An experimental study was conducted to compare heat transfer performance between three micro fin array configurations for transient and steady periodic operation. The study evaluates the time a microchannel takes to reach steady-state conditions for a given flow rate and heat input. It is crucial to investigate the response of the thermal device to overcome a sudden overheating. The experiment aims to analyze the effects of flow boiling in microchannels for extended periods. The study focuses on three novel microchannel cooling devices with different micro fin array configurations. The first design consists of an array of parallel straight fins. The second design resembles the first with the addition of diagonal cuts separating the channel into segments. The third and final design adds another set of diagonal cuts in the opposite direction, creating a diamond lattice of micro fins. It is believed that adding flow-disrupting geometries such as those found in designs 2 and 3 will be beneficial for both single and two-phase flow by improving flow mixing and reducing flow instability, respectively. The experimental results of each fin configuration were compared against a smooth plate (dummy channel) used as a reference. Each device was tested at flow rate of 0.1 to 0.5 ml/min at different heat inputs up to 500W. Temperature and pressure sensors located at the inlet and outlet of the channel measured and gathered fluid data every second for 1800 seconds. The surface temperature near the center of the channel was also collected every second. Once the system achieved steady-state conditions, the surface temperatures at the inlet and outlet of the plate were gathered to ensure correct readings. For this experiment, distilled water is the selected working fluid. Previous experimental studies have shown that adding turbulence caused by cut segments, like those in designs 2 and 3, may significantly improve the heat transfer effectiveness for flow boiling. The experimental results revealed a heat transfer enhancement during flow boiling for designs 2 and 3. Furthermore, for single-phase flow at low heat inputs, the straight parallel micro fins array exerted the highest pressure drop. The pressure drops for designs 2 and 3 were similar during flow boiling. The present study included the straight fin array design to a variable flow rate and increment heat input every 300 seconds. It was found that while the surface temperature data can easily be used as a reference to determine the onset of flow boiling, it cannot be used to detect flow instability effectively. Conversely, the pressure drop across the device provides valuable data for determining the onset of flow instability but is not very effective when used to assess flow boiling. As a result, a composite plot overlaying the surface temperature and pressure drop of the device over time is a great way to determine the onset of each phenomenon simultaneously.

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