2.1 storage devices using phase change materials and vapour

2.1 OVERVIEW

This chapter gives overall idea about cold storage
devices using phase change materials and vapour compression refrigeration
system. Thermal energy storage systems are known to mankind from long time ago,
but in current years more attention has been drawn by latent heat storage
system because of the idea towards making the refrigeration process effective
and cheaper. Since cold storage devices integrated with phase change materials
are in development phase in many researches so for better understanding of
comparative study, various literature available for vapour compression refrigeration
systems and cold storage device using phase change materials has been studied
and applied accordingly. Many studies have been done for phase changing
materials applications for cold storage system using latent heat and thermal
energy management are also presented hereafter.

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2.2 VAPOUR COMPRESSION
REFREIGERATION SYSTEM

Many researchers have studied analyzed the vapour
compression refrigeration system out of which some literatures have been
presented here.

Chetan Papade, Biranna Solankar (2016) have studied the performance of vapour
compression refrigeration system with and without a Matrix
Heat Exchanger. The

concept of
analytical study of vapour compression refrigeration system using matrix
heat-exchanger carried out to improve the coefficient of performance of system.
In order to improve the coefficient of performance (COP), it is necessary that
compressor work must decrease & refrigerating effect must increase. Large
number of refrigeration system uses conventional vapour compression
refrigeration (VCR) cycle which has a low coefficient of performance (COP), But
it has been observed in this paper that installing a heat exchanger to the
vapour compression refrigeration (VCR) system  makes it more efficient. Energy consumption
can be reduced by using counter flow matrix heat exchanger. As energy
consumption is reduced coefficient performance of refrigeration system may
increase.

 

 

Fig 2.1 Proposed vapour compression refrigeration system using matrix heat
          exchanger

A K Bajpai, Vivek Dwivedi (2014) have observed various modifications in their research paper
that have been seen in last two or three decades but invention of compressor
which is free from oil, that can work under the dry condition is the fabulous
discovery . It is also observed that there are so many refrigerants which are
used in VCRS, but the requirement of CFC free refrigerants is increasing day by
day, in previous decade so many researches have been done in such areas. Some other modifications and important invention
that provide simplified dynamic model of a liquid chiller and study of the
thermodynamic mechanism of
hybrid cycle, study about the concentration of Refrigerants, investigation of a
twin screw oil free compressor, dynamic neural network model so on support to
give an optimized model of VCRS in all respects.

Rahul Wandra, Taliv
Hussain, Jagannath Verma, Arjun Sharma, Gaurav Roy (2011)
have concentrated on the more accurate approach of effect of refrigerant
superheating on refrigeration effect of modified vapour compression system and further
investigate the work input in compressor and volumetric efficiency. By
undertaking different configuration and different models of compressor it is
well evaluated that compressor plays a big role in refrigerant superheat losses
where superheat is not only responsible for compression losses but also effects
positively on refrigeration effect .Experimental results show that the
coefficient of performance (COP) of simple vapour compression system with
lesser superheated refrigerant is 3.5 where as the coefficient of performance (COP)
of vapour compression system with higher superheated refrigerant is 3.17 by
varying different ambient air conditions. VCRS having more superheated
refrigerant R-134a decreases coefficient of performance (COP) by 9.4% and this
paper will give us the clear evidence that what would be the required
conditions that can fulfill our control over coefficient of performance (COP).

 

   Fig 2.2 Comparison of less superheated and
high superheated VCRS cycle

 

                  Fig 2.3 Compressor Work Vs Ambient
Temperature

 

2.3 PHASE CHANGE MATERIALS
(PCM)

Abundant
amount of research paper have been published studying about the properties of
phase changing materials out of which few literatures have been presented here.

E. Oro, A.de Gracia, A.
Castell, M.M. Farid, L.F. Cabeza (2012) have carried out  a review of thermal energy storage for cold
storage applications using solid–liquid phase change materials (PCM) in this
paper. The scope of the work was concentrated on different aspects: phase
change materials (PCMs), encapsulation techniques, heat transfer enhancement,
and the effect on food quality which are being stored for long time. Materials
used by researchers as potential phase change materials (PCM) at low temperatures
( less than 200C ) are summarized and some of their thermophysical properties
are reported. Over 80 materials that can be used as phase change materials (PCM),
and about 35 to 40 are commercially available that PCM have been listed.
Problems associated with long term stability of the materials, like corrosion,
phase segregation, stability under extended cycling or subcooling have been
discussed. Heat transfer has been considered for both theoretical and experimental
point of view and the different techniques of PCM encapsulation are reviewed. Many
applications of PCM at low temperature may be found, such as, ice storage,
conservation and transport of temperature sensitive materials and in air conditioning,
cold stores, and refrigerated vehicles.

 

Fig. 2.3 Schematic temperature change during melting and
solidification of a PCM with subcooling

 

Jianqing Chan, Donghui Yang, Jinghua Jiang, Aibin Ma,
Dan Song (2014) In
this research paper the research progress on the properties of phase change
materials (PCM) embedded with metal foam has been reviewed. The conduction,
convection and latent heat transfer process in the PCM has been intensively
investigated. Embedding metal foam into PCM is an effective method to enhance
the heat transfer in the PCM. Due to the high thermal conductivity, surface
area volume ratio, porosity and complicated three dimension network, metal foam
in the composite PCM  increase the
effective thermal conductivity of the composite PCM, and thus improve the
uniformity of the temperature distribution in the PCM. Generally the natural
convection in the PCM is suppressed by the metal foam embedded and thus
reducing the convective heat transfer performance. Metal foam structure governs
the heat transfer performance of the PCM significantly. It is advised to
consider both the effects, foam porosity and pore size on conduction and
convection heat transfer as well as engineering requirements to determine
porosity in the design of foam metal heat storage device.

 

Marta Kuta, Tadeusz M.
Wojcik (2015) In this paper, attention has been
drawn by application of PCM in energy field. PCM are interesting for the energy sector because their use enables
thermal stabilization and storage of large amount of heat. It is major issue
for safety of electronic devices, governing of temperatures of buildings and
vehicles, solar power, refrigeration, air conditioning and many others energy
domains. Research has been done on solid-solid phase change materials designed
for thermal stabilization of electronic devices. Due to required thermophysical, structural and
economical properties solid solid PCM are becomimg more and more popular. Group of novel
solid-solid phase change materials based on polyethylene glycol and cellulose
has been synthesized. Materials were examined and one of them has been chosen
for further work. Chosen material will be tested for the possibility of thermal
stabilisation of electronic devices. Preliminary results of tests on the material
confirmed possibility of its use for mentioned application.