Cryogenics

A broad term describing the development of technologies operating, or producing, low-temperatures is “cryogenics.” Many fascinating phenomena occur when materials are cooled to temperatures not found in the earth environment. Instruments that operate in space are one example of devices that operate in a cryogenic regime. A central engineering theme in cryogenic work is heat transfer and often requires detailed designs and high vacuums to either augment or reduce heat fluxes. In the lab, closed-cycle cryocoolers are used with vacuum chambers to create space-like environments (10-7 torr vacuum, and temperature ~ 3 K). Currently magnetic refrigeration, superconducting magnets, cryogenic actuators, and cryofuel storage tanks are some of the cryogenic technologies being used or developed.

Thermoacoustics

Thermoacoustic energy conversion is a process for heat-work conversion. Engines convert heat energy into high amplitude acoustic waves and subsequently into electric power. One of the advantages of this approach is that heat is converted to work with no moving parts making the engine reliable and maintenance free. Heat may be provided by renewable sources (sun, earth), by combusting fuel such as natural gas or biomass, or by utilizing waste heat. The temperature difference needed for a device to start producing acoustic power depends on the design and operating conditions, but it can be relatively low compared to other heat engines. The technology has significant potential for increasing energy system efficiency through waste-heat utilization for mobile, distributed, or remote combined heat and power generation.

One of the current challenges with using thermoacoustic generators driven by waste-heat is creating an efficient coupling between the heat source and the thermoacoustic engine. To maximize efficiency, the temperature of the heat input should be high; however, poor thermal transport between the waste-heat source can lead to temperature a decrease due to limited overall transfer coefficient. Waste-heat is often low-grade, hence, thermal efficiency may already be limited by the source temperature. Novel ways to solve this challenge are being investigated.