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.