Continuous flow calorimeter systems and related methods
A method for determining specific heat capacity of fluids includes: (a) injecting a reference fluid into at least one channel of a reference substrate and a sample fluid into at least one channel of a sample substrate; (b) establishing a temperature gradient along the at least one channel of each substrate; (c) measuring temperature differential between the reference and sample substrates along the temperature gradient for a stagnant condition to define a baseline temperature differential, and for each of a plurality of flowrate ratios of the reference and sample fluids flowing through respective channels; and (d) based on the measuring in (c), determining a thermally-balanced flowrate ratio at which the temperature differential corresponds to the baseline temperature differential, and evaluating the specific heat capacity of the sample fluid based on the thermally-balanced flowrate ratio.
1 . A method for determining specific heat capacity of fluids, comprising:
a) injecting a reference fluid having a known specific heat capacity into at least one channel extending along a reference substrate and a sample fluid having an unknown specific heat capacity into at least one channel extending along a sample substrate;
b) establishing a temperature gradient along the at least one channel of each substrate;
c) measuring a temperature differential between a reference location along the temperature gradient of the reference substrate and a corresponding sample location along the temperature gradient of the sample substrate, the temperature differential being measured for a stagnant condition in which the reference and sample fluids are stagnant in respective channels to define a baseline temperature differential, and for each of a plurality of flowrate ratios, each flowrate ratio defined by a different sample flowrate at which the sample fluid flows through the at least one channel of the sample substrate relative to a constant reference flowrate at which the reference fluid flows through the at least one channel of the reference substrate; and
d) based on the measuring in (c), determining a thermally-balanced flowrate ratio of the sample flowrate relative to the reference flowrate at which the temperature differential corresponds to the baseline temperature differential, and evaluating the unknown specific heat capacity based on the thermally-balanced flowrate ratio.
2 . The method of claim 1 , wherein each substrate comprises a respective microfluidic chip and the at least one channel comprises at least one microfluidic channel in the chip.
3 . The method of claim 1 , wherein the measuring in (c) comprises receiving voltage signals representative of the temperature differential from at least one differential thermocouple comprising at least one reference junction at the reference location and at least one sample junction at the sample location.
4 . The method of claim 1 , wherein each of the reference location and the sample location is at a midpoint along the temperature gradient of a respective substrate.
5 . The method of claim 1 , further comprising determining a functional relation between the plurality of flowrate ratios and corresponding temperature differentials measured in (c), and wherein the determining in (d) comprises evaluating the thermally-balanced flowrate ratio based on the functional relation.
6 . The method of claim 1 , wherein the temperature differential is measured using a temperature-differential sensor system including at least one thermoelectric sensor having at least one reference sensor element positioned at the reference location along the temperature gradient of the reference substrate and at least one sample sensor element positioned at the corresponding sample location along the temperature gradient of the sample substrate.
7 . The method of claim 1 , wherein the reference substrate and the sample substrate are generally identical and interchangeable.
8 . The method of claim 1 , wherein each of the at least one channel extending along the reference substrate and the at least one channel extending along the sample substrate comprises a plurality of channels extending generally parallel with each other.
9 . The method of claim 1 , wherein (b) comprises maintaining a heated section of each substrate at a first temperature and maintaining a cooled section of each substrate at a second temperature that is less than the first temperature to establish the temperature gradient between the heated and cooled sections.
10 . The method of claim 9 , wherein the heated section is maintained at the first temperature by a thermoelectric heater, and the cooled section is maintained at the second temperature by a thermoelectric cooler.
11 . The method of claim 1 , further comprising operating a pump system to pump the reference fluid and the sample fluid at the plurality of flowrate ratios.
12 . The method of claim 11 , wherein operating the pump system includes operating a reference fluid pump to pump the reference fluid through the at least one channel extending along the reference substrate at the constant reference flowrate, and operating at least one sample fluid pump to pump the sample fluid at each different sample flowrate.
13 . The method of claim 12 , wherein the at least one sample fluid pump comprises a plurality of fluid pumps for pumping respective fluids, and the pump system includes a mixer for mixing the respective fluids when being pumped to produce the sample fluid.
14 . A method for determining specific heat capacity of fluids comprising:
a) injecting a reference fluid into at least one reference channel and a sample fluid into at least one sample channel;
b) establishing a temperature gradient along the at least one reference channel and along the at least one sample channel;
c) measuring a temperature differential between the at least one reference channel and the at least one sample channel, including for a plurality of flowrate ratios, each flowrate ratio defined by a reference flowrate of the reference fluid and a sample flowrate of the sample fluid; and
d) based on the measuring in (c), determining a thermally-balanced flowrate ratio of the sample flowrate relative to the reference flowrate at which a strength of both the reference and sample fluids in changing the temperature gradient along respective channels becomes generally equal, and evaluating the specific heat capacity of the sample fluid based on the thermally-balanced flowrate ratio.
15 . The method of claim 14 , wherein each of the at least one reference channel and the at least one sample channel comprises at least one microfluidic channel.
16 . The method of claim 14 , wherein in (c), the temperature differential is measured for a stagnant condition in which the reference and sample fluids are stagnant in respective channels to define a baseline temperature differential, and for each of the plurality of flowrate ratios.
17 . The method of claim 16 , wherein each flowrate ratio is defined by a different sample flowrate at which the sample fluid flows through the at least one sample channel relative to a constant reference flowrate at which the reference fluid flows through the at least one reference channel.
18 . The method of claim 17 , wherein the thermally-balanced flowrate ratio corresponds to the flowrate ratio of the sample flowrate relative to the reference flowrate at which the temperature differential corresponds to the baseline temperature differential.
19 . The method of claim 18 , wherein the thermally-balanced flowrate ratio is determined by adjusting the sample flowrate while maintaining the reference flowrate constant until the measured temperature differential corresponds to the baseline temperature differential.