https://www.mdu.se/

This work mainly involved the preparation and characterization of form-stable polyethylene glycol (PEG)/silicon dioxide (SiO₂) composite as a novel solid–liquid phase change material (PCM). In this study, the polyethylene glycol/silicon dioxide composites as form-stable, solid–liquid phase change material (PCM) was prepared. In this new material, the polyethylene glycol acts as the latent heat storage material and silicon dioxide serves as the supporting material, which provides structural strength and prevents the leakage of the melted polyethylene glycol. Results indicated that the composite remained solid when the weight percentage of silicon dioxide was higher than 15%. Moreover, the polyethylene glycol was observed to disperse into the network of the solid silicon dioxide by investigation of the structure of the composite PCMs using a scanning electronic microscope (SEM). The properties of the porous materials and phase change materials were characterized using Fourier transformation infrared spectroscope (FTIR). The transition process was observed using polarizing optical microscope (POM) and dynamic thermo mechanic analysis (DMA). The melting temperatures and latent heats of the form-stable PEG/SiO₂ composite PCMs were determined using differential scanning calorimeter (DSC).

Energy consumption for space heating and hot tap water in residential and service sectors accounts for one third of total energy utilization in Sweden. District heating (DH) has been used for heat supply to areas with high energy demand. However, there are still a lot of detached houses and sparse areas with no connection to a DH network where electrical heating or oil/pellet boilers are used to meet heat demand. Sometimes, extending the existing DH network to those spare areas is not economically feasible because of the small heat demands and the large investment. Mobilized thermal energy storage (M-TES) system is an alternative way to supply heat for detached buildings or sparse areas by using industrial heat. In this paper, integration of a combined heat and power (CHP) plant and an M-TES system is analyzed. The impacts of four options of the integrated system are discussed including the power and heat output in the CHP plant, as well as the performance of M-TES system.

β-Aluminum nitride powder is a promising additive due to its great conductivity value, which can enhance the thermal conductivity of organic phase change materials. In this paper, a high conductivity form-stable phase change material was prepared by blending polyethylene glycol, silica gel, and β-Aluminum nitride powder. The conductivity value of the composite PCMs was determined using the Hotdisk thermal analyzer, which is based on the transient plane source technique. Experiment of heat storage and release performance was carried out to investigate heat efficiencies of TES system. The results showed that thermal conductivity of composite PCMs increased with an increase in β-Aluminum nitride content, but the value of latent heat decreased correspondingly. There was no change on the melting temperature while different ratios of composites. The value of thermal conductivity changed from 0.3847 W m⁻¹ K⁻¹ to 0.7661 W m⁻¹ K⁻¹ with the increase of mass ratio of β-Aluminum nitride from 5% to 30%. The heat storage and release rate of the composite PCMs was higher than that of pure polyethylene glycol.

A direct-contact mobilized thermal energy storage (M-TES) system with high heat density and heat transfer rate has been exploited to transport industrial heat for distributed users. In this paper, a lab-scale experimental setup has been built consisting of a direct-contact thermal energy storage (TES) container, oil/water tank, electrical boiler, oil/water pump and plate heat exchanger. Erythritol was chosen to work as an organic phase change material (PCM) due to its large heat density, suitable melting point (118^oC) for industrial heat recovery, and non toxic and corrosive. Heat transfer oil (HTO) served as a heat transfer medium to carry and transfer heat. The theoretical heat capacity of the TES container is 13.1 kWh with 74 kg of Erythritol and 42 kg of HTO. In the charging process, electrical boiler heated HTO first, and then HTO was pumped into the bottom of the TES container to melt Erythritol directly. In the discharging process, heat was transferred to the cooling water through a plate heat exchanger. Results show that, the sub-cooling problem of Erythritol, which was found in the static experiments, was totally solved by dynamic heat exchange between Erythritol and HTO. During the whole process, the two liquid phases (oil and melted Erythritol) were separated clearly due to the big difference of their densities, and meanwhile a foam layer was also observed between the two sectors. In the charging process, the higher the flow rate of HTO, the less the charging time was needed, which resulted in the lower charging heat consumption. In the discharging process, the maximum heat of 10.6 kWh was released with the HTO flow rate of 12.5 l/min, which accounted for 80.9 % of the theoretical heat capacity of the TES container.

Expanded graphite is a promising heat transfer promoter due to its high conductivity, which improves the thermal conductivity of organic phase change materials. Moreover, it can also serve as supporting materials to keep the shape of the blends stable during the phase transition. After various investigation, the results showed that the maximum weight percentage of polyethylene glycol was as high as 90% in this paper without any leakage during the melting period, with the latent heat of 161.2 J g⁻¹ and the melting point of 61.46 °C. It was found that the value of the latent heat was related to the polyethylene glycol portion, increased with the increase in polyethylene glycol content. Moreover, the measured enthalpy of the composite phase change materials was proportional to the mass ratio of the polyethylene glycol component. The melting temperatures were almost the same with different ratios of composites. The conductivity of blends was improved significantly with the high value of 1.324 W m⁻¹ K⁻¹ compared to the pure polyethylene glycol conductivity of 0.2985 W m⁻¹ K⁻¹.

This paper introduces a new mobilized thermal energy storage (M-TES) for the recovery ofindustrial waste heat for distributed heat supply to the distributed users which have not beenconnected to the district heating network. In the M-TES system, phase-change materials (PCM)are used as the energy storage and carrier to transport the waste heat from the industrial site to theend users by a lorry. A technical feasibility and economic viability of M-TES has been conductedwith the comparison of the district heating system as a reference. Thermal performance and costimpacts by different PCM materials have been analyzed compared, aiming at determining theoptimum operation conditions. A case study is investigated by utilizing the waste heat from acombine heat and power (CHP) plant for the distributed users which are located at over 30kilometers away from the plant. The results show that the M-TES may offer a competitivesolution compared to building or extending the existing district heating network.