The design and construction of a novel heat pipe apparatus is described, and results from experiments that employed the apparatus are presented. The apparatus is designed to permit visual and photographic study of liquid flow and vapor formation within the heat pipe wick structure, artery, and vapor flow channel. The vapor temperature field in the vapor flow channel is displayed by use of thermochromic liquid crystal material. Liquid and vapor flow phenomena observed during normal and the approach to boiling-limited heat pipe operation are described.