INTRODUCTION

There
are many types of air conditioning system that can be bought and used. Air
conditioning becomes particularly useful at most places especially in hot
weather country since it can help to cool down the hotness at certain places that
have air conditioner. The entire process of making the air in your property a
comfortable temperature is based on a simple scientific principle and the rest
achieved by mechanical means. Air conditioner use chemical that converts gas to
liquid.

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Basically
air conditioning system has four important parts in order to produce good and
cool air which is compressor, condenser, evaporator and expansion valve. As it
uses refrigerant to chill indoor air, the compounds that involved are
refrigerant that have properties that enabling them to change at relatively low
temperature. The air conditioner contains fans where it moves the warm interior
air over the cold filled coils.

At
first, the cooling fluid reaches the compressor as low temperature gas. As the
compressor squeezes the fluid, the molecules in the liquid are packed close
together. The closer the compressor forces these molecules together, the higher
the temperature and energy rise. Then it exits as a high pressure, hot gas and
moves to the condenser where the outside unit of an air conditioning system
that has metal fins all around the housing and it works like the radiator on
vehicle as they help to dissipate heat more quickly when the fluid leaves the
condenser , it is much cooler. It also changes from gas to liquid for because
of the high pressure.

The
hot liquid refrigerant passes through a tiny opening, high pressure in the
valve on one side. It emerges as a cool low- pressure mist on the other side.
Now, the low pressure cold liquid mist that moves onto the evaporator coil. The
fluid then makes its way to evaporator through the evaporator tube. When the
liquid reaches the other side its pressure drops and fluid begins to evaporate
to gas phase. From there it moves back onto the compressor and exterior
condensing unit and the cooling cycles continues, as this occurs, the heat will
extracted to the surrounding blow air back into the house. The air conditioning
process continues until the inside air at the selected place reaches its
desired temperature.

Air
conditioner should be maintained properly. Especially in the places where the
weather is hot, a place without a proper air conditioning is nothing less than
a solar heater. There can be various reasons behind it when it has problems.
There are various parts/components in air conditioning system that will create
troubles when it is not properly taken care of. For example, here is absolutely
no cold air produced then it may have some troubles in one of the units. There
might be any blockage and leakage in the systems that need to be check as soon
as possible. Minor leaks in some refrigerant is considered normal unless the
leakage increase over time , then seek for repair immediately. Air conditioners
have provided a great service. Not only cool the home’s or office’s interior
air and create comfortable environment, but also improve the air quality.
Modern units are equipped with washable or disposable filter that discourages
allergies and pollutants from circulating throughout the interior spaces.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PROBLEM STATEMENT

 

Generally all working
fluid that moves to one and another places especially at small tube will
eventually cause blockage. For this case, blockage in the evaporator tube
because of impurities during the flow boiling process as it affects the tube
caused high pressure. As mentioned before the low pressure liquid moves into
evaporator tube. When the liquid reaches into the tube, the pressure drops and
fluid begins to evaporate to gas phase. That is where when the tube
experiencing thermal shock that will affect the tube surface.

The evaporator tube
predicted to be very small where it depends on the velocity and temperature of
the fluids as it will cause high pressure especially at the U-bend area. The
working fluid has impurities that sometimes can form into something that will
cause blockage too not only the erosion in the tube.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

OBJECTIVES

The aim of this project
is to do a research as well as to model the clogging and erosion issues in the
evaporator tube during the flow.

1.       
To develop understanding of the
methodology about causes of blockage in evaporator tube and its effect towards
the tube.

2.       
To analyse behaviour of the flow in
the evaporator tube ways to improve the flow by adjusting the velocity of the
flow

3.       
To simulate model of blocking/
erosion in the evaporator tube.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

METHODOLOGY

The
methods apply in this project is to perform feasibility research besides
analyse the potential .Flowchart as below:

                  

 

 

 

 

   

 

  

 

 

 

 

 

 

 

 

 

 

LITERATURE
REVIEW

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CHAPTER 3

METHODOLOGY

 

3.1 INTRODUCTION

 

Water has been the most commonly used working fluid with nanoparticles
so far in the literature especially for boiling purposes. Boiling heat transfer
is almost used in every industrial works and applications such as power
generation, heat exchangers, cooling high power electronics and so on.
Enhancements in boiling heat transfer processes are vital, and could make these
typical industrial applications, previously listed and more energy efficient.
But for this, work focuses on evaporator tube.

 

Nanoparticles deposition has been observed by all researchers. This is
main reason for the critical heat flux enhancement (CHF) especially that have
conducted in Nano fluid boiling and both pool and convective .This cause in
increasing of the surface roughness, surface area as well as the surface
wettability. Boiling performance is dependent on the combined effect of
particle concentration, surface properties, and the nature of base fluid if
it’s highly wetting.

 

In terms of boiling regimes, nucleate boiling is an efficient
heat-transfer mechanism; however, for the incorporation of nucleate boiling in
most practical applications, it is imperative that the critical heat flux (CHF)
is not exceeded. When the CHF point the heat transfer is maximised, followed by
a drastic degradation after the CHF point. Basically, the boiling process
changes from efficient nucleate boiling to lesser-efficient film boiling at the
CHF point. The occurrence of CHF is accompanied by localised overheating at the
heated surface, and a decrease in the heat-transfer rate. An increase in the
CHF of the boiling system would therefore allow for more compact and effective
cooling systems for nuclear reactors, air-conditioning units, etc.

 

Nanofluids are colloidal suspensions of nanoparticles (length scales
1-100 nm) in a base fluid. These particles can be metallic (Cu, Au) or metal
oxides (Al2O3, TiO2, ZrO2), carbon (diamond, nanotubes), glass or another
material, with the base fluid being a typical heat-transfer fluid, such as
water, light oils, ethylene glycol (radiator fluid) or a refrigerant. The base
fluids alone have rather low thermal conductivities.1

 

Manufacturing limitations in the past allowed only the creation of
microparticles, and these particles quickly settled out of the fluid, and
deposited in pipes or tanks, clogging flow passages, causing damage and erosion
to pumps and valves, and increasing pressure drop. Nanoparticles, however, can
be dispersed in base fluids and remain suspended in the fluid to a much greater
extent than was previously achieved with microparticles. This is mainly thought
to be due to Brownian motion preventing gravity settling and agglomeration of
particles, resulting in a much more stable, suspended fluid.

 

An interesting advantage of using nanofluids for heat transfer
applications is the ability to alter their properties. That is, the thermal
conductivity and surface wettability, for example, can be adjusted by varying
the particle concentration in the base fluid, and hence allowing nanofluids to
be used for a variety of different applications. However, it is also important
to note that addition of nanoparticles to a base fluid also changes the
viscosity, density and even the effective specific heat; these properties also
have a direct effect on the heat transfer effectiveness.

 

Normally, the enhancement of the heat-transfer coefficient for
single-phase laminar flow was found. However , in the two-phase regime, the
Nanofluids caused surface deposition in the microchannels, and large clusters,
agglomerates of nanoparticles, were formed.

 

3.2  EVAPORATOR TUBE BLOCKAGE

 

Evaporator tubes are specifically designed to efficiently boil off
process fluids from the outside of the tube. This is most commonly used in
chiller evaporators, where the boiling of refrigerant creates rapid cooling of
the water in the tube side for use in comfort cooling as well as process
cooling, most evaporator tube is made from copper metal.2

 

Dirty evaporators display multiple symptoms that indicate that it is
dirty and needs to be cleaned. The evaporator is designed to convert warm and
often humid air into dry and cooler air. This process removes the heat and
humidity by using refrigerant circulating through a series of metallic coils.
When this occurs, the humidity is converted to liquid (H2O) and needs to be
removed from the evaporator in order to reduce the build-up of mildew and mold.
Noted below are a few of the common warning signs that a problem with the AC
evaporator exists and that it needs to be cleaned.

 

The inside diameter of the tubes is as small as 5mm . Dealing with
such small diameters can lead to blockage if large particles reach the tube. If
the tube does become blocked, then the evaporator becomes starved. The suction
pressure drops, less refrigerating effect takes place, and the compressor is
forced to work harder, resulting in increased head pressures with accompanying
increases in temperature. By this. The simulation will be done by using
ANSYS-FLUENT for the clogging removal process.

 

Material and size are important properties influencing the
characteristics of nanoparticles. The choice of nanoparticles to be suspended
in a base fluid is expected to have an essential influence on the maximum
possible increase in CHF.

 

 

3.3 ANSYS-FLUENT

 

ANSYS FLUENT is basically a main software for computational fluid
dynamics (CFD) tools that available and most used in this generation. It is
mainly used for prototype and testing, simulation, modelling and designing. It
uses numerical analysis and data structures to solve and analyze problems that
involve fluid flows. Computers are used to perform the calculations required to
simulate the interaction of liquids and gases with surfaces defined by boundary
conditions. With high-speed supercomputers, better solutions can be achieved.
On going research yields software that improves the accuracy and speed of
complex simulation scenarios such as transonic or turbulent flows.3 The
advantage of ANSYS-FLUENT is the number of turbulent model adapted to special case.

For this case, the blockage in evaporator tube can be seen and examine
by using ANSYS-FLUENT software. By this, the flow or blockage can be reduced.
The blockage normally happens in the tube where the tube is very small and
long, the only way to see it by cutting the tube so can see what’s inside. But
since doing that will damage the tube, it’s better to do simulation and see
what’s going on inside even when the flow is on going.

 

3.4 METHODOLOGY

 

3.4.1 CFD methodology

Preprocessing 

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