Valve World Magazine April 2023 | Page 17

the behaviour of molecules . In 1877 , he laid the foundations of statistical mechanics ; the gigantic number of particles in the molecular world could be taken into account using probability theory . In the 1970s , the theory of chaos and dissipative structures turned our ideas upside down . We left behind the much-celebrated determinism and entered into chaos , but one of the many surprises was that there was order hidden in this chaos . This startling news caused astonishment in many fields . A system pushed far into disorder can create order . For example , from the initial equilibrium point of a valve , the disorder increases as soon as the valve is opened , and by further increasing the disequilibrium , one can reach a bifurcation from which some order is created . Indeed , nothing prevents the emergence of locally ordered parts . The only condition is that the global disorder increases . In its march towards disorder , the fluid system is thus capable of creating self-organized structures : these are the supersonic flows ( figure 1 ). Another very convincing example is that of hurricanes , whose formation is due to the excessive increase of the surface temperature of tropical seas in the warm season . Too great a temperature imbalance between the surface of the oceans and those aloft can transform a tropical depression into a tropical storm , and then into a hurricane when the system crosses a bifurcation . Recent developments in nonlinear thermodynamics and chaos physics show that order appears , characterised by an eye and a wall π www . valve-world . net Valve World April 2023

NUCLEAR ENERGY

Physics to the rescue … improving safety & operation of nuclear and industrial facilities

Vistemboirs , or kinetic energy degraders , eliminate many valve vibrations in industrial and nuclear power plants , improving operational safety .
By Dr Michel Pluviose , Honorary Professor , Conservatoire
National des Arts et Métiers

In 2020 the media reported serious valve design problems in third-generation EPR nuclear reactors . For example , during the commissioning of the Olkiluoto reactor in Finland , a safety valve was found to be cracked and leaking . Such failures are reminiscent of the Three Mile Island ( TMI ) accident , which was the subject of an open letter to President Jimmy Carter published by the Valve World team in its sister magazine Nuclear Exchange in 2013 . The causes of these malfunctions and the solutions are deeply hidden in the physics of valves .

Causes of flow instabilities
Order and disorder play an important role in physics . Valves must degrade a certain amount of energy , thus creating a lot of disorder . Since Galileo and Newton , physics has established its laws based on order . The principle of least action summarises the situation in classical mechanics . The introduction of irreversibilities in the equations of mechanics has complicated their resolution . We have therefore simplified , linearised and minimised to get by as best we can . In fluid mechanics , this led to the Navier- Stokes equations , then to the Reynolds equations , when turbulence came into play . Little by little , determinism was discarded . These equations , by the non-linear terms that compose them , carry the seeds of chaos . In the industrial era , thermodynamics appeared with its two laws . The first is : ‘ Energy is conserved ,’ while the second : ‘ Energy degrades ’ was in charge of finally taking disorder into account . Nicolas Sadi Carnot and Rudolf Clausius , the two legislators of this science that associates heat and motion , wanted to distance thermodynamics from any molecular reference ; they made it a purely macroscopic discipline . Entropy , the new name for disorder , measures the degradation caused by all kinds of irreversibilities . To grasp the deep meaning of the second principle , it is necessary to analyse how the production of entropy is related to the different irreversible processes . The exchange or transfer of mechanical and thermal properties takes place through molecules , each of which carries energy and momentum before colliding with another molecule . By using the phenomena of heat , matter and momentum transfer , a bridge could be built between the macroscopic system and the molecular phenomena . Ludwig Boltzmann , on the other hand , was not satisfied with the abstract aspect of the second principle and sought an explanation based on
Figure 1 . Formation of supersonic flows in a valve .

the behaviour of molecules . In 1877 , he laid the foundations of statistical mechanics ; the gigantic number of particles in the molecular world could be taken into account using probability theory . In the 1970s , the theory of chaos and dissipative structures turned our ideas upside down . We left behind the much-celebrated determinism and entered into chaos , but one of the many surprises was that there was order hidden in this chaos . This startling news caused astonishment in many fields . A system pushed far into disorder can create order . For example , from the initial equilibrium point of a valve , the disorder increases as soon as the valve is opened , and by further increasing the disequilibrium , one can reach a bifurcation from which some order is created . Indeed , nothing prevents the emergence of locally ordered parts . The only condition is that the global disorder increases . In its march towards disorder , the fluid system is thus capable of creating self-organized structures : these are the supersonic flows ( figure 1 ). Another very convincing example is that of hurricanes , whose formation is due to the excessive increase of the surface temperature of tropical seas in the warm season . Too great a temperature imbalance between the surface of the oceans and those aloft can transform a tropical depression into a tropical storm , and then into a hurricane when the system crosses a bifurcation . Recent developments in nonlinear thermodynamics and chaos physics show that order appears , characterised by an eye and a wall π www . valve-world . net Valve World April 2023

17