On the hysteresis phenomenon during flow boiling heat transfer on a hydrophilic carbon/carbon surface

doi:10.1016/j.icheatmasstransfer.2020.104795

International Communications in Heat and Mass Transfer

Volume 117, October 2020, 104795

https://doi.org/10.1016/j.icheatmasstransfer.2020.104795 Get rights and content

Highlights

•
R245fa flow boiling on a Carbon/Carbon surface is studied.
•
A hysteresis of boiling heat transfer is observed and studied.
•
A combined experimental methodology is applied to study the surface activation process.
•
The dewetting/rewetting phenomenon during flow boiling was linked to the activation process.

Abstract

This paper presents a detailed discussion on the hysteresis phenomenon caught during the flow boiling heat transfer of R245fa on a Carbon/Carbon surface. Due to the partial hydrophilicity of the Carbon/Carbon surface, a hysteresis in flow boiling heat transfer is observed and studied to understand the underlining heat transfer mechanisms on the basis of the surface activation. A combined experimental approach is developed by monitoring the local wall temperature and contemporarily recording the two-phase flow patterns using a high-speed video camera. The observed dewetting/rewetting phenomenon is linked to the activation process of the Carbon/Carbon surfaces giving new insights on the boiling behavior of hydrophilic surfaces. The results show that after activation the heat transfer coefficients increases up to 20%. The experimental results are compared against the estimations of a model recently proposed by the present Authors and based on R134a measurements. The proposed model is able to predict the heat transfer coefficients within ±20%.

Introduction

In the last decade, micro- and nano-structured materials (among those: micro-porous layers, graphene-Cu nanocomposite coated copper surfaces, nanowires coatings, nano-porous layers, Carbon Nano Tube arrays, and nano-structured surfaces, etc.) have been proposed to enhance either pool and flow boiling heat transfer [[1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13]].

Carbon/Carbon (C/C) can be considered one of the most high-tech materials, developed by the aerospace industry and then applied to critical components in several different applications. This composite material appears to be a viable option for future thermal management devices because it presents excellent thermophysical properties, among those a low density and a relatively non-isotropic high thermal conductivity as compared to metals.

Besides, C/C has already been used in many industrial applications where it was shaped in various, even complex, forms. C/C composites could be used in the replacement of heavy copper spreaders to dissipate high heat fluxes and lowering the weight and volume of the heat sinks. Nevertheless, their development is still limited because of economic and technical constraints, both of them being critical [14,15]. Furthermore, as found by Doretti et al. [16], this material also offers great capabilities during flow boiling heat transfer, especially for high heat flux dissipation.

With reference to the hysteresis phenomenon, Forrest et al. [17] conducted a comprehensive study on the pool boiling on super-hydrophilic wires, showing that the hysteresis can be attributed to the high surface wettability that led the majority of cavities to be flooded at the beginning of each experiment, which, in turn, required higher wall superheats for nucleation (i.e. activation). However, upon the first nucleation, vapor became entrapped in the cavities, lowering the required superheat in boiling heat transfer.

Similar results were found by Mancin et al. [6] during flow boiling heat transfer on a microparticle coated copper surface. The authors founded that the coating changed the wettability of the surface, which became hydrophilic and showed a similar hysteresis during the boiling process: once activated the coated surface exhibited heat transfer coefficient 2.5 times higher.

More recently, Doretti et al. [16] showed that the C/C surface is hydrophilic and thus presents a hysteresis during the boiling process. This behavior, the so-called activation process, was observed during flow boiling of R134a, a medium pressure refrigerant, and led to an enhancement of the heat transfer coefficient of around 20%.

A more detailed and comprehensive analysis is surely needed to understand the underlying heat transfer mechanisms on the basis of this hysteresis, in particular, as a function of the refrigerant properties on the same hydrophilic surface.

For these reasons, this work aims at giving new insights on the study of the activation process of C/C surfaces and, in general, of hydrophilic surfaces by investigating the flow boiling heat transfer of a low-pressure refrigerant R245fa, which presents different thermo-physical and transport properties and, consequently, a different behavior as compared to R134a. The experimental tests are run on an electrically heated C/C surface by varying the refrigerant mass velocity from 50 kg m⁻² s⁻¹ to 200 kg m⁻² s⁻¹ and the heat flux of 50 kW m⁻² to 100 kW m⁻², at a constant mean saturation temperature of 30 °C.

Section snippets

Carbon/Carbon sample

Carbon fiber reinforced Carbon matrix (C/C) are commonly manufactured by Chemical Vapor Infiltration (CVI) of porous carbon fiber preforms [18,19]. This is also the case of the sample used in the present experimental campaign. It is realized by CVI of a 3D preform, previously heated up to more than 1800 °C. Then, the C/C block undergoes a thermal treatment to enhance the thermal conductivity of the deposited carbon matrix, which, through the thickness, is estimated to be 65 W m⁻¹ K⁻¹ [16]. The

The activation process

As described before, when dealing with hydrophilic surfaces, a possible hysteresis on the boiling performance can be expected. Forrest et al. [17], experimentally analyzed the boiling heat transfer of super-hydrophilic wires, the authors found that the high wettability led to a hysteresis on cavities activation. This hysteresis in the boiling curve was observed and it was explained considering the entrapment of vapor in cavities that became activated at high wall superheats. Mancin et al. [6]

Conclusions

This paper focuses on the hysteresis phenomenon showed during R245fa flow boiling by a C/C surface. The use of experimental measurements of local wall temperatures and simultaneous two-phase flow visualization allowed for a detailed description of the activation process of this partially hydrophilic surface. Moreover, by varying the mass velocity, vapor quality, and heat flux, the experimental results revealed how the combination of the two main boiling heat transfer mechanisms affects the

Nomenclature

area (m²)

c_p

specific heat capacity (J kg⁻¹ K⁻¹)

d_h,t

thermal hydraulic diameter (m)

gravitational acceleration (m s⁻²)

mass velocity (kg m⁻² s⁻¹)

HTC

heat transfer coefficient (W m⁻² K⁻¹)

heat flux (W m⁻²)

specific enthalpy (J kg⁻¹)

coverage factor (−)

parameter defined by Eq. (20) (−)

Laplace number (−)

electrical current (A)

ṁ

mass flow rate (kg s⁻¹)

molecular mass (kg kmol⁻¹)

pressure (Pa)

P_EL

electrical power (W)

Prandtl number (−)

heat flow rate (W)

roughness parameter (μm)

Reynolds number (−)

Declaration of Competing Interest

None.

Acknowledgement

This work was partly funded by PRIN2017 2017KAAECT FlexHeat - The energy FLEXibility of enhanced HEAT pumps for the next generation of sustainable buildings.

References (22)

C. Zhang et al.
Investigation of flow boiling performance and the resulting surface deposition of graphene oxide nanofluid in microchannels
Exp. Thermal Fluid Sci.
(2017)
A.K. Sadaghiani et al.
Boiling heat transfer performance enhancement using micro and nano structured surfaces for high heat flux electronics cooling systems
Appl. Therm. Eng.
(2017)
V.V. Nirgude et al.
Enhancement of nucleate boiling heat transfer using structured surfaces
Chem. Eng. Proc.
(2017)
J.M. Kim et al.
Smart surface in flow boiling: spontaneous change of wettability
Int. J. Heat Mass Transf.
(2017)
S.J. Hong et al.
Enhanced flow boiling heat transfer characteristics of R134a on graphene- cu nanocomposite coating on copper substrate
Int. Commun. Heat Mass Transf.
(2019)
S.K. Gupta et al.
Experimental study of pool boiling heat transfer on copper surfaces with cu- Al₂O₃ nanocomposite coatings
Int. Commun. Heat Mass Transf.
(2018)
M.S. Sarwar et al.
Subcooled flow boiling CHF enhancement with porous surface coatings
Int. J. Heat Mass Transf.
(2007)
B. Bourdon et al.
Enhancing the onset of pool boiling by wettability modification on nanometrically smooth surfaces
Int. Commun. Heat Mass Transf.
(2013)
M.M. Sarafraz et al.
Nucleate pool boiling heat transfer characteristics of dilute Al₂O₃–ethyleneglycol nanofluids
Int. Commun. Heat Mass Transf.
(2014)
M.M. Sarafraz et al.
Pool boiling heat transfer to aqueous alumina nano-fluids on the plain and concentric circular micro-structured (CCM) surfaces
Exp. Thermal Fluid Sci.
(2016)

D. Rovillain et al.

Film boiling chemical vapor infiltration. An experimental study on carbon/carbon composite materials

Carbon

(2001)

Cited by (6)

Pool boiling heat transfer of ammonia outside a single tube with fin structures: Hysteresis phenomena and boiling enhancement
2023, International Communications in Heat and Mass Transfer
Pool boiling heat transfer of ammonia outside a single tube was investigated at three saturation pressures of 6.15, 8.57, and 11.7 bar (saturation temperature of 10, 20, and 30 °C) at the heat fluxes ranging from 1.2 to 72.9 kW/m². Hysteresis in a boiling curve and boiling enhancement were examined on both the smooth tube with machined roughness and two enhanced tubes with low fins and re-entrant cavities. All three tubes have outermost diameters from 15.68 to 15.87 mm and the same length of 796 mm. A large hysteresis between increasing the heat flux and decreasing the heat flux was observed on the smooth tube, and the hysteresis increased as the saturation pressure decreased. The boiling hysteresis of ammonia was reasonably explained from the thermodynamic analysis based on Clausius-Clapeyron and Young-Laplace equations. Heat transfer coefficients on the enhanced tubes were increased by 47% to 105% (Low-fin) and 103% to 159% (Turbo-E) compared with the smooth tube at the saturation pressure of 8.57 bar. However, the hysteresis itself was increased on the enhanced tubes owing to the wall temperature decrease along the fin. Hydrophobic coating and the enhanced tube having re-entrant cavities with cavity mouths of a few micrometers were suggested to mitigate the hysteresis phenomena in the pool boiling of ammonia.
Mechanistic model of combined pressure drop and heat transfer for the entire growth stage of an elongated bubble in a rectangular microchannel
2022, International Journal of Heat and Mass Transfer
Citation Excerpt :
This model used the capillary flow theory for calculating the nose velocity of the elongated bubble and could estimate the experimental database with a mean absolute error of 19.3% and predicts 83% of the database to within ±30%. Apart from the modelling efforts discussed above, in recent years a lot of progress has been reported in the experimental domain in terms of developing new designs for microchannel [39–41], correlations [42–45] and studying phenomena like boiling hysteresis [46,47]. In the recent work by Arcasi et al. [46], the hysteresis phenomenon was studied for flow boiling in a horizontal tube.
A one-dimensional flow-boiling model for the slug-flow regime is formulated to describe the pressure drop and heat transfer mechanism in a microchannel of rectangular cross-section. The pressure drop model considers three stages of bubble growth namely: (i) partial confinement, (ii) full confinement and (iii) vapour venting. The heat transfer coefficient at any particular location is obtained by assuming the periodic passage of four zones: (i) liquid slug zone, (ii) elongated bubble zone, (iii) partially dryout zone, and (iv) fully dryout zone. The model is evaluated using constant fluid properties, to study the parametric variation of channel pressure drop and heat transfer coefficient. The effects of variation in channel dimension, flow velocity, heat flux and properties of working fluid on pressure drop and heat transfer coefficient have been studied using the model. The model is capable of simulating all the transport processes for a single bubble from its inception till it leaves the microchannel and thereby it can estimate the pressure drop in the channel along with the heat transfer coefficient i.e. spatially averaged over the channel length and at any location from channel upstream to the downstream end.
Unidirectional wicking-driven flow boiling on tilted pillar structures for high-power applications
2022, International Journal of Heat and Mass Transfer
Citation Excerpt :
On the other hand, although enhancement of surface hydrophobicity augments heat dissipation, a hydrophobic surface is very prone to premature dry-out due to its poor wickability that compromises the rewetting capacity of the heated surface [8–9]. Furthermore, the influence of surface topography (the wicking characteristics) on boiling heat transfer has been experimentally explored [10–16]. Wen et al. [10] created surfaces of Cu-woven micro-meshes (one or more layers) to explore pool boiling heat transfer.
Energy management issues of data center cooling systems have been aggravated because of the miniaturization of electronic components. The cooling systems consume considerable energy, requiring more electric power supplied by power plants to prevent system failure from overheating. Among cooling methods applied in industrial fields, two-phase immersion cooling is the most potential cooling method for resolving energy consumption issues with extraordinary heat transfer capacity. To further augment the overall heat transfer performance, we propose polymerized surfaces with anisotropic pillar structures, generating a unidirectional wicking behavior to augment capillary-driven force when liquid propagation corresponds with the pillar tilted direction.
Further, we first experimentally determined the effect of the anisotropic pillar structures concerning wicking direction on heat transfer in subcooled flow boiling (40 K). When micropillars were tilted toward the convective flow direction (compared to against the flow direction), the unidirectional wicking enhanced the critical heat flux (CHF) by 31%, showing a directional dependence on tilted pillars. The anisotropic wicking surfaces can apply to high-power applications with their unique unidirectional wicking-driven heat transfer and high substrate selectivity.
New correlation of the subcooled flow boiling heat transfer coefficient for hybrid micro/nanostructured surfaces with high heat flux incidence
2024, Physics of Fluids
Advances in micro and nanoengineered surfaces for enhancing boiling and condensation heat transfer: a review
2022, Nanoscale Advances
Experimental Study of Pool Boiling Enhancement Using a Two-Step Electrodeposited Cu-GNPs Nanocomposite Porous Surface with R-134a
2021, Journal of Heat Transfer

View full text

On the hysteresis phenomenon during flow boiling heat transfer on a hydrophilic carbon/carbon surface

Highlights

Abstract

Introduction

Section snippets

Carbon/Carbon sample

The activation process

Conclusions

Nomenclature

Declaration of Competing Interest

Acknowledgement

Exp. Thermal Fluid Sci.

Appl. Therm. Eng.

Chem. Eng. Proc.

Int. J. Heat Mass Transf.

Int. Commun. Heat Mass Transf.

Int. Commun. Heat Mass Transf.

Int. J. Heat Mass Transf.

Int. Commun. Heat Mass Transf.

Int. Commun. Heat Mass Transf.

Exp. Thermal Fluid Sci.

Carbon