## 1 Introduction
The higher vapour quality cases were more sensitive to the mass flux than lower vapour quality cases, except at low heat flux conditions. For all other heat fluxes, the heat transfer coefficient was found to be independent of the vapour quality, except when the mass flux was high, where an increase in the vapour quality resulted in improved heat transfer coefficients. The authors of [3] focused on experimental boiling heat transfer during the R-245 fa flow in a small circular channel. In the test section, there was a horizontal polyimide tube of 2.689 mm inner diameter and 285 mm long, heated by a counter-current water flow in an annulus around the test tube. Mass fluxes ranged from 100 to 500 kg/(m\({}^{2}\)s) and heat fluxes from 15 to 55 kW/m\({}^{2}\). It was noticed that a higher mass flux resulted in a higher heat transfer coefficient. At a mass flux of 100 kg/(m\({}^{2}\)s), the vapour quality had a negligible effect on the heat transfer coefficient. Heat flux did not have a noticeable effect. Furthermore, the authors claimed that increasing the saturation temperature had an almost negligible effect on the heat transfer coefficient at a mass flux of 200 kg/(m\({}^{2}\)s) and a heat flux of 15 kW/m\({}^{2}\) and at higher mass and heat fluxes the heat transfer coefficient was lowered with increasing temperature. The works [4; 5; 6] refer to boiling heat transfer in an asymmetrically heated minichannels. The article [4] describes the results of subcooled flow boiling heat transfer in a group of five 1 mm deep in several spatial orientations. The heat transfer problem was solved using the Trefftz method and the FEM with Trefftz type basis functions. The main objective of [5] was the mathematical modelling of the time-dependent heat transfer processes during FC-72 flow boiling in a minichannel heat sink. Three mathematical methods were applied in the calculations: the FEM with Trefftz type basis functions, the Classical Trefftz Method and the Hybrid Picard-Trefftz Method. The authors of [6] focused on studying boiling heat transfer during the cooling liquid flow (FC-72, HFE-649, HFE-70 00 and HFE-7100), along a single depth of 1.7 mm, vertical or horizontal oriented minichannel. The inverse heat conduction problem in the heated wall was solved by the Finite Element Method with shape functions based on the Hermite interpolation and the Trefftz functions. There are well-known commercial computational fluid dynamics (CFD) programs. The most popular are the following: ANSYS CFX/Fluent [7; 8] and COMSOL Multiphysics [9]. In [7] the authors have considered four-row finned-tube heat exchangers. The main result was the proposition of new correlations for the air-side Nusselt number for the four-row finned tube heat exchanger. ANSYS Fluent software has been used in [8]. The study focuses on comparing experimental heat transfer coefficients on the local air side with numerical results obtained with the help of the ANSYS Fluent software. The authors have achieved good agreement between the heat transfer coefficients obtained from the experimental measurements and the numerical computations. They have found that the agreement decreases as the complexity of the geometry increases. The article [9] concentrates on forced convection with a high Reynolds number of the water-alumina-based nanofluid in the square cavity containing a rotating disk with unit speed. The influence of the rotating disc on the temperature distribution and the value of the Nusselt number has been investigated. The OpenFOAM and Simcenter STAR-CCM+ software are also mentioned as useful CFD applications. In [10], a wall nucleation model was proposed for subcooled boiling flow in narrow rectangular channels, implemented in a two-phase Eulerian-Eulerian CFD model, using the OpenFOAM platform, utilizing experimental data.