Outer Heat Transfer Coefficient Research Articles

Experimental investigation of the impact of non-condensing gas on the condensation of n-propanol on a low-finned tube

This paper investigates the impact of a non-condensing gas on the condensation heat transfer of n-propanol on a low-finned and plain tube. Despite the potential of low-finned tubes to enhance outer heat transfer during condensation, the literature lacks measurement data on the condensation of solvents and bulk chemicals on these tubes. No experimental investigations on the impact of non-condensing gas on the heat transfer during the condensation of solvents on low-finned tubes are available in the literature. This paper addresses these gaps by presenting measurements of the heat transfer during the condensation of n-propanol in the presence of nitrogen on a horizontal GEWA-K28 low-finned tube and a plain tube using a novel test rig design. The results show that even a small amount of nitrogen significantly reduces the outer heat transfer coefficient. This effect is more pronounced on the low-finned tube than on the plain tube. The experimental data provided in this article can serve as a basis for developing calculation models for the condensation heat transfer of substances from the chemical industry on low-finned tubes.

Experimental comparison on condensation and evaporation outside double-side enhanced horizontal tubes

Experimental investigations of the condensation and evaporation of R410A on the outside of two double-side enhanced heat transfer tubes were conducted, and the tube performance was compared with that of a smooth copper tube. The research object consisted of a smooth tube with a length of 2000 mm and an outer diameter of 25.4 mm and two double-side enhanced tubes of the same size. The evaporation experiments were run under the following conditions: the evaporation saturation temperature was 7°C, water inlet temperature was 8°C–18°C, and water flow rate was 0.6–1.6 m3/h. The condensation experiments were run under the following conditions: the saturation temperature was 35°C, water inlet temperature was 21°C–30°C, and water flow rate was 0.4–1.6 m3/h. During the data processing, the heat transfer coefficient of the water side was obtained using the Gnielinski-Wilson method, and that of the refrigerant side was obtained using the thermal resistance separation method. The effect of the surface structure on the heat transfer performance was analyzed, and a strengthening measure was proposed. The experimental results indicate that the evaporation heat transfer coefficients outside the smooth tube increased with the raise of the inlet water temperature, while the double-side enhanced tubes decreased; both the condensation heat transfer coefficients outside the smooth tube and the enhanced tubes increased with the increase of the water flow rate. Due to the different type of enhanced tube ribs, tube #3 surface structure is more conducive to the formation of vaporization core, which is about 30% higher than the outer heat transfer coefficient of tube #2. It is more in line with the requirements of strengthening horizontal single tube external pool boiling heat transfer. In the condensation experiment, the condensation heat transfer coefficients outside the smooth tube increased with the raise of the inlet water temperature, while the double enhanced tubes decreased; both the condensation heat transfer coefficients outside the smooth tube and the enhanced tubes increased with the increase of the water flow rate. With the analysis of the rib structure, the outer surface structure of tube #2 has stronger drainage capacity, and the external average condensation heat transfer coefficient is about 7% higher than that of tube #3, which is more in line with the requirements of condensing heat transfer outside the single tube.

CHAOTISED POLYMERIC HOLLOW FIBRE BUNDLE AS A CROSSFLOW HEAT EXCHANGER IN AIR-WATER APPLICATION

Fifteen years ago, polymeric hollow fibre heat exchangers were presented for the first time. Nowadays there are not only the shell-and-tube types as there were at the beginning. In this paper, six chaotised polymeric hollow fibre bundles with a different number of fibres were studied. The bundles presented varied in their fibre diameter, number and shape. These bundles were fixed into the module in such a way that the middle part serves as a cross-flow heat exchanger in an air tunnel. They were tested for air-water application with three different airflow rates. The overall heat transfer coefficients were determined, and the inner and outer heat transfer coefficients were derived. The modules presented achieved a heat transfer rate of up to 1309 W. The overall heat transfer coefficient reached a maximum of 339 Wm−2 K−1.

Finned Electric Motor with Prescribed Heat Flux and Influence of the Internal and External Heat Convection Coefficients on the Temperature of the Core

One of a major objective is to analyze the effect of internal and external convection coefficients in the heat transfer generated by electric motors and characterize intervals of feasible values, in practical terms, for these coefficients. Another objective is to determine the motor core temperature, considering the environmental and operational conditions of the motor installation and the heat flux Q0 (fixed) in the fins. To achieve the objectives were developed analytical solutions for determining the temperature variations in the fins, performance and electric motor efficiency, considering heat flow constant at the base of the fins and the possible variations in temperature of surround media. The heat flux at the base of the fins, in this case, is the minimum necessary for satisfactory electric motor performance and the core temperature is within the safety range stipulated by the manufacturer. The obtained results characterize a range of possible values for the inner and outer heat transfer coefficients.

Condensation of binary mixtures on horizontal tubes

The two most common models to describe the condensation of binary mixtures are the equilibrium model by Silver (Trans Inst Chem Eng 25:30–42, 1947) and the film model by Colburn and Drew (Transactions of the American Institute of Chemical Engineers 33:197–215, 1937), which is stated by Webb et al. (Int J Heat Mass Transf 39:3147–3156, 1996) as more accurate. The film model describes the outer heat transfer coefficient by subdividing it into two separate resistances against the heat transfer. The resistance of the liquid condensate film on the tube can be calculated with equations for the condensation of pure substances for the analogous flow pattern and geometry using the property data of the mixture. The resistance in the gas phase can be described by a thermodynamic parameter Z and the single phase heat transfer coefficient αG. In this work measurements for condensation of the binary mixtures n-pentane/iso-octane and iso-propanol/water on horizontal tubes for free convection are carried out. The obtained results are compared with the film model by Colburn and Drew (Transactions of the American Institute of Chemical Engineers 33:197–215, 1937). The comparison shows a rather big deviation between the theoretical model and the experimental results. To improve the prediction quality an own model based on dimensionless numbers is proposed, which describes the experimental results of this work significantly better than the film model.

Outer heat transfer coefficient for condensation of pure components on single horizontal low-finned tubes

The outer heat transfer coefficient is determined for the condensation of pure components (iso-propanol, n-pentane, n-heptane, iso-octane and water) on low-finned carbon steel, stainless steel and titanium tubes. The outer heat transfer coefficient on these tubes is 3 to 8 times higher than on a smooth tube with the same reference surface area. The experimental data are compared with theoretical models from literature for the condensation of refrigerants and water. These models do not predict all experimental data for the condensation of iso-propanol and hydrocarbons on low-finned tubes with the accuracy given in the respective papers. Therefore, a new approach for calculation of the outer heat transfer coefficient based on dimensionless numbers is developed. With this new equation, it can be predicted with a maximum deviation of ±20%.

Towards a thorough Validation of Simulation Tools for CO2 Pipeline Transport

In this work the Schlumberger flow assurance tool OLGA and SINTEF Energy Research in-house CFD tool are assessed for their ability to describe depressurization behaviour of CO2 pipelines. For this purpose, three full-bore experimental depressurization tests with pure CO2 have been performed at the Statoil's R&D center in Trondheim, Norway.Simulations results are in general agreement with the experiments with the exception of the behaviour at the innermost position of the where OLGA predicts significantly lower temperatures, and SINTEF tool over-estimate the temperature. Both models predict liquid dry-out time with an error of a few seconds.The simulation results are sensitive to the pipe outer heat transfer coefficient, used between the pipe surface and the ambient humid air. Reduction of the uncertainty in the heat-flux to the pipe is identified as a key factor for further validation.

Analytical solution for the study of time lag and decrement factor for building walls in climate of Iran

More than 40% of energy consumption in Iran associated with the building sector. Among the factors affecting energy consumption, time lag and decrement factor of the walls can be mentioned, which usually are not considered in the design of building of Iran. Therefore, in the present study, time lags and decrement factor for different building materials that prevalently are utilized in Iran have been investigated. In this research, the transient heat conduction equation is solved analytically using Green function under time-dependent convection boundary conditions. The effect of different parameters such as wall thickness and both inner and outer heat transfer coefficients as well as the effect of the thermal insulation layer in sandwich wall on time lag and decrement factor is investigated. The results indicate that the thickness and the type of the building material have a significant effect on the time lag and decrement factor of the wall. Also, it is shown that inside combined convection and radiation heat transfer coefficients affects time lag and decrement factor of the walls. The results of the present study are applicable for designing more effective passive solar buildings in Iran and optimal design of walls and other related areas resulting in energy saving.

Surface coking deposition influences on flow and heat transfer of supercritical hydrocarbon fuel in helical tubes

Surface coking deposition influences on flow and heat transfer of aviation kerosene RP-3 in helical tubes were experimentally investigated at supercritical pressure. Four types of helical tubes with fixed pitch and various helical diameters have 1.86mm inner diameter and 2.2mm outer diameter. The system pressure, inlet temperature, mass flow rate were fixed at 5MPa, 400K and 1178kg/m2s, respectively. The results indicate that the helical centrifugal force could inhibit the thermal oxidation coking and slow down the growth rate of press drop within maximum value of 47.6%. For the same cross section, the outer heat transfer coefficient (HTC) decreases gradually and eventually is less than the inner side due to coking deposition. Finally, a correlation of Nusselt number considering coking deposition was simulated to predict the heat transfer characteristics.

Heat Transfer Characteristics of a Pipeline for CO2 Transport with Water as Surrounding Substance

The heat transfer characteristics of pipelines for transport of CO2 is crucial for the events following a depressurization or a crack formation, involving rapid cooling. In this work, we present and analyze recent experiments from an experimental facility tailored to investigate these phenomena. With stagnant water as the surrounding substance, we quantify the contribution to the heat transfer from the surroundings, the insulation and the CO2 boiling inside the pipeline, for a large set of operating conditions. We discuss whether empirical expressions in the literature can describe the outer heat transfer coefficient and analyze the experimental results in detail using computational fluid dynamical simulations. The work gives insight into and quantifies the heat transfer characteristics of a CO2-pipeline. In particular, the outer heat transfer coefficient was between 80 and 210W/m2K, the thermal conductivity of the insulation was well described by a linear temperature relation and the mean value of the overall heat transfer coefficient was 44.7W/m2K. The work lays the foundation for future work on this subject, which will involve other surrounding substances such as clay and gravel as well as the forming of ice.

유동층 반응기에서의 목질계 바이오매스 입자의 탈휘발 예측 모델

Devolatilization is an important mechanism in the gasification and pyrolysis of woody biomass, and has to be accordingly considered in designing a gasifier. In order to describe the devolatilization process of wood particle, there have been proposed a number of empirical correlations based on experimental data. However, the correlations are limited to apply for various reaction conditions due to the complex nature of wood devolatilization. In this study, a simple model was developed for predicting the devolatilization of a wood particle in a fluidized bed reactor. The model considered the drying, shrinkage and heat generation of intra-particle for a spherical biomass. The influence of various parameters such as size, initial moisture content, heat transfer coefficient, kinetic model and temperature, was investigated. The devolatilization time linearly increased with increasing initial moisture content and size of a wood particle, whereas decreases with reaction temperature. There is no significant change of results when the external heat transfer coefficient is over 300 W/m2K, and smaller particles are more sensitive to the outer heat transfer coefficient. Predicted results from the model show a similar tendency with the experimental data from literatures within a deviation of 10%.

CO2 transport–Depressurization, heat transfer and impurities

Abstract Detailed knowledge on depressurization, heat transfer and impurities in CO2 pipelines has shown to be important for safe and cost effective design of CCS chains. The aim of this paper is to present the latest results on the modelling and experimental verification of these aspects. A newly developed CO2 module in the flow engineering software OLGA from SPT Group has been used to model experimental results on depressurization, which is a two-phase transient flow with evaporation and Joule-Thomson cooling. A visual comparison of model and experiments in PT-diagrams showed that the new CO2 module in OLGA captures the depressurization behaviour reasonably well, but still has room for improvement. Heat transfer coefficients for heat transfer from aqueous surroundings to cold CO2 in a pipeline segment was measured in a dedicated rig. A thin layer of ice formation was observed on the bottom of the pipeline. The overall heat transfer coefficient at the experimental conditions has been calculated to be 45.0 W/m2K, where the outer heat transfer coefficient was 162.3 W/m2K, and the inner heat transfer coefficient 166.2 W/m2K. 46 Experiments and modelling of H2O solubility in vapour and liquid CO2 were performed for verifying the VLHE-behaviour at low H2O concentrations down to −50 °C. Hydrafact’s model HWHyd 2.2 model predicted the experimental result with average 8.2% deviation. Hence, the model can be used for setting hydrate formation limited H2O specifications in transport of pure CO2.

Comparison of flow-reversal, internal-recirculation and loop reactors

In this work, we compare the performance of flow-reversal, internal-recirculation and loop reactors. In the absence of analytical results we use asymptotic, approximate and simulated solutions and present some experimental results. As criteria for comparison we use the maximal temperature achieved and the robustness of solution. Experiments and simulations of ethylene oxidation in the flow-reversal and internal-recirculation reactor, showed that the technically simpler inner–outer internal-recycle reactor may operate better at low flow rates than that with flow reversal, but the conclusion is reversed at high flow rates. Using approximate solutions, we show the dependence of the maximal temperature on the inner–outer heat-transfer coefficient. Loop reactor can generate rotating pulse solution: we simulate such solutions for two asymptotic cases where the ratio of switching velocity (i.e., unit length/switching time) to pattern velocity is either around unity or very large. We compare them with solutions of 4–8 units reactors. The slow-switching regimes require a delicate control. The fast-switching solution is robust but its peak temperature depends on the kinetic parameters and reactor length, compared with that of the flow-reversal reactor where it depends mainly on bed conductivity.