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Abstract: An experimental study was conducted to investigate the effect of advanced surfaces on the ammonia absorption process in tubular bubble absorbers using NH3/LiNO3 as a working pair at operating conditions of interest for absorption chillers. The tubular bubble absorber is a vertical double-pipe heat exchanger in which absorption takes place in the inner tube. In order to compare the effect of surface enhancement, a smooth tube and an internally micro-finned tube were tested. The inner tube of the absorber is made of aluminium and has an outer diameter of 8.0mm and the micro-finned tube has internal helical micro-fins measuring 0.3mm in length. The effect of tube length on absorption was also studied using two tube lengths (1 and 3m) and two tube diameters (8 and 9.5mm). Our results show that the absorption rate achieved with the micro-finned tube is up to 1.7 times higher than with the smooth tube at a solution mass flow rate of 40kgh−1. We also found that absorption mass flux increases when tube diameter is reduced and decreases when tube length is increased. [Copyright &y& Elsevier]

Abstract: The classic conservative approach for thermal process design can lead to over-processing, especially for laminar flow, when a significant distribution of temperature and of residence time occurs. In order to optimize quality retention, a more comprehensive model is required. A model comprising differential equations for mass and heat transfer is proposed for the simulation of the continuous thermal processing of a non-Newtonian food in a tubular system. The model takes into account the contribution from heating and cooling sections, the heat exchange with the ambient air and effective diffusion associated with non-ideal laminar flow. The study case of soursop juice processing was used to test the model. Various simulations were performed to evaluate the effect of the model assumptions. An expressive difference in the predicted lethality was observed between the classic approach and the proposed model. The main advantage of the model is its flexibility to represent different aspects with a small computational time, making it suitable for process evaluation and design. [Copyright &y& Elsevier]