Performance investigation of shell and helical tube heat exchanger with graphene dispersed erythritol as thermal energy storage medium

Abstract

Latent Heat Storage is one of the most efficient thermal energy storage systems because of its compactness as well as the operational advantage of a nearly constant storage-cycle temperature. Phase Change Material (PCM) is used as storage medium in Latent Heat Thermal Energy Storage (LHTES) system. The performance of the LHTES system depends on the thermal conductivity of phase change material used. The thermal conductivity of the PCMs is usually very low and it results in low heat transfer rates during both charging and discharging processes. In order to enhance thermal conductivity and hence the heat transfer rate, ultrafine solid particles (nanoparticle) are added to the PCM. Nanoparticles Dispersed Phase Change Material (NDPCM) is a new kind of PCM developed by suspending nano-size particles in base PCM for the main purpose of enhancing the thermo-physical properties of the base PCM. In the present research work, the feasibility and thermal conductivity enhancement of dispersing graphene particles in three different mass fractions (0.1%, 0.5% and 1%) into the erythritol base PCM were examined. The FTIR spectrum showed that the graphene nanoparticles integrated well into erythritol PCM without affecting its chemical properties. The DSC results revealed that the change in latent heat and phase change temperature of NDPCM is less before and after 100 melting and solidification cycles. Addition of 1wt. % graphene led to 53.1% increase in thermal conductivity with only 6.1 % decrease in latent heat enthalpy. Also, there was a 5.8 % decrease in melting temperature and 18.76 % increase in solidification temperature relative to pure erythritol resulting in 30.66% reduction in degree of super cooling. Experiments were conducted by changing the mass flow rate of Therminol 55, Heat Transfer Oil (HTO) from 0.5 to 2 kg/min, inlet temperature of hot HTO from 160 to 180 oC during charging process and inlet temperature of cold HTO from 30 to 45 oC during discharging to investigate the melting and solidification behaviour of the newly developed erythritol PCM with graphene nanoparticles (NDPCM) in a shell and helical tube heat exchanger newline