Journal article
Experimental comparison and visualization of in-tube continuous and pulsating flow boiling
Department of Mechanical Engineering, Technical University of Denmark1
Thermal Energy, Department of Mechanical Engineering, Technical University of Denmark2
Fluid Mechanics, Coastal and Maritime Engineering, Department of Mechanical Engineering, Technical University of Denmark3
KTH Royal Institute of Technology4
This experimental study investigated the application of fluid flow pulsations for in-tube flow boiling heat transfer enhancement in an 8 mm smooth round tube made of copper. The fluid flow pulsations were introduced by a flow modulating expansion device and were compared with continuous flow generated by a stepper-motor expansion valve in terms of the time-averaged heat transfer coefficient.
The cycle time ranged from 1 s to 7 s for the pulsations, the time-averaged refrigerant mass flux ranged from 50 kg m−2 s−1 to 194 kg m−2 s−1 and the time-averaged heat flux ranged from 1.1 kW m−2 to 30.6 kW m−2. The time-averaged heat transfer coefficients were reduced from transient measurements immediately downstream of the expansion valves with 2 K and 20 K subcooling upstream, resulting in inlet vapor qualities at 0.05 and 0.18, respectively, and covered the saturated flow boiling range up to the dry-out inception.
Averaged results of the considered range of vapor qualities, refrigerant mass flux and heat flux showed that the pulsations at low cycle time (1 s) improved the time-averaged heat transfer coefficients by 5.6% and 2.2% for the low and high subcooling, respectively. However, the pulsations at high cycle time (7 s) reduced the time-averaged heat transfer coefficients by 1.8% and 2.3% for the low and high subcooling, respectively, due to significant dry-out when the flow-modulating expansion valve was closed.
Furthermore, the flow pulsations were visualized by high-speed camera to assist in understanding the time-periodic flow regimes and the effect they had on the heat transfer performance.
Language: | English |
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Year: | 2018 |
Pages: | 229-242 |
ISSN: | 18792189 and 00179310 |
Types: | Journal article |
DOI: | 10.1016/j.ijheatmasstransfer.2018.04.060 |
ORCIDs: | Kærn, Martin Ryhl , Markussen, Wiebke Brix , Meyer, Knud Erik and Elmegaard, Brian |