Refrigeration increasing rapidly. Now-a-days power cuts are very often

Refrigeration and Air conditioning
systems are directly or indirectly responsible for present energy crisis
problem as their use in household, commercial and transportation sector are
increasing rapidly. Now-a-days power cuts are very often due to accidents, or
could be due to implementation of demand side management schemes to shift power
usage to avoid high loads by the electricity supplier, or by the user to shift
their electricity usage to off-peak pricing periods (electrical load shifting)
and it is important to maintain regular temperatures inside cold storage
facilities and cold transport vehicles. A major contribution to the heat
loadings for a cold store comes from heat penetrating the walls. The
refrigeration system removes this heat load, but if there is a power failure,
cooling is not provided to the stored product. Thermal Energy storage systems
(TES) will use phase change materials for storage of heat and cold at shifted
time. Phase change material (PCM) melts within a narrow temperature range, and
absorbs a large amount of energy while in the transition state, thus minimizing
the rise in the environment temperature. PCM with a suitable melting
temperature may be used to provide thermal capacity to maintain suitable
internal temperature during power failure. PCM may also be used in load
shedding applications to shift electricity usage to an optimum time. Many Cold
Thermal Energy Storage (CTES) systems have gained attention in recent years.
Cold Storage is a special kind of room, the temperature of which is kept very
low with the help of machines and precision instruments. This paper aims to
combination of cold store using with the inclusion of PCM. The effect on the
change in air temperature during loss of electrical power (and thus loss of
cooling) is investigated and validated for a cold store and then extended to
predict the transient performance of a typical cold store. The energy used can
have different sources, which are renewable and non-renewable. Especially solar
energy is not continuous and thus heat storage is necessary to supply heat
reliably. When solar collectors are used to heat domestic hot water, the
storage also matches the different powers of the solar collector field, which
collects the energy over many hours of the day, to meet the demand of a hot
bath that is filled in only several minutes. Sensible heat storage is used for
example in hot water heat storages or in the floor structure in under floor
heating. An alternative method is changing the phase of a material. The
best-known examples are ice and snow storage. The storage of thermal energy in
the form of latent heat in phase change materials (PCMs) represents an
attractive option for low and medium temperature range energy applications.
Wide ranges of PCMs have been investigated, such as paraffin wax, salt hydrates
and non-paraffin organic compounds. The economic feasibility of employing a
latent heat storage material in a system depends on the life span and cost of
the storage materials. In other words, there should not be major changes in the
melting point and the latent heat of fusion with time, due to thermal cycles of
the storage materials. For latent heat storage, commercial grade PCMs is
preferred due to various reasons, such as low cost and easy availability. This
is one of the important aspects for a PCM-based energy storage system.
Eliminating the problems of super cooling, phase separation and stability over
a long period of application is an important criterion for the successful
application of suitable PCMs for thermal energy storage systems. The latent
heat over the sensible heat is clear from the comparison of the volume and mass
of the storage unit required for storing a certain amount of heat. It shows
that inorganic compounds, such as hydrated salts, have a higher volumetric
thermal storage density than the most of the organic compounds due to their
higher latent heat and density. The various PCMs are generally divided into
three main groups: organic, inorganic and eutectics of organic and/or inorganic
compounds. Organic compounds present several advantages such as no
corrosiveness, low or no under cooling, possess chemical and thermal stability,
ability of congruent melting, self-nucleating properties and compatibility with
conventional materials of construction. Subgroups of organic compounds include
paraffin and non-paraffin organic. Technical grade paraffin has been
extensively used as heat storage materials due to wide melting/solidification
temperature ranges and has a relatively high latent heat capacity. They also
have no sub cooling effects during the solidification as well as small volume
change during the phase-change process. They are chemically stable, nontoxic
and non-corrosive over an extended storage period. Widely used non-paraffin
organics, as latent heat storage materials are fatty acids like lauric,
myristic, palmitic and stearic acid. Their advantages are a possibility for
reproducible melting and solidification behavior and little or no sub cooling
effects. Disadvantages of organic compounds include lower phase-change
enthalpy, low thermal conductivity and inflammability. Inorganic phase changes
of materials are a perspective way of thermal energy storage. Big latent heat,
good thermal conductivity and inflammability are the main advantages of inorganic
materials. But they cause corrosion and suffer from loss of H2O. Incongruent
melting and super cooling are the biggest problem with their exploitation.
During melting and freezing there are precipitations of other phases which do
not take part in next process of charging and discharging. The use of phase
change materials (PCMs) in energy storage has the advantage of high energy
density and isothermal operation.

 

 

       
I.           
Energy
storage system

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Thermal
energy storage (TES), also commonly called heat and cold storage, allows the
storage of heat or cold to be used later. To be able to retrieve the heat or
cold after some time, the method of storage needs to be reversible. Sensible
heat By far the most common way of thermal energy storage is as sensible heat.
A sensor can detect this temperature increase and the heat stored is thus
called sensible heat. Latent heat if heat is stored as latent heat, a phase
change of the storage material is used. There are several options with distinct
advantages and disadvantages. The phase change solid-liquid by melting and
solidification can store large amounts of heat or cold, if a suitable material
is selected. Melting is characterized by a small volume change, usually less
than 10 %. If a container can fit the phase with the larger volume, usually the
liquid, the pressure is not changed significantly and consequently melting and
solidification of the storage material proceed at a constant temperature. Upon
melting, while heat is transferred to the storage material, the material still
keeps its temperature constant at the melting temperature, also called phase
change temperature.Heat transfer in PCM storage is characterized by a moving
solid–liquid interface, generally referred to as the “moving boundary” problem.
It is a transient, non-linear phenomenon. Analytical solutions for phase change
problems are only known for a couple of physical situations which possess a
simple geometry and simple boundary conditions, as nonlinearity poses major
difficulties in moving boundary problems. Neumann originated the most
well-known precise analytical solution for a one-dimensional moving boundary
problem, called the Stefan problem. Some analytical approximations for
one-dimensional moving boundary problems with different boundary conditions are
the quasi-stationary approximation, perturbation methods, the Megerlin method
and the Heat-balance-integral method. It has been assumed here that the melting
or solidification temperature is constant. However, for example technical grade
paraffin has a wide temperature range at the points where melting and
solidification occur. Phase change problems are usually solved with finite
difference or finite element methods in accordance with the numerical approach.
The phase change phenomenon has to be modeled separately due the non-linear
nature of the problem. A wide range of different kinds of numerical methods for
solving PCM problems exist. The most common methods used are the enthalpy
method and the effective heat capacity method.

III. Characteristics and Classification of
PCM

PCMs latent heat storage can be achieved
through solid–solid, solid–liquid, solid–gas and liquid–gas phase change.
However, the only phase change used for PCMs is the solid– liquid change.
Liquid-gas phase changes are not practical for use as thermal storage.
Liquid–gas transitions do have a higher heat of transformation than
solid–liquid transitions. Solid–solid phase changes are typically very slow and
have a rather low heat of transformation. PCM stores 5 to 14 times more heat
per unit volume than conventional storage materials such as water, masonry or
rock. The classification of PCM is shown in figure

Figure-1
Classification of PCM

IV.           
Properties
Affecting TESS

 

A.      
Melting Point

 

Melting
point is the temperature at which the first crystal of the material collapses.
It is imperative to have the melting point of TESD within the temperature range
of application. The melting point as such does not affect the energy storage
capacity of a material. However, as a phase change is involved in melting, the
inclusion of melting point in temperature range of application can permit the
use of phase change as an on-off switch. Melting point lower as well as higher
than the temperature range of application prohibits the use of the material in
TESS.

 

B.      
Heat of Fusion

 

Heat
of fusion also known as enthalpy of fusion or latent heat of fusion is a very
important property useful in selecting a TESD. It refers to the amount of
thermal energy that a material must absorb or evolve in order to change its
phase from solid to liquid or vice versa. Large values of heat of fusion aid in
increasing the efficiency of TESS.

 

C.     
Heat Capacity

 

Heat
capacity refers to the amount of energy per molecule that a compound can store
before the increase in its temperature. This energy is generally stored in
translational, vibration and rotational modes. Thus materials with greater
number of atoms in its composition are expected to have higher heat capacity.

 

D.     
Thermal Conductivity

 

Thermal
Conductivity   measures the ability of a
material to conduct heat. Greater values of k imply an efficient heat transfer.
Thermal conductivity is a property which needs to be optimized. Since thermal
conductivity is phase dependent property, it is important to know values   in both the solid as well as molten phases.
It has been observed that most of molten materials exhibit much higher values
of thermal conductivity as compared to that in their solid state.

 

E.      
Density

 

Density
of a material refers to its mass per unit volume. Density values can readily be
measured using densitometers. Materials with higher density thus occupy less
space which in turn increases the energy storage capacity. Materials with high
density obviously possess higher energy storage capacity but many of them show
a significant decrease in density in their molten state.

 

 

 

 

Required
Properties of a PCM

 

S. No

Properties

Selection Criteria

 
 
1.

Thermal Properties

 
a. Suitable Melting
Temperature
 
b. High Latent Heat of Fusion

 
c. Good Heat transfer Rate

 
 
2.

 
 
Physical Properties

 
a. Favorable Phase
Equilibrium
 
b. High Density
 
c. Small Volume Change

 
 
3.

 
 
Chemical Properties

 
a. Long Term Chemical
Stability
 
b. Compatibility with
Construction Materials
 
c. Non-Toxicity

 
 
4.

 
 
Economical Properties

 
a. Cost Effective
 
b. Abundant in Nature
 
c. High Scale Availability

 

 

V.           
Futuristic
application OF PCM

 

Many
research articles concluded that PCM is used for increasing the performance and
efficiency of solar panels. Available solar panels efficiency is very less and
one of key reason is high temperature loss. Maximum efficiency of solar panels
only exists at Standard Test Condition (STC). According to STC during the
working of solar panels temperature cell should be 25oC in another statement it
also states that efficiency is decreased by 0.5% for an increase in each 1oC
from the nominal temperature of 25oC. A high class thermal management leads to
increase the efficiency of solar panels through significant amount. PCM can use
for the thermal management in solar panels. Some other use of PCM like
application in ceiling fan for cooling of room, cooling of motorcycle helmet,
applications in textiles for providing high class human comfort, combat
vehicles for controlling the high internal temperature, Cold Storage plant etc.
34-37&43.

 

VI.           
Phase Change Material
Applications

 

ü  Building and
construction

ü  Energy storage

ü  Shipping and
transportation

ü  Others
(Textiles, Protective clothing)

 

VII.           
Selection of PCM

 

Solid liquid PCMs are useful because
they store a relatively large quantity of energy over a narrow temperature
range, without a corresponding large volume change and currently appear to be
of greatest practical value. A good design of latent thermal energy storage
requires the knowledge of PCM and the latent exchange process especially the
melting and solidification process.

 

VIII.           
Properties
of Selected PCM

 

 
Selected PCM

Calcium chloride
 Hexahydrate
(CaCl2.6H2O)

    
Paraffin wax

Melting
temperature

27 o C

36 o C

Heat
of fusion

190.8
KJ/Kg

146.9
KJ/Kg

Thermal
conductivity

0.540
W/m K

0.464W/m K

Density

1562
kg/

1828
kg/

 

 

 

IX.           

Hot
Air

 

OVER VIEW

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

X.           
Experiment
Description

At the beginning, phase change materials
are in idle mode when they are purchased from the chemical industry. Soon after
it was incinerated to the temperature of 50 degree Celsius as the passive
crystals of PCM melts. At this moment, the PCM is made active. Then the aluminum
packets are used to seal the PCM and its better conductivity is the ultimate
reason for its preference. The control volume of air is affected by very small
extent and it is equalized by increasing the fans speed. On comparing the
entire control volume, the reduction in control volume is insignificant.

The
speed of the fan and heat absorbed by the PCM are the two governing factors
based on which the adjustment of mass flow rate is done. According to the
prevalence of temperature in the PCM, the heat is efficaciously transferred by
the water within certain time. The PCM material used is PARAFFIN WAX whose latent
heat is 180 KJ/Kg K and the melting point is 29 Degree Celsius.

When the fan is
set in motion, the discharge of air takes place from top of the housing to the
person remaining at rest beneath the fan. The air flow is enhanced and the air
is squeezed downwards due to the arrangement of blades in angles. The postulate
of ceiling fan is that the hot air flows upward and air at ambient temperature
is squeezed downwards. Because of the installation of PCM a lot of the fans
housing, the hot air which is directed up passes through the perforated holes
in the circular disc of the PCM. Owing to the contact of PCM with hot air, the
forced convection process takes place. The PCM which is placed a lot of fans
housing absorbs the heat of air because the melting point of PCM is lesser than
ambient temperature. The high latent heat of fusion of PCM per unit mass
results in small amount absorbing huge amount of heat energy. Due to the high
specific heat, it provides additional sensible heat storage and also avoid sub cooling.
Water flows through the aluminum piping which absorbs the latent heat of
melting of PCM, thereby carries away the heat to outside of the home. The
discharge of water to the environment is comparatively low which flows like a
pattern of droplets of water and hence there is no difficulty in letting and
discharging of water. PCM which is at low temperature absorbs the heat
continuously from the hot air and the cooled air is squeezed downwards by the
fan blades. The cooling effect is similar to AC whereas it eradicates
environmental hazards like ozone depletion and global warming. The
self-regulating valve present in the inlet of the insulated piping is kept
slightly open so that the flow will be laminar and it is automatically adjusted
by sensing temperature of PCM and the fan’s speed. When the fan’s speed and
temperature is high then Due to the high conductivity of aluminum, heat
transfer is effective and room temperature keep on decreasing.           

Figure-2- Experimental Setup

 

    Duct with CaCl2        Duct with paraffin wax

XI.           
Result
and Discussion

 

 The temperature distribution of PCMs and
recording during discharging process. Performance
charts are shown in below. From that result we can select the PCM which gives
comfort cooling than normal condition. Also it is economically low cost.

Figure-3 Performance on Day 1

Figure-4
Performance on Day 2

 

 

          Figure-5 Performance
on Day 3

Figure-6 Performance on Day 4

 

Figure-7
Performance on Day 5

 

XII.           
Conclusion

The aim of this work was to verify PCM usage
on free air cooling testing using experimental method. The result show, that
PCM could be useful for high temperature climatic condition for passive
cooling. PCM usage significantly helps to increase thermal inertia of
buildings. During the summer days in a controlled temperature of 25 degree
Celsius condition using PCM together with night ventilation.  Different PCM with different peak temperatures
can be incorporated in a building to envelope to ensure thermal comfort for
different indoor temperature. The next step would be comparison of the results
obtained in experiments on similar duct with theoretical calculation. Such
experiments are planned to be carried out in the further test methods.