Isobaric Expansion Engine Compressors: Thermodynamic Analysis of the Simplest Direct Vapor-Driven Compressors

Abstract

Isobaric expansion (IE) technology is a promising solution for mini- and medium-scale low-grade heat utilization. IE engines directly convert heat to mechanical energy and are particularly interesting as direct-acting, vapor-driven pumps and compressors. The elimination of multiple energy transformations, technical simplicity and the ability to use widely available low-grade heat (<100 °C) instead of fossil fuels are attractive features of this technology. The purpose of this paper was to present a new compression technology based on IE Worthington type engines, analyze the process analytically and numerically, and provide a first assessment of its potential. The simplest single- and double-acting schemes were considered for arbitrary low and high pressures of the compressed gas/vapor and driving vapor. In these schemes, the compressor piston was rigidly connected to that of an engine/driver. The vapor use efficiency of the driver process was characterized by the ratio of the network carried out in the cycle to the consumed mass of the driving vapor. The performed thermodynamic analysis showed how the vapor use efficiency depends on the process parameters. It was found that the efficiency of vapor use in the simplest schemes was low in comparison with the efficiency in pumps if the compressor work was much less than the pump work at the same pressure ratio. This occurred because the energy of the driving vapor was spent on the compression of the vapor itself. As a result, the thermal efficiency of the IE engine compressors was lower than that of the IE engine pumps. The difference was very large if the work of the engine feed pump was significant and no heat regeneration is applied. The results obtained are very useful for achieving improvements in this interesting technology, which will be reported in subsequent publications.

Isobaric Expansion Engines–Compressors: Thermodynamic Analysis of Multistage Vapor Driven Compressors

“…Therefore, arbitrary low and high driver pressures (𝑃 and 𝑃 ) can be utilized for a given set of low and high compressor pressures (𝑃 and 𝑃 ). If friction is neglected, the relationship between the pressures and areas of the piston ensuring uniform piston movement (excluding top and bottom dead centers) can be expressed as [31]: The processes occurring within the compressor and driver are described in reference [10]. The compressor's operation can be orchestrated by appropriately selecting the dimensions of the compressor and driver pistons and the high and low pressures of the driving vapor.…”

“…Therefore, arbitrary low and high driver pressures (P dL and P dH ) can be utilized for a given set of low and high compressor pressures (P cL and P cH ). If friction is neglected, the relationship between the pressures and areas of the piston ensuring uniform piston movement (excluding top and bottom dead centers) can be expressed as [31]:…”

“…A new vapor-driven reciprocating compressor based on IE engines has recently been presented, and a preliminary assessment of its feasibility has been carried out [31]. There are many potential applications for the presented technology.…”

“…The findings in reference [31] indicated that the driving vapor is utilized inefficiently in the simplest compressor configurations. This inefficiency arises because a significant portion of the driving vapor's energy is consumed by compressing the vapor itself.…”

Waste Heat Recovery Systems with Isobaric Expansion Technology Using Pure and Mixed Working Fluids

“…Afterwards, many aspects of IE-technology were investigated. Among them are problems of regeneration efficiency [12], as well as operation of IE engines as pumps [13] and compressors [14].…”