Multi-cavity tubes for air-over evaporative heat exchanger
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Solution Overview
Problem
Conventional evaporative heat exchangers with elliptical tubes face increased weight and cost due to the need for thicker walls to maintain internal pressure, which limits their thermal capacity and efficiency, especially when airflow is involved.
Innovation Solution
The use of multi-lobed tubes with a smaller effective diameter allows for thinner walls while maintaining internal pressure, increasing the surface area in contact with the airstream, thus enhancing thermal capacity and reducing costs without compromising airside pressure drop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If elliptical tubes are used to increase heat exchanger tube density, then thermal capacity is improved, but weight and cost increase due to thicker walls required for internal pressure
Solution Approach 1:
The tube cross-section is segmented into multiple lobes (typically 3-5 lobes) around the circumference, creating a multi-lobed configuration. This segmentation allows the tube to maintain structural integrity for pressure containment while reducing the material required compared to a solid elliptical tube, thereby decreasing weight while preserving thermal capacity.
Solution Approach 2:
The multi-lobed tube design effectively creates a composite structural solution by distributing the pressure containment function across multiple lobed sections rather than requiring a thick-walled solid tube. This composite approach to structural design achieves the same pressure containment with reduced material, lowering weight while maintaining thermal performance.
2Strength
If tube wall thickness is increased to maintain internal pressure, then structural strength is improved, but cost increases
Solution Approach 1:
The tube wall is segmented into multiple lobed sections that collectively provide the necessary structural strength for internal pressure containment. Each lobe acts as a structural element, and the distributed segmentation approach achieves the required strength with less total material than a thick-walled conventional tube, thereby reducing manufacturing cost.
Solution Approach 2:
The invention changes the geometric parameters of the tube cross-section from a simple elliptical shape to a multi-lobed configuration. This parameter change in the cross-sectional geometry allows the tube to achieve the necessary structural strength with reduced wall thickness, lowering material cost while maintaining pressure containment capability.
3Productivity
If external surface area is increased using extended fins, then thermal capacity is improved, but weight and cost increase
Solution Approach 1:
Instead of adding fins in the radial direction to increase surface area, the invention increases the effective surface area by changing the cross-sectional geometry to multi-lobed shapes. This dimensional change in the tube profile provides additional surface area for heat transfer without requiring external fins, thereby avoiding the associated weight and cost increases.
Solution Approach 2:
The multi-lobed tube design uses curved surfaces and optimized geometric profiles to maximize the external surface area available for heat transfer. The curved lobe structures provide efficient heat transfer surfaces without requiring additional finned extensions, achieving enhanced thermal capacity with reduced weight compared to finned conventional tubes.
4Productivity
If tube density is increased, then thermal capacity is improved, but airside pressure drop increases, lowering effectiveness
Solution Approach 1:
The invention changes the cross-sectional parameters of the tubes to multi-lobed configurations with optimized lobe dimensions and spacing. This parameter change allows for increased tube density in the heat exchanger assembly while maintaining adequate airflow passages, thereby increasing thermal capacity without excessively increasing airside pressure drop.
Solution Approach 2:
By changing the cross-sectional geometry to multi-lobed shapes, the invention efficiently packs more tubes into the same heat exchanger volume while maintaining airflow channels. This dimensional optimization in the tube profile allows increased tube density without proportionally increasing the airflow resistance, thus improving thermal capacity while controlling pressure drop.
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 design achieves superior thermal efficiency and cost-effectiveness by maintaining or improving airflow volume per horsepower while reducing the weight and cost of the heat exchanger, with the multi-lobed tubes providing up to twice the surface area of conventional designs within the same volume.
Implementation Method 1
an array of tubes multi-lobed tubes connecting said inlet header and said outlet header... Heat exchanger for cooling or condensing a process fluid... indirect heat exchange section
Implementation Method 2
airflow over the coil... air mover configured to move ambient air into said plenum and up through said indirect section... water-air interaction
Implementation Method 3
evaporative heat exchanger... water distribution system located above the indirect heat exchange section and configured to spray water over the indirect heat exchange section... water having received heat from said indirect section is cooled by direct contact with air
Data Source
AI summary
An air-over evaporative heat exchanger with multi-lobed or “peanut” shaped tubes replacing conventional round or elliptical tubes. The tubes have a narrow horizontal cross section and tall vertical cross section to allow the multiplication of surface area in the same coil volume while maintaining or increasing the open-air passage area. This configuration allows the coil to have an overall external heat transfer coefficient much higher than a conventional coil, while the tube shape allows the use of thinner material, reducing the weight and cost of the heat exchanger.