The Hilton H971 Laminar/Viscous Flow Heat transfer unit has been designed to provide students with experimental work related to the transfer of heat in a concentric tube heat exchanger, when flow is laminar.
Heat transfer is allowed to take place between oil and water in a concentric tube. Oil flowing in the inner tube is raised to a maximum temperature of 90°C in a tank fitted with an electric heating element. Control is by a panel mounted digital PID controller and the maximum temperature is limited by a separate thermostat for operator safety.
The heated oil is pumped from the tank into the core tube of the diagonally mounted concentric tube heat exchanger. As it flows downwards, the oil is cooled as heat is transferred to the flow of cooling water which surrounds the core tube.
On leaving the oil passes through a flow control valve to a strong glass measuring cylinder fitted with a contents scale. By measuring the volume change over time, an accurate flow rate may be determined. A quick acting valve and internal overflow allows oil back to the heater tank for re-circulation.
Mains cold water passes through a combined flow control valve and flowmeter to a separate pair of valves mounted on the front panel. These valves direct the cold water to either end of the heat exchanger and allow instantaneous flow reversal from concurrent to counter-current flow.
Thermocouples sense the hot and cold stream temperatures and the wall temperatures on entry and exit. A digital thermometer with a selector switch, displays the temperature sensed by the oil, water and pipe temperature thermocouples.
Specifications and resources
i) Thermostat to limit oil temperature to 90°C,
ii) Combined main switch and overload cut out,
iii) Residual current circuit breaker,
iv) All metal components connected to common earth conductor
