It is widely recognized among specialists that PCMs (Phase Change Materials) typically have low thermal conductivity, which significantly restricts their commercial use. This study presents alternative, low-cost, yet effective approaches to enhance the average thermal conductivity of a PCM system (a commercially available paraffin wax with a phase change temperature around 40 °C) intended for thermal energy storage. The system contains 600 g of PCM within an annular space around an inner tube, through which heat is either added to or removed from the PCM. Experiments were conducted to assess the effects of water flow rate and temperature, used as the heat transfer fluid, on the system's performance. The flow rate was varied from 2 to 8 L/min, and the temperature was set between 45 and 55 °C. We tested three types of aluminum-based thermal enhancers: a commercial metal foam, a wire mesh, and irregular aluminum flakes (chips) produced as waste from machining processes. The PCM-only sample required the longest time for both charging and discharging, while the PCM with metal foam had the shortest times. The intermediate solutions, using chips and wire mesh, showed moderate phase change times. To evaluate the economic feasibility, we introduced a performance metric based on cost per phase change rate, showing that these two affordable thermal conductivity enhancers could play a vital role in promoting the broader application of latent thermal energy storage technology across various fields.

Among experts, it is well-known that the thermal conductivity of PCMs (phase change materials) is low hence a major limitation for their commercial application. This work proposes alternative, inexpensive, but nevertheless effective solutions to increase the average thermal conductivity of a PCM system (a commercial paraffin wax, having a phase change temperature of about 40 °C) used for thermal energy storage. 600 g of PCM fills an annulus wrapping an inner tube used to either charge or discharge heat to the PCM. The effect of the flow rate and temperature of the water used as heat transfer fluid was experimentally analysed. The flow rate was set to vary between 2 and 8 l min^-1 and the temperature between 45 and 55 °C. We tested three different aluminum-based thermal enhancers: a commercially available metal foam sample, a wire mesh, and irregular flakes (chips) obtained as waste product of machining operations. The PCM-only sample exhibited the longest charging and discharging times, while the PCM + foam sample shortened them the most. The two cost-effective solutions (chip and wire mesh) resulted in intermediate phase change times. A performance indicator, in terms of cost per phase change rate, is proposed to compare different enhancers. It demonstrated that these two cost-effective thermal conductivity enhancing solutions can become a key enabling method to widely deploy latent thermal energy technology widely in many different applications.

Thermal energy storage is increasingly needed in a sustainable world because of its potential of capturing waste heat and being incorporated in solar power plants. For power generation, in particular, as turbine technology advances, a demand for higher temperature thermal energy storage materials also grows. For this purpose, latent thermal energy storage fits in well since it uses phase change materials (PCMs) which generally have a higher energy density compared to their sensible heat counterparts. In the present study, a eutectic Na₂CO₃(41.69%)-(33.1%)KCl-(25.21%)NaCl phase change material (PCM) with a melting temperature of 569 ° C was chosen as the storage material to experimentally assess the performance benefit of using a readily available stainless steel (ss304) wire mesh (as the periodic structure) to enhance heat transfer within the domain. In addition, for discharging, a numerical model was developed and compared with the experimental results. Furthermore, for discharging, a numerical investigation of the influence of the heat transfer fluid (HTF) flow-rate to the rate of heat transfer was performed. Overall, it was experimentally observed that the charging time for the composite case was shortened by about 35%, compared to the pure PCM case. For discharging, in the axial direction, the composite solidification time when compared to the pure PCM case was on average 10% shorter. Regarding the radial discharging performance of the composite, there was only about 5% improvement compared to the pure PCM case, which was expected due to the thermal contact resistance in the radial direction. Discharging experimental results were used to validate a discharging numerical model. Discharging results from the model showed that increasing the flow rate of the heat transfer fluid (HTF) reduced the time for solidification. It was observed that for the HTF flow rate of 5 L/min, 10 L/min, 20 L/min and 30 L/min, the discharge time was shortened by 23%, 30%, 33% and 35%, respectively.

The transportation of perishable products is a crucial activity that must be carefully managed along the cold chain. The refrigerated transport aims at ensuring the suitable transportation conditions by maintaining the desired temperature level in the refrigerated compartment. Moreover, the carriage of perishable fresh foodstuffs calls for additional precautions due to the intrinsic metabolic activity of fresh foods which causes them to be highly temperature sensitive. About 30% of fresh products perishes on the route due to the loss of suitable temperature values. Recently, scientists have been focusing their efforts on the development of innovative solutions, which ensure a proper refrigerated products distribution and transportation in a more environmental-friendly and cost-effective way. Hence, in this work, a novel concept of a Latent Thermal Energy Storage (LTES) system consisting of an insulation layer of poly-urethane foam wrapping a second one of Phase Change Material (PCM) is proposed. In particular, the thermal performance is investigated by running numerical CFD analyses in Ansys Fluent. The effect of different product loads (25%-50%-75%) is studied. Besides, the contributions of the heat respiration and diverse food pre-cooling temperatures on the system performance are also analysed. For the long-distance route no door openings nor additional heat infiltrations are considered.

In this work, melting of a high-temperature inorganic phase change material (PCM) eutectic (with a melting point of 569 °C) within a vertical cylindrical tank has been experimentally investigated. To promote the heat transfer rate, a periodic structure that is constructed by a commercial SS-304 mesh screen has been considered and immersed into the PCM tank. Thermal characteristics of the PCM-periodic structure tank under different initial temperatures (450, 490 and 546 °C) and wall temperatures (620, 640, 660, 680 and 700 °C), are then investigated and reported. The presented experimental data can facilitate practical engineers to find the best operating condition of similar PCM tanks; meanwhile, it can be also employed for the investigation of thermal response of transient heat conduction before melting starts.

The use of metallic periodic structures was considered for melting rate enhancement of a phase change material (PCM) contained in a rectangular enclosure isothermally heated from the side. The critical (optimized) cell size, or pore size, of a periodic structure with fixed porosity, realising the shortest melting time by maximizing the convection and conduction heat transfer rate into the PCM, was studied. Furthermore, the effects of material properties (copper, aluminium, nickel, and stainless steel), enclosure length, wall-melting temperature difference and porosity were numerically investigated. It was observed that increasing porosity and/or reducing thermal conductivity enlarged the critical cell size (i.e. the optimal cell size that minimizes the melting time). The critical PPIs (pores per inch) of copper and aluminium periodic structures for all studied porosities were 10; for nickel, the critical values were 10 PPIs for porosity values of 0.75, 0.8 and 0.85 while it reduces to 5 PPI for the highest porosity considered here being 0.95. Interestingly, showing a different trend, the critical PPI of stainless-steel structures was 5 for the lowest porosity (0.75) and reduced to 3 for higher porosities. The results clearly demonstrated localised melting which was observed in all periodic structures except for the 10 PPI stainless-steel case. Scattered melting islands are observed as opposed to a moving interface when ϕ=(d_p/L)α_ligament/α_PCM>1. For such cases, localized melting occurs and the PCM is melted at the ligaments away from the heated wall before the melt front reaches those ligaments.

Foodstuff has to be transported from where it is produced or packaged to the market. It is important to control the temperature and humidity of the delivered food to minimize the waste and ensure customer satisfaction. At the same time, unfortunately, the transport sector is among the polluting sectors. Therefore, innovative solutions have been proposed such as the adoption of Latent Thermal Energy Storage (LTES) systems based on Phase Change Materials (PCMs) to control the food temperature. Such systems minimize the fuel consumption and thereby reduce the emission. LTES systems rely on the phase change process to absorb and store heat in a more sustainable way while ensuring a nearly constant temperature for the foodstuff while being transported. Hence, we first present a general overview of the application of PCMs at low temperatures. Then, the literature on the adoption of PCMs in the refrigerated transport sector is critically surveyed. Different proposals offered in the literature are recovered, compared, and critically assessed based on their merits. Despite the differences between the proposed technologies, significant advantages in terms of temperature uniformity in the refrigerated space, product thermal stress reduction, product quality, energy consumption, and pollutant emissions reduction are reported in the literature as surveyed in this paper.