Thermal resistance measurements from a microchannel fluorescent melting curve analysis platform

Heat Transfer and Thermal Management have become important aspects of the developing field of μTAS systems, particularly in the development of micro PCR thermocyclers. Due to the development of flowing PCR thermocyclers in the field of μTAS, the authors have previously developed a melting curve analysis technique that is compatible with these flowing PCR thermocyclers. The test rig induces a linear temperature gradient along a sample carrying microchannel (0.8mm ID Teflon tubing). Hence, any flow passing through the microchannel is subject to linear heating. The ramp rate seen by the sample is equal to the flow velocity times the thermal gradient across the test rig. This paper presents a characterisation of this test rig, performed by positioning a thermocouple within the teflon tubing. A thermal lag is observed between the temperature of the fluid in the channel and the temperature predicted by ID conduction heat transfer theory. This lag is as a result of the thermal resistance of the tubing walls and substrate. This lag is measured for three different substrate compositions; each subjected to varying temperature gradients and with sample flow at different velocities. The thermal lag is found to be linearly proportional to flow ramp rate. This finding is supported by a theoretical treatment and numerical simulation of the test rig. Additionally, the contact thermal resistance between the thermal blocks and the fluid within the channels can be made by substituting experimental measurements into the theoretical treatment. This measurement technique is independent of knowledge of substrate dimensions, contact surface quality and substrate composition/material properties.