Łukasz Cieślikiewicz

Heat and moisture transfer in porous materials play a critical role in a wide range of engineering and environmental applications, particularly in the building sector, where such processes affect energy efficiency, material durability, and indoor comfort. Accurate experimental data are essential for understanding these phenomena and for validating numerical models that simulate heat, air, and moisture (HAM) transport. However, acquiring reliable measurements under controlled conditions remains a significant challenge due to the complexity of coupled transport processes. This paper presents the development of an experimental bench designed to investigate heat and moisture transfer in porous materials. The system enables precise control and measurement of key environmental parameters, including air temperature (15–50 °C), relative humidity (15–98%), and velocity (0.1–5 m/s). Operating in a closed-loop configuration, the setup ensures high stability, minimises the influence of external conditions, and reduces the power consumption of system components. The experimental bench was equipped with a cooler/moisture condenser, a variable-speed fan, a humidifier, and a heater, each regulated by custom-designed Proportional–Integral–Derivative (PID) controllers to maintain precise and stable operating conditions. Temperature within the samples was monitored using multiple first-class T-type thermocouples, while moisture content was measured gravimetrically through continuous mass monitoring. A feature of the setup is the inclusion of two parallel measurement ducts, which allow for simultaneous testing under identical conditions and enable faster verification of repeatability and reliability. Initial tests conducted with autoclaved aerated concrete samples are presented in the paper and confirm the system’s capability for stable and repeatable operation. The maximum standard deviation observed in temperature control was approximately 0.22 °C, while for relative humidity it reached up to 0.93%. These levels of precision support the acquisition of representative experimental data suitable for validating HAM transfer models in porous materials.

Pipes for heat exchangers are widely utilized in various thermal systems, with notable applications in the building industry, such as underfloor heating and heat pump systems. To reduce manufacturing costs, these components are often fabricated from polymeric materials, which offer favorable mechanical properties and high corrosion resistance. However, their relatively low thermal conductivity can limit overall heat transfer efficiency. This study presents the design and implementation of an experimental setup for the comparative evaluation of convective heat transfer in polymeric pipes. The setup employs a tube-in-tube configuration, with 2-meter-long pipe samples mounted within a purpose-built assembly. The pipe under investigation serves as the inner tube, with water-glycol mixtures flowing on both the inner and outer sides to facilitate controlled heat transfer. Depending on the selected operating mode, heat can be transferred either into or out of the tested pipe. Temperature regulation of both fluid streams is achieved using two immersion circulation baths, while a 5.5 kW chiller is employed to maintain the temperature of the cold stream. A variable speed pump and a control valve ensure precise flow control within the test sample. The mass flow rate is measured accurately using a Coriolis flow meter. Inlet and outlet temperatures for both streams are monitored with Class A PT100 sensors, and pressure drop across the pipe sample is recorded using a piezoelectric differential pressure transmitter. A dedicated LabVIEW application enables real-time data acquisition and system monitoring. Initial system verification and testing were performed using three commercially available pipes for heat exchangers, i.e., two PEX pipes with outer diameters of 32 and 40 mm, designed for underfloor heating and ground heat exchanger applications, respectively, and a multilayer PE-RT pipe with a 32 mm outer diameter, also intended for underfloor heating systems.

Organic Rankine Cycle (ORC) devices are systems that implement the basic Rankine cycle, but use an organic medium instead of water. These devices can use low-temperature heat, but it should be remembered that the achievable efficiency decreases as the source temperature decreases. Previous publications have shown that maximizing capacity, rather than efficiency, is the main goal of the ORC system. This can be achieved by establishing the correct operating conditions, while ensuring the correct mass flow of the working medium to each component. For instance, the expander must reach the required rotational speed. This work focuses on using genetic algorithms to determine optimal operating conditions and maximize capacity. A genetic algorithm was developed for a newly built ORC device, enabling determination of optimal operating conditions. The results were implemented in the device driver and validated experimentally, confirming that genetic algorithms can easily achieve the desired effect.

The paper presents a method of calculating the thermal conductivity of bio-based building composites enhanced with microencapsulated PCM to improve their thermal mass. The proposed numerical approach uses the real sample morphology for which the unsteady heat conductivity equation was solved, and a local (micro-scale) transient temperature field was obtained. The 3D sample microstructure was obtained by applying micro X-ray tomography (μCT) scanning. Then, by assuming a certain weight fraction, the microencapsulated phase change material (PCM) was randomly distributed in the space of the computational domain occupied by the binder. In this way, the artificial bio-composite with micro-capsules with PCM was generated based on the real distributions of pores, hemp shives, and binder. Using artificially generated PCM-enhanced composites and based on the local transient temperature distribution, the effective thermal conductivities of the composites in the direction of heat flow were calculated by applying the volume averaging technique. In the first step, the model was tuned by selecting representative elementary volume (REV) and adjusting the predicted thermal conductivity with a measured one for bio-based composite without PCM additives. In the second step, the method was applied for predictions of thermal conductivities of composites with three amounts of microencapsulated PCM, i.e., 5, 10, and 20 % wt. The simulation results were also compared with experimental measurements, and the matching accuracy of the predicted and measured thermal conductivity values on the average level of 8.1% was achieved.

The paper presents the investigation of heat transfer in hemp shives and magnesia binder composite with microencapsulated phase change material (PCM) to increase the building material’s thermal mass. The investigated sample was prepared as a three-layer block of dimensions 600×400×480 mm. The external layers of the block had a density of approximately 400-450 kg/m3 and a thickness of 50-60 mm, while the inner layer had a density of approximately 200-250 kg/m3 and a thickness of 290 mm. The study was performed with a block placed between two specially designed climatic chambers. Conditions in chambers were fully stabilized. Additionally, 50 mm wide channels with fans in both chambers were added close to the sample surfaces to force uniform airflow along both sample surfaces. For parameters control in the chambers, dedicated software was developed. Inside the sample nine temperature sensors were placed. During measurements, the temperature of 30°C and relative humidity of 40% was maintained in one chamber, while in the second one, after stabilization in temperature of 20°C and relative humidity of 50%, the temperature was decreased to 15°C without humidity control. During measurement insulating properties of PCM in dynamic conditions were analyzed.