Numerical Investigation of Supercritical N-Dodecane Flows in a Heated Circular Pipe With Thermal Cracking

Supercritical n-dodecane (C12H26) flows in heated circular pipes with thermal cracking were numerically investigated using a numerical preconditioning method for solving the compressible Navier–Stokes equations. The reaction rate constants for thermal cracking of n-dodecane were determined using Cantera. The thermophysical properties of pure n-dodecane and its decomposed components were calculated using the Helmholtz free-energy equation of state. The outlet temperatures agreed well with experimental results, and the maximum error was 3.2%. The outlet temperature increased with the wall temperature condition, although the rate of increase became slightly smaller when the wall temperature was high. We discussed the relationship between the wall temperature condition and heat transfer in terms of thermal diffusivity in the radial direction. We also compared the radial distributions with those of n-octane (C8H18) in terms of temperature, thermal diffusivity, and mass fraction of unreacted fed hydrocarbons. Thermal cracking mainly occurred in a high-temperature region near the heated wall. The density of the decomposed components was much lower than that of n-dodecane and n-octane, resulting in a significant decrease in the mixture’s density near the heating wall. The decomposed components affected the supercritical hydrocarbon flows owing to changes in their thermophysical properties. The thermal diffusivity due to the decomposed components and turbulence affects the temperature distributions and mass fraction in n-dodecane and n-octane flows. Finally, we compared the outlet conversion rates of n-dodecane and n-octane flows.

Numerical and experimental analysis of parallel-pass forced convection solar air heating wall with different plenum and absorber configurations

Purpose Over the recent years, solar energy has received outstanding attention from researchers. Solar energy applications and related large-scale projects are increasing to meet growing global energy demand as an economical, non-polluting and renewable energy source. The purpose of this study is investigating different plenum and absorber configurations of solar air heating wall (SAHW) experimentally and numerically. Design/methodology/approach In this study, various configurations of SAHW have been numerically simulated to determine the most effective design. According to the simulation results, two SAHWs with various plenum thicknesses have been fabricated and tested at different conditions. Findings Numerical simulation results indicated that parallel-flow SAHWs exhibited better performance in comparison with other placements of absorber plate. Regarding to the experimentally attained results, the highest thermal efficiency was reached to 80.51%. Also, the average deviation between experimentally and numerically obtained outlet temperature is 5.5%. Originality/value Considering the obtained results in the present study, designed SAHW has admissible efficiency to be used in various industrial and residential applications such as; air preheating, space heating and drying.

Experimental investigation on adiabatic two-phase frictional pressure drop of R1234ze(E) and R134a in a horizontal minichannel

A numerical investigation on the melting process of paraffin wax RT44 under supergravity (5–20 g) was conducted to evaluate the effect of supergravity on the melting heat transfer characteristics. The simulations were conducted in a horizontally placed container with constant heat flux of 5–50 kW/m2 maintained on the bottom wall under both supergravity and the Earth gravity (1g). The numerical data under supergravity are compared with those under the Earth gravity for all circumstances. The results indicate that the melting heat transfer characteristics of the phase change material (PCM) are affected by supergravity significantly (around 30%) within 20 g. With the increase of supergravity, the heating wall temperature decreases, and the liquid fraction as well as the melting rate increase. Meanwhile, the variation amplitudes of these melting characteristics decrease gradually until less than 2% at 20 g. The effect of supergravity can be attributed to the intensification of the natural convection due to buoyancy, yielding vortexes in internal flow and fluctuations of solid-liquid interface and temperature field.

Development of rational technological parameters for heating of a coke battery with a stamped charging of coals.

DEVELOPMENT OF RATIONAL TECHNOLOGICAL PARAMETERS FOR HEATING OF A COKE BATTERY WITH A STAMPED CHARGING OF COALS © V.I. Goncharov, I.I. Sikan, Ya.I. Dyachuk, N.V. Mukina (Coke production of PJSC «ArcelorMittal Kryvyi Rih», 50095, Dnipropetrovsk region, Kryvyi Rih, Kryvorizhstal str., 1, Ukraine), I.V. Shulga, PhD in technical sciences (State Enterprise "Ukrainian State Research Coal Chemical Institute (UHIN)", 61023, Kharkov, Vesnina st., 7, Ukraine) The article is devoted to the introduction at the PJSC «ArcelorMittal Kryvyi Rih» coke plant of a promising technology for compaction of a coal charge, which allows obtaining blast furnace coke of high mechanical and "hot" strength from charges characterized by an increased content of lean components of various stages of metamorphism. Under the present circumstances, this is of great importance for increasing the economic indicators of the production of blast furnace coke and the operation of blast furnaces. The start-up of coke oven battery No. 6, designed for the application of this technology, necessitated the determination of rational technological parameters of heating: the temperature level in the control verticals and the location of the burners for supplying coke oven gas in the vertical along the heating wall. The article presents the calculations, the results of which confirm the expediency of rationalizing the actual starting (design) distribution of burners on coke oven battery No. 6. First of all, attention is drawn to the insufficient diameters of the holes in the burners for the extreme and pre-extreme verticals. This, according to the authors, caused underheating of the head zones and resin spills, which were observed during start-up operations on the battery. The replacement of burners at the edges of the walls by large diameters, carried out by the personnel of the coke shop of the coke plant PJSC “ArcelorMittal Kryvyi Rih” and LLC “Koksokhimstanciya”, combined with the full opening of the recirculation windows in these zones, improved the heating of the charge and significantly reduced the intensity of spills. The experience gained was taken into account when locating the control devices at coke oven battery No. 5, which was put into operation later. The article also formulates recommendations for adjusting the temperature regime of coking, depending on the grade and component composition, as well as the technological properties of coal charges. Keywords: coke oven battery, stumping of coal charge, temperature in control verticals, location of burners along the length of the heating wall. Corresponding author Ya.I. Dyachuk, е-mail: [email protected]

Uncertainties Analysis on the Prediction of Flow and Heat Transfer of Liquid Sodium with CFD Technology

The prediction of flow and heat transfer characteristics of liquid sodium with CFD technology is of significant importance for the design and safety analysis of sodium-cooled fast reactor. The accuracies and uncertainties of the CFD models should be evaluated to improve the confidence of the numerical results. In this work, the uncertainties from the turbulent model, boundary conditions, and physical properties for the flow and heat transfer of liquid sodium were evaluated against the experimental data. The results of uncertainty quantization show that the maximum uncertainties of the Nusselt number and friction coefficient occurred in the transition zone from the inlet to the fully developed region in the circular tube, while they occurred near the reattachment point in the backward-facing step. Furthermore, in backward-facing step flow, the maximum uncertainty of temperature migrated from the heating wall to the geometric center of the channel, while the maximum uncertainty of velocity occurred near the vortex zone. The results of sensitivity analysis illustrate that the Nusselt number was negatively correlated with the thermal conductivity and turbulent Prandtl number, while the friction coefficient was positively correlated with the density and Von Karman constant. This work can be a reference to evaluate the accuracy of the standard k-ε model in predicting the flow and heat transfer characteristics of liquid sodium.

Effects of Temperature on the Flow and Heat Transfer in Gel Fuels: A Numerical Study

In general, rheological properties of gelled fuels change dramatically when temperature changes. In this work, we investigate flow and heat transfer of water-gel in a straight pipe and a tapered injector for non-isothermal conditions, which mimic the situations when gelled fuels are used in propulsion systems. The gel-fluid is modeled as a non-Newtonian fluid, where the viscosity depends on the shear rate and the temperature; a correlation fitted with experimental data is used. For the fully developed flow in a straight pipe with heating, the mean apparent viscosity at the cross section when the temperature is high is only 44% of the case with low temperature; this indicates that it is feasible to control the viscosity of gel fuel by proper thermal design of pipes. For the flow in the typical tapered injector, larger temperature gradients along the radial direction results in a more obvious plug flow; that is, when the fuel is heated the viscosity near the wall is significantly reduced, but the effect is not obvious in the area far away from the wall. Therefore, for the case of the tapered injector, as the temperature of the heating wall increases, the mean apparent viscosity at the outlet decreases first and increases then due to the high viscosity plug formed near the channel center, which encourages further proper design of the injector in future. Furthermore, the layer of low viscosity near the walls plays a role similar to lubrication, thus the supply pressure of the transport system is significantly reduced; the pressure drop for high temperature is only 62% of that of low temperature. It should be noticed that for a propellent system the heating source is almost free; therefore, by introducing a proper thermal design of the transport system, the viscosity of the gelled fuel can be greatly reduced, thus reducing the power input to the supply pressure at a lower cost.

Simulation and experimental study of phase change cooling and heating wall radiation air conditioning system

This paper presents a case study of phase change cooling and heating wall radiant (PC-CHWR) air conditioning system application in an energy-saving renovation project in a laboratory in Wuhan, Hubei province in China. To test the thermal performance of the system, the PHOENICS software was utilized to simulate and analyse the indoor thermal environment in the laboratory under both winter and summer operating conditions. In addition, field experiments were also conducted under winter operation condition. By comparing the results between numerical simulation and field experiment, it is found that thermal performance of the PC-CHWR air conditioning system evaluated by these two evaluation methods are quite match. Moreover, the results also show that the PC-CHWR system can meet the cooling and heating load of the building within the acceptable range.

Heat transfer and evaporation of salt solution on a horizontal heating wall

An experimental study of non-isothermal heat transfer and evaporation of thin layers of aqueous solutions of salts has been carried out. Evaporation was realized on a horizontal heated wall in the air atmosphere at a pressure of 1 bar. In the evaporation of water and salt solution, the heat transfer coefficient is constant for a long time period and increases in the final stage due to the multiple reduction of the layer thickness. Evaporation curves for different types of salt solutions have a different character. Due to the increase in salt concentration, the evaporation rate of LiBr-water, CaCl2-water, LiCl-water, and MgCl2-water decreases over time. Salt solutions decreases with time. Evaporation rates for solutions of NaCl-water, CsCl-water, and BaCl2-water slightly change over time. To analyze the effect of free convection on heat transfer, experimental curves for the ratio of Nusselt numbers (A = Nu(salt)/Nu(water)) for the salt and water solution have been built. Parameter A is greater than one and increases with time. The effect of convection on heat transfer varies with time and depends on the current salt concentration and solution layer height, which should be considered in the simulation.