WHY DOES LIGHTNING EXPLODE AND GENERATE MHD POWER?
Center for Electromagnetics Research, Northeastern University Boston, MA 02115
Presented at Infinite Energy Magazine’s Cold Fusion and New Energy Symposium on October 11, 1998, Manchester, NH.
提出了一种无限能源杂志冷聚变和新能源座谈会在 1998 年 10 月 11 日，曼彻斯特，新罕布什尔州。
The talk given at the Manchester symposium reviewed the long history of thunder research and proposed, for the first time, that it is arc liberated chemical energy from the air which explodes the lightning channel. Regardless of the cause of thunder, the ejection of ions from the atmospheric arc through the strong encircling magnetic field should generate MHD (mag-neto-hydrodynamic) power. This is expected to augment the flow of discharge current in the lightning stroke. Experimental evidence provided by laboratory arcs of lightning strength supports current augmentation by MHD action.
The best known electric arc in air is the lightning stroke. It explodes and sends a shock wave through the surrounding air, which is known as thunder. Thinking man has observed thunder and lightning for thousands of years. This spectacle plays a role in both Eastern and Western mythology. Thunder is recognized as one of the oldest riddles of recorded scientific inquiry. At the end of the twentieth century we are still questioning what makes the lightning channel explode. Remillard1 published an excel- lent review of thunder research from Aristotle to 1960.
空气中最著名的电弧是雷击。它爆炸并发送通过周围的空气，被称为雷电冲击波。思考的人已经观察了几千年的雷声和闪电。这奇观在东方和西方神话中扮演着一个角色。雷被公认为记录科学探究的最古老的谜题之一。在第二十世纪末，我们仍然在质疑究竟是什么让闪电通道爆炸。remillard1发表一个Excel斋评论从亚里士多德到 1960 年的雷电研究综述。
In the middle of the present century it was firmly believed, but poorly substantiated, that it was the thermal expansion of the lightning plasma which set up the shock wave in air. Then in 1961 Viemeister2 published his findings with regard to “cold” and “hot” lightning. He wrote:
在本世纪中期曾坚定地认为，但差证实，它那是闪电等离子体的热膨胀，在空气中建立了冲击波。然后维美斯特（Viemeister）2 1961 年出版了他的"冷"与"热"闪电定论。他写道︰
Cold lightning is a lightning flash whose main return stroke is of intense current but of short duration. Hot lightning involves lesser currents but of longer duration. Hot lightning is apt to start fires while cold lightning generally has mechanical or explosive effects.
In the 1980s we proved at MIT3 with photography and other means that the shock wave emanating from a short air arc of less than one centimeter length and carrying current of lightning strength, between metal electrodes, did not propagate with a spherical front, as it should have if random thermal collisions between air molecules provided the driving force. Instead the explosion was found to be a distinctly radial blast. The expanding air plasma disk, of a thickness equal to the arc length, was ablated by the environmental atmosphere and formed a supersonic edge. By Viemeister’s definition, this was a cold arc. A sheet of newsprint stretched across the arc gap was mechanically torn, but did not catch fire, so long as it did not touch the electrodes,which exhibited surface melting. No charring or any signs of heating could be detected on the paper.
在20世纪80年代，我们在麻省理工学院通过摄影和其他手段证明，冲击波来自一个短的空气弧小于一厘米的长度和载流电流的雷电强度，在金属电极之间，没有传播与一个球形的前端，作为它应该有，如果空气分子之间的随机热碰撞提供了动力。相反，爆炸被认为是一个明显的径向爆炸。膨胀的空气等离子体盘的厚度等于弧长，消融的环境气氛，形成超音速的边缘。根据 Viemeister 的定义，这是一个寒冷的弧。一张新闻纸横跨电弧间隙被机械撕裂，但没有着火，因此，只要它没有触及的电极，展出表面熔化。在纸上检测不到任何炭化或加热的任何迹象。
If not heat, what is it that propels the radial arc explosion? The process of gas breakdown and ionization absorbs rather than liberates energy. Arc plasmas are charge neutral and have never exhibited Coulomb force implosions or explosions. Fifteen years ago we thought the forces which drove the arc ions apart had to be of electrodynamic origin, that is they had to be ponderomotive magnetic forces between current elements. Measurements4 confirmed decisively that the explosion strength increased with arc current in conformity with an electrodynamic explanation.
Unfortunately, according to conventional electromagnetic theory, the dominant electrodynamic force on the arc should be the Lorentz pinch force. This could cause an arc implosion but it acts in the wrong direction for the observed explosion. The Newtonian electrodynamics4 with Ampere's force law agrees with the Lorentz pinch force but, in addition, predicts strong axial pressure in the arc column. Without a containment tube, the axial pressure will break out in the radial direction. Ten years ago this appeared to be the most likely cause of thunder and air arc explosions.
Intense research of high current arcs at MIT and Northeastern University did, however, reveal that the Ampere forces were too small, by at least a factor of ten, to create the measured arc pressures. This research also involved water arcs in which the explosion pressure was a hundred times that which could be justified with Ampere forces. Then it was discovered that the water arc explosions were the result of the liberation of internal chemical energy. This led to a complete change of the under- standing of the dynamics of pulsed arc explosions.
Liberating Chemical Bond Energy with an Electric Arc
All substances owe their existence to chemical bonding. The bonds involve largely electrical forces of attraction and repulsion. In the bonding of any two particles, the attraction must be balanced by nuclear or atomic repulsion, otherwise matter would collapse and fuse. Forces of repulsion are said to store positive potential energy, while forces of attraction store negative potential energy. If negative potential energy were to annihilate positive potential energy, there would exist no stored bond energy, no bonding, and no matter. We are driven to the conclusion that both these energies must be able to exist side by side.
What is known is how much heat it takes to break a bond. This should be—and sometimes is—described as bond dissociation energy. There is no reason to believe that bond dissociation energy must be equal to the stored bond energy. In fact, a given bond may be broken in an electric arc without heating and the dissociation energy is then likely to be very different from the thermal dissociation energy. Bond energy tables actually list thermal dissociation energies. In general, we do not know what the stored potential energies of bonding are.
Water arc experiments have shown4,5 that a small amount of electrodynamic energy can unlock a much larger amount of stored intermolecular bond energy, which then causes an explosion. It is not unreasonable to suspect that a similar arc-triggered bond energy release is responsible for the explosion of lightning channels. That lightning and arcs in atmospheric air are responsible for chemical reactions has been known for a long time. In fact, electric arcs are used commercially to convert N2 and O2 molecules of air to NO, that is nitric oxide.
水下电弧实验表明，少量的电能可以解锁一个更大的存储量的分子间的键能，从而导致爆炸。这是不是不合理的怀疑，一个类似的电弧触发键能释放是负责雷电通道的爆炸。在大气中的闪电和电弧是负责化学反应已经知道了很长一段时间。事实上，人们将商业上用于电弧将空气 N2 和 O2 分子转换 NO，那就是一氧化氮。
A considerable body of knowledge exists regarding the heat required to break up the strongly bonded N2 molecule, but there exists no information indicating how much potential energy is stored in the molecule. When the N-N bond of the N2 molecule is deprived of its attraction force by a small electrodynamic force, or action, in the arc, the remaining large repulsion force between the two atoms may instantly drive the atoms apart in an event which could be described as an explosion.
In view of the fact that more than two thousand years of research have not found the cause of thunder, it now looks entirely possible that this cause is the unknown amount of chemical bond energy stored in N2 and O2 molecules.
鉴于两千多年的研究没有发现有雷声的原因，它现在看起来完全有可能，这原因是存储在 N2 和 O2 分子中的化学键能量的未知的量。
The Exploding Air Arc as an MHD Generator
Ordinary MHD generators, used in military and space applications, employ a rectangular plasma duct of heat resisting dielectric material. This duct is shown in Figure 1. Typically the plasma traveling at high velocity v down the duct is the flame of an oil burner. Electromagnets are usually employed to set up the magnetic flux ??across the duct which intersects the plasma stream. The ion motion at right angles to the magnetic flux induces the electromotive force (emf) in the direction perpendicular to plasma flow and magnetic field.
Figure 1. Conventional MHD generator.
Figure 2. The arc as an MHD generator.
As shown in Figure 1, metal electrodes are built into the duct wall so that electrons accelerated by the MHD emf can flow from the electrodes through an external load. This current i represents the electrical energy output of the MHD generator.In the electric arc, the current creates an encircling magnetic field of considerable strength. Now consider vertical electrodes with an arc gap between them. The magnetic flux circles then lie in horizontal planes. Explosively driven ions, moving radially outward from the arc gap, cross the magnetic flux lines and induce a vertical MHD emf, or the field Em, in the expanding plasma. Electromagnetic theories are found to demand that the induced emf acts in the direction of arc current flow, as shown by Em in Figure 2. Hence, the electric arc has to behave like an MHD power generator.
The motionally induced emf in the direction of current flow is a forward emf associated with the conversion of mechanical energy, derived from chemical sources, to electrical energy. The reverse process of the conversion of electrical energy to mechanical energy, as in a motor, produces a back emf. For example, if an electric current is forced to flow through the electrodes of the MHD device of Figure 1 and the plasma is replaced with liquid metal, the apparatus becomes a liquid metal pump, which is the linear motion equivalent of a rotating motor. The motionally induced emf then opposes current flow and therefore is a back emf.
The back emf per unit current has the dimension of a resistance.It adds to the resistance of the current circuit through the electrodes. Similarly, a forward emf per unit current subtracts from the resistance. Hence, we may argue that in the MHD generator the current is increased by a reduction of the internal resistance of the arc plasma.
Experimental Indication of the Presence of MHD Energy in an Air Arc
The cause of thunder has eluded scientists from Aristotle on right up to the end of the twentieth century. All explanations advanced in this long search have been disproved with laboratory experiments involving atmospheric air arcs of lightning strength. Now a new explanation has been put on the table. It claims the explosion of the lightning channel is due to the impulsive liberation of chemical bond energy stored in the diatomic molecules of nitrogen and oxygen. It will take time before this suggestion is widely confirmed or rejected.
The lightning channel undoubtedly explodes and thereby shoots air ions through the magnetic field of the lightning cur rent. This should result in the generation of MHD power and an augmentation of the arc current. It now appears that notice of this fact has escaped arc scientists. Maxwell's field theory and the Newtonian electrodynamics agree that the effect should exist, but it remains to be established if it is of significant or negligible magnitude. The first experimental findings suggest that it is significant.