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Transformer Installation and Maintenance
Published in Leonard L. Grigsby, Electric Power Transformer Engineering, 2017
Cold trap—The cold trap serves as a condensate trap located between transformer and vacuum pump or between degassing chamber and vacuum pump to trap oil and water vapors. These trapped vapors can then be collected and measured to determine the actual amount of moisture being removed from the transformer and insulating fluid by means of physical measurement of the condensate. Cold traps can be constructed with self-contained refrigeration units or can be mechanical traps utilizing liquid nitrogen or a dry ice and acetone mixture as the coolant.
Advances in Microwave Drying
Published in Arun S. Mujumdar, Hong-Wei Xiao, Advanced Drying Technologies for Foods, 2019
In order to further promote drying uniformity, Wang et al. (2013a) developed a newly laboratory-scale PSMFD apparatus at Jiangnan University, as shown in Figure 6.10. The apparatus can be used for FD, MFD, and PSMFD tests. During PSMFD test, the pressure range inside the drying chamber was held at 80 ± 5 Pa to 1.2 kPa by a vacuum pump. The pressure fluctuation was typically 800 Pa for spouting. The dried samples were spouted in the time interval of 10 min and held for 2 s. Nitrogen gas temperature and velocity in PSMFD were set at 25°C ± 1°C and 3.5 m/s. The temperature of the cold trap was −40°C to −45°C. Four microwave generators (2,450 MHz) were used in the drying, and the power output range of each magnetron was 0.1–0.6 kW. The bottom of the drying chamber was blocked with a silicon rubber stopper together with the gas distributor and fiber optic temperature probe in order to monitor the temperature of the dried sample. The main advantage of this equipment can solve the drying nonuniformity of the MFD process by using pneumatic pulse agitation. This equipment has been applied in the drying of different products. For example, PSMFD of stem lettuce slices shortened the total drying time by more than 20% compared to MFD. PSMFD had better quality such as lower color difference value, higher rehydration capacity, and greater hardness after rehydration (Wang et al., 2012b). Fresh duck egg white powder produced by PSMFD shortened the drying time by 50% compared to the conventional FD. Duck egg white powder dried by PSMFD presented good color and low apparent density (Wang et al., 2013a). PSMFD of banana cubes carried out at the microwave power of 1 W/g took 1 h longer than that at 2 and 3 W/g. Color and temperature distribution of banana cubes dried by PSMFD had good uniformity (Jiang et al., 2015). Therefore, PSMFD can further improve the drying uniformity.
Analysis of a pharmaceutical batch freeze dryer: resource consumption, hotspots, and factors for potential improvement
Published in Drying Technology, 2019
Ana Gabriela Renteria Gamiz, Pieter-Jan Van Bockstal, Steven De Meester, Thomas De Beer, Jos Corver, Jo Dewulf
Typically, the temperature of the shelf and subsequently the product is controlled by a thermal fluid that circulates within shelf channels that create a flow path. The fluid is pumped through the shelves and through heat exchangers where it is cooled down by the refrigeration system or heated up by the heater depending on the needs. The refrigeration system is also used to cool the cold trap which can reach temperatures of −85 °C. The cold trap is used to condense and freeze (deposition) the vapors produced due to sublimation during primary drying and desorption during secondary drying. Vapor condensation is desirable to avoid contamination of the vacuum pump used to decrease the chamber pressure. In Figure 1, a simplified scheme of a typical batch freeze dryer including its main components is represented.