Determine the optimum tube dimensions for Robert evaporators through experimental investigations and CFD modelling: final report 2012/054

Abstract

Experimental investigations were undertaken in a single tube pilot evaporator for nine tubes of three different lengths and three different diameters to determine the optimum tube dimensions for Robert evaporators. Heat transfer performance was determined at operating conditions typically encountered in sugar factory evaporators. Juice of three brix levels were selected to mimic conditions for the 1st, 3rd and 5th effects in a quintuple evaporator set. For each brix, the heat transfer coefficient (HTC) was calculated at four juice levels, two headspace pressures and two pressure differences between the steam chest and the headspace. Of the four juice levels, one juice level was identified as the optimum juice level corresponding to the maximum HTC. In total, 432 tests were undertaken with nine tubes and a further 128 tests were replicated with four tubes. The maximum HTC and optimum juice level results, linked together with a capital cost analysis and sucrose loss considerations, determined the preferred tube dimensions for Robert evaporators in a quintuple evaporator set.

Tubes of 3 m length and either 44.45 mm or 38.1 mm outside diameter are preferred for the 1st, 2nd and 3rd effects instead of the traditionally used tube of 2 m length and 44.45 mm outside diameter. The tube of 2 m length and 44.45 mm outside diameter is recommended for the 4th and 5th effects.

The investigations in this project were undertaken by Omkar Thaval for his PhD thesis at QUT “Investigating the effect of tube dimensions and operating conditions on heat transfer performance in a rising film vertical tube evaporator”.