The effect of mean pressure on the performance of a single-stage heat-driven thermoacoustic cooler

Waste heat is an environmental issue in the world. There are some technologies that can be used to recovery the waste heat, one of which is thermoacoustic cooler technology. Thermoacoustic technology can be divided into two parts: one is thermoacoustic engine and cooler. To design the cooler system having high efficiency and lower onset heating temperature, the effect of mean pressure is investigated. By increasing mean pressure from 0.5 to 3 MPa, the heating temperature generating acoustic power can be decreased from 831 to 580 K. Moreover, 15% of Thermodynamic upper limit value of the whole cooler system is achieved.

Experimental Study of Condensation in Different 3D Printed Regenerators in a Thermoacoustic Cooler

Thermoacoustics (TA) deals with the conversion of heat into sound and vice versa. The device that transfers energy from a low temperature reservoir to a high temperature one by utilizing acoustic work is called TA cooler (TAC). The main components of a typical TA device are a resonator, a regenerator (stack of parallel plates) and two heat exchangers. The thermoacoustic phenomenon takes place in the stack when a nonzero temperature gradient imposed along the regenerator (i.e. parallel to the direction of the sound wave propagation) interacts with the sound wave oscillations. The low temperature at the cold of TAC can be used to condense humid water from the air and also reduce the moisture in the air at some humid areas. In the current study, the high intensity sound waves was produced by the speaker to drive a TA cooler to produce cooling power at a cold temperature of around 18°C. The drainage of condensate in the regenerator is the key for the system performance, because if the porous structure will be blocked by the condensate, TA phenomenon cannot take place in the regenerator. This work is dedicated to investigate the effect from temperature gradient created in TAC for condensation enhancement. 3D printer was used to design and fabricate different structures of regenerator, and then the systematic cooling capacity was measured and compared with different designs of regenerators. Energy balance was also discussed for each type of regenerator. The potential application of this investigation can be an autonomous thermoacoustic cooler system for water harvesting in arid areas. This work can be used to evaluate how the TA effect can be affected by the condensation if humid air is used as the working fluid.

Feasibility Study on Thermoacoustic Cooling for Low-Power Handheld Electronic Devices

A feasibility study on developing a small-scale thermoacoustic cooler based on form and size factors for a typical cell phone is presented. First, an approximate analytical model for the temperature difference was derived using the linear theory of thermoacoustics. Cooling performance could be reasonably predicted with the analytical model proposed in this study. Air and helium as the working gases and the operating frequencies of 3 kHz for air and 9.2 kHz for helium are considered within the scope of typical cell phone configurations. A stack as a core of thermoacoustic cooler is designed to accomplish the most effective performance based on normalized parameters. For the 57 mm thermoacoustic cooler operating at 3 kHz with air, the maximum temperature difference of 23.13 °C across the stack in the resonance cavity is achieved with a drive ratio of 2% with air as the medium and Mylar as a stack material. This temperature difference varies depending on the stack placement along the length of the resonance cavity, but the maximum difference was achieved when the center of stack is placed at around 7 mm away from the driver end. The drive ratio, which is proportional to the power required to produce the thermoacoustic effect, is shown to be directly related to the cooling performance achieved by thermoacoustic drivers. For example, while a drive ratio of 2% results in a temperature difference of over 20 °C at its maximum, a drive ratio of 0.2% causes a temperature difference less than 1 °C. This will be one of hardware issues to be considered in making commercially viable products. The possibility of omitting heat exchangers in the thermoacoustic cooler is investigated considering their manufacturing cost and the relatively minute improvement they bring to overall cooling for small-scale systems. The numerical result of the thermoacoustic cooling system based on design environment for low-amplitude thermoacoustic energy conversion (DeltaEC) is compared to the theoretical result. Discrepancies between the two results exist in the range of 10–15% mainly due to the limitation imposed by short stack considerations and the linear theory of thermoacoustics.