Experimental investigation of latent heat storage integrated on top of wood stoves

INTRODUCTION: Wood stoves depend on batch combustion processes yielding a high transient heat production, often reaching higher peak heat outputs than desired by the users. Latent heat storage (LHS), which relies on phase change materials (PCM), comes as a promising solution to this challenge. A compact integrated LHS unit can flatten the wood stoves' peak heat output and prolong it over several hours. A LHS concept has been investigated as a unit to be integrated on top of wood stoves, where a significant share of the heat output could be harvested from the top plate and the stovepipe. The stored heat would then be released to the room, mostly after the combustion ends. MATERIALS AND METHODS: The concept geometry is based on an annular container, filled with PCM. The experiments use a quarter of the annular container laying on a custom heating plate for finer control of the heat input. High-density polyethylene (HDPE) is used as PCM due to its melting temperature in the range 120-140 °C, its relatively high latent heat and its ability to stand temperatures up to 300 °C without material degradation. Two configurations are tested: (1) with only the PCM is the container and (2) using heat transfer enhancement through metallic rods screwed to the bottom plate. Temperatures are recorded at various locations in the LHS units during 3-6 h charges (melting) and up to 18 hours discharges (solidification). RESULTS: The melting time is about twice shorter using the specified heat transfer enhancement method. The viscosity of the selected HDPE is insufficiently low to allow free convection to take place and which could have further enhanced the melting process. Even though prolonged over 12-18 hours, the heat transfer to the room during discharge (solidification) is limited and would require additional enhancement features to yield a more substantial thermal output to the room. CONCLUSION: The experimental results with the LHS concept show that a significant share of the heat output of wood stoves can be harvested and released over a longer time period and yield an overall lower peak heat output to the room. The test results enabled to draw conclusions regarding the design of the next test setup. Additional features will be tested to enhance the heat output to the room during discharge. Alternative HDPE with lower viscosity and eventually higher latent heat will also be investigated.