How Low Can You Go?
Plants must evaluate a number of design factors when operating heat exchangers at ultra-low temperatures
Pharmaceutical, biotechnology and specialty chemical companies are challenging the heat transfer community to provide solutions that enable critical processes to operate at extremely cold temperatures. In the past, it was adequate to operate at temperatures as low as -80°F (-62.2°C). Now industry continues to push for colder temperatures. Low-temperature heat transfer fluid manufacturers and heat transfer companies are being asked to provide systems that can run reliably at -148°F to -184°F (-100°C to -120°C).
Why such low temperatures? For certain chemical reactions the rule of thumb is that the reaction time is increased by a factor of two for each 18°F (10°C) reduction in operating temperature. If the temperature is too high, the reaction time is very quick, adversely impacting quality and repeatability of results.
A number of design considerations must be taken into account when operating at these extreme conditions. This article reviews the outcome of recent research of heat exchanger design and heat transfer fluid performance for lowtemperature operation. It defines practical low-temperature operation of the various heat transfer fluids for a given type of heat exchanger. The performance characteristics of the different fluids are discussed, as is the performance of heat exchangers as heat transfer fluids begin to freeze within them.
Common low-temperature applications in a pharmaceutical plant are reactor jacket cooling and vacuum freeze drying (lyophilization). A heat transfer system that can provide consistent heat transfer fluid temperature is essential for product quality and repeatable results from batch to batch....