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HEAT TRANSFER IN NANOCHANNELS, MICROCHANNELS, AND MINICHANNELS

Theoretical and Experimental Study of a Flexible Wiretype Joule–Thomson Microrefrigerator for Use in Cryosurgery

[+] Author and Article Information
Adhika Widyaparaga

Department of Mechanical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan; Department of Mechanical and Industrial Engineering,  Gadjah Mada University, Jl. Grafika 2, Yogyakarta 55281, Indonesiaadhikayev@gmail.com

Masashi Kuwamoto

Department of Mechanical Engineering,  Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan

Naoya Sakoda

International Research Center for Hydrogen Energy,  Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan

Masamichi Kohno, Yasuyuki Takata

Department of Mechanical Engineering; International Institute for Carbon-Neutral Energy Research,  Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan

J. Heat Transfer 134(2), 020903 (Dec 13, 2011) (7 pages) doi:10.1115/1.4004937 History: Received January 09, 2011; Revised August 08, 2011; Published December 13, 2011; Online December 13, 2011

We have developed a model capable of predicting the performance characteristics of a wiretype Joule–Thomson microcooler intended for use within a cryosurgical probe. Our objective was to be able to predict cold tip temperature, temperature distribution, and cooling power using only inlet gas properties as input variables. To achieve this, the model incorporated gas equations of state to account for changing gas properties due to heat transfer within the heat exchanger and expansion within the capillary. In consideration of inefficiencies, heat in-leak from free convection and radiation was also considered and the use of a 2D axisymmetric finite difference code allowed simulation of axial conduction. To validate simulation results, we have constructed and conducted experiments with two types of microcoolers differing in inner tube material, poly-ether-ether-ketone (PEEK) and stainless steel. The parameters of the experiment were used in the calculations. CO2 was used as the coolant gas for inlet pressures from 0.5 MPa to 2.0 MPa. Heat load trials of up to 550 mW along with unloaded trials were conducted. The temperature measurements show that the model was successfully able to predict the cold tip temperature to a good degree of accuracy and well represent the temperature distribution. For the all PEEK microcooler in a vacuum using 2.0 MPa inlet pressure, the calculations predicted a temperature drop of 57 K and mass flow rate of 19.5 mg/s compared to measured values of 63 K and 19.4 mg/s, therefore, showing that conventional macroscale correlations can hold well for turbulent microscale flow and heat transfer as long as the validity of the assumptions is verified.

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Figures

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Figure 1

(A) capillary a, average inner diameter 114.5 μm, (B) capillary b, average inner diameter 100.1 μm

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Figure 2

Microcooler configuration for unloaded trials

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Figure 3

Microcooler configuration for heat load trials

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Figure 4

Apparatus setup; p, t, and f designate measurement locations of pressure, temperature, and flow rate, respectively

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Figure 5

Diagram of theoretical model. (A) setup of elements and (B) breakdown of heat transfer processes.

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Figure 6

Unloaded theoretical and experimental results of mass flow rate for (A) microcooler A and (B) microcooler B in both atmospheric and vacuum environments

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Figure 7

Unloaded theoretical and experimental results of temperature drop for (A) microcooler A and (B) microcooler B in both atmospheric and vacuum environments

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Figure 8

Predicted surface temperature distribution and measurements

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Figure 9

Temperature measurements [12] and calculation of heat load trials

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