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Nanoparticle concentrations have recently attracted attention as a means to increase the effectiveness of parabolic trough solar collectors (PTSC). Computational fluid dynamics (CFD) study has recently gained popularity for evaluating the performance of PTSC with Dimpled Tubes using a nanofluid made of TiO2 nanoparticles distributed in deionized water (DI-H2O). The effect of using Dimpled Tubes with varied turbulent flow rates, from 0.5 kg/minto 2.5 kg/min, is studied via a battery of tests and computational fluid dynamics simulations. TiO2nanofluid performance is compared to water, the “base fluid,” in this study.This study investigates the utilization of TiO2 nanofluids in enhancing the heat transfer performance of parabolic trough solar collector (PTSC) technology, particularly when integrated with dimpled tubes.The importance of this research lies in the quest for improving the efficiency of solar thermal systems, which is crucial for sustainable energy production.Variables such as solar collector efficiency, Reynolds number, and Nusselt number are tracked as the inquiry progresses. When TiO2 nanofluids are added to the base fluid within the dimpled tube, the convective heat transfer coefficient increases by an astonishing 34.25 percent.This improvement is most pronounced at a mass flow rate of 2.5 kg/min and a volume concentration of TiO2 nanofluid of 0.3 %. Parabolic trough solar collectors have recently been the focus of attempts to improve efficiency via nanoparticle concentrations. The paper uses Computational Fluid Dynamics analysis to investigate how well Dimpled Tubes work with TiO2/DI-H2O nanofluid. The significant increase in the convective heat transfer coefficient was clarified by experimental and CFD calculations that considered fluctuations in turbulent flow rates. The improvement is particularly striking at a mass flow rate and a volume concentration of TiO2 nanofluid.Findingsindicate a significant improvement in heat transfer rates when TiO2 nanofluids are used, particularly in conjunction with dimpled tubes. The combined effect leads to a notable thermal efficiency enhancement, representing the potential of nanofluid-based improvements in optimizing PTSC performance.

The ternary nanofluids are considered due to their advantages in overcoming the stability drawback of mono and binary nanofluids. This study aims to heat transfer performance of Al2O3-TiO2-SiO2 ternary nanofluids in plain tube with wire coil under experimental. The ternary nanofluids were formulated using the composition ratio of 20:16:64 by volume in various volume concentrations ranging from 0.5 to 3.0%. Thermal conductivity and dynamic viscosity of ternary nanofluids were measured with KD2 Pro Thermal Properties Analyzer and Brookfield LVDV III Rheometer. Experimental forced convection heat transfer was carried out using a fabricated setup for Reynolds numbers from 2,300 to 12,000 at bulk temperature of 70 °C in plain tubes with wire coil inserts (0.83 ≤ P/D ≤ 2.50). Experimental results are highest thermal conductivity enhancement of 24.8% was obtained for ternary nanofluids at 3.0% volume concentration. The 3.0% volume concentration also shows the highest viscosity at all temperatures. The maximum heat transfer improvement for ternary nanofluids in a plain tube with wire coil (P/D-0.83), was attained by 3.0% volume concentration of up to 199.23%. The average TPF of the wire coil increases compared to the plain tube and improves further with volume concentrations in the range of 2.39 to 2.84. [ABSTRACT FROM AUTHOR]

LNG corrugated hoses have better flexible mechanical properties and compliance. However, due to the influence of its outline structure and the large heat transfer coefficient, large heat loss is caused during LNG transportation, with the transportation efficiency reduced. Therefore, the flow and heat transfer characteristics of LNG in the plain tube and the corrugated hoses with 5 types of different structural parameters were analyzed with the numerical simulation method. Meanwhile, the influence laws of the corrugation depth,corrugation pitch and Reynolds number on the heat transfer characteristics of the hoses were explored, and the heat transfer characteristics of the hoses were characterized with the thermal performance evaluation criterion(PEC). The results show that: The corrugated hoses have higher Nusselt number, greater friction coefficient and better heat transfer characteristics than the plain tubes. The Nusselt number in the corrugated hoses increases with the increase of Reynolds number, while the friction coefficient decreases with the increase of Reynolds number and becomes stable at high Reynolds number. Under the same Reynolds number, the Nusselt number of the corrugated hoses increases with the increase of the corrugation depth, but decreases with the increase of the corrugation pitch. Besides, the friction coefficient is proportional to the change of the corrugation depth and pitch, and the corrugation depth has the greatest influence. Generally, the research results could provide theoretical guidance for the engineering application and the structural optimization design of LNG cryogenic corrugated hoses.

Solar power is often regarded as one of the most promising forms of alternative energy since it is both sustainable and renewable. It is difficult to utilize and benefit from solar energy in residential and industrial applications because of the intermittent nature of its supply. A solar-based water heating system is efficient for using solar thermal conversion, the simplest and most successful method of turning solar energy into thermal energy. In this research, the performance analysis of Parabolic Trough Solar Collectors (PTSCs) with aluminum-coated copper dimple tubes was computationally and experimentally analyzed. For computational analysis, a Computational Fluid Dynamics (CFD) tool was used. For experimental analysis, aluminum-coated dimple tubes were used to pass the base fluid (water) in it while varying the mass flow rate from 1.0 to 3.0 kg/min at steps of 0.5 kg/min to examine the effect of dimple texturing and aluminum coating on the performance of the solar water heater. The parameters, such as thermal efficiency, friction factor, convective heat transfer coefficient, Nusselt number, and effectiveness of the PTSC, were analyzed, and we found remarkable improvement towards high conversion efficiency. At a flow rate of 2.5 kg/min, the thermal efficiency was improved by about 36%, the friction factor increased by about 0.32%, the convective heat transfer coefficient was improved by 1150 W/m2K, Nusselt number was improved by about 53.8 and the effectiveness was enhanced by 0.4. The simulation results were compared with the experimental results, and the deviation was about ±3.8%, which may be due to an error in the instrument as well as environmental conditions during the analysis. The outcome of results can be used for real-life applications in industrial water heating and domestic water heating especially, the places exposed to low solar radiation intensity throughout the year. [ABSTRACT FROM AUTHOR]

Recently, parabolic trough solar collector (PTSC) efficiency enhancement with nanoparticle concentrations has been identified as a potential research area. In this research, the performance of PTSC with dimple tube with TiO2/DI–H2O (De-Ionized Water) nanofluid has been analysed using computational fluid dynamics (CFD). The size of the nanoparticle was in the range of 10–15 nm. Different volume concentrations of the nanoparticles in the range of 0.1–0.5%, in steps of 0.1%, were chosen to prepare the nanofluids to carry out the experiments. Experimental and CFD analysis is compared to TiO2 nanofluid with water (base fluid) at varying mass flow rates (0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 kg min−1) in a turbulent flow system using Dimples tube. Furthermore, PTSC parametric values were determined from test results such as friction factor, uncertainty analysis, Reynolds number, solar collector efficiency, Nusselt Number, and Convective heat transfer coefficient. In comparison, the convective heat transfer coefficient of the TiO2 nanofluids with the base fluid is increased to 34.25% with the dimples tube. The highest performance increase in PTSC with a mass flow rate of 2.5 kg min−1 and 0.3% volume concentration gives overall optimized results in absolute energy absorption, gradient temperature, and efficiency of the solar water heater. The nanofluid's output index is 2.42 with a 0.3% mass flow rate and a concentration of 1.5 kg min−1. The PTSC with TiO2 nanofluid has a maximum overall efficiency of 34.25%, which is 11% higher than the overall efficiency of the base fluid. At a mass flow rate of 3.0 kg min−1 and 0.5% volume concentration, the pressure drop was increased by about 5.68% compared to the mass flow rate of 2.5 kg min−1. [ABSTRACT FROM AUTHOR]

In modern condensers of air conditioning systems, heat pumps, evaporators of seawater desalination systems, and heaters of power plants, the process of vapour condensation is carried out mainly inside the horizontal tubes and channels. Heat transfer processes occurring in condensers have a significant effect on the overall energy efficiency of the mentioned systems. In this paper, the experimental investigation of heat transfer during condensation of freons R22, R406a, and R407c in the plain smooth tube with d = 17 mm were carried out with the following parameters: ts = 35–40°C, G = 10–100 kg/ (m2 s), x = 0.8–0.1, q = 5–50 kW/m², ∆T = 4–14 K. The unique measurements of circumferential heat fluxes and heat transfer coefficients were carried out with the thick wall method during different condensation modes. It can be inferred that with the increase of the heat flux, at the top part of the tube the thickness of the condensate film increases, which leads to the decrease in heat transfer. At the bottom of the tube, the increase in the heat flux enhances heat transfer coefficient, that is characteristic of the turbulent liquid flow in the tube. The obtained results allowed improving the prediction of effective heat transfer coefficients for vapour condensation, which takes into account the influence of condensate flow in the lower part of the tube on the heat transfer. This method generalises with sufficient accuracy (error ± 30%) the experimental data on condensation of freons R22, R134a, R123, R125, R32, R410a, propane, isobutene, propylene, dimethyl ether, carbon dioxide, and methane under stratified flow conditions. Using this method for designing heat exchangers, which utilise such types of fluids, will increase the efficiency of thermal energy systems. [ABSTRACT FROM AUTHOR]

Solar power is often regarded as one of the most promising forms of alternative energy since it is both sustainable and renewable. It is difficult to utilize and benefit from solar energy in residential and industrial applications because of the intermittent nature of its supply. A solar-based water heating system is efficient for using solar thermal conversion, the simplest and most successful method of turning solar energy into thermal energy. In this research, the performance analysis of Parabolic Trough Solar Collectors (PTSCs) with aluminum-coated copper dimple tubes was computationally and experimentally analyzed. For computational analysis, a Computational Fluid Dynamics (CFD) tool was used. For experimental analysis, aluminum-coated dimple tubes were used to pass the base fluid (water) in it while varying the mass flow rate from 1.0 to 3.0 kg/min at steps of 0.5 kg/min to examine the effect of dimple texturing and aluminum coating on the performance of the solar water heater. The parameters, such as thermal efficiency, friction factor, convective heat transfer coefficient, Nusselt number, and effectiveness of the PTSC, were analyzed, and we found remarkable improvement towards high conversion efficiency. At a flow rate of 2.5 kg/min, the thermal efficiency was improved by about 36%, the friction factor increased by about 0.32%, the convective heat transfer coefficient was improved by 1150 W/m2K, Nusselt number was improved by about 53.8 and the effectiveness was enhanced by 0.4. The simulation results were compared with the experimental results, and the deviation was about ±3.8%, which may be due to an error in the instrument as well as environmental conditions during the analysis. The outcome of results can be used for real-life applications in industrial water heating and domestic water heating especially, the places exposed to low solar radiation intensity throughout the year.

In this paper, the experimental study of heat transfer during condensation of freons R22 and R407С in a plain smooth tube with 17 mm inner diameter was carried out at saturated condensing temperature 40 °C, while mass velocity ranged between 6 and 57 kg/(m2s) and vapour quality changed from 0.23 to 0.95. The unique measurements of circumferential heat fluxes and heat transfer coefficients were performed with the thick wall method during the stratified flow of the phases. The authors performed numerical simulation of heat transfer from condensing vapour to cooling water through the thick-walled cylindrical wall. The CFD model was validated by conducting the physical experiment, which indicated the results coincidence with an error from 7 to 20%. The obtained results allowed improving prediction of effective heat transfer coefficients for vapour condensation, which takes into account the influence of condensate flow in the bottom part of the tube on the heat transfer. This method generalizes with sufficient accuracy (error ± 30%) the experimental data on condensation of freons R22, R134a, R123, R125, R32, R410a, propane, isobutene, propylene, dimethyl ether, carbon dioxide and methane under the stratified flow conditions. Using this method for designing heat exchangers, which utilize such types of fluids, will increase the efficiency of thermal energy systems. [ABSTRACT FROM AUTHOR]

The use of heat transfer enhancement techniques, can improve the thermal performance of the tubes. In this study, the convective heat transfer from nanoparticles TiO2–SiO2 was dispersed to W/EG in the plain tube, under constant wall heat flux studied numerical and experimental. The type of nanofluid used is the TiO2–SiO2 base fluid EG/water mixture. The volume concentrations used were 1.0, 2.0 and 3.0%. The Reynolds number (Re) used ranges from 2900 to 11,200. The effect of nanofluids on heat transfer coefficients and friction factors is presented in this work. The results show that heat transfer increases with Reynolds number for numerical and experimental in plain tube. Hybrid nanofluids at volume concentration of 3.0% had the highest amount of Nusselt and the highest friction factor was followed by 2.0% and then 1.0%. Experimental and numerical results are compared in terms of Nusselt number average deviation found was 8.8, 8.9 and 7.9% for the volume concentration of 1.0, 2.0, and 3.0% in this study. The friction factor average deviation is 4.1, 3.8 and 3.5% for the volume concentration of 1.0, 2.0, and 3.0%, respectively.

In modern condensers of air conditioning systems, heat pumps, evaporators of seawater desalination systems and heaters of power plants, the process of vapour condensation is carried out mainly inside the horizontal tubes and channels. Heat transfer processes occurring in condensers have a significant effect on the overall energy efficiency of the mentioned systems. In this paper, the experimental investigations of heat transfer during condensation of freons R22, R406a and R407c in the plain smooth tube with d = 17 mm were carried out with the following parameters: saturation temperature - 35÷40 ºC, mass speed - 10÷100 kg/(m2s), massive steam content - 0.8÷0.1, specific heat flux - 5÷50 kW/m2, the difference between the temperature of condensation and the temperature of the pipe wall - 4÷14 K. The unique measurements of heat fluxes and heat transfer coefficients local by circumference were carried out with the thick wall method during different condensation modes. It can be inferred that at the top part of the tube, with the increase of the heat flux, the thickness of the condensate film increases, which leads to the decrease in heat transfer. At the bottom of the tube, the increase in the heat flux enhances heat transfer, that is characteristic of the turbulent liquid flow in the tube. The obtained results allowed improving a heat transfer method for steam condensation, which takes into account the influence of condensate flow in the lower part of the tube on the heat transfer. This method generalizes with sufficient accuracy (error ±30%) the experimental data on condensation of freons R22, R134a, R123, R125, R32, R410a under the stratified flow conditions. Using this method for designing heat exchangers, which utilize such types of fluids, will increase the efficiency of energy systems. [ABSTRACT FROM AUTHOR]

Since the first work of Tepe and Mueller [1] and until now, there have been published hundreds of studies with the results of heat transfer investigations in vertical and horizontal tubes with vapour condensing of various liquids. Dozens of methods and formulae based both on the results of the theoretical research and on the experimental data have been proposed. The existence of more than 50% discrepancy in different experimental data and various empirical and theoretical relationships is shown. Thus, the absence of both substantiation of different methods and explanations of methods disagreement both between themselves and with different experiments is noted. Also, there are often no remarks concerning boundaries for the use of proposed relationships. There is proposed a simple semi-empirical correlation for heat transfer prediction in condensing inside the plain tubes at the annular and intermediate flow of the phases. This correlation is based on the nature of film condensation process and on the specific features of the results of theoretical solutions. The range of application of complexes, which determine the heat transfer process, is also substantiated. Good convergence of the new method with the experimental data on condensation of steam, carbon dioxide, hydrocarbon refrigerants and other various fluids inside horizontal and vertical tubes is shown. [ABSTRACT FROM AUTHOR]

Falling film towers are popular in process industries due to moderate air side pressure drop, less energy ingesting liquid distribution and easy cleanup features. Two major limitations of falling film towers are the uneven distribution of liquid across solid surfaces (maldistribution) and contraction of falling liquid film on the solid surface (poor wetting). Maldistribution of liquid is primarily dependent on the type of liquid distributor and scope of liquid flow (slit opening) across solid surfaces. In the current communication; the influence of liquid distributor on maldistribution problem for vertical plate falling film tower has been experimentally investigated. Four types of liquid distributors: plain tube, spray nozzle, perforated plate, and branch tube distributor have been tested. Effect of parameters: slit opening, liquid flow rate, and the number of plates on maldistribution are also explored. It is found that branch tube distributor is best suited for vertical plate falling film tower application. [ABSTRACT FROM AUTHOR]

This study describes an experimental investigation on the heat transfer characteristics of MWCNT (Multi walled Carbon Nano-tube)–heat transfer oil based nanofluid during mixed convection inside inclined plain and microfin copper tubes under uniform heat flux condition. Data were acquired for the laminar flow in the thermal entrance region and for tube inclination angles of 0, 45° and 90°. Pure heat transfer oil and nanofluids with nanoparticles weight concentrations of 0.05%, 0.1% and 0.2% were used as the working fluids. Effects of nanoparticles concentration, heat flux, tube inclination and free convection on the development of the thermal field are studied under buoyancy assisted flow condition for Grashof number, Reynolds number and Richardson number between 500 and 10 4 , 10–100, and 0.1–10, respectively. Results show that Nusselt number increases slightly with an increase of nanoparticles weight concentration from 0 to 0.2% under a given Grashof number. Moreover, increasing Grashof number can raise the heat transfer coefficient in horizontal tube more than the inclined tubes under assisted flow condition. The effect of nanoparticles on heat transfer enhancement decreases by increasing of inclination and Richardson number, also, this effect is more pronounced in the plain tube rather than the microfin one. [ABSTRACT FROM AUTHOR]

Abstract: In the heat transfer area researches have been carried out over several years for the development of convective heat transfer enhancement techniques. The use of additives in the base fluid like water or ethylene glycol is one of the techniques applied to augment the heat transfer. Recently an innovative nanometer sized particles have been dispersed in the base fluid in heat transfer fluids. The fluids containing the solid nanometer size particle dispersion are called ‘nanofluids’. The dispersed solid metallic or nonmetallic nanoparticles change the thermal properties like thermal conductivity, viscosity, specific heat, density, heat transfer and friction factor of the base fluid. Nanofluids are having high thermal conductivity and high heat transfer coefficient compared to single phase fluids. The enhancement in heat transfer coefficient with the effect of Brownian motion of the nanoparticles present in the base fluid. In this paper, a comprehensive literature on the correlations developed for heat transfer and friction factor for different kinds of nanofluids flowing in a plain tube under laminar to turbulent flow conditions have been compiled and reviewed. The review was also extended to the correlations developed for the estimation of heat transfer coefficient and friction factor of nanofluid in a plain tube with inserts under laminar to turbulent flow conditions. However, the conventional correlations for nanofluid heat transfer and friction factor are not suitable and hence various correlations have been developed for the estimation of Nusselt number and friction factor for both laminar and turbulent flow conditions inside a tube with inserts. [Copyright &y& Elsevier]

Abstract: In this study, external condensation heat transfer coefficients (HTCs) of HFC134a and R1234yf are measured on a plain, low fin, and Turbo-C tubes at the saturated vapor temperature of 39 °C with the wall subcooling of 3–8 °C. R1234yf is a new alternative refrigerant of low greenhouse warming potential for replacing HFC134a, one of the greenhouse gases in Kyoto protocol, used extensively in automobile air conditioners and other refrigeration systems. Test results show that the condensation HTCs of R1234yf are very similar to those of HFC134a for all three surfaces tested. For the development of heat transfer correlations, thorough property measurements are needed for R1234yf in the near future. [ABSTRACT FROM AUTHOR]

New predictive methods for R-134a condensing on vertical arrays of horizontal tubes are proposed based on visual observations revealing that condensate is slung off the array of tubes sideways and significantly affects condensate inundation and thus the heat transfer process. For two types of three-dimensional (3D) enhanced tubes, the Turbo-CSL and the Gewa-C, the local heat flux is correlated as a function of condensation temperature difference, the film Reynolds number, the tube spacing, and liquid slinging effect. The measured heat transfer data of the plain tube were well described by art existing asymptotic model based on heat transfer coefficients for the laminar wavy flow and turbulent flow regimes or, alternatively, by a new model proposed here based on liquid slinging. For the 26 fpi low finned tube, the effect of inundation was found to be negligible and single-tube methods were found to be adequate. [ABSTRACT FROM AUTHOR]

The aim of the present investigation was to study the effect of condensate inundation on the thermal performance of a vertical array of horizontal tubes with plain and enhanced surfaces. Refrigerant R-134a was condensed at a saturation temperature of 304 K on tube arrays with up to ten tubes at pitches of 25.5, 28.6. and 44.5 mm. Notably, local condensing heat transfer coefficients were measured at the midpoint of each tube, as opposed to mean values. Four commercially available copper tubes with a nominal diameter of 19.05 mm (0.75 in.) were tested: a plain tube, a 26 fpi/1024 fpm low finned tube, and two tubes, with three-dimensional (3D) enhanced surface structures. At low liquid inundation rates, the tubes with 3D enhanced surface structures significantly outperformed the low finned tube. Increasing liquid inundation deteriorated the thermal performance of the 3D enhanced tubes, whereas it had nearly no affect on the low finned tube, resulting in a higher heat transfer coefficients for the low finned tube at high liquid film Reynolds numbers. All the tests were performed with minimal vapor shear. [ABSTRACT FROM AUTHOR]

The intent of the present investigation is to conduct; experimentally, the effects of nanofluid of water/magnetite and flow channel arrangement on photovoltaic thermal (PVT) systems. Three different configurations of the collector in PVT were researched in various nanofluid's flow rate of M ˙ = 20.0 − 80.0 (k g / h r) , and nano concentration of φ = 0.0 − 2.0 %. The studied arrangements of flow channels in the collector are a sheet-and-plain serpentine tube (PVT-0S), a sheet-and-finned serpentine tube with four fins (PVT-4S) and a sheet-and-finned serpentine tube with eight fins (PVT-8S). The electrical efficiency is compared between the cited three cases and the PV panel without cooling system. The maximum energetic, exergetic and electrical performances were found at the flow rate of M ˙ = 80 (k g / h r) and nano concentration of φ = 2.0 %. It was observed that the PVT-8S system provides the most efficient configuration since the overall energy efficiency (η) in the PVT-8S system are 5.87 % , and 15.59 % higher than the PVT-4S, and PVT-0S systems. Further, the PVT-8S system demonstrated the maximum value of exergy efficiency (Γ = 14.51 %) compared to other studied systems. It was also shown that the electrical efficiency (Λ) augments significantly with the adding the cooling systems to the PV panel. The increase in the electrical efficiency was 12.06 % , 10.87 % , and 8.40 % for the PVT-8S, PVT-4S, and PVT-0S systems; respectively. • The maximum energetic performance is obtained at the flow rate, and volume fraction of 80 (kg/hr) and 2.0%. • The highest overall energy and exergy efficiencies were achieved for the PVT-8S system. • PVT-8S, PVT-4S, and PVT-0S have 12.06%, 10.87%, and 8.40% higher electrical efficiency than PV panel. [ABSTRACT FROM AUTHOR]