Experimental Study Of Heat Transfer Research Articles

Experimental Study of Condensation Heat Transfer and Droplet Dynamics on Multiple Horizontal Copper Tubes with Superhydrophobic Characteristics

We conducted an experimental study on the condensation heat transfer and droplet dynamics on multiple horizontal copper tubes with superhydrophobic characteristics. Condensation heat transfer has various industrial applications such as power plants and air-conditioning systems. Because condensers are typically designed in multiple-tube configurations, studying the phenomenon of multiple tubes is important. We investigated the effect of a superhydrophobic surface modification, which induces dropwise condensation, on the heat transfer performance of multiple-tube condensers. The purpose of this research is to evaluate the extent to which heat transfer performance is improved by comparing superhydrophobic tubes with bare tubes and to analyze the impact of droplet dynamics on heat transfer performance. The results show that the heat transfer coefficient of the superhydrophobic tubes is improved by approximately 9.5%–44.9% compared to that of bare tubes. Droplet dynamic analysis revealed differences in droplet behavior between the superhydrophobic tubes and bare tubes, including the formation of droplets by condensation, the process of droplets falling on the tube surface, and the impact of droplets falling on other tubes in a multiple-tube configuration. Based on these results and observations, it can be concluded that the heat transfer performance of the superhydrophobic tube is superior to that of the bare tube. The droplet dynamic analysis demonstrated that the droplets formed on the superhydrophobic surface could be easily removed by the flow, leading to more efficient heat transfer. These findings highlight the potential for more efficient heat transfer in multiple tubes through superhydrophobic modifications.

Experimental and numerical study of conductive heat transfer in aggregate particles using a flighted, rotary drum

Heating aggregates and recycled materials is an energy intensive part of the process of producing asphalt pavement. Sustainability can be improved by increasing the portion of recycled materials while decreasing the energy required to produce the asphalt mixture. A common method to incorporate recycled materials is to mix heated aggregate with cold recycled materials. Interstitial gas conduction is the dominant mode of heat transfer in this process due to the low thermal conductivity of these materials. In this study, a particle-based model that includes the contribution of the interstitial gases was validated with a novel experimental method using infrared (IR) thermography to track the temperature evolution of a mixture of hot and cold aggregates in a flighted, inclined drum. The simulation results showed good agreement with the experiment demonstrating the model’s ability to capture the heat transfer and the particle flow in the dynamic system of irregular shaped particles.

An Experimental Study of Heat Transfer in Pool Boiling to Investigate the Effect of Surface Roughness on Critical Heat Flux

Utilizing pool boiling as a cooling method holds significant importance within power plant industries due to its ability to effectively manage temperature differentials amidst high heat flux conditions. This study delves into the impact of surface modifications on the pool boiling process by conducting experiments on four distinct boiling surfaces under various conditions. An experimental setup tailored for this investigation is meticulously designed and implemented. The primary objective is to discern the optimal surface configuration capable of efficiently absorbing maximum heat flux while minimizing temperature differentials. In addition, this study scrutinizes bubble dynamics, pivotal in nucleation processes. Notably, surfaces polished unidirectionally (ROD), exhibiting lower roughness, demonstrate superior performance in critical heat flux (CHF) compared to surfaces with circular roughness (RCD). Moreover, the integration of bubble liquid separation methodology along with the introduction of a bubble micro-layer yields a microchannel surface. Remarkably, this modification results in a noteworthy enhancement of 131% in CHF and a substantial 211% increase in the heat transfer coefficient (HTC) without resorting to particle incorporation onto the surface. This indicates promising avenues for enhancing cooling efficiency through surface engineering without additional additives.

CFD simulation and experimental study of calcium carbide heat transfer under natural convection and radiation heat transfer

ABSTRACT Few studies on the heat transfer of calcium carbide (CA) under natural convection exist currently. Studying the radiative heat transfer of CA is of significant importance for its waste heat utilization. Therefore, this paper, based on CFD simulations, investigates the heat transfer processes of CA under natural convection and radiative heat transfer. Additionally, on-site experiments are conducted to measure the temperature of CA. The results indicate that considering radiation, the maximum discrepancy between simulation and experimentation is 11.9%, while without considering radiation, the maximum discrepancy increases to 85%. Based on the temperature variations on the surface of CA and changes in cooling rates, it is inferred that waste heat recovery should occur within the first three hours after the CA is taken out of the furnace. Within the initial six hours, the convective and radiative heat transfer amounts are 17.1 kW•h and 155.67 kW•h, respectively, with the latter constituting 90.11% of the total heat exchange. Therefore, adopting a radiation-based approach is recommended for the recovery of waste heat from CA. Finally, employing data regression analysis, a functional relationship between the natural convection-radiation coupled heat transfer coefficient and time is derived.

Experimental Study of Flow and Heat Transfer in Granular Media

AbstractIn this paper, granular flow is studied using particle image velocimetry (PIV) in two different geometries, that is, rectangular box and cylindrical bladed mixer. Effects of parameters like blade rake angle, bed height, moisture content, and the number of blades were studied. The shear rate and velocity magnitude of granular bed were calculated using PIV. The presence of moisture in the granular bed added additional cohesive forces and reduced shear rate between different layers of particles. Shear rate and shear forces were maximal at the tip of the blade. Temperature variations in the granular bed were measured experimentally and results were compared for static and mixing beds.

Experimental Investigation of Forced Convection in Plain or Partly Inserted Square Channel with Porous Media

Several techniques are used to improve the channels' heat transfer coefficient and Nusselt number. One of the methods used for these improvements is porous media (PM). This research deals with an experimental study of heat transfer by forced convection inside a square-shaped channel (0.12 x 0.12 m2) with a length of (0.5 m) and a hydraulic diameter of (0.12 m). The heat flux (4791.7 W/m2) is exposed below the test section, and other walls are thermally insulated. The air was used as the working fluid for the Reynolds number range (2689.6 to 5806.3). The channel was partially filled with the PM (glass spheres with 5mm diameter) by taking three different heights layers (20, 40, and 60 mm) and knowing its effect on the temperature distribution, the local heat transfer coefficient, locally Nusselt number, and the average heat transfer coefficient and Nusselt number. Also, the same parameters were studied without PM inside the channel (plain). The results showed that the PM improved the heat transfer coefficient and the Nusselt number. Also, the temperature distribution decreased gradually with the Reynolds number increase for each height layer, the local heat transfer coefficient and local Nusselt number gradually reduced with the length of the test section increase for each Reynolds number, average Nusselt number increased gradually with the growth of the Reynolds number for each height layer. The PM layer at a height of (60 mm) gave the best improvement in the heat transfer coefficient and Nusselt number compared to the other layers. In addition, the friction factor across the test section at this layer decreases gradually with increasing fluid velocity.

Experimental and numerical study of mixed convection heat transfer in a vented cavity partially filled with a porous medium: Effects of reynolds and rayleigh numbers on Nusselt number and flow regimes

This article presents a comprehensive investigation of mixed convection flow and heat transfer within a vented, partially side-heated cubical cavity, incorporating a porous medium with low-conductivity square-shaped inclusions. The study encompasses an extensive range of Rayleigh numbers (106 < Ra < 6 × 106) and Reynolds numbers (200 < Re < 4000) while maintaining a fixed Prandtl number of Pr = 0.71. This investigation spans over three decades in Richardson numbers (Ri = Ra/(Re2 Pr)), aiming to discern the interplay between the Nusselt number, Nu, and the Richardson number. Our understanding of Nusselt number dependencies is enhanced by combining PIV measurements of heat transfer and velocity fields with temperature field data. The study uses both experimental and numerical PIV data, incorporating porous media representation to reveal heat transfer scaling with both Reynolds and Rayleigh numbers. Computational Fluid Dynamics (CFD) methods are used to explore the complex physical behavior under different flow conditions. Three distinct flow and heat transfer regimes have been identified, predicated upon the Richardson number. For Ri < 25, the flow structure and Nusselt number exhibit similarities with pure forced convection, where the Nusselt number scales as Nu ∼ Re0.6, independent of the Rayleigh number. Conversely, for Ri > 70, natural convection dominates the vicinity of the heating wall, rendering the Nusselt number less sensitive to Reynolds number variations and predominantly dictated by the Rayleigh number. Notably, the intermediate regime, ranging from 25 < Ri < 70, witnesses a competition between upward-directed natural convection flow at the heating wall and downward-directed forced flow, culminating in a minimum effective Nusselt number.

Experimental Study of Heat Transfer of Different-Thickness Plate Modules of Heat and Mass Transfer Device

Experimental Study of Heat Transfer of Different-Thickness Plate Modules of Heat and Mass Transfer Device

Experimental, numerical and deep learning modeling study of heat transfer in turbulent pulsating pipe flow

Pulsating heat transfer is important in many engineering applications but is not fully understood or easily modeled. This work helps understand the phenomenon and demonstrates the efficacy and utility of deep learning modeling for pulsating heat transfer. The convective heat transfer coefficient (HTC) of pulsating flow through a copper tube was experimentally investigated at seventy-seven different operating conditions (500,000 time-series data points were collected at each operating condition) corresponding to different pulsating waveforms, frequencies, mass flow rates and pressures. The intensity of pulsation ranged from mild to strong enough to cause reverse flow. The literature on pulsating HTC is mixed, with several researchers reporting increased heat transfer and several other reporting decreased heat transfer relative to steady flow. The experimental data showed that both could be true depending on the ratio of the amplitude to mean flow velocity (amplitude ratio AR). The enhancement ratio (ER) of pulsating HTC relative to steady-flow HTC was measured to vary between 0.48 and 2.18 for AR ranging from 0.64 to14.42. A numerical study showed that this was only a (positive) correlation; fundamentally the overall pulsating HTC could be approximately explained by the variation of instantaneous Reynold’s number (Re) during the pulsating cycle. The distribution of instantaneous Re and hence the ER is primarily determined by the pulsating waveform, and this explains the disparate observations by different researchers. Long Short-Term Memory (LSTM) networks have been used to model pulsating HTC as a function of pulsating waveforms occuring across a measurement orifice. The ‘Toy Model’ concept where physics-based variables are used to increase generalization was implemented with the LSTMs for increased model robustness. These models could be used to maximize pulsating heat transfer by optimizing the waveform.

Aerothermal Optimization of Film Cooling Hole Locations on the Squealer Tip of an HP Turbine Blade

Abstract This paper presents a time-efficient method to optimize the positions of film cooling holes on a gas turbine blade's squealer tip for cooling and aerodynamic performance. A computational approach is employed for the optimization, including validations against experiments. Five discrete film cooling holes are considered, and two different blowing ratios of 0.4 and 1.0 are studied. The positions of cooling holes on the tip along the tangential direction are varied as the input parameters of optimization. The multi-objective optimization uses an algorithm with an artificial neural network for fast fitness function predictions. The best cooling configuration found by the optimization achieves a 13.43% reduction in total heat flux and a 0.4% increase in aerodynamic loss when the blowing rate is 1.0. Including the casing relative motion in the computations results in a total pressure loss coefficient increase of about 8 % for both blowing ratios. For M=1.0, imposing the casing's motion results in a 10.2% reduction in total heat transfer to the tip compared to the stationary casing. For the lower blowing rate of 0.4, the total heat flux reduction to the tip is 12.0% because of imposed casing motion. Hence, the cooling effectiveness can be improved by employing the particular position optimization method presented in this study. The results suggest that experimental and computational heat transfer studies on cooled turbine blade tips, especially in cascade arrangements, need to consider the relative motion of the blade tip.

Experimental Study of Heat Transfer in an Insulated Local Heated from Below and Comparison with Simulation by Lattice Boltzmann Method

Experimental Study of Heat Transfer in an Insulated Local Heated from Below and Comparison with Simulation by Lattice Boltzmann Method

Experimental study of heat transfer using nanofluids in a coiled agitated vessel equipped with impeller propeller

In this study, the heat transfer enhancement was made by using multiwalled carbon nanotubes (MWCNTs) with distilled water (i.e . nanofluid) in a coiled agitated vessel. The thermal conductivity of the nanofluid at a volume fraction of (0.3 Vol%) was estimated with different parameters (temperature, propeller speed, flow rate, and time ultrasonication). The statistic program Minitab software 2019 by the method of Box–Behnken design (BBD) was used to identify the important and effective parameters of the process. The optimum parameters were found 55°C,300 rpm, 1 L/min, and time ultrasonication of 100 min with enhanced thermal conductivity of about 76.5%.

Experimental study of nanofluid heat transfer for geothermal applications

The paper presents a performance study of a lab-scale geothermal coaxial heat exchanger with an aqueous nanofluid with the nanoparticles of Al2O3. The concentration of nanoparticles was in the interval 2% wt. to 8% wt. We describe the nanofluid production method resulting in samples that are stable in static conditions for 50 days. The average size of the particles was 183 nm in−situ. We found that the thermal conductivity of the nanofluid may increase up to 13%, and the maximum apparent viscosity grows to 20% relative to the base fluid. The nanofluid was tested in a lab-scale geothermal heat exchanger. The best thermal performance of the heat exchanger with nanofluid was 9% higher than for the experiments with the base fluid.

Theoretical and experimental study of heat and mass transfer, evaporation and ignition drops of monoatomic ethanol/butanol binary mixture in cold air

The study evaporation process results of lower alcohols' single drops (ethanol, butanol and their binary mixtures) with an initial droplet size of 1.5-2.5 mm in air at room temperature and atmospheric pressure are presented. To describe the heat and mass transfer of the fuel mixture's drops with different initial composition, prognostic evaluation of dynamics' changes fuels drops size, composition and temperature during their evaporation are proposed. Taking into account the temperature dependence of the heat of vaporization, an analytical dependence for evaluating the drop surface temperature of one-component evaporating fuels is proposed. Comparative analysis of the calculated model's data allowed to suggest a possible evaporation mechanism of multi-component fuel mixtures droplets and to explain some peculiarities in the behavior of the main characteristics this process. It is shown that the thermocouple wires qualitatively affects the behavior with time of temperature and droplet size. Formula for the drop's temperature during evaporation into account the influence of thermocouple are presented.

Conjugate heat transfer of a turbulent tube flow of water and GaInSn with azimuthally inhomogeneous heat flux

An experimental study of the conjugate heat transfer in a turbulent tube flow with azimuthally homogeneous and inhomogeneous heat flux distribution, where the tube is heated with a constant heat flux only over the half circumference, is presented. Using two fluids with clearly different Prandtl numbers (water and a liquid metal alloy), thermohydraulic effects that occur when fluids with very low Prandtl number are used in contrast to ordinary fluids (e.g. water with Pr≈1) are discussed. The test section is validated with water (Pr=5−7.4) for a Reynolds number in the range of 5·103<Re<4.2·104. The experimental data agree excellently with literature data. The maximum nondimensional temperature at the inner surface of the tube is expressed using a simple relationship based on the efficiency of a fin with an adiabatic tip. A near eutectic alloy of gallium, indium and tin (GaInSn, Pr=0.03) is used for the liquid metal experiments. The Péclet number is varied within the range of 240<Pe<3·103. Based on the experimental data of this work, an adapted correlation for the Nusselt number in a turbulent liquid metal tube flow with azimuthally homogeneous heat flux is provided:Nu=4.364+0.0276·Pe0.803The experimental data underlines, that the azimuthally averaged Nusselt number for an azimuthally inhomogeneous heat flux distribution can also be calculated with this correlation with an acceptable level of accuracy. Remarkably, the ratio of the local convective heat transfer coefficient to the azimuthally averaged value for GaInSn reaches a value up to 0.6 at the location of the maximum wall temperature. This is in strong contrast to water, where this ratio is close to unity.

Numerical and experimental study of inverse natural convection-conduction heat transfer in an inclined rectangular cavity

In this work, the inverse three-dimensional (3D) computational fluid dynamics (CFD) method combined with overdetermined experimental data and least squares method is applied to predict the unknown heat transfer rates and the suitable turbulent flow model in an inclined rectangular cavity. The conjugate heat transfer of two 3D natural convection systems at different temperatures separated by a cavity is solved by coupling. The effect of inclination angle θ on the appropriate flow model is investigated. The RMSE obtained by the appropriate flow model is smaller than that obtained by other flow models. The obtained Nusselt number on the hot wall also needs to be closer to the proposed correlation. An interesting finding is that the zero-equation model and RNG k-ε model are respectively more suitable for problems with 0≤θ ≤ 30° and 60°≤θ ≤ 90°, respectively. The number of natural circulation decreases with increasing θ. The obtained estimates of Nuh agree well with the proposed correlation and existing experimental results. A review of the literature revealed that these findings have not yet appeared in the open literature.

Experimental investigation of heating augmentation by particle kinetic energy conversion in dust-laden supersonic flows

The presence of particles in supersonic flows can cause significant increases in stagnation point heat fluxes (Dunbar et al. in AIAA J 13:908–912, 1975). This effect is commonly named ‘particle-induced heat flux augmentation’ or just ‘heating augmentation.’ Heating augmentation can be described as the sum of the conversion of kinetic energy of the particles into thermal energy, characterized by the energy conversion efficiency, also called accommodation coefficient, and the increase of convective heat flux (Polezhaev et al. in High Temp 30:1147–1153, 1992; Vasilevskii and Osiptsov in Experimental and numerical study of heat transfer on a blunt body in dusty hypersonic flow 33rd thermophysics conference, American Institute of Aeronautics and Astronautics, 1999). Although the accommodation coefficient is fundamental for heating augmentation characterization, there is only a small number of experimental datasets for it. This work focusses on the experimental determination of the accommodation coefficient in flow regimes at Mach number 2.1, Reynolds number, based on the probe nose diameter, from approx. 6e5 to 1.8e6, and nominal particle sizes of approx. 20 µm. The decrease of particle velocity and kinetic energy flux in the shock layer is measured with highly resolved shadowgraphy for individual particles. The particle kinetic energy flux is decreased by 29% on average by particle deceleration in the shock layer. Negligible kinetic energy fluxes of rebounded particles were measured. The accommodation coefficient is approx. 0.36 for Al2O3 and SiO2 particles, while it is approx. 0.09 for MgO particles. Hence, it is significantly smaller than the widely used value of 0.7, based on the study of (Fleener and Watson in Convective heating in dust-laden hypersonic flows 8th thermophysics conference, 1973), but in good agreement with values given in (Hove and Shih in Reentry vehicle stagnation region heat transfer in particle environments 15th aerospace sciences meeting, 1977) and (Molleson and Stasenko in High Temp 55:87–94, 2017. https://doi.org/10.1134/S0018151X1701014X ). No difference between erosive and elastic particle reflection mode was detected on the conversion efficiency. The data from a simplification of the modeling approach of the conversion efficiency for elastic particle reflection by Molleson and Stasenko (2017) are in poor agreement with experimental data.

Experimental study of heat transfer and frictional characteristics of impinging jet solar air heater with wire-mesh attached to the absorber plate

This study revolves around improving the thermal performance of impinging jet solar air heater (IJSAH) by using wire mesh of three different sizes. The wire mesh sizes were 0.5×0.5, 1.5×1.5, and 3×3 inches with nozzle diameter (Dj) equal to 3 and 6 mm and Reynolds number (Re) ranging from 4913 to 13103. The variation of Nusselt number (Nu), friction factor (f), thermo-hydraulic performance parameter (THPP), and effective efficiency (ηeff) were evaluated for varying Re. Maximum Nu was developed for case 3 and equalled 109.86, which was 7.3 % and 246 % higher than a smooth IJSAH and flat plate solar air heater (FPSAH), respectively. The minimum friction factor attained equated to 0.0314 for case 2 at Re = 13103. Maximum THPP attained by the setup equalled 1.78 for case 4, having Dj = 6 mm. The THPP attained by case 4 across the range of Re was on an average 9.15 % higher when compared to smooth IJSAH with Dj = 3 mm. Additionally, the system achieved maximum ηeff of 0.53695 at Re = 4913 for case 4. Finally, it was recommended to use a wire mesh having a mesh size equal to 1.5×1.5 inch with Dj = 6 mm for optimum performance.

REDUCED HEAT LOSS THROUGH WINDOW STRUCTURES

The results of theoretical and experimental studies of heat transfer through the window structures of the building are presented, the thermal characteristics of the windows are established and the level of heat loss realized through them is estimated. To determine the heat transfer resistance of two-chamber double-glazed units, numerical modeling of radiative-convective heat transfer is performed, taking into account the thermal conductivity of the gas layer between the glasses. Natural free convection of the gaseous medium in the double-glazed chambers occurs as a result of the temperature difference between the side glass surfaces of the chamber. Modeling is performed by numerically solving the system of fluid dynamics and energy equations for the air layer and glass. On the inner surfaces of the chambers, conditions of the fourth kind are set, which take into account the radiation and conductive components of the total heat flow coming from the glass surface. The results of simulation of heat transfer through double-glazed windows with ordinary glass indicate that about 60 % of heat is transferred by radiation. Therefore, an effective measure to reduce heat loss through windows is to reduce the radiation component of the total heat flow by applying a low-emissivity coating to the inner surfaces of the glass unit. This makes it possible to reduce the total heat flow (and, accordingly, heat loss to the environment) by 20–34 %, depending on the number of glass surfaces with this coating. Conducted independent experimental studies confirm the modeling results. In order to comply with the current requirements of state building regulations and to achieve the energy efficiency class of type C buildings (specific heat consumption for heating 1 sq. m of usable area is less than 75 kWh), for the climatic conditions of Kyiv, it is recommended to use double-chamber windows with two low-emission coatings with the formula of the glass unit: 4M1-10-i4M1-10-i4M1. Bibl. 22, Fig. 8.

Experimental heat transfer study of an enhanced storage medium

Phase change materials (PCMs) are suitable for storing solar energy due to their high-density energy storage and ability to operate in a wide range of temperatures. However, the lower thermophysical properties of PCMs limit their use in solar energy storage applications. Therefore, the incorporation of nanoparticles has emerged as a promising technique to enhance the storage density of PCMs.Extensive studies have been conducted on the measurement of thermophysical properties of both PCMs and nano-PCMs (PCMs with nanoparticles dispersed in them). However, there has been no comprehensive study covering the following aspects: (a) the measurement of thermophysical properties of NaNO3 (PCM) and nano-NaNO3 (nano-PCM), (b) solar energy storage of NaNO3 involving both sensible heat and latent heat in the same study, (c) the construction and implementation of an experimental rig capable of studying heat transfer in PCM and nano-PCM for solar energy storage applications (with a maximum temperature of up to 350 °C), and (d) investigating the effect of nanoparticles on large-scale solar energy storage systems. Therefore, the aim of this study is to experimentally investigate all of the aforementioned points. In order to develop and test these solar storage mediums, an experimental setup has been designed and manufactured, as mentioned earlier.Furthermore, limited studies have considered sodium nitrate salt (NaNO3) as a PCM. In this study, NaNO3 is used as the base material, and two types of materials are considered: PCM1, which consists of sodium nitrate salt (NaNO3), and PCM2, which consists of sodium nitrate salt (NaNO3) with 0.75 wt% iron oxide nanoparticles (Fe2O3) added. The experiments conducted involved both steady-state and transient conditions. The results showed that the addition of nanoparticles improved the charging and discharging by 25.6 % and 23.929 %, respectively. Moreover, the specific heat capacity and latent heat of the developed PCMs increased by 17.857 % and 9.97 %, respectively. These findings suggest that PCM2, with the presence of nanoparticles, melts and discharges energy faster compared to PCM1. Overall, this study contributes to the understanding of solar energy storage using PCMs and nano-PCMs, highlighting the potential benefits of nanoparticle incorporation in enhancing their performance.