Thermodynamics deals with irreversible transformations of substances. Every thermodynamic property of a substance, as a function of two parameters describing its state, can be illustrated as a simply connected manifold. The term manifold stands for the Methods of Geometrical Representation of Thermodynamic Properties of Substances by Means of Surfaces. Generally, every transformation of a substance changes its energy (or enthalpy) by heat transfer and work done on it. All such changes (transformations) are considered to be irreversible and can be described using appropriate manifolds. Studies show that every transformation is associated with the degradation of energy. Such relations (between heat, work and other forms of energy or enthalpy) can be described by the Pfaff formulas and their integrations.

This article discusses the issue of irreversible energy degradation in heat transfer between two fluids. Irreversible heat transfer between separated fluids most often occurs through surface heat exchangers. All such processes are determined by convective heat transfer in thermal boundary layers and conduction through the wall. Consequently, entropy changes of fluids in heat and mass transfer can be observed in these layers. While the entropy rate of the heating fluid is negative and that of the heated medium is positive, the sum of entropy changes of all substances involved in the heat transfer process is always positive. These sums, known as entropy increase (entropy generation), can be interpreted as the measure of irreversible degradation of energy in heat transfer processes. The consequence of this degradation is that an arbitrary engine powered by the degraded (lower-temperature) heat flux will operate at a lower efficiency. The significance of this discussion relates especially to cases in power plants and cooling systems where surface heat exchangers are used. In the discussion proposed is the entropy increase as a criterion of irreversible energy degradation in heat transfer. Such introduced measure of effectiveness leads to an analysis of local overall heat transfer coefficient optimization on the cone-shaped manifold.

Pressure pulsations occurring in volumetric compressors manifold are still one of the most important problems in design and operation of compressor plants. The resulting vibrations may cause fatigue cracks and noise. Accuracy of the contemporary method is not sufficient in many cases. The methods for calculating pressure pulsation propagation in volumetric compressors manifolds are based on one-dimensional models. In one-dimensional models, the assumption is made that any installation element may be simplified and modeled as a straight pipe with given diameter and length or as a lumped volume. This simplification is usually sufficient in the case of small elements and long waves. In general, the geometry of the element shall be also considered. This may be done using two ways: experimental measurements of pressure pulsations, which lead to transmittance approximation for the investigated element, or CFD analysis and simulation for the acoustic manifold element. In this paper, a new method based on Computational Fluid Dynamics (CFD) simulation is presented. The main idea is to use CFD simulation instead of experimental measurements. The impulse flow excitation is introduced as a source. The results of simulation are averaged in the inlet and outlet cross sections, so time only dependent functions at the inlet and outlet of the simulated element are determined. The transmittances of special form are introduced. On the basis of introduced transmittances, the generalized four pole matrix elements and impedance matrix elements may be calculated. The method has been verified on the basis of experimental measurements.