Abstract
This work investigates melting and solidification processes of four different Phase Change Materials (PCM) used as latent heat thermal storage system. The experimental rig was consisted of an insulated tank, filled with the under investigation PCM, a staggered heat exchanger to supply or extract heat from the PCM cavity and a water pump to circulate Heat Transfer Fluid (HTF). Both charging (melting) and discharging (solidification) processes were conducted for two different HTF flow rates. The main scope of this work was to develop a first approach and to investigate the behaviour of PCM under various load conditions (different HTF flow rates). Results show that different HTF flow rates affect melting and solidification time periods; in both processes time was reduced while HTF flow rate was increased but in differentways due to the transition from conduction to convection heat transfer mechanisms.
Highlights
Solar energy has been extensively utilized in residential cooling/heating and DHW production systems
Melting and solidification process of a material, in both sensible or latent heat storage procedures is related to the energy provided or extracted by the Heat Transfer Fluid (HTF)
By Eq 1 it is concluded that the larger the value of HTF flow rate the larger the heat flux by the pipes to the Phase Change Materials (PCM) the shortest the period to complete the process of charging
Summary
Solar energy has been extensively utilized in residential cooling/heating and DHW production systems. LHTES can store 5–14 times more heat per unit volume than sensible storage materials, such as water [2]. These materials have low thermal conductivities requesting large power density. Paraffin waxes are promising materials because they exploit efficient energy storage in an optimal temperature range for integration into residential heating/cooling systems. Regarding the design of commercial thermal energy storage units, further investigation is required to assess the physical phenomena and successfully implement PCM. Their proper design must take into account material characteristics, desired storage rate, transient PCM heat exchange and required energy storage capacity. In order to overcome low conductivity, various methods have been proposed including the use of nano-particles or the use of fins to maximize heat transfer [3, 4]
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