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Offensive Heat Transfer in the Middle Ages

Offensive Heat Transfer in the Middle Ages. Brady Aydelotte Spencer Harding. To=1120K. 120lb draw weight. Pre-launch Assumptions. The surface of the arrow had sufficient time to come to the adiabatic flame temperature of the residual fuel oil

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Offensive Heat Transfer in the Middle Ages

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  1. Offensive Heat Transfer in the Middle Ages Brady Aydelotte Spencer Harding

  2. To=1120K 120lb draw weight Pre-launch Assumptions • The surface of the arrow had sufficient time to come to the adiabatic flame temperature of the residual fuel oil • The surface of the arrow was burned away, leaving only a uniform coating of carbon • Modern compound bows have arrow speeds of approximately 100 m/s for 65lbs of draw weight. Medieval compound bows had draw weights in excess of 120lbs. We assumed a velocity of 100 m/s for our arrow.

  3. In-flight Assumptions • Time = 3.5 seconds • Distance = 250 meters • X-Velocity = 71m/s Assume spherical tip • Arrow velocity is much greater than flame velocity so the flame on the arrow goes out immediately • The effect of radiation and convection were combined into a convective coefficient • The Whitaker correlation (eq 7.56) for spheres is still valid for Re# above 8e4

  4. Equations Radiation: Convection: Lumped Capacitance:

  5. Straw: Ti = 580 K Wood: Ti = 610 K Results Tf = 1070 K The final temperature, 1070 K is much greater than the ignition temperatures of wood and straw (610 and 580 K respectively) common building materials of the day.

  6. Conclusion • Medieval flaming arrows would be capable of igniting wooden and straw thatched structures even when the flame on the end went out.

  7. References • Flame Structure and Processes, R.M. Fristrom, Oxford university Press, 1995 • http://www.engineeringtoolbox.com/fuels-ignition-temperatures-d_171.html • http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V3B-47D05P2-2&_user=456938&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000021830&_version=1&_urlVersion=0&_userid=456938&md5=c2f18d43d39f4b7051f3489c022f65c4 • http://www.economy-point.org/i/ignition-temperature.html • The Great Warbow: From Hastings to the Mary Rose (Hardcover). Matthew Strickland. Sutton Publishing 2005. ISBN-10: 0750931671, ISBN-13: 978-0750931670 • Fuels and Engines: Technology, Energy, Environment  By Jean-Claude Guibet, Emmanuelle Faure-Birchem

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