Thermal-based flow sensing apparatuses and methods for high-performance liquid chromatography

A method of sensing a flow rate through a fluid channel having a first thermoelectric sensing element and a second thermoelectric sensing element equally spaced along the fluid channel from heating element, the method comprising:

• oppositely-doping material of the first and second thermoelectric sensing elements;
• electrically connecting the first and second thermoelectric sensing elements in series so that temperature information from the first and second thermoelectric sensing elements is a highly sensitive response;
• actuating the heating element;
• flowing a sample through the fluid channel;
• receiving the temperature information from the first thermoelectric sensing element and the second thermoelectric sensing element;
• and
• calculating a flow rate based on a difference in temperatures between the first thermoelectric sensing element and the second thermoelectric sensing element.

A kit comprising:

• (a) a flow sensing apparatus comprising:
• a fluid channel that allows a fluid to flow in a first direction;
• a first thermoelectric sensing element arranged at a first position along the fluid channel such that the first thermoelectric sensing element senses a temperature of the fluid, wherein the first thermoelectric sensing element is doped with a N-type charge carrier;
• a second thermoelectric sensing element arranged at a second position along the fluid channel and separated from the first sensing element by a predetermined distance along the fluid channel, wherein the second thermoelectric sensing element is doped with a P-type charge carrier;
• and
• a heating element arranged between the first and second thermoelectric sensing elements, the heating element being equally spaced from the first and second thermoelectric sensing elements;
• and
• (b) instructions for installation and/or use.

A High Performance Liquid Chromatography (HPLC) device comprising a flow sensing apparatus comprising:

• a fluid channel that allows a fluid to flow in a first direction;
• a first thermoelectric sensing element arranged at a first position along the fluid channel such that the first thermoelectric sensing element senses a temperature of the fluid;
• a second thermoelectric sensing element arranged at a second position along the fluid channel and separated from the first sensing element by a predetermined distance along the fluid channel;
• a heating element arranged at a heater position between the first and second thermoelectric sensing elements, the heating element being equally spaced from the first and second thermoelectric sensing elements;
• and
• an amplifier element coupled to the first and second thermoelectric sensing elements for sampling, subtracting and amplifying temperature measurements from the first and second thermoelectric sensing elements,
• wherein:
• at zero-flow condition, a temperature profile curve of temperature versus distance is symmetrical about the heater position;
• and
• the first position and the second position are at inflection points of the temperature profile curve so that an amount of time required to detect a difference between measured temperatures is minimized and, in turn, a response of the amplifier element to flow rate change is maximized.