Furnace Heat Exchanger Coupling Box for Low-Condensation Flue Flow
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Solution Overview
Problem
In multi-position gas furnaces, inadequate flue gas distribution through the coupling box between primary and condensing heat exchangers leads to localized condensation, increased pressure drop, and potential corrosion, while the need for a larger combustion blower limits furnace size reduction.
Innovation Solution
A coupling box design with a tube sheet at the condensing heat exchanger inlet and a liner at a distance, creating an insulating space to reduce condensation and include a containment plate with a lip to evenly distribute flue gas, maintaining low pressure drop and preventing corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If flue gas distribution is improved through the coupling box, then condensation is reduced, but pressure drop increases requiring a larger blower
Solution Approach 1:
The patent applies local quality by providing insulation specifically at the coupling box where condensation occurs, rather than insulating the entire heat exchanger system. The insulation is applied locally to the coupling box exterior surface to maintain its temperature above the dew point, preventing condensation in this specific vulnerable area while minimizing overall pressure drop.
Solution Approach 2:
The patent introduces an intermediary insulating layer between the cold exterior environment and the coupling box. This insulation layer acts as a thermal barrier that prevents heat transfer from the flue gas to the exterior, maintaining the coupling box temperature above the dew point and preventing condensation without affecting the internal flue gas flow characteristics.
2Object-affected harmful factors
If a larger combustion blower is used to compensate for pressure drop, then flue gas distribution improves, but furnace size increases
Solution Approach 1:
The patent addresses flue gas distribution by providing localized insulation at the coupling box rather than redesigning the entire flow distribution system. This local intervention prevents condensation that would otherwise disrupt flow patterns, maintaining good distribution characteristics without requiring a larger blower or increasing furnace size.
Solution Approach 2:
The insulation is installed beforehand on the coupling box to prevent condensation before it can form and disrupt flue gas flow. This proactive measure ensures consistent flow distribution through the coupling box without requiring compensatory increases in blower capacity or furnace dimensions.
3Object-affected harmful factors
If insulation is added to the coupling box, then condensation is reduced, but device complexity increases
Solution Approach 1:
The patent applies insulation only to the coupling box exterior surface, which is the specific location where condensation occurs. This localized approach prevents condensation without adding insulation to other parts of the heat exchanger system, thereby minimizing the increase in device complexity while effectively addressing the condensation problem.
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 solution effectively reduces condensation, maintains low pressure drop, and prevents corrosion, allowing for a smaller furnace size without compromising efficiency or increasing blower size, ensuring effective operation in various orientations.
Implementation Method 1
The liner and the tube sheet define an insulating liner space therebetween reducing condensation on the liner
Implementation Method 2
air is blown across the exterior of the PHX thus removing heat from the PHX by convection
Implementation Method 3
The CHX makes up the remainder of the furnace efficiency by reducing the flue gas temperature below the dew point of the flue gas and thus taking advantage of the latent heat from the water byproduct of combustion
Data Source
AI summary
A coupling to connect a primary heat exchanger to a condensing heat exchanger of a furnace includes a coupling box extending between a primary heat exchanger and a condensing heat exchanger. The coupling box defines a flow path for flue gas between a primary heat exchanger outlet and a condensing heat exchanger inlet. A tube sheet is located at a distance from the tube sheet in the coupling box. The liner and the tube sheet define an insulating liner space therebetween reducing condensation on the liner.