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Research Papers: Bio-Heat and Mass Transfer

Numerical Simulation of the Effects of a Thermally Significant Blood Vessel on Freezing by a Circular Surface Cryosurgical Probe Compared With Experimental Data

[+] Author and Article Information
Genady Beckerman, David Degani

Department of Mechanical Engineering, Israel Institute of Technology, Haifa, Israel 32000

Avraham Shitzer1

Department of Mechanical Engineering, Israel Institute of Technology, Haifa, Israel 32000mersasa@tx.technion.ac.il

1

Corresponding author.

J. Heat Transfer 131(5), 051101 (Mar 20, 2009) (9 pages) doi:10.1115/1.3001035 History: Received May 30, 2008; Revised July 29, 2008; Published March 20, 2009

The dynamic thermal interaction between a surface cryosurgical probe (heat sink) and an embedded cylindrical tube (heat source), simulating a thermally-significant blood vessel, has been studied. The cryoprobe was operated by liquid nitrogen while the embedded tube was perfused by water at a constant inlet temperature. Previous experimental data were obtained in a phase-changing medium (PCM) made of 30%/70% by volume mashed potato flakes/distilled-water solution. A parametric study was conducted without the embedded tube, and with flow rates of 30 ml/min and 100 ml/min in the tube, while cooling rates at the tip of the cryoprobe were maintained at 4°C/min, 8°C/min, or 12°C/min. Numerical thermal analysis was performed by ANSYS7.0 and showed good conformity to the experimental data. The results quantify the effects of these parameters on both the shape and extent of freezing obtained in the PCM. For 20 min of operation of the cryoprobe, water temperatures inside the tube remained well above the freezing point for all assumed operating conditions. Frozen volumes of the 0°C isotherm, approximating the “frozen front,” and the 40°C isotherm, representing the “lethal temperature,” were smallest for the combination of highest cooling rate at the cryoprobe and the highest flow rate in the tube, (12°C/min and 100 ml/min). The results indicate that both the flow rates in the embedded tube, and the cooling rates applied at the cryoprobe, have similar qualitative effects on the size of the PCM frozen volumes; increasing either one will cause these volumes to decrease. Under the conditions of this study the effects of flow rate in the tube are more pronounced, however, effecting relative frozen volumes decreases by about 10–20% while those of the cooling rate at the cryoprobe are in the range of 7–14%.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 8

Computed effects of embedded tube flow rates on isothermal fronts location at section C after 20 min of operation. Probe cooling rate: −8°C/min.

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Figure 9

Computed effects of flow rates in the embedded tube on the temperature field inside the tube and its wall and in the PCM at section C after 20 min of operation. Probe cooling rate: −8°C/min; temperatures in degrees centigrade.

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Figure 10

Computed effects of flow rates in the embedded tube on the axial temperature variations along the tube centerline. Probe cooling rate: −8°C/min.

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Figure 11

Computed evolution of the volumes enclosed by 0°C and −40°C isotherms for three different probe cooling rates without the embedded tube. Final probe temperature: −142°C.

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Figure 12

Computed effects of flow rates in the embedded tube and probe cooling rates on the evolution of the volumes enclosed by the 0°C and −40°C isotherms. Final probe temperature: −142°C.

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Figure 7

Computed comparison of three isothermal fronts in sections B (upstream) and D (downstream) after 20 min of operation. Probe cooling rate: −8°C/min. Embedded tube flow rate: 100 ml/min.

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Figure 6

Computed advancements of the 0°C and −40°C isothermal fronts at section C for embedded tube flow rate of 100 ml/min. Probe cooling rate: −8°C/min.

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Figure 5

Measured and computed isotherms in sections A–E in the PCM after 20 min of operation. Probe cooling rate: −8°C/min. Embedded tube flow rate: 100 ml/min.

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Figure 4

Comparison of measured and computed isotherms in the PCM after 20 min of operation without the embedded tube. Probe cooling rate: −8°C/min.

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Figure 3

Schematic of the numerical solution domain

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Figure 2

Positioning of the thermocouple junctions on a 5×5 mm2 grid in the PCM at each measuring section A–E

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Figure 1

Schematic of the experimental setup showing temperature measuring sections A–E

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