A new transient method for determining thermal properties of wall sections

This investigation outlines a straight-forward and low cost methodology for determining thermal properties of wall structures. The method eliminates the need to produce a step change boundary condition, and the error inherent in the departure from a step change that finite properties necessarily impose. The transient technique involves an experimental component whereby a high temperature thermal ramp boundary condition is applied to one wall face with the other exposed to the cooler ambient surroundings. Temperature and heat flux sensors are installed to monitor the transient heating behaviour at the wall faces. The measured transient wall temperature profiles are subsequently imposed as boundary equations to Fourier's equation in such a way that the analytic solution can provide a prediction of the transient surface heat flux. With this, the thermal diffusivity is estimated by using the effective thermal diffusivity of the wall material as a tuning parameter to regression fit the predicted and measured heat flux histories. Additionally, the steady solution facilitates the approximation of the effective thermal conductivity when used in conjunction with the steady surface temperature and heat flux measurements. To illustrate the technique, a test was performed on a 900 mm × 900 mm × 120 mm thick solid concrete wall section. The effective thermal diffusivity was determined to be 7.2 × 10⁻⁷ m²/s with corresponding effective thermal conductivity of 1.64 W/m K and specific heat of 0.99 kJ/kg K. Each property value is within the range of published literature for concrete.