Studies on a Batch Vacuum Crystallizer

Abstract

Studies were made on a batch vacuum crystallizer with water and aqueous solutions of Na₂CO₃·10H₂O and Na₂SO₄·10H₂O.
Exhausting rate of the rotary vacuum pump was found to follow the equation,
S=a ln P+b (1)
and the time required to reduce the pressure from P1 to P2 by a rotary vacuum pump was determined
by,
(2)
The time required to cool the solution frorn tl to t2 was fbund to be practically equal to that calculated by the following equation,
(3)
In Eq. (3), (Δt)' l.m. is to be L.M.T.D. in the temperature range of cooling water and vapor, but not so in that of cooling water and solution. This is because there exists a thermal resistance between the surface of the solution and its body.
From these considerations, the coefficient of heat transfer was obtained by the dimentional analysis, as follows:
(4)
Using Eq.(3), difference between vapor temperature and liquid temperature was obtained, and the time required for cooling the solution was determined by the use of Eqs.(3) and (4). Under certain assumptions, Equation (3) may be simplified as,
(5)