Heat transfer flowmeters this type of flowmeter measures the rise in temperature of the fluid after a known amount of heat has been added to it. Its theory is based upon the specific heat equation which is given as.
Q = W Cp (T2 – T1)
W = Q / Cp (T2 - T1)
When Q = heat transfer W = mass flow rate of liquid CP = specific heat of fluid T1 = initial temperature of the fluid after heat has been transferred T2 = final temperature after heating the fluid A schematic diagram of a heat transfer flowmeter, which consist of an electric immersion heater for the heating of flowing fluid. Two thermocouples (or resistance thermometers) T1 and T2 are placed at each side of the heater. The thermocouple T1 measures the temperature of fluid before it is heated, while the thermocouple T2 measures the temperature so after. The power supply to the heater equals the heat transferred to the fluid, i.e. Q, and is measured by a wattmeter. Thus by measuring the values of Q, T1 and T2 the flow rate W of liquid is determined Principle: The basic principle principle of operation operation of the system is the heat transfer transfer from the heated wire to the cold surrounding fluid, heat transfer which is function of the fluid velocity. Thus a relationship between the fluid velocity velocity and the electrical electrical output can be established established. The purpose of the electronic circuit is to provide to the wire a controlled amount of electrical current, and in the constant temperature method, to vary such a supply so as to maintain the wire temperature constant, when the amount of heat transfer varies