Tank jackets are used to heat and cool the contents of a storage tank or pressure vessel. That’s the simple definition of a tank jacket. A jacket is a cavity external to the vessel that permits the uniform exchange of heat between the fluid circulating in it and the walls of the vessel. Jacketed vessels can be employed as chemical reactors (to remove the elevated heat of reaction) or to reduce the viscosity of high viscous fluids (such as tar). Agitation can be also used in jacketed vessels to improve the homogeneity of the fluid properties (such as temperature or concentration).