Abstract: A fluid heat transfer apparatus having an expandable housing defining an enclosed interior space including fluid inlet and outlet manifolds communicating with said interior space and the exterior of said housing. The apparatus including heat transfer modules stackable in said interior space and each module comprising a flat supporting structure including upstanding elongated posts extending from one side thereof and lengths of flexible plastic tubing wound about the posts in basket-weave fashion with the ends of the tubing being connected to said inlet and outlet manifolds to provide conduction of fluid flow from said inlet to said outlet manifold. The housing being expandable to receive pluralities of said modules to selectively increase fluid heat transfer characteristic of said apparatus. The interior space being filled with a heat transfer fluid heated by a controlled heat producing medium such as electric heating elements.

Abstract: An electronic system for determining, indicating and regulating the level of semi-solid matter, such as sludge, in a fluid medium. The system produces and directs ultrasonic signals toward the matter, and the reflected signals are used to compute signal transit time and thus indicate incremental sludge levels. An output signal is produced when the matter reaches a preset level, to activate a pump and thus regulate the sludge level.