A Novel Isothermal Compression Method for Energy Conservation in Fluid Power Systems

Abstract

Reducing carbon emissions is an urgent problem around the world while facing the energy and environmental crises. Whatever progress has been made in renewable energy research, efforts made to energy-saving technology is always necessary. The energy consumption from fluid power systems of industrial processes is considerable, especially for pneumatic systems. A novel isothermal compression method was proposed to lower the energy consumption of compressors. A porous medium was introduced to compose an isothermal piston. The porous medium was located beneath a conventional piston, and gradually immerged into the liquid during compression. The compression heat was absorbed by the porous medium, and finally conducted with the liquid at the chamber bottom. The heat transfer can be significantly enhanced due to the large surface area of the porous medium. As the liquid has a large heat capacity, the liquid temperature can maintain constant through circulation outside. This create near-isothermal compression, which minimizes energy loss in the form of heat, which cannot be recovered. There will be mass loss of the air due to dissolution and leakage. Therefore, the dissolution and leakage amount of gas are compensated for in this method. Gas is dissolved into liquid with the pressure increasing, which leads to mass loss of the gas. With a pressure ratio of 4:1 and a rotational speed of 100 rpm, the isothermal piston decreased the energy consumption by 45% over the conventional reciprocation piston. This gain was accomplished by increasing the heat transfer during the gas compression by increasing the surface area to volume ratio in the compression chamber. Frictional forces between the porous medium and liquid was presented. Work to overcome the frictional forces is negligible (0.21% of the total compression work) under the current operating condition.

Influence of Rotational Speed on Isothermal Piston Compression System

“…The isothermal piston compression system was discussed in our former studies [ 28 , 29 ]. Compression work is the work produced by volume change.…”

“…An isothermal piston is a kind of device that can achieve isothermal compression, and the performance of an isothermal piston was discussed in our former study [ 28 , 29 ]. It was verified that the isothermal piston can lower the air temperature significantly, but the resistance between the isothermal piston and liquid was introduced causing additional energy input.…”

Anaerobic Digestion for Producing Renewable Energy—The Evolution of This Technology in a New Uncertain Scenario

“…Developing and evaluating new methods for reducing energy consumption is of great relevance. An example of the different fields where energy efficiency can be improved is the technological development of Ren et al [ 180 ], who proposed a novel isothermal compression method to lower energy consumption by designing an isothermal piston where a porous medium was placed. The design allows one to absorb the compression heat, and this heat is then conducted through the liquid at the chamber bottom.…”

Theoretical study on the application of isothermal compression technology in vapor‐compression refrigeration systems with an isothermal piston

“…The pump in the system can exchange heat with the external heat exchanger through liquid circulation in practical applications and dissipate heat to the environment. 26 As indicated in Figure 1, this is a traditional single-loop vapor-compression refrigeration cycle (VRC) system composed of a condenser, evaporator, compressor, expansion valve, and internal heat exchanger. In a VRC system, an improved vapor-compression refrigeration cycle (ISO-VRC) system can be obtained by employing an isothermal piston to optimize the refrigeration compressor, which ensures that the pressure ratio of the refrigeration compressor effectively reduces its exhaust temperature, improves the efficiency of the refrigeration compressor, and improves the COP of the system.…”