Design and Construction of a Four-Stage Travelling-Wave Thermo-Acoustic System for Power Generation

This work describes the design and construction of a four-stage travelling-wave thermo-acoustic system for electricity generation. Thermo-acoustic devices are systems which utilized what is known as thermo-acoustic effect to convert thermal energy to acoustic energy or vice versa. Thermo-acoustic conversion consists of using a sound-wave for the transfer of heat from a low to high temperature medium or the use of heat energy to generate a sound wave. Both the absence of moving parts and simplicity of thermo-acoustic systems demonstrate that they have the potential for developing low-cost power generators. Many existing studies have pointed out the acoustic-to-electric potential of thermo-acoustic systems. Hence in this work, a thermo-acoustic system have been developed in order to get an insight into the designing of the system with respect to the geometrical configuration. The thermo-acoustic system core consists of three crucial parts: hot heat exchanger, regenerator and cold heat exchanger, where the thermo-acoustic processes take place. The total length of the travelling-wave system is 3560 mm and each engine stage is placed at a mutual distance of 640 mm. The engine stage is having four cartridge heaters connected in parallel at one side of the regenerator. Heat is transferred to the regenerator by conduction through copper strip. Between the hot heat exchanger and the regenerator, there is some holes where thermocouples can be placed for temperature measurements. The maximum operating temperature for the hot heat exchanger is between 650 and 1000. Copper strip has been selected because of its high thermal conductivity properties. Copper strips is cut into 200 mm, folded around a bench vice to obtain a 90º angle, drilled and placed over the cartridge heaters inside the regenerator tube. Water with ambient temperature is used to cool the system which is fed to the ambient heat exchanger. The circulation water used for the ambient heat exchanger is supplied from a tape through tubing transparent pipes of 6 mm. Copper strips (5×20×80 mm) are drilled and placed over the tubes touching the regenerator to ensure proper heat conduction from the regenerator to the water flow. The honeycomb ceramic has been selected for this design, due to its good thermal contact, availability and low thermal conductivity. The honeycomb ceramic in the square shape is cut by (85 × 95 mm) and sandwiched between both heat exchangers. The honeycomb ceramic regenerator used in this experimental research has 400 CPSI, with square spores. The engine core has four flanges. Each side of the regenerator tube has two flanges that are connect by four bolts and between these flanges there is a gasket of 5 mm in thickness. Flange gasket are used to create a static seal between two flanges faces, at various operating conditions, with varied pressure and temperature ratings. This gasket fills the microscopic spaces and irregularities of the flange faces, and then it forms a seal that is designed to keep gases.. An audio loudspeaker has been used to generate acoustic power. This experiment was conducted at atmospheric pressure and ambient room temperature. The working fluid used for the thermo-acoustic system was air. The maximum recorded average sound pressure level (SPL) is 219.3 dB corresponding to an output voltage of 4.218 V. The onset temperature difference across the regenerator was determined to be 200.19 at the highest heating power of 190 W. The time taken by the engines to produce sound was determined to be 105 seconds. Clarity about the material selection, constraints and calculation of the geometrical configuration describing the device constitute the main contribution of this work