Energy losses in Minoan terracotta pipes

In this Diploma Thesis, head loss measurements in flow through terracotta tapered pipes are experimentally investigated. This type of pipes were found in Minoan Palace of Knossos at Crete. It is assumed that they were used in middle Minoan period (1900-1700 B.C.) for supply purposes and operated mostly under pressure. The tapered pipes had an average length about 70 cm, upstream inside diameter around 135mm and downstream inside diameter 85 mm. They were made of clay while the connections of some kind of cement. Recently the pipes have been studied experimentally in the laboratory, as well as numerically using computational fluid dynamics (CFD) software. Webster, et al. (2010), researchers from Melbourne, conducted experiments with replicas of Minoan pipes that they made of papier machè. In their paper it is reported that great energy losses occurred along an array of four pipes, which were assumed to be due to the sudden expansion in the joints. In a computational work by Tseropoulos et al. (2012), the same pipe has been simulated numerically. The latter authors have found that through each pipe a recirculation region is observed due to the large difference in diameters at joints. In the present thesis we tested a sequence of six handmade pottery replicas similar to those that were excavated in the palace of Knossos. The replicas were placed in a series and connected to the supply network with two straight PVC pipes placed before and after the array. The PVC pipes had sufficient length so as to obtain a fully developed, uniform flow at the entrance and exit sections of the array. The aim of this research was to determine the energy losses along the pipe array. Three sets of experimental measurements were made for this reason. A differential compressed air pressure gauge was used to obtain the hydraulic grade line and calculate the energy loss. In the first set, the energy loss between the PVC pipes, before and after the array, was obtained. In the second set the energy loss through the first two tapered pipes was measured, via an array of piezometers placed at the axis elevation of the array. Finally, in the last set of measurements, energy loss through all six Minoan pipes was obtained. The discharge varied between 5 and 14 L/s in each one of the three sets. A simple, one-dimensional computer model was created to calculate the friction losses in one tapered pipe section along with the local loss at the joints. The results from the third set of measurements are near those obtained by our one-dimensional model, and quite near those reported by Tseropoulos et al (2012). This investigation was made in order to explain why Minoans used tapered instead of cylindrical pipes, and also to explain why they eventually abandoned this tapered shape. We cannot give a convincing answer to it, but we can make an educational guess that they were possibly used to increase energy loss of excess energy that was due to the multifarious landscape in this area of Crete.