Papers by Keyword: Heat Transfer Enhancement

Abstract: Wire-net stainless steel (WS) is an alternative material used to enhance heat transfer in solar air heater (SAH) by inducing swirling or rotating airflow as air passes through its pores. In this study, WS with varying porosity—corresponding to pore per inch (PPI) of 16, 20, and 25—and a constant pitch distance (P) of 0.06 m was installed within the flow channel of the SAH, and air was used as the working fluid under turbulent flow. The results showed that WS significantly improved heat transfer performance, though accompanied by increased pressure drop. An increase in PPI resulted in a maximum of Nusselt number and friction factor by factors of 13.81 and 238.61, respectively, compared to SAH without WS. The highest thermal enhancement factor of 2.48 was observed at PPI=20.

Abstract: Phase Change Materials (PCMs) have become popular for thermal energy storage (TES) uses due to their large latent heat capacity and almost isothermal performance. However, melting rates and the overall effectiveness of the system are constrained by their intrinsically poor heat conductivity. Considering latest studies investigating innovative shapes and combinations to optimize heat transfer achievement, fin insertion has become an effective and affordable upgrade technique. The most recent computational and experimental studies on fin-enhanced latent heat thermal energy storage (LHTES) systems are covered in this review, with a concentrate on how fin materials, forms, and configurations enhance PCM melting performance. Fin shapes such as longitudinal, radial, tree-like, spiral, T-shaped, V-shaped, fractal, and hybrid fins have been studied with respect to temperature uniformity, natural convection impacts, and melting time decrease. The outcomes demonstrate that improving fin shape could decrease melting times by as much as 70%, with geometric and tree-like fins performing better due to increased conduction–convection coupling. Furthermore, included in the research are design trade-offs involving fin volume against surface area as well as the impact of computational optimization in the design of fin shape. subsequently, research gaps and future initiatives are noted, with a focus on the possibility of hybrid improvement techniques that combine heat transfer fluid optimization or high-conductivity additives with advanced fin design.

Abstract: This paper focuses on the influence of obstacles and the use of nanofluid on heat transfer in turbulent flow along the channel. The governing equations were solved utilizing finite volume method. The main objective is to study the variations of the Reynolds number, as well as the a/b ratio, the distance between obstacles, and the volume fraction influencing the Nusselt number and the friction factor. The results indicate that the presence of obstacles in a channel and increase of Reynolds number can increase the heat transfer by inducing the formation of turbulent zones. As well, the use of nanofluids with a volume fraction also proves beneficial for heat transfer due to the increased thermal conductivity of the fluid. These results could have significant industrial and technological importance.

Abstract: An experimental study is performed on thermal fluid transport phenomenon in plate heat exchanger. Emphasis is placed on enhancement of heat transfer performance in plate heat exchanger with the aid of silica-nanofluid as a working fluid. A plate heat exchanger (PHE), manufactured by HISAKA company (RX-O15A-KNHJ-7), is used as the test section. The PHE has 3 stainless steel plates (271.3mm X 136.5mm) with a nominal gap of 2.5 mm between any two plates. Thermal energy of the hot working fluid is transferred to that of the cold one through the titanium plate in the test section. Here, hot and cold working fluids are supplied by the independent loops, i.e., hot and cold fluid loops, respectively. It is found that (i) heat transfer is enhanced due to particle suspension in comparison with the pure working fluid, and (ii) heat transfer performance is substantially intensified with an increase in volume fraction of nanoparticle and Reynolds number.

Abstract: Sustainability in energy production, energy security, and global warming are major concerns facing the globe today. Cylindrical Solar Concentrator is extensively utilized for technologically advanced processes, heat, and power plant applications by utilizing daylight sunshine at no running cost. Numerous inputs and characteristics impact the concentrator's performance, with the type of heat transfer fluid and its mass flow rate being two of the most important. This paper gives a numerical investigation of the influence of thermo-physical attribute of CuO water-based nanofluids on the effectiveness of the Parabolic Trough Solar Concentrator in Ogbomosho weather condition (lat. 8^o01¹, long. 4^o11¹).The governing equations of nanofluids with laminar flow and steady state, using iterative relaxation techniques, as well as the efficiency of the concentrator, were solved. A C++ simulation program was developed to investigate the impacts of thermo physical parameters on concentrator efficiency, with nanoparticle sizes ranging from 1 to 10 percent and mass flow rates of 0.1 kg/s, 0.15 kg/s, and 0.2 kg/s, at a constant incident solar insolation flux of 186 W/m². The results demonstrated that increasing the mass flow rate of the nanofluids improves the heat transmission properties. The thermo physical properties of CuO-based nanofluids and its effects on the performance of the solar parabolic trough collector are being examined. The impact of thermophysical attributes on thermal effectiveness results in improved thermal efficacy, heat transfer characteristics of nanofluids, and factors influencing its features in solar collectors, which determines its usability. The Parabolic Trough Collector system based on nanofluids is a promising technology with applications in green surroundings.

Abstract: This study investigates transport process in circular tubes cross-flow Heat Exchanger (HEX) using water-CuO-nanofluids cooling media. The effects of nanoparticle volume fractions (Ø) and Reynolds number (Re) on the flow structure, coefficient of skin friction, isotherms and Nusselt number (Nu) are determined for steady laminar flow. The governing equations of continuity, momentum and energy are discretized over the flow domain and solved using SIMPLE method of the Finite Volume Method with ANSYS Fluent 16. The results show that the flow field for the conventional fluid is concentric around the inner tubes for Re up to 60 after which vortices evolve downstream behind the tubes, elongate and eclipse with the increase in Re. Vortex inception occurs at Re between 60 and 45 for 0 ≤ Ø ≤ 10%. The temperature fields are characterized by plume-like structure which envelopes the two inner cylinders between which heat transfer occurs. The average Nusselt number is correlated as Nu = 22.4 - 411,588س + 0.757Re + 1803.31/ln(Re) in which the interaction between Re and Nu has significant (p ≤ 0.05) effect. The addition of nanoparticles in the range 2 ≤ Ø ≤ 10% results in the increase in Nu from 0.55 to 5.84%. It follows that the thermal performance of the cross flow heat exchanger could be enhanced with CuO-based nanofluids.

Abstract: The article contains the results of a research in constructing of modern heat exchangers form of heat exchanging surfaces and modes of heat media flux, providing minimum area (size) of heat exchanging apparatus. Decreasing of heat-transferring area is achieved by using different techniques of intensification of convective heat exchange. Intensification of the heat exchange is accompanied by increasing of energy consumption for pumping the coolant. It is concluded that under the conditions of turbulent flow, the transport mechanism does not strongly depend on the shape of the perturbations introduced into the flow, while the tendency to approach the dependences is common to the curves for the considered surfaces, and the experimental data obtained on pipes with a periodic section of the flow cross-section along the length. Using surfaces creating channels with a greater coefficient of hydraulic resistance when creating a compact heat exchangers, which corresponds to surfaces for which the principle of trans-verse flow is realized.

Abstract: Heat transfer enhancement technology has the aim to develop more efficient systems as demanded in many applications in the fields of automotive, aerospace, electronics and process industry. A possible solution to obtain efficient cooling systems is represented by the use of confined impinging jets. Moreover, the introduction of nanoparticles in the working fluids can be considered in order to improve the thermal performances of the base fluids. In this paper a numerical investigation on mixed convection in confined slot jets impinging on a porous media by considering pure water or Al₂O₃/water based nanofluids is described. A two-dimensional model is developed and different Peclet numbers and Rayleigh numbers were considered. The particle volume concentrations ranged from 0% to 4% and the particle diameter is equal to 30 nm. The target surface is heated by a constant temperature value, calculated according to the value of Rayleigh number. The distance of the target surface is five times greater than the slot jet width. A single-phase model approach has been adopted in order to describe the nanofluid behaviour while the hypothesis of non-local thermal equilibrium is considered in order to simulate the behaviour in the porous media which is featured by a porosity value of 0.87. The aim consists into study the thermal and fluid-dynamic behaviour of the system. Results show increasing values of the convective heat transfer coefficients for increasing values of Peclet number and particle concentration. This behaviour is more evident at low Peclet number values and Rayleigh number ones.

Abstract: In this work, Nusselt number and friction factor are calculated numerically for turbulent pipe flow (Reynolds number between 6000 and 12000) with constant heat flux boundary condition using nanofluids. The nanofluid is modelled with the single-phase approach and the simulation results are compared with experimental data. Ethylene glycol and water, 60:40 EG/W mass ratio, as base fluid and SiO2 nanoparticles are used as nanofluid with particle volume concentrations ranging from 0% to 10%. A prior turbulence model evaluation of k-ε-, k-ω- and k-ω-SST-model revealed substantial deviations between the tested models and resulted in applying the k-ω-SST-model for the simulation. Nusselt number predictions for the nanofluid are in agreement with experimental results and a conventional single-phase correlation. The mean deviation is in the range of 5%. Friction factor values show a mean deviation of 1.5% to a conventional single-phase correlation, however, they differ considerably from the nanofluid experimental data.

Abstract: A numerical study using computational fluid dynamics method with an approach of single phase has been presented in order to determine the effects of the concentration of the nanoparticles and flow rate on the convective heat transfer and friction factor in turbulent regime flowing through three different straight channels (straight, circular and triangular) with different Reynolds number (5000 ≤ Re ≤ 20000) using constant applied heat flux. The nanofluid was used consist of Fe3O4 magnetic nanoparticles with average diameter of (13nm) dispersed in water with four volume fraction (0, 0.2, 0.4, 0.6%). The results revealed that as volume fraction and Reynolds number increase Nusselt number increase and the heat transfer rate in circular cross section tube is better than that in square and triangular cross section channels.