FIELD OF THE INVENTION:
The present invention generally relates to a technique which can be used for
early stage boiling detection of nanofluids. More particularly the present
invention relates to a device and process for detection of nucleation stage of
vapour bubbles formed during boiling of opaque fluids.
BACKGROUND OF THE INVENTION:
Liquids are the common coolant in industrial applications. However, solids have a
higher thermal conductivity than the liquids. Nanofluids prepared by colloidal
suspensions of nanoparticles into liquid are potential heat exchanger for
industries because of their improved thermal conductivity and the convective
heat transfer coefficient compared to the base liquid [1]. It is desirable to
improve the understanding of heat transfer mechanism of nanofluid which also
involves boiling for its efficient use [2].
Boiling of any liquid occurs in three characteristic stages, which are nucleate,
transition and film boiling. These stages generally take place as the heating
surface temperatures changes from low to high. Nucleate boiling is characterized
by the growth of bubbles on a heated surface, which rise from discrete points on

a surface, whose temperature is only slightly above the liquid. In general, the
numbers of nucleation sites are increased by an increasing surface temperature.
Boiling experiments are usually done for transparent liquid by observing density
of nucleation sites with increasing surface temperature. Nanofluid prepared by
adding nanoparticles to water are opaque and usually show same colour as the
nanoparticles. With increasing particle concentration, the colour of nanofluid
becomes much deeper. As visible light cannot penetrate the nanofluid due to
scattering of light with nano-particles, it has been a technological challenge to
the researchers to propose means for viewing and detecting nucleation of
bubbles during boiling tests of nanofluid.
WO2007103497 describes a gear oil and other lubricating oil composition
containing nanomaterials. The nanomaterials act as a viscosity modifier and
thermal conductivity improver for the gear oil and other lubricating oil
compositions, compared to prior art gear oils. The preferred nanoparticles also
impart a reduction in the coefficient of friction, including reduced friction in the
boundary lubrication regime. These properties are obtained by replacing part or
all of the polymer thickener or viscosity index improver or some other part of the

composition normally used in gear oils with nanomaterials of suitable shape, size,
and compostition.
US2009042751 teaches a lubricant having nanoparticles and microparticles to
enhance fuel efficiency, and a laser synthesis method to create dispersed
nanoparticles. According to the invention, the nanoparticles are chosen from a
class of hard materials, preferably alumina, silica, ceria, titania, diamond, cubic
boron nitride, and molybdenum oxide. The microparticles are chosen from a
class of materials of layered structures, preferably graphite, hexagonal boron
nitride, magnesium silicates (talc) and molybdenum disulphide. The nano-micro
combination can be chosen from the same materials. This group of materials
includes zinc oxide, copper oxide, molybdenum oxide, graphite, talc, and
hexagonal boron nitride. The ratio of nano to micro in the proposed combination
varies with the engine characteristics and driving conditions. The laser synthesis
method can be used to disperse nanoparticles in engine oil or other compatible
medium. The nano and microparticle combination when used in engine oil can
effect surface morphology changes such as smoothening and polishing of engine
wear surfaces, improvement in coefficient of friction, and fuel efficiency
enhancement up to 35% in a variety of vehicles (cars and trucks) under actual
road conditions, and reduction in exhaust emissions up to 90%.

WO2007082299 teaches nanoparticle composition that includes solid lubricant
nanoparticles and an organic medium. The nanoparticles may include layered
materials. A method of producing a nanoparticle by milling layered materials is
also provided. Also disclosed is a method of making a lubricant, the method
including milling layered materials to form nanoparticles and incorporating the
nanoparticles into a base to form a lubricant.
WO2006119502 discloses lubricant oil and grease composition containing an
additive package comprising wear-resistant additives in the form of
nanoparticles, wherein the additives are a carbonate selected from the group
consisting of a carbonate of a Group la alkali metal and a carbonate of a Group
2a alkaline earth metal, a sulfate of a Group la alkali metal of a Group 2a
alkaline earth metal, a phosphate of a Group la alkali metal or Group 2a alkaline
earth metal, a carboxylate of a Group la alkali metal and a carbonate of a Group
2a alkaline earth metal, or a combination thereof.
US2010029518 teaches a lubricating composition and method of making the
same. The lubricating composition comprises a lubricant fluid, water, and carbon

nanoparticles comprising nanodiamonds. The method comprises mixing the
lubricating composition under high shear followed by ultrasonication.
Nanofluid prepared by adding nanoparticles to water are opaque and usually
show same colour as that of the nanoparticles. Due to opacity of liquid, the
nucleation of bubbles cannot be observed in known boiling tests.
OBJECTS OF THE INVENTION:
It is therefore an object of the invention to propose a device for detection of
nucleation stage of vapour bubbles formed during boiling of nanofluids, which
eliminates the disadvantages of the prior art.
Another object of the invention is to propose a process for detection of
nucleation stage of vapour bubbles formed during boiling of nanofluids.
SUMMARY OF THE INVENTION:
According to the present invention there is provided a device and process for
early stage boiling detection of nanofluid during boiling of opaque fluids. The

present invention is based on heating a transparent horizontal plate using a ring
shape heater and viewing the heated surface from bottom using a high speed
camera. As the bubbles nucleate and remain attach to the heated surface, the
nucleation of the bubbles can be observed with camera.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 shows a schematic of a device to detect nucleate stage of bubbles
during boiling of opaque fluids according to the invention.
Figure 2(a) to 2(1) shows boiling of a single droplet of nanofluid placed on a glass
plate being heated by a heater, while figure 2(a) shows an image of a stable
droplet just before beginning of nucleation of vapour bubbles, and figures 2(b) to
2(1) exhibit images showing evolution of droplet with instantaneous time
indicated at bottom right corner of every image including nucleation sites.
DETAILED DESCRIPTION OF THE INVENTION:
As shown in figure 1, the inventive device comprises a glass plate (2) supporting
a droplet of nanofluid (1) placed on a brass ring (3), a large portion of the brass
ring (3) inserted and tightly fitted to a ring shape heater (4), exposing only 15%

of the brass ring (3) outside as shown in figure 1. A high speed camera (6) with
frame rate of 150 f/s is mounted vertically downward to the glass plate (2). A
plurality of clamps (5, 7) is used to hold the heater (4) and the camera (6)
respectively.
For conducting the measurements, a small droplet (10 micro litre) of nanofluid is
placed on the glass plate (2). The camera is focused at the interface of the
droplet (1) and plate (2).
For heating the glass plate (2), 220 V ac voltages is applied to the heater (4)
through a rheostat connected in series. Rheostat can be adjusted to vary the
temperature of the glass plate (2). According to the invention, a series resistance
of 770 Ω has been used to maintain a temperature of 107°C on the glass plate
(2), near a contact area with the brass ring (3). As heating is progressed by the
ring shape heater (4), a radial thermal gradient is produced within the area
covered by the brass ring (3). This thermal gradiant is minimized by selecting a
high thermal conducting transparent plate (2). Moreover, nucleation of bubbles
depends on surface roughness and wetting behaviour with a particular surface.
Accordingly, the glass plate (2) is coated with different transparent materials to
see the surface effects. Furthermore, metal films of thickness 5 to 10 nm remain

fairly transparent (3) and can be coated on glass to study the boiling behaviour
of nanofluid on metal surfaces.
According to the invention, the nanofluid is prepared by adding TiO2
nanoparticles (size 50 - 80 nm) in de-ionized water in 0.5% volume fraction. A
droplet (10 µl volume) of nanofluid is placed on the glass plate, at the centre of
brass ring (3). The glass plate (2) is heated by the ring shape heater (6) through
the brass ring (3). Figure 2(a) shows a stable droplet (1) on the hot glass plate
(2) at time t = 0. Subsequent images show evolution of the droplet (1) with
time, as time is mentioned at bottom right corner of all images. Figure 2(b)
shows nucleation of a vapor bubble, marked as '1' near periphery of the droplet.
A dark circle is drawn around the nucleation sites for better visualization. Size of
the vapor bubble increases as shown in figure 2(c) and finally disappears in
figure 2(d). Density of the nucleation of bubble increase as temperature of the
glass plate (2) rises, which is evident from the images shown in figure 2(e) to
figure 2(k).
References:
[1] S. U. S. Choi, Z. G. Zhang, W. Yu, F. E. Lockwood, and E. A. Grulke, Appl.
Phys. Lett. 79, 2252 (2001).
[2] S.M. Sohel Murshed et al., Applied Mechanics and Materials 393,110, (2011)
[3] I.D. Parker and H.H. Kim, Appl. Phys. Lett. 64,1774 (1994).

WE CLAIM:
1. A device for detection of nucleation stage of vapour bubbles formed
during boiling of nanofluids, comprising:
- a transparent glass plate supported over a metal ring;
the metal ring holding a droplet of nanofluid, and disposed over
- a heater such that a substantial portion of the metal ring
inserted tightably inside the heater, a smaller portion of the
metal ring being exposed outside the heater;
a high-speed camera with frame speed of at least 150 f/s
mounted vertically downward to said glass plate;
wherein when the heating temperature by the heater progressively
increased, a thermal radial gradiant at the contact area between the
glass plate and the metal ring is generated, and wherein the
transparent layer on said glass plate minimizes the thermal radial
gradiant allowing capturing the images of the vapour bubbles at the
nucleation stage.

2. The device as claimed in claim 1, wherein a plurality of clamps is provided
to hold the heater and the camera, and wherein the heater is provided
with a rheostat.
3. A process for detection of nucleation stage of vapour bubbles formed
during boiling of nanofluids, comprising the steps of:
- forming a nanofluid by adding TiO2 or other nanoparticles in de-
ionized water in 0.5% volume fraction;
- placing a droplet of the nanofluid on the centre of transparent
glass plate;
heating the glass plate via a metal ring by a heater having
adjustable rheostat;
- providing a high-speed camera to capture the images of the
droplet at various time frame;
progressively increasing the heating temperature to maintain a
series resistance about 770 Ω to increase the temperature
around 107°C near the contact area between the metal ring and
the glass plate; and

capturing the images of the vapour bubbles formed during
boiling of the droplet in particular at nucleation stage to detect
early stage of boiling.
4. The process as in claim 3, wherein the size of the TiO2 or other
nanoparticles is between 50-80 nm, and wherein a transparent layer
disposed on the glass plate constitutes a metal film of thickness between
5 to 10 nm.

ABSTRACT
The present invention relates to a device for detection of nucleation stage of
vapour bubbles formed during boiling of nanofluids, comprising a transparent
glass plate supported over a metal ring; the metal ring holding a droplet of
nanofluid, and disposed over a heater such that a substantial portion of the
metal ring inserted tightably inside the heater, a smaller portion of the metal ring
being exposed outside the heater; a high-speed camera with frame speed of at
least 150 f/s mounted vertically downward to said glass plate; wherein when the
heating temperature by the heater progressively increased, a thermal radial
gradiant at the contact area between the glass plate and the metal ring is
generated, and wherein the transparent layer on said glass plate minimizes the
thermal radial gradiant allowing capturing the images of the vapour bubbles at
the nucleation stage.