Natural convection cooling is widely used in compact electronic systems but often fails to provide sufficient heat removal at low flow velocities. Piezoelectric fans offer a low-power alternative to conventional fans, while porous fin structures increase surface area for enhanced heat transfer. This study experimentally investigates piezoelectric fan-assisted natural convection cooling of three heat sink configurations mounted on one wall of a vertical duct: a flat plate, a rectangular corrugated porous finned heat sink, and a triangular corrugated porous finned heat sink. The piezoelectric fan is placed vertically with its tip near the leading edge of the heat sink and operated at its first resonance frequency. Experiments are performed in a predominantly laminar natural convection regime, and local and area-averaged heat transfer coefficients are obtained for cases with and without the fan. Under an identical power input, the triangular corrugated porous finned heat sink with the fan active achieves the highest heat transfer coefficient of approximately 102 W/m2K, corresponding to about 133% enhancement compared with the flat plate with the fan active. These results indicate that combining a piezoelectric fan with a triangular corrugated porous fin heat sink can substantially improve passive cooling performance in compact, low-power thermal management applications by exploiting fan-induced vortices and the converging-diverging porous passages.

This paper investigates randomly distributed streamwise jets generated due to flow through thin open-porous materials and the jet coalescence phenomenon. The pattern and coalescence of jets at the exit of thin porous materials impact their use as membranes, papers and cartons, filters, filtration cakes, porous coatings, fuel cells, textiles, and hygiene products such as wipes and diapers. Computational fluid dynamics (CFD) simulations are performed on the geometry reconstructed using X-ray micro-computed tomography to predict the pressure drop, permeability, and inertial coefficient and validated by measurements. Furthermore, a novel methodology is developed to estimate the jet dimensions by performing a fast Fourier transform of the voxelized streamwise velocity component at the exit of the porous material. Statistical analysis of the resulting spectra reveals the jet length distribution in the flow field and quantitatively confirms jet coalescence. The present work illustrates the jet formation, emergence, and jet coalescence at the exit of a thin porous foam. The proposed methodology allows jet flow characterization and avoids extensive experimentation. Also, the results offer guidelines for jet impingement heat and mass transport augmentation and flow uniformity, and study the impact of flow on sound propagation and mixing.

Fans used in convective cooling applications generate undesirable broadband and tonal noise at the blade pass frequency (BPF) and its harmonics. Using separate noise-reducing devices such as mufflers and acoustic linings often increases the overall size of systems, presenting a challenge in space-constrained systems. A noise-reducing heat sink (NRHS) concept is studied to integrate heat dissipation and noise reduction within the same space to address this. A novel Helmholtz resonator (HR) based heat sink, which targets low-frequency noise reduction and heat dissipation, is demonstrated first. The length of the HR neck is increased to reduce its natural frequency, and this long neck made of copper tube is used as a fin for heat dissipation. A long-neck HR array is experimentally tested for acoustic and thermohydraulic performance. Further, the long-neck HR array is integrated with the corrugated periodic cellular materials (CPCM) heat sink, reducing broadband, tonal noise, and heat dissipation. The experimental results for the combined arrangement show that the proposed arrangement can reduce the low-frequency noise along with the broadband noise and also shows an improvement in the thermal performance compared to only a CPCM heat sink at the cost of a minor increase in the pressure drop.

The present paper reports the energy and environmental impacts of integrating a column of activated alumina (AA) for fluoride adsorption with a humidification-dehumidification (HDH) desalination system. The effects of fluoride concentration (Ci), the mass of AA (maa), and the mass flow rate ratio (MR) on the yield and gained-output ratio (GOR) of the considered system have been investigated using an experimental approach. The experiments are conducted for 5 to 30 mg/L, 1 to 2 kg, and 1 to 6 for Ci, maa, and MR, respectively. The effect of brine recirculation on the investigated system is also reported in this paper. The obtained results have shown an enhancement of up to 21% in the value of GOR with this system. Moreover, nearly 80% of the fluoride disposal to nature as concentrated brine can be prevented using the adsorption unit. The current study is carried out to prevent fluoride disposal in the reject stream. However, the proposed system can obtain freshwater at the community level without disposing of harmful contaminants in rejected water by incorporating other adsorption materials. The results presented in this paper may be useful for the stakeholders working on sustainable freshwater production.

This study presents an experimental investigation of the thermal and hydrodynamic performance of a rectangular channel heat sink partially filled with unstructured open-cell copper foam. The foam has a porosity of 0.9625, 30 pores per inch (PPI), and a height of 20 mm. Three configurations are examined based on the foam-to-channel height ratio (Blockage ratio = Hf/H = 1.0, 0.75, and 0.5), representing fully and partially filled cases. The Reynolds number, calculated using channel hydraulic diameter, varies between 5000 and 25000. Local temperature distributions along the heater wall are captured using infrared (IR) thermography and a thin stainless-steel foil technique. Results show that the pressure drop decreases by factors of 5and 19 for Hf = 0.75H and Hf = 0.5H configurations, respectively, relative to the fully filled configuration, due to lower flow resistance in the gap regions. The fully filled foam configuration (Hf = H) yields the highest heat transfer performance due to complete fluid-foam interaction, with a decreasing temperature difference ( Tw(pixel) -Tf(Pixel)) along the flow direction. In contrast, the partially filled cases exhibit increasing temperature differences downstream due to reduced fluid penetration into the foam. The thermal-hydraulic performance assessed using the Colburn factor j and friction factor f indicates that the Hf = 0.75H configuration provides an optimal tradeoff between heat transfer and pressure loss. A two-model framework is developed to predict mass flow separation and heat transfer in partially foam-filled channels, wherein Model 1 (experiment-based) establishes the benchmark and Model 2 (analytical) provides predictive capability. This integrated approach uniquely addresses flow partitioning in porous-bypass systems, a phenomenon not reported previously to the best of our knowledge. Generalised correlations are proposed for predicting heat transfer coefficients in partially filled porous channels. Overall, the study provides a design framework for optimising thermal performance while minimising pressure drop in systems employing unstructured metal foams.

The rapidly growing field of electronic devices, with increasing computational power and the integration of new features such as AI models and compact sizes, requires effective cooling techniques for reliable operation. Vapor chambers meet these needs due to their high heat transport and spreading capabilities. This work presents the design and fabrication of a cooling package comprising a vapor chamber and an air-cooled, corrugated foam heat sink. An experimental investigation on finding better working fluids and their optimum filling amount is conducted by considering two classes of working fluids: (a) pure fluids: water and 2-propanol and (b) 2-propanol/water mixtures at different concentrations. An optimum charge amount of 35

Temporal fluctuations in power consumption and associated temperature in electronic devices lead to performance degradation and early device failure due to thermal fatigue. These issues are prevalent in applications such as power inverters, data center servers, and others. Effective transient thermal management is critical to mitigate these issues and prolong device lifespan. This study presents the design, development, and experimental evaluation of a novel vapor chamber heat sink integrated with solid-liquid phase change materials (PCMs) to reduce temperature spikes under transient power pulses. The reported prototype features PCM integration inside a vapor chamber and a micro-pillar capillary wick fabricated by electroplating onto the inner surface of the condenser. Tests are conducted under different dual-power pulse conditions using two PCM types with an identical melting temperature of 58 degrees C: a low thermal conductivity paraffin-based PCM and a high thermal conductivity metallic alloy PCM, with more than 10 times higher figure-of-merit than the paraffin-based PCM. It is observed that the paraffin PCM-integrated vapor chamber has significantly larger evaporator temperature fluctuations than the metallic alloy PCM, indicating the importance of PCM selection for transient thermal management. Integrating PCM into the vapor chamber reduced temperature swings by 0.9 to 2.1 degrees C and the maximum evaporator temperature by 2 to 6.2 degrees C compared to the vapor chamber without PCM. The most pronounced reduction in temperature swing occurs when operating around the PCM melting point, underscoring the importance of the PCM melting point in thermal design. Standard deviation in transient temperature corresponding to transient power reveals a more than 23% improvement in temperature stability when metallic PCM is integrated inside the vapor chamber. Lifetime analysis prediction using the Coffin-Manson-Arrhenius model suggests a 76 to 134% increase in the number of cycles to failure, using the fatigue exponent value adopted from literature. Findings from this study showcase the promising capability of novel PCM-integrated two-phase cooling devices for effective transient thermal management and prolonged device life by suppressing thermal fatigue.

The present study investigates the thermal and hydrodynamic performance of a heat sink channel partially filled with open-cell AlSi10Mg metal foam. Three configurations are considered : Hf = 0.5H, Hf = 0.75H and Hf = H, where Hf is the foam height and H is the height of the channel, and they are referred to as Cases 1, 2 and 3, respectively. The study examined over a Reynolds number range of 5000-25,000. The metal foam has a thickness of 12.5 mm and a porosity of 0.706. Wall temperature distributions are captured using a thin stainless steel foil coated with high-emissivity paint and measured through infrared thermography. Results show that reducing the foam height significantly decreases pressure drop, with the 0.5H configuration exhibiting a 10-12 times lower pressure drop than the fully filled case. However, there is a corresponding reduction in heat transfer. Thermal performance evaluation indicates that each configuration achieves a favourable PEC and CPPC values. To isolate the heat transfer mechanisms, complementary resin foam experiments demonstrate that nearly 80 % of the total heat transfer is contributed by the metal foam. A unified two-model analysis framework is introduced to quantify mass flow separation, heat transfer, and pressure drop in partially filled channels using structured foams: a behaviour not previously characterised in the literature. Using combined experimental measurements and analytical modelling, the study develops predictive relations capable of accurately estimating both thermal and hydrodynamic performance across porous bypass configurations. A generalised correlation is further proposed to estimate the Nusselt number for both gap and no-gap configurations, formulated using the Reynolds number based on the strut diameter and effective thermal properties. Together, these contributions provide the comprehensive predictive tools tailored specifically for structured lattice foam channels, enabling more reliable design and optimisation under practical heat-transfer and pressure-drop constraints.

An ultra-thin vapor chamber setup with aqueous alcohol mixtures as working fluids is experimentally investigated. The thermal performance of the vapor chamber with three 1-butanol-water mixtures of different concentrations is compared against 4.2M 2-propanol-water, which was the previously obtained best fluid. Among the three 1-butanol-water solutions, the 1.5wt% mixture has the best thermal performance in the horizontally positioned ultra-thin vapor chamber. The effect of vapor chamber inclination was examined, with the vapor chamber rotated to 30 deg and 45 deg. The thermal performance deteriorates with an increase in inclination. Further, at each inclination, the 1.5wt% 1-butanol solution outperforms the 4.2M 2-propanol solution.

The increasing complexity of chip packaging, driven by 3D-stacked architectures and heterogeneous integration, demands advanced thermal management solutions. This study presents an experimental and numerical analysis of a Low-Temperature Co-Fired Ceramic (LTCC) cold plate with embedded microchannels and thermal vias for liquid cooling of High-Performance Computing (HPC) processors. A custom clamping setup replicating server board conditions was developed using Intel's bolster plate and heating element. Thermal performance was evaluated under 200 W and 350 W heat loads, corresponding to the thermal design power (TDP) of Intel (R)'s 4th and 5th generation processors. A combined numerical and experimental approach characterized the thermal resistance, yielding an interface resistance of 0.0500 K/W or 12.6 x 10 - 5 m2K/W at 200 W. Experimental validation confirmed the predictive accuracy of this approach at 350 W. To mitigate thermal spreading resistance, the LTCC cold plate's bottom surface was coated with conductive AgPd paste, reducing spreading resistance by 0.0305 K/W and lowering the case temperature by 11 degrees C. The coated LTCC cold plate achieved comparable performance to Intel's benchmark conditions while requiring significantly lower coolant flow, dissipating 350 W at 35 degrees C with only 1.5 LPM, compared to over 3 LPM in conventional systems. At 200 W, stable performance was maintained even at 60 degrees C coolant inlet temperature at 5 LPM, indicating reduced chiller dependency and improved efficiency.

This study presents an experimental investigation into the heat transfer, fluid flow, and acoustic performance of a combined piezoelectric fan-porous fin heat sink system operating in an assistive mode. Experiments are conducted within a custom-designed plane wave duct setup that enables simultaneous thermal and acoustic measurements in a controlled environment. Three heat sink configurations are evaluated to assess heat transfer enhancement and the influence of piezoelectric fan placement. Acoustic metrics are also analyzed, including level gain-representing noise introduced by the piezo fan-and transmission loss across the heat sinks. Results showed maximum heat transfer enhancement due to the piezoelectric fan occurring at lower mean flow velocities for all configurations. Among the designs, the triangular corrugated porous finned heat sink demonstrated a 52.6% increase in Nusselt number compared to a flat plate. In contrast, the rectangular corrugated porous finned heat sink exhibited superior acoustic performance, with lower level gain and higher transmission loss.

In compact air cooling applications, there is a need to dissipate heat and reduce noise within the same functional space. While metal foam blocks are effective in heat dissipation and noise reduction, they often result in a high pressure drop. This study investigates the combined thermal, acoustic, and flow performance of six additively manufactured corrugated periodic foam heat sinks, varying in unit cell topology (octet and simple cubic, SC) and the number of corrugations (two, four, and eight). The novelty of this study lies in the experimental investigation and demonstration of corrugated metal foam heat sinks as low-pressure drop, high-performance, broadband noise-reducing heat sinks. Experimental investigations were conducted using a custom-built setup complemented by numerical simulations to analyze the velocity field within the corrugated sample. A thermo-fluidic index was employed to compare the thermo-hydraulic performance of the samples, while transmission loss was used to evaluate their acoustic performance. The results indicate the trade-off between thermo-hydraulic and acoustic performance.Corrugated periodic foam samples showed a substantial improvement in thermal, flow, and acoustic performance compared to block foams. Among the studied geometries, 2 corr. SC-0.42 showed the highest transmission loss of around 7 dB average over the studied frequency range and the lowest thermohydraulic performance. On the other hand, 8 corr. octet-0.56 shows the highest thermo-hydraulic performance and lowest transmission loss of 1.2 dB on average. If a combined performance is preferred, then among the samples tested, the 4 corrugated octet geometry may be a reasonable compromise.

This study investigates local heat transfer distribution and pressure drop in octet-structured aluminium foam (AlSi10Mg) within a rectangular channel. The local heat transfer distribution is analysed using a thin metal foil technique and an IR camera. The foam has a thickness of 12.5 mm and 70.6 % porosity. Experiments were performed to study the effect of Reynolds numbers on heat transfer performance and assess the contribution of conductive versus convective heat transfer. A range of Reynolds numbers were tested from 1000 to 25000. The heat transfer coefficient asymptotes to a constant value beyond the Reynolds number of 20000. To segregate the effect of fin and wall heat transfer, separate experiments are conducted using resin foam. The effect of conduction heat transfer (fin) dominates convection heat transfer (wall), with a contribution ratio of 81-19 %. Metal foam exhibits a 3.5-5 times higher heat transfer coefficient than resin foam. The performance enhancement over smooth channels is 5 times higher for resin foam and 18 to 29 times higher for metal foam. The Performance Evaluation Criterion for metal foam ranges from 2.02 to 3.11, while for resin foam, Performance Evaluation Criterion is between 0.56 and 0.63. The Constant Pumping Power Criterion shows a 32 % higher thermal performance than the Performance Evaluation Criterion.

An ice slurry-based cold storage unit is a promising option for the on-farm packhouses. However, it is associated with a few challenges, such as low energy efficiency and high maintenance costs. Given this, the present study explores the surface-scraped method for ice slurry generation and makes the system viable for on-farm cold storage applications. In the present work, experiments are carried out for scraper speed, propylene glycol (PG)-water solution flow rate, PG concentration in solution, and storage volume within the range of 15 to 40 RPM, 0.1-0.5 m3/h, 5%-15%, 8 and 12 L, respectively. Moreover, experiments are also performed outdoors powered by solar photovoltaic (PV) modules to compare the results with those from the indoor experiments. The identified optimal scraper speed and PG-water flow rate values are 35 RPM and 0.3 m3/h, respectively. The optimal balance between the PG concentration and storage volume is recommended to capture the maximum amount of thermal energy for a fixed charging period, which is crucial in solar PV-based systems due to limited daylight availability. These findings enhance the understanding of ice slurry generation under varying conditions.

This paper reports experimental investigations on cold plates made from Low-Temperature Co-fired Ceramic (LTCC) technology for liquid cooling of supercomputer microprocessors. LTCC, a ceramic substrate-based technology with lightweight and ease of fabrication for miniaturization of cooling devices, can be a potential alternative to the existing copper cold plates for future three-dimensional stacked chip architectures. LTCC cold plates were fabricated using ceramic substrates whose thermal conductivity was enhanced using thermal vias. They were embedded with microchannels for liquid with different flow configurations. Their thermal performance is compared against copper cold plates. Deionized (DI) water is used as a coolant. Pressure drop and thermal resistance across different cold plates are measured as per water-cooled data center standards (W3 and W4 class). Obtained experimental results show that the tested LTCC cold plates can be used to cool supercomputer processors. It is concluded that LTCC cold plates can be a potential alternative for existing copper cold plates.

This work aims to develop a low-cost, simple, closed-loop two-phase thermosiphon (CLTPT) to function as a pumpless loop for power inverter applications. Certain alcohols, when mixed with water, exhibit self-rewetting behavior during boiling. Three mixtures of 2-propanol-water and three mixtures of 1-butanol-water were studied as working fluids and compared to pure water to determine the benefits of alcoholic mixtures on heat transfer performance. The CLTPT was operated in two distinct modes: (i) heat pipe mode and (ii) mixed mode, using a ball valve for positioning. Depending on the valve position, a stable thermosiphon operation was demonstrated. In terms of evaporator plate temperature and heat transfer coefficient, the 15 wt% 2-propanol-water solution outperformed pure water and the butanol-water mixture as a working fluid in most test cases.

The local heat transfers of a thermally developing region in a rectangular channel filled with porous metal foam are investigated experimentally. A thin metal foil technique and thermal IR imaging are adopted for the measurement of the local temperature distribution. An open-cell metal foam made from copper having a porosity of 0.96 is used. The pore density of the foam is 30 PPI (pores per inch). Fluid flow characteristics like permeability and foam drag coefficient are measured by conducting local pressure drop experiments. Additionally, by utilizing local pressure measurement data, the non-dimensional pressure coefficient is quantified. The non-dimensional pressure coefficient increases in the streamwise direction, irrespective of the Reynolds number, and remains almost constant in the spanwise direction for Reynolds numbers greater than 2000. The effect of the metal foam thickness on local heat transfer and pressure drop is investigated for 13 and 20 mm thick porous metal foam. It is compared with a smooth channel to quantify the heat transfer augmentation in a channel filled with metal foam. Compared to a smooth channel, the channel with 20 mm thick metal foam shows 14 to 25 times augmentation in the Nusselt number. Similarly, the channel with 13 mm foam shows 10 to 15 times augmentation in Nusselt number. The increasing trend of the local Nusselt number is observed in a streamwise direction. The different criteria are studied to understand the thermal performance evaluation. In the Constant Pumping Power Criterion (CPPC), enhancements ranged from 3.14 to 6.72 for a 20 mm thickness and 2.62 and 4.34 for a 13 mm foam thickness. Similarly, in the Performance Evaluation Criterion (PEC), enhancement ranges from 2.23 to 4.83 for a 20 mm foam thickness and 1.89 to 3.16 for a 13 mm foam thickness. A generalized correlation is suggested to describe the average Nusselt number considering the foam material, foam thickness, pore density, and porosity as parameters.

This paper investigates the heat transfer characteristics of a channel system consisting of a finned heat sink and two piezoelectric devices, the piezoelectric fan (PF) and the piezoelectric translational agitator (PTA), both experimentally and computationally. In the proposed system, the mean flow is generated by a cantilevered PF, and the flow between the fins is agitated using a PTA. A single-channel system consisting of a PTA, the PF, and two fins is analyzed numerically using ANSYS Fluent software after validating numerical predictions against experimental measurements. The effect of design variables such as frequency ratio, phase difference, PF's tip distance from PTA, and squeezing fraction is explored. A PTA increases the heat transfer from the heated surfaces without incrementally aiding in the mass-flow rate. Velocity and temperature fields are plotted to understand the physics of the system for one complete cycle of a PTA blade. The concept of total Reynolds number that incorporates the effect of both axial and transverse fluid flow is used in this study. The Nusselt number increases with an increment in the total Reynolds number. It is noted that the integration of the PF and the PTA with the finned heat sink system has enhanced the heat transfer coefficient by 76.88% compared to the system with PTA and by 30.92% as compared to the system with the PF only.

The effect of the metal foam thickness on the conduction and convection heat transfer for a metal foam flat plate impinged by a circular air jet is investigated. The IR thermography and thin-metal foil technique are used for the measurement of local heat transfer. An open-cell aluminum metal foam is used for the metal foam flat plate. A 3D-printed resin foam and detached metal foam flat plate are used for the appreciation of the conduction and convection heat transfer. The varying parameters are the thickness of the foam, Reynolds number, and the nozzle exit to plate distance. The presence of the metal foam offers a conduction effect. This predominates over the attenuation in the convective heat transfer by foam due to additional hydraulic resistance. The additional hydraulic resistance offered by the porous foam increases with the increase in the foam thickness. The heat transfer of a porous foamed flat plate decreases with the increase in the foam thickness. The local Nusselt number of the resin foam and detached foam flat plate is almost the same. The conduction effect and attenuation in the convection heat transfer of a metal foam flat plate are quantified by attenuation and enhancement factors. The overall augmentation offered by 4, 8, and 12 mm thick metal foam flat plates is 1.71, 1.42, and 1.43 times compared to the smooth flat plate case, respectively. Hence, it is advisable to use a metal foam flat plate with 4-mm-thick metal foam under circular air jet impingement.

Applications requiring high heat transfer rates, such as cooling of high-density electrical equipment, cooling of gas turbine components, cooling of rocket launcher components, cryosurgery, etc., are frequently use impinging jets. Non-uniformity in the heat transmission from the impingement surface is the main drawback of jet impingement heat transfer. In order to achieve uniform heat transfer, the current study examines the presence of porous carbon foam on a targeted surface. Using a thin metal foil and infrared thermography, the local heat transfer distribution of a porous carbon foamed surface is determined. The findings of the porous carbon foamed surface are compared to the bare surface (smooth surface without foam) for local Nusselt number and uniformity in the heat transfer (coefficient of variance). The effects of Reynolds number, foam height, and the distance between the nozzle exit to the targeted plate are examined. The results of the carbon foamed surfaces are also compared with the aluminium metal foamed surface results available in the literature. The current work also describes the separation of the modes of heat transfer that exist with porous carbon foamed surfaces while under jet impingement. The findings imply that, depending on the height of the carbon foam, the porous carbon foam on a targeted surface gives a lower or equivalent heat transfer rate compared to a bare surface. In comparison to a bare surface, carbon foam on a targeted surface provides uniform heat transfer that is independent of foam height. The study of the separation of modes of heat transfer suggests that heat from the porous carbon foamed surface is conveyed by conduction induced by carbon foam and convection induced by jet fluid. The convection provided by the jet fluid is compromised by the carbon foam on a targeted surface. The conduction induced by carbon foam makes the heat transfer from the targeted surface more uniform. The conduction and convection factors can be used to present the conduction and convection heat transfer from porous carbon foamed surfaces, respectively. Regression analysis is used to develop a region-wise correlation for the conduction and convection components. The local Nusselt number of a carbon foamed flat plate can be predicted using the local Nusselt of a bare surface utilizing the provided correlations for conduction and convection factor.