Trianco Redfyre Limited, the UK's leading manufacturer of oil-fired heating appliances, recently called upon TWI's experimental stress analysis service to help assess its new boilers at the prototype stage.
Today's markets demand greater heat output from smaller boilers and heat exchanger design is now necessarily quite sophisticated. Long-term reliability is important to Trianco's design team and a major priority is achievingperformance targets and eliminating the risk of thermal fatigue.
The recent project focused on a new design of an extremely compact high-output wall-mounted boiler. Design calculations showed that the heat exchanger had a satisfactory fatigue life but confirmation of this by experimentalmeasurement was required. TWI was called upon to take strain measurements from the prototype using electrical resistance strain gauges.
The boiler was of double-skin construction with a water-filled cavity. The areas of interest were on the inner shell around the burner chamber, but the strain gauges and thermocouples had to be mounted on the water cavity side toavoid being burnt away. Because there was no access to the water cavity on a fully assembled boiler, the gauges were attached to a bare inner shell prior to testing. The outer panels were then carefully welded in place whilsttemperatures were monitored and cooling periods allowed to avoid 'cooking' the gauges. Wiring was extracted via a specially-installed fitting in the final panel to be welded in place.
This assembly procedure proved to be entirely successful, with the instrumentation performing perfectly during subsequent trials. Analysis of the data showed that the minimum fatigue life of this model was around 150 years - a mostsatisfactory outcome for both Trianco Redfyre and its customers.
For more information on TWI's stress analysis service, call Graham Slater graham.slater@twi.co.uk.
