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Heat storage technology has a critical role for a number of applications involving renewable thermal energy (such as solar water heater). The application of wax (n-octacosane/ OCT) as a medium for storing heat brings many positive influences for the system. However, the operational curve is undesirable for the OCT-based energy storage, which makes it necessary to use a binding material. The present work employed LD-class polymer (LDPE) and linear-LDPE as binding materials for OCT. The mixture is prepared through mechanical hot stirring, which comes into two categories: SOCT1 (OCT/LD) and SOCT2 (OCT/LLD). The assessment through the calorimetry method shows an increment in transition temperature for SOCT with a value of 2.1 °C and 5.5 °C. This contributes to the variation of fusion energy for solid-liquid change for both materials, which amounted to 132.05 J/g (SOCT1) and 113.4 J/g (SOCT2). Another assessment related to its chemical and structural phase demonstrates that SOCT has an identical structure to OCT, indicating that SOCT is mixed physically. At the operational level, SOCT is more optimal than OCT according to the indicator related to charge and discharge duration for energy exchange. SOCT1 demonstrates a short plateau line as the indication of a steady transition between 65.4–67.9 °C, while SOCT2 indicates the average heating rate, which is higher than for single OCT. The heat releasing curve for SOCT1 varies at a lower value between 1.92 °C/min and 0.77 °C/min, while SOCT2 has the lowest variation, which is only 0.17 °C/min. Moreover, the self-insulation for SOCT2 has the lowest rate, which is only 0.3 °C/min. The evaluation and analysis from this work show that SOCT is reliable to increase the operational curve of OCT and can be implemented for thermal systems [ABSTRACT FROM AUTHOR]

In this study, an indirect burner system for solid biomass fuel is designed. The design is motivated by the need to solve the problem related to a direct burner system, such as slagging and high pollutant emissions due to the high-temperature burning process. Therefore, the utilization of an indirect burner is expected to improve the reliability of the solid biomass combustion process. It also can be used to reduce coal consumption by using an indirect burner where the working fluid reaches a relatively higher temperature before entering the boiler. The design used the first principle method for creating the regenerator heat exchanger. The regenerator consists of a mantle and coil heat exchanger. The test used solid biomass fuel for the combustion process where the working fluid first enters the mantle heat exchanger and then the coil heat exchanger. As a result, the mantle absorbs sufficient heat losses from the combustion chamber with the highest temperature increment of 19 °C. The warm water from the mantle then flows to the coil arrangement within the combustion chamber. As a result, the highest temperature of the coil is 84.5 °C. The heat transfer rate for the coil and mantle is 57.2–85.6 and 124.9–141.5 W. The key finding is that the combined regenerative heat exchanger can deliver a higher transfer rate. This can be achieved since the heat exchanger utilizes the same flow distribution, increasing the mean temperature differences at the inlet. Thus, it can produce an average heat transfer rate of 210.5 W. Therefore, energy consumption for coal or other fossil fuels can be reduced significantly. The data can be used for further improvement of the existing boiler system and help to increase the thermal efficiency of the system. [ABSTRACT FROM AUTHOR]