Water heater having highly efficient and compact heat exchanger
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Solution Overview
Problem
Coil finned heat exchangers face a trade-off between size and thermal efficiency, with single-coil designs being large but efficient, and two-layer coil designs being compact but having lower efficiency due to non-countercurrent flue gas flow, which affects thermal performance in gas instantaneous water heaters.
Innovation Solution
A heat exchanger design featuring an inner and outer coil with a radial-flow baffle system, including a drum baffle and slotted baffle, that directs flue gases to create a countercurrent flow path between the coils, enhancing heat transfer and efficiency while maintaining compactness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a single coil heat exchanger is used, then thermal efficiency is high, but the device size becomes large and difficult to package
Solution Approach 1:
The patent implements a nested coil configuration where an inner coil is positioned within an outer coil, both wound in the same helical direction. This nesting arrangement allows the heat exchanger to maintain the thermal efficiency of a single coil design while reducing the overall volume and footprint, making it suitable for compact water heater applications.
Solution Approach 2:
The patent utilizes the radial dimension by positioning the inner coil concentrically within the outer coil, creating a radial flow path for flue gases. This dimensional arrangement allows compact packaging while maintaining efficient heat transfer through the radial movement of gases between the coils.
2Volume of moving object
If a two-layer coil layout is used, then the device becomes compact, but flue gas flow becomes radial rather than countercurrent, reducing thermal efficiency
Solution Approach 1:
The patent employs dynamic flow control elements including baffles and flow directors that actively guide flue gases to follow a countercurrent path through the inner and outer coils. These dynamic flow management features ensure that despite the compact nested arrangement, the thermal efficiency is maintained by preventing radial short-circuiting of the flue gas flow.
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 a thermal efficiency of 95.4%, improving upon previous radial flow heat exchangers by maximizing surface area contact and time, and reducing the risk of scaling through optimized flue gas bypass paths and water recirculation, maintaining high efficiency with reduced scaling propensity.
Implementation Method 1
heat transfer... to heat water flowing through the inner coil and the outer coil
Implementation Method 2
flue gases flow radially outward over the inner coil... over the outer coil to heat water
Data Source
AI summary
A water heater includes an inner water tube coil and an outer water tube coil separated by a drum baffle. The inner and outer coils extend above a top edge of the drum baffle by at least a full turn of each coil. A flue gas bypass path is defined between a top edge of the drum baffle and a top insulation layer above the inner and outer coils. Flue gases flow radially though the inner coil, up along the drum baffle, through the flue gas bypass path, and downwardly over the outer coil to heat water flowing through the inner and outer coils. The water flows into the outer coil at the bottom of the coil, winds upwardly through the outer coil in countercurrent flow with respect to the flue gases, then down through the inner coil.