scholarly journals Numerical Analysis of the Convective Heat Transfer Coefficient Enhancement of a Pyro-Breaker Utilized in Superconducting Fusion Facilities

Energies ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7565
Author(s):  
Jun He ◽  
Ke Wang ◽  
Jiangang Li
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Cylindrical Cavity ◽  
Thermal Flux ◽  
Convective Heat Transfer Coefficient ◽  
Water Channel ◽  
Water System

The conductive components of the pyro-breaker in the quench protection system (QPS) have high current density, a large number of electrical contacts and high thermal flux. The water system needs to meet the requirements of cooling and arc extinguishing at the same time. In a previous study, the bottleneck of the steady-state capacity appeared in the barrel conductor of the commutation section, which has a cylindrical cavity. The thermal stability of the commutation section at 100 kA level was simulated in ANSYS/Workbench. The results indicate a certain level of enhancement of the convective heat transfer coefficient of the cavity is required to reach the current capacity. However, the fluid flow inside the cavity is very complex, and the convective heat transfer coefficient is difficult to calculate. In this paper, Computational fluid dynamics (CFD) is applied to the optimization of the cooling water system of the pyro-breaker. By studying the enhancement method of convective heat transfer, optimization of the structure and processing method of the water channel are proposed. The convective heat transfer coefficients of the cylindrical cavity in these optimizations were calculated in CFX. A set of optimizations of the cavity, which can meet the requirements of China Fusion Engineering Test Reactor (CFETR), were obtained and verified by experiments.

Thermal Analysis for Cryosurgery of Nodular Basal Cell Carcinoma

2006 ◽  
Author(s):  
Feng Sun ◽  
G. Aguilar ◽  
K. M. Kelly ◽  
G.-X. Wang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cell Carcinoma ◽  
Convective Heat Transfer ◽  
Cooling Rate ◽  
Convective Heat ◽  
Thermal History ◽  
Convective Heat Transfer Coefficient ◽  
Target Tissue

Basel cell carcinoma (BCC) is the most common human skin malignancy. Its incidence has increased significantly in Australia, Europe and North America over the past decade. A number of modalities are currently used for treatment of BCC, including cryosurgery which offers a potential for high cure rate, low cost, minimal bleeding and good cosmetic effect. However, cryosurgery is not used frequently for BCC because no current method exists to design adequate treatment parameters. We present a numerical analysis on the thermal history of the target tissue during cryosurgery of a nodular BCC using liquid nitrogen (LN2) spray. The model uses Pennes equation to describe the heat transfer within the target tissue. A convective thermal boundary is used to describe the heat interaction between the tissue and LN2, and the apparent heat capacity method is applied to address the tissue phase change process. A parametric study is conducted on the convective heat transfer coefficient (hs: 104~106 W/m2·K), cooling site area (rs/R0: 0.5~1.0) and spray time (t: 0~30 sec.), with the objective to understand the thermal history during tissue freezing, including lethal temperature (-50 °C) and cooling rate (CR). Results demonstrate that propagation of the lethal isotherm is sensitive to the convective heat transfer coefficient, hs, with a range of 104~5×104 W/m2·K. Increasing the cooling site area can significantly enhance cooling efficiency, producing dramatic increase in the amount of tissue encompassed by the lethal isotherm. The cooling rate (CR) shows a highly dynamic distribution during the cooling process: the highest CR drops quickly from 140 °C/sec. (t=0.5 sec.) to 20 °C/sec. (t=5 sec.). The highest CR is initially located close to the cooling site but moves toward the inside of the tissue as treatment proceeds. The model presented herein provides a simulation tool for treatment planning of cryosurgery using LN2 spray, in which the protocol parameters, e.g. cooling site area and spray time, can be determined for an optimal outcome. The quantitative predictions on the propagation of lethal isotherm and the distribution of CR should help to optimize cryosurgery efficacy.

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