Because high pressure steam is very valuable, exhaust steam is often used for juice heating or, if possible, preferably bled vapour from the evaporators. It is thus necessary to have a heat exchanger between vapour and juice; this is provided by the juice heaters.
The juice heater (below) consists of an assembly of tubes; the juice circulates through the tubes, and the vapour outside them. Suitable headers force the juice to pass a certain number of times from bottom to top and from top to bottom of the heater by restricting the juice each time to a few of the tubes.
The basic calculation of the juice heater is to calculate the amount of heat transferred using the overall heat transfer co-efficient (OHTC), the log mean temperature difference (LMTD) and the heating surface area.
Values of OHTC from various sources
Perk, ISSCT 1962, p601
Webre in Hugot, 2nd Ed p452
Quoting Cuban conditions
Oliver Lyle EUS Table XLVII
Calorifiers - low velocity
Calorifiers - high velocity
Bubnik et al 1995, table 445/2
water heated by saturated steam
raw juice heated by vapour
1 BTU/ft2/°F/h = 5.678 W/m2K