Heat and Mass Transfer

In the paper performance of the prototype design of the condensation hood is analysed. Results of some experiments/measurements as well as results of CFD simulations are used to investigate the dependence of quantity called the condensation efficiency on selected working parameters. It was found that both the air inlet temperature and the air mass flow rate have significant impact on the performance of the heat exchanger. However, such changes did not influence the condensation efficiency which stays stable at the level of 100% for quite wide range of parameters changes. The same applies to the relative humidity of the inlet air. The only parameter which causes changes of the condensation efficiency is the steam mass flow rate when it exceeds 2.0 g/s. Nevertheless, operation of the hood with the steam mass flow rate up to $$\approx 3.0$$ g/s guarantees that at least 90% of the steam is condensed.

Transesterified vegetable oils are becoming increasingly important as alternative fuels for diesel engines due to several advantages. Biodiesel is a renewable, inexhaustible and green fuel. This paper presents the various properties of the oils derived from Jatropha and Pongamia, their mixes and biodiesels derived from the mixes. An innovative lab scale reactor was designed and developed for biodiesel production from mixed vegetable oils and used for the study of optimization of biodiesel yield [1]. Also, the analysis of data of experimental investigations carried out on a 3.75 kW computerized CI engine at injection pressures of 160 and 180 bar with methyl esters of mixed Jatropha and Pongamia in various proportions are also presented. The brake thermal efficiency for biodiesel blends was found to be higher than that of petrodiesel at various loading conditions. In case of Composite biodiesel blended fuels, the exhaust gas temperature increased with increase in load and the amount of composite biodiesel. The highest exhaust gas temperature was observed as 213 °C for biodiesel among the five loading conditions. When petrodiesel was used the exhaust gas temperature was observed to be 220 °C. The CO2, CO, HC and NOx emissions from the biodiesel blends were lower than that of petrodiesel.

The present comment concerns some doubtful results included in the above paper.

This paper aims to investigate the heating behaviors of block rubber by experimental and simulated method. The COMSOL Multiphysics 5.0 software was utilized in numerical simulation work. The effects of microwave frequency, power and sample size on temperature distribution are examined. The effect of frequency on temperature distribution is obvious. The maximum and minimum temperatures of block rubber increase first and then decrease with frequency increasing. The microwave heating efficiency is maximum in the microwave frequency of 2450 MHz. However, more uniform temperature distribution is presented in other microwave frequencies. The influence of microwave power on temperature distribution is also remarkable. The smaller the power, the more uniform the temperature distribution on the block rubber. The effect of power on microwave heating efficiency is not obvious. The effect of sample size on temperature distribution is evidently found. The smaller the sample size, the more uniform the temperature distribution on the block rubber. However, the smaller the sample size, the lower the microwave heating efficiency. The results can serve as references for the research on heating rubber material by microwave technology.

Es wird ein mathematisches Strömungsmodell für Gas-Flüssigreaktoren aufgestellt, das auf der Filmtheorie basiert. Für den Fall einer chemischen Reaktion erster Ordnung läßt sich eine geschlossene analytische Lösung finden, mit deren Hilfe man den Stoffaustauschgrad, den Reaktionsumsatz und die Reaktorkapazität leicht ermitteln kann. Das Modell eignet sich also unmittelbar als Auslegungsbasis für Gas-Flüssigreaktoren.

This paper is concerned with the development of a new approach to model the fluctuation of fouling in general. The proposed modeling concept is to split a property into a mean variable and a fluctuating variable. The goal is to investigate the oscillatory characteristic of fluctuating fouling resistance. Long-term fouling data collected from seven 15.54 mm ID copper, helically ribbed tubes with water velocity at 1.07 m/s in a cooling tower system were used to present oscillatory behaviors. An uncertainty analysis indicates that a minimum water temperature difference of 3.0°C between inlet and outlet of each test tube is needed to observe the oscillatory behavior of fouling data. The frequency of fluctuation is independent of tube interior geometries on which fouling deposit develops; the amplitude of fluctuation is related to tube interior geometries and is a function of the ratio of rib pitch to rib height. There are two ranges of amplitude of fluctuation of fouling characteristics based on internal dimensions: linear range and non-linear range. A series of semi-theoretical amplitude correlations as a function of the ratio of rib pitch to rib height were developed. They were applicable to different internally ribbed geometries within the dimensional range in the study.

The effect of time-dependent pressure pulsations on heat transfer in a pipe flow with constant temperature boundaries is analysed numerically when the viscosity of the pulsating fluid is an inverse linear function of the temperature. The coupled differential equations are solved using Crank-Nicholson semi-implicit finite difference formulation with some modifications. The results indicate local variations in heat transfer due to pulsations. They are useful in the design of heat exchangers working under pulsating flow conditions. The analytical results are presented for both heating and cooling. The conditions under which pulsating flows can augment the heat transfer are discussed. The results are applicable for heat exchangers with fluids of high Prandtl number.

In the current work, the capturing of carbon dioxide from flue gases of post combustion emission using fixed bed adsorption has been carried out. Two grades of commercial activated carbon (sorbent-1 and sorbent-2) were used as adsorbent. Feed consisting of CO2 and N2 mixture was used for carrying out the adsorption. The influence of bed temperature, feed rate, equilibrium partial pressure and initial % CO2 in feed were considered for analyzing adsorption-desorption process. It was found that the total adsorption-desorption cycle time decreases with increased column temperature and feed rates. The time required to achieve the condition of bed saturation decreases with increased bed temperature and feed rates. The amount of CO2 adsorbed/Kg of the adsorbent declines with increased bed temperature with in studied range for sorbent-1 and sorbent-2. It was suggested that the adsorption capacity of the both the sorbents increases with increased partial pressure of the gas.

The effects of different drying temperatures on the drying kinetics of tomato slices were investigated using a cabinet-type dryer. The experimental drying data were fitted best to the to the Page and Modified Page models apart from other theoretical models to predict the drying kinetics. The effective moisture diffusivities varied from 1.015 × 10−9 to 2.650 × 10−9 m2 s−1over the temperature range studied, and activation energy was 22.981 kJ mol−1.

This paper shows first some results of experimental studies made on a vertically oriented steady state axisymmetric laminar hydrogen-oxygen-diffusion flame. All experiments were at 1 atm pressure. Hydrogen exhausted with a mass flow rate of 0.019kg/h from the inner tube of the burner and an annular stream of oxygen with a mass flow rate of 5.76kg/h was delivered by the outer nozzle. A laser doppler anemometer working in the crossbeam mode was used to measure velocity profiles. In order to determine the variation of the concentrations of the stable chemical compounds H2, O2 and H2O gas samples were withdrawn from the flame and analysed with a mass spectrometer. The distributions of the temperature and the OH-concentration were obtained by spectroscopic measurements. These measurements were made with different lines of the band head of the 0-0 vibrational transition of the2Σ-2Π electronic system. Additional measurements were made with the Na-D1-line at 5896 Å. Temperature measurements below 2000K were carried out with thermocouples. To predict the detailed flow field of the flame a mathematical model was developed which describes the flame flow to be a shear flow in chemical nonequilibrium. This mathematical model consists of a coupled system of nonlinear parabolic partial differential equations. An implicit finite difference approximation was used to solve this equation system. The numerical predictions were compared with the experimental results. b]de|Zusammenfassung Es werden die in einer laminaren rotationssymmetrischen Wasserstoff-Sauerstoff-Diffusionsflamme gemessenen Verteilungen der Geschwindigkeit, der Temperatur und der Konzentrationen der chemischen Komponenten H2, O2, OH und H2O gezeigt. Die untersuchte Flamme brannte bei Atmosphärendruck auf einem vertikal angeordneten Brenner, der einen inneren Wasserstoffstrom von $$\dot m_{H_2 } $$ =0,019kg/h und einen dazu konzentrischen äußeren Sauerstoffstrom von $$\dot m_{o_2 } $$ =5,76kg/h lieferte. Die Geschwindigkeitsmessung erfolgte mit einem Laser-Doppler-Anemometer in Kreuzstrahlanordnung. Die Konzentrationen der stabilen chemischen Komponenten H2, O2 und H2O wurden durch Gasprobenabsaugung mit einer wassergekühlten Mikrosonde und anschließende Analyse in einem Massenspektrometer bestimmt. Mit Hilfe direkter spektroskopischer Messungen auf verschiedenen Rotationslinien der 0-0-Vibrationsbande des2Σ-2Π-Systems von OH im UV-Bereich konnten die Temperaturverteilung und die Konzentrationsverteilung der chemischen Komponente OH ermittelt werden. Zusätzliche spektroskopische Temperaturmessungen wurden auf der Na-D1-Linie bei 5896 Å durchgeführt. Temperaturmessungen unterhalb 2000K erfolgten mit Thermoelementen. Zur Vorausberechnung der Flammenfelder wurde ein mathematisches Modell entwickelt, das die Flammenströmung als schichtförmige Scherströmung im chemischen Nichtgleichgewicht beschreibt. Zur numerischen Lösung des zu diesem Flammenmodell gehörenden Systems nichtlinearer parabolischer partieller Differentialgleichungen wurde ein implizites Differenzenverfahren benutzt. Die berechneten Felder wurden mit den experimentellen Resultaten verglichen.