Noise is one important factor for product performance of compressor & refrigerator. Products must satisfy with not only meeting the national standards but also the consumers’ gradually increasing requirements for sound quality because of market competition. Near field acoustical holography is a high-resolution imaging technique for reconstructing the vibro-acoustical field that will guide to locate noise source and understand the relationship between structure vibration and sound radiation. Near field acoustical holography method based on the Equivalent Source Method is applied to analyze the vibro-acoustical characteristics of both compressor and refrigerator. Equivalent Source Method is applicable for arbitrary shaped vibrating surface, presenting calculation faster than the Boundary Element Method, and better than the Helmholtz Equation Least Square Method, especially for elongated and planar sources. In virtue of this approach, velocity & sound pressure distribution over the sample geometry of compressor & refrigerator were gotten at critical frequencies, so main noise sources were located.
In this paper, an algebraic formulation which expresses the dimensionless rate of entropy generation as a function of the heat exchanger geometry (number of transfer units), the thermal-hydraulic characteristics (friction factor and Colburn j-factor), and the operating conditions (heat transfer duty, core velocity, coil surface temperature, and fluid properties) is derived. It is shown that for heat exchanger with constant wall temperature (i.e., condensers and evaporators), there does exist a particular number of transfer units which minimizes the dimensionless rate of entropy generation. An algebraic expression for the optimum heat exchanger effectiveness, based on the working conditions, heat exchanger geometry and fluid properties, is also presented. The theoretical analysis led to the conclusion that a high effectiveness heat exchanger does not necessarily provide the best thermal-hydraulic design.