# Review of the State of the Art for Radial Rotating Heat Pipe Technology Potentially Applicable to Gas Turbine Cooling

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## Abstract

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## 1. Introduction

## 2. Heat Pipes with Radial Fluid Recirculation

## 3. Development of the Concept of RRHP for Turbomachinery Cooling

## 4. Heat Transfer of the RRHP

#### 4.1. Factors That Influence Heat Transfer

#### 4.2. Operational Limits

#### 4.3. Summary

## 5. Secondary Flow Effects

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^{5}) to allow the thermosyphon to operate between the upper limit of the conduction regime and the lower limit of the boundary layer regime. In particular, the role of Coriolis force effects was investigated at low rotational speeds. It was found that at such speeds, the Ekman layers, located at the upper and lower surfaces of the cavity, improved the heat transfer rates in what has been called the Coriolis-enhanced regime. Compared with stationary tilted systems, the rotating system tended to flatten the velocity profiles at each cross-section.

## 6. Numerical Simulation of Mass Transfer

## 7. Conclusions and Recommendations

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

## Abbreviations

Nomenclature | Greek symbols | ||

$A$ | area | $\alpha $ | volume fraction |

$a$ | thermal diffusivity | $\beta $ | thermal expansion coefficient |

$Ar$ | Archimedes number | $\gamma $ | specific heat ratio |

$C$ | time relaxation factor | ε | molecule ratio |

$D$ | diameter | λ | thermal conductivity |

${D}_{sm}$ | Sauter mean diameter | μ | dynamic viscosity |

$Ek$ | Ekman number | ρ | density |

$F$ | force | Ω,ω | angular velocity |

$g$ | gravitational acceleration | ||

${h}_{fg}$ | Latent heat of vaporization | Subscripts | |

$Ja$ | Jacob number | c | condensation |

$L$ | length | cen | centrifugal |

$M$ | molecule weight | Cor | Coriolis |

$Ma$ | Mach number | e | evaporation |

$\dot{m}$ | mass transfer rate | l | liquid |

$Nu$ | Nusselt number | sat | saturation |

$p$ | pressure | v | vapor |

$Pr$ | Prandtl number | ||

$Q$ | power | ||

$R$ | radius of rotation | ||

$Re$ | Reynolds number | ||

${R}_{g}$ | gas constant | ||

$T$ | temperature | ||

$U$ | radial velocity |

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**Figure 2.**Schematic of: (

**a**) forced convection cooling; (

**b**) free convection open thermosyphon cooling; (

**c**) free convection closed thermosyphon cooling; (

**d**) two-phase closed thermosyphon cooling.

**Figure 3.**Schematic illustration of the RRHP designed by Townsend et al. [38].

**Figure 4.**Schematic illustration of the RRHP designed by Cao et al. [40].

**Figure 5.**Heat transported by RRHP and metal rods (data from [24]).

**Figure 6.**Temperature profiles with two pipe inner diameters (The dimensionless length along the pipe is the ratio between the distance from the evaporator end and the total pipe length; data from [14]).

**Figure 7.**Temperature profile along the RRHP by experiment and analytical solutions (data from [47]).

**Figure 8.**Temperature drop across the condensate film as a function of rotational speed (data from [46]).

**Figure 9.**Dimensionless vapor temperature drop due to centrifugal acceleration as a function of rotational speed (data from [45]).

**Figure 11.**(

**a**) Schematic illustration of cross-stream secondary flow; (

**b**) local analogous Nusselt number in laminar regime (Re 2200, wall temperature 314.4 K, air temperature 302 K, rotational speed 920 rpm; data from [50]).

**Figure 13.**Flow pattern in the inclined closed single-phase thermosyphon [54].

**Figure 14.**Heat transfer rates in an inclined closed thermosyphon with water (data from [54]; ${t}_{ct}=\beta g{D}^{4}\Delta T/\nu aL$).

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**MDPI and ACS Style**

Wang, Z.; Turan, A.; Craft, T.
Review of the State of the Art for Radial Rotating Heat Pipe Technology Potentially Applicable to Gas Turbine Cooling. *Thermo* **2023**, *3*, 127-147.
https://doi.org/10.3390/thermo3010009

**AMA Style**

Wang Z, Turan A, Craft T.
Review of the State of the Art for Radial Rotating Heat Pipe Technology Potentially Applicable to Gas Turbine Cooling. *Thermo*. 2023; 3(1):127-147.
https://doi.org/10.3390/thermo3010009

**Chicago/Turabian Style**

Wang, Zhao, Ali Turan, and Timothy Craft.
2023. "Review of the State of the Art for Radial Rotating Heat Pipe Technology Potentially Applicable to Gas Turbine Cooling" *Thermo* 3, no. 1: 127-147.
https://doi.org/10.3390/thermo3010009