Investigation on Droplet Heat Transfer Characteristics of Continuous-Flow PCR

Droplet digital polymerase chain reaction (ddPCR) is of great significance in precision medicine, including nucleic acid molecule quantification and DNA methylation detection. However, for continuous-flow PCR devices, precisely controlling droplet temperature within the microchannels to ensure efficient amplification is a challenge. In this study, we investigated the heat transfer characteristics of droplets in microchannels by combining numerical simulation with PCR experiments. Key findings include the following: 1) As droplets traverse the microchannels, internal vortices develop, transporting high-temperature fluid from the periphery toward the droplet's center. The most intense vorticity occurs at the droplet's rear. 2) While higher flow rate enhance overall heat transfer efficiency, they simultaneously increase the thickness of the insulating oil film between the droplet and channel wall, which impedes heat transfer. We characterized the system heat exchange capacity using the Nusselt number (<i>Nu</i>) and determined its variation against flow rates. This analysis provides guidance for optimizing DNA amplification efficiency in a continuous-flow PCR system. 3) A higher droplet volume fraction induces greater interference with the continuous phase flow. This results in densely packed droplets within the continuous phase, disrupting its laminar flow profile and thereby enhancing the overall heat transfer capacity of the microfluids in the microchannel.