Tube shape selection for heat recovery from particle-laden exhaust gas streams

Heat recovery from exhaust gas streams is applicable to a wide variety of industries. Two problems encountered in exhaust gas heat recovery are: the high heat transfer resistance of gases and the presence of entrained particulate matter, which can limit the use of extended surface area. Standard heat exchangers use round tube. This study uses Computational Fluid Dynamics (CFD) to investigate whether round or another shape is the best tube selection for exhaust heat recovery. Tube shape rankings are based on taking into account heat transfer, gas flow resistance and foulability. Foulability is inferred from the average wall shear stress around the front or back of each shape. An estimated asymptotic fouling resistance is used to calculate an equivalent fouled j factor, jf. CFD results suggest the best tube for exhaust heat recovery is an elliptical tube. The ellipse shape produced j/f and jf/f ratios (where f is the tube bank friction factor) over 1.5 times larger than that of standard round tube. A flattened round tube is also promising and may be the practical and economic optimum

Settling of bentonite in gelatine solutions

New Zealand has a sizeable meat by-products processing industry, associated with significant aqueous effluent called stickwater. Stickwater has a biological oxygen demand of 50-150 g O₂/l and has to be treated prior to disposal. Currently, stickwater is dried and added to meat and bone meal in some inedible meat rendering plants. In edible rendering plants, the gelatin can be removed and the remaining broth is concentrated as a flavor enhancer. Where no further unit operations are carried out on stickwater, the stickwater must be treated to reduce the BOD. A medium size meat rendering plant in NZ can produce up to 30,000 L of stickwater at 2-5% solids per day¹. In Hamilton, waste water treatment costs NZ$0.90 per kg solids or approximately NZ$1350 per day. In comparison, abattoir waste treatment costs NZ$ 0.23/kg in the US.

A tail of two countries

The outlook for two of the euro areaÂ?s best performing economies to date, Ireland and Spain, has darkened dramatically recently amid severe downturns in housing markets. What do these countriesÂ? experiences tell us about the functioning of EMU? BruegelÂ?s new policy brief Â?A Tail of Two CountriesÂ? examines the behaviour of housing markets in Ireland and Spain during EMU and considers what features and policies may have facilitated the overheating of housing markets in these countries. It also discusses the role of large migration flows in spurring growth in housing.

Poorer European Countries are Less Concerned about Biotechnology than Richer Countries

The author examines the relationship between GNP, media coverage, and public perceptions of the utility, risk, and acceptability of medical and food-related applications of biotechnology

Cities and Countries

If one ranks cities by population, the rank of a city is inversely related to its size, a well-documented phenomenon known as Zipf's Law. Further, the growth rate of a city's population is uncorrelated with its size, another well-known characteristic known as Gibrat's Law. In this paper, I show that both characteristics are true of countries as well as cities; the size distributions of cities and countries are similar. But theories that explain the size-distribution of cities do not obviously apply in explaining the size-distribution of countries. The similarity of city- and country-size distributions is an interesting riddle.