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In this paper, the increases in heat transfer intensity in a square tube as well as the pressure losses from 3D printed elements are experimentally measured. To measure the heat transfer coefficient, we chose a dynamic, thermal oscillation method (or TOIRT method), which we validated on a well-known experiment of water flow in a pipe and compared the data with the most frequently cited Gnielinski correlation with Hausen correction. A twisted tape with different pitches was chosen as an element and its pressure loss was measured simultaneously, which we converted to a Fanning friction factor. We determined the thermal enhancemet factor by the ratio of heat transfer gain and pressure loss and found the optimal helix pitch $$p = 0.87h$$ .

The paper deals with a static and dynamic calibration of selected wide-range thermochromic liquid crystals (TLC - SolarDust 24C), which are very easy to ingest and can provide accurate information on the temperature distribution on different surfaces. Static calibration problems, such as TLC illumination angle or illumination intensity, are solved and conclusions are drawn for the application of such a measurement. Dynamic experiments also indicate a certain time delay (around 50 ms) of the applied TLC measurement layer, which is very important to know for dynamic experimental methods, but the error and inaccuracy of the experiment is too high to draw conclusions.

This paper presents a new non-contact transient method for measuring the heat transfer coefficient. The proposed method is based on measuring the temperature response of the surface temperature to the heat flux irradiating the same surface, which is affected by the heat transfer coefficient on the back of the surface. The theoretical solution of this problem together with the measured experimental data then enables an evaluation to be made of the local value of the heat transfer coefficient and the corresponding integral value. We present the theoretical foundations, a description of the required experimental setup, the methodology for evaluating the heat transfer coefficient, and an error analysis. The results of forced convection inside the tubes and the incident geometry of the impinging jets in comparison with the experimental results from the literature are presented as validation experiments. Very good agreement is demonstrated and the experimental results obtained by the proposed method lie in the standard range of 10%.

This article deals with the derivation of the temperature response of the finite thickness wall, which is heated by heat flow, as a possibility to measure the local values of the heat transfer coefficient with a very high spatial resolution. In addition to its own experimental measurement technique, it is also possible to use this derivation to describe the gradual heating of the wall while using the temperature oscillation (TOIRT) method for the heat transfer measurement. The system of the partial differential equations and the boundary and initial conditions is solved by a transformation into Laplace’s space, where the task is easier to solve. At the end of the article, the results of the analytical solution are compared with a numerical solution of this problem.

The heat transfer coeffcient is one of the most important parameters in the design of apparatuses in which convective heat transport takes place. Classical direct methods based on determining basic thermal quantities can be used for measuring heat transfer coeffcients. Another option is to measure concentrations, electric current or other quantities that can be transformed to thermal quantities using the analogy between heat and mass transport. The temperature-oscillation method is less frequently used, although the theoretical basis of the method dates back to 1997, and although the method has the major advantage that the heat transfer coeffcients can be measured without making any contact with the heat transfer surface. In the temperatureoscillation method, the heat transfer surface is exposed to an oscillating heat flux, and the temperature response on this surface can be measured by a contactless method (e.g. infra-red thermography). The heat transfercoeffcients can be determined on the basis of mathematical relations between the oscillating heat flux and the temperature response. However, the method depends on an appropriate method for processing the measured data when it is necessary to correct some conditions that are not included in the mathematical model. This paper evaluates the impact of processing the experimental data on the resulting heat transfer coeffcients in one of the basic geometrical configurations – the flow of a liquid in a pipe with a circular cross section. In this paper, we present the results of a comparison of real experiments based on the temperature oscillation method and numerical modeling of the heat transfer in this geometry, using the ANSYS CFD commercial system.

This contribution deals with the investigation of the bovine collagen flow in the rectangular slit. The slightly compressible collagen liquid (9.5% mass fraction of native bovine collagen in water) was extruded by capillary rheometer of given geometry. A piston pushed the collagen sample from a container to the rectangular capillary. The extrusion rheometer is equipped by pressure sensors mounted at wall of capillary and manually adjusted hydraulic drive enables continuous variation of the piston velocity. The pressure profiles are measured in five places along the capillary simultaneously with increasing shear rate within the range from 1500 to 5000 s−1. It is possible to identify non-elastic shear flow characteristic and the compressibility of collagen matter.

The Temperature Oscillation Infra-Red Thermography (TOIRT) was used to measure convective heat transfer coefficients at the inner vertical wall of an agitated and baffled vessel. Two impellers were used: an axial six-blade impeller with pitched blades and the Rushton turbine. The TOIRT method represents an indirect method based on measuring the phase shift between the oscillating heat flux applied to one side of the heat transfer surface and the wall temperature response monitored by a contactless infra-red camera at the same side. On the basis of this phase shift, the TOIRT method can indirectly evaluate the heat transfer coefficient on the other side of the heat transfer surface. Two forms of experimental results are presented in this paper. The first one describes graphical dependencies of the local Nusselt number on the dimensionless distance from the vessel bottom for various Reynolds numbers. The second form describes the mean Nusselt number along the wall as a function of the Reynolds number.

Temperature Oscillation Infra-Red Thermography (TOIRT) method was used to measure heat transfer coefficients between a at surface and a confined impinging jet generated by an impeller in a difusor and baffled vessel. The TOIRT method is based on measuring a phase-lag between the oscillating heat flux applied to the heat transfer surface and the surface temperature response using a contactless infra-red camera. The phase lag is in a direct relationship with the heat transfer coefficient.