Low temperature thermal resistance for a new design of silver sinter heat exchanger

TL;DR

This paper introduces a new silver sinter heat exchanger design with enhanced thermal conductance for low-temperature applications, demonstrated by a 3-He melting curve thermometer with a thermal relaxation time of about 490 seconds at 1 mK.

Contribution

A novel construction method for high surface area silver sinter heat exchangers using nylon fibers and silver wires, improving thermal performance at millikelvin temperatures.

Findings

Achieved a thermal relaxation time of ~490 s at 1 mK.

Characterized the heat exchanger with SEM and BET surface area measurements.

Demonstrated effective thermal conductance in a 3-He melting curve thermometer.

Abstract

We have developed a novel procedure for constructing high surface area silver sinter heat exchangers. Our recipe incorporates nylon fibers having a diameter of ~ 50 microns and thin wires of bulk silver in the heat exchanger. In order to increase the thermal conductance of liquid helium within the heat exchanger, prior to sintering, the nylon fibers are dissolved with an organic acid leaving a network of channels. In addition, the silver wires reinforce the structural integrity, and reduce the resistance, of the silver sinter. We have constructed a 3-He melting curve thermometer (MCT) with this type of heat exchanger and measured the thermal time response of the liquid 3-He inside the MCT in the temperature range T = 2-150 mK. We find a thermal relaxation time of ~ 490 s at T ~ 1 mK. We have used scanning electron microscopy (SEM) to characterize the heat exchanger and BET absorption for determination of the specific surface area.