Pulse jet orchard heater system development: Part I. Design, construction, and optimization.

摘要

The objective of this six-year project, conducted in the USA, was to develop a more efficient and effective supplemental orchard field heater technology. In addition to being low-cost and mobile, these devices should be useable with or without wind machines, reduce labour requirements, and greatly reduce air pollutants compared to conventional orchard heating systems. The new generation orchard heaters that were developed in this process are portable, auto-regulating, horizontal pulse jet engines (combustors) with no moving parts. These devices utilize air ejector technology to reduce the temperature of the high-velocity combustion stream by thoroughly mixing it with the surrounding ambient (cold) air, producing a net effective temperature increase of only 2 degrees C to 5 degrees C above ambient. Buoyant forces of warm air are therefore small, and fewer heaters would be needed. The design achieved pressure oscillations that were free of combustion instabilities, and amplitudes were maximized for high exhaust jet velocities for deep hot jet penetration and mixing into the surrounding cold air. The overall size and weight of the heater system were minimized while maintaining optimum operation. Finally, anti-phase operation of paired heaters for noise level reduction from 130 dB to near 75 dB was achieved by implementing optimized silencing plenums at the inlet and exhaust of the paired heaters.