Dimensionless Heat Research Articles

The effect of fire-wall distance on the flame attachment characteristics and flame height of near-wall fires

Near-wall fires happen frequently in buildings and may ignite the solids on the wall, leading to a rapid spread of fire. A series of experiments and numerical simulations were conducted on near-wall and free (the same as that of near-wall fire source after mirroring) fires using propane and methane as the fuel to investigate the effect of the wall on flame attachment properties and flame height. The presence of a wall decreases the degree of turbulence for downstream flame and influences the velocity and temperature evolutions due to the no-slip and impermeability conditions. Due to the asymmetric evolution of vortices, intermittent flame attachment emerges at a certain downstream location and is intensified with decreasing fire-wall distance. The upper attachment limit increases with the heat release rate, however, the dependence of the lower attachment limit on the heat release rate is related to the fire-wall distance. The flame attachment probability increases with the aspect ratio of the gap between the fire source and the wall. Grashof number is a suitable parameter to correlate the flame attachment parameters of near-wall fires, including flame attachment limit, length and probability. The flame height increases with decreasing fire-wall distance and is 17.8%∼46.5% higher than that of free fires. By defining a dimensionless heat release rate incorporating the flame attachment probability, a unified model was built to predict the flame height of near-wall and free fires. The data and models are expected to be useful for evaluating the risk of early-stage near-wall fires.

Upper bound of heat flux in an anelastic model for Rayleigh–Bénard convection

Bounds on heat transfer have been the subject of previous studies concerning convection in the Boussinesq approximation: in the Rayleigh–Bénard configuration, the first result obtained by Howard (J. Fluid Mech., vol. 17, issue 3, 1963, pp. 405–432) states that the dimensionless heat flux $\textit {Nu}$ carried out by convection is such that $\textit {Nu} < (3/64 \ Ra)^{1/2}$ for large values of the Rayleigh number $Ra$ , independently of the Prandtl number $Pr$ . This is still the best-known upper bound, only with the prefactor improved to $\textit {Nu} -1 < 0.02634 \ Ra^{1/2}$ by Plasting & Kerswell (J. Fluid Mech., vol. 477, 2003, pp. 363–379). In the present paper, this result is extended to compressible convection. An upper bound is obtained for the anelastic liquid approximation, which is similar to an anelastic model used in astrophysics based on a turbulent diffusivity for entropy. The anelastic bound is still scaling as $Ra^{1/2}$ , independently of $Pr$ , but depends on the dissipation number $\mathcal {D}$ and on the equation of state. For monatomic gases and large Rayleigh numbers, the bound is $\textit {Nu} < 25.8\, Ra^{{1}/{2}} / (1-\mathcal {D}/2 )^{{5}/{2}}$ .

Experimental study on the effect of dual fire sources elevation on flame merging characteristics in road tunnels with natural ventilation

A series of experiments was carried out using a 1:10 small-scale model tunnel to investigate the effect of different fire source elevations on the flame merging characteristics of dual fire sources under natural ventilation. CFD numerical simulation software was used to analyze the impact of fire source elevation on flame merging characteristics and air entrainment from the perspectives of lateral velocity, longitudinal velocity, vertical velocity and air entrainment rates. The effects of fire source spacing and heat release rate on the probability of flame merging and the height of the flame merging point under different fire source elevations were investigated. It is found that as the fire source spacing S increases, the flame tilt angle θ first increases and then stabilizes for the first time. With a further increase in S, θ increases again and stabilizes for the second time. The first stabilization is mainly controlled by the interaction between the fire sources, while the second stabilization is primarily influenced by natural ventilation from both ends of the tunnel. As the fire source elevation increases, the flame merging probability decreases with the addition of air entrainment between the fire sources. What is more, when the fire source elevation exceeds 8 cm, the effect of the fire source elevation on the flame merging probability is no longer obvious. The prediction model of flame merging probability under different fire source elevations is proposed. Meanwhile, the dimensionless fire source elevation h/D and the modified dimensionless heat release rate Q̇DS∗ are used to express the dimensionless height of flame merging point Zm/Hef. The piecewise function of Zm/Hef and Q̇DS∗ is obtained. WhenQ̇DS∗≤88,h/D≤8, the relationship between Zm/Hef and Q̇DS∗ could be described with exponential function and whenhD>0.8, the fire source elevation has little impact on Zm/Hef. WhenQ̇DS∗>8, Zm/Hef is approximately constant and increases with fire source elevation.

Thermal analysis of packed bed thermal energy storage system with dimpled spherical capsules

The thermal storage potential of a packed bed filled with paraffin wax capsules was examined. Heat transfer fluid (HTF) at 70 °C inlet temperature for dimpled and plain stainless-steel capsules was compared for three different flow rates, 1 L/min, 3 L/min and 5 L/min. In general, dimpled spherical capsules sustain more heat than plain spherical capsules at the same flow rate, according to instantaneous and cumulative heat stored. Spherical capsules with dimples exhibited a 30 % improvement in charging rate compared to smooth spheres, particularly at elevated flow rates. Specifically, at a flow rate of 5 L/min, dimpled capsules achieved faster charging and sustained higher temperature compared to plain capsules. Higher flow rates (3 and 5 L/min) result in steeper temperature increases and an earlier peak temperature phase compared to the lower flow rate (1 L/min). Key dimensionless heat transfer numbers were examined. The Stefan number was found to be 0.1966 for an HTF inlet temperature of 70 °C and a latent heat of fusion (Lm) of 213 kJ/kg. Heat transfer increases when Reynolds numbers increased from laminar (123.8 at 1 L/min) to turbulent (619.1 at 5 L/min). Rayleigh number decreased over time but increased for dimpled capsules, indicating improved convection. Dimpled capsules had higher Nusselt numbers and increases with flow rate, indicating better convective heat transfer. Dimpled capsules absorbed heat faster and stored more energy, giving them a viable and efficient Packed Bed Latent Thermal Energy Storage system design.

Evaluation and Research on Correlation for Spray Cooling

Abstract Spray cooling is influenced by many related parameters, making analysis of heat transfer mechanisms and prediction of cooling performance challenging. After summarizing and analyzing fifteen different forms of correlation in spray cooling literature, it appears that there are four expressions for spray cooling correlation. 2989 experimental data under different experimental conditions in twelve studies were collected to form an experimental database to evaluate the prediction of correlations. The prediction accuracy of Nusselt number correlations based on droplet diameter is considered the best, while that of correlations based on dimensionless heat flux is considered the worst. The factor analysis method was used to analyze the prediction differences of correlations and investigate the correlation between parameters and the heat transfer process. We found that the correlation with the best evaluation accuracy must contain more parameters with high correlation. A new correlation was derived based on this conclusion to predict the data better.

Innovative approaches to optimizing Li-Ion battery cooling performance using gas mixtures

This study investigates the critical issue of thermal management in lithium-ion batteries, a vital concern for enhancing battery performance, safety, and longevity. While more complex cooling systems like liquid cooling, phase change materials, and two-phase systems offer superior thermal performance due to their higher heat transfer capabilities, they come with significant drawbacks. These include increased system complexity, higher costs, added weight, and the potential for leaks or other failures that can compromise safety and reliability. Consequently, simpler air-based cooling systems are often preferred in many applications, despite their inherently lower h coefficient. To bridge the performance gap between air and liquid cooling without resorting to complex engineering solutions, this study focuses on enhancing the h coefficient of air-based systems using innovative refrigerant gas mixtures. The use of refrigerant gas mixtures, specifically a blend of R1234ze(E), nitrogen, and neon, as an alternative to traditional cooling methods was explored. The study employed a comprehensive FEM model and experimental validation to evaluate free and forced convection in a slender, vertical cylindrical configuration. To analyze the impact on convective heat transfer, the key parameters CRate, T0 and Tamb were systematically varied. A dimensionless analysis then evaluated how thermodynamic properties influence h coefficient. This analysis led to the derivation of a dimensionless heat transfer function h(ρ, Cp, k, μ). The study aimed to significantly improve the efficiency of h by optimizing the gas mixture properties. The “Mixture Study” identifies the optimal refrigerant composition, where a specific mixture α of 86 % R1234ze(E), and 14 % neon demonstrated the best balance between heat transfer efficiency and enhanced thermal capacity. The heat transfer coefficient increases by around 65 % during natural convection and by around 80 % during forced convection. The percentage reduction of the thermal difference in temperature reaches approximately 10 % with a maximum of 4 K in natural convection conditions and a maximum of 36.5 % and a reduction of approximately 10 K compared to air cooling alone, effectively maintaining the battery within the optimal operating range of 293.15 K to 333.15 K. Notably, this composition increased the thermal power absorbed by the mixture by over 100 % under the same thermal difference. This research therefore provides valuable insights for developing more effective gas cooling strategies that ultimately enhance the performance, safety, and durability of batteries in various applications. By integrating the benefits of both cooling methods, the study paves the way for innovative thermal management solutions in battery technology.

Neural network approach to investigate heat transfer in SWCNTs nanofluid within trapezoidal cavity with varied corrugated rod amplitudes

This article presents Artificial Neural Networks (ANN) for convective heat transfer in a trapezoidal cavity subjected to corrugated heated rod inside it. The LevenbergMarquardt algorithm is utilized to optimize the Neural Networks. The trapezoidal cavity has low-temperature inclined walls and adiabatic upper and lower walls compared to the corrugated heated rod. Single-wall carbon (SWCNTs) nanomaterials are submerged in the base liquid water. The flow of SWCNTs-water is generated due to the temperature gradient in the cavity. The system of dimensional partial differential equations has been formulated for the physical setup under investigation. The dimensional system has been converted into a non-dimensional form using dimensionless variables. Finite element is used for the solutions. The dimensionless functions velocity, temperature, and heat transfer rates are studied against the Rayleigh number (Ra). The outcomes are presented in the form of isotherms, contours, tabular values, and graphs. The data for Artificial Neural Networks (ANN) has been generated by FEM against the Nusselt number. The ANN has been trained for a specific amplitude of the rod and predicted heat transfer against a larger amplitude. The results show good agreement for both training and testing data. The outcomes of analysis reveals that convection caused by temperature gradient is dominant for higher values of the Rayleigh number (Ra). Local Nusselt number has been discussed against different amplitudes, and predicted enhancement for the larger amplitude of the rod.

Impinging ceiling flame behaviors induced by wall-attached gaseous fuel fires at one end in a narrow building corridor: Different phases and generalized correlations

This work investigated the flame extension behavior after impinging upon a ceiling induced by wall-attached fires at the closed end in a narrow building corridor. Experiments were conducted in a reduced scale corridor with one end closed and the other opened, under various fire heat release rates and source-ceiling heights (from 0.05 m to 0.50 m) of totally 353 test conditions. The flame morphological characteristic parameters involving the flame extension length in the center of the ceiling and in the two sides were measured and analyzed comprehensively. By a careful observation, it was found that, as the fire heat release rate increased or the source-ceiling height decreased, the ceiling flame extension behavior can be divided into different behavior phases: the flame spreads to the two sides after impinging the narrow building ceiling; flame extends longitudinally after reaching side walls, presenting a semi-elliptical shape; flame in the two sides extends farther than that in the center of the ceiling, presenting a “U” shape; and flame presents a cellular structure (the fire source is near the building ceiling). The dimensionless critical fire heat release rates for the transition of these phases were identified, and non-dimensional correlations were obtained for the prediction of flame extension lengths of different phases. This work provides new observations of different phases and generalized correlations for impinging ceiling flame behaviors induced by wall-attached gaseous fuel fires at one end in a corridor.

A numerical investigation on heat transfer characteristics of a particle cluster in fluid with variable properties

This work investigates the heat transfer characteristics of particle clusters under the effects of the complex properties of supercritical water (SCW). It analyzes the heat transfer characteristics of sub-particles and the average heat transfer characteristics of particle clusters. The results reveal a phenomenon of shifting positions of high specific heat regions. It led to variations in the dimensionless heat transfer coefficient distribution. Furthermore, the results indicate that as the heat transfer process strengthens, the effects of variations in property distribution on heat transfer tends to stabilize. Based on this conclusion, the effects of variations in property distribution on heat transfer are categorized into Stable Effects Region and Non-Stable Effects Region. By utilizing the principles of fluid flow-heat transfer coupling and similarity, a heat transfer prediction model for particle clusters in SCW is established.

Heat Transfer and Fluid Flow Over A Bank of Longitudinally Finned Flat Tubes: A Numerical Study

This computational study investigates the heat transfer rate and fluid flow characteristics of a staggered arrangement of longitudinally finned flat tube banks ( ) with a constant surface temperature. The finite volume method ( ) is used to solve the governing equations using the commercial software . This study considers longitudinal pitch ratios ( ). In addition, the dimensionless transverse pitch ratio ( )=3 and both the dimensionless upstream fin length ratio ( )= ( ) =0.8 is the dimensionless fin angle . The focus of the investigation is a Reynolds number range between with constant physical properties. The analysis examines pressure drop, dimensionless heat transfer rate, and the average Nusselt number. Results indicate that as Reynolds numbers increase and dimensionless longitudinal pitch ratios decrease, the heat transfer rate between tube surfaces and airflow increases to reach maximum value of 275. In addition, the Reynolds number affects the pressure drop, Began number, average Nusselt number, and thermal hydraulic performance.

Instability of penetrative convection in a vertical porous layer with non-Dirichlet temperature conditions

The linear stability of penetrative convection in a differentially heated vertical porous layer with non-Dirichlet boundary conditions on the perturbed temperature field is investigated. The penetrative convection is realized through a uniform internal heating in a porous medium. The instability-driving parameters are the Darcy-Rayleigh number, dimensionless internal heat source strength, the Prandtl-Darcy number, and the Biot number. Neutral stability curves and the critical values of the Darcy-Rayleigh number, the wave number, and the wave speed are computed numerically by employing the Chebyshev collocation method. A comprehensive analysis is conducted on the onset of thermal instability, focusing on the effects of transitioning temperature boundary conditions from Dirichlet to Neumann. A novel finding is the emergence of bi-modal or tri-modal neutral stability curves, which unveil distinct onset modes arising from the combined effects of a heat source and the transition of boundary conditions from isothermal to adiabatic. The threshold value of the Biot number, at which the transition to instability occurs, shows a significant dependence on the internal heat source strength and this threshold value diminishes as the Prandtl-Darcy number attains higher values. Moreover, increase in the Biot number advances the onset of convection, while the Prandtl-Darcy number is found to exert both stabilizing and destabilizing influences on the stability of the base flow.

Experimental investigation of laminar forced convection along flat tubes with longitudinal fins

ABSTRACT The present work experimentally investigates laminar forced convection in staggered finned-flat tubes bank. The study is based on dimensionless downstream fins length, i.e. = 0.4, 0.6, 0.8, and 1, and Reynolds number (Re) range from 223 to 1114. The study was conducted under dimensionless transverse pitch ( = 3.0), longitudinal pitch ( = 4.0), upstream fin length ( = 8), and fin angle (θ = 30°). As the dimensionless downstream fins length increased from 0.4 to 1.0, the dimensionless heat transfer rate was improved up to 6.7%, the dimensionless pressure drop significantly increased up to 225%, and the thermal-hydraulic performance decreased up to 68.5%.

Experimental research on the flow field and flame geometry of free buoyant diffusion flames with low dimensionless heat release rates

The flame geometry of turbulent diffusion flames is dominated by the turbulent mixing between the gaseous fuel and the entrained air. The significant variations of the power law for the mean flame height regarding the dimensionless heat release rate (Q˙*) in different Q˙* ranges implied that the turbulent mixing characteristics would change greatly among these Q˙* regimes. This paper presents a combined experimental and analytical study to reveal the turbulent transport properties and flame shape of free turbulent buoyant diffusion flames of relatively low Q˙* prevalent in large-scale fires. The instantaneous velocity fields of free buoyant methane diffusion flames (burner diameter: d = 0.30 m, Q˙*= 0.22–0.40) were measured by the stereo particle image velocimetry (SPIV) technique. The results indicate that the radial profiles of the time-averaged axial velocity, axial normal stress, radial normal stress, shear stress, and turbulent kinetic energy exhibited self-similarity at different heights under all the heat release rates. The turbulent flow in the buoyant flame was found to be anisotropic. Based on the gradient transport approximation, the mean turbulent viscosity within the mean flame height (νt=) was scaled by g1/2d3/2, where g is the gravitational acceleration. The semi-physical correlations for the mean flame height and width were derived based on the concepts of turbulent mixing and equal axial convection and radial diffusion times, respectively. The two correlations agreed reasonably with the experimental data of this work.

A dimensionless heat transfer coefficient for free convection that is more appropriate than Nusselt number

Heat transfer in flows created by buoyancy, or natural convection, is a widely studied topic across various disciplines spanning natural flows as well as those with engineering applications. The convective heat transfer rate on a surface is commonly represented by the Nusselt number (Nu), a ratio of convective to diffusive transport, expressed often as RanPrm, where Ra is the Rayleigh number, the buoyancy forcing parameter, and Pr the Prandtl number. Motivated by the observation that n∼1/3 for turbulent convection, which implies the heat flux is independent of the length scale (L, characteristic length related to the geometry), we propose an alternate and physically more meaningful non-dimensional heat transfer parameter, denoted by Cq. Cq is derived using only the near wall variables and does not contain L. For n=1/3, Cq is constant. Even for laminar convection, where n∼1/4, Cq∼Ra−1/12, a weak function of Ra. We show that for natural convection over several geometries and a wide range of Ra, the Cq values within a narrow range while the corresponding Nu values span several orders of magnitude. We also show that Cq is akin to the non-dimensional representation of wall shear stress, skin friction coefficient Cf. We believe that just like Cf, Cq will be an equally useful non-dimensional measure of heat transfer in natural convection flows.

Characteristics of concurrent flame spread over convex charring materials

In real forest fire scenarios, there are a large number of convex and concave terrains at the junction of flat land and slopes. In this paper, a typical charring material, kraft paper, is selected as the experimental sample, and the variation law of key characteristic parameters of flame spread over convex solid surface are investigated. The experimental results show that all the flame spread processes have obvious deceleration behaviors, and the influence mechanism of flame tangent angle on the flame spread deceleration of convex surfaces is revealed. The characteristic length of the pyrolysis zone shows a tendency of increasing and then decreasing with time. The variation curves of radiant heat flux present two peaks. Combining with the characteristic length, the reason for the occurrence of two peaks is explained. The exponential relationship between the instantaneous mass loss rate and the characteristic length of the pyrolysis zone is obtained. Based on the range of power exponents, the heat transfer controlling mechanism in the pyrolysis zone is classified into three categories for all the working conditions. Moreover, a piecewise power-law relationship between the dimensionless maximum flame height and the dimensionless heat release rate is established. The results of this study will fill the research gap of flame spread of solid materials with curved surfaces, and will be of great academic value for the improvement and development of theories on building and forest fire safety.

Impact of ventilated tunnels on smoke peculiarities in train carriage fires with multiple lateral openings

This research investigates the dynamics of smoke dispersion in a subway train carriage with multiple lateral openings within a ventilated subway tunnel. Numerous extensive full-scale numerical simulations were conducted to analyze the thermal plume distribution within multiple lateral openings of a train carriage, and the longitudinal and transverse maximum excess ceiling temperature. The results reveal that the heat release rates have a greater impact on the airflow in the carriage than velocities ,even when the longitudinal ventilation velocity reaches 8 m/s or the heat release rate reaches 15 MW. The multiple lateral openings cause significant differences in smoke flow characteristics compared to tunnels with both ends open. Additionally, the transverse maximum ceiling excess temperature inclines towards the lateral opening side due to asymmetrical air entrainment. The analysis of longitudinal maximum ceiling excess temperature identified two regions based on the dimensionless heat release rate, showing a linear increase followed by a constant phase dependent on the heat release rate, with a maximum longitudinal excess gas temperature of 1242 K. Additionally, a relationship between the dimensionless heat release rate and the transverse dimensionless maximum ceiling excess temperature was established. This study can be used as a guide for smoke exhaust mitigation and fire safety measures in the event of subway train carriage fires.

Numerical simulation and thermodynamic test analysis of plate heat exchanger based on topology optimization

Efficient heat transfer in PHEs relies on optimizing flow distribution to minimize thermal dead zones. Existing studies have predominantly focused on single-phase fluids as working media and employed density-based methods for structural optimization of microchannel heat exchangers at small scales. In this study, the Brinkman term from the porous media flow model is introduced in an innovative manner, along with the utilization of a material density interpolation model, which builds upon the density-based approach. A novel two-phase fluid topology optimization method is proposed, specifically tailored for large-scale PHE operating conditions, resulting in the successful design of a new PHE topology. To compare the performance of the two heat exchangers, finite element simulation, visualization experiments, and thermodynamic performance testing are conducted. The simulation results reveal that the heat transfer capacity of the topological PHE is 810 W with pressure drops of 18.8 kPa, while the dimple PHE exhibits heat transfer capacity of 652 W with pressure drops of 25.9 kPa. Compared to the dimple PHE, the topological PHE demonstrates 24.2 % improvement in heat transfer performance and 27.8 % reduction in pressure drop. The dimensionless comprehensive heat transfer coefficient (j/f) indicates that the overall performance of the topological PHE significantly surpasses that of the traditional PHE. Furthermore, the visualization experiment results demonstrate that the complex texture structure of the topological PHE effectively induces fluid motion, compelling the fluid to flow along the texture direction. This significantly mitigates the issue of uneven flow within the PHE, thus enhancing heat transfer efficiency. Specifically, the topological PHE exhibits inlet–outlet temperature difference of 10.3 °C and pressure drops of 11.2 kPa, while the dimple PHE shows inlet–outlet temperature difference of 6 °C and pressure drops of 12.9 kPa. The findings of this study provide guidance for future research endeavors aimed at evaluating potential solutions to advance heat transfer in PHEs and facilitate the implementation of thermal management strategies.

Heat transfer measurement near injection hole of supersonic nozzle with a sonic jet injection

Heat transfer measurements were conducted to investigate surface heat transfer characteristics resulting from the interaction between a sonic jet and supersonic nozzle crossflow. A sonic jet was injected into the nozzle where the average Mach number is 2.88. Experiments were carried out for three different momentum flux ratios (J=0.5, 1.0, 1.5). A half-nozzle was introduced to measure heat transfer on the inner walls of the nozzle using Infrared thermography. Pressure measurements using PSP and oil flow visualization were also conducted to understand the heat transfer. From the oil flow visualization and heat transfer results, it was found that the area around the hole influenced by recirculation vortexes exhibited high heat transfer coefficients, showing up to 5 times higher values compared to the freestream. Furthermore, as the momentum flux of the jet increased, both the heat transfer augmentation area and the heat transfer coefficient also increased. To analyze the heat transfer characteristics between the nozzle and flat surface, comparisons were made using dimensionless heat transfer coefficients. The nozzle exhibited higher heat transfer in a smaller interaction area compared to that of a flat surface, but the average heat transfer coefficient near the hole was lower. Accordingly, distinct thermal treatment strategies should be employed for nozzles and flat surfaces, especially near injection holes. These insights could be valuable for the thermal design of rockets and other supersonic/hypersonic mobility systems.

Relation between characteristic temperature and elution temperature in temperature programmed gas chromatography – Part II: Influence of column properties

The method development process in gas chromatography can be accelerated by suitable computer simulation tools using knowledge about the solute-column interactions described by thermodynamic retention parameters. Since retention parameters usually are determined under isothermal conditions, the presented work offers a step to estimate one of the most important retention parameters, the characteristic temperature Tchar by less laborious temperature programmed measurements.In the first part an empirical multivariate model was introduced describing the correlation between the elution temperature Telu of a solute and its characteristic temperature Tchar. Now in the second part a simulation model of GC and available retention data from a retention database was used to investigate the correlation between Telu and Tchar for an expanded range of heating rates and initial temperatures. In addition to part I, the simulation is used to investigate the influences of different properties of the separation column such as different phase ratios and column geometries like length and diameter or various stationary phases including SLB-5 ms, SPB-50, Stabilwax, Rtx-Dioxin2, Rxi-17Sil MS, Rxi-5Sil MS, ZB-PAH-CT, DB-5 ms, Rxi-5 ms, Rtx5 and FS5ms. The fit model is valid for all investigated stationary phases. The influence of the phase ratio to the correlation could be determined. Therefore, the model was expanded to this parameter.The expanded range of heating rates and the normalization for the system independent dimensionless heating rate required a further modification of the previously presented correlation model. The model now fits also under isothermal conditions. The results were used for estimation of the Tchar of an analyte from the elution temperature in the temperature program. The prediction performance was investigated and evaluated for 20 different temperature program conditions and at two phase ratios (β=125 and β=250). Under best conditions the estimated and the measured Tchar values show relative differences <0.5 %. With this novel model estimations for Tchar are possible at 20 °C above the initial temperature, which expands the prediction range even for low and medium retained analytes compared to earlier approaches.

Experimental studies on the effect of Al2O3 + water nanofluid concentrations on dimensionless heat transfer parameters in a cleanroom air handling unit

Nanofluid, a colloidal suspension of nonmetallic or metallic nanoparticles into conventional base fluid and used for heat transfer characteristics enhancement for many industrial applications. Cleanrooms are essential at various industries for controlling airborne contamination and environmental parameters. In this article, heat transfer properties of nanofluid (Al2O3 + water) at various nanoparticle concentrations (1%, 2%, and 3%) on a prototype cleanroom air handling chiller unit was investigated experimentally in laminar flow zone. Thermal conductivity ratio, Nusselt number, Peclet number, and pressure drop were obtained for above nanoparticle concentrations. Experimental investigations indicate the heat transfer properties improvement in a prototype cleanroom air handling chiller unit by using nanoparticle at base fluid. Experimental investigation on varying Al2O3 + water nanofluid concentrations in a cleanroom air handling chiller unit heat exchanger revealed a notable increase in heat transfer by reducing nanoparticle size from 50 to 10 nm and increasing concentration from 1% to 3% volume, resulting in a 17.70% rise in thermal conductivity ratio and a significant 9.23% increase in Nusselt number at higher Peclet numbers. However, this improvement in heat transfer was accompanied by a substantial 72.5% increase in pressure drops, particularly with increased Reynolds number and particle concentration. Manipulating nanoparticle characteristics resulted in substantial improvements in Nusselt number across a wide range of Reynolds numbers, with smaller particle sizes and higher volume concentrations yielding more significant heat transfer improvements. The novelty of this research lies in its investigation of the influence of variable Al2O3 + water nanofluid concentrations, encompassing different nanoparticle sizes, and volume concentrations, on dimensionless heat transfer parameters within a cleanroom air handling unit, offering valuable insights into optimizing heat transfer efficiency in a controlled and critical environment, addressing a significant research gap in the field.