Experimental studies of flow boiling heat transfer by using nanofluids

Journal of Thermal Analysis and Calorimetry - Flow boiling heat transfer widely utilized in numerous industrial applications such as boiler tubes, evaporators and cooling of reactors in a nuclear...     

Animal-fat investigation and combustion test

The department was commissioned to investigate the possibilities for animal-fat combustion in industrial steam generators operating originally on fuel–oil or natural gas. There are two main reasons for operating generators on animal fat as a fuel: On one hand, this material is considered as hazardous waste, thus an important goal is its environmentally benign elimination or disposal. On the other hand, fat is an excellent energy source and can be used as combustion fuel. This way fossil fuel usage can be saved while environmental regulations can also be met. The usage of animal fat as a fuel for furnaces required classification according to fuel classification rules, and comparison with the properties of fuel oil. In addition, its pollutant content was determined and the effects on the combustion process and emission were investigated. Finally the savings in fossil fuel energy consumption and related CO₂ emission achieved were determined. The first stage involved the determination of the composition of animal fat. Subsequently other properties such as viscosity and flash point variation were investigated. These data were compared to the properties of fuel oil. The theoretical investigations of animal-fat classification were promising. Initially one steam generator, originally designed for fuel oil combustion, was modified and fitted with a parallel animal fat fuel supply system. The results of the test were encouraging, although there were some problems with power regulation and later with fuel supply. A rotary cup type burner was then fitted to the boiler. Using this system, all the requirements including environmental regulations were met.     

Simulation of pool boiling of nanofluids by using Eulerian multiphase model

In the present work, a new simulation of nanofluid/vapor two-phase flow inside the 2-D rectangular boiling chamber was numerically investigated. The Eulerian–Eulerian approach used to predict the boiling curve and the interaction between two phases. The surface modification during pool boiling of silica nanofluid represented by surface roughness and wettability is put into the account in this simulation. New closure correlations regarding the nucleation sites density and bubble departure diameter during boiling of silica nanofluid were inserted to extend the boiling model in this work. Besides, the bubble waiting time coefficient which involved in quenching heat flux under heat flux partitioning HFP model was corrected to improve the results of this study. The numerical results validated with experimental works in the literature, and they revealed good agreements for both pure water and nanofluids. The results found that when improving the heat flux partitioning model HFP by considering the surface modification of nucleate pool boiling parameters, it will give more mechanistic sights compared to the classical model, which is used for predicting of boiling heat transfer of pure liquid.

     

Correlation between heating values and thermogravimetric data of sewage sludge, herbaceous crops and wood samples

The thermal behaviours of a sewage sludge sample, woody (black locust, poplar and willow) and herbaceous (energy grass and wheat straw) biomass as well as mixed (sewage sludge and black locust in ratios 1:1 and 1:3) samples were compared under inert and oxidative atmosphere. The thermogravimetric experiments of each sample demonstrate that the beginning temperature of decomposition is similar in inert and oxidative atmospheres, i.e. the primary bond scissions are not affected by the atmosphere. Nevertheless, oxygen increases the decomposition rate and the volatile evolution of all samples at higher temperatures. Thermogravimetry/mass spectrometry (TG/MS) experiments have been performed to determine the mass loss of the samples and the formation of volatile products as a function of temperature in inert atmosphere. Wood and herbaceous biomass samples evolved various organic products (aldehydes, ketones, acids, furan derivatives, etc.) beside water and gaseous products. Sewage sludge released mainly water, carbon oxides, methane, hydrogen, hydrocarbons, ketones, acids as well as sulphur- and nitrogen-containing products. High heating value and low heating value of the samples have been determined by a bomb calorimeter. Principal component analysis (PCA) has been used to find statistical correlation between the data. The results unambiguously support the correlation between the thermogravimetric parameters (e.g. DTG_max) and the heating values of the samples.