Rationalized Concise Descriptions of Fluid Motions in an Oscillating/Pulsating Heat Pipe

Furukawa, Masao

doi:10.1115/1.4027553

Cited by 9 publications

(1 citation statement)

References 34 publications

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“…Analytically-predicted oscillation frequencies from Furukawa [33] are also provided in Figure 11 Note that the same averaging technique that was used to compute the amplitude spectra was also used to compute the frequency response functions. Applying this analogy to filters, Fig.…”

Section: Temperature Signal Analysismentioning

confidence: 99%

Analysis and comparison of internal and external temperature measurements of a tubular oscillating heat pipe

Monroe

Aspin

Fairley

et al. 2017

Experimental Thermal and Fluid Science

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The current study examines the relationship between internal/fluidic and external/wall temperature measurements along the adiabatic section of an operating tubular oscillating heat pipe (T-OHP) for varying heat inputs. Temperature measurements were achieved using type-T thermocouples located either inside or along the OHP wall in a region between the evaporator and condenser. These temperature measurements are utilized to elucidate the effects of wall thermal capacitance, external wall temperature gradient, and internal fluid advection. The internal, singlephase heat transfer coefficient is estimated, and the effective thermal conductivity of the OHP is also discussed. The internal thermocouples allowed the oscillating liquid/vapor temperature to be measured directly. A 4-turn copper T-OHP (3.25 mm ID) was charged with water (75% by volume) and tested in the bottom-heating condition. The heating power input was varied in increments of 25 W from 60 W to 300 W. Results indicate that the external thermocouples were unable to capture frequency components larger than ~1 Hz, while the internal measurements showed that the average fluid oscillation frequency near the evaporator varied from ~1.5 Hz at 60 W to ~2.5 Hz at 300 W, whereas the frequency in the condenser remained fairly constant at ~0.5 Hz. The frequency transfer function for the thermal network between the internal/external thermocouples was constant across all tested power inputs. The low-frequency, large-amplitude changes of internal temperature associated with bulk fluid motion were not measured at the external OHP tube surface for ~1.5 s. The effective thermal conductivity calculated using only external temperature measurements was found to be 4-12% lower than when internal measurements are used. The maximum calculated effective thermal conductivity using only internal or external temperature measurements was 15,300 W/mK and 14,000 W/mK, respectively. This difference arises from there being a smaller temperature gradient in the fluid than in the tube wall due to the strong advection component of OHP heat transfer. Tube wall conduction was found to account for 2-10% of the overall heat transfer, with its significance decreasing as fluid advection increases at higher heat inputs. The heat transfer coefficient for single-phase fluid oscillation inside the OHP is estimated to be ~1000 W/m 2 K for power inputs larger than 100 W; corresponding to Nusselt numbers between 4 and 6.

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Section: Temperature Signal Analysismentioning

confidence: 99%