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DIVING PHYSICS

DIVING PHYSICS. 한국 잠수응급구난망 WWW.DENKOREA.CO.KR 김 희덕. DIVING PHYSICS. Pressure Temperature Immersion Gas laws Light Sound. DIVING PHYSICS Units of Pressure. 1 atmosphere ata 1 bar (1000millibar) bar (mbar) 760 mm mercury mmHg 760 torr torr 14.7 pounds per sq. in psi

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DIVING PHYSICS

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  1. DIVING PHYSICS 한국 잠수응급구난망 WWW.DENKOREA.CO.KR 김 희덕

  2. DIVING PHYSICS • Pressure • Temperature • Immersion • Gas laws • Light • Sound

  3. DIVING PHYSICSUnits of Pressure 1 atmosphere ata 1 bar (1000millibar) bar (mbar) 760 mm mercury mmHg 760 torr torr 14.7 pounds per sq. in psi 100 kilopascal kPa 33 feet of seawater fsw 10 metres of seawater msw 100,000 Newton per sq.m Nm-2 10.000 Kilopond per sq.m kp m-2

  4. DIVING PHYSICSGAS LAWS Boyle’s Law - if temperature remains constant, the volume of a given mass of gas is inversely proportional to the absolute pressure P1V1 = P2V2 or P / r= constant 10 litres of gas at sea level ( 1 ata) compresses to 5 litres at 10 msw ( 2 ata) and to 2 litres at 40 msw ( 5 ata) and to 1 litre at 90 msw (10ata)

  5. DIVING PHYSICSGAS LAWS Charles’s Law - if the pressure is constant, the volume of a given mass of gas is proportional to the absolute temperature V increases with T where 00C = 2730 absolute

  6. DIVING PHYSICSGAS LAWS Henry’s Law - at constant temperature, the mass of gas that will dissolve in a liquid is proportional to the partial pressure of the gas over the liquid. hence when the pressure is doubled the mass of gas in solution will increase by a factor of 2 when equilibrium is reached

  7. DIVING PHYSICSGAS LAWS Dalton’s Law - the total pressure exerted by a mixture of gases is the sum of the partial pressures that would be exerted by each of the gases if it alone occupied the the total volume. e.g. in air at 1 ata ppN2 = 0.79 = 1 ata * 79% ppO2 = 0.209 = 1 ata * 20.9% .

  8. DIVING PHYSICSGAS LAWS Pascal’s Law - the pressure exerted on a liquid is uniformly experienced throughout. since fluid is not compressible it transmits pressure. However, in a column of water the pressure at any point depends upon both the pressure applied at the surface and the height of the column above that point.

  9. DIVING PHYSICSImmersion • Archimedes principle - any object, wholly or partially immersed in liquid, is buopyed up by a force equal to the weight of liquid displaced. • Since water is very dense, objects which are heavy on the surface weigh less when in the water and divers who are almost equally dense as water become virtually weightless and their buoyancy depends critically on the gas within the body or their equipment.

  10. DIVING PHYSICS SOUND Speed of sound in water is much greater than in air travels long distances is reflected off bottom and surface Speech is distorted by alteration in gas density and resonant characteristics in different gases

  11. DIVING PHYSICS SOUND Velocity of sound MaterialV (ms-1) Change in V per0C Air (00C) 331.45 0.59 Helium 965 0.8 Hydrogen 1284 2.2 Nitrogen 334 0.6 Oxygen 316 0.5 Sea water 1531 -2.4 Pure water 1497 -2.4

  12. DIVING PHYSICS LIGHT Water absorbs light 20% incident light reaches 10msw 1% incident light reaches 85 msw Clear water is most transparent to light of wavelength at 480nm which produces the blue green colouration. Refractive effects occur at interfaces e.g air/water, water/glass, glass air

  13. DIVING PHYSICSHEAT water conducts heat better than air divers cool rapidly in water unless protected helium conducts heat better than air divers in a helium environment lose heat both through the skin and through the respiratory tract

  14. DIVING PHYSICS Fourier’s Law of Thermal Conductivity H = - K A (T1 - T2) L K = thermal conductivity A = cross sectional area of conductor L = length of conductor T1-T2 = temperature drop

  15. DIVING PHYSICS RESPIRATORY HEAT LOSS Heat(resp)=Ve r Cp (Te - Ti) + Ve 226 (We - Wi) Ve = respiratory minute volume r = gas density Cp = gas specific heat T = temperature W = water content

  16. DIVING PHYSICS RESISTANCE DURING LAMINAR FLOW (Poiseulle’s Law) P = 8 h l V p r4 P = pressure drop across tube l = length of tube h = viscosity V = flow r = radius of tube

  17. DIVING PHYSICS REYNOLDS NUMBER Rn = r V 2 p r h r = density h = viscosity V = flow

  18. DIVING PHYSICS CRITICAL VELOCITY Vc = Nr h r r Nr = Reynold’s No r = radius r = density h= viscosity

  19. DIVING PHYSICS RESISTANCE DURING TURBULENT FLOW P = ( f L / 4p2 r5) * V2 f = friction factor (Reynold’s No and tube surface) r = radius L = length of tube P = pressure drop across tube V = flow

  20. DIVING PHYSICS 1. with increasing depth the volume of a closed gas filled space will shrink 2. with increasing depth the density of a gas increases 3. the work exerted on a gas during compression causes heating - the increase in temperature increases the pressure 4. the partial pressure of a constituent of a gas mixture can be calculated from the total pressure and the fractional concentration (%) of that constituent of the gas 5. the amount of gas dissolved in body tissues depends upon the partial pressure and the solubility fo the gas 6. body tissues behave as liquid - the pressure exerted on the body surface is uniformly experienced throughout the body

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