ABSTRACT
The experimental free-piston Stirling cooler was described in a previous
article and has now been improved. A sieve layer was added to the displacer
(regenerator), which significantly enhanced the cooling performance of the
cooler. A two-way analysis of variance test was used to confirm the optimal
conditions (the type of mesh and thickness of the sieve layer) of the modified
displacer, which was used in butter churning experiments. The results showed
that only the thickness of the sieve layer had a statistically significant main
effect on the cooling performance of the Stirling cooler. A comparison of the
efficiency of butter churning using the original and modified displacer showed
that with the modified displacer, butter clusters formed rapidly and that the
quality of the butter was improved. Differential scanning calorimetry analysis
showed that although the two types of butter cluster produced using the
original and modified displacers had the same configuration, the content of fat
and water was different. The results showed that the mass of the butter cluster
manufactured with 25% fat content cream is higher than that of the butter
cluster manufactured using 15 and 35% fat content cream. The results showed
that the production of butter with more than 80% fat content seemed feasible.