Measuring procedure and heat transfer modelling of a four-compartment isothermal liquid foodstuff tank tested according to the international ATP Agreement

The preservation of the cold chain is one of the most important requirements in order to maintain quality in the transport of perishable foodstuffs. A significant part of the aggregate of the universally transported perishable foodstuffs and more specific liquid foodstuffs like milk, wine, juice, etc. is carried out by multi-compartment isothermal tanks. According to the international ATP Agreement these special equipment used for international transport of perishable foodstuffs have to be tested periodically in officially recognized national ATP Test Stations to ensure that they meet the specifications. Because of the number of the compartments that have to be measured the testing of a multi-compartment isothermal tank presents special difficulties in comparison to the testing of a refrigerated truck. The instrumentation needed for testing a specimen in these cases is complex and that is why only few ATP Test Stations conduct such tests.In this study a heat transfer numerical simulation is described by a four compartment isothermal tank for the transport of perishable liquid foodstuffs tested inside an ATP chamber. The simulated tests were conducted according to the regulations specified in the United Nations ATP Agreement. A transient finite difference model is developed for a typical four compartment isothermal tank tested inside an ATP Testing Chamber with dimensions and specifications like that of the ATP chamber of the Zografou Campus of the National Technical University in Athens. For the control of the cooling/heating system a proportional–integral controller is employed. The study describes a method for measuring the k-coefficient of a four compartment isothermal tank according to ATP specifications using ordinary laboratory equipments. With the suggested method, the testing of a four compartment tank is possible using only one P–I controller and one thyristor instead of the normally needed four independent P–I controllers and four thyristors in order to adjust the heat power needed inside each compartment of the four compartment isothermal tank.