The paper deals with the visualization of temperature fields in the vicinity of profiled heat transfer surfaces and a subsequent analysis of local values of Nusselt numbers by forced air convection in an experimental channel. Holographic interferometry was used for visualizing the temperature fields. Experiments were carried out at Re 462 up to 2338 at the distances between heat transfer surfaces of 0.025 m and 0.035 m. Temperature contours were determined from the obtained images of holographic interferograms of temperature fields and the local values of Nusselt numbers along the profiled surface for x/s = 0 up to x/s = 1.25 were calculated from them. A significant effect of the profiled surface on the local values of Nusselt numbers can be observed from the obtained results.

Laminar free convection heat transfer from a heated cylinder and tube arrays is studied numerically to obtain the local and average Nusselt numbers. To verify the numerical simulations, the Nusselt numbers for a single cylinder were compared to other authors for the Rayleigh numbers of 103 and 104. Furthermore, the vertically arranged heated tube arrays 4 × 1 and 4 × 2 with the tube ratio spacing SV/D = 2 were considered, and obtained average Nusselt numbers were compared to the existing correlating equations. A good agreement of the average Nusselt numbers for the single cylinder and the bottom tube of the 4 × 1 tube array is proved. On the other hand, the bottom tubes of the 4 × 2 tube array affect each other, and the Nusselt numbers have a different course compared to the single cylinder. The temperature fields for the tube array 4 × 4 in basic, concave, and convex configurations are studied, and new correlating equations were determined. The simulations were done for the Rayleigh numbers in the range of 1.3 × 104 to 3.7 × 104 with a tube ratio spacing S/D of 2, 2.5, and 3. On the basis of the results, the average Nusselt numbers increase with the Rayleigh numbers and tube spacing increasing. The average Nusselt number and total heat flux density for the convex configuration increase compared to the base one; on the other hand, the average Nusselt number decreases for the concave one. The results are applicable to the tube heaters constructional design in order to heat the ambient air effectively.

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This paper deals with the visualization and analysis of interaction of a cutting wedge disintegrator with plastic at low loads. For exploratory research, a contactless optical holographic interferometry method was used, allowing a comprehensive picture of the stress state when opening microcracks. An experimental model was set up for the purposes of the research. The structure of the model as well as its geometric parameters had to comply with the applied optical method. The method of holographic interferometry enabled us to record even the initial stages of the crack. Pictures of holographic interferograms allowed us to observe stress fields on the cutting wedge as well as on the loaded body in the form of interference fringes. In order to record the interferograms, we used the method of two exposures so that we gained double-exposure interferograms, which represent the state of the object during the second exposure. The first exposure was caused by superposition of object-related and reference wave after the object was subjected to a load; the second exposure occurred after the load was removed. We used quantitative analysis to determine stress intensity coefficients from holographic interferograms as followed by the calculation of stresses with respect to axes x and y . The analysis was done for loading forces 1.57 N and 3.14 N. As the load applied to the cutting material was increasing, the density of interference fringes was increasing, too.

The paper deals with the research of temperature fields in the proximity of heated pipes arranged above each other in a natural air convection. The holographic interferometry method was used for the visualization of temperature fields. The experiments were made with pipes, diameter of 20 mm, length 200 mm, spacing two-dimensional (2D) at surface temperatures of 40 °C, 50 °C, and 60 °C, with the vertical arrangement of the pipes as well as with the horizontal shift of their centers by 1/4D and 1/2D (on a surface temperature of 50 °C). Temperature profiles were determined from the experimentally obtained images of temperature fields, and local parameters of heat transfer were calculated. Under the same marginal and geometric conditions, computational fluid dynamics (CFD) simulations of temperature fields were performed as well, while the results (temperature fields, local and mean parameters of heat transfer) were also calculated for various distances between the pipe centers (1D, 2D, and 3D). From the obtained experimental results and CFD simulation results, it is possible to observe the impact of the arrangement and spacing of pipes on heat transfer parameters. The achieved results imply the change in the spacing of the pipes has a greater impact on heat transfer parameters in the bundle of heated pipes located above each other than a moderate horizontal shift of their centers.