UNDERSTANDING JUICE FLOW PATTERNS IN ROBERTS EVAPORATORS

JUICE sampling trials were undertaken on conventional Roberts evaporators at Tully Mill and on the new SRI Roberts evaporator at Broadwater Mill to determine the brix of juice at different locations within these vessels under typical operating conditions. The sampling trials provided consistent information regarding brix profiles for the juice, and good insight into the juice flow patterns within the vessels has been obtained. Major differences in the juice brix profiles among the vessels were found to exist. The juice below the calandria of the conventional Roberts evaporator, and the juice entering the base of the heating tubes at all radial positions, was within 0.5 units of the brix of the outlet juice. For the SRI Roberts evaporator, the juice below the calandria was at an intermediate brix between the brix of the juice at the inlet and the outlet. The supply of juice of lower brix to the base of the heating tubes, across the full width of the calandria in the SRI Roberts vessel, is considered to be beneficial to heat transfer performance. For all vessels, the juice within the heating tubes near the top tube plate was of higher brix than the juice at the base of the heating tubes. This change in brix is expected, as Roberts evaporators operate in rising film evaporation mode. The juice above the top tube plate in both the conventional and SRI Roberts evaporators was at the highest brix within the vessel. This information on juice brix profiles and inferred juice flow patterns within Roberts evaporators is useful for developing design improvements.