Condensing Boiler Heat Transfer Tube With Flow Constriction
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Solution Overview
Problem
Existing heat exchanger tubes in condensing boilers experience reduced flow velocity and turbulence due to cooling combustion gases, leading to inefficient heat transfer, as the volume reduction of gases decreases flow velocity and turbulence from inlet to outlet, negatively affecting energy utilization and heat transfer efficiency.
Innovation Solution
Incorporating a cross-sectional constriction element, designed as a tube insert like a nozzle, within the heat exchanger tube, which increases pressure loss upstream and enhances flow velocity, combined with a profile insert having ribs to increase the heat transfer surface, promoting turbulent flow and efficient cooling of exhaust gases below the dew point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If combustion gases are cooled through heat exchanger tubes, then heat transfer to heating water is achieved, but flow velocity and turbulence are reduced due to volume reduction, negatively affecting heat transfer efficiency
Solution Approach 1:
The heat exchanger tube is divided into multiple sections with different cross-sectional areas. The tube has an enlarged cross-section in the inlet region and a reduced cross-section in the outlet region, creating distinct flow zones that maintain velocity differentials along the tube length, preventing flow stagnation while enabling effective heat transfer.
Solution Approach 2:
Different sections of the heat exchanger tube are given different geometric properties - the inlet section has a larger cross-section to maintain high flow velocity and turbulence, while the outlet section has a smaller cross-section to facilitate heat transfer. This local variation in geometry optimizes both flow characteristics and heat exchange efficiency in different regions.
2Temperature
If combustion gases are cooled through heat exchanger tubes, then heat transfer to heating water is achieved, but heat transfer efficiency is reduced due to decreased turbulence
Solution Approach 1:
The tube is segmented into regions with different cross-sectional areas, creating zones of varying flow velocity. The enlarged inlet section maintains high velocity and turbulence for efficient heat transfer, while the reduced outlet section allows for effective cooling, resolving the contradiction between maintaining turbulence and achieving heat transfer.
Solution Approach 2:
The non-uniform cross-sectional geometry of the tube creates curved flow paths and varying flow velocities along the tube length. This geometric curvature promotes turbulence and enhances heat transfer efficiency by preventing laminar flow conditions that would reduce heat exchange effectiveness.
3Productivity
If flow velocity is increased to improve heat transfer, then energy utilization improves, but pressure loss increases
Solution Approach 1:
The tube cross-section is segmented into different regions along its length. The inlet region has a larger cross-section that maintains high flow velocity and turbulence for efficient heat transfer, while the outlet region has a smaller cross-section. This segmentation allows high velocity zones to be localized where they are most beneficial, minimizing overall pressure loss while maintaining heat transfer efficiency.
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
This configuration significantly improves heat transfer efficiency by increasing energy utilization and heat transfer, allowing 85-90% more energy to be transferred compared to conventional designs, enhancing the overall efficiency of the boiler's condensing technology.
Implementation Method 1
the pressure loss upstream of the cross-sectional constriction element, i.e. between the combustion chamber and the cross-sectional constriction element, is increased by the at least one cross-sectional constriction element
Implementation Method 2
In the longitudinal section in front of the cross-sectional constriction element, the flow velocity of the exhaust gas is massively increased by the reduced flow cross section
Implementation Method 3
heat transfer tube with an outer tube (10) through which combustion gases flow
Implementation Method 4
combustion gases are cooled until the exhaust gas moisture is condensed in order to utilize the heat of condensation
Implementation Method 5
In the longitudinal section downstream of the narrowing of the flow cross section, ie downstream of the cross-sectional narrowing element, the exhaust gas expands again and is guided into the longitudinal section of the outer pipe with the profile insert. With the very large surface due to the ribs of the profile insert running in the longitudinal direction of the heat exchanger tube
Implementation Method 6
the heating boiler or condensing boiler is operated with a heating water temperature that is lower than the dew point temperature of the combustion gases at the end of the combustion gas path through the boiler
Implementation Method 7
the exhaust gas is cooled to below the dew point in the first longitudinal section of the outer tube, which has an advantageous effect on the condensing technology
Data Source
Figure 1~3
Figure 4~7
Figure 8~13
AI summary
In a heat exchanger tube (5) of a heating boiler (2), having an outer tube (10) through which exhaust gases from the boiler furnace can flow and which can be surrounded on the outside by the heating water, and a profile insert (11) pushed into the outer tube, which is used for enlargement the inner surface of the outer pipe (10) has ribs (14) running in its longitudinal direction (12) and is in thermally conductive contact with the outer pipe (10), a solution is to be provided which enables an even greater heat transfer capacity from the combustion gases to the heating water in the boiler allows. This is achieved in that a first longitudinal section (22) of the outer tube (10) is designed with smooth cylindrical walls and a second longitudinal section (23) of the outer tube (10) has at least one cross-sectional narrowing element (24) narrowing the flow cross-section, with the profile insert (11 ) extends exclusively over the first longitudinal section (22) of the outer tube (10).