This systematic review presents and discusses the previous research about hybrid devices which combine latent thermal energy storage (TES) technology and heat pipes. A bibliometric analysis of this issue shows how hybrid systems have globally grown popularity during time, providing details about the main researchers and research centres on this particular field. Then, the identified papers are assessed and categorized in two main sections, the experimental research carried out, and the numerical modelling of hybrid systems. Experimental research is later classified regarding the operating temperature range, and their final application. Numerical studies are also further categorized, accordingly to how heat pipes were modelled in this case. This review points out the lack of experimental studies at high temperatures, especially when many simulations extended their models (validated at low temperatures) to higher temperature designs. The paper provides details about the research performed, so the gap for future investigations can be spotted.

Systematic review on the use of heat pipes in latent heat thermal energy storage tanks

Personal cooling devices reduce energy loads by allowing buildings to operate with elevated setpoint temperatures, without compromising on the occupant comfort. One such novel technology called the Roving Comforter (RoCo) uses a compact R134a based vapor compression system for cooling. Following its cooling operation, during which waste heat from the condensing refrigerant is stored in a phase change material (PCM), a two-phase loop thermosiphon is used to discharge (solidify) the PCM to enable its next operation. The transient operation of this thermosiphon is the focus of the present article. Use of a PCM as the storage medium provides high energy density due to the ability to store thermal energy as latent heat during the phase transition; however, the discharge rate is limited by the low thermal conductivity of the PCM. Insertion of a graphite foam within the PCM can increase the rate of discharge and decrease the downtime of the cooling device. Since graphite enhancement involves a tradeoff between improving the discharge time at the expense of PCM volumetric latent heat, the impact of graphite foam density on the PCM discharge rate is investigated by using a Modelica-based transient model of the thermosiphon. The semi-empirical model, which uses relevant heat transfer coefficient and pressure drop correlations for both refrigerant and airside heat transfer, captures the complex phenomena involving simultaneous phase change of the refrigerant and the PCM. The graphite enhanced PCM selected from this analysis results in a 51% reduction in the discharge time with addition of only 5% to the thermal storage weight, without compromising the required cooling time.

Enhancing the thermosiphon-driven discharge of a latent heat thermal storage system used in a personal cooling device

Two-stage heat transfer characteristics of constrained melting inside an isothermally heated horizontal cylinder

Applications of coupling thermosyphons with phase change materials: A review

Melting of a phase change material assisted by a thermosyphon inside a two dimensional rectangular domain is numerically investigated. The PCM used is n-eicosane and the thermosyphon is made of copper. The working fluid is water. The fill ratio of the working fluid (water) is taken to be 50%. A lumped model is used for the simulation of transient operation of the thermosyphon and enthalpy-porosity method is employed for numerical simulation of melting of PCM. The effects of inclusion of multiple heat pipes on the melting of the PCM inside the enclosure is studied. Simulation results indicate that the addition of heat pipes enhances the performance of latent heat thermal energy storage system only upto a certain extent.

https://iopscience.iop.org/article/10.1088/1742-6596/745/3/032130/pdf

Rohit S Nair

Papers

Thermosyphon assisted melting of PCM inside a rectangular enclosure:A synergistic numerical approach