Air Conditioning with PCM

Description

This project simulates an air conditioning system that uses phase change material (PCM) as its thermal storage medium, modeled in ANSYS Fluent. PCMs are organic compounds that absorb and store large amounts of latent heat as they melt, drawing heat from the surrounding air and cooling the room during hot periods, then release that stored heat back as they re-solidify, providing warmth during cooler periods. The specific PCM used here is rubidium-rt20, with a density of 1480 kg/m³, specific heat of 2500 J/kg·K, thermal conductivity of 0.6 W/m·K, and viscosity of 0.164428 kg/m·s. The model is a 2D rectangular domain of 0.09 m × 0.5 m containing four distinct PCM zones, built in Design Modeler and meshed in ANSYS Meshing with a structured grid of 45,000 elements. Given the time-dependent nature of the phase change process, a transient solver is used throughout.

Methodology

The PCM behavior is captured through Fluent's Solidification and Melting model, with the phase transition defined by a solidus temperature of 295.15 K, a liquidus temperature of 297.15 K, and a latent heat of melting of 150,000 J/kg, giving the material a very narrow 2 K melting range characteristic of organic PCMs. Warm air enters the domain horizontally from the upper inlet at 0.018 kg/s and 302.15 K, exits at atmospheric pressure through the lower outlet, and as it passes the PCM zones, the temperature difference drives heat transfer into the material and triggers melting. Turbulence and temperature distribution are resolved with the RNG k-epsilon model and energy equation, and the simulation runs with a time step of 0.5 s.

Analysis

The results include 2D contours of pressure, velocity, temperature, and liquid mass fraction extracted at multiple time steps throughout the simulation. The temperature and liquid mass fraction contours together show the PCM progressively melting over time as it absorbs heat from the warm airflow, with the liquid fraction increasing steadily as the simulation advances. Pressure and velocity fields, by contrast, stabilize relatively quickly and remain approximately constant thereafter, indicating that the flow field reaches a quasi-steady condition while the slower phase change process continues to evolve in the PCM zones.