Heat Transfer Augmentation Research Articles

Thermohydraulic Performance and Flow Structures of Diamond Pyramid Arrays

Abstract Surface features are a common heat transfer enhancement method used in a myriad of applications including gas turbines and heat exchangers. One such style of surface features are diamond pyramids, which offer significant heat transfer augmentation for moderate increases in overall pressure losses. This study investigated a suite of additively manufactured pyramids in a variety of sizes and arrangements at relevant scale contained in test coupons. Designs were printed with low surface roughness relative to typical additive components (Ra < 5µm), and pyramids were printed within 100 µm of the design intent. Experimental and computational results indicate that the pressure penalty and heat transfer increased as the pyramids increased in size with aligned pyramids on both channel walls having higher values than staggered pyramids. It was found that implementing the pyramids onto a rough surface had a lesser impact on the friction factor than implementing on a smooth surface, but that the relative increase in heat transfer was the same regardless of the roughness of the endwall. The greatest enhancement to local heat transfer and pressure loss was offset from the location of minimum flow area due to local acceleration around the wake regions. The vortices formed in the wake of the pyramid structures enhanced the endwall heat transfer and shear stress. The performance of the pyramids investigated in this study follows a similar trend to prior studies investigating smooth rib geometries, though certain rib designs had higher heat transfer at lower pressure losses.

Review on Heat Transfer Augmentation in Helically Coiled Tube Heat Exchanger

Review on Heat Transfer Augmentation in Helically Coiled Tube Heat Exchanger

Design and assessment of an adapted absorber solar air collector tailored for sustainable drying applications

The design of a relevant solar air collector (SAC) is imperative to make the drying industries self-reliant and sustainable in terms of energy. However, the literature doesn’t describe the coherent design assessment of SAC, and its viability for a drying system provided the scale-up opportunity for commercial applications. Hence, the present work was devoted to estimating the heat load for a particular drying condition, a methodological understanding of SAC design, and an investigation of the performance of the newly developed solar collector. The essential design criteria were the moisture content of fresh and intended dried items, physical attributes of items, dryer capacity, preferred drying temperature, projected drying duration, required air speed (based on dryer type), and local climate (solar radiation, ambient temperature and relative humidity). The regular semi-hexagonal shape aluminium (Al) sheet was chosen to introduce air turbulence while maximizing the surface area available for heat transfer. The regular semi-hexagonal absorber was outfitted with helical springs to generate air turbulence and augment heat transfer. A double glazing (polycarbonate) of 5 mm apart was mounted to impede radiation heat loss. Three successive days of the experimental study showed that the average temperature increases of air passing through SAC were 36.02 °C, 37 °C, and 39.2 °C. The optimal tilt angle with the horizontal surface was found to be 35° in a south-facing direction for the month of January. The highest energy efficiency was found to be 40.5 %, while the lowest was found to be 24.73 %. The sustainability index of the SAC was found to be 1.02. The experimental results clearly demonstrate that the designed SAC was capable of supplying adequate heat energy (at the minimum of 155.86 W/hr.) to meet the necessary heat load (125.82 W/hr.) for agro-products drying at the designed capacity.

Thermal characteristics of a double-tube heat exchanger with different twist directions of the inner oval tube

A new configuration featuring an inner oval tube with alternating twist directions is proposed to improve the thermal performance of double-tube heat exchangers. This design enhances the heat transfer efficiency by inducing longitudinal vortices within the annular space, thereby disrupting the boundary layer on the heat transfer surface, promoting fluid mixing, and significantly augmenting heat transfer. Numerical simulations were conducted to investigate the effects of alternating twist directions of the inner oval tube on thermal performance. The results demonstrate that alternating twist direction of the inner tube creates more pronounced vortices, significantly enhances heat transfer performance compared with the conventional tubes. This novel oval tube led to a substantial enhancement of up to 173.6 % in the Nu, with a corresponding increase of 96.4 % in the f. At Re = 2600, the highest thermal performance factor of the reported annular tube with an alternately twisted oval inner tube can reach up to 2.18, indicating a 118 % improvement in overall heat transfer performance. Fitted correlations for Nu and f are provided to facilitate engineering applications.

Experimental investigation of heat transfer augmentation of impinging jet solar air heater with stepped transverse ribs

The current experimental investigation analyses the thermal and frictional attributes of an impinging jet solar air heater (IJSAH) with stepped transverse ribs, having varying pitch and size, affixed to the absorber plate. Two ribs of dimension 2 × 4 (R1) and 4 × 6 cm (R2) were tested. The pitch (p) between ribs was 2, 4, and 8 cm, with Reynolds number (Re) varying from 4913 to 13103. The jet hole diameter (Dj) considered were 3, 6 and 9 mm. The maximum Nusselt number (Nu) with the recommended R1 rib having p = 4 cm and Dj = 3 and 6 mm equalled 128.784 and 104.5004 at Re = 13103, respectively, which was 31.22 and 21.76 % higher than that generated by smooth IJSAH. The friction factor (f) generated by the ribbed IJSAH having Dj = 6 mm and p = 4 cm was 57.08 % lower than ribbed IJSAH with Dj = 3 mm. The peak thermohydraulic performance parameter (THPP) achieved was for R1 rib with p = 4 cm and Dj = 6 mm and equalled 1.75, which was 19.49 % higher than smooth IJSAH. The R1 rib with p = 4 cm at Re = 11465 demonstrated better thermal characteristics based on detailed investigation.

V-spline design for enhanced performance in turbine blade internal cooling

Abstract Past experiments have consistently shown that V-shaped rib turbulators are among the best in heat transfer performance. While there is literature on the V rib design in various experimental studies, there is no literature that shows the V rib design applied on any current turbine blades. Instead, the straight and angled rib design are used. The V rib only offers a marginally better heat transfer performance over the angled rib, but it has a severe stress concentration at the rib tip. In this research, multiple design augmentations were analyzed, with the addition of a spline at the center of the V exhibiting alleviation of the tip stress concentration. The results show that the presence of the spline not only resolves the fatigue issues but also increases the heat transfer performance by 4.3% and 8.2% against the V rib and angled rib design respectively. With a better heat transfer performance, the creep analysis shows that the turbine blade with a V-spline rib design can operate at temperatures 203°C hotter than an angled rib at the same fluid power. Given the dependence of engine thermal efficiency on turbine inlet temperature, this simple design shows good potential for heat transfer augmentation.

Enhancement of heat transfer characteristics in wavy microchannel heat sinks with streamlined micropins within convergent-divergent flow passages

In the current study, the heat transfer characteristics of a novel design microchannel with a wavy sinusoidal convergent-divergent wall structure featuring streamlined pins have been numerically investigated under laminar flow conditions. Various amplitudes, wavelengths, pin heights, and Reynolds numbers are considered as parameters. The thermal and hydraulic characteristics are analyzed in terms of Nusselt number, Fanning friction factor, and Performance Evaluation Criteria number (PEC), which evaluates the heat transfer enhancement against the associated pressure drop. It is revealed that increasing the amplitude and decreasing wavelength, along with moderate pin heights, significantly augment heat transfer. The streamlined pins effectively direct the flow, and the resulting secondary flow and chaotic advection considerably enhance heat transfer in the designed configuration. The study demonstrates that the heat transfer can be improved by a factor of 4.79 compared to a straight microchannel. Under these geometric and flow conditions, the pressure drop increases by a factor of 9.87, and the PEC is found to be around 2.23. A multi-objective optimization study using the Non-dominated Sorting Genetic Algorithm (NSGA-II) is conducted with Genetic Aggregation Response Surface Methodology to evaluate the impact of various parameters on thermal-flow performance and to identify the optimal design with material quantity variation. According to the optimal results, a 5 % increase in material can augment thermal-flow performance by approximately 206.6 % compared to traditional microchannels. Finally, practical correlations for the Nusselt number and friction factor, accounting for various parameters, have been developed to facilitate in designing of microchannel cooling systems.

Heat transfer augmentation in a double lid-driven trapezoidal porous cavity with heated block using hybrid nanofluid

This study intends to understand the fundamental characteristics of hybrid nanofluids (HNF) in a porous cavity using computational modeling, which will aid in developing HNF within hydrodynamics and enable adaptability. The present research investigates the enhancement of the transmission of heat in a double lid-driven trapezoidal porous cavity containing a heated block, utilizing a HNF composed of aluminum oxide/copper-water (Al2O3/Cu-H2O) employing the Finite Element Method (FEM) based on Galerkin weighted residual (GWR). Additionally, the Darcy-Brinkman-Forchheimer comprehensive approach has been used to demonstrate fluid flow in the porous media. The governing parameters such as the Darcy number (10−4 ≤ Da ≤ 10−2), the porosity of the porous medium (0.6 ≤ ε ≤ 0.9), inclined angle (π/16 ≤ ϕ ≤ π/3), and solid volume fraction (0.001 ≤ δ ≤ 0.05) have been chosen to evaluate the impact within dimensionless time (0.1 ≤ τ ≤ 1). The simulation outcomes of flow and thermal fields are shown through streamlines, isotherms, average heat transfer rate at the hot surfaces, and average temperature inside the cavity. The outcomes of this study show that the HT rate rises by 41.02% when increasing the solid volume fraction (svf) from 0.1% to 5%. Also, it has been found that if the inclined angle is enhanced from π/16 to π/3 at non-dimensional time τ = 0.5, the average HT augmented by 63.16%.

Heat transfer enhancement and flow resistance reduction characteristics of non-uniform electrohydrodynamic conduction pumping in microchannels

In this study, the thermo-hydraulic performance of non-uniform electrohydrodynamic (EHD) conduction pumping in rectangular and straight microchannels was experimentally investigated. Electrodes are arranged in two ways: dimensions constant, spacing varies (Cases 1–3); both dimensions and spacing vary (Cases 4–6). The results show that EHD conduction pumping significantly enhances heat transfer performance, increasing the average Nusselt number (Nu) by 17.9 %-87 % compared to a smooth microchannel. As Re increases, the inertial force of the fluid dominates, diminishing EHD-induced vortices and limiting heat transfer enhancement. EHD conduction pumping enhances heat transfer by creating vortices that mimic solid pseudo-roughness microelements, increasing fluid disturbance and mixing near the wall. However, these vortices also impede the flow, resulting in a trade-off with increased pressure drop resistance. This paper innovatively adopts an arrangement of increasing electrode size (non-uniform), which effectively reduces the pressure drop resistance in the microchannel while maintaining the advantage of enhanced heat transfer. Cases 4, 5, and 6 exhibit significantly higher comprehensive heat transfer performance (η) than Case 0 (without electrodes), especially at low Re. While the inertial force at high Re suppresses vortex formation and heat transfer enhancement, η remains superior to Case 0. Notably, Case 5 maintains a minimum η of 1.18 even at Re = 1000. Furthermore, this paper proposes an equivalent slip drag reduction mechanism to elucidate the drag reduction effect of the increasing electrode size arrangement. Heat transfer augmentation and pressure drop reduction, as mentioned here in microchannels, are crucial for electronics cooling and microfluidic devices.

Heat transfer enhancement in cylindrical heat pipes with MgO-Al2O3 hybrid nanofluids in water-ethylene glycol mixture: An RSM approach

Heat pipes are passive devices crucial for thermal management in various applications. However, conventional water-based fluids can limit their heat transfer capacity, especially in cold environments where freeze protection is necessary. This study investigates the potential of MgO-Al2O3 hybrid nanofluids to enhance heat transfer performance in cylindrical mesh heat pipes while addressing these limitations. The research demonstrates significant improvements in thermal performance compared to a water-ethylene glycol mixture. The MgO-Al2O3 hybrid nanofluid reduces thermal resistance by enhancing surface wettability in the evaporator section. Additionally, the formation of a nanofluid coating on the evaporator surface leads to a higher heat transfer coefficient. Furthermore, RSM successfully models the relationship between nanoparticle concentration, power input, and key thermal responses (thermal resistance and heat transfer coefficient). These findings highlight the effectiveness of MgO-Al2O3 hybrid nanofluids for augmenting heat transfer in heat pipes and provide valuable RSM models for predicting thermal behavior within the investigated range.

Performance analysis of Plate type Steam Condenser Using Nano-fluid

Abstract This paper investigates the application of nanofluid coolant, specifically a mixture of water and aluminium dioxide (Al2O3) nanoparticles, to augment heat transfer efficiency within flat plate heat exchanger. Beginning with an introduction highlighting the pivotal role of heat exchangers in industrial processes, the study emphasizes the imperative for enhanced efficiency and reduced energy consumption. The system description delineates the components and functionality of flat plate heat exchanger, elucidating operational and experimental conditions including initial temperatures and subsequent temperature transitions during cooling. Key parameters such as effectiveness and overall heat transfer coefficient are identified, with an exploration of their variation when comparing water alone to nanofluid coolant. Comparative data showcases experimentally obtained effectiveness and heat transfer coefficient values for both coolant types, revealing a substantial enhancement in efficiency with nanofluid coolant. Like effectiveness for water was 18% while that for nanofluid was 35%. The future potential and broader applications of nanofluid coolant in heat transfer technologies, advocating for continued research to unlock further advancements and efficiencies in industrial processes. By this technology we can reduce water losses as well as reduce power consumption in plants.

Heat transfer augmentation by using different techniques in small scale channels: A review study

In this paper highlights the most significant recent developments in scientific study on Heat sinks are thermal management components made of materials with sufficient thermal conductivity qualities. Due to the increase in operating power and speed as well as the general reduction in system size, the issues of heat removal and temperature management have taken on increasing importance in these studies. Changing the geometry of extended surfaces, the material from which they were made, the working fluid that ran over them and or the dimension of the channel, are some of the subcategories in which studies have been conducted. The current review addresses the main recent findings in the forced convection heat transfer happened at laminar flow inside small scale diameters channels. The recent studies indicated a remarkable enhancement with the change of Re, D and internal geometry of channel. The configuration of flow passages also adopted as a different passive technique to enhance thermal fluid flow.

Performance Analysis of Corrugated Twisted Tape Inserts for Heat Transfer Augmentation

This study explores the impact of wavy corrugated twisted tape inserts on enhancing heat transfer and reducing pressure drop in a double pipe heat exchanger. Cu inserts with twist ratios of 3.2, 4.2, and 5.2 were used to create turbulence in the inner tube. Varying water flow rates and measuring bulk mean temperatures at different points revealed significant improvements in heat transfer over smooth tubes. The insert with a 3.2 twist ratio achieved the highest Nusselt number increase (185%) and a 36.33% rise in the friction factor. These results highlight the effectiveness of wavy corrugated twisted tape inserts for optimizing heat transfer, with a 3.2 twist ratio identified as the most effective. Across Reynolds numbers from 4000 to 18000, Nusselt number increases were 77.75% for a 5.2 twist ratio, 167% for a 4.2 twist ratio, and 185% for a 3.2 twist ratio. Friction factors rose by approximately 10.42% for a 5.2 twist ratio, 32.54% for a 4.2 twist ratio, and 36.33% for a 3.2 twist ratio, demonstrating the relationship between twist ratio, heat transfer enhancement.

Effect of charcoal balls on distillation productivity in hemispherical solar stills: Experimental investigation and performance analysis

This study investigates the enhanced performance of hemispherical solar stills by integrating charcoal balls. The method showcases improved efficiency by augmenting heat transfer mechanisms and enhancing solar radiation absorption. Reducing the surface tension of basin water is a solution to increase its heating, enhancing the softwater yield of solar stills. The novelty of the research lies in the innovative integration of charcoal balls to improve the performance of hemispherical solar stills. This method presents a unique approach to enhancing heat transfer and evaporation dynamics, potentially revolutionizing the efficiency of solar desalination systems. Therefore, the impact of charcoal balls at a diameter of 1 cm on the performance of distillation productivity was studied. A hemispherical solar still containing charcoal balls (HSS-CB) was compared with a simple hemispherical solar still (SHSS) in the same conditions. Experiments were conducted at El-Oued-Algeria in June 2024. The method employed in this research offers distinct advantages, primarily in its ability to enhance solar still efficiency by incorporating charcoal balls. These advantages stem from the increased surface area for heat transfer, improved solar radiation absorption, and potential enhancement of evaporation and condensation processes. Cumulative return results for SHSS and HSS-CB are 4.80 and 6.20 L/m2/day, respectively. The rate of improvement in the cumulative return was 29.16 % for SHSS using the quantity of coal powder. It is recommended that charcoal balls be used to boost solar stills productivity.

Augmentation of heat transfer in a DPHE with bowl cut twisted tape inserts and TiO2/CuO hybrid nanofluids

Double pipe heat exchangers, or DPHEs, are employed in the power, oil, and process sectors. They cannot handle demanding applications. They have restrictions if they have to be utilized for heavy-duty applications. To get beyond these restrictions and use them for heavy-duty applications, heat transmission must be improved. In this work, a DPHE fitted with bowl-cut twisted tapes at different scale ratios (25, 50, and 75%) width (D) of bowl-cut from the center and circulated with TiO2/CuO hybrid nanofluids (NFs) is studied to assess its friction factor, thermal performance factor and Nusselt number. The working fluid was TiO2/CuO hybrid nanofluids (NFs) at varying concentrations (0.01, 0.03, and 0.05%) with Reynolds numbers from 2000 to 12,000. The bowl-cut twisted tape’s twisted ratio (H/D = 3) was kept constant. The hybrid NFs’ Nusselt number improvement was 66.09% more than that of the conventional tube. For varying scale ratios, the improvement in heat transfer was found to be 83.35, 115.31, and 172% with the bowl-cut twisted tapes and hybrid NFs. It was discovered that the friction factor penalty was 8.28, 0.83, and 1.075 times greater than that of the carrier fluid. Additionally, it was noticed that the thermal performance factor (TPF) was 1.65 times higher than the original fluid.

Comparative investigation on heat transfer augmentation in a liquid cooling plate for rectangular Li-ion battery thermal management

This work conducted a numerical study with experimental validation to improve the performance of a rectangular multi-channel cooling plate utilised for cooling lithium batteries. Seven different designs on a cold plate for laminar flow conditions were evaluated using numerical modelling simulations in the 3D ANSYS program. Three cooling plate designs were proposed with channel arrangements: arc, convergent–divergent and different channel widths (narrow central channels and wide peripheral channels). The other four proposed cooling plate designs included representations of variable-sized pin fins with different shapes: oval, drop, rhombus and trapezoidal within different channel widths. Real experiments were conducted on a manufactured conventional cooling plate to verify the results of the numerical simulation. Results indicated that all proposed designs improved the heat transfer of the cooling plate. The percentage of enhancement in Nusselt number due to the presence of rhombus-shaped pin fins inside different channel widths is approximately 95.5 %, which is about three times the enhancement in pin fins that used only smooth different channel widths, which is approximately 33.5 %. Amongst the studied designs, incorporating different channel widths with the addition of rhombus-shaped pin fins exhibited the largest heat dissipation capacity and the best thermal–hydraulic performance. The highest temperature uniformity enhancement ratio and performance evaluation parameter for this case reached about 71.96 % and 1.68, respectively.

Water flow boiling heat transfer and pressure drop in smooth, etched, and herringbone aluminum tubes

Designing next generation heat exchangers for efficient heat transfer and minimal material consumption is required for sustainable development of society. While several heat transfer augmentation techniques are available, extended surfaces have been the most widely adopted due to their relative ease of integration and high heat transfer enhancement. However, since extended surfaces are mainly applicable for soft metals, and require significant capital investment for manufacturing, we propose scalably fabricated microstructures as an alternative and scalable heat transfer augmentation technique. Our etching-based structures are cost-effective, scalable, and applicable to a wide array of metallic tubing. The conformal microstructures, which have length scales ranging between ∼ 1 to 12 μm, are introduced through chemical etching of internal tube walls using hydrochloric acid. To test the water flow boiling performance of our etched surfaces, experiments were conducted on 0.25-inch diameter aluminum tubes over a range of mass and heat fluxes spanning 200 kg/(m2·s) <G < 380 kg/(m2·s) and 60 kW/m2 <q″ < 125 kW/m2, respectively. Using deionized water as the working fluid, an enhancement of up to 104 % in the tube-averaged heat transfer coefficient with a concurrent increase of up to 65 % in pressure drop was observed. The increase in the heat transfer coefficient and pressure drop is attributed to the microstructures increasing the surface roughness and creating additional nucleation sites for bubble entrapment. When compared to commercially available finned herringbone tubes, we observed that for certain operating conditions, the enhancement in heat transfer due to use of microstructures in smooth tubes can exceed that of the enhancement observed using un-structured herringbone tubes. However, the pressure drop due to the increased surface area and fluid flow disruption of the chevron shaped herringbone fins always exceeded the etched aluminum round tube. This work provides insights and understanding related to how chemical etching and surface structuring can be utilized as an alternative passive heat transfer enhancement technique in flow boiling applications.

Experimental investigations on thermo-fluid performance of perforated baffle aided with oppositely oriented sawtooth deflector in tubular heat exchanger

Purpose The investigation concentrated on studying a distinct category of tubular heat exchanger that uses swirling airflow over tube bundle maintained at constant heat flux. Swirl flow is achieved using a novel perforated baffle plate with rectangular openings and multiple adjustable opposite-oriented saw-tooth flow deflectors. These deflectors were strategically placed at the inlet of the heat exchanger to create a swirling flow downstream. Design/methodology/approach The custom-built axial flow heat exchanger consists of three baffle plates arranged longitudinally supporting tube bundle maintained at constant heat flux. The baffle plate equipped with saw-tooth flow deflector of various geometry represented by space height ratio(e/h). Next, ambient air was then directed over the tube bundle at varying Reynolds number and the effect of baffle spacing (PR), Space height ratio (e/h) and inclination angle(a) of deflectors on performance of heat exchanger was experimentally analyzed. Findings The heat transfer augmentation of heat exchanger for given operating condition is strongly dependent on geometry, inclination angle of deflector and baffle spacing. Originality/value An average improvement of 1.42 times in thermal enhancement factor was observed with inclination angle of 30°, space height ratio of 0.4 and a pitch ratio of 1.2 when compared to a heat exchanger without a baffle plate under similar operating conditions.

Augmentation of Pool Boiling Heat Transfer Using Graphene-MWCNT/Distilled Water Hybrid Nanofluids

Augmentation of Pool Boiling Heat Transfer Using Graphene-MWCNT/Distilled Water Hybrid Nanofluids

A second law analysis on flow of a PCM based nanofluid in a shell-and-tube heat exchanger: An experimental study for sustainable energy

In the foreseeable future, heat exchangers will continue to play an important role in environmental management and have numerous applications, their geometry has been the subject of interest for many researchers. The main goal of this research is to improve the heat exchangers' thermal performance and exergetic efficiency using new type of nanofluid. In this concept, the effect of nanoencapsulated phase change material (NEPCM) addition to water and producing NEPCM nanofluid for heat transfer augmentation in shell and tube heat exchanger (STHE) was investigated, experimentally. Nanocapsules were synthesized by miniemulsion polymerization containing phase change material (PCM) as core and chitosan (GO/CS) as shell material. After synthesis of nanocapsules, nanofluids with different concentration of NEPCM have been prepared and the stability and thermophysical properties of the nanofluids were characterized. In the subsequent stage, thermal and exergy efficiencies test was conducted on STHE using response surface method. The experiments were performed at different conditions; NPCM concentration (φ), inlet temperature (Tin) and Re number to optimse exergy efficiency. The optimum level of the φ, Tin and Re inlet for maximum ɛ (73 %) were found to be 10.55 %, 78.35 °C and 10365, respectively. The experimental results demonstrated that proposed nanofluid could enhance exergy efficiency for thermal system. It appears that a combination of NEPCM nanofluids gives a better cooling rate in the heat exchangers and could be a promising alternative along with other cooling techniques.