Abstract
Wood stoves have a long history of providing thermal comfort in the Nordic climate. Households are steadily becoming more insulated to reduce their heating demand, while wood stoves typically have a high heat release. The results is that utilizing wood stoves for heating in modern homes gives a mismatch in the heat required and delivered. Therefore new solutions are required to reduce potential overheating. Latent heat thermal energy storage (LHTES) is an exciting concept for intermediate thermal energy storage. Traditionally, energy from wood-firing has been stored in soapstone or other types of rock. An LHTES can hold 5-14 times the energy per volume compared to a sensible storage. The cornerstone in an LHTES is the Phase Change Material (PCM). Several important considerations are needed regarding the choice of PCM, like the ability to store as much energy as possible. Furthermore, a phase change temperature in connection with the thermal process is essential to utilize the latent part of the energy storage. For an application placed in a household, potential health hazards also need to be considered. The purpose of this thesis was thus to investigate a novel concept of LHTES in wood stoves. The main focus was directed at the heat release period post-combustion. First, a search for a suitable PCM was conducted. Important considerations were melting temperature, latent heat of fusion, and health hazards. High-density polyethylene(HDPE) was the PCM of choice. Attempts at characterizing thermo-physical properties of HDPE were carried out through a Differential Scanning Calorimetry (DSC) analysis and Hot Disk Transient Plane Source (TPS) analysis. These properties were latent heat of fusion, phase change temperature, specific heat capacity, and thermal conductivity. A Computational Fluid Dynamics (CFD) model of the LHTES concept with vertical plate fins as heat transfer enhancement was developed and tested for charging and discharging, with realistic initial and boundary conditions. Based on the numerical model, an experimental test container was designed, and tests were conducted with different degrees of insulation. Conclusions from this thesis indicate that HDPE appears to be a viable choice as PCM for the LHTES concept on top of a wood stove. Numerical investigations revealed that a vertical arrangement of 3 mm thick steel plates as heat transfer enhancement could ensure satisfactory discharging. From experimental testing, it was observed that local expansion of HDPE could cause issues with overflow, and it is suggested that with a vertical plate fin arrangement, they should extend through the entire volume and thereby separate the volume into smaller parts. It is also recommended to explore other solutions to the issue of local expansion.