A Literature Review on the Effect of Nanoparticles in Refrigeration System

According the protocols devised to curtain the environmental pollution as well as to maintain eco friendly surroundings and to improve the thermo physical properties of the refrigeration system, it is very important to look for energy efficient and safe refrigerants so as to improve the effect of refrigeration and co-efficient of performance. Nanoparticles and Nano fluids have grabbed the attention scenario with its enhanced properties and its potential applications like high heat transfer rates as well as better thermo physical characteristics. This is a study attempted to bring out some of the important woks done in the field of Nano refrigerants as well as Nano lubricants. This work also encapsules some of the works done using nanoparticles in the refrigeration system so as to study its effect on the process variables of the refrigeration system. Thus it is evident that Nano refrigerants have great capability of increasing heat transfer rates as well as performances of refrigeration system and has significant effect on other thermo physical properties as well as various other variables pertaining to refrigeration system


INTRODUCTION
In accordance with Kyoto and Montreal protocol, it is highly indispensable to look for eco-friendly as well, energy efficient refrigerants thereby improving the refrigerating effect, co-efficient of performance as well as the thermo physical properties of refrigerant. Nano fluids enticed many attentions around the world as a substantial alternative to @ IJTSRD | Available Online @ www.ijtsrd.com | Volume -2 | Issue -3 | Mar-Apr 2018 According the protocols devised to curtain the environmental pollution as well as to maintain ecofriendly surroundings and to improve the thermo physical properties of the refrigeration system, it is very important to look for energy efficient and safe refrigerants so as to improve the effect of refrigeration efficient of performance. Nanoparticles and Nano fluids have grabbed the attention of present scenario with its enhanced properties and its potential applications like high heat transfer rates as well as better thermo physical characteristics. This is a study attempted to bring out some of the important woks rigerants as well as Nano lubricants. This work also encapsules some of the works done using nanoparticles in the refrigeration system so as to study its effect on the process variables of the refrigeration system. Thus it is have great capability of increasing heat transfer rates as well as performances of refrigeration system and has significant effect on other thermo physical properties as well as various other variables pertaining to refrigeration system ient of Performance, thermo physical, refrigerants, process variables, Nano In accordance with Kyoto and Montreal protocol, it is friendly as well, energy efficient refrigerants thereby improving the efficient of performance as well as the thermo physical properties of the refrigerant. Nano fluids enticed many attentions around the world as a substantial alternative to increase the heat transfer performance. In present investigation, a thorough study has been made in the field of nanoparticles and its effects on the refrigeration system. A brief summary about the refrigeration system and the nanoparticles has been discussed below.

A. Refrigeration system:
Many research papers have investigated the effect of nanoparticles in vapour compression refrigeration system. Refrigeration is a method of taking out heat from a low-temperature reservoir and transporting it to a high-temperature reservoir. It is also defined as the process of attaining and retaining a temperature below that of the surrounding, the aim of cooling some product or space to the required temperature. Perhaps the popular applications of refrigeration are storing perishable food, Refrigeration is used to deliquesce gases like oxygen, nitrogen, propane and methane, while transferring the food and dairy products, cryogenic applications as well as in many power plants, chemical processes with low temperature requirements. A refrigerant is a substance basically in the liquid or gaseous state which brings out the refrigeration effect. The normal refrigeration cycle is a closed cycle process. Nearly all the domestic refrigeration is Vapour Compression Refrigeration type. The main processes in this cycle are listed below. increase the heat transfer performance. In present investigation, a thorough study has been made in the field of nanoparticles and its effects on the frigeration system. A brief summary about the refrigeration system and the nanoparticles has been Many research papers have investigated the effect of nanoparticles in vapour compression refrigeration ation is a method of taking out heat temperature reservoir and transporting it temperature reservoir. It is also defined as the process of attaining and retaining a temperature below that of the surrounding, the aim of cooling duct or space to the required temperature. Perhaps the popular applications of refrigeration are storing perishable food, Refrigeration is used to deliquesce gases like oxygen, nitrogen, propane and methane, while transferring the food and dairy cryogenic applications as well as in many power plants, chemical processes with low temperature requirements. A refrigerant is a substance basically in the liquid or gaseous state which brings out the refrigeration effect. The normal refrigeration a closed cycle process. Nearly all the domestic refrigeration is Vapour Compression Refrigeration type. The main processes in this cycle Nanoparticles as well as Nano fluids have grabbed attention of many in this present scenario. Nanoparticles are nanometer sized particles in the order of 10-9 m. Nano fluids are engineered colloids which consist of a base fluid with Nano sized particles (1-100 nm) suspended within them.Nanofluids have special advantage that these fluids possess enhanced properties than the base fluids. They possess many attractive features like enhances thermo physical properties, higher thermal conductivity and higher surface area. There are several classifications of Nano fluids in which the nanoparticles dispersed in the base fluids may be of metal oxides, carbides, nitrides, carbon nanotubes, diamond, graphite etc.
More than a century ago, Maxwell et al. initiated the efforts to enhance inherently poor thermal conductivity of liquids by adding solid particles in base fluids. Earlier studies used millimetre or micrometre solid particles, which led to problems such as rapid settling of solid particles, clogging, surface abrasion & high-pressure drop, limiting their practical applications. Nano fluids have good potential to overcome these problems. Choi (1995) et al. conceived the novel concept of Nano fluids by making use of particles sizes in the order of 1 to 100 nm. Research on heat transfer enhancement by adding nanoparticles has had mixed results since then. Gains & losses of heat transfer have been reported. Main factors, which influence the results, are nanoparticle material, nanoparticle concentration, Nano fluid preparation methods & testing consistency. In last decade, the number of published articles mentioning nanoparticles has increased significantly in refrigeration field.
Amy Majgaonkar (2016) et al. reviewed in his article that in refrigeration systems, Nano lubricant improves tribological characteristics improving compressor performance; Nano refrigerant improves thermophysical properties, improving refrigerating effect. Presence of nanoparticles enhances solubility between oil & refrigerant and returns more oil back to the compressor. He has also enclosed that in refrigeration systems, preparation of Nano lubricant is comparatively easier than direct preparation of Nano refrigerant, as only few refrigerants are available in liquid state at atmospheric pressure. Nanoparticles of required type & size are dispersed in base fluid after precise weighing on electronic balance. Stirring is done in a mechanical stirrer for some period followed by ultra-sonic vibration technique to form a stable Nano fluid. Surface-active agents and/or dispersants are generally not used. Nanoparticles increase the surface area; improve mixing, turbulence & temperature distribution in Nano fluids. Suspension of highly thermally conductive materials is not always effective to improve the thermal transport properties of Nano fluids. CNT has highest thermal conductivity. Aligned CNTs are easier to disperse. However it is most expensive option. Natural Diamond has second highest thermal conductivity with no significant health risks but is second most expensive option. CuO & ZnO can be dangerous for health. Al 2 O 3 reacts with water & heat is generated. Oil has low thermal conductivity whereas refrigerant has very low thermal conductivity. For other nanoparticles study is limited.
Anoop.k (2014) et al. experimented with the mixture of mineral oil and 20 nm silicon dioxide (SiO 2 ) and of 1, 2 Nano Particle Volume Fraction in Lubricant and resulted more about the viscosity of the mixture. He stated that viscosity is directly proportional to Nano Particle Concentration as well as pressure. He also concluded that at high temperature viscosity of the Nano lubricant is less affected by pressure. Also viscosity is inversely proportional to temperature and below 100°C viscosity remains almost same [1]. When the temperature and the pressure is very high the viscosity of the Nano fluid is unexpectedly affected. While mentioning about viscosity Dhindsa.G   In many studies, where nanoparticles are directly mixed with refrigerants following terminology shall be useful NPMFR = Nanoparticle mass fraction in refrigerant = Ratio of mass of NP to mass of NP-refrigerant mixture. In many studies Nano lubricant is first prepared by mixing nanoparticles with lubricant. Nanolubricant is then mixed with pure refrigerant, thereby making Nano refrigerant. In such cases following terminology & equations shall be useful. However, the effect of compressor suction pulling force also needs to be considered in such studies to make it applicable to real cases. A large amount of study is still needed to investigate the mechanism of migration. To the author's knowledge no study is yet published with application of nanoparticles in refrigeration systems having flooded evaporators. Density of Nano refrigerant needs to be investigated as depth of the pool of boiling refrigerant in a flooded evaporator exerts a liquid pressure on lower part of heat transfer surface. Therefore, saturation temperature at this surface is higher than that in suction line, which is not affected by the liquid pressure. This temperature gradient must be considered when designing the flooded evaporator. Also oil return ports needs to be located on flooded evaporator shell considering miscibility & relative density of Nano lubricant/refrigerant. Most of the literature reports that only one type of nanoparticle is studied to make a particular type of Nano fluid. To the author's knowledge, a mixture of different types of nanoparticles dispersed in a base fluid to make Nano fluid containing different types of nanoparticles is not published yet. Also many studies also do not publish nanoparticle size in dry & in suspension states.