Mark Worall

An experimental investigation of steam ejectors for applications in jet-pump refrigerators powered by low-grade heat

Abstract The jet-pump refrigerator cycle offers a low-capital-cost solution for utilizing low-grade waste heat in the production of cooling for buildings and process refrigeration. The heart of the jet-pump refrigerator is an ejector, the performance of which strongly determines the thermal efficiency of the cycle. This paper describes and evaluates the results of an experimental investigation into the operation of ejectors primarily for use in jet-pump refrigerators. The construction of a steam-steam ejector test facility and experimental method are described. Experimental results are provided concerning the effects of primary nozzle exit position within the mixing-entrainment section, primary nozzle exit and diffuser throat areas. The causes and effects of flow instability under conditions of high secondary pressure ratio are also discussed and methods of increasing the critical condenser pressure are identified and rated in order of effect.

A variable buoyancy system for deep ocean vehicles

A variable buoyancy system has been developed for underwater vehicles operating deep in the ocean. This paper reports on the design, testing and development of the system. The system was designed to change buoyancy at up to 1 l/min at a depth down to 6000 m. The results showed that the system worked at its design specifications after modification but that friction losses resulted in a relatively low efficiency of around 35 % at low working depth, but efficiency increased with increasing depth to about 70% at 6000 m. Efficiency could be increased further with redesign or with changes in specification.

Homeostasis in nature: Nest building termites and intelligent buildings

Homeostasis is a process that counteracts out-of-balance fluxes of energy and matter so that a variety or conditions can be maintained. In buildings, we use mechanical assistance to counteract out-of-balance fluxes to achieve comfortable living conditions. Many species in nature have evolved behaviours that are homeostatic, and we might learn alternative strategies by studying them. The mound building termites, Macrotermes, construct sophisticated structures that enable the metabolic demand of the nest to be met by intercepting the prevailing wind. Ventilation of the mound and nest is ‘tidal’ and the internal structure is vascularized, so by mimicking tidal and vascularized systems in our own natural ventilation designs we could improve performance and effectiveness. The principle of homeostasis could be used as a concept to develop building elements that adapt to changes in environmental conditions and indoor demands. Distributed communication and control based on ‘stigmergy’ may enable engineers to design systems that required less energy and computing power. Additive construction methods give us freedom to design more flexible and natural looking building forms within the constraints of homeostasis and to integrate sophisticated internal configurations, with integrated adaptive and responsive capabilities.