Values Of Heat Transfer Coefficient Research Articles

Estimation of heat transfer coefficient for intermediate fluid stream in triple concentric tube heat exchanger

The design of triple concentric tube heat exchanger (TCTHE) requires heat transfer coefficient (HTC) values for all three fluid streams as input parameters. The fluid through intermediate tube transfers heat to other fluids simultaneously. The present study applies a concept of thermal resistance network and quadratic equation is developed for computing HTC of intermediate fluid for TCTHE under adiabatic condition. ‘Oil ISO VG 22’ is taken as intermediate fluid and is cooled by using water as inner and outer cooling fluid in the present work. The HTCs of inner and outer cooling fluids are calculated from the well-established empirical correlations available in the literature. CAD modelling is done using Catia V5 and simulation is carried out using STAR CCM+ CFD software. The results of the method are compared with those obtained from mathematical models in the literature as well as results from CFD analysis are validated.

Study of Non-condensable Gas, Fouling, and Plugging Effects on Condenser Performance Using NTU-Effectiveness Analytic Method and 2D Numeric Simulation

This paper was objected to determine the effect and how sensitive the variation of the percentage of non-condensable gas, fouling thickness and the amount of plugging to the performance of the condenser and the steam turbine power output. This study was conducted using the NTU-effectiveness analytical method, and specifically for the study of the effects of non-condensable gas combined with numerical simulations to obtain the value of the condensation heat transfer coefficient as an input for analytical calculations. The study was conducted with a variation of the percentage of non-condensable gas 0% (new and clean), 2%, 5%, and 8%, with fouling thickness 0 µm, 2 µm, 5 µm, and 8 µm, and the amount of plugging 0%, 5%, 10%, and 15%. 2D numerical simulation was used to determine the impact of non-condensable gas percentage variation on the value of the condensation heat transfer coefficient on the outside of the tube, both qualitatively and quantitatively along the circumference of the condenser tube. The results of this study were, the greater the percentage of non-condensable gas, the thicker the fouling layer, and the more amount of plugging, would have an impact on decreasing the net turbine work. Consequently for new and clean conditions, the percentage of non-condensable gas were 2%, 5%, 8%, fouling thickness 2 um, 5 um, 8 um, and the amount of plugging were 5%, 10%, 15%, resulting in net turbine work to 202.55 MW, 192.08 MW, 189.08 MW, 185.85 MW (non-condensable gas), 200.05 MW, 196.01 MW, 192.08 MW (fouling), 195.2 MW, 185.27 MW, and 174.77 MW (plugging). A financial loss simulation was also carried out due to the decline in electricity sales affected by the decreasing of power plant’s net turbine work.

Enabling Taguchi method with grey relational analysis to optimize the parameters of TiO2/ZnO heat transfer nanofluid for heat pipe application

Our previous work demonstrated that the TiO2/ZnO (1:1) nanocomposite suspended in ethylene glycol with CTAB (0.5 ml) as surfactant exhibits better heat transfer property than TiO2 and ZnO nanofluid. As an extension, the influence of parameters such as wt.% of ZnO Nps in TiO2/ZnO nanocomposite (0 wt.%, 25 wt.%, 50 wt.%, and 100 wt.%), the quantity of CTAB (250 μl, 500 μl, 750 μl, and 1000 μl) and vol.% of TiO2/ZnO nanocomposite (1 vol.%, 2 vol.%, 4 vol.%, and 8 vol.%) are analyzed through Taguchi design constructed with L16 orthogonal array is emphasized in the present work. As per the Taguchi design, the responses such as viscosity, thermal conductivity, and normalized height % for the set of input parameters are evaluated. Besides, the multiple responses are graded employing Grey relational analysis and the optimum set of parameters to achieve the preparation of the best nanofluid is identified as 25 wt.% ZnO, 1 vol.% nanocomposite and 500 μl CTAB which display viscosity of 0.043 Pa.s, thermal conductivity of 0.35 Wm−1 K−1, and normalized height % as 1%. Further, the optimal TiO2/ZnO nanofluid is used as working fluid in heat pipe and compared its results with ethylene glycol. From the calculated thermal resistance and heat transfer coefficient values, the TiO2/ZnO nanofluid outperforms the base fluid in a significant manner.

Entropy generation in thermal radiative oscillatory MHD couette flow in the influence of heat source

Entropy generation and their minimization for magnetohydrodynamic oscillatory couette flow through a vertical channel, soaked with a porous medium in the existence of heat source and thermal radiation has been deliberated. In the present analysis, flow governing equations are elucidated and extricated with the help of analytical technique for the fluid velocity profile, temperature field, irreversibility distribution and Bejan number. Also, the numerical value of dimensionless shearing stress and heat transfer coefficient are obtained and presented through tables with reference to flow governing parameters. It has noticed that entropy generation can be regulated or minimized with the change in the applied magnetic field and thermal radiation, and this result is useful in several thermodynamic industries and engineering field for attaining the high performance of devices with minimum heat loss.

Non-contact experiments to quantify the microlayer evaporation heat transfer coefficient during isolated nucleate boiling regime

Experiments to understand the relationship between dynamics of superheat layer, microlayer evaporation and bubble growth process during single bubble formation under saturated pool boiling regime have been conducted. Thin film interferometer and rainbow schlieren deflectometry have been employed in tandem to simultaneously map the transient evolution of microlayer and superheat layer along with the bubble growth process. During initial time instances of growth process, heat flux dissipated in the microlayer region is determined to be as high as ~1 MW/m2 for the range of experimental conditions employed. As a result, a large temperature drop is observed in the microlayer region. As the bubble growth process enters its final stages, reduced temperature levels of the heated substrate result into a significant reduction in the depletion rate of the inner core region of microlayer, while the evaporation rate of its peripheral region is seen to increase. The consolidated evaporative heat transfer coefficient for the entire bubble cycle is determined to be ~140 kW/m2K for q″ = 50 kW/m2 and 170 kW/m2K for q″ = 80 kW/m2. The corresponding accommodation factor required for predicting the evaporative heat transfer coefficient values through kinetic theory-based model is determined to be ~0.015.

Heat Transfer Process During Filtration Drying of Grinded Sunflower Biomass

Filtration drying of grinded sunflower stems as the unit operation of the technological line for solid biofuel production has been proposed. Theoretical aspects of heat transfer processes during filtration drying have been analyzed. The effect of the drying agent velocity increase from 0.68 to 2.05 m/s on the heat transfer intensity has been established. The values of heat transfer coefficients have been calculated on the basis of the thin-layer experimental data and equation . Calculated coefficients for grinded sunflower stems have been correlated by the dimensionless expression within Reynolds number range of and the equation has been proposed to calculate the heat transfer coefficients, that is important for forecasting the heat energy costs at the filtration drying equipment design stage.

Application of the Trefftz Method for Pool Boiling Heat Transfer on Open Microchannel Surfaces

In the paper, the results of tests on pool boiling heat transfer on open microchannel surfaces were discussed. Nucleate pool boiling from copper microchannel surfaces was examined using ethanol as a working fluid. Parallel microchannels fabricated by machining were about 0.2 to 0.4 mm wide and 0.2 to 0.5 mm deep. In the mathematical model the heat transfer process was in steady state. The heat transfer in copper block was assumed axisymmetric while the specimen temperature distribution was not. The temperature of the copper block and the specimen were assumed to satisfy Laplace’s equations with adequate boundary conditions. The problem was solved by the Trefftz method with two sets of Trefftz functions. Graphs were used to represent the copper block and the specimen temperature distributions, local values of heat transfer coefficients as a function of the heat flux and fin temperature distribution. Uncertainty analysis was presented.

Exergo-economic optimization of concentrated solar photovoltaic and thermoelectric hybrid generator

Exergo-economic analysis of a concentrated photovoltaic–thermoelectric generator (CPV-TEG) hybrid system is investigated. The specific exergy costing is employed to study the cost effectiveness of the CPV-TEG system. A multi-dimensional single-objective optimization is carried out to optimize the CPV-TEG hybrid system. The performance of the CPV-TEG system is found to be better than that of the concentrated photovoltaic (CPV) system alone in terms of overall energy and exergy efficiencies. From an exergo-economic standpoint, the CPV-TEG system is more cost effective as compared to the CPV system alone. The low value of the exergo-economic factor of the system indicated that the associated cost was mostly due to irreversibilities in the system. A compromise is made by optimizing the CPV-TEG system for maximum exergy efficiency using an optimum thermal resistance of the thermoelectric generator (TEG). For the operating conditions and the geometry considered, integration of CPV and TEG is not found to be feasible (in terms of exegetic performance) below certain values of heat transfer coefficients (< 2500 Wm−2 K−1). A minimum value of heat transfer coefficient of 5266 Wm−2 K−1 is determined for a water-cooled heat sink to limit the cell temperature to 100 °C under the studied set of operating conditions and the geometric configuration. Optimization results yielded exergy efficiencies of 42.22% and 43.48% for the stand-alone CPV system and CPV-TEG system, respectively. The minimum costs of electricity under the optimum conditions were obtained as $$0.57\;\$ \; {\text{kW}}\,{\text{h}}^{ - 1}$$ and $$0.53\;\$ \; {\text{kW}}\,{\text{h}}^{ - 1}$$ for the stand-alone CPV system and CPV-TEG system, respectively.

Study of the performance of multiple v-type fin arrangements as an enhancement of natural heat transfer from a vertical surface

Thermal influence on home appliances, devices and other engineering systems is so high that it causes a system failure. The dominant mode of heat transfer through these systems is the natural heat transfer. As the value of heat transfer coefficient is low, an extension in the heat transfer area becomes essential. The extension is merely to add fins with different shapes and configurations depends on the geometry of systems and space available. One of these configurations is the V type fin array. A testbed was built using two different configurations of fin array. The first array looks like the letter “V” with two discrete parts and the other array is the upset of the letter “V”. The array consists of two columns and five rows separated by a certain distance. The variable heat fluxes were achieved by changing the voltage of three heating elements fixed to the backside of the testbed. Seven thermocouples were fixed at different positions on the testbed and the experiment was run to calculate the natural heat convection through the testbed. The configuration with upset V shape fin shows better performance because it allows the air to flow faster through the middle passage separating the fin array.

Investigating the effects of fin geometry on motorcycle cylinder cooling

This work aimed to improve the heat transfer process in motor engine cylinders by adding eight fins with different shapes around such a cylinder. This process was carried out numerically Fluent software (Ansys 19.0) for different Reynolds numbers (4, 6, and 8 × 104) under constant heat flux (6, 12, 25 kw/m2). The metal used for the fin bodies was aluminium alloy, with a thermal conductivity of 237 W/m-k. Four types of fin, square, circular, elliptical, and air foil, all with the same thickness (5 mm), pitch, gap between each fin (3 mm), and surface area (0.0745 m2) were investigated. The working fluid used was air. The results indicated that the best case was seen in the cylinder with square fins, which obtained the highest value of heat transfer coefficient. The results also indicated that, more generally, the rate of the heat transfer increases when the Reynolds number increases.

Experimental studies of the efficiency of a solar system, including a passive water heater and an active seawater distiller

In the hot climate of the Mangistau region, located on the eastern coast of the Caspian, there are no sources of freshwater. Of the available groundwater deposits, only three are suitable for drinking water supply. The scarcity is felt in remote areas and coastal areas, where the population uses groundwater.The provision of the population is carried out by a seawater desalination plant. In the hot summer period, due to high temperatures, the productivity of desalination plants decreases (the water in the channels reaches 30 °C, and the plants are designed for 20 °C). This factor provides opportunities for the development of desalination plants using this heliopotential.Easy to manufacture, environmentally and economically viable solar desalination plants are essential for coastal areas where water is scarce.The article presents the results of experimental studies of the heliosystem, which consists of a passive solar water heater (SWH) and an active solar desalination plant (SW). Water is heated in the SWH pool and supplied to the lower SW pool-1, in which the desalination process is achieved by cooling the water pool-2.By reducing the temperature in the SW volume, the condensation temperature is reached. The coating of 2 layers of glass with an air gap reduces heat losses and raises the temperature in the installations by 10–12 °C and keeps it at night. Horizontal glass coverings provide a large area for solar radiation to enter the pool surface. Heat transfer by convection, in the volume between the "cold" and "hot" basins, is determined using the convection coefficient, which depends on the product of the numbers Gr and Pr. According to the results of experiments, the daily productivity of the desalter was 1.97, 1.83 and 2.31 l/m2 on the day of July 20, 21 and 22, 2019. The maximum value of the total heat transfer coefficient for SVN was 32.9 W/m2 °C, for SW 49.4 W/m2 °C.

The Study of the Onset of Flow Boiling in Minichannels: Time-Dependent Heat Transfer Results

The paper describes the results of boiling heat transfer during FC-72 flow in minichannels, obtained on the basis of time-dependent experiments. The main goal of the work was to determine the heat transfer coefficient by means of the finite element method with the spacetime Trefftz-type basis functions based on the Hermite interpolation. The crucial part of the experimental stand was the test section with minichannels of 1.7 mm depth. One wall of the minichannels constituted a heated foil which was resistive heated. Temperature of outer foil surface was measured due to thermocouples in the test minichannel. The onset of flow boiling was induced by two ways: lowering the pressure in the circulating system or increasing the heat flux supplied to the heater. Dynamic changes in thermal and flow experimental parameters accompanying the onset of flow boiling, including: temperature of the heater, pressure and mass flow rate, were illustrated. The results were performed as: foil temperature and heat transfer coefficient versus the distance from the minichannel inlet or time. It was observed that heat transfer coefficient values increased at the boiling incipience region for both analyzed experiments. Boiling curves were discussed. The error analysis of the results was provided. Mean relative errors of the heat transfer coefficient did not exceed 11%. Our results were compared with selected correlations from the literature.

Local Thermal Nonequilibrium Natural Convection in a Cavity with Heat-Generating Porous Layer

Natural convection in a partially porous cavity with a heat generating source in the solid phase is studied numerically under a local thermal nonequilibrium condition. The right and left walls of the cavity are maintained at hot and cold temperatures, respectively. The horizontal walls are thermally insulated. The finite volume method and the semi-implicit method for pressure-linked equations (SIMPLER) algorithm are used to solve the conservation equations. The effects of relevant parameters, such as internal and external Rayleigh numbers , , interphase heat transfer coefficient , modified thermal conductivity ratio , and dimensionless porous layer thickness are discussed. The results revealed that at high values of the interphase heat transfer coefficient, the impact of an internal Rayleigh number on the dynamic and thermal fields decreases with an increase in the modified thermal conductivity ratio.

Homogeneous and Multiphase Analysis of Nanofluids Containing Nonspherical MWCNT and GNP Nanoparticles Considering the Influence of Interfacial Layering.

The practical implication of nanofluids is essentially dependent on their accurate modelling, particularly in comparison with the high cost of experimental investigations, yet the accuracy of different computational approaches to simulate nanofluids remains controversial to this day. Therefore, the present study is aimed at analysing the homogenous, multiphase Eulerian–Eulerian (volume of fluid, mixture, Eulerian) and Lagrangian–Eulerian approximation of nanofluids containing nonspherical nanoparticles. The heat transfer and pressure drop characteristics of the multiwalled carbon nanotubes (MWCNT)-based and multiwalled carbon nanotubes/graphene nanoplatelets (MWCNT/GNP)-based nanofluids are computed by incorporating the influence of several physical mechanisms, including interfacial nanolayering. The accuracy of tested computational approaches is evaluated by considering particle concentration and Reynolds number ranges of 0.075–0.25 wt% and 200–470, respectively. The results demonstrate that for all nanofluid combinations and operational conditions, the Lagrangian–Eulerian approximation provides the most accurate convective heat transfer coefficient values with a maximum deviation of 5.34% for 0.25 wt% of MWCNT–water nanofluid at the largest Reynolds number, while single-phase and Eulerian–Eulerian multiphase models accurately estimate the thermal fields of the diluted nanofluids at low Reynolds numbers, but overestimate the results for denser nanofluids at high Reynolds numbers.

CFD-based calculation method of convective heat transfer coefficient of spiral bevel gear in intermediate gearbox under splash lubrication

Purpose This paper aims to propose a numerical method to calculate the convective heat transfer coefficient of spiral bevel gears under the condition of splash lubrication and to reveal the lubrication and temperature characteristics between the gears and the oil-air two-phase flow. Design/methodology/approach Based on computational fluid dynamics, the multiple reference frames (MRF) method was used to simulate the rotational characteristics of gears and the motions of their surrounding fluid. The lubrication and temperature characteristics of gears were studied by combining the MRF method with the volume of the fluid multiphase flow model. Findings The convective heat transfer coefficient can be improved by increasing the rotational speed and the oil immersion depth. Moreover, the temperature of the tooth surface having a large convective heat transfer coefficient is also found to be low. A large convection heat transfer coefficient could lead to a good cooling effect. Originality/value This method can be used to obtain the convective heat transfer coefficient values at different meshing positions, different radii and different tooth surface positions. It also can provide research methods for improving the cooling effect of gears under the condition of splash lubrication. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2020-0233/

Forced Convection Heat Transfer in Circular Meso-Tubes.(Dept.M)

Convection heat transfer of water flow inside a circular meso-channel was investigated experimentally. To perform this experimental study, an experimental test rig was designed and constructed. Test section was shell and tube heat exchanger. It consists of seven meso scale circular tubes surrounded by a saturated steam to perform its outer surface at constant temperature, Water flows inside these tubes in steady flow and pulsating flow. The ranges tested for pulsation frequencies are 0.5 Hz to 5 Hz and Reynolds number is of 200 to 5000. Four values of inner diameters was tested in this study ; 0.25, 0.35, 0.52 and 0.7 mm. Experimental measurements for mass flow rate, temperature, pressure, pressure drop and pulsation frequency are taken to perform the required analysis. Therefore, the average value of convection heat transfer coefficient and friction factor for different operating parameters are computed The experimental results show that, the friction factor in the studied operating range decreases as Reynolds number increases but its values are deviated from those reported in conventional tubes due to the small dimensions of the meso-tubes. The friction factor decreases with decreasing tube diameter. Also, Nusselt number increases with increasing Reynolds number for pulsating flow and steady flow. For pulsating flow, Nusselt number takes lower values than steady flow for the same conditions in the studied operating ranges. Comparison between the obtained experimental results with the previous data and the classical correlations for conventional tubes was done and the disagreement among the researchers was still. Two empirical correlations for both friction factor and Nusselt number were obtained in the range of the studied operating parameters.

Louver and effusion cooling heat transfer for a double wall effusion plate with impingement jet array coolant supply

Louver slot cooling is employed, which consists of an aligned collection of film cooling holes, contained within a specially-designed device which concentrates, and directs the coolant from a slot, so that cooling air then advects as a layer downstream along the test surface. This louver-supplied coolant is then supplemented by coolant which emerges from different rows of downstream film cooling holes. Coolant for both cooling arrangements is supplied using an array of impingement jets. Experimental data are provided for a mainstream Reynolds number Rems range of 168,000–181,000. Full-coverage film cooling initial blowing ratio values are 2.5, 3.2, 4.4, and 5.2, with respective louver slot blowing ratios of 1.2, 1.5, 2.1, and 2.4. Measured lateral-averaged adiabatic effectiveness results show that, with impingement supply cooling only, for blowing ratios of 4.4 and lower, the louver and effusion cooling arrangement generally provides higher effectiveness, relative to an effusion cooling only arrangement. For all blowing ratios considered, another advantage of the louver slot is more uniform values of increased effectiveness along the entire test surface, including locations which are just downstream of the slot. Relatively weak dependence on blowing ratio is present for the louver and film cooling arrangement, in contrast to the effusion only configuration, where effectiveness data generally increase progressively and substantially (at most x/de locations) as the blowing ratio becomes larger. Lateral-averaged heat transfer coefficient values for the effusion cooling only arrangement, and for the louver and effusion cooling arrangement, are approximately quantitatively similar when the blowing ratio is 4.3 to 4.4. Data for blowing ratios BR of 5.2 to 5.5 show that the louver and effusion cooling gives much lower lateral-averaged heat transfer coefficients, compared to the effusion cooling only arrangement. This is a result of reduced local turbulent thermal transport levels within the wake flows which are present downstream of the louver leap device.

Computational fluid dynamic simulations of solidification for enhancing speed of continuous cast copper

In this research experiment computational fluid dynamic (CFD) models were constructed, within Ansys Fluent TM v.R1, to investigate phenomena occurring during the Vertically Upwards Continuous Casting (VUCC) of 8 mm diameter, oxygen free copper (OFCu) for alterations to the casting speed. The simulated influence of heat transported over a 0.1 mm air gap formed within the casting die was investigated and a value for the die wall heat transfer coefficient (hc) of (9.0 ± 0.2) × 104 W/m2K, was extracted. Using this value for hc, simulations of the entire casting crucible and die were made for casting speed settings: pushback motion at 0.06 m/s, average; dwell motion (pause) at 0.05 m/s, average; and continuous motions at 0.022 m/s, 0.015 m/s and 0.008 m/s; and were validated against literature values for measured thermal distribution within the casting die. The fastest casting speed for 8 mm OFCu was investigated and a trend between simulated solidification front and measured grain growth direction was identified, highlighting, the casting motions pushback and dwell yield improved casting conditions. Fluid flow rate was investigated within the casting crucible and showed a small influence on casting due to natural convection relative to flow within the die, 0.001 ± 0.0005 m/s compared with 0.1 ± 0.01 m/s for pushback casting, respectively.

Experimental study of nucleate pool boiling heat transfer improvement utilizing micro/nanoparticles porous coating on copper surfaces

Pool boiling has gained tremendous attention in an efficient transferring of high thermal energy for diverse industrial applications. Surface coating is considered as a common approach for achieving an enhanced boiling heat transfer. In this paper, spin-coating technique is scrutinized experimentally for modifying the surface and enhancing the heat transfer in nucleate pool boiling of distilled water at atmospheric pressure. The images of Scanning Electron Microscopy (SEM) as well as Atomic Force Microscopy (AFM) are utilized for obtaining the phase structure and surface morphology in the prepared materials. Regarding the results of experimental tests, considerable improvements in surface roughness and porosity were achieved by the use of surface coating. Furthermore, the positive effect of adding an appropriate amount of material in achieving the enhanced overall performance of pool boiling was found. Also, higher nucleation sites densities (NSD) were formed by coating the surface, and consequently, improved boiling performance was reached.The maximum heat flux of 101.78 W/cm2 was associated with sample 4 regarding the highest roughness as well as the highest NSD. In addition, it was inferred that the superior surface characteristics of the micro/nanostructured coatings resulted in an enhanced heat transfer coefficient (HTC) value.

A novel contactless transient method for measuring local values of heat transfer coefficient

This paper presents a new non-contact transient method for measuring the heat transfer coefficient. The proposed method is based on measuring the temperature response of the surface temperature to the heat flux irradiating the same surface, which is affected by the heat transfer coefficient on the back of the surface. The theoretical solution of this problem together with the measured experimental data then enables an evaluation to be made of the local value of the heat transfer coefficient and the corresponding integral value. We present the theoretical foundations, a description of the required experimental setup, the methodology for evaluating the heat transfer coefficient, and an error analysis. The results of forced convection inside the tubes and the incident geometry of the impinging jets in comparison with the experimental results from the literature are presented as validation experiments. Very good agreement is demonstrated and the experimental results obtained by the proposed method lie in the standard range of 10%.