The color exhibited by tungsten trioxide (WO₃) can be associated with both its stoichiometry and crystallinity. Correlation between the color exhibited by WO₃ powders and their purity and crystalline properties is reported in this paper. The WO₃ powders were deposited by evaporation of tungsten trioxide from the surface of a tungsten filament. The WO₃ powders exhibited three different shades of blue: navy, royal, and sky. The color of the WO₃ powders changed to white after thermal treatment at 500 °C for 30 min in an ambient atmosphere. Raman analyses showed that transition from amorphous to crystalline WO₃ started when the powders exhibited navy-blue color and ended when WO₃ powders exhibited a white color. Scanning electron microscopy analysis showed particle agglomeration characteristics in all WO₃ powders, even after they were thermally treated. The mechanism of deposition of WO₃ from the tungsten filament was suggested to be governed by thermal evaporation of tungsten trioxide from the surface of the oxidized tungsten filament.

The studies of nested helical coil heat exchangers for an absorption heat transformer are very limited, although this arrangement has a greater heat transfer area in a smaller volume. The heat exchangers are vertically placed to develop the desorption, condensation, evaporation and absorption processes by falling film mode. The usage of energy from point of qualitative view in these times is mandatory, due to the fossil fuels reduction and pollution. This experimental study analyses the behavior the nested helical coils heat exchangers through the first and second law of thermodynamics. The physical and chemical exergy for the main components and whole system is calculated by using the conventional method. All the experimental tests are carried out by varying the source temperature from 343.15 to 358.15 K with heating mass flow rate in the generator between 0.07 and 0.13 kg/s. For this study, the condensation and absorption processes reach the highest exergy destruction at high temperatures, while the solution heat exchanger presents the lowest irreversibility. The exergy coefficient of performance always improves when the supplied heat in the generator increases owing to the heating mass flow rate and temperature, however there is an increment considerably of total irreversibility at 349.15 K.