Thermal storage system with phase change material

Transcription

1 Thermal storage system with change material Priyanka Borkar, Pramod Walke Department of Mechanical Engineering, G.H.Raisoni College of Engineering, Nagpur, India Abstract: India is lagging with the fossil, so the energy need to be converted and should be stored. This paper revels the secret of change material of storing the energy. The PCM helps to store the latent heat with thermal energy storage. Keywords: free cooling, PCM, thermal storage. I. INTRODUCTION A PC material is a substance with a high temperature of combination. It is capable of storing the heat while melting and releasing it during solidification. Latent heat can be stored by using PC material. They are chemical tied together to store and release heat. The heat transfer occurs when a material change from a solid to liquid or from liquid to solid form. This is called a change in state. Phase change system are normally limited to solid- solid and solidliquid changes. Since changes involving gaseous s are complicated due to the expenses linked into containing a pressurized gas. Classification of change material Phase change material are classified are as follows i) Organic ii) Inorganic iii) Eutectic i) Organic PCM is classified into two types a) Paraffin compound b) Non- Paraffin compound ii) Inorganic PCM is classified into two types a) Salt Hydrate b) Metallic iii) Eutectic PCM is classified into three types a) Organic- Organic b) Inorganic- Inorganic c) Inorganic- Organic Table: 1. Comparision between organic and inorganic PCM [4] Organic Inorganic Advantage No corrosion Have greater No subcooling Chemically and thermally stable Disadvantage Low enthalpy of change enthalpy of change Sub-cooling takes place 685

2 Low thermal conductivity Flammability Not thermally stable Corrosion takes place, separation also place. takes PC material has the property of storing or releasing latent heat from a material over a small temperature range. Also it has the ability to change their state with certain temperature range. Thus it can be used for absorbing energy during the heating process and releasing energy to the environment during cooling process. [5] There are basically three methods of storing thermal energy. Latent, sensible and thermo-chemical heat or cold storage. But the thermal energy in solid to liquid change using PCM material is being used widely due to its following advantages: (i) (ii) It has PC material that have high capacity of latent heat storage PC material changes its from solid to liquid and liquid to solid at nearly same temperature. Lot types and lot number of solid to liquid PC materials have been experimentally tested for heating and cooling applications. PC materials that is to be used in thermal storage systems must have thermo physical, chemical and kinetics properties that are mentioned in the Table 1. An ideal Phase change material for heat storage system must have the following requirements. (i) High sensible heat capacity& heat of fusion. (ii) Stable composition (iii) High Density & Heat Conductivity (iv) Chemically Inert (v) Non-toxic & Non-Inflammable (vi) Reasonable & Inexpensive. Salt hydrates, paraffin & paraffin waxes, fatty acids and some other coumpounds are naturally occurring materials that has high latent heat of fusion with the temperature range of 0 to 150 O C. Important Properties of change materials [5] Thermal Properties: Suitable transition temperature high latent of transition food heaet transfer Physical Properties: Favorable equilibrium high density, small volume change, low vapor pressure. Kitentic Properties: Long term chemical stability compatibility with material of construction, non-toxic & non-inflamable. (iii) The volume required for latent heat storage system is small, therefore heat losses during the operation is minimized. Economics: Readily and easily available & affordable 686

3 2. TYPES OF PHASE CHANGE MATERIAL The stage change temperature ought to compare with the vanishing temperature of the aerating and cooling framework so that the working state of the refrigeration unit and the icy stockpiling unit can be concordant. A few classes of PC materials are picked and composited into paired or numerous mixtures with the end goal of getting an outlined stage change temperature. As indicated by the stage change temperature working together with a certain useful aerating and cooling framework, the composite PCMs can be sorted as takes after. [3] 2.1. LOW TEMPERATURE COOLING SYSTEM WITH PCM Icy air dissemination is a commonplace cooling supply application in which the supply air has a much lower temperature and littler volume. Accordingly, its chilled water temperature is for the most part lower than that of a customary aerating and cooling framework. Plus, the chilled water in numerous mechanical ventilating frameworks has an even lower temperature. 2.2 CONVENTIONAL AIR CONDITIONING SYSTEM WITH PCM 7 C is the temperature of the conventional air conditioning system. Therefore the PC materials temperature should be less than that of AC system. It has been found that with the increase in the evaporating temperature the coefficient of performance of the system also increase. 3. FREE COOLING SYSTEM WITH PCM In this system when ambient temperature is lowered than the room temperature the storage is used for the cooling purpose. For cooling the system the storage medium is of the sensible and latent heat type. During the night time the air is used to cool the building walls but in the free cooling system the storage is use for cooling the building with its stored cold air, which can be extracted by using fan whenever needed. Advantage of free cooling over the night air cooling is that the collected cold can be extracted whenever it is needed by circulating ambient or room air through storage unit. [1] Free cooling based on two operation, one is the charging process and other is discharging process. Charging of PC materials: When the ambient temperature is lowered than the room temperature the charging process is done. The ambient air allows to flow through the storage unit in which PC materials is stored, the heat is extract from the liquid PC materials which then starts solidifying at certain temperature. For the removal of heat the electric fan is used. The process of charging continues until the ambient temperature is get enough lower than the melting temperature of PC materials Fig.1. charging process [1] 687

4 energy ISSN No: Discharging of PC materials: When the room temperature is above the comfort limit of the person the discharging process is start. The hot air passes through the PC materials storage unit which has to be cooled. The PC materials which in the charging state absorbs heat from the air. The which in the solid stars converting into liquid. This is known as discharging process Fig.3. graph plotted energy vs. time :30:00 12:30:002:30:004:30:006:30:00 AM PM PM PM PM time For the energy to be stored the PC material should be selected with a proper care. The material which is to be used should have large latent heat and high thermal conductivity. Fig. 2. Discharging process [1] 4. RESULT AND DISCUSSION With the use of the PC material the energy stored in the thermal storage varies with the change in the temperature. The following graph shows the variation in the useful energy with respect to time. The below graph shows that when the time changes from morning to the evening the energy which needed to heat the substance goes on decreasing. Hence the charging of the substance should be done while considering all this facts. With the discharging the energy should be constant, it should not decrease with a high frequency. The energy which stored while charging should be maintain during the discharging. 4. CONCLUSION With this literature it can be concluded that the change material can be effectively capable of improving the efficiency of the air conditioning system. For cold storage the matrials is the important aspect. PC materials with free cooling is now days been used widely for building cooling application. This system shows the effectiveness of reducing the temperature of the building during summer. PC materials is the important component for free cooling system. So care should be taken while selecting the PC material. Due to the high cost of the PC material the research and development is still under process. 4. REFERENCES [1] Adeel Waqas, ZiaUdDin, Phase change material (PCM) storage for free cooling of buildings A review, Renewable and Sustainable Energy Reviews 18 (2013)

5 [2] L.F. Cabeza Castell, C. Barreneche, A. de Gracia, A.I. Fernández, Materials used as PCM in thermal energy storage in buildings: A review, Renewable and Sustainable Energy Reviews 15 (2011) [3] X.Q. Zhai, X.L.Wang,T.Wang, R.Z.Wang K. Elissa, Title of paper if known, unpublished., A review on change cold storage in air-conditioning system: Materials and applications, Renewable and Sustainable Energy Reviews 22 (2013) [4] Abhishek Saxena, Shalini Lath, Vineet Tirth, Solar Cooking by Using PCM as a Thermal Heat Storage [5] Atul Sharma C.R. Chen, V.V.S. Murty, Anant Shukla, Solar cooker with latent heat storage systems: A review, Renewable and Sustainable Energy Reviews 13 (2009)