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Experimental investigations of heat transfer characteristics and performance enhancement of shell and helical coil water coolers using external radial fins and different shells diameters were conducted. The study aims to enhance the water coolers performance in a trial to improve coil compactness. Two helical coils; one with a plain tube and the other with external radial fins, were tested in four shells of different tube diameters. Refrigerant passing inside the helical coils was used to cool water that enclose/passes in the space between the helical coil and the shell. Tests were conducted under mixed convection heat transfer regimes. Results showed performance and compactness enhancement with the insertion of external radial fins and increasing the shell diameter to helical coil diameter ratio. For nonfinned and finned coils, Nusselt number increased with increasing Reynolds number, Grashof number, and shell diameter. Correlations were predicted to give the Nusselt number in terms of Reynolds number, Grashof number, and shell diameters for finned and nonfinned helical coils. Correlations predictions were compared with present and previous experimental results and good agreements were obtained. [ABSTRACT FROM AUTHOR]

The augmentation in heat transfer can be achieved by improving either transport phenomena with geometry perturbation or thermal conductivity of the fluid itself. In the present study, the simultaneous effects of both the geometry and improved thermal conductivity have been tried on heat transfer enhancement by using two different nanofluids (Al2O3-water and TiO2-water). An innovative three-dimensional device called a coiled flow inverter (CFI) is proposed for the process intensification. The CFI is made up of helical coiled tube, which is bent periodically to 90 ° at equidistant length. In addition to a CFI, the performance characteristics of helical coil and straight tube have been investigated. The Reynolds numbers are in the range of 25-4000, while the nanoparticle volume fraction varied from 0.25-4 %. It was noted that the heat transfer in a CFI improved considerably as compared to helical coil and straight tube of same dimension. The Nusselt number in helical coil augments by 2.5 times to that of straight tube. In the CFI, the Nusselt number further enhanced by 23-35 % as compared to helical coil, with 0-4 % increase in the nanoparticle volume fractions. The new correlations are developed to predict the Nusselt number and friction factor for the flow of nanofluids in the CFI. The number of merit in the CFI to that of straight tube are 1.6-1.8 times, with 0-4 % nanoparticle volume fractions. The present study may motivate the design and development of novel compact heat exchangers as well as a new-generation microfluidic device. [ABSTRACT FROM AUTHOR]

The paper presents numerical investigations of a three fluid heat exchanger (TFHE), which is an improvement on the double pipe heat exchanger, where a helical tube is inserted in the annular space between two straight pipes. The helical tube side fluid, that is, hot water continuously transfers heat to the outer annulus side fluid and innermost tube side fluid. The heat transfer and pressure drop characteristics of the TFHE are assessed for different flow rates and inlet temperatures. With an increment in the volumetric flow rate of the helical tube side fluid and outer annulus side fluid, the overall heat transfer coefficient increases, and the effectiveness decreases for heat transfer from the helical tube side fluid to outer annulus side fluid in both parallel flow and counter flow configurations. It is also observed that with increment in the helical tube side fluid inlet temperature, the overall heat transfer coefficient and effectiveness increases for heat transfer from the helical tube side fluid to outer annulus side fluid in both flow configurations. The parameter, JF factor, has been proposed to evaluate the thermohydraulic behavior of the TFHE, where it is obtained that the behavior of the TFHE is better at a lower helical tube side fluid velocity and higher outer annulus side fluid velocity. [ABSTRACT FROM AUTHOR]

Rates of mass and heat transfer at vibrating helical coils were studied by the electrochemical technique with the object of using helical coils as heat exchanger/reactor for conducting liquid-solid diffusion controlled reactions. Variables studied were frequency and amplitude of vibration, tube diameter, and superimposed axial flow velocity. The data for vibrating coil (batch reactor) were correlated for 59 < [ABSTRACT FROM AUTHOR]

Abstract: Agitation is one of the widely used engineering operations in all of the chemical industries, which involves both material transport and heat transfer in the system. In order to conserve energy spent in heat transfer systems, enhancements to heating and cooling in industrial processes can be achieved by dispersing small‐sized particles having high thermal conductivity in a base fluid. This article reports an experimental study on the heat transfer characteristics of graphite–water microfluid in a coiled agitated vessel equipped with propeller and six bladed disc turbine impellers. The heat transfer coefficient for the graphite–water microfluid is found to be higher than that for the base fluid (water) and increased with higher volume concentrations of graphite and higher impeller speed. Comparison of the graphite–water microfluid and water is found to demonstrate a significant enhancement in the convective heat transfer coefficient. Empirical correlations for the calculation of Nusselt numbers are performed, and the calculated Nusselt number is found to be in good agreement with experimental values within ±10% deviation. [ABSTRACT FROM AUTHOR]

This study presents analytical formulation used for design of helical coil for induction heating of solid and hollow cylindrical non‐magnetic workpiece (graphite crucible). This formulation is applied for estimation of the active power in graphite crucibles and reactive power drawn by the induction coil in presence of different wall thickness (30, 20, 10 and 5 mm) of graphite crucibles at different frequency (1–50 kHz). Magnetic field produced by induction coil is estimated by using empirical factors suggested by kNagaoka et al. Induction heating processes, i.e. electromagnetism and heat transfer physics are mathematically modelled by Maxwell and Fourier equations, respectively. Finite‐element method is used to solve the electromagnetic field in frequency domain and heat transfer in transient domain. Numerical analysis is carried out by using two‐dimensional axisymmetric geometry. Analytical results and numerical results are compared and are found to be in good agreement with each other. Experimentally obtained coil voltage and graphite crucible temperature were compared with numerical results and the authors found that they also match very well confirming the validity of their assumptions in analytical/numerical approach. [ABSTRACT FROM AUTHOR]

Heat exchangers are extensively used in various industries. In this study, the impact of geometric and flow parameters on the performance of a shell and double helical coil heat exchanger is studied numerically. The investigated geometric parameters include external coil pitch, internal coil pitch, internal coil diameter, and coil diameter. The influences of considered geometrical parameters are analyzed on the output temperature of the hot and cold fluid, convective heat transfer coefficient, pressure drop, and average Nusselt number. Water is considered as working fluid in both shell and tube. As an innovation, double helical coils are used instead of one in the heat exchanger. To compare the obtained results accurately, in each section, the heat transfer area (coil outer surface) is kept constant in all models. The results show that the geometrical parameters of double helical coils significantly affect the heat transfer rate. [ABSTRACT FROM AUTHOR]

Results of heat transfer coefficient measurements in an agitated vessel heated or cooled by the liquid media flowing in a helical pipe coil are presented in this paper. The multistage impeller made of two pitched six-blade impellers and adjustable clearance was used in a vessel with conical bottom. The transient method based on measuring the temperature dependency on time and solving the unsteady enthalpy balance was used to determine the heat transfer coefficients between the agitated liquid and the helical pipe coil. The results are summarized by the Nusselt number correlations, which describe the dependency on the impeller Reynolds number. The second part of this paper introduces a theoretical analysis of the flow in the liquid batch near the helical pipe coil. Based on the known pumping capacity of the multistage impeller, the characteristic velocity near the helical pipe coil can be evaluated. This characteristic velocity can be then used to determine the Nusselt number describing the heat transfer in a flow around a cylinder with the same cross-section profile as the helical pipe coil. A clear correlation between this Nusselt number and the integral Nusselt number is presented in this paper and introduces an alternative approach for prediction of heat transfer characteristics on the basis of hydrodynamic parameters describing an agitated system. [ABSTRACT FROM AUTHOR]

Thermal energy storage (TES) system is the most eminent storage method that aids in the power generation. Latent heat storage (LHS) is on the rapid mark‐up that fosters the TES with the utilization of the phase transition of a material to store the heat. Typically the phase change materials (PCM) are used in the LHS system to store the energy. During the material's phase transition, thermal energy is stored and released. Nevertheless, the low thermal conductivity of the PCM in the LHS is susceptible to deteriorate the charging and discharging of the thermal energy. Hence there is a necessity to enhance the thermal performance of the LHS system, on which various studies have been done. Therefore this paper aims in providing a review on the enhancements of the LHS system with improved heat transfer rate and heat transfer enhancement techniques in the PCM for better efficiency. A comprehensive review on the LHS system component is provided to make an emphasis on the heat transfer enhancement rate and storage time. Various characterizations and categories of the PCM are provided to intensify the outcomes of the review as PCMs are most viable materials for storing thermal energy. In addition the recent researches on the integration of PCM with other materials are also discussed that help in the improvements of the thermal conductivity of the PCM. The selection parameters of the PCM materials are also discussed in brief to avoid the poor performance of the PCMs. The heat transfer analysis methods are analyzed to improve the efficiency and reduce the heat loss. Finally, advancements in the future trends for the enhancement of heat transfer is provided. [ABSTRACT FROM AUTHOR]

Eco‐friendly mixtures may substitute pure working fluids in thermodynamic cycle processes, yet the existing calculation approaches of mixture condensation are complex due to iterative procedures and multiple input data. To simplify condenser design, this project aims for a new calculation method of mixtures. On this behalf, experimental data for the condensation of ethanol/water and ethanol/octamethyltrisiloxane is provided within a wide composition range to identify the most influential parameters. Finally, a practical prediction method for heat transfer coefficients of mixtures is suggested. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics and fuzzy logic (FL) modeling methods were used to estimate heat transfer and fluid flow characteristics in conical spiral tubes. The effects of coil pitch p and cone angle θ at Reynolds numbers Re of 1500–5500 on flow and heat transfer were investigated. Water with an inlet temperature of 298 K was considered as the working fluid, and a constant wall temperature of 398 K was used in the study. FL was used to predict the Nusselt number and friction factor in conical spiral tubes as functions of Re, θ, and p. FL is an efficient method for predicting complex systems and is a valuable complement to classical hard computing techniques. The purpose of the study was to find a relationship between heat exchanger parameters and performance characteristics. It was also investigated how the FL expert system plays an important role in predicting heat transfer performance. [ABSTRACT FROM AUTHOR]

The authors investigated four different fin geometries to select the best fin geometry in their previous work. They found out that the Nusselt number of the shell side is 80.79% higher for the stepped fin geometry compared to the simple annular fin at best. In this study, for the first time the heat transfer in a shell and helically coiled finned tube heat exchanger with stepped annular fins is investigated. The coiled tube and the stepped ring fins that are welded to the outside surface of the tube are all made of copper. After examining network independence, 27 cases were designed using Response Surface Methodology (RSM). Correlations have been proposed to predict Nuc$N{u}_c$ and Nush$N{u}_{sh}$ by considering all geometric and operating parameters. These correlations have very high accuracy and can be used in a specific range of parameters. The effect of each of the parameters on Nuc$N{u}_c$ and Nush$N{u}_{sh}$ are also specified. Re${\mathop{\rm Re}\nolimits} $ and Pr$\Pr $ are the parameters that have the most impact on the Nusselt number on the same side, but at the same time have almost no effect on the Nusselt number on the other side. Rec${{\mathop{\rm Re}\nolimits} }_c$ and Resh${{\mathop{\rm Re}\nolimits} }_{sh}$ have the highest participation rate in determining Nuc$N{u}_c$ and Nush$N{u}_{sh}$ with 82.62% and 71.13%, respectively. The results are presented based on dimensionless parameters. The optimization process is performed for each of the responses, and the values ​​of the corresponding parameters are also shown. Nush$N{u}_{sh}$, which is the most critical response in this study, has improved 19.59% in the optimized case, even compared to the best of the 27 cases studied. To have the best overall heat performance of the heat exchanger, the optimization process has been performed. [ABSTRACT FROM AUTHOR]

In this study, we analyze the magnetohydrodynamic flow of magnetite‐engine oil nanofluid in the presence of nonidentical shaped nanoparticles subject to the porous medium and velocity slip effect. Energy analysis is carried out with the Ohmic heating and thermal radiation impacts. The system of partial differential equations are transformed into the system of ordinary differential equations using similarity variable. The Hamilton–Crosser model is used. The exact solutions for the momentum and heat transport analysis are found. The impact of various emerging parameters on the velocity and temperature profiles are analyzed by graphs. Furthermore, the local skin friction and heat transfer rate are examined graphically. It is examined that the velocity field increases with an increment in the magnitude of ϕ and L. An increase in the value of Hartman number enhancing the temperature profile. [ABSTRACT FROM AUTHOR]

This paper examines experimentally the effect of jet vortex technology on enhancing the heat transfer rate within a double pipe heat exchanger by supplying the heat exchanger with water at different vortex strengths. A vortex generator with special inclined holes with different inlet angles was designed, manufactured, and integrated within the heat exchanger. In this study, four levels of Reynolds number for hot water in the annulus (Reh) were used, namely, 10,000; 14,500; 18,030; and 19,600. Similarly, four levels of Reynolds number for cold water in the inner tube (Rec) were used, namely, 12,000; 17,500; 22,500; and 29,000. As for the inlet flow angle (θ), four different levels were selected, namely, 0°, 30°, 45°, and 60°. The temperature along the heat exchanger was measured utilizing 34 thermocouples installed along the heat exchanger. It was found that increasing the inlet flow angle (θ) and/or the Reynolds number results in an increase in the local Nusselt number, the overall heat transfer coefficient, and the ratio of friction factor. It is revealed that the percentage increase in the average Nusselt number due to swirl flow compared to axial flow was 10%, 40%, and 82% for an inlet flow angle of 30°, 45°, and 60°, respectively. [ABSTRACT FROM AUTHOR]

Researching new and optimizing existing methods of cooling electronic devices are the most important tasks in the modern world. Based on this, our work is devoted to the study of the possibility of intensifying the heat removal from a heated element using natural convective energy transport of a pseudoplastic nano liquid in a cavity. The problem is described by unsteady Oberbeck‐Boussinesq differential equations and is solved on the basis of the finite difference method. To calculate the effective parameters of a nanofluid, three sets of different models are used, including temperature dependences. The work also studied the effect of nanoparticles' various types and their volume fraction on flow structure and heat transfer. The results showed that the use of copper oxide as nanoparticles and the correlations of Guo et al. and Jang & Choi can lead to intense cooling of the bottom wall heated section. [ABSTRACT FROM AUTHOR]

In boiling phenomena, the heater surface gets covered by a vapor, which results in a decrease in the overall heat transfer coefficient (HTC). The curvature of the surface helps to reduce this vapor blanketing by vapor sliding over the curved surface. The sliding generates fluid circulation and makes the heater surface available for boiling liquid. Therefore, in the present work, the vapor dynamics, nucleation and growth, pinch‐off of the bubble, and heat transfer characteristics over smooth and uniform surfaces with different curvature ratios (δ = 0, 0.01, 0.05, 0.15, and 0.25) are numerically studied. Also, the effect of the degree of superheat (ΔT = 10, 20, 30, and 40 K) on the bubble formation, vapor sliding, and fluid recirculation over the curved surface have been observed. Furthermore, investigated the dome formation and multiple pinch‐off of the bubble on the heated curved surfaces. The dominance of the curvature and degree of superheat on the bubble departure has been investigated using PDF of FFT of vapor void fraction at the surface. At higher curvature of the surface, there is less significance of the degree of superheat on the departure frequency of vapor bubbles. Furthermore, it is found that there is an increase in the average HTC with an increase in the curvature ratio, while the pinch‐off time of the bubble decreases. The HTC is enhanced by 86% with curved surfaces as compared to flat surfaces. Furthermore, the curved surface with a curvature (δ) of 0.15 showed better performance than the curved surface with δ = 0.25. Boiling over a curved surface leads to vapor sliding and recirculation of the fluid, leading to enhancement in surface renewal and an increase in HTC. [ABSTRACT FROM AUTHOR]

This study investigates turbulent heat transfer performance (HTP) and entropy production rate (EPR) of CuO/H2O nanofluid flowing through Bessel‐like converging pipes. The effects of Reynold's number (5.0×103≤Re≤3.0×105), nanoparticle volume ratio (0%≤φ≤4%), and convergence index (0≤n≤3) on the hydrodynamic, HTP, and EPR were examined. The results show that an increase in the convergence index enhances pressure drop, Nusselt number, and viscous EPR. However, the opposite is the case for the thermal EPR. Furthermore, the multiobjective optimization of pressure drop, Nusselt number, and EPR show that both Nusselt number and pressure drop attained the optimum value simultaneously. [ABSTRACT FROM AUTHOR]

Enhancement in the heat transfer of the working fluid flowing inside the tube is achieved by modification of tubes and changing the direction of fluid flow. For this purpose, the straight tube can be changed into a conical coil tube, thereby, heat transfer is increased due to the centrifugal effect caused by the curvature of the tube. Furthermore, the circular cross‐section of the tube is modified into an oblong shape for more heat transfer enhancement. In this study, the numerical heat transfer and pressure drop characteristics of Al2O3–water nanofluids in the flattened conically coiled tube are studied. The effect of the aspect ratio, cone angle, coil pitch, and solid volume fraction of nanofluids on heat transfer and pressure drop are examined. It is found that the heat transfer coefficient and pressure drop increase with the rise of aspect ratio, Reynolds number, and solid volume fraction of nanofluid, while it decreases with the increment of cone angles and coil pitches of conical coil tube. Furthermore, the effect of aspect ratio on the heat transfer enhancement factor, pressure drop ratio, and thermal performance index for Al2O3–water nanofluid are presented. [ABSTRACT FROM AUTHOR]

A computer program was developed for the performance analysis and design optimization of a cylindrical shell and helical tube type HFC134a condenser and its predicted results were verified against the experimentally determined data. The computer model is based on a numerical method of cell discretization. The local values of variables like heat transfer rate, pressure drop, and the properties of refrigerant are calculated on the basis of appropriate theoretical and empirical correlations available in the literature and the mass, momentum, and energy balance is applied to each cell. The whole sequential and iterative procedure to satisfy the boundary conditions of each cell and of the whole condenser has been transformed into a computer program written in C++. This computer model was used in a parametric study to analyze the effects of varying the input parameters of both fluids on the performance of the condenser. It gives the optimal values of refrigerant mass velocity and of the tube diameter against the available conditions of external cooling fluid, mass flow rate of refrigerant, and degree of subcooling of the refrigerant at the condenser outlet. Its utility was found in the performance optimization of an existing condenser as well as in the design optimization of a new condenser. [ABSTRACT FROM AUTHOR]

Most of the energy consumption in a hot and dry area is used for the air‐conditioning systems. This study aims to investigate the possibility of reducing the electricity consumption in air conditioners using ground cold energy to cool the hot fluid in the pipes. Several experiments were carried out to investigate the performance of the proposed system to be used in the weather conditions of Baghdad city (i.e., hot and dry). Two configurations of ground source heat exchangers (GSHEs) were developed and constructed. The first configuration comprised coil type with two different materials (copper and polyvinyl chloride [PVC]). The second configuration was the 3U type, which was made from copper, PVC, and galvanized. Three water flow rates were considered (5, 10, and 15 L/min) with water inlet temperatures (80°C, 70°C, and 60°C). The experiments' results showed that the type of material of the pipe has a significant influence on both the heat transfer effectiveness and the system performance. Copper tubes were the best type of heat exchanger (type coil) to be used in this regard. The highest recorded values of the heat exchange rate were 5.81, 4.81, 2.72, 1.60, and 1.32 kW with an inlet temperature of 80°C and a flow rate of 5 L/min for the case of copper coil, copper 3U, galvanized 3U, PVC profile, and PVC 3U, respectively. These findings can be used as a guideline for future studies of GSHEs, particularly for the applications fixed in unsaturated soils. [ABSTRACT FROM AUTHOR]

Helically coiled tubes offer improved residence and thermal time distributions due to the formation of Dean vortices via centrifugal forces. Design and fabrication of several milli/microstructured helically coiled tube reactors are described for processes requiring a narrow residence time distribution (RTD) and efficient heat transfer at laminar flow regime. The performance of microstructured reactor capillaries, which provide a high specific surface area, is combined with a type of helically coiled tube, namely, a coiled flow inverter allowing for the narrowest RTD in laminar flow regimes. Axial dispersion is characterized by obtaining the RTD curves from different reactor setups. Overall heat transfer coefficients of a new reactor setup are measured in order to determine the heat transfer efficiency. [ABSTRACT FROM AUTHOR]

Three concentrations of 0.2, 0.6, and 1.0 vol.% Copper/25 nm and silica/22 nm nanofluids are prepared in a base liquid glycerol–water mixture of 30:70 ratio by volume (GW70). The thermophysical properties of Cu and SiO2 nanofluids are determined with a TPS500S hot disc thermal analyzer and Brookfield viscometer in the temperature range of 20–80°C. The maximum enhancement in Cu and SiO2 nanofluid viscosity (63.4%, 35.7%), thermal conductivity (100.4%, 71.3%), and density (7.5%, 1.5%) while specific heat (7.8%, 2.3%) determined for 1.0% concentration at 80°C compared to base liquid GW70. Heat transfer experiments are conducted in a short‐length double pipe heat exchanger. The flow rates resulted in the lamifnar entry length region. A maximum enhancement in the overall heat transfer coefficient (HTC; 25.0%, 19.7%) and convective HTC (46.2%, 34.8%), respectively for Cu and SiO2 nanofluids is estimated at 1.0% concentration compared to base liquid at a bulk temperature of 35°C. [ABSTRACT FROM AUTHOR]

Stirred tank reactor systems often employ jackets/limpets, single/multiple internal coils for heat transfer. Internal coils are used for heat removal in the case of exothermic reaction systems. The desired heat transfer area can be accurately estimated based on the overall heat transfer coefficient (HTC) considering the process side, utility side, and wall conduction resistance. For estimation of process side HTC, a large number of empirical/semi‐empirical correlations are available in the published literature. These correlations account for impeller Reynolds number, fluid Prandtl number, viscosity ratio, dimensionless geometric factors, and so forth. However, all the factors over the entire range of industrial operation do not get covered in a single study, hence the predictions may involve significant errors for industrial cases. The advanced artificial intelligence‐based techniques can provide unified correlation based on the experimental data set extracted from various investigations and the predictions can be accurate and reliable. In the present work, three techniques random forests (RF), artificial neural networks with Bayesian optimization (ANN‐BO), and support vector regression with grid search optimization (SVR‐GS) have been used with a data set of 1297 points with R2 values of 0.995, 0.972, 0.990 on the training data set and 0.962, 0.945, 0.905 respectively on the testing data set. Furthermore, the statistical measures show that RF provides a better fit as compared with other AI models, so RF is used for parametric sensitivity analysis. The permutation feature importance shows that the agitation speed, impeller dimensions, and positioning has a significant impact on the HTC. [ABSTRACT FROM AUTHOR]

Taking supersaturation and heat transfer rate as evaluation indexes, two typical internal geometries of an oscillatory flow crystallizer (OFC) with circular‐orifice baffles (OFC‐COB) and smooth periodic constrictions (OFC‐SPC) were studied by numerical simulation. The results indicated that OFC‐SPC could provide a relatively high heat transfer rate, supersaturation, and similar or lower power density consumption, as well as a uniform flow field distribution without vortex dead zone. Further, a method to prejudge the supersaturation in oscillatory flow crystallizer is proposed, which would be good guidance to determining the operating parameters. [ABSTRACT FROM AUTHOR]

The objectives of this study are (i) to find exact analytical solutions to the unsteady hybrid nanofluid flow and heat transfer due to a moving infinite flat plate, and (ii) to investigate the impacts of different hybrid nanofluids (Cu‐Al2O3/water, CuO‐Al2O3/water, and Ag‐Al2O3/water) on the unsteady flow and heat transfer characteristics with MHD and variable temperature. The Laplace transform technique is employed to find the exact analytical solutions of the partial differential equations with appropriate boundary conditions governing the problem considered. The results computed for engineering quantities, namely skin friction coefficient and Nusselt number and velocity and temperature profiles by the Laplace transform technique are analyzed using graphs and tables. It has been found that there is a significant increase in the heat transfer rate for hybrid nanofluids than for nanofluids and we observed a higher heat transfer rate for Cu‐Al2O3/water and a lower heat transfer rate for Ag‐Al2O3/water than for the others. The novelty of this study is finding an exact analytical solution to the problem of hybrid nanofluid flow due to moving vertical plate where the effects of magnetic field and variable plate temperature conditions are considered. The obtained results can be used in various engineering applications, including geothermal reservoirs, packed‐bed storage tanks, packed‐bed catalytic reactors, thermal insulation, grain storage, porous solids drying, and petroleum resource gas production. Furthermore, the findings can be used to validate numerical solutions for more complex transient hybrid nanofluid flow and convective heat transfer problems. [ABSTRACT FROM AUTHOR]

Generally, coil‐tubes are utilized to extract heat from solar ponds. There are different coil‐tubes in which their thermal and hydraulic characteristics depend on configuration and geometrical parameters. In this study, the performance of three well‐known coil‐tubes, namely helical, colubrine, and spiral, as the core of solar ponds is investigated at both smooth and twisted forms. Moreover, different levels of coil‐pitches and twist‐lengths are examined to explore the effects of geometrical parameters. First, the validity of the results is checked by the previous correlations proposed for the coil‐tubes. A good agreement is found, so that the average absolute deviation is about 6%. The results show that the heat extraction is affected by the configuration of coil‐tubes so that at the same geometrical parameters and operating conditions, the highest values are obtained for the spiral coil‐tube and the helical and colubrine coil‐tubes come in the second and third, respectively. It is found that, in all cases, twisting walls lead to higher rates of heat extraction. The enhancement range for the helical, colubrine, and spiral coil‐tubes is 0.3–19.8%, 0.3–46.1%, and 0.6–27.0%, respectively. At the same time, the pumping power augments in the range of 1.0–31.7%, 0.6–70.1%, and 0.4–43.5%. Furthermore, the models with lower level of coil‐pitch and twist‐length provide higher values of heat extraction and pumping power. At the considered ranges, the greatest overall performance is obtained for the colubrine coil‐tube with high coil‐pitch and twist‐length, which presents the performance index of 1.14. [ABSTRACT FROM AUTHOR]

Experimental investigation on the thermal performance of a shell and helical tube latent heat thermal energy storage system for medium temperature applications is reported in the article. Commercial grade erythritol having a melting temperature of 120°C was employed as the phase change material (PCM). The thermal conductivity of the erythritol had been usually very low (0.73 W/mK) and it results in low heat transfer rates during both charging and discharging processes. In the study, an attempt was made, this inherent limitation of erythritol, high thermal conductive graphene nanoparticles, which are dispersed into erythritol matrix, referred to as nanoparticle dispersed phase change material (NDPCM). The effect of the addition of graphene nanoparticles on the performance of the storage system such as heat flow rate, overall heat transfer coefficient, charging and discharging efficiency and effectiveness was evaluated and compared with the storage system with only base erythritol during both energy storage and retrieval processes. The efficiency of the NDPCM system increased to 16.29% during the storage period and 28.48% during the retrieval period compared with the base PCM system. Further, it was observed that the effectiveness is about 14% greater at the beginning of the melting process and about 12% greater at the beginning of the solidification process for NDPCM. [ABSTRACT FROM AUTHOR]

Miniature reactors are important devices used for process intensification. They provide a larger surface‐to‐volume ratio and enhance mass transfer and heat transfer significantly. This paper presents a review of transport processes of gas‐liquid and liquid‐liquid two‐phase flow in miniature geometries, in which the hydraulic diameter of the channel lies between 0.2 mm to 3.0 mm. Correlations for predicting the pressure drop in case of both adiabatic and non‐adiabatic gas‐liquid flows are summarized. Gas‐liquid distributions are observed to be different from liquid‐liquid flow distributions. Cross‐sectional geometry does not have any effect on the flow regimes in this range. In case of liquid‐liquid flow, the wall material plays an important role on flow distribution. Miniaturization is a widely used tool for process intensification in various industries due to the larger surface‐to‐volume ratio, enhanced head and mass transfer as well as the diminished use of reactants. This review summarizes the transport processes in miniature geometries with two‐phase flow by compar gas‐liquid flows with liquid‐liquid flows. [ABSTRACT FROM AUTHOR]

A methodology to obtain a Nusselt correlation for stirred tank reactors is presented. The novelty of the approach is the use of a validated computational model to obtain the heat-transfer coefficients. The advantages of this new approach are many, including the possibility of testing different heat-transfer configurations to obtain their Nusselt correlation without performing experimental runs. Physical phenomena involved was represented both qualitatively and quantitatively. The classical experimental work of (Oldshue and Gretton, Chem Eng Prog. 1954;50(12):615-621) illustrates the procedure. A sufficient number of virtual points in the whole range of the Reynolds number should be obtained. Results strongly depend on mesh refinement in the boundary layer, so a procedure is suggested to guarantee heat-transfer coefficients are accurately estimated. The final Nusselt correlation was compared against all the 107 experimental points of the work by (Oldshue and Gretton, Chem Eng Prog. 1954;50(12):615-621), and an average deviation on the results of 10.7%. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3912-3924, 2017 [ABSTRACT FROM AUTHOR]

Multiphase Reactors Engineering and Applications Laboratory (mReal) has designed and constructed a scaled-down dual-channel facility to investigate plenum-to-plenum natural circulation heat transfer through two channels for coolant flow that would be encountered during a loss of flow accident in the prismatic modular reactor (PMR). Heat transfer characterization of the current facility has been investigated under different upper plenum and cooled channel outer surface temperatures using sophisticated flush mounted heat transfer sensors. Results show a reduction in the values of local heat-transfer coefficient and Nusselt number along the heated channel with increasing outer surface temperatures. One significant observation was the heat transfer reversal close to heated channel exit, where the heat flows from gas to the channel wall. This flow reversal is attributed to recirculation at the heated channel exit to the upper plenum. The average heat transfer results, when compared with previous literature, showed a similar qualitative trend. © 2016 American Institute of Chemical Engineers AIChE J, 63: 387-396, 2017 [ABSTRACT FROM AUTHOR]

Large-and-small-hole (LASH) baffle is a new shell-side fluid flow-guide structure, and corrugated tube is the widely used as the heat transfer enhancement tube. In this paper, numerical simulations and experimental studies were carried out for the fluid flow and heat transfer in six shell-and-tube heat exchangers designed with LASH baffles, segmental LASH baffles, traditional single-segmental baffles, and corrugated and plain tubes. It is found that under the same fluid flow conditions, the tube vibration in the heat exchangers with LASH baffles are significantly reduced and the shell-side pressure drops are decreased compared with those having the conventional single-segmental baffles. In terms of the overall heat transfer coefficient, the heat exchangers with the corrugated tubes are much better than those with the plain tubes. Heat exchangers with the LASH baffles and corrugated tubes have the best comprehensive properties and thus will inspire broader application for engineering considerations. © 2016 Curtin University of Technology and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

An adapted radiant syngas cooler (RSC) with water spray for entrained-flow gasifier has been technically reformed to achieve higher reliability and availability of coal-gasification-based system. The multiphase flow, heat transfer and mass transfer processes in this adapted RSC have been studied by a developed 3D computational fluid dynamics model. A Eulerian-Lagrangian method is adopted to describe the flow behavior of the syngas, slag/ash particle and water droplets. The surface temperature of water wall Ta is calculated using heat flux balance equations by compiling user-defined functions. The predicted values agree well with the measured ones obtained from a practical gasification plant. In the inner cylinder, syngas temperature contours are similar to circulars dispersed from center to the division walls and have a high gradient near water walls, especially close to the division walls. The gradient of Ta from center to division walls is similar to that of gas temperature. This adapted RSC with water spray has a better flexibility, while the flow rate of water spray can be adjusted for different operating conditions of gasifier. © 2016 Curtin University of Technology and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A new chaotic duct is shown to enhance heat transfer at lower Reynolds numbers. The structure can be used as a heat transfer enhancement duct or as a flow channel in compact heat exchangers. The characteristics of the fluid flow and heat transfer in the duct were studied numerically, and the accuracy of the numerical calculations was verified experimentally. An orthogonal experiment was designed to optimize the geometric parameters of the duct. The mechanism of heat transfer enhancement in the duct was analyzed. Chaotic advection occurs in the duct at lower Reynolds numbers. By means of chaotic advection, fluid mixing is enhanced and heat exchange is increased between the fluid in the center and that near the duct boundary. The fluid temperature is distributed more uniformly at the cross-sections of the duct, and heat transfer is apparently enhanced. [ABSTRACT FROM AUTHOR]

CFD simulation of heat transfer and friction factor characteristics in a circular tube fitted with twisted tape inserts in laminar flow and constant heat flux is conducted using FLUENT version 6.3.26. Plain and alternate axis twisted tape inserts with twist ratios ( y = 2.93, 3.91, 4.89) and alternative angles ( β = 30 °, 60 °, 90 °) have been used for the simulation. The simulated results are matched with the literature correlations for a plain tube with a discrepancy of less than ±8% for Nusselt number and ±6.25% for friction factor. The results also revealed that the heat transfer in terms of the Nusselt number increased with increases of Reynolds number, alternative angles, and decreases of twist ratio. Among the various twist ratios and alternative angles, the twist ratio of y = 2.93 and alternative angle β = 90 ° offered a maximum heat transfer enhancement. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(4): 384-396, 2014; Published online 3 October 2013 in Wiley Online Library (). DOI 10.1002/htj.21089 [ABSTRACT FROM AUTHOR]

This article presents a novel design of smart scale PTFE tubular reactor systems for continuous polymerization reactions. To optimize the flow pattern, CFD calculations and RTD experiments were done. These results led to an unique tube geometry combined with a specialized arrangement of static mixers. A comparison of heat transfer properties of two different types of tubular reactors shows the feasibility of using PTFE instead of stainless steel as reactor construction material. The versatility of the operation modes is demonstrated for emulsion copolymerization experiments with the same recipe but at the different modes. [ABSTRACT FROM AUTHOR]

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Focused microwave heaters have potential to replace heat exchangers in continuous flow pasteurization of liquid foods. The objective of this work was to evaluate a pilot scale unit used for microwave assisted pasteurization of low viscosity liquid foods in order to model the heat transfer and residence time distribution (RTD) to, subsequently, predict the average time–temperature history and estimate the level of heat treatment of the process and contributions from each step. RTD data using water showed that it was possible to assume plug‐flow (negligible axial dispersion). Heat transfer experiments using water provided heat transfer coefficients as functions of Reynolds number and microwave power absorption. Mathematical modeling was used to determine the temperature distribution along the product path, and results were validated. Integrated lethality calculated from the time–temperature histories (pasteurization at 70 °C) revealed the contribution of each process step. Results showed that focused microwave heating provided the necessary temperature increase in a very short time, with a lethality contribution of only 0.7% as compared to 59–68% when using only the conventional heat exchanger. The methods described can be useful for the evaluation of other continuous flow pasteurization units processing low viscosity liquid foods. Practical applications: The mathematical modeling approach and experimental methods presented herein can be used for the analysis of continuous flow pasteurization systems based on tubular heat exchangers and with low axial dispersion (plug flow), providing temperature and lethality distribution along the product path, showing the contribution from each section on inactivation. Specifically for the equipment used in the experiments, the obtained heat transfer and resident time distribution parameters will be useful to study the processing of low viscosity foods such as fruit juices and nectars on ongoing works from the group. [ABSTRACT FROM AUTHOR]