Coupled Heat and Mass Transfer during Crystallization of MgSO4 ...

Crystallization of MgSO 4 · 7H 2 O on a Cooled Surface Crystal Growth & Design, Vol. xxx, No. xx, XXXX Edifferent approaches all of which overlap perfectly well witheach other. These approaches were using the Image J programfor measuring the crystal size changes in time, weighing thecrystal amount at the end of the experiment, and also doingconcentration measurement in the beginning and at the end ofthe experiment and extracting the mass flux value from eq 10.The chemical potential difference in eq 15 was calculatedusing Pitzer model. 15 The various equations and the constantsneeded in the calculations are presented in the Appendix.Figure 3. Magnified view (figure is not drawn proportional to its origin)of the surface of Figure 2; k, fraction of the enthalpy of crystallizationcarried out via the cooled surface, see eq 21.The thickness of the salt (δ s ) growing into the liquid directionand the mass flux (J) of the crystals were estimated using fourResults and DiscussionIn Figure 4, single (a) and (c) MgSO 4 · 7H 2 O crystal photoson the TLC surface are presented. The transparency propertyof MgSO 4 · 7H 2 O crystals allows us to follow the temperatureprofiles of the TLC surface both on crystal-free and for thecrystal covered areas. Undistinguished crystal borders on thepost-processing temperature images (b) and (d) support this fact.The part of the heat (due to heat of crystallization) evolved inthe crystal side is transferred both under and near the bordersof the crystal on the TLC.Crystallization is a dynamic process in which molecules orions dissolve and absorb on the crystal surface simultaneouslyduring growth. Therefore warmer or colder temperature readingsunder the crystals compared to the surrounding is possible beforeFigure 4. (a, c) Picture of single crystals (labeled 1 to 7) on the TLC surface; (b, d) crystals post-processing temperature images on the TLCsurface; 1 pixel is 65 µm.