cm² to 85 W/cm²) and mass fluxes (320 kg/m²s) in a high aspect ratio configuration (500 µm channel height and 230 µm channel width) of 44 parallel microchannels. Through the decomposition of pressure signals into different scales, the study elucidates the contribution of various frequency components to the overall system dynamics. This approach enables the identification of dominant frequencies linked to the flow boiling phenomenon, based on the temporal variation of pressure drop. Consequently, a more profound understanding of the predominant flow boiling regime within the MCHS during flow oscillations is achieved with identification of multiple dominant frequencies and with associated power. Additionally, the research highlights the efficacy of the flow restrictor in mitigating flow boiling instability within the MCHS.

Presenting Author: Nishant Shah Sardar Vallabhbhai National Institute of Technology

Presenting Author Biography: Author is PhD Student from Department of Mechanical Engineering, Sardar Vallabhbhai National Institute of Technology Surat.
Author is working on Flow Boiling Heat Transfer in Microchannel.

Authors:

Nishant Shah Sardar Vallabhbhai National Institute of Technology
Hemantkumar B. Mehta Sardar Vallabhbhai National Institute of Technology
Jyotirmay Banerjee Sardar Vallabhbhai National Institute of Technology