Novel Infrared Approach for the Evaluation of Thermofluidic Interactions in a Metallic Flat-Plate Pulsating Heat Pipe

Abstract

A novel and advanced analysis tool, based on the resolution of the inverse heat conduction problem, is used to evaluate wall-to-fluid heat fluxes in a metallic flat-plate pulsating heat pipe. The device under analysis is made of copper and formed by 16 channels having a squared section of 3 × 3 mm2 and filled with a water–ethanol mixture (20 wt.% of ethanol) with a volumetric filling ratio of 50%. One flat side of the device is externally coated with a highly emissive paint to perform temperature measurements by means of a medium-wave infrared camera. The acquired infrared maps are first processed by a three-dimensional Gaussian filter and then used as inputs for the inverse approach for the evaluation of heat fluxes locally exchanged between the fluid and the thin walls of each channel. The suggested procedure is successfully validated by means of synthetic data. The resulting space–time heat flux distributions are therefore statistically investigated in terms of amplitude and space–time variations, providing quantitative references for the identification of two-phase flow regimes. These unique data give an evaluation of the local heat transfer behavior, which is essential to provide empirical values for the numerical models of pulsating heat pipes.

Are Local Heat Transfer Quantities Useful for Predicting the Working Behavior of Different Pulsating Heat Pipe Layouts? A Comparative Study

“…Conclusions on the fluid oscillations and heat flux amplitudes were drawn. Lastly, a novel method, similarly based on the IHCP resolution approach, was proposed by Pagliarini et al [26] for wall-to-fluid heat flux estimation in an FPPHP made of copper. Statistical reductions were performed on the resulting wall-to-fluid heat flux amplitudes.…”

“…Statistical reductions were performed on the resulting wall-to-fluid heat flux amplitudes. In [27], the figures of merit referred to fluid oscillations and transverse conduction in the same FPPHP device, analyzed through the same experimental and post-processing approach in [26], were collected and presented. The outcomes resulting from each experimental campaign were capable of quantitatively outlining the inner thermo-fluid dynamics of the investigated systems, even without any presence of transparent inserts for direct fluid visualizations.…”

“…Due to the greatly promising results of wall-to-fluid heat fluxes for PHP descriptions, local heat transfer quantities are believed to be a straightforward and powerful tool for the generalization and prediction of the PHP operation regardless the adopted layout, the manufacturing material, the working fluid, or the operating condition. Hence, the aim of the present work is to disclose the potentiality of wall-to-fluid heat fluxes locally exchanged at the wall-fluid interfaces for PHP working behavior prediction through the comparison of results provided by the previous literature [24][25][26][27], available, to the authors' best knowledge, for metallic devices, which are of greater manufacturing and application appeal for the general industry.…”

“…• The temperature distributions referring to every device channel are therefore processed by means of the IHCP resolution approach, resulting in wall-to-fluid heat flux distributions q n (for the n-th channel). For the sake of brevity and clarity, the theoretical formulations assumed by the IHCP resolution method for the geometries under investigation are left to the reader ( [23] for tubular layouts, [26] for FPPHP layouts). • The wall-to-fluid heat fluxes are processed through different reduction approaches; statistical approaches are used to provide figures of merit for all the collected wall-tofluid heat flux distributions, while the wavelet method is adopted to assess heat flux oscillation frequencies, which directly reflect fluid oscillation frequencies.…”

Experimental Analysis of an Innovative Electrical Battery Thermal Management System

“…PHPs are extremely easy and cost effective compared to other heat transport devices [20]. They cope with elevated heat power due to the phase change phenomena and to the substantial sensible heat transfer carried out by the continual pulsations [21,22]. Moreover, PHPs are totally passive, so they avoid electric energy consumption and allow a compact power supply unit, and their adoption in the battery pack could also represent a promising approach to attain a uniform temperature.…”