The growing demand for efficient heat transfer and energy conversion systems require advanced working fluids with superior thermal and electrical transport properties. In this study, investigation on the thermophysical behaviour of Al2O3/MWCNT–DI water hybrid nanofluids through comprehensive experimental characterization and predictive modelling was carried out. Hybrid nanofluids of 0.05–0.25 vol

Extensive research and empirical evidence demonstrate the superior thermal performance of nanofluids compared to DIW. Magnetic hybrid nanofluids, such as Fe3O4/TiO2, are currently being explored for their enhanced thermal properties. This study evaluates Fe3O4/TiO2 nanofluids for heat transfer and hydraulic resistance across Reynolds numbers from 3200 to 5300 and volume fractions from 0.00625 % to 0.3 % vol. UV-Vis spectroscopy shows that lower volumetric fractions correlate with decreased sedimentation. Over 30 days, nanofluids with 0.3 % vol, 0.2 % vol, and 0.1 % vol exhibited high sedimentation factors (SF) of 31.79 %, 11.88 %, and 11.44 %, respectively, while 0.00625 % vol, 0.0125 % vol, and 0.025 % vol demonstrated better stability with SFs of 8.89 %, 9.82 %, and 10.24 % respectively. Volume fractions significantly impact heat transfer, with CHT coefficients increasing by 11.42 % at 0.3 % vol, 14.03 % at 0.2 % vol, 18.04 % at 0.1 % vol, and 19.98 % at 0.05 % vol. The greatest enhancements are at lower concentrations: 22.91 % at 0.025 % vol, a peak of 26.33 % at 0.0125 % vol, and 24.30 % at 0.00625 % vol. Pressure drops are highest at 21 % for 0.3 % vol at Re 5018, decreasing with lower concentrations: 13.10 % at Re 5144.4 (0.2 % vol), 11.94 % at Re 5041.6 (0.1 % vol), 9.82 % at Re 5112.2 (0.05 % vol), 7.67 % at Re 5258.7 (0.0125 % vol), and 10.29 % at Re 5094.0 (0.00625 % vol). These results highlight that higher nanoparticle concentrations increase pressure drop, impacting energy efficiency. Lower concentrations (0.0125 % Vol and 0.00625 % Vol) provided better heat transfer with lower pressure losses. Total Efficiency Index (TEI), The optimal nanoparticle concentration for maximum thermal efficiency was approximately 0.0125 % Vol. TEI values were highest at this concentration, indicating enhanced heat transfer with minimal thermal resistance and pressure drop. Higher concentrations (0.2 % Vol and 0.3 % Vol) showed lower TEI values, suggesting reduced thermal efficiency due to increased flow resistance. These findings highlight the importance of selecting an appropriate nanoparticle concentration to optimize thermal performance in heat transfer systems, balancing the benefits of enhanced heat transfer with the drawbacks of higher-pressure losses.

This study investigates the heat transfer characteristics of Fe3O4-MgO/DIW Magnetic Hybrid Nanofluids (MHNFs) compared to deionized water (DIW) across turbulent, laminar and transition flow regimes. Results reveal that the transition of MHNFs begins at significantly higher Reynolds numbers than DIW, contradicting previous findings. This disparity may be due to the specific characteristics of MHNFs, such as altered thermal conductivity and viscosity. Heat transfer results demonstrate enhancement within the fully developed transition regime, with improvements observed for MHNF concentrations from 0.3 to 0.00625 vol%. Volume fraction significantly impacts nanofluids' convective heat transfer characteristics, with higher volume fractions corresponding to higher critical Reynolds numbers. Even at 0.00625 % vol, the transition begins at a lower Reynolds number than DIW. The maximum enhancements in heat transfer were 26 % for 0.3 vol%, 25.8 % for 0.2 vol%, 25.7 % for 0.1 vol%, 17.9 % for 0.05 vol%, 25.6 % for 0.025 vol%, 31.6 % for 0.0125 vol%, and 30.2 % for 0.00625 vol% MHNFs. The optimum enhancement was observed with MHNF concentrations of 0.0125 vol% and 0.00625 vol%. Higher volume fractions led to increased pressure drops, indicating a complex interplay between fluid dynamics and nanofluid properties. The study highlights notable enhancements in thermal efficiency across transition and laminar flow regimes.

This study presents a comprehensive experimental and analytical investigation into the thermophysical and magneto-hydrodynamic (MHD) properties of Fe_3O_4 / Al_2O_3 /MWCNT/DIW tri-hybrid nanofluids (THNFs) across varying nanoparticle ratios with Sample A (15 wt. Fe_3O_4 , 80 wt. Al_2O_3 , 5 wt. Fe_3O_4 , 70 wt. Al_2O_3 , 10 wt. Fe_3O_4 , 60 wt. Al_2O_3 , 20 wt. Fe_3O_4 , 50 wt. Al_2O_3 , 25 wt. Al_2O_3 content enhances stability by reducing particle agglomeration, while increased Fe_3O_4 and MWCNT fractions elevate EC, however, excessive MWCNT raises viscosity, potentially impacting pumping efficiency. Notably, Sample E offers an optimal balance of TC, stability, and viscosity at lower concentrations. pH measurements reveal an acidic trend that decreases with rising temperature and volume fraction, potentially leading to corrosion in metallic systems. Strategies such as surfactant addition and surface functionalization are proposed to mitigate these effects. Moreover, machine learning models (Gradient Boosting, Random Forest, LightGBM) identified temperature as the dominant factor influencing TC and viscosity, while nanoparticle volume fraction primarily affected pH and EC, achieving high predictive accuracy (R2 > 0.96, MSE < 0.000025).

This study experimentally investigates the influence of hybridization mixing ratio (HMR), nanoparticle size, and temperature on the stability, thermal conductivity, viscosity, and thermoelectric conductivity of $${\text{Fe}}_{3}{\text{O}}_{4}/$$ Fe 3 O 4 / Ti $${\text{O}}_{2}$$ O 2 -DIW, $${\text{Fe}}_{3}{\text{O}}_{4}/$$ Fe 3 O 4 / MgO-DIW, and $${\text{Fe}}_{3}{\text{O}}_{4}/$$ Fe 3 O 4 / ZnO-DIW magnetic hybrid ferrofluids (MHFs). A two-step preparation technique was used to synthesize 0.3% volume concentration of the MHFs at HMRs of 80:20, 60:40, and 40:60, respectively. The study’s result revealed that the thermal and electrical conductivity of the MHF was proportional to the temperature of the MHF. Also, the viscosity and thermoelectric conductivity (TEC) of the MHF was inversely related to the MHF’s temperature. The (80:20) ratio consistently stands out for superior stability and thermal conductivity. An exceptional electrical conductivity of 4.23 mS/cm was displayed by the $${\text{Fe}}_{3}{\text{O}}_{4}/$$ Fe 3 O 4 / Ti $${\text{O}}_{2}(18\text{ nm})$$ O 2 ( 18 nm ) -DIW at 50 °C. The best thermal conductivity–viscosity balance was observed for the $${\text{Fe}}_{3}{\text{O}}_{4}/$$ Fe 3 O 4 / ZnO-DIW with HMR of 80:20 at 50 °C as it has the highest thermal conductivity enhancement of 31.28% and the least viscosity. These findings guide MHF customization, emphasizing stability and thermophysical performance balance. $${\text{Fe}}_{3}{\text{O}}_{4}/$$ Fe 3 O 4 / ZnO-DI also had the best TEC value, making it most suitable for cooling PEM fuel cells. Linear regression analysis was used to generate the thermal conductivity correlations for the MHFs, while feature importance analysis highlights temperature as the most significant variable influencing their thermal conductivity.

There are very few models in the open literature for predicting the water uptake characteristics of grains. Peleg's equation (1988) is a widely used empirical model that does not involve important soaking parameters to describe water uptake. Other existing models have been developed based on the diffusion theory. However, these existing models are strongly connected to experimental data for predicting the equilibrium moisture of the grain (maximum water uptake with time). In practice, the soaking of grain involves many physical parameters such as time, temperature, the viscosity of the soaking medium, the density of grain and soaking medium, diffusion coefficient, and solid loss from the grain (for example alpha-galactosides). However, there is no documentation of a model involving these physical parameters. This present work proposed a generalized mathematical model for predicting water uptake of grain (cowpeas) using non-dimensional analysis. The proposed model was successively applied to predict the soaking of cowpeas via the simplification of the model using six data points from experimental works in the literature. In predicting the soaking characteristics of different cowpeas, a good agreement was observed when the proposed model was compared with existing experimental data in the literature. This work presents a novel way of predicting water uptake in cowpeas using non-dimensional analysis which can be applied by food scientists and food engineers to model the water uptake for other grains. However, the physics of soaking, particularly as the porous structure of the grain evolves, could be analyzed using fractal mathematics. This approach should be considered for future studies to capture the complex, irregular dynamics of the process more accurately.

Effective thermal management is crucial for optimum performance and energy conservation in energy-intensive industries and power systems. This study explores the influence of TiO2-water nanofluids on enhancing heat transfer during impinging jet-cooling of a heated copper surface, both under transient and steady-state cooling conditions. TiO2-water nanofluids, with volume fractions (0.025 vol% ≤ ɸ ≤ 1 vol%), were prepared, characterized, and utilized in the investigation. The experimental setup involved a dimensionless nozzle-to-target gap (H/D = 4) and Reynolds number (10000 < Re < 30000), with transient cooling behavior tracked through a dimensionless cooling curve. The TiO2-water nanofluids demonstrated significant thermal enhancement of 14.75% and 16% at ɸ = 0.05 vol% and Re ≈ 22000, outperforming DI water in both steady-state and transient cooling conditions, respectively. The result also shows that heat transfer rates increase with higher Reynolds numbers but follow an ascent and descent pattern with increasing nanofluid volume fractions. Notably, for volume fractions exceeding ɸ = 0.1%, the nanofluid exhibited reduced heat transfer efficiency compared to DI water. The acquired data have been utilized to establish a correlation for estimating the Nusselt number as a function of Reynolds number and fluid volume fraction.

In this research, an experimental investigation of hybrid nanofluid mixed convection heat transfer characteristics is conducted. The research specifically investigates the effects of percentage weight composition (PWC) of nanoparticles in the hybrid nanofluids on mixed convection heat transfer characteristics along the lamina, transition and turbulent regions. Transition boundaries, thermal entrance effects, and the influence of tube axial position were also critically investigated and analysed experimentally. Three hybrid nanofluids of Al2O3 – MWCNT (i.e., Al2O3 (60%) – MWCNT (40%), Al2O3 (50%) – MWCNT (50%) and Al2O3 (40%) – MWCNT (60%)) were prepared using two-step method and then subjected to a constant heat flux through a horizontal circular copper tube with an internal diameter of 8mm. Results show a significant change in heat transfer characteristics with different PWCs. Al2O3 (60%) – MWCNT (40%) have shown a better heat transfer enhancement among the three fluids investigated. Its Nusselt number has an enhancement of more than 5 % better than the other two fluids. Along the transition regime, critical Reynold numbers (Recr) of the three nanofluids were found to have differed slightly, with Recr = 2020, 2000 and 2100 for Al2O3 (60%) – MWCNT (40%), Al2O3 (50%) – MWCNT (50%) and Al2O3 (40%) – MWCNT (60%) respectively. Mixed convection effects were found to be more significant with Al2O3 (60%) – MWCNT (40%) than with the other two fluids. At the axial position of 63.75, its mixed convection strength (Ὠ) was about 41%, which is the highest among the three fluids. Its strength of mixed convection was also found to deteriorate to about 14.75% with an increase in axial distance from the tube inlet. A similar observation was also noticed with other fluids. Thermal entrance effects were only found to be significant at x/d = 15 and 31.25, as their influence diminishes with an increased x/d distance from the tube inlet. It was concluded that both mixed convection and thermal entrance effects resulted in heat transfer enhancement, especially in the lamina region. Their influences decrease with an increase in axial distance from the tube inlet. Mixed convection influences were only present in the lamina and transition region, and their strength was reduced with an increase in Reynold number and axial position.

Nanofluids (NFs) have emerged as a revolutionary medium for enhancing heat transfer, with magnetohydrodynamics (MHD) gaining particular attention for its potential to improve system efficiency. Despite this growing interest, a critical gap remains in understanding the combined impact of Fe3O4 and its hybrid nanofluids under magnetic fields, especially in turbulent and transition flow regimes of internal forced convection. This review offers an in-depth exploration of MHD-NF internal forced convection, addressing key aspects such as magnetic field dynamics, nanoparticle clustering, stability, dispersion, flow control, and responsive rheology. Leveraging a comprehensive bibliographic analysis of 100 experimental studies from 2010 to the 2024, along with data from the Scopus® database, this work highlights how optimized nanofluid volume concentrations, magnetic field intensities, and frequencies significantly enhance heat transfer coefficients. The findings underscore that both magnetic field strength and nanoparticle concentration critically influence particle motion, flow patterns, entropy generation, thermal performance, and pressure drops, offering new insights into system design. The versatility of MHD-NF systems presents promising applications in fields ranging from advanced cooling technologies to solar thermal systems and material processing. Furthermore, this review addresses ongoing debates on the efficacy of alternating versus constant magnetic fields, advocating for customized magnetic field configurations to unlock the full potential of MHD-enhanced heat transfer. This work not only identifies existing gaps but also lays the foundation for future breakthroughs in magnetically influenced nanofluid systems.

Unlocking optimum heat transfer is essential for enhancing solar thermal collector efficiency and advancing sustainable energy solutions. This experimental study investigates a simulated solar thermal collector's heat transfer behavior using jet impingement cooling, emphasizing hydrodynamic effects in pulsating nanofluid-jet impingement. Al2O3-MWCNT/water hybrid nanofluid is utilized, varying pulsating frequency (0.2 Hz <= F <= 20 Hz), amplitude (4 Vp <= A <= 20 Vp), waveform (sine, squared, triangular), wave offset (0 <= Ⴋ <= 4), and nanofluid volume fraction (0.05 vol% <= phi <= 0.3 vol%) to optimize heat transfer. Results show a significant influence on heat transfer performance for all parameters except waveform. A peak heat transfer enhancement of 24 % is observed for 0.3 vol% Al2O3-MWCNT/water compared to de-ionized water under continuous jet impingement. Additionally, a 20 % enhancement is achieved with a sine waveform at phi = 0.3 vol%, F = 0.2, A = 8, and Ⴋ = 2. Pulsating jet impingement generally yields higher cooling rates, as the cooling curves indicate. These findings provide crucial insights for optimizing heat transfer in solar thermal collectors through pulsating hybrid nanofluid jet impingement cooling.

It is difficult to make a single choice of the type of exchanger to use because many factors such as adequate space, financial matters, common use of a given exchanger type in a specific country or region, availability of manufacturing equipment, and maintenance issues can greatly influence the decision. This chapter presents contributing factors in the decision about the type of exchanger. This chapter discusses useful guidelines for designers to select the best type of exchanger among different common types. The summary of this chapter is also presented in the form of a table to facilitate the decision process.

There are three main approaches to the thermal design of all exchangers: Direct approach Rating Simulation In this chapter, readers will be introduced to these approaches. Also, the thermal design methods of shell-and-tube heat exchangers as the most widely used type of exchangers are presented. In this regard, first, different stream types inside a shell are presented, and later two common methods for thermal design, i.e. Kern’s method and Bell-Delaware method are detailed. At the end of this chapter, a common industrial software for the thermal design of shell-and-tube exchangers, i.e. Aspen HTFS+ is presented and the process of exchanger simulation in the software is presented step by step for a few practical examples. The results of the software are compared in detail with the results of Kern’s and the Bell-Delaware methods. Consequently, the readers verify the accuracy of each method.

The second part of the book is dedicated to the thermal design of heat exchangers. As an introduction to thermal design, heat transfer mechanisms including, i.e. conduction, convection, and radiation and the governing equations are briefly explained. A review of fundamental concepts of heat transfer in a tube is presented in the form of a few examples.

A tubesheet is a flat, circular sheet with holes, which are responsible for holding the tube ends in a shell-and-tube exchanger, as well as separating the shell-side fluid from the channel-side fluid. The TEMA standard adopts a different approach to tubesheet design from the ASME code and the standard is not intended to be used in addition to ASME design rules. In TEMA, the equations for tubesheet design are summed up in two general equations relating to bending and shear strength. Although these equations are less complex than the ASME equations, they are less commonly used in industries today. This chapter explains the TEMA method for designing different types of tubesheet.

Applying a magnetic field to influence convective flow of ferrofluids has become an efficient method for enhancing heat transfer in thermal systems, particularly in straight tubes. This study investigates the heat transfer properties of Fe3O4/TiO2 nanofluids within a heated copper tube under varied magnetic field strengths and waveforms. Optimal magnetic field conditions were determined at 4 V and 60 Hz across all waveform types, as higher frequencies and voltages increased magnetic field intensity, thereby reducing heat transfer rates. Magnetic waveforms exerted differential influences on pressure drop, indicating varied nanoparticle alignment and turbulence levels, impacting fluid flow dynamics and viscosity. Higher nanoparticle concentration (0.1% vol) correlated with increased pressure drops across sine, square, and triangular waveforms, suggesting heightened flow resistance and potential nanoparticle agglomeration, thus reducing thermal efficiency. Conversely, lower concentrations exhibited enhanced thermal performance due to improved nanoparticle dispersion and reduced thermal resistance. At 0.1% vol, heat transfer enhancement without a magnetic field was 16.5%. The introduction of magnetic field waveforms attenuated this enhancement: 15.3% (sine), 13.26% (square), and 12.59% (triangular). Conversely, at lower volume fractions, heat transfer enhancements with magnetic fields exceeded those without at 0.05% vol, enhancements were 20.92% (sine), 21.3% (square), and 21.34% (triangular); at 0.025% vol, enhancements were 22.07% (sine), 22.3% (square), and 21.32% (triangular); at 0.0125% vol, enhancements were 27.87% (sine), 28.21% (square), and 26.74% (triangular); and at 0.0065% vol, enhancements were 22.24% (sine), 22.3% (square), and 24.49% (triangular).

This study reports an experimental investigation of nanoparticle sizes effects on the heat transfer characteristics of hybrid nanofluids along the transitional flow regime. Four different particle sizes were used to prepare hybrid nanofluids of Al2O3 and MWCNT (i.e., 5 nm and 20 nm for Al2O3 and <7 nm and 30–50 nm for MWCNT nanoparticles). Three hybrid nanofluids with different particle combinations (i.e., Al2O3(5 nm) – MWCNT (<7 nm), Al2O3(20 nm) – MWCNT(<7 nm) and Al2O3(20 nm) – MWCNT (30–50 nm)) at a percentage weight composition (PWC) of 60:40 and 0.3 volume concentration were prepared. Results showed that particle sizes significantly affected the convective heat transfer characteristics of the nanofluids. Along the transition region, all three fluids were found to have different critical Reynold numbers 1152, 1172, and 1898 for Al2O3(20 nm) – MWCNT (<7 nm), Al2O3(5 nm) – MWCNT (<7 nm) and Al2O3(20 nm) – MWCNT (30–50) respectively. Al2O3(20 nm) – MWCNT (<7 nm) have shown better heat transfer performances. Its Nusselt number shows an enhancement of about 48.86 % along the transition region. And its coefficient of thermal performance (COP) was better than that of Al2O3(20 nm) – MWCNT (30–50 nm) and Al2O3(5 nm) – MWCNT (<7 nm) with 43.53 % and 21.89 %, respectively. While its friction factor and pressure drop were lower than that of Al2O3(5 nm) – MWCNT (<7 nm) nanofluid by 5.2 % and 12.78 %. It was concluded that for a 60:40 hybrid nanofluid of Al2O3 and MWCNT, particle sizes have influenced heat transfer characteristics and affected other flow characteristics along the transition regime.

Openings are holes that are drilled on the exchanger body and used as fluid inlets and outlets or for access to the inside of the exchanger. Nozzles are pipes used for fluid inlets and outlets or to connect measuring equipment and instruments. Since a portion of the body area is reduced due to the drilling of openings for installing nozzles, it is necessary to compensate for the reduced surface area by increasing the thickness around the nozzles or using reinforcement pads. The requirements for reinforcing the openings and the calculations are presented in this chapter. Some colourful pictures are provided to make the design method more comprehensible. A summary of the steps involved in the designs is presented in the form of tables.

Due to operation under high pressures and temperatures, the design of boilers, heat exchangers, and pressure vessels is a difficult and high-risk task; hence, there is a need for universal standards that are accepted by the scientific-engineering community. The ASME code is one of the most common standards that covers the requirements of design, fabrication, materials selection, and the necessary tests at the time of manufacturing. The ASME code itself is very comprehensive and sometimes vague, which led to confusion in the design. Therefore, there is a demand for much shorter and direct guidelines to make the design procedure of the ASME code more understandable. This chapter, along with the upcoming chapters, will attempt to simplify the ASME code for readers. In this chapter, the history of the ASME code as well as stress categories are discussed.

Among tubular heat exchangers, the double-pipe or hairpin heat exchanger is the closest to a shell-and-tube exchanger. A simple double-pipe exchanger consists of a single tube or pipe with or without longitudinal fins, which are concentrically fitted inside a larger tube or pipe. In its basic form, both ends of the pipes are sealed together by a flat plate. In this chapter, the structure of these exchangers, different parts, etc. are detailed. Methods of cleaning and testing are also explained. This chapter includes several unique industrial pictures that make the concepts of these exchangers more understandable.