The current study presents experimental pressure drop and heat transfer data for subcooled flow boiling of water in a 1.0 mm wide × 0.49 mm deep × 40 mm long aged copper microchannel. The experiments were performed for three inlet temperatures: 30 o C, 50 o C and 70 o C, each with mass flux range of 528–1188 kg/m 2 s and heat flux range of 260–1100 kW/m 2 . The trends observed in experimental subcooled boiling heat transfer and pressure drop are reported. The performance of existing predictive methods in predicting pressure drop, heat transfer and boiling incipience is also assessed. The study also evaluates the appropriateness of using singe phase correlations for predicting subcooled boiling pressure drop, a practice which is used in many flow boiling studies, and recommends that the approach be not used for low inlet subcooling. © 2019 Elsevier Ltd

Sateesh Gedupudi

Department of Mechanical Engineering

Prasanna Jayaramu

Copper

Drops

Heat flux

Heat transfer

Microchannels

Pressure drop

BOILING INCIPIENCE

Experimental investigations

HEAT TRANSFER DATA

Inlet sub-cooling

Predictive methods

Sub-cooled boiling

SUBCOOLED BOILING HEAT TRANSFER

Subcooled flow boiling

Heat transfer performance

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IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

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IIT Madras

International Communications in Heat and Mass Transfer

Heat-sinks based on flow boiling in microchannels have the potential to mitigate temperature rise in high heat flux devices such as electronic equipment. One of the major challenges is the instability associated with pressure fluctuations caused due to the confined bubble growth during boiling in a microchannel. This paper presents a comprehensive model to estimate the dynamic pressure fluctuations in a channel of rectangular cross-section and compares with the experimental results. The time-averaged pressure drop obtained from the transient model has been verified with the experimental results and the steady two-phase flow pressure drop correlations. Effects of various parameters such as heat flux and mass flux on the time-averaged pressure drop and the transient pressure fluctuations are presented. The paper also provides an approximate methodology to estimate the nucleation frequency derived from the waiting period of the bubble. The calculated frequency is validated qualitatively with the experimental observation available in the literature. The current work also demonstrates that the transient pressure drop models, which, with suitable inputs, predict the local pressure fluctuations during confined bubble growth, can also be used to predict the steady- flow pressure drop. © 2019, © 2019 Taylor & Francis Group, LLC.

Heat Transfer Engineering

On the Prediction of Pressure Fluctuations and Pressure Drop Caused by Confined Bubble Growth During Flow Boiling in a Rectangular Mini/Micro-Channel

Subcooled flow boiling heat transfer is one of the most preferred heat removal methods, especially in areas where high heat fluxes are encountered. The design of heat sinks employing subcooled flow boiling involves prediction of pressure drop, in addition to heat transfer coefficient, as it exerts a huge influence on the local heat transfer, stability of the system and the critical heat flux. This paper provides a systematic review of the performance of the prior correlations and their applicability for different conditions based on a large experimental database compiled from 12 sources containing 1365 data points in total, focussing on water as the working fluid. The results of the assessment are used to identify the right correlation applicable for a specific operating range. New correlations are proposed for the cases and ranges for which the predictability of the prior correlations is unsatisfactory. © 2019 Elsevier Ltd

Applied Thermal Engineering

On the prediction of pressure drop in subcooled flow boiling of water

Experiments were carried out to investigate the effect of surface characteristics on flow boiling heat transfer and pressure drop in a microchannel using degasified and deionized water as the working fluid. Test section consists of a 40 mm long, 0.5 mm wide and 0.24 mm deep microchannel machined in copper. Experimental results are reported for three different surface characteristics – fresh machined surface (case-1), the same channel surface when aged after repeated experimentation (case-2) and the surface obtained after cleaning the same aged surface with 0.1 M hydrochloric acid (case-3). Parameters considered include inlet temperature 95 °C, mass flux from 1000 to 2220 kg/m2 s and heat flux from 400 to 1200 kW/m2. Single-phase experiments have been performed to estimate the heat loss from microchannel and also to validate the experimental setup. The results indicate that the boiling heat transfer performance of case-2 is lower than that of case-1 and the performance of case-3 is higher than that of case-1. The main reason behind the reduction of two-phase heat transfer coefficient for case-2 as compared to case-1 is attributed to the increased wettability due to the thermal oxidation of the heating surface caused by the repeated experimentation. The enhanced boiling performance of case-3 is attributed to the increased nucleation site density. However, the change in the two-phase pressure drop is relatively small. The experimental results were compared with the available correlations in the literature to check the predictability of the correlations for the three cases. The degree of agreement (or disagreement) varies depending on the correlation and the surface characteristic. The reasons for the deviations are discussed. © 2018 Elsevier Ltd

International Journal of Heat and Mass Transfer

Influence of heating surface characteristics on flow boiling in a copper microchannel: Experimental investigation and assessment of correlations

Convective Flow Boiling

Investigation of Bubble Departure Mechanism in Subcooled Flow Boiling of Water Using High-Speed Photography

An Alternative Model for Flow Boiling Heat Transfer

Experimental investigation of flow boiling in single minichannels with low mass velocities

A simplified energy dissipation based model of heat transfer for subcooled flow boiling

Subcooled flow boiling of water in a copper microchannel: Experimental investigation and assessment of predictive methods

Journal	Data powered by TypesetInternational Communications in Heat and Mass Transfer
Publisher	Data powered by TypesetElsevier Ltd
ISSN	07351933
Open Access	No