FIELD OF INVENTION
The present invention relates to a process of improving the Coefficient of
Performance of a Vapor Compression Refrigeration system by dispersing a very
low volume fraction of TiO2 nano particles into the mineral oil used for lubricating
the system.
BACKGROUND OF THE INVENTION
Most of the domestic and industrial refrigeration and air-conditioning systems
operate on the principle of Vapor Compression Refrigeration (VCR) and find wide
applications in air conditioners used in buildings, automobiles and domestic
refrigerators. Many methods have been conventionally tried for increasing the
Coefficient of Performance (COP) of the VCR system. Experimental studies [1-2]
clearly explain such conventional methods for the performance improvement in
Vapor compression refrigeration system. With the advent of nanotechnology,
studies have been conducted to examine the effect of the nano-sized particles on
the COP of the Vapor compression refrigeration system by adding them in the
lubricating oil used in the system.
The patents (KR2009132146, KR20050089412 and WO2007018323 - all filed by
LG Electronics) teach the methodology for improvement of the performance of a
compressor by adding fullerene nano material in the lubrication oil. Review of
literatures [3-5] reveals that the nanoparticles added to the mineral oil can
improve the performance of the refrigeration system, by altering the viscosity
and friction characteristics.

Accordingly, there is a need to propose a system that can be used to reduce the
energy consumption of a vapor compression refrigeration system by adding
nanomaterials in the lubricating mineral oil. Furthermore, the nanomaterials
added to the mineral oil should be minimal.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a device for comparing
percentage enhancement of COP of a vapor compression refrigeration system
operable with a wide range of refrigerants and a mineral oil as the lubricant.
Another object of the invention is to propose a device for comparing percentage
enhancement of COP of a vapor compression refrigeration system operable with
a wide range of refrigerants and a mineral oil as the lubricant, in which low
volume fraction of TiO2 nanoparticles can be dispersed in the lubricant to form a
stable homogeneous solution and enhance COP without the addition of any
external surfactant.
A further object of the invention is to propose a process to enhance the
performance of the refrigeration system by achieving percentage enhancement
of COP for the proposed volume fraction of nanoparticles added to the lubricant.
SUMMARY OF THE INVENTION
Accordingly there is provided a device to compare the COP of a vapor
compression refrigeration system with and without nanoparticles in the mineral
oil the system comprising : a compressor, a condenser, a capillary tube, an
evaporator cabin; an energy meter, at least four pressure gauges and T-type

thermocouples to measure the properties of refrigerant at various stages of the
system. The wide range of refrigerants usable in the system, are all compatible
with the mineral oil used as the lubricating oil of the vapor compression
refrigeration system. There is a systematic procedure to synthesize nanofluid by
homogeneous dispersion of TiO2 nanoparticles in the base fluid: mineral oil.
Standard tests are conducted to identify the optimum concentration of
nanoparticles added to the mineral oil to meet the object of the invention.
Viscosity changes of the nanoparticles added mineral oil are examined, using a
Redwood viscometer; the lubrication characteristics of the mineral oil is studied,
by a friction tester; optical measurements using a Speckle Interferometer have
been conducted to study characteristics following the friction test. The COP
enhancement for the proposed volume fraction of nanoparticles in the mineral oil
is calculated using the standard convention; hence, a method is found to reduce
the energy consumption of a vapor compression refrigerator for a wide range of
refrigerants, by adding the judiciously correct amount of nanoparticles in the
mineral oil.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The scope of the invention can be better understood by the description provided
here in below with reference to the accompanying drawings, in which :
Figure 1 represents the SEM image of TiO2 nanoparticles used in the invention.
Figure 2 represents a comparison of viscosities of pure mineral oil with different
volume fractions of nanoparticles-mineral oil combinations.

Figure 3 represents the schematic of a test pin on a disk, of a known pin-on disk
friction tester.
Figure 4 represents the time-dependent variation of friction forces between pin
and disk, calculated using the pin-on disk tester for pure mineral oil and
nanofluids with a range of volume fractions of nanoparticles; used as lubricant.
Figure 5 shows the photograph of raw mineral oil and nano particle added
mineral oil.
Figure 6 represents schematic layout of a known Speckle Interferometer.
Figure 7 represents the friction surfaces of the test pin captured using the
Speckle Interferometer.
Figure 8 represents the schematic layout of a vapor compression refrigerator for
COP comparison.
Figure 9 represents the enhancement of COP obtained using different volume
fractions of mineral oil.
Table 1 shows experimental parameters for evaluating friction characteristics of
the pin tested in the pin-on disk tester.
Table 2 shows the Optical Roughness Index values of the pin surface obtained
using the Speckle Interferometer.

DETAILED DESCRIPTION OF THE INVENTION
Hereafter the embodiments of the invention are described with reference to the
accompanying figures and tables. The methods followed to obtain an enhanced
COP of the vapor compression refrigeration system, and thereby a reduced
power consumption of the system by the addition of low volume fraction of TiO2
nanoparticles in the mineral oil to meet the object of the invention, are explained
in this section.
Figure 1 shows the SEM image of TiO2 nanoparticles, used in the invention. The
average size of the particles is 40 nm. These nanoparticles are used to prepare
the nanofluid by a two step method using a standard Ultrasonic agitator by
sonicating the nanoparticles-mineral oil mixture for 300 minutes to prevent
agglomeration of nanoparticles. The sonication is done for various combinations
of the nanoparticles-mineral oil mixture by maintaining the mineral oil as the
base fluid and varying the volume fraction of the added nanoparticles. No
surfactant is added, as it would lead to the deterioration of the performance of
the vapor compression refrigeration system by formation of froth inside the
equipment.
Nanofluids with Various volume fractions of nanoparticles (all less than 0.02%)
are prepared and the variation of viscosity corresponding to temperature is
recorded.
Figure 2 shows the change in the viscosity of the pure mineral oil, when added
with various volume fractions of nanoparticles in it. The kinematic viscosities of
the mineral oil as well as the nanofluid are calculated using a Redwood
viscometer. In the Redwood viscometer the test oil is filled up to a marked

standard head in the viscometer and allowed to fall freely. The oil is collected in
a beaker and the time taken to fill the quantity is the factor to estimate the
kinematic viscosity of the test oil. From the tribological characteristics of the
bearings of the system, it is known that in a boundary lubrication system,
optimum viscosity increase results in a notable reduction in power consumption.
With a view of increasing the viscosity of the mineral oil, the nanopartides are
added with mineral oil separately to obtain different volume fractions. Figure 2
shows that the viscosity of the mineral oil increases with the increasing volume
fraction of nanopartides in it; further the viscosity variation with temperature
follows the standard pattern [6]. The viscosity increase of the mineral oil is due
to the increase in the fluid layer resistance caused by nanopartides [7]; which is
more at lower temperature and decreases as the temperature increases. To
identify the optimum volume fraction of nanopartides mineral oil mixture, friction
coefficient test was conducted.
Figure 3 shows the schematic of the pin and the disk located in the pin-on disk
tester calibrated in accordance with ASTM G99 standards; which mimics the real
piston cylinder arrangement in the hermitically sealed compressor used in the
vapor compressor refrigerator. Table 1 shows the experimental parameters
considered for the friction test with a view of reproducing the real boundary
lubrication system. A polished aluminum pin is held against a rotating steel disk
under the application of the load for a predetermined time to run for a standard
distance. The friction force developed between the pin and the rotating disk,
obtained directly from the digital meter of the pin-on disk tester, is used to
estimate the friction coefficient; which is the decisive factor to identify the
optimum volume fraction of nanopartides. The friction test of the pin surface
reveals the lubrication characteristics of pure mineral oil and the nanofluids. This
friction test helps to shortlist the range of volume fractions of nanopartides from

among a wide series of nanofluids which can give a minimum friction coefficient,
when used as lubricant for the compressor in the Vapor compression
refrigeration system. Figure 4 shows that the average friction force comes down
drastically for a specific range of volume fractions of nanoparticles (0.008-
0.012% VF) compared to a wide range of nanoparticles-mineral oil combinations
and these volume fractions of nanoparticles are furthermore checked for their
stability in the mineral oil. Figure 5 shows the photograph of the raw refrigerant
mineral oil and mineral oil containing 0.008-0.012% VF of TiO2 nano particles.
The nano mineral oil is stable even after 800 hours of its preparation. From the
Dynamic Light Scattering System (DLS) studies the Zeta potential value of the
nano lubricating mineral oil is found to be 70 mV, which shows that nano mineral
oil prepared is stable even after 800 hours of preparation, as a Zeta potential
value greater than 30 mV is a stable suspension.
Figure 6 shows the schematic view of a speckle interferometer. The speckle
interferometer uses a Helium-Neon laser beam of 2 mm beam diameter to have
an in-depth view of the friction (pin) surfaces on which friction tests are
conducted. The laser beam is focused through a biconvex lens to the work piece
kept in the work holding stand. The laser beam which hits the friction surface of
the pin reflects back at an angle in the same plane, depending on the orientation
of the pin surface. The reflected laser beam is captured by a CCD camera at a
speed of 5 frames per second to generate the image of the pin surface clearly.
The generated image is then used to obtain the Optical Roughness Index (ORI)
value using a MATLAB code; which tells the relative surface roughness of the pin
surface. This method is used to identify the effect of volume fraction of
nanoparticles in the mineral oil, which the pin was earlier subjected to, on the
surface roughness of the friction surfaces. Figure 7 shows speckle interferometry
images of the pin surfaces which were tested on the pin-on disk tester with the

various volume fractions of nanofluids used as the lubrication oil between the pin
and rotating disk. Table 2 shows that nanoparticle-base fluid combination used in
the set II (0.008-0.012 % VF) gives the maximum ORI, which suggests that the
surface will be the smoothest when that particular volume fraction is used.
Figure 8 shows the schematic layout of the vapor compression refrigeration
system to measure the Coefficient of Performance. The system comprises a
hermetically sealed compressor, a condenser, a capillary tube and an evaporator
cabin for cooling of water. T-type (copper-constantan) thermocouples calibrated
to a range ± 0.5°C, and at least four pressure gauges in the range of 0-300 psi
each are used to find the state of the refrigerant at each phase within the circuit.
The power consumption of the compressor was measured using a digital energy
meter. Figure 9 represents the COP enhancement obtained by using
nanoparticle-added mineral oil in the Vapor Compression Refrigeration system. It
is found that the percentage enhancement is maximum, when mineral oil
containing 0.008-0.012% volume fraction fraction of TiO2 nano particles (Set II)
is used.

WE CLAIM :
1. A process for determining lubricant composition in a vapor compression
refrigeration system to enhance the co-efficient of performance, the
system comprising a hermitically sealed compressor, a condenser, a
capillary tube including an evaporator cabin for cooling of water, a
plurality of thermocouples, at least four pressure gauges, and a digital
energy meter, the system being operable with different varieties of
refrigerants and a mineral oil as the lubricant, the process comprising the
steps of:
- preparing a nano-fluid sample in an ultrasonic agitator by dispersing TiO2
nanoparticles having average particle size of 40 nm in a mineral oil;
- preparing a plurality of volume fractions of nano-fluid by varying the
volume fraction of the nanoparticles and maintaining the volume of the
mineral oil as the base fluid as constant;
- determining the kinematic viscosity of the base fluid and the nanoparticles
in a viscometer including the variation of the kinematic viscosity of the
different volume fractions of the nanofluid samples;
- identifying an optimum volume fraction of nanoparticles mineral oil
mixture based on a minimum friction co-efficient value in a pin-on desk
tester having a digital meter; and
- validating the identified optimum volume fraction of the nanofluid capable
of enhancing co-efficient of performance of the refrigeration system when
used as the lubricant, the validation being carried-out in a speckle

interferometer which determined optical roughness index (ORI) value
representing the effect of volume fraction of nanoparticles in the mineral
oil.
2. The process as claimed in claim 1, wherein the mineral oil containing
0.008-0.012% volume fraction of TiO2 nanoparticles provides the optimum
volume fraction.

The invention relates to a process for determining lubricant composition in
a vapor compression refrigeration system to enhance the co-efficient of
performance, the system comprising a hermitically sealed compressor, a
condenser, a capillary tube including an evaporator cabin for cooling of
water, a plurality of thermocouples, at least four pressure gauges, and a
digital energy meter, the system being operable with different varieties of
refrigerants and a mineral oil as the lubricant, the process comprising the
steps of preparing a nano-fluid sample in an ultrasonic agitator by
dispersing TiO2 nanoparticles having average particle size of 40 nm in a
mineral oil; preparing a plurality of volume fractions of nano-fluid by
varying the volume fraction of the nanoparticles and maintaining the
volume of the mineral oil as the base fluid as constant; determining the
kinematic viscosity of the base fluid and the nanoparticles in a viscometer
including the variation of the kinematic viscosity of the different volume
fractions of the nanofluid samples; identifying an optimum volume fraction
of nanoparticles mineral oil mixture based on a minimum friction co-
efficient value in a pin-on desk tester having a digital meter; and
validating the identified optimum volume fraction of the nanofluid capable
of enhancing co-efficient of performance of the refrigeration system when
used as the lubricant, the validation being carried-out in a speckle
interferometer which determined optical roughness index (ORI) value
representing the effect of volume fraction of nanoparticles in the mineral
oil.