Performance Analysis of Ice Plant Test Rig Using Nano Fluids

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1.4.2 STABILITY OF NANO FLUIDS

1.4.3 MECHANISM OF HEAT TRANSFER IN NANO FLUID

1.4.4 VAPOUR COMPRESSION REFRIGERATION CYCLE

1.4.5 EXPERIMENTAL SETUP

2 LITERATURE REVIEW

3 EXPERIMENTAL VALIDATION

4 REFERENCES

ABSTRACT

Refrigeration may be defined as the process of achieving and maintaining a temperature below that of the surroundings, the aim being to freeze ice, cool some product, or space to the required temperature. The basis of modern refrigeration is the ability of liquids to absorb enormous quantities of heat as they boil and evaporate. One of the important applications of refrigeration is in ice plant. Ice plant is used for producing refrigeration effect which uses the vapour compression cycle and by using this cycle we are doing Performance Analysis of Ice Plant Using Nano fluids as a secondary refrigerants.

In this project we are going to select two nano fluids which comprises of Al2O3 which will be of various sizes and composition which will be used as a secondary refrigerant to increase heat enhancement in the test rig. We will calculate the compressor discharge temperature, discharge pressure and evaporator temperature, Coefficient of performance (COP), vapour pressure.

A Nano refrigerant has higher heat transfer coefficient than the other secondary refrigerants and it can be used to improve the thermodynamic and mechanical performance of the refrigeration systems.

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INTRODUCTION

Refrigeration may be defined as the process of achieving and maintaining a temperature below that of the surrounding. The aim is to freeze ice, cool some product or space. The basis of modern refrigeration is the ability of liquids to absorb enormous quantities of heat as they boil and evaporate. One of the important applications of refrigeration is in ice plant. Ice plant is used for producing refrigeration effect to freeze potable water in standard cans placed in rectangular tank which is filled by brine. Brines are secondary refrigerants and are generally used where temperature is required to be maintained below the freezing point of water i.e. 0°C. Brine is a solution of a salt in water. It may be noted that when a salt is mixed in water, then the freezing temperature of the solution becomes lower than that of the water. This is due to the fact that the salt while dissolving in water takes off its latent heat from the solution and cools it below the freezing point of water. The mass of the salt in the solution is known as concentration of the solution. As the concentration of the solution increases its freezing point decreases. The point, at which the freezing temperature is minimum, is known as eutectic temperature and the concentration at this point is known as eutectic concentration. A typical phase diagram for aqueous solutions is shown in Fig.1. The curves of the freezing points show that in many cases the solution of the two constituents has a lower freezing point than either substance individually. The diagram shows the possible phases and mixtures that can exist at various concentrations and temperatures. Assume that the brine is a solution of saltand water. If the brine at temperature A has a concentration M, the brine remains a liquid until the temperature drops to B.

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Figure 1 Phase diagram of an aqueous secondary coolant

Further cooling to C results in slush, which is a mixture of ice and brine. The brine at C has concentrated itself by freezing out some of its water into ice. Cooling the solution below D solidifies the entire mixture. Point E is called the eutectic point and represents the concentration at which the lowest temperature can be reached with no solidification. The brines commonly used are calcium chloride (CaCl2), sodium chloride i.e. common salt (NaCl), and glycols such as ethylene glycol, propylene glycol etc. For ice plant ethylene glycol, propylene glycols, sodium chloride are widely used as secondary refrigerants. However, due to poor thermal conductivity of secondary refrigerants, the heat transfer performance of these refrigerants is restricted. An innovative way of improving the thermal properties of these secondary refrigerants is to suspend nanometer sized metallic or non-metallic solid particles in them. Such fluids are called secondary refrigerant based nanofluids. Nanofluids are suspensions of solid nanoparticle in base fluid with sizes generally less than 100nm. Nanofluid technology becomes a new challenge for the heat transfer fluid since it has been reported that the thermal conductivity of nanofluid enhances at a very low volume fraction as explained by Choi et.al. [2] and also observed an increase up to approximately two times in the thermal conductivity of the fluid with the addition of a nanoparticle less than 1% volume concentrations. Most of the metallic or nonmetallic solid particles have thermal conductivity higher than those of the secondary refrigerants or convection fluids. Therefore, high heat transfer performance may be obtained when such particles are dispersed in conventional secondary refrigerants. A nanoparticles suspension is considered as a three phase system including the solid phase (nanoparticles), the liquid phase (fluid media) and the interfacial phase, which contributes significantly to the system properties because of their extremely high surface to volume ratio in nanofluid. The review showed that the thermal conductivity of Al2O3 nanofluid increases with the increase in the Al2O3 nanoparticle concentrations in the base fluids. This study would be useful in the field of secondary refrigerants.

Nano fluids are a relatively new class of fluids which consist of a base fluid with Nano-sized particles (1–100 nm) suspended within them. These particles, generally a metal or metal oxide, increase conduction and convection coefficients, allowing for more heat transfer in wide application such as in heat exchanger, automotive cooling and refrigeration system. Figure 1.2 provides an example of nanometer size of particles in comparison with millimeter and micrometer in order to understand the concept of nanoparticles clearly.

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Figure 1.2 Length scale of Nano fluids

In the past few decades, rapid advances in nanotechnology