Heat Transfer Coefficient Model Research Articles

Experimental research on the convective heat transfer coefficient of photovoltaic panel

The convective heat transfer between wind and photovoltaic (PV) panels will cause fluctuations in the temperature and performance of PV cells, which have a great negative impact on the grid-connected solar energy. The development of large-scale PV power plants in desertification areas has certain advantages, but the output power fluctuations caused by windy-dusty environment will be more common and important. This paper established a new model of convective heat transfer coefficient with and without dust deposition. Results show that the convective heat transfer coefficient of PV panel is not only affected by wind speed and dust density, but also related to the tilt angle of panel. As the dust accumulation density increases, the convective heat transfer coefficient of the dusty PV panel firstly increasing and then decreasing, and the maximum value appears when the dust deposition density is 20 g/m2. In addition, the average heat transfer coefficient of dusty PV module is slightly higher than that of clean PV panels by 4.13%, which can be revealed by the thermal diffusivity. This work confirms the influence of dust on the convective heat transfer characteristics, and provides an important basis for establishing a more practical PV panel temperature prediction model.

New general models for condensation heat transfer coefficient of carbon dioxide in smooth tubes by intelligent and least square fitting approaches

The heat transfer characteristics of carbon dioxide (R744) as a natural and safe refrigerant are quite different from the other refrigerants due to the CO2 unique physical properties. So, it is essential to develop accurate general models for predicting the heat transfer coefficient (HTC) of CO2 condensation inside smooth tubes. In this study, an extensive experimental databank for the CO2 refrigerant including 1,016 data samples was gathered from 13 published studies, covering a broad range of operating conditions and channel sizes. Ten earlier well-known HTC models for other refrigerants showed high deviations (average absolute relative deviations (AARDs) higher than 49%). To overcome this research gap in the literature, the machine learning methods, namely, multilayer perceptron (MLP), interpolating radial basis function (RBF), and Gaussian process regression (GPR), were used for developing the predictive models for two-phase Nusselt number. The GPR model showed the best outcomes among the studied models with AARD values of 1.5% and 7.32% for training and testing data points, respectively. In addition, a new general HTC correlation for condensation of CO2 was proposed by considering two surface tensions ranges, which showed good accuracy with an AARD of 17.61% for the entire database. It was found that the developed models are reliable for designing heat exchangers with different channel sizes and various flow patterns. Finally, a sensitivity analysis using the most accurate GPR model showed that the channel diameter is the most critical factor in controlling the HTC of CO2 when the Bond number is higher than 0.5.

Evaluation of the performance parameters of a PVT system: Case study of composite environmental conditions for different Indian cities

The efficiency of the photovoltaic thermal (PVT) system is affected by the meteorological and climatic conditions. Studies based on mathematical modeling has been applied to optimize the PVT system using absorber shape factor (Z) and mass flow rate (m). Mathematical modeling of heat transfer coefficients and their simulation in MATLAB is presented in the current study using the meteorological data of three major cities (Ahmedabad, Delhi, and Pilani) of India. The scope of the present work is not only limited to finding the effect of solar radiation intensity and ambient temperature but also to establish the optimized value for Z and the best suitable shape for the absorber plate. The detailed analysis of results obtained shows higher values of m gives better total efficiency. For m = 0.02 kg/s but it is observed Z = 1.3 gives maximum efficiency, 48% at noon, in comparison to Z = 2 which is 43% for m = 0.1 kg/s. Hence curved grooved absorber plate is predicted to give better performance for various geographical locations.

A Calculation Model for Cooling Rate of Aluminum Alloy Melts during Continuous Rheo-Extrusion.

The melt temperature of aluminum alloys plays a significant role in determining the microstructure characteristic during continuous rheo-extrusion. However, it is difficult to measure the actual melt temperature in the roll-shoe gap. In this work, based on the basic theory of heat transfer, a calculation model for heat transfer coefficient of cooling water/roll interface and melt/roll interface is established. In addition, the relationship between the temperature at the melt/roll interface and the velocity of cooling water is investigated. Combined with the CALPHAD calculation, the melt temperature during solidification in the continuous rheo-extrusion process is calculated. Using this model, the cooling rate of an Al–6Mg (wt.%) alloy melt prepared by continuous rheo-extrusion is estimated to be 10.3 K/s. This model used to determine the melt parameters during solidification provides a reference for optimizing the production process of continuous rheo-extrusion technology.

Experimental study on flow boiling heat transfer characteristics of multi-channel modified filled foam metal small channel

This experiment reports the experimental study on the heat transfer performance of water in the flow-boiling heat transfer process of different modified foam metal-filled channels. In the experiment, the foam metal has subjected to surface hydrophobicity treatment, surface roughness modification treatment, and gradient pore density stacking treatment. The mass flow rate is 50–150 ml/min, and the heat flux is 15 kW/m2 – 25 kW/m2. The pore density of foam metal is 20 PPI, 50 PPI, and 110 PPI. A high-speed camera, micro camera, and electron microscope are used to record and observe the internal flow of the channel, the results after surface treatment, and the related reaction mechanism. The experiment uses different modifications as the basis for grouping and uses heat flux and mass flow rate as variables to perform multiple sets of orthogonal experiments. At the same time, the prediction model of matching heat transfer coefficient and the correlation of pressure drop gradient are proposed. Construct a comprehensive evaluation index of heat exchange of porous foam metal, which is evaluating the heat exchange performance of foam metal that matches the change of resistance.

Experimental Investigation and Mathematical Modelling of Heat Transfer Coefficient in Double Slope Solar Still

In this study, a double slope solar still has been designed and fabricated with the help of locally available materials for the climatic condition of Sultanpur, India. The experimental study was performed to investigate the effect of basin water, wind velocity on the heat transfer coefficient (convective, evaporative, and radiative) and yield of solar still. A mathematical model is developed to understand the impact of wind velocity and basin water depth in the double slope solar still on the heat transfer coefficient. It was found that the convective heat transfer coefficient depends upon the water mass and the temperature of basin mass, and glass cover temperature. The maximum value of hew (55.05 W/(m²K) and 31.80 W/(m²K)) and hcw , (2.48 W/(m²K) and 2.38 W/(m²K)) found for depths of 2 cm and 5 cm, respectively. The radiative heat transfer coefficient found to be a maximum of 8.31 W/(m²K) for 2 cm depth, and it increases as the condensation increases, because the glass surface temperature increases as vapour transfers its energy to the surface. On increasing the depth from 2 cm to 5 cm, the yield from the solar still decreases by 25.45 %. The maximum yield of 2.5 l/m²/day was found for a 2 cm water depth. The theoretical and experimental yield agreed with an error of 7.5 %, 3.25 %, 7.4 %, and 8.4 % for water depths of 2 cm, 3 cm, 4 cm, and 5 cm, respectively. It was also found that the yield from the solar still increases as the wind speed increase because this leads the faster condensation at the glass surface.

Experimental Study on the Convection Heat Transfer Coefficient of Ti-5553 in Liquid Nitrogen Cryogenic Cutting Condition

In order to determine the convective heat transfer coefficient of liquid nitrogen during cryogenic cooling, this paper uses a combination of temperature simulation and cryogenic cooling experiments to study the cooling rate and the liquid-gas scale affected by the four jet parameters for cooling the Ti-5553 and cemented carbide WC-Co plates in cryogenic liquid nitrogen cooling, then establishes a prediction model of convective heat transfer coefficient and verifies the accuracy of the convective heat transfer coefficient model by cutting temperature simulation and cutting experiments. The results of experimental research show that the larger the nozzle diameter, the larger the spray pressure, the smaller the spray angle, the smaller the spray distance, and the greater the cooling rate of the sheet surface. The order of the influence of the jet parameters on the convection coefficient is spray diameter Φ, injection pressure P, jet angle A, and standoff distance D.

Accurate numerical modeling of convective heat transfer coefficient for a high power PLA-core toroidal electromagnetic coupler subject to cooling

The toroidal electromagnetic coupler has many advantages over the classical transformer. It is widely used in low-power applications. However, there are some limits that hamper its use in modern and high-power applications, such as the cost, the difficulty of winding and, especially, the limited number of studies carried out on the thermal aspect. In this article, we look at the problem of cooling a high-power and very compact toroidal electromagnetic coupler used in smart grid systems. The cooling is modeled thanks to heat transfer coefficients considering the windings as a surface heat source. A mathematical model which is quick and useful for a first approach is developed, and the results obtained show the temperature distribution for convective boundary conditions inside and outside the hollow torus. In addition, a parametric study is carried out. It aims to determine the optimal internal and external convective heat transfer coefficients for which the temperature of the coupler remains below the material’s destruction threshold. Additionally, a 3D numerical model taking into account the wires of the toroidal coupler is studied and compared with the mathematical model. The good consistency between the two methods ensures that this simplified thermal modeling can be trusted for the study of thermal management during the design of future electromagnetic couplers.

Potential of Fuzzy Methodology for Investigation in Nanofluids Heat Transfer

In this paper, the Fuzzy Nanofluid Model (FNFM) used to develop a fuzzy analysis investigation on heat transfer optimal performance at different Nanofluids flow rate. The fuzzy Nanofluid model is applied to examine the effects of heat transfer parameters on heat transfer performance. Silicon Oxide SiO2 Nanofluid is used to explain their effects on heat transfer by two methods traditional and fuzzy (with two shapes of member ship function triangular and trapezoidal). This study evaluates the effects of nanoparticles SiO2 with different value of particle concentration PC (0.0-4.0%) using the water as a base fluid. This investigation covers a Reynolds number (Re) in the range of (100-500) as a flow rate (FR) for laminar flow. The main objective of present research, first one, compared a developed FNFM model with traditional model (TM) and determines how fuzzy model plays a significant role in prediction of Heat Transfer performance. Second one, to provide developed methodology for performance evaluation of heat transfer by connecting more than one parameter to a single output which is invaluable supplements relative to classical models. Third one, a developed FNFM can be used as a help tool for decision making to get the best judge (optimum) the performance of any system. The results of fuzzy model showed the heat transfer of SiO2/H2O Nanofluids significantly increased the PC compared with the increase in FR. However, however, using this method, there will be no need to resort to solving complex equations to arrive at a representation of the performance of any system. Finally, the study shows that fuzzy model plays significant role in prediction of heat transfer investigation without the complexity of mathematical tradition models. The correlations coefficients R2 between TM and FNFM models for heat transfer coefficient (0.97) and the average relative error (ε) is ((4.4%). FNFM models can predict heat transfer characteristics with higher accuracy than that of the traditional model.

Preliminary development and validation of ACENA code for heavy liquid metal-gas two phase flow simulation

To simulate the heavy liquid metal-gas (HLM-gas) two phase flow phenomena that may occur during postulated accidents of Lead-based fast reactors (LFRs), a 2D multiphase fluid dynamics code, ACENA, is preliminarily developed and validated in this study. A brief description of theoretical models, including governing equations, auxiliary models and material properties are listed in this study. The capability of simulating flow and heat transfer characteristics between gas and liquid phases has been examined by typical air-water bubble column experiment, LBE-N2 two phase flow experiment and Lead-Ar heat transfer experiment, and the comparison results show that this code could attain acceptable accuracy in simulating flow and heat transfer characteristics of HLM-gas two phase flow with appropriate interfacial drag coefficient and heat transfer coefficient models.

Study of the film boiling heat transfer and two-phase flow interface behavior using image processing

In the current study, based on a small-scale quench test facility, the two-phase flow interface behavior during quench transients is visualized and analyzed utilizing an image processing framework. The high-fidelity experimental results obtained for two-phase flow in the current framework can support various studies both in the time domain and in the frequency domain. In particular, visualization of the data obtained from different heating surfaces under different test conditions are used to perform a full-scale transient 2-D vapor film reconstruction. The liquid-vapor interface variations in various heat transfer regimes as well as at the initial film breakup point can be directly obtained through the processed data. Moreover, the temporal variation of the interfacial wave frequency approaching quench is investigated in detail. Based on the high-resolution data obtained for the liquid-vapor interface, the detailed phase velocity and temperature profiles are obtained through theoretic analysis, based on which the film boiling heat transfer coefficient (HTC) can be determined. In addition, an improved film boiling HTC model is developed considering the effects of wall superheat, liquid subcooling temperature, vapor film thickness as well as fluid properties. The model is found to predict film boiling HTC well within 15% error.

Modeling of condensation heat transfer coefficients and flow regimes in flattened channels

In this paper, an adaptive neuro-fuzzy inference system (ANFIS) with fuzzy C-means clustering (FCM) structure identification is proposed to model condensation heat transfer and flow regimes in flattened smooth tubes with different aspect ratios. The FCM-ANFIS model was trained by using experimental data points for six effective chosen parameters of saturation temperature, heat flux, mass flux, aspect ratio and hydraulic diameter of the flattened tube, and vapor quality. Three flow regimes of annular flow, stratified, and intermittent flow were linked to the effective parameters based on the experimental data. Two models were proposed to predict the condensation heat transfer coefficient and the flow regime of R134a and R410a in flattened smooth tubes. Three statistical criteria were used to ascertain the accurateness of the models compared to the experimental results. It is found that while among benchmarked cases, the proposed model for the condensation heat transfer coefficient performs well, the best result with the lowest error (MAE = 0.029, RMSE = 0.036 and MRE = 2.83%) is when Tsat = 45 °C, q″ = 10 kW/m2, G = 100 kg/m2. s, β = 6 and Dh = 2.3 mm. On the other hand, in the worst-performing case when the errors are MAE = 0.239, RMSE = 0.239 and MRE = 13.36%, the predicted results are still in the uncertainty range of the experimental result when Tsat = 45 °C, q″ = 5 kW/m2, G = 200 kg/m2. s, β = 6 and Dh = 2.3 mm.

Predictive model of convective heat transfer coefficient in bone micro-grinding using nanofluid aerosol cooling

In grinding, the convective heat transfer coefficient (CHTC) determines the heat transfer ratio and the grinding temperature, and it indirectly identifies the surface integrity. No effective method for calculating CHTC is available for aerosol cooling, and it still lacks the measuring equipment that accords with the actual condition of aerosol cooling. On this basis, the atomization mechanism of nanofluid aerosol cooling (NAC) was studied, the influence of jet parameters on the spray boundary was revealed, and the probability density of droplet size in the grinding zone was statistically analyzed. A theoretical model for the CHTC of NAC was developed on the basis of the analysis of the heat transfer coefficient of a single nanofluid droplet. Furthermore, a new method for measuring the CHTC of aerosol cooling was proposed, and the measuring equipment was designed and built. The measurement error of the measurement system was calculated, and results showed that the measurement error of the new measuring equipment is 0.044 (10−2 W/mm2·K). Nanofluids were prepared by using medical nanoparticles and normal saline, and the CHTC was calculated and measured. The results showed that the theoretical model error is 7.26%, which verifies the correctness of the theoretical model.

Effect of layer-by-layer assembled carbon nanotube coatings on dropwise condensation heat transfer associated with non-condensable gas effect

The purpose of this study is to investigate the effect of layer-by-layer (LbL) assembled carbon nanotube (CNT) coatings on dropwise condensation heat transfer under steam–air mixture conditions. To promote dropwise condensation, an additional hydrophobic coating was added to the LbL-assembled CNT coatings, which resulted in a 16% enhanced condensation heat transfer coefficient (HTC) compared to that of the bare surface under saturated steam conditions. Despite the existence of the nanostructures on the CNT-layered surface, the larger droplet size was observed from the high-speed images than that of the bare surface due to flooding condensation phenomenon. Considering that the HTC was enhanced without smaller droplet size, it is evident that this enhancement was mainly attributed to the reduced constriction resistance driven by the high thermal conductivity of the CNT layers. A new HTC model for dropwise condensation incorporating constriction resistance was developed to better predict the measured condensation HTC. Although the enhancement of the condensation HTC on the LbL-assembled CNT coatings was diminished with the air mass fraction, this work reports a new perspective to enhance the dropwise condensation heat transfer performance by controlling the constriction resistance using a highly thermally conductive coating.

Experimental study on temperature drop during roller quenching process of large-section ultra-heavy steel plate.

Large-section ultra-heavy steel plates feature low cooling rate of central part during quenching process, as well as great differences in texture and performance along thickness direction. Wet jet impingement quenching test apparatus and multi-channel temperature recorder were developed to explore the temperature drop characteristics and its influential factors of ultra-heavy steel plate. The temperature drop curves of plates with different thickness (160, 220, and 300 mm) and weight (23-43 tons) were recorded during the quenching process, accompanied with the exploration on distribution rules of temperature gradient, heat flux density and cooling rate along thickness direction under different water volumes (9000-9400 m3/h) and pressures (0.4-0.8 MPa), upon which the three-dimensional inverse heat conduction model, surface heat transfer coefficient model and thermophysical parameter model were established using finite element and optimization methods. The overall results indicate the symmetric heat transfer between the upper and lower plate surfaces can be realized, when the water flow ratios of the upper and lower surfaces were 1:1.25 and 1:1.4 under pressures of 0.8 MPa and 0.4 MPa, respectively. The "temperature return" phenomenon was accompanied with changing heat flux density of wall surface of 220 mm- and 300 mm-thick plates. The lowest cooling rate along thickness direction appeared at 1/4 thickness position for the 160 mm- and 220 mm- thick plates during quenching, which was attributable to the synergy between heat flux density and temperature gradient. This work may pave a way for improving the cooling rate and quenching uniformity of ultra-heavy steel plates along thickness direction.

Numerical and artificial neural network modeling study on the first-law and second-law performance of a novel helical heat sink filled with water–silver nanofluid

This paper is devoted to studying the first-law and second-law performances of a novel helical heat sink (HS). The biologically synthesized water–Ag nanofluid is considered as the coolant. The impacts of volume concentration of nanoparticles ( $$\varphi$$ ), Reynolds number ( $$\mathrm{Re}$$ ) and geometrical parameters of HS on the hydrothermal aspects and irreversibility behavior of HS are evaluated, and their optimal values are found. It was noted that the intensification of both the $$\varphi$$ and $$\mathrm{Re}$$ causes an augmentation in the convection coefficient, average CPU temperature and maximum CPU temperature, while the thermal resistance diminishes by rising $$\varphi$$ and $$\mathrm{Re}$$ . In addition, the fluid friction and heat transfer irreversibilities growth by intensifying the $$\mathrm{Re}$$ diminished with the increment of $$\varphi$$ . Furthermore, the outcomes showed that the best first-law performance of the HS occurs at $$\varphi =1\%$$ and $$\mathrm{Re}=1500$$ , while the lowest irreversibility occurs at $$\varphi =1\%$$ and $$\mathrm{Re}=500$$ . Finally, the obtained numerical data were utilized to develop a predictive model for convective heat transfer coefficient, thermal entropy generation rate and frictional entropy generation rate. The accuracy of the models was evaluated based on three statistical indices including mean relative error percentage (MRE), root mean square error (RMSE) and coefficient of determination (R2). It was found that the $${R}^{2}$$ value for all the developed models is higher than 0.99.

Experimentation and modeling of convective heat transfer coefficient for evaporation of liquid foods in a pilot plant double effect

Abstract Even though the evaporation is a common process in the food industry, there is scarce information about the convective coefficient evaluation as an important parameter for equipment and process design. A research on evaporation of sugar solution in a double effect was carried out. The experimental results obtained in this equipment, from the heat transfer and concentration processes are presented, a range of 2658–6091 W of heat flow was quantified implying computed values of 1431–3763 W/m2K for the convective coefficients and 1020–1815 W/m2K for the overall coefficient. The quantification of the convective coefficient, the fitting methodology and modeling were developed in order, to obtain the correspondent correlations. Then, from a set of several equations, two general relationships are proposed. Both correlations were applied to experimental and supposed data, finding a difference lower than 30% between the experimental and predicted values of the Nusselt number, that was considered as satisfactory.

Heat flux and heat transfer coefficient model analysis during turning of al (7068) alloy

Variation of temperature during turning is the major cause of tool wear and that is one of the responsible factor for reducing tool life due to excessive tool wear. Presented work is an experimental investigation of heat flux and heat transfer coefficient due to increasing temperature cause of variation of cutting speed feed rate and depth of cut, all experiments are performed based on the design of experiment followed by response surface methodology and mathematical relations are established in between dependent and independent variables. Experimental work is performed in dry conditions by selecting Aluminium alloy (7068) as a work piece with Titanium Nitride coated carbide tool bits. The comparison results show high agreement between the physical cutting experiments with an analytical model that are also drawn with the help of MATLAB (simulink). The aim of presented work is to develop mathematical model of generated temperature on tool work interface at different input parameters during machining of turning operation. Utility of the whole study is beneficial for an aerodynamic in which the application of this alloy plays a vital role.

Development of a RELAP5 model for the thermo-hydraulic characteristics simulation of the helically coiled tubes

In helically coiled tubes, the geometry induced centrifugal forces exert the fluid enhancement upon the heat transfer and pressure drop. Hence, it is essential to develop a thermo-hydraulic model for helical tubes. This paper reviewed many previous studies and summarized the published correlations. The heat transfer coefficient and friction factor models were respectively developed by evaluating the applicability of these correlations in various operating parameters. Then the developed models were applied in RELAP5 code to simulate the flow and heat transfer behavior in a helical tube under steady-state conditions, and it was found that the simulation results were in good agreement with the experimental data. The modified code was also used to simulate flow instability phenomena in parallel helical tubes. And the results showed the modified code can accurately predict the oscillation periods and the instability thresholds of density-wave oscillations in helical tubes within a wide range of operating parameters.

Development and modelling of heat and mass transfer analysis of a low-cost solar dryer integrated with biomass heater: Application for West African Region

The main objective of this study is to design and fabricate a low-cost hybrid solar drying system and present the drying kinetics, heat transfer coefficient and thin layer models for the dried product. For this purpose, two solar dryers one equipped with biomass heater and the other without biomass heater were constructed and tested. The results show that the developed solar dryers can save between 27.78% and 58.33% of drying time compared to open sun drying method at ambient temperature ranging between 30 and 40 °C and a humidity ranging from 55% to 70%. Under these operating conditions, the collector efficiency is 20.81–21.89%. The values for the heat transfer coefficient ranged from 0.64 to 10.5 W/m2 °C. Verma et al. model gave the best result for drying with biomass heater while logarithmic model was best for drying without biomass heater.