Condensing Flue Conduit Layout to Prevent Water Heater Corrosion
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Solution Overview
Problem
Existing domestic gas-fired water heaters face inefficiencies in heat transfer due to condensation in the flue pipe, leading to corrosion and suboptimal exhaust gas temperatures, and multi-pass designs increase costs and occupy space, while existing solutions fail to effectively prevent condensation and maximize heat extraction.
Innovation Solution
A condensing flue system with an external high-efficiency heat exchange flue conduit surrounded by water, featuring a narrow internal passage and a blower to direct hot flue gases, and an inverted U-shaped flue pipe with a heat exchange water conduit that recirculates water to enhance heat transfer and prevent condensation, acting as a baffle to improve turbulence and retention time of flue gases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If heat is extracted from flue gases through the flue pipe, then thermal efficiency is improved, but condensation forms in the flue pipe causing corrosion
Solution Approach 1:
The flue system is divided into two separate components: an internal flue pipe for gas flow and an external heat exchange conduit for heat transfer. This segmentation allows the heat extraction function to be separated from the gas flow path, preventing condensation in the internal flue while maintaining thermal efficiency through the external conduit surrounded by water circulation.
Solution Approach 2:
Water acts as an intermediary medium between the flue gases and the water tank. The external heat exchange conduit transfers heat from flue gases to the circulating water, which then heats the tank water. This intermediary approach enables efficient heat transfer without direct contact between cold tank water and hot flue gases, preventing condensation formation.
2Loss of energy
If multi-pass flue designs are used to increase heat extraction, then thermal efficiency is improved, but tank space is occupied and costs increase
Solution Approach 1:
The heat exchange function is moved from the internal volume of the tank to the external surface of the tank. The external heat exchange conduit is surrounded by water circulation outside the tank, allowing multi-pass heat extraction without occupying internal tank space. This dimensional shift enables maintaining full tank capacity while achieving enhanced heat transfer.
3Object-affected harmful factors
If flue gases are exhausted at higher temperatures, then condensation is reduced, but thermal efficiency decreases
Solution Approach 1:
The system maintains continuous heat extraction from flue gases through the external heat exchange conduit at multiple points along the flue path. This continuous heat removal allows the flue gases to be cooled to near condensation temperatures (maximizing thermal efficiency) without actually forming condensation, as the heat is continuously transferred to the water circulation system before condensation can occur.
4Loss of energy
If baffles are installed in the flue pipe to increase heat transfer, then thermal efficiency is improved, but condensation and corrosion are exacerbated
Solution Approach 1:
The heat transfer function is extracted from the internal flue pipe and placed in the external heat exchange conduit. By removing the heat extraction activity from the gas flow path, the system achieves high heat transfer efficiency without creating the conditions (cooling zones, turbulence, prolonged residence time) that lead to condensation and corrosion inside the flue pipe.
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 system effectively extracts heat from flue gases, reduces condensation, and allows for efficient heat transfer to the water tank, while being reusable and compact, thus improving thermal efficiency and reducing corrosion risks.
Implementation Method 1
A blower is secured to the flue pipe above the top wall for directing hot flue gases from the combustion chamber to an external heat exchange flue conduit section
Implementation Method 2
The water channel has an inlet connection at a lower end thereof and an outlet connection at an upper end thereof. The inlet connection receives water from a lower section of the water tank and the outlet connection delivers heated water from the water channel to an upper section of the water tank
Implementation Method 3
Various flue pipe heat exchange arrangements and designs are known to extract heat from the hot flue gases leaving the combustion chamber and convected through the flue pipe extending in the water tank to transfer the heat from the flue gases to the water within the tank
Implementation Method 4
Baffles are commonly installed in the flue pipe to increase the heat transfer by slowing the speed of the flue gases while increasing turbulence thereof for longer contact of the hot gases with the flue pipe wall
Data Source
AI summary
A domestic gas-fired water heater condensing flue system wherein in one embodiment a blower is secured at the outlet end of the flue pipe to direct the hot flue gases through an external heat exchange flue conduit. The external heat exchange flue conduit has a sealed water channel surrounding a narrow flue gas internal passage. Water from the bottom end of the tank is circulated in the external heat exchange flue conduit and release in the top part of the tank. In a further embodiment, an inverted U-shaped flue pipe is supported vertically in the water tank and the domestic water supply for the tank is disposed in a downward section of the flue pipe to pre-heat the water supply to the tank and cool the flue gases before being released to atmosphere. The water in the tank is heated by the upward and downward sections of the U-shaped flue pie.