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Novel scheme for a PCM-based cold energy storage system. Design, modelling, and simulation

G. Bejarano, J. J. Suffo, M. Vargas, M. G Ortega

TL;DR

This work addresses designing and dynamically modelling a PCM-based cold-energy TES integrated with a laboratory refrigeration plant. It develops two modelling approaches: a continuous model suitable for decoupled full-charge or full-discharge cycles, and a discrete spatial model that can represent partial charging/discharging operations and multiple moving latent fronts. The study introduces a novel TES layout comprising macro-encapsulated PCM spheres in a high-conductivity intermediate fluid, interfaced with a refrigerant and a secondary fluid through dual pipe bundles, and uses NTU-based heat transfer descriptions to capture exchanger dynamics. The findings show that a 10-layer discrete model closely approximates the continuous model (relative energy error under 7%), while enabling analysis of complex charging schedules and stand-by periods, thereby informing design choices and control strategies; future work will explore alternative coolants and optimization of operation policies.

Abstract

This paper studies the design and dynamic modelling of a novel thermal energy storage (TES) system combined with a refrigeration system based on phase change materials (PCM). Cold-energy production supported by TES systems is a very appealing field of research, since it allows flexible cold-energy management, combining demand fulfilment with cost reduction strategies. The paper proposes and compares two different simulation models for a cold-energy storage system based on PCM. First, a continuous model is developed, the application of which is limited to decoupled charging/discharging operations. Given such conditions, it is a relatively precise model, useful for the tuning of the TES parameters. The second proposed model is a discrete one, which, despite implementing a discrete approximation of the system behaviour, allows to study more general conditions, such as series of partial charging/discharging operations. Simulation results of both models are compared regarding decoupled charging/discharging operations, and the ability of the discrete model to represent more realistic partial operations is analysed.

Novel scheme for a PCM-based cold energy storage system. Design, modelling, and simulation

TL;DR

This work addresses designing and dynamically modelling a PCM-based cold-energy TES integrated with a laboratory refrigeration plant. It develops two modelling approaches: a continuous model suitable for decoupled full-charge or full-discharge cycles, and a discrete spatial model that can represent partial charging/discharging operations and multiple moving latent fronts. The study introduces a novel TES layout comprising macro-encapsulated PCM spheres in a high-conductivity intermediate fluid, interfaced with a refrigerant and a secondary fluid through dual pipe bundles, and uses NTU-based heat transfer descriptions to capture exchanger dynamics. The findings show that a 10-layer discrete model closely approximates the continuous model (relative energy error under 7%), while enabling analysis of complex charging schedules and stand-by periods, thereby informing design choices and control strategies; future work will explore alternative coolants and optimization of operation policies.

Abstract

This paper studies the design and dynamic modelling of a novel thermal energy storage (TES) system combined with a refrigeration system based on phase change materials (PCM). Cold-energy production supported by TES systems is a very appealing field of research, since it allows flexible cold-energy management, combining demand fulfilment with cost reduction strategies. The paper proposes and compares two different simulation models for a cold-energy storage system based on PCM. First, a continuous model is developed, the application of which is limited to decoupled charging/discharging operations. Given such conditions, it is a relatively precise model, useful for the tuning of the TES parameters. The second proposed model is a discrete one, which, despite implementing a discrete approximation of the system behaviour, allows to study more general conditions, such as series of partial charging/discharging operations. Simulation results of both models are compared regarding decoupled charging/discharging operations, and the ability of the discrete model to represent more realistic partial operations is analysed.
Paper Structure (27 sections, 92 equations, 12 figures, 6 tables)

This paper contains 27 sections, 92 equations, 12 figures, 6 tables.

Table of Contents

  1. Introduction
  2. System description
  3. TES on the actual mother refrigeration plant
  4. A novel layout proposal of the TES system
  5. Design specifications
  6. Continuous modelling of the cold-thermal energy charge/discharge cycles
  7. General description of the charging state
  8. General description of the discharging state
  9. Charge ratio estimation in the continuous model
  10. Intermediate fluid dynamics
  11. PCM-intermediate fluid dynamics
  12. Refrigerant - intermediate fluid dynamics
  13. Notation for the effectiveness-NTU method
  14. Heat transfer between the refrigerant and the intermediate fluid
  15. Secondary fluid - intermediate fluid dynamics
  16. ...and 12 more sections

Figures (12)

  • Figure 1: Schematic diagram of the experimental refrigeration plant.
  • Figure 2: Schematic picture of the proposed configuration of the TES tank and input-output conceptualisation of the TES system.
  • Figure 3: Temperature-enthalpy diagrams of PCM and refrigerant.
  • Figure 4: Schematic picture of the PCM capsule during charging/discharging cycle (left/right, respectively). Electric analogy of the thermal resistances is shown.
  • Figure 5: Schematic picture of the thermal exchange along refrigerant and secondary fluid single pipes.
  • ...and 7 more figures