High response speed microfluidic ice valves with enhanced thermal conductivity and a movable refrigeration source

Abstract

Due to their ease of fabrication, facile use and low cost, ice valves have great potential for use in microfluidic platforms. For this to be possible, a rapid response speed is key and hence there is still much scope for improvement in current ice valve technology. Therefore, in this study, an ice valve with enhanced thermal conductivity and a movable refrigeration source has been developed. An embedded aluminium cylinder is used to dramatically enhance the heat conduction performance of the microfluidic platform and a movable thermoelectric unit eliminates the thermal inertia, resulting in a faster cooling process. The proposed ice valve achieves very short closing times (0.37 s at 10 μL/min) and also operates at high flow rates (1150 μL/min). Furthermore, the response time of the valve decreased by a factor of 8 when compared to current state of the art technology.

Ice formation modes during flow freezing in a small cylindrical channel

“…Considerable effort has been directed at developing innovative microvalves that have alternative actuation mechanisms using phase-change materials including hydrogels [13,14], solgels [15], paraffins [16,17], and ice [7,[18][19][20][21][22]. This alternative microvalving approach introduces other challenges while benefiting from operation with no moving parts.…”

“…The long response time is principally due to: (1) the high thermal inertia and limited cooling capacity of the refrigeration systems used to cool the liquid, and (2) the need to supercool the working fluid to temperatures below the freezing point to trigger phase change. To speed up the cooling process, multi-stage thermoelectric cooling units have been employed that generate a large temperature difference between the cooling surface and the channel [22], or the initial temperature of the system has been lowered by pre-cooling the fluid/device. Even with these advances, the response time of current state-of-the-art ice valves remains on the order of 1 s [22].…”

“…To speed up the cooling process, multi-stage thermoelectric cooling units have been employed that generate a large temperature difference between the cooling surface and the channel [22], or the initial temperature of the system has been lowered by pre-cooling the fluid/device. Even with these advances, the response time of current state-of-the-art ice valves remains on the order of 1 s [22].…”

Use of Ice-Nucleating Proteins To Improve the Performance of Freeze–Thaw Valves in Microfluidic Devices

“…Paraffin valves belong to a class of microvalves known as phase-change valves. This type of valve controls flow by using a phase transition between the liquid and solid states. − Another type of phase-change valve is the freeze–thaw valve (FTV) or ice valve. − FTVs are an attractive strategy for fluid flow control in microfluidic devices due to their low cost, ability to be automated, and compatibility with easily fabricated, simple devices made from rigid materials such as glass and plastic. FTVs operate by cooling the liquid in a channel until it freezes, creating an ice plug that stops flow.…”

“…These pressures far exceed the needs of most microfluidic devices. Microfluidic FTV technology has evolved from utilizing ultralow temperature fluids such as liquid nitrogen or carbon dioxide , to utilizing Peltier thermoelectric coolers (TECs) to effect freezing in microfluidic chips. − …”