The present work describes an experimental study and CFD modeling of fluid flow and heat transfer characteristics in a heat sink with several asymmetrical heated mini-channels. The data from the experimental research were the basis for numerical calculations. During experiments, the temperature measurement of the outer heater surface was performed by infrared thermography to verify the results of numerical calculations performed in Simcenter STAR-CCM+ software. The main objective was to determine the values of the parameters tested to evaluate the intensity of the heat transfer processes. In the numerical simulations, important variables, mainly the working fluid, heater material, the spatial orientation of the test section, and the number of mini-channels, were assumed. The results of the numerical computations were discussed. Due to simulations, it was possible to indicate which parameters tested in terms of heat transfer turned out to be the most effective. Furthermore, a mesh dependency analysis based on the grid convergence index (GCI) was performed. The residuals, as good indicators of convergence, achieved low values. Generally, the data presented showed satisfactory convergence of the results achieved as a result of the computational procedure.

The article aims to explore boiling heat transfer in mini-channels with a rectangular cross-section using various fluids (HFE-649, HFE-7000, HFE-7100, and HFE-7200). Temperature measurements were conducted using infrared thermography for the heated wall and K-type thermocouples for the working fluid. The 2D mathematical model for heat transfer in the test section was proposed. Local heat transfer coefficients between the heated wall and the working fluid were determined from the Robin condition. The problem was solved by means of the finite element method (FEM) with Trefftz functions. The values of the heat transfer coefficient that were obtained were compared with the results calculated from Newton’s law of cooling. The average relative differences between the obtained results did not exceed 4%. The study included uncertainty analyses for temperature measurements with K- and T-type thermocouples. Expanded uncertainties were calculated using the uncertainty propagation and Monte Carlo methods. Precisely determining the uncertainties in contact temperature measurements is crucial to ensure accurate temperature data for subsequent heat transfer calculations. The results of the heat transfer investigations were compared in terms of fluid temperature, heat transfer coefficients, and boiling curves. HFE-7200 consistently exhibited the highest fluid temperature and temperature differences at boiling incipience, while HFE-7000 demonstrated the highest heat transfer coefficients. HFE-649 showed the lowest heat transfer coefficients. The boiling curves exhibited a typical shape, with a notable occurrence of ‘nucleation hysteresis phenomena’. Upon the analysis of two-phase flow patterns, bubbly and bubbly-slug structures were observed.

This article proposes a passive cooling system for photovoltaic (PV) panels to achieve a reduction in their temperature. It is known that the cooling of PV panels allows for an increase in the efficiency of photovoltaic conversion. Furthermore, reducing the high temperature of the surfaces of PV panels is also desirable to ensure their long-lasting operation and high efficiency. Photovoltaic panels were modified by adding copper sheets to the bottom side of the panels. Two types of modification of the outer surface of the sheet were investigated experimentally, which differed in surface roughness. One was characterised by the nominal roughness of the copper sheet according to its manufacturer, while the other was enhanced by a system of pins. Numerical simulations, performed using the Simcenter STAR-CCM+ software, version 2020.2.1 Build 15.04.010, helped to describe the geometry of the pins and their role in the resulting reduction in the temperature of the PV panel surface. As a result, modifying a typical PV panel by adding a copper sheet with pins helps to achieve a higher decrease in the temperature of the PV panel. The addition of a copper sheet with a smooth surface to the bare PV panel improved the operating conditions by lowering its surface temperature by approximately 6.5 K but using an enhanced surface with the highest number of pins distributed uniformly on the copper sheet surface resulted in the highest temperature drop up to 12 K. The highest number of pins distributed uniformly on the copper sheet surface resulted in the highest temperature drop in its bottom surface, that is, on average by more than 12 K compared to the surface temperature of the bare PV panel surface. The validation of the numerical calculations was performed on data from the experiments. An analysis of the quality of the numerical mesh was also performed using a method based on the grid convergence index.

This work presents experimental and numerical studies of heat transfer during cooling fluid flow in a group of five minichannels 1 mm deep. The main purpose was to determine the heat transfer coefficient on the contact surface between the fluid and the heated wall of the selected minichannel at subcooled boiling. The temperature distribution on the outer surface of the heated plate was measured by means of an infrared camera. Thermal and flow parameters were monitored by an appropriate data-acquisition system. The test section was placed horizontally with fluid flowing above the heated wall. The HFE-649, HFE-7100 and HFE-7200 working fluids were examined in the experiments. Simcenter STAR-CCM+ software was used for numerical analysis of heat transfer in the test section. Furthermore, a simplified two-dimensional (2D) model was proposed that designates subcooled boiling heat transfer during fluid flow in a central minichannel. The heat-transfer process in the heated plate and the working fluid was described using indicated partial differential equations with appropriate boundary conditions. The solution to the proposed system of equations led to the solving of two more inverse Cauchy-type problems. The classical Trefftz method (TM) and the homotopy perturbation method (HPM) combined with the TM allowed for obtaining temperature distributions in the heater and the fluid and consequently, the heat transfer coefficient at the heater–fluid interface from the Robin boundary condition. Comparison of the results from numerical simulation due to Simcenter STAR-CCM+ showed similar temperature distributions at the heated surface. The calculated heat transfer coefficients, by HPM and Simcenter STAR-CCM+, were validated using the 1D approach. Furthermore, the results from simulations in Simcenter STAR-CCM+ in the form of local temperatures of the heater were confronted with experimental data for comparison. Similar results were achieved.

In this study, the uncertainty of measurement paths was estimated using selected statistical methods. Specifically, temperature measurements obtained from contact temperature sensors used in a heat transfer test section were investigated. The experiments utilized a drywell temperature calibrator, thermoelements (types K, J, N, and T), and a data acquisition station. Additionally, a certified Pt-100 resistance sensor connected to the temperature meter was considered during measurements. The temperature range for the selected measurement points was 0.3 to 100 °C, covering both increasing and decreasing temperatures. To calculate the expanded uncertainty, both the uncertainty propagation method and the Monte Carlo method were employed. The results were analyzed and found to be similar.

Analizy porównawcze pomiarów temperatury powierzchni wykonano na podstawie wyników badań wykonanych na stanowisku badawczym z wymiennymi foliami ze stopów Haynes-230 i Hastelloy X, o różnych grubościach. Podczas eksperymentów realizowano pomiar temperatury metodą kontaktową (czujnikami rezystancyjnymi i termoelementami) oraz metodą bezkontaktową (dwie kamery termowizyjne). Tor pomiarowy zawierał termometr o wysokiej dokładności współpracujący z czujnikiem RTD 1/10 DIN (o klasie B) oraz kalibrator podczerwieni.