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Research Papers: Melting and Solidification

# Experimental and Numerical Study of One, Two, and Three Embedded Needle Cryoprobes Simultaneously Operated by High Pressure Argon Gas

[+] Author and Article Information
Z. Magalov, D. Degani

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

A. Shitzer

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

J. Heat Transfer 130(3), 032301 (Mar 06, 2008) (12 pages) doi:10.1115/1.2804943 History: Received September 15, 2006; Revised June 18, 2007; Published March 06, 2008

## Abstract

One, two, and three needle cryoprobes, $1.47mm$ outside diameter, simultaneously and uniformly operated by high pressure argon gas, were tested in a gel simulating the thermal properties of biological tissues. The probes were inserted into the same depth in the gel through two parallel templates with holes drilled on a $5×5mm2$ mesh. The temperature of the active segment of the probe was monitored by a single soldered thermocouple (TC). Temperatures in the gel were monitored by K-type TC strings in the radial, and in the downward and upward axial directions. The phase-change problem in the gel was solved by ANSYS7.0 , based on the enthalpy method. Calculated and measured results compared reasonably well with the most deviations observed in the upward axial direction. Results of this study may be summarized as follows: (a) Due to the cylindrical structure of the probe, the advancement of the frozen fronts was more pronounced in the upward axial and the radial directions than in the downward direction. (b) The farthest placement of the two probes $(10mm)$ yielded the largest volumes enclosed by the isothermal contours. (c) In the tightest two placement configurations of the three probes, the $−40°C$ fronts of all frozen lumps have joined together even after $1min$ of operation, while in the less tight configurations, joining occurred later. (d) In multiprobe applications and for a given duration of application, there exists a certain placement configuration that will produce the maximal volume of any temperature-specific frozen lump. The computational tool presented in this study could assist the surgeon in the preplanning of cryosurgical procedures and thus reduce uncertainties and enhance its success rate.

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Topics: Probes , Temperature

## Figures

Figure 10

Comparison of the experimental and numerical results for one-probe application in the upward axial direction. Upper and lower bounds are for ±10% uncertainties in the thermal diffusivity and length of the thermally active segment of the probe and ±1mm in the positions of the TCs.

Figure 11

Schematic of the assumed uncertainties in the radial, and upper and lower axial locations of the TCs. Circles’ radii are 1mm.

Figure 12

Ellipsoidal approximations of measured data of isothermal contours in the frozen gel after 6min and 10min of a single-probe application

Figure 13

Measured and calculated side cross-sectional views of 0°C and −40°C isothermal contours for two probes positioned 5mm and 10mm apart after 10min of operation

Figure 14

Calculated −40°C isothermal 3D fronts for the four configurations of the three-probe applications after 1min of operation

Figure 15

Frozen volume variations obtained by three cryoprobes for different placement configurations: Volumes enclosed by the (a) −40°C, (b) −20°C, and (c) −0°C isothermal surfaces, respectively. (d) Percentages of the volumes enclosed by the −40°C isothermal surface relative to the total frozen volume (0°C isotherm).

Figure 1

Schematic drawing of the experimental setup showing two embedded cryoprobes

Figure 2

Schematic drawing of the placement of the TCs for a single cryoprobe embedded in the gel. Dimensions are in mm.

Figure 3

Placement configurations for the three-probe experiments. Dimensions are in mm.

Figure 4

Schematic drawing of the numerical solution domain for the one-probe application

Figure 5

Temperature variations measured by the TC soldered onto the surface of the cryoprobe 5mm above its tip. Circles designate the numerical approximations of the measured data.

Figure 6

Finite element mesh for the two- and three-probe applications

Figure 7

Comparison of the analytical and numerical solutions for the half-space solidification problem after 5min at 1–5mm distances from the surface. Assumed solidification temperature range is ±0.5°C (numerical model only).

Figure 8

Comparison of the experimental and numerical results for one-probe application in the radial direction. Upper and lower bounds are for ±10% uncertainties in the thermal diffusivity and length of the thermally active segment of the probe and ±1mm in the positions of the TCs.

Figure 9

Comparison of the experimental and numerical results for one-probe application in the downward axial direction. Upper and lower bounds are for ±10% uncertainties in the thermal diffusivity and length of the thermally active segment of the probe and ±1mm in the positions of the TCs.

## Errata

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