# The Heat Transfer of Microencapsulated Phase Change Material Slurry and Its Thermal Energy Storage Performance of Combined Heat and Power Generating Units

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## Abstract

**:**

## 1. Introduction

_{16}H

_{34}) capsules as the PCM chemical. Huang et al. [18] developed a test system that was configured as a traditional hot water storage cylinder and used to examine the performance of MPCMS in residential thermal energy storage applications.

## 2. Thermal Physical Characteristics of the Selected MPCMS

^{3}is the density of a single MPCM particle, ${\rho}_{p,c}$ in kg/m

^{3}is the density of the MPCM particle core material, ${\rho}_{p,w}$ is the density of the MPCM shell material, ${\rho}_{b}$ is the density of the MPCMS, ${\rho}_{f}$ is the density of the carrier fluid, c

_{m}in % is the core material concentration, and c in % is the MPCM particle concentration.

## 3. Flow and Heat Transfer for MPCMS

#### 3.1. Simulation for Single MPCM Particle

#### 3.2. Simulation for MPCMS

- (1)
- The fluid can be considered as a Newtonian fluid.
- (2)
- The MPCM particles are uniformly distributed in the slurry.
- (3)
- The viscous dissipation and axial heat conduction can be ignored.
- (4)
- The no-slip condition is considered.
- (5)
- The interfacial thermal resistance for MPCM particles is too small to be neglected.

## 4. Results with Discussions

#### 4.1. The Melting Process of a Single MPCM Particle

#### 4.2. MPCMS Heat Transfer in Circular Tube

#### 4.3. A 300 MW CHP Unit Case Study

## 5. Conclusions

- (1)
- The MPCM particle’s total melting time is very short, which indicates that the thermal resistance between the carrier fluid and the MPCM particle is very small. This proves that the equivalent specific heat model used in heat transfer simulations is effective.
- (2)
- Both the wall temperature and the ball diameter are important factors for the MPCM particle melting process. A ball with a small diameter is ideal in MPCMS. Raising ∆T cannot always achieve obvious improvement when ∆T is high enough. So the wall temperature is recommended to choose in a small range higher than the melting point.
- (3)
- It was found that the heat transfer characteristics of MPCMS are different depending on whether the heat transfer is in a laminar and a turbulent flow. Only in a turbulent flow condition will there be an isothermal process along the tube. The heat transfer characteristics in a turbulent flow are much greater than those in a laminar flow.
- (4)
- The research also indicates that thermal storage system increases the peak shaving capacity of cogeneration units. For a 300 MW CHP unit, the peak shaving capacity increases from 52.2 to 92.19 MW, which is an improvement of 81.4%.

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## References

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**Figure 1.**Schematic of a single microencapsulated phase change material (MPCM) particle melting process. (

**a**) An MPCM particle structure. (

**b**) The phase change inside an MPCM particle.

**Figure 4.**Melting process at different wall temperatures. (

**a**) Melting process; (

**b**) Total melting time.

**Table 1.**Thermal and physical properties of the microencapsulated phase change material slurry (MPCMS).

Parameters | Carrier Fluid | Core Material | Wall Material |
---|---|---|---|

Material | Water | Hentetracontane | Urea resin |

Density/(kg/m^{3}) | 998 | 870 | 1420 |

Specific heat/(J/kg·K) | 4180 | 2200 | 1672 |

Melting point/(°C) | - | 84.1 | - |

Latent heat/(J/g) | - | 262.1 | - |

conductivity/(W/m·K) | 0.67 | 0.21 | 0.56 |

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**MDPI and ACS Style**

Guo, Y.; Zhang, X.; Yang, L.; Xu, C.; Du, X.
The Heat Transfer of Microencapsulated Phase Change Material Slurry and Its Thermal Energy Storage Performance of Combined Heat and Power Generating Units. *Energies* **2017**, *10*, 1662.
https://doi.org/10.3390/en10101662

**AMA Style**

Guo Y, Zhang X, Yang L, Xu C, Du X.
The Heat Transfer of Microencapsulated Phase Change Material Slurry and Its Thermal Energy Storage Performance of Combined Heat and Power Generating Units. *Energies*. 2017; 10(10):1662.
https://doi.org/10.3390/en10101662

**Chicago/Turabian Style**

Guo, Yonghong, Xinglong Zhang, Lijun Yang, Chao Xu, and Xiaoze Du.
2017. "The Heat Transfer of Microencapsulated Phase Change Material Slurry and Its Thermal Energy Storage Performance of Combined Heat and Power Generating Units" *Energies* 10, no. 10: 1662.
https://doi.org/10.3390/en10101662