Paraffins as phase change material in a compact plate-fin heat exchanger

Two journal scientific publications from our partner AIT – Autrian Institute of Technology – highlighting HYBUILD results have been published in the Journal of Energy Storage. Abstracts and links to the full publications are provided below.

Paraffins as phase change material in a compact plate-fin heat exchanger – Part I: Experimental analysis and modeling of complete phase transitions

Abstract: Thermal energy storages with phase change materials (PCM’s) based on plate-fin and tube-fin (gas-to-liquid) heat exchanger (HEX) designs show a comparatively high heat transfer performance and compactness. High heat transfer rates allow for optimal storage designs and operation close to the PCM’s phase change temperature. However, industrial-grade solid–liquid PCM’s and mixtures usually show a non-isothermal phase change behavior over an extended temperature range, sometimes with multi-step transitions, hysteresis and supercooling. These complex phenomena depend on the physical dimensions of the PCM in the HEX and the operating conditions. They need to be verified for each particular application and cannot be neglected. This contribution presents an experimental and model-based analysis of the phase transition behavior of three commercial paraffins filled in compact plate-fin HEX’s. The results indicate that non-isothermal phenomena critically affect the storage temperatures. Their impact on the thermal performance can be studied using relatively simple numerical models.

Read the full article here.

Paraffins as phase change material in a compact plate-fin heat exchanger – Part II: Validation of the “curve scale” hysteresis model for incomplete phase transitions

Abstract: Technical-grade and mixed solid–liquid phase change materials (PCM’s), such as commercial paraffins, can show a complex non-isothermal phase transition behavior, possibly with hysteresis and supercooling, two-step transitions and asymmetric phase transition peaks. Phenomenological modeling approaches can use data-driven methods to derive phase transition models represented by enthalpy–temperature or apparent heat capacity–temperature curves. These curves are then linked with simulation models for heat transfer in thermal storages with PCM’s. If the phase change is significantly affected by hysteresis, different curves might be tracked either for heating or for cooling. This “curve track” modeling approach is straightforward and easy to implement. However, it shows a poor performance considering conditions with interrupted phase change, which are relevant for the partial charging and discharging operation of thermal storages. This contribution presents a novel so-called “curve scale” model. Its superior performance is proved for three commercial paraffins and experiments with 31 interrupted phase change scenarios.

Read the full article here.