The design and construction of a novel heat pipe apparatus is describe
d and results from experiments that employed the apparatus are present
ed The apparatus is designed to permit visual and photographic study o
f liquid flow and vapor formation within the heat pipe wick structure,
artery, and vapor flow channel. The vapor temperature field in the va
por flow channel is displayed by use of thermochromic liquid crystal m
aterial. Liquid and vapor flow phenomena observed during normal and th
e approach to boiling-limited heat pipe operation are described.