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How the Heat Pulse Flow Meter Works
The purpose of the groundwater flowmeters is to quantify the velocity and direction of groundwater flow. Understanding where and how much groundwater is flowing within the Biscayne BAM helps manage water to meet the various needs. The goal of the BAM project is to monitor surface and groundwater flow changes as described in the Background Section.

Heat pulse flowmeters modify the inherent temperature of water to indicate flow. Although the ambient temperature of groundwater may change somewhat rapidly based on inputs, it is possible to control and measure these changes over very small distances. A heat-pulse sensor is designed to monitor the changing temperatures of water, and thereby the direction and velocity of that water. A center heater, denoted by a red circle in the figure below, is surrounded by eight temperature sensors (or thermistors) depicted by the orange, red, and green circles. Water moving across the heater becomes warmed relative to ambient water. The eight sensors can detect these differences in temperature as the warmed water moves past. These sensors are useful for groundwater monitoring applications, such as BAM, because the sensors are small enough to fit inside a groundwater well pipe. Groundwater flowmeters are installed in five wells at L30 and four wells at L31NN. The monitoring wells have been specially constructed for use with flowmeters (see Well Construction).
Schematic of axial view of probe showing the manner in which the eight thermistors are oriented radially around the heater. Water flow from northwest towards the southeast is shown with associated conduction of heat (red lines).
Two heat pulse flow probes. The top one has the 2” fuzzy packer removed. A connector allows for quick exchange.
These plots of absolute (top) and differential (bottom) temperature illustrate typical output from the heat pulse probe over six hours. The heater is activated for 30 seconds at the top of each hour. The differential temperature signal in mV is the difference between each of the four pairs of sensors.
The fuzzy packer is perforated beneath the beige fuzz material, allowing water flow. Glass beads surround the thermistors and improve the rate of heat conduction by flowing water, enhancing probe sensitivity.