Values Of Heat Transfer Coefficient Research Articles

Simulation of shell and tube type heat exchanger for square geometry using computational fluid dynamics method

Heat exchangers have various types of design models, one example is the shell and tube type heat exchanger. This tool is useful for raising or lowering the temperature. One of its uses is in the hydroelectric power generation industry, namely as an oil cooler bearing. This study aims to design and simulate a shell and tube type heat exchanger with tube inner diameters of 20 mm and 25 mm and also tube arrangement square and rotated square. From the design results obtained a total length of 1318.59 mm, 300 mm outer diameter of the shell and 320 mm inner diameter of the shell. The simulation results show that variations in tube diameter and tube arrangement greatly affect the performance of the heat exchanger, the highest value for the overall heat transfer coefficient is found in the tube square arrangement variation with the number of tubes 61 of 112.15 W/m2.K and the lowest value in the tube arrangement variation square with the number of tubes 55 is 106.48 W/m2.K, the highest value of pressure drop on the shell side is found in the variation of the tube square arrangement with the number of tubes 55.

Thermal-hydraulic characterization of R513A during flow boiling inside a 6.0 mm horizontal tube, comparison with R134a and development of a new correlation

This paper presents two-phase heat transfer coefficient and pressure drop data of refrigerant R513A, a new azeotropic mixture conceived as possible alternative to R134a for medium temperature small-size refrigeration systems. All the experiments were performed in a commercial horizontal stainless-steel tube having an internal diameter of 6.0 mm and an outer diameter of 8.0 mm. The channel heating was obtained through DC current and Joule effect. The effect of the main operating parameters in terms of mass flux (from 150 to 500 kg/m2s), heat flux (from 5.0 to 40 kW/m2), saturation temperature (from 30 to 50 °C) and vapor quality (from the onset of boiling up to the dry-out occurrence) was analyzed and discussed for the heat transfer coefficient values, finding that both convective and nucleate boiling were significant contributions. The same ranges of mass flux and saturation temperature were also applied to frictional pressure gradient trends with vapor quality, taken in adiabatic conditions. The thermo-hydraulic performances were then compared with those of R134a, obtaining lower heat transfer coefficients and very similar pressure gradients. Finally, the collected experiments were assessed with values predicted from the most quoted correlations available in literature. A new composite method for nucleate-dominant or convective-dominant mechanisms was proposed for the evaluation of the heat transfer coefficient, with a mean absolute error of 25.3%, whereas the frictional pressure gradient values were well predicted with the Friedel correlation, that provides a mean absolute error of 13.8%.

Transient thermal behavior of a passive heat sink integrated with phase change material: A numerical simulation

This paper presents a numerical investigation of the thermal performance of a heat sink augmented with phase change material (PCM) for passive electronic cooling applications. The PCM-based heat sink employed N-eicosane as the PCM, which has a suitable melting temperature and high latent heat capacity for electronic cooling applications. A numerical simulation based on the enthalpy-porosity method was developed to analyze the impact of both PCM inclusion and induced natural convection airflow on the base temperature of the heat sink. The operational conditions were selected as three constant heat fluxes of 2, 3, and, 4 kW/m2 and four critical base temperatures of 40, 45, 50, and 55 °C. The influence of fin numbers on the thermal behavior of both PCM-based and conventional (without PCM) heat sinks was also investigated by considering the three fin numbers of 4, 5 and, 6. The PCM integration into the heat sink effectively delayed the rise of base temperature and extended the safe operation time compared to a conventional one. The thermal performance enhancement ratio of the PCM-based heat sink over the conventional heat sink ranged from 1.53 to 2.81, depending on the selected heat flux and critical temperature. The effect of fin numbers on thermal performance was more significant at lower heat fluxes. It was observed that the PCM-based heat sinks achieved a higher time-averaged heat transfer coefficient than the conventional heat sinks, and this coefficient increased with the heat flux and decreased with the fin number. For both PCM-based and conventional heat sinks, it was observed that increasing the fin number reduces the heat transfer coefficient value due to the suppressing effect of fins on natural convection current. The results demonstrate the potential of using passive PCM-based heat sinks for improving the reliability and efficiency of electronic devices compared to conventional heat sinks.

Enhanced liquid replenishment for pool boiling heat transfer and its CHF mechanism on patterned freeze-casted surfaces

In the current investigation, the pool boiling heat transfer process of patterned porous surfaces, as well as a smooth surface, in ethanol was examined from an academic perspective. The freeze casting (also known as ice-templating) processes was used to fabricate the structured surfaces. It was discovered that freeze-casted coatings significantly improved the performance of boiling heat transfer in comparison to the smooth surface (SMS). The most remarkable increase in Critical Heat Flux (CHF) was achieved by checkerboard porous surface(CHECKERBOARD), with an improvement of 81.6% relative to that of SMS. The maximum Heat Transfer Coefficient (HTC) enhancement was obtained by full porous surface (FULLY-COVERED), with an HTC value 215.8% higher than that of the SMS. For the semicircular porous surface (SEMICIRCULAR), striped porous surface (STRIPED), annular porous surface (ANNULAR) and checkerboard porous surface(CHECKERBOARD) with 50% coating coverage, CHECKERBOARD demonstrated the best heat transfer performance, with CHF and HTC increased by 32.3% and 48.9%, respectively, compared to the SEMICIRCULAR surface. The mechanism of liquid supply at the CHF of the patterned porous surfaces was investigated through phenomenological observations of the boiling phenomena. A modified model, accounting for the coalesced bubble departure frequency and capillary wicking effects, was proposed for CHF prediction. It is noteworthy that the fluid replenishment considers both vertical and lateral replenishment of porous coatings. The CHF data from this study, along with existing literature, were utilized to validate the model, and the predicted results exhibited good agreement with the experimental data, with errors within ±8%.

Математичне моделювання пристінної оливної плівки в камері підшипника ГТД

The most preferable result of modeling the flow in the BC is the determination of the heat transfer coefficient to the inner wall. The complexity of solving this problem is due to both the complex geometry of the BC and the presence of a two-phase flow, the structure of which changes from air-droplet in the core to a nearly liquid in the wall oil film. Available research results show that even three-dimensional CFD modeling of such a flow does not completely solve the problem. At the same time, the calculation time is long, and the results require, at a minimum, selective experimental validation. At the same time, it can be considered proven that the main mechanism of heat transfer from the core to the wall region of the BC is related to the radial flow of droplets, and the thermal resistance of the wall oil film has a decisive effect on the value of the internal heat transfer coefficient. It is advisable to model these media on the basis of a two-dimensional problem with the averaging of phase parameters along the axis. Considering the small volume fraction of droplets, the Lagrangian approach can be used to model the two-phase flow in the core of the BC. This allows consideration of not only the polydispersity of the droplets, but also the creation and movement of secondary droplets during the formation of the wall oil film. One of the main problems in the modeling of the wall film is the definition of its flow regime and the corresponding criterion equations for calculating the coefficients of friction and heat transfer. Most of the equations use the longitudinal coordinate of the plate as a geometric parameter and cannot be applied to the bearing chamber. In this study, the possibility of converting the film flow into a flow similar to that occurring in a flat pipe is substantiated. This allows not only to consider the geometric features of the BC, but also to use the corresponding Reynolds numbers and similarity equations for the equivalent flow. Along with the use of a two-layer model for the boundary region and the concept of the analogy of transfer processes, this made it possible to form a mathematical model of the film, which considers all the components that determine the formation, movement, and heat transfer of the wall oil film. In addition, the model does not contain restrictions on the appearance of the parameters transverse profile, which are, for example, for the EWF model of the oil film in ANSYS FLUENT. The obtained results along with the previously developed air-droplet flow model in the core provide a complete two-dimensional model of the gas-liquid flow in the GTE bearing chamber, which allows the main geometric and all mode parameters to be used to determine the heat transfer coefficient to the inner wall of the chamber. Given the short calculation time, the proposed model allows for a detailed investigation of each factor’s contribution and element-by-element identification of the model based on the results of more detailed modeling and by comparing calculated and experimental data.

Numerical analysis of fluid type and flow mass rate on logarithmic temperature difference and heat transfer coefficient of double pipe heat exchanger

This CFD and statistical article aims to evaluate the impact of fluid type and flow mass rate on the log-mean temperature difference (ΔTLM) and the heat transfer coefficient (Ushell) in a double tube heat exchanger (DPHEX) using computational fluid dynamics (CFD) and statistical analysis. ANSYS Fluent software was utilized to conduct CFD calculations. CFD analyses were implemented using Taguchi L8 orthogonal array containing two variables such as the fluid types and the flow mass rates. The levels of fluid types were considered as water-liquid, ethylene-glycol, engine-oil, and benzene-liquid. The levels of fluid types were decided as 1.1 kg/s to 1.5 kg/s. To determine the optimal levels of variables and their impacts on the ΔTLM and Ushell in DPHEX, analysis of Signal to Noise (S/N) ratio was employed. Analysis of Variance (ANOVA) was also utilized to decide the effective variables and their percentage contribution rates on the outcomes. The CFD result obtained using the optimum levels of variables were compared with Taguchi estimation result. According to the study, the highest effects were obtained using ethylene-glycol, engine-oil, water-liquid, and benzene-liquid on the highest log-mean temperature difference values, respectively. In addition, the highest heat transfer coefficient values were found utilizing water-liquid, benzene-liquid, ethylene-glycol, and engine-oil, respectively. Increasing flow mass rate from 1.1 kg/s to 1.5 kg/s causes an increase in both outcomes. The study provides a reference for resolving issues that may arise in the production of experimental DPHEXs.

The Heat Transfer in Plate Fin Heat Exchanger for Adsorption Energy Storage: Theoretical Estimation and Experimental Verification of the Methodology for Heat Accumulation Process

Adsorption energy storage is a promising resource-saving technology that allows the rational use of alternative heat sources. One of the most important parts of the adsorption heat accumulator is the adsorber heat exchanger. The parameters of heat transfer in this unit determine how fast heat from an alternative energy source, such as the Sun, will be stored. For the design of adsorption heat accumulators, plate fin heat exchangers are mainly used. In this paper, the procedure for the estimation of the global heat transfer coefficient for the adsorber heat exchanger depending on its geometry is considered. The heat transfer coefficient for a LiCl/SiO2 sorbent flat layer under conditions of heat storage stage was measured. Based on these data, the global heat transfer coefficients for a number of industrial heat exchangers were theoretically estimated and experimentally measured for the adsorption cycle of daily heat storage. It was shown that theoretically obtained values are in good agreement with the values of the global heat transfer coefficients measured experimentally. Thus, the considered technique makes it possible to determine the most promising geometry of the plate fin heat exchanger for a given adsorption heat storage cycle without complicated experiments.

Synchronized measurement of instantaneous convective heat flux and velocity fields in wall-bounded flows

This work presents an experimental setup for acquiring synchronized wall and flow field measurements in a turbulent boundary layer (TBL). Instantaneous measurements of the convective heat transfer distribution at the wall and of the flow field are carried out simultaneously, using synchronized wall-parallel planar particle image velocimetry and infrared thermography. A low-thermal-inertia heated-thin-foil sensor is embedded in the wall beneath the TBL to measure the wall temperature maps with enough temporal resolution. The unsteady energy balance of the heated foil can be solved to restore the instantaneous value of the convective heat transfer coefficient on the wall. A detailed description of the sensor design is included. Furthermore, owing to the relatively low signal-to-noise ratio of instantaneous temperature fluctuation measurements, a recipe for data processing is proposed. A study to characterize the uncertainty of the experimental setup design is also performed. The overall agreement in the correlation between wall heat transfer and velocity fields with the literature supports the validity of the proposed approach. This solution is potentially interesting for flow control purposes, where sensing is performed at the wall.

Natural Convection in a Newtonian Nanoliquid-Saturated Porous Enclosure with Local Thermal Non-Equilibrium Effect

Buoyancy-driven convective flow and heat transfer characteristics in a Newtonian nanoliquid-saturated porous square enclosure are analyzed numerically using a local thermal non-equilibrium model. An enclosure’s horizontal walls are considered free–free and adiabatic, and the vertical walls are free–free isothermal boundaries. The dimensionless governing equations are solved using a central finite difference scheme with second-degree accuracy, and the results are in satisfactory agreement with the earlier works. The impact of various parameters on streamlines and isotherms is analyzed and depicted graphically. The effect of Darcy number, thermal Rayleigh number, and the ratio of thermal conductivities slow down the liquid flow. The temperature distribution is maximum at sidewalls and diminishes the amount of heat transport. The opposite phenomenon is observed for the solute Rayleigh number and interphase transfer coefficient of liquid-particle phases. For large values of interphase heat transfer coefficients, liquid-solid and liquid-particle are said to be in the local thermal equilibrium phase. The amount of heat transfer increases with an increasing interphase heat transfer coefficient and the ratio of the phases’ thermal conductivities. Results of local thermal equilibrium situation can be obtained as the particular case of the study. The amount of heat transfer is maximum in the local thermal non-equilibrium situation, and enhanced by 0.09% compared with the local thermal equilibrium situation. Heat transport is 0.74% less in the sparsely packed porous medium compared with the low-porosity medium.

Nanoparticle Size and Heat Pipe Angle Impact on the Thermal Effectiveness of a Cylindrical Screen Mesh Heat Pipe

This study examines the effects of particle size and heat pipe angle on the thermal effectiveness of a cylindrical screen mesh heat pipe using silver nanoparticles (Ag) as the test substance. The experiment investigates three different particle sizes (30 nm, 50 nm, and 80 nm) and four different heat pipe angles (0°, 45°, 60°, and 90°) on the heat transmission characteristics of the heat pipe. The results show that the thermal conductivity of the heat pipe increased with an increase in heat pipe angle for all particle sizes, with the highest thermal conductivity attained at a 90° heat pipe angle. Furthermore, the thermal resistance of the heat pipe decreased as the particle size decreased for all heat pipe angles. The thermal conductivity measurements of the particle sizes—30, 50, and 80 nm—were 250 W/mK, 200 W/mK, and 150 W/mK, respectively. The heat transfer coefficient values for particle sizes 30 nm, 50 nm, and 80 nm were 5500 W/m2K, 4500 W/m2K, and 3500 W/m2K, respectively. The heat transfer coefficient increased with increased heat pipe angle for all particle sizes, with the highest heat transfer coefficient obtained at a 90° heat pipe angle. The addition of Ag nanoparticles at a volume concentration of 1% reduced the thermal resistance of the heat pipe, resulting in improved heat transfer performance. At a heat load of 150 W, the thermal resistance decreased from 0.016 °C/W without nanoparticles to 0.012 °C/W with 30 nm nanoparticles, 0.013 °C/W with 50 nm nanoparticles, and 0.014 °C/W with 80 nm nanoparticles. This study also found that the heat transfer coefficient increased with increased heat pipe angle for all particle sizes, with the highest heat transfer coefficient obtained at a 90° heat pipe angle.

The role of external heat exchangers in the performance of active magnetic refrigerator

The static performance of an Active Magnetic Regenerator Refrigerator (AMRR) can be evaluated using various indicators, such as the refrigeration capacity, coefficient of performance, and efficiency, for a given temperature span (that is, the hot-to-cold heat source temperature difference). The two main control parameters (cycle frequency and fluid mass flow rate) must be adjusted according to the imposed temperature span to achieve optimum performance. However, in real-world operations, heat exchangers at both ends of the regenerator thermally connect the device to the surroundings, and the hot and cold temperatures are no more imposed quantities. Under these heat transfer constraints, the device performance, in terms of refrigeration capacity, could be suboptimal, even after adjusting the two control parameters. Indeed, to provide optimal performance, heat exchangers must have precise values of the overall heat transfer coefficient, depending on the desired operating temperature difference. So, if a single pair of heat exchangers are used, it is impossible to characterize the performance of the magnetic refrigerator at different temperature spans. This work compares the systematic procedures for evaluating the performance of a magnetic refrigeration device either with heat exchangers at the cold and hot ends or with an imposed temperature span. Both procedures can be used to obtain the optimal AMRR performance curves. However, this work highlights the necessity to use different (or variable heat transfer coefficient) heat exchangers when the first procedure is adopted. The needed overall heat transfer characteristic of both heat exchangers will be lower for a higher temperature span.

Numerical Simulation of Unsteady Turbulent Flow and Heat Transfer of Dynamic Thermal Flow Sensor

Improving energy efficiency in the building’s design is a priority area. To avoid unnecessary energy consumption, electronic control (intelligent) systems can be used to measure and monitor heat exchange between building walls and the surrounding environment, as (Calorimetric Sensor, Heat Flux Sensor ...). They are ideally suited for research in rationalizing and improving thermal efficiency. The aim of this study was a computational fluid dynamics investigation of unsteady turbulent flow and heat transfer of dynamic heat flux sensor for quantitative description of the heat transfer between the building's walls and the surrounding environment.Using CFD software, we numerically simulated the wind tunnel where the sensor was installed; we used six different air speeds (Vinlet=2m/s to 12m/s) in the inlet. To improve the standard features of the CFD code, the User-Defined Function (UDF) was written in the C language program and integrated into the solver of ANSYS Fluent, in order to determine the thermal flow file applied to the surface of the sensor. Heat transfer coefficient (h0) values are obtained according to each speed. The results obtained were compared to results in previous experimental and theoretical literature. There is a good compatibility of all results that allows dependence on numerical simulations in the future as a way of stewardship when studying energy rationalization.

Experimental and numerical investigations of heat transfer and flow characteristics during flow boiling in straight and diverging PDMS microchannel

Recent trends of miniaturization and densely packed circuits have necessitated the development of novel cooling methods, especially for emerging fields like flexible microelectronics, biotechnology, and nanotechnology. A polydimethylsiloxane (PDMS) based microchannel flow boiling heat sink can be used for these applications due to its unique properties as such as unique mechanical properties, biocompatibility, optical transparency, etc. PDMS microchannels are fabricated using soft lithography techniques, which involve using a mould to pattern the PDMS material. The mould is created using photolithography, and the PDMS is poured over the mould and cured to create the microchannels. In this study, an effort is made to compare the flow and heat transfer performance of a PDMS microchannel heat sink with different channel shapes, i.e. straight and diverging microchannel heat sinks for different heat flux and mass flux conditions. The PDMS microchannel was fabricated using the soft lithography technique and a flexible laser-induced graphene heater was fabricated and integrated with the developed PDMS microchannel to act as a heat source. Experimentally, the parameters like bubble pattern, pressure drop, exit vapour quality, and corresponding heat transfer coefficient were determined at varying mass and heat flux ranging from 19 to 114 kg m−2s−1 and from 13.3 to 156.6 kW m−2 respectively for both the microchannels. It was observed that the flow in the diverging microchannel is more stable and has a 13% higher heat transfer coefficient value compared to the straight microchannel under similar conditions. Further, a 3D numerical study was carried out to corroborate and elaborate on the results. The heat transfer, flow characteristics, and bubble pattern results show an excellent agreement with experimental results. This work has significant relevance in designing flexible microchannel heat sinks.

Effect of flow rate and CNM concentration in nanofluid on the performance of convective heat transfer coefficient

The aim of this study is to investigate the thermal performance of water-based Carbon Nano Material (CNM) nanofluids, particularly in the convective heat transfer coefficient (h) parameter, and to analyze the effects of nanoparticle concentration and flow rate on an experimental heat transfer system. To achieve this, the researchers prepared the nanofluid through a 2-step method. In the first step, we mixed the nanoparticles with the base fluid using a magnetic stirrer to ensure homogenization, with the CNM-Water ratio set at 30, 75, 120, and 150 ppm. In the second step, we characterized the prepared samples, determining their size, composition, and particle morphology through PSA and SEM-EDX examination, as well as measuring their density (ρ) and specific heat (Cp). The experiments were carried out using a flow rate simulation test rig with a data acquisition system, at different flow rates of 0.2, 0.6, 1, and 1.4 L/min. Temperature (T) was measured at the inlet, outlet, and heater to determine the convective heat transfer coefficient value. The study successfully investigated the direct impact of CNM concentration and flow rate, with the results showing a consistent and expected value of the coefficient compared to previous studies. The highest coefficient value was observed at 150 ppm CNM-Water ratio and a flow rate of 1.4 L/min, with a value of 1825.37 W/(m2.K).

A Modified Correlative Model for Condensation Heat Transfer in Horizontal Enhanced Tubes with R32 and R410A Refrigerants

An experimental study was performed that compared tube side condensation heat transfer characteristics of enhanced tubes (hydrophobic surface tubes (HYD), herringbone micro fin tube (HB), and a composite hydrophobic/herringbone (micro fin) tube (HYD/HB)) to the performance of a smooth tube (ST). The condensation heat transfer coefficient (HTC) was calculated from data that were recorded for smooth and enhanced tubes that had an outer diameter (OD) of 12.7 mm. Data were collected (as a function of mass flow rate) using a couple of refrigerants (R410A and R32), for saturated temperatures of 35 °C and 45 °C, with vapor qualities that ranged from 0.8 to 0.2. Several previously reported smooth tube HTC models were used to calculate values that could be compared to experimentally obtained HTC values. The correlation model that demonstrated the best accuracy (for the conditions considered) was then modified for use with the enhanced tubes from this study. Results from the modified correlation show differences with experimental values that ranged from −10% to +17%; the new modified correlation demonstrates high prediction accuracy. An accurate correlation allows the evaluation of enhanced heat transfer tubes for use in high-efficiency heat exchanger systems. The development of this new model is significant in the study of enhanced heat transfer.

Scrutinization of Solar Thermal Energy and Variable Thermophysical Properties Effects on Non-Newtonian Nanofluid Flow

Nanofluids generate high values of convection heat transfer coefficients, low specific heat, and density, which improve the solar thermal energy performance by making it work effectively. By utilizing nanotechnology and solar thermal radiation, the modern world is moving in the direction of new technologies. Therefore, this research is communicated to explore the significance of solar thermal energy, variable properties on non-Newtonian nanofluid flow. However, to exemplify the fluid transport features of the Casson nanofluid (CF), the Buongiorno nanofluid model was utilized. Also, the Lie-group technique is used in the framework to develop similarity variables that will be used to reduce the number of independent variables in partial differential equations (PDEs) and is solved numerically by using the weighted residual Galerkin method (WRGM). The graphical findings revealed that when the variable viscosity parameter is increased, the fluid temperature decreases, while the presence of the solar radiation parameter has the opposite impact. Additionally, when the non-Newtonian parameter approaches infinity, the Casson fluid obeys the viscosity law. The report of this study will be of benefit to thermal and chemical engineering for nanotechnology advancement. KEYWORD: Solar Thermal Energy, Nanofluids, Non-Newtonian, weighted residual Galerkin method (WRGM).

Cooling Rate Modeling and Evaluation during Centrifugal Atomization Process

Centrifugal atomization is a rapid solidification technique involving fast cooling rates to produce high-quality powders. The final microstructure of the atomized particles is closely linked with the thermal history and cooling rates experienced during the atomization process. However, there is insufficient research on the temperature evolution of metal particles produced by this technique, and most works evaluate the thermal history of the droplet through semi-empirical correlations that lie outside the conditions where they were derived. In this work, the cooling rate of centrifugally atomized Al-4%Cu was studied via mathematical modelling and experimental validation. A heat transfer model was implemented, and the value of the convective heat transfer coefficient was obtained from the Whitaker semi-empirical correlation considering three cases of study for the thermophysical properties of the gas. The validity of the Whitaker correlation was experimentally evaluated by means of cooling rates based on the Secondary Dendrite Arm Spacing (SDAS) technique. The Whitaker correlation with the Reynolds and Prandtl numbers evaluated at the ambient temperature and the gas conductivity evaluated at the film temperature gave the best agreement with the experimental results, with cooling rates in the order of 105 Ks−1 for <32.5 µm powders atomized in He atmosphere.

Numerical analytical model of metal temperature of steam boiler drum

The problem of developing and identifying a temperature distribution model in the wall of the boiler drum was solved. The numerical model is based on the analytical solution of the one-dimensional heat conduction equation with heat exchange at the boundaries at constant heat transfer coefficients. The model is implemented in a dynamic systems simulation package. Using the bounded series of eigenfunctions of the analytic solution, a representation of the plant in the state space was obtained. A universal algorithm for calculating the eigennumbers of the analytic solution was proposed. The eigenvalues dependences of the analytical solution on the values of heat transfer coefficients and thermal conductivity was investigated. Based on the results of the study, data tables were obtained to approximate the dependences of eigennumbers on heat transfer coefficients in a limited range of variation. The methodology for implementing a dynamic temperature distribution model, which takes into account changes in heat transfer coefficients during simulation, was tested. The time of change of coefficients is perceived as the beginning of a new transient from the current state of the model. Presented structural diagrams of the implementation of the model in dynamic systems simulation packages. The proposed structures allow the introduction of parametric disturbances at the time of their occurrence in the simulation. According to the experimental data of steam boiler firing, identification of the dependence of the heat transfer coefficient on the temperature of the metal wall of the boiler drum was carried out. The results showed that the heat transfer coefficients are influenced not only by the metal temperature, but also by additional parameters of the steam boiler operation. As a result of experiments, it was found that the accuracy of the model can be improved by taking into account the dependence of the heat transfer coefficient on the internal surface of the drum on the flow rate of feed water into the boiler drum. The results of the numerical experiment are presented.

Performance evaluation of nano refrigerant operated thermosyphon using artificial neural network technique

The present work is focused on evaluating the performance of a thermosyphon with internal fin and internal cut arrangement employing a mixture of nano particle Al2O3 and refrigerant R134a using artificial neural network. Using feed forward back propagation algorithm technique has used the data from the experimental studies to predict the thermosyphon performance. The input parameters to the algorithm were heat input, heat flux and cooling water temperatures and the output parameter predicted by the algorithm is heat transfer coefficient. It was inferred from the analysis that the predicted values of heat transfer coefficient were close to the actual experimental data. The artificial neural network model predicted the values in close agreement with the experimental values with an error of ±3%.

Heat transfer and gas dynamics numerical modelling of compact pipe bundles of new design

Weight and size characteristics, heat transfer efficiency across the surface, pressure losses in the flow paths for each heat transfer medium, and other parameters that characterise the heat exchanger play an important role in the development of new types of heat exchanger designs. This predefines the research relevance and the need for a solution. The research aims to develop and implement fundamentally new approaches to the design parameters of shell-and-tube heat exchangers, in which smooth-tube bundles are placed as compactly as possible in their crossflow. For this purpose, numerical modelling in the heat exchanger channels and studies of heat transfer and gas dynamics were carried out. The ANSYS Fluent software package was used to calculate the hydrodynamics and heat transfer in the tube bundle channels. Numerical modelling of hydrodynamics and heat transfer processes in the flow of a compact bundle of small-diameter pipes was carried out. The mathematical model includes the Navier-Stokes equation, the energy equation, and equations describing the turbulence of the external flow. The turbulence model was chosen as a model that describes turbulence in channels well. The results of numerical modelling showed a compact bundle of pipes at the outlet of the channels, with an average value of +20.1ºС. Notably, the local temperature values near the channel walls are close to +30 °C. The air velocity at certain points of the duct reaches 85.1 m/s. At the same time, the average air velocity in the cross-section of the channel is about 41.2 m/s at Re=21420. It is demonstrated that the maximum values of local heat transfer coefficients for pipes in a compact bundle are observed in the areas where the flow joins the pipe surface and at the beginning of the boundary layer formation. The maximum values of the heat transfer coefficient reach up to 1335.5 W/m2·ºС for the second and third rows, and at the front point of the first order, it is 1042.3 W/m2ºС. These results will improve the weight and dimensions of shell-and-tube heat exchangers and reduce their cost