Experimental Analysis and Numerical Modeling of a Shell and Tube Heat Storage Unit with Phase Change Materials

Abstract

Thermal storages are part of highly integrated energy systems. The development of accurate and reduced models is critical for efficient simulations on a system-level and the analysis of the storage design, control, and integration. We present the experimental analysis and numerical modeling of a lab-scale shell and tube latent heat thermal energy storage (LHTES) unit with a (latent) storage capacity of about 10–15 kWh. The phase change material (PCM) is a high density polyethylene (HD-PE) with phase change temperatures between 120 and 135 °C. An efficient 2D numeric storage model is derived which accounts for design and material parameters of PCM, storage, and heat transfer fluid (HTF). Different probability distribution functions are used to model the PCM apparent specific heat capacity. From these functions the state of charge (SOC) can be predicted, which indicates the extent to which a LHTES is charged relative to storeable latent heat. Model predictions are fitted to experimental data from thermophysical measurements and from LHTES operation with partial and full charging/discharging. The storage model agrees well with experimental results. However, thermosphysical material analysis and storage operation indicated that the temperature range of phase transition is noticeable affected by storage loading operating condition, i.e., heating and cooling rates, which is not considered in the model. With this simplification it turns out that the model is limited by the quality of prediction of internal storage PCM temperatures.

Dynamic modelling of ice‐based thermal energy storage for cooling applications

“…In this case, an energy balance for the HTF describes how the mean temperature T f [°C] of the fluid varies with respect to the x direction along the tube only and how the convection heat transferred is affected by this change. To further reduce model complexity, viscous dissipation, radial fluid flow, axial heat conduction, external forces, and compressibility are ignored [30,36,37]. The heat transferred to a specific volume of HTF is described by the variation of its internal energy [37], which is defined by…”

“…where β is a correction factor. In this paper, β = 1.5, and this value was obtained through a heuristic process as in [30] to fit simulation with experimental results.…”

“…With regards to 2-D models, a comparison between simulation results with experimental data is included in [29,30]. An active air-PCM heat exchanger unit is presented in [29].…”

“…Although there is a good agreement between simulation and experimental results, the enthalpy curve of the PCM is not shown. Conversely, a 2-D model of a PCM-based TES unit is presented in [30], where detailed calculation of the heat transfer coefficient and a well-defined specific heat-enthalpy curve of the PCM are considered. This work is relevant as the analysis allows to compute temperature variations using energy balance through the x and y directions.…”

An experimental facility for latent heat thermal energy storage units

“…To assess the enhancements brought by the previous options, mathematical models are employed [16]. However, the accuracy of simplified models or the large computing time required to simulate very detailed models are limitations when analyzing the performance of LH-TES units.…”