Effect of Nozzle-to-Target Spacing on Fin Effectiveness and Convective Heat Transfer Coefficient for Array Jet Impingement Onto Novel Micro-Roughness Structures

2018 ◽  
Author(s):  
Prashant Singh ◽  
Mingyang Zhang ◽  
Shoaib Ahmed ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat ◽  
Roughness Element ◽  
Convective Heat Transfer Coefficient ◽  
Heat Removal ◽  
Jet Impingement ◽  
Target Surface ◽  
Target Spacing

With recent advancements in the field of additive manufacturing, the design domain for development of complicated cooling configurations has significantly expanded. The motivation of the present study is to develop high-performance impingement cooling designs catered towards application’s requiring high rates of heat removal, e.g. gas turbine blade leading edge and double-wall cooling, air-cooled electronic devices etc. Jet impingement is a popular cooling technique which results in high convective heat rates. In the present study, jet impingement is combined with strategic roughening of the target surface, such that a combined effect of impingement-based and curved-surface area based enhancement in heat transfer coefficient could be achieved. Traditionally, for surface roughening, cylindrical and cubic elements are used. We have demonstrated, through our steady-state experiments, a novel “concentric” shaped roughness element design which has resulted in about 20–60% higher effectiveness compared to smooth target jet impingement, for jet-to-target spacing of one jet diameter. The cubic shaped roughened target yielded about 20% to 40% enhancement in effectiveness, and the cylindrical shaped roughened target yielded 10% to 30% enhancement. Through the plenum pressure measurements, it was found that the addition of the micro-roughness elements does not result in a discernable increment in pressure losses, compared to the standard impingement on the smooth target surface. Hence, the demonstrated configuration with the highest heat transfer coefficient also resulted in the highest thermal hydraulic performance.

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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