https://orcid.org/0000-0002-4059-6588
![Sample our Engineering & Technology journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5933/TOC-Subject-Sample-2021-Engineering-Tech.jpg"})
ABSTRACT
In this study, the flow and heat transfer characteristics of microencapsulated phase change material (MPCM) slurry were experimentally investigated using a newly designed helical coil heat transfer device. The conventional helical coil has been structurally modified with passive enhancement features aiming to further promote fluid mixing. Specifically, 360° plastic tubing with or without wire coil inserts was added after each 180° of the main helical loop to enhance fluid mixing and improve the overall thermal performance of the device. Pressure drop and heat transfer experiments with MPCM slurry were conducted under turbulent flow and constant heat flux conditions. A new friction factor and Nusselt number correlations for MPCM slurry in helical coils with reversed loops and wire coil inserts are proposed. Experimental results show that the structural modifications did enhance the heat transfer performance of MPCM slurry. The experimental results revealed that the phase change process of MPCM considerably enhanced the heat transfer rate of MPCM slurry. Furthermore, the use of reversed loops and wire coil inserts led to better fluid mixing within the coil, resulting in improved convective heat transfer of the MPCM slurry.
Nomenclature
| A | = | helical coil surface area |
| cp | = | specific heat |
| CHX | = | coil heat exchanger |
| CH | = | chiller |
| d | = | inner tube diameter, m |
| D | = | coil curvature diameter, m |
| DAQ | = | data acquisition system |
| De | = | Dean number |
| DPT | = | differential pressure transducer |
| f | = | friction factor |
| FM | = | flow meter |
| FOM | = | figure of metric |
| h | = | heat transfer coefficient, kW/m2-°C |
| HCE | = | heat capacity efficiency index |
| HTE | = | heat transfer efficiency index |
| HX | = | heat exchanger |
| k | = | thermal conductivity of the fluid, W/m-°C |
| kw | = | thermal conductivity of water, W/m-°C |
| L | = | tube length, m |
| Lactual | = | actual melting length, m |
| Lideal | = | ideal melting length, m |
| = | mass flow rate, kg/s | |
| MF | = | mass fraction of microencapsulated phase change material |
| MPCM | = | microencapsulated phase change material |
| Nu | = | Nusselt number |
| P | = | wire coil inserts pitch, m |
| P1 | = | pump |
| PH | = | preheater |
| PCM | = | phase change material |
| PEC | = | performance enhancement index |
| Pr | = | Prandtl number |
| ΔP | = | pressure difference between inlet and outlet of the tube, kPa |
| q” | = | heat flux, kW/m2 |
| = | Heating rate, kW | |
| r | = | tube inner radius, m |
| R | = | coil curvature radius, m |
| RPM | = | revolution per minute |
| Re | = | Reynolds number |
| R2 | = | coefficient of determination |
| T | = | temperature, °C |
| ΔT | = | fluid temperature change during phase change process, °C |
| u | = | fluid velocity, m/s |
| wt. | = | weight percentage |
| x | = | position along the tube, m |
Greek Symbols
| ρ | = | fluid density, kg/m3 |
| μ | = | dynamic viscosity, Pa-s |
| η | = | performance enhancement index |
| = | percentage of MPCM particles undertaken phase change | |
| λ | = | latent heat of fusion |
Subscripts
| b | = | bulk |
| c | = | coil |
| eff | = | effective |
| HC | = | heat capacity |
| w | = | tube wall/surface |
Acknowledgments
The authors would like to acknowledge the contributions of Dr. Curt Thies of Thies Technology Inc. for his support and expertise during the execution of the project.
Disclosure statement
No potential conflict of interest was reported by the author(s).