WO2012156980A1

WO2012156980A1 - A process for determining lubricant composition in a vapor compression refrigeration system to enhance the co-efficient of performance

Info

Publication number: WO2012156980A1
Application number: PCT/IN2011/000514
Authority: WO
Inventors: Sabareesh R. KRISHNA; Das SUMITESH; N Gobinath; V. Sajith; Thomas SHIJO; C.B. Sobhan; T. Hanas
Original assignee: Tata Steel Limited; National Institute Of Technology Calicut
Priority date: 2011-05-18
Filing date: 2011-08-05
Publication date: 2012-11-22
Also published as: MX2012010582A; BR112012027927B1; BR112012027927A2; ZA201208923B; MX344162B

Abstract

The invention relates to a process for determining lubricant composition in a vapor compression refrigeration system to enhance the co-efficient o 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.

Description

TITLE : A PROCESS FOR DETERMINING LUBRICANT COMPOSITION IN A VAPOR COMPRESSION REFRIGERATION SYSTEM TO ENHANCE THE CO-EFFICIEINT OF PERFORMANCE

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 T1O2 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 ^"ΠΟ2 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 ΤΊΟ2 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 T1O₂ 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 Ti0₂ nanoparticles in the mineral oil to meet the object of the invention, are explained in this section.

Figure 1 shows the SEM image of ΤΊΟ₂ 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 nanoparticles 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 nanoparticles 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 nanoparticles [7]; which is more at lower temperature and decreases as the temperature increases. To identify the optimum volume fraction of nanoparticles 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 nanoparticles. 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 nanoparticles 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 ^"ΠΟ2 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 T1O2 nano particles (Set II) is used.

Claims

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 ^"ΠΟ₂ 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 determines 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 ΤΊΟ2 nanoparticles provides the optimum volume fraction.