An alternative stack arrangement for thermoacoustic heat pumps and refrigerators

Abstract

One major setback of thermoacoustic engines-when comparing them with ''conventional'' heat-engines or refrigerators-is their low power density. In this work a new attempt for achieving higher power densities was undertaken. The stack of a thermoacoustic engine, which usually consists of parallel plates much longer than the acoustic displacement amplitude, was substituted by parallel-plate segments, which were only a fraction of the displacement amplitude long and randomly orientated to each other. This alternative stack arrangement was expected to benefit from improved heat transfer characteristics and an anisotropic thermal conductivity. A simplified numerical model confirmed these expectations. Experiments with a thermoacoustic heat pump were carried out. The experimental results qualitatively agreed with the numerical model. At most, the power density was raised by approximately 50%. The coefficient of performance-defined as useful heat output divided by work input-increased by approximately one-third.

Effects of variation in working fluids and operating conditions on the performance of a thermoacoustic refrigerator

“…Tijani [5] calculated the cooling power and the acoustic work using Eq. (76) and (80) of Swift [8]. The present numerical modeling result is for an isothermal stack plate of spacing y 0 =3.33δ k , a frequency of 48.99 Hz, and DR= 1.7%.…”

“…While these thermoacoustic devices are environmentally benign, simple in design and maintenance free the major problem associated with these devices is their low thermal efficiency (which is limited to 20%). Several approaches have been examined to improve the efficiency of such devices (Tijani [5], Poese and Garrett [6], Adeff et al [7], Bösel et al [8], Tasnim [9] etc.). One approach to increase the performance (power density) of a thermoacoustic device is to increase the DR which is the ratio of acoustic pressure amplitude to mean pressure.…”

Development and study of stack for thermoacoustic refrigerator

“…It was also experimentally proved in [3] that switch from continuous stack to the one consisting of many segments in the same length helps increase the density of heat flow transferable in the stack. In this context, further investigations are recommended: 1) it is necessary to determine the length of the element of the discontinuous stack because the optimum length was not determined (segments longer than 1/3 of the acoustic displacement amplitude were used, but it is advisable to try to reduce it to lower values, say, to 1/10 of the acoustic displacement amplitude);…”

“…Analysis has shown [3] that switch from packet of parallel long plates to structures having fins, pins, etc., makes it possible to increase the density of heat flow transferable in the stack. It was also experimentally proved in [3] that switch from continuous stack to the one consisting of many segments in the same length helps increase the density of heat flow transferable in the stack.…”

Thermoacoustic energy analysis of transverse-pin and tortuous stacks at large acoustic displacements

“…Stacks with non-uniform cross-sectional geometry comprise wire mesh screens [4], rigid foams [5,6], intermittent plate stacks [7], wools [8], and transverse-pin arrays [9]. Some of these stacks demonstrated a potential of higher performance in comparison with regular stacks that have longitudinal orientation of solid constituents.…”