Concentric Vertical Pipe Heat Exchanger for Drain Water Recovery
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Solution Overview
Problem
Current drainpipe heat exchanger designs are inefficient due to 75% of the copper water pipe being out of thermal contact conductance, leading to low performance and long payback periods, while drainwater requires fast and continuous heat exchange to recover energy from low-level heat sources like sinks and showers.
Innovation Solution
A drainpipe heat exchanger design that uses a thermally conductive inner sleeve surrounding the drainpipe with a gasket and outer sleeve configuration to maximize thermal contact conductance, allowing for counterflowing fresh water through arcuate conduits, ensuring full thermal contact and efficient heat transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a copper water tube is spirally wound on a copper drainpipe, then the heat exchanger can be assembled, but 75% of the copper water pipe is out of thermal contact conductance with the drainpipe, resulting in low heat transfer performance
Solution Approach 1:
The heat exchanger is divided into multiple axial segments, with each segment containing a separate water tube. This segmentation allows each tube to be independently positioned to achieve full thermal contact with the drainpipe, eliminating the 75% contact loss problem while maintaining assembly capability.
Solution Approach 2:
A thermally conductive compound is introduced as an intermediary substance between the copper water tube and the copper drainpipe. This compound ensures complete thermal contact conductance across the entire surface area, maximizing heat transfer performance while allowing the tube to maintain its structural integrity during assembly.
2Ease of operation
If the heat exchanger uses a large bore drainpipe to match plumbing code diameter requirements, then it can accommodate drainwater flow, but the thermal contact area between the water pipe and drainpipe is reduced
Solution Approach 1:
The patent transitions from radial thermal contact (where the tube touches the pipe wall at a limited circumference) to axial thermal contact (where multiple segmented tubes provide distributed contact areas along the length of the drainpipe). This dimensional change allows the system to maintain large bore capacity while maximizing total thermal contact area through cumulative axial segments.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves exceptionally high thermal contact conductance, resulting in fast heat exchange and reduced energy waste, shortening recovery time and providing a cost-effective solution for energy recovery from drainwater.
Implementation Method 1
the rate of heat transfer between solids is a function of: thermal conductivity; contact area; contact pressure
Implementation Method 2
The term 'thermal contact conductance' is used for heat transfer between solids. The rate of heat transfer between solids is a function of: thermal conductivity; contact area; contact pressure
Implementation Method 3
each fluid changes temperature where the fresh water is either heated or cooled
Data Source
AI summary
An outer plastic tube has water connections through the wall into an arcuate space defined by an O-ring spacer-gasket positioned between the wall and the perimeter margin of an inner cylinder rolled from a single-layer of sheet metal. A metal drainpipe with a removable bullet-shape at one end is forced through the cylinder to expand it and to thereby compress the gasket sealing the arcuate space. Thermal contact conductance is increased by the compressive force of water pressure. Water flow through the heat exchanger is both arcuate and turbulent to optimize heat transfer.