Omar Rafae Alomar

Multi-heat-source thermal management in compact electronic and process systems increasingly relies on porous metal inserts to intensify convective transport, yet experimental data for duct-embedded configurations that combine mixed convection, multiple heat sources, and high-porosity metal foam remain scarce. To address this gap, we experimentally investigate mixed convective heat transfer from two heated copper cylinders embedded in a high-porosity (95%, 40 PPI) open-cell copper metal foam inside a vented acrylic duct, using a spatially resolved twelve-point thermocouple array together with directly measured air velocity and static pressure. Following review, all cylinder-scale dimensionless groups are defined on a single characteristic length, the cylinder diameter D: Re_D = ρVD/μ, Gr_D = gβ(T_s − T_∞)D³/ν², Ri_D = Gr_D/Re_D² and Nu = hD/k. Five fan settings, with velocities measured by a calibrated low-range thermal anemometer (0.05–1 m/s range), gave Re_D = 117–498 and Ri_D = 0.204–5.200; all five cases lie within the mixed-convection band 0.1 ≤ Ri ≤ 10. The average Nusselt number, obtained from electrical power and measured temperatures and therefore independent of the velocity measurement, increased from 32 to 58 across the fan settings. In terms of the indicated Re_D it follows Nu = 4.68 Re_D^0.399 (R² = 0.978, five points); so, this fit is a provisional description of the present dataset and not a design correlation. Based on this preliminary comparison, the measured Nu exceeds the classical Hilpert correlation by an apparent factor of 467–541%. This discrepancy reflects a combination of inferred mechanisms: the foam’s extended surface area, duct confinement, cylinder interaction, and the use of a foam-embedded temperature proxy, and should not be interpreted as a direct measure of the foam’s intrinsic heat transfer coefficient. The static pressure drop across the foam follows a Darcy–Forchheimer relation, ΔP = 95.7V + 92.8V² (Pa), analyzed on the foam thickness L_f, which is the physically appropriate length scale for the porous matrix. These results provide original, design-oriented experimental data on the thermal-hydraulic behavior of a dual-cylinder, foam-filled vented duct, together with a preliminary correlation and clearly identified limitations, including an air-side energy-balance imbalance whose cause could not be verified, to guide future generalization. To isolate the individual contributions of the foam, duct confinement, and cylinder interaction, additional baseline experiments were performed. At Re_D = 348, the empty-duct configuration yields Nu = 15.4 (+90% over the unconfined Hilpert baseline), while the foam-filled configuration yields Nu = 46.0 (+467% over Hilpert), with a corresponding Performance Evaluation Criterion (PEC) of 0.91, indicating a substantial thermal gain at the cost of a significant hydraulic penalty. The air-side energy balance does not close: the air-side heat gain computed from the point-measured outlet velocity and temperature exceeds the electrical input by 15–180%. Thermocouple radiation error was bounded at about 1–3 K and excluded as the cause; the discrepancy is attributed, without direct verification, to non-representative single-point sampling of the outlet flow, and it does not affect the electrically derived Nusselt numbers.

Solar air heaters (SAHs) are promising low‐cost solar thermal systems for heating and drying applications; however, their performance is limited by the low convective heat transfer coefficient between the absorber and the flowing air. Double‐pass configurations incorporating porous media have therefore attracted increasing attention because they enhance airflow mixing and heat transfer. Nevertheless, existing reviews mainly focus on individual enhancement techniques or thermal efficiency, with limited attention to the combined effects of porous‐medium characteristics, airflow configurations, operating conditions, and associated hydraulic penalties. To address this gap, this review provides an integrated critical and quantitative assessment of double‐pass SAHs, emphasizing porous‐media and packed‐bed configurations and the trade‐off between thermal enhancement and pressure loss. The literature was systematically analyzed by comparing collector configurations, porous‐media characteristics, operating and meteorological parameters, enhancement strategies, experimental testing, and CFD investigations. The reviewed studies demonstrate that porous media, fins, artificial roughness, and optimized airflow configurations can substantially enhance heat transfer, with thermal efficiencies reaching approximately 87% in advanced systems. However, excessive turbulence and flow obstructions can significantly increase pressure drop and pumping power requirements. High‐porosity media and optimized airflow arrangements generally provide a more favorable thermohydraulic compromise. The review highlights the need for standardized thermohydraulic evaluation, systematic optimization of porous‐media properties and airflow conditions, long‐term outdoor validation, and integrated experimental–CFD investigations.

This study investigates the impacts of varying mass flowrate on thermal and exergetic performances of spiral solar collector during summer in Duhok, Iraq. Experimental data are collected in June and July under various mass flowrates, solar irradiance and environmental conditions. Analysis encompasses temperature distributions across system components, useful heat gain, heat loss coefficient, thermal efficiency, exergy destruction and exergy efficiency. Energy and exergy efficiencies are obtained by solving governing equations using MATLAB program. Findings indicated that the glass cover and absorber plate temperatures have positive relationships with solar irradiance reaching peaking values of 67.4°C and 86.2°C, respectively. Results indicated that the useful heat gain is steadily increased with mass flowrate achieving peak value of 341 W at 0.067 kgs ⁻¹ . Thermal efficiency of the system is found within a range from 60.1% to 66.3%, where the highest value occurred at 0.042 kgs ⁻¹ . Findings revealed that the exergy destruction varied from 388 W to 492.5 W, where this value decreases with increasing mass flowrate and reducing wind speeds. Exergy efficiency and second‐law performance metric are significantly improved from 5.4% at 0.025 kgs ⁻¹ to 20.5% at 0.067 kgs ⁻¹ . The overall heat loss coefficient is affected by environmental factors and hence, this value increases with increasing wind speed reaching peaking value of 5.36 Wm ⁻² K ⁻¹ at wind speed reached 1.2 m s ⁻¹ . Results demonstrated that spiral solar collector can affect the system performance across higher mass flow rates leading to improve the thermal output and exergy efficiency while reducing system irreversibilities.

Photovoltaic/thermal (PV/T) collectors co‐located with heat pumps are a potential hybrid solution for simultaneous electricity and useful heat recovery in architectural applications. This brief review summarizes the latest developments in PV/T heat pump systems, focusing especially on system integration concepts (direct‐expansion and indirect coupling), reported performance indicators, and sensitivity to operating conditions. The review brings out three key outcomes. First of all, treating PV/T heat pump systems as coupled electro‐thermal units reveals strong interactions among electrical output power, compressor input power, condenser heat recovery, and the overall coefficient of performance (COP). Second, refrigerant selection—in particular the move towards low‐GWP alternatives—has a substantial impact on discharge conditions, pressure ratio, and attainable COP and accounts for part of the variability reported in the literature. Third, inconsistencies in performance definitions and boundary conditions limit direct comparisons across studies, highlighting the need to harmonize reporting of electrical, thermal, and heat pump metrics. By synthesizing recent experimental and numerical results within a unified framework, this review not only explains current trends in performance but also identifies research gaps and offers guidelines for the design and assessment of next‐generation PV/T‐heat pump systems.

Solar thermal (ST) collectors are an efficient technology for generating thermal energy without the need for an electrical source, unlike photovoltaic thermal (PVT) collectors, which combine photovoltaic and thermal conversion to produce electricity and low-grade thermal energy. This research aims to present a low-cost strategy for improving the dual performance of PVT and ST systems by connecting them in series, under operating conditions that include different water flow rates and constant air flow in the ST unit. This work evaluates the thermal and electrical performance of a hybrid (PVT-ST) system, focusing on the effect of incorporating porous media and phase change materials (PCMs) into the system design. The results demonstrate that the integrated system enhances the heating efficiency of both water and air, contributing to an increase in the overall energy production efficiency. Experimental data showed that decreasing the water flow rate increased temperatures, while increasing the flow reduced temperature fluctuations and improved thermal production. The highest water temperature difference in the PVT system was recorded at 15.9°C at the lowest water flow, and the highest outlet air temperature was 58.5°C under the same conditions. The PVT-ST system's maximum total thermal power output was 756.13 W, achieving an overall thermal efficiency of 110.6%, an electrical efficiency of 12.22%, and a maximum electrical output of 142.69 W. The integration of thermal energy storage technologies enhances the stability of the system's performance, especially during periods of low solar radiation. The use of porous media improves internal heat transfer and distribution, while phase change materials help store and gradually release thermal energy, reducing temperature fluctuations and enhancing the stability and efficiency of the thermal and electrical systems