Any sudden temperature change on either glass or jacket side can result in damage to the glasslining and should be avoided. Most damaging thermal shocks are caused by splashing of cold products on to a hot glass surface. This causes formation of fine surface cracks which lead to glasslining failure. Most thermal shock damage results in flaking of the lining in relatively small but thick pieces of glass with a characteristic shape.

Guideline for maximum allowable temperature difference are given in adjoining figure 6. The left half of the chart gives maximum & minimum temperature of fluids which are introduced in the jacket for various temperature of products in the reactor. e.g. if the temp. of product & the glass wall is 140 oc, the temp. of fluid introduced in jacket should be between - 15 oc & 255 oc.

The right half of the figure gives maximum & minimum temp. of products which are charged in the reactor for various temperature of glass and heating / cooling fluid in the jacket. e.g. if the temp. of jacket fluid & the glass wall is 180 oc, the temp. of product charged in reactor should be between 50 oc & 255 oc.

However, for safe use of the equipment, 80% of figures given in the table should be used as a guideline.

Thermal Conductivity

Steel allows the glass lining to be kept relatively thin compared to self-supporting glass equipment. Thus, the low thermal conductivity of the glass is counter-balanced by the high heat transfer coefficient of the steel. Due to the chemical bond between glass and steel, no interface heat transfer resistance needs to be taken into account. Figure 7 gives the values of Overall heat transfer coefficient for various heating and cooling conditions