Home  About us  Contact
 

Safety Valves (safety + valve)

Distribution by Scientific Domains
Chemistry66%

Selected Abstracts

Sizing of throttling device for gas/liquid two-phase flow part 1: Safety valves

PROCESS SAFETY PROGRESS, Issue 4 2004
Ralf Diener
The calculation of the mass flow rate through throttling devices is difficult when handling two-phase flow, especially when boiling liquids flow into these fittings. Safety valves are typically oversized by a significant extent, if sizing methods like the ,-method (originally developed by J. Leung), are used in case of low-quality inlet flow. Within this method the boiling delay of the liquid and the influence of the boiling delay on the mass flow rate are not considered. In this paper the HNE-DS model is proposed, where the compressibility coefficient , is extended by adding a boiling delay coefficient. It includes the degree of thermodynamic nonequilibrium at the start of the nucleation of small mass fractions of vapor upstream of the fitting. In Part 1 the sizing of safety valves is described. Additionally, the derivation of the HNE-DS method is given in detail. Part 2 considers the mass flow rate through short nozzles, orifices, and control valves. The HNE-DS model can be used for all those fittings. A comparison with experimental results on safety valves with steam/water and air/water flow has emphasized the excellent accuracy of the new model. © 2004 American Institute of Chemical Engineers Process Saf Prog, 2004 [source]

Zeitarbeit in Deutschland: Trends und Perspektiven

PERSPEKTIVEN DER WIRTSCHAFTSPOLITIK, Issue 2 2006
Michael C. Burda
In addition, THS can facilitate new employment for both labor market entrants and job losers. This survey examines the economic significance, the changing regulatory framework, and the recent development of the THS sector in Germany. Declining wages and rising employment shares in THS are suggestive of a safety valve for the primary labor market, especially for unskilled workers. High markups charged by THS firms despite declining relative compensation of THS workers suggest a high shadow price for this form of labor input. [source]

Trouble on the reef: the imperative for managing vulnerable and valuable fisheries

FISH AND FISHERIES, Issue 3 2005
Yvonne Sadovy
Abstract Reef fishes are significant socially, nutritionally and economically, yet biologically they are vulnerable to both over-exploitation and degradation of their habitat. Their importance in the tropics for living conditions, human health, food security and economic development is enormous, with millions of people and hundreds of thousands of communities directly dependent, and many more indirectly so. Reef fish fisheries are also critical safety valves in times of economic or social hardship or disturbance, and are more efficient, less wasteful and support far more livelihoods per tonne produced than industrial scale fisheries. Yet, relative to other fisheries globally, those associated with coral reefs are under-managed, under-funded, under-monitored, and as a consequence, poorly understood or little regarded by national governments. Even among non-governmental organizations, which are increasingly active in tropical marine issues, there is typically little focus on reef-associated resources, the interest being more on biodiversity per se or protection of coral reef habitat. This essay explores the background and history to this situation, examines fishery trends over the last 30 years, and charts a possible way forward given the current realities of funding, capacity, development patterns and scientific understanding of coral reef ecosystems. The luxury live reef food-fish trade is used throughout as a case study because it exemplifies many of the problems and challenges of attaining sustainable use of coral reef-associated resources. The thesis developed is that sustaining reef fish fisheries and conserving biodiversity can be complementary, rather than contradictory, in terms of yield from reef systems. I identify changes in perspectives needed to move forward, suggest that we must be cautious of ,fashionable' solutions or apparent ,quick fixes', and argue that fundamental decisions must be made concerning the short and long-term values of coral reef-associated resources, particularly fish, for food and cash and regarding alternative sources of protein. Not to address the problems will inevitably lead to growing poverty, hardship and social unrest in many areas. [source]

Sizing of throttling device for gas/liquid two-phase flow part 1: Safety valves

PROCESS SAFETY PROGRESS, Issue 4 2004
Ralf Diener
The calculation of the mass flow rate through throttling devices is difficult when handling two-phase flow, especially when boiling liquids flow into these fittings. Safety valves are typically oversized by a significant extent, if sizing methods like the ,-method (originally developed by J. Leung), are used in case of low-quality inlet flow. Within this method the boiling delay of the liquid and the influence of the boiling delay on the mass flow rate are not considered. In this paper the HNE-DS model is proposed, where the compressibility coefficient , is extended by adding a boiling delay coefficient. It includes the degree of thermodynamic nonequilibrium at the start of the nucleation of small mass fractions of vapor upstream of the fitting. In Part 1 the sizing of safety valves is described. Additionally, the derivation of the HNE-DS method is given in detail. Part 2 considers the mass flow rate through short nozzles, orifices, and control valves. The HNE-DS model can be used for all those fittings. A comparison with experimental results on safety valves with steam/water and air/water flow has emphasized the excellent accuracy of the new model. © 2004 American Institute of Chemical Engineers Process Saf Prog, 2004 [source]

Sizing of Safety Valves Using ANSYS CFX-Flo®

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 2 2009
D. Moncalvo
Abstract This work discusses the effect of the degree of fineness of the flow volume discretization and that of the turbulence model on the accuracy of reproduction of air mass flow rates in two safety valves using the CFD software ANSYS Flo®. Calculations show that the degree of fineness of the discretization is the decisive factor affecting the exactness of the calculations and that the best reproduction is achieved with grids where at least two cells are built on the smallest edge. The selection of the turbulence model has by far in comparison a lower impact; however, the best accuracy is obtained using the standard k - , model and the SST modification of Menter. [source]