Regulated transient pool boiling of water during quenching on
nanostructured surfaces with modified wettability from
superhydrophilic to superhydrophobic
Li-Wu Fan
a,
⇑
, Jia-Qi Li
a
, Dan-Yang Li
a
, Liang Zhang
a,b
, Zi-Tao Yu
a
a
Institute of Thermal Science and Power Systems, Department of Energy Engineering, Zhejiang University, Hangzhou 310027, People’s Republic of China
b
State Key Laboratory of Clean Energy Utilization, Department of Energy Engineering, Zhejiang University, Hangzhou 310027, People’s Republic of China
article info
Article history:
Received 15 January 2014
Received in revised form 7 April 2014
Accepted 11 April 2014
Available online 14 May 2014
Keywords:
Phase change
Boiling
Quenching
Wettability
Nanostructured surfaces
Film boiling
abstract
The effects of surface wettability, from superhydrophilic to superhydrophobic, on transient pool boiling
of water under atmospheric pressure were experimentally examined by means of the quenching method
with hot stainless steel spheres. The wettability changes, with a contact angle ranging from nearly 0° to
more than 160°, were realized by nanostructured coating on the spheres. The quenching cooling rate was
shown to slow down with increasing the contact angle as the vapor film was stabilized and retained by
surface hydrophobicity even at very low wall superheats. Remarkable boiling heat transfer enhancement,
with critical heat flux (CHF) increase up to nearly 70%, was achieved for the superhydrophilic case as
compared to the original hydrophilic baseline case. As observed by high-speed imaging on the dynamic
quenching processes, violent rewetting that stems from superhydrophilicity facilitated early collapse of
the vapor film, thus leading to the great increase in film boiling heat transfer and CHF. The observations
suggested an active means of regulation of transient pool boiling by employing the nanostructured
surfaces with modified wettability to the extremes, toward either enhanced boiling heat transfer or
retention of stable film boiling phase.
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
As a highly-efficient heat transfer mode involving intensive
liquid/vapor phase change [1], boiling has long been studied and
practiced toward thermal energy conversion and management.
Transient pool boiling during quenching processes has found
numerous industrial applications from materials processing to
thermal management of nuclear reactors. In laboratory experi-
ments, the quenching method enable a rapid and easy means of
establishment of complete boiling curves, encompassing the film,
transition, and nucleate boiling regimes [2]. The critical heat flux
(CHF) and Leidenfrost point (LFP) along with its associated mini-
mum heat flux (MHF) can also been readily reduced from the
quenching data. In the literature, enhancement of pool boiling with
respect to the representative boiling regimes and critical points has
been studied for decades. Recent efforts on pool boiling heat trans-
fer enhancement, especially the CHF enhancement [3], may be
classified into two categories: (a) utilization of nanoparticle sus-
pensions (nanofluids) [4–6] and (b) boiling surface modification
with micro-/nanostructures [7–9]. Experimental evidence has
revealed the mechanisms of pool boiling enhancement of nanofl-
uids as a result of modification of the boiling surface properties,
wettability for example [10–13], due to deposition of nanoparti-
cles. This indicates that the utilization of nanofluids for enhanced
pool boiling may be considered as a passive approach to boiling
surface modification.
Three predominant boiling surface properties, i.e., roughness,
porosity, and wettability, have been identified to have separate
effects on boiling heat transfer [14,15], among which the wettabil-
ity, usually quantified by a contact angle, has mostly been explored
from thermodynamic point of view. A low contact angle, i.e., good
wettability (or hydrophilicity), is preferred to enhance the CHF,
whereas hydrophobicity, represented by a high contact angle, is
desirable to retain the stable film boiling phase [16]. Since the
primary phase change modes during nucleate (and CHF) and film
boiling (and LFP and MHF) regimes are essentially different, there
is no simple guide to expect how a transient pool boiling process
is regulated through modification of wettability of the boiling
surface. Concurrent with the development of advanced nanomate-
rials, the emergence of micro-/nanostructured superhydrophilic
(contact angle < 10°) and superhydrophobic (contact angle > 150°)
http://dx.doi.org/10.1016/j.ijheatmasstransfer.2014.04.025
0017-9310/Ó 2014 Elsevier Ltd. All rights reserved.
⇑
Corresponding author. Tel./fax: +86 571 87952378.
E-mail address: liwufan@zju.edu.cn (L.-W. Fan).
International Journal of Heat and Mass Transfer 76 (2014) 81–89
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