Determination of flow rate and fluid temperature

A method for determining the flow rate in a pipe includes measuring a temperature difference between the pipe and the temperature of the surroundings of the pipe and dividing this difference by the difference between the temperature of the fluid entering the pipe and the temperature of the surroundings of the pipe. A non-linear conversion between the ratio derived in this way and the flow rate is used to estimate the flow rate. The non-linear conversion may be a sigmoid or inverse tangent function. A calibration step may include selecting a combination of non-linear functions, and may be performed periodically. The determination of the temperature of the fluid entering the conduit may include determining a rolling average of the outside air temperature. Also disclosed are methods for estimating the temperature of the fluid entering the pipe using either the temperature of the pipe or the local air temperature. The method can be used in the detection of leaks, particularly at low flow rates.