Helical Double Pipe Channels for Heat Exchange and Low Pressure Drop
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Solution Overview
Problem
The existing double pipe configurations for heat exchangers, particularly in automotive air-conditioning systems, face challenges in achieving optimal heat-exchanging performance due to suboptimal flow velocity and pressure drop in the straight-pipe parts, where the channel cross-sectional shape of the outer-side channels has not been sufficiently elucidated, leading to potential performance deterioration.
Innovation Solution
A double pipe design with an inner pipe having protruding parts that are helically offset and contact the outer pipe, forming outer-side channels with specific depth-to-arc length ratios (D/L values between 0.09 and 0.20) in the straight-pipe parts, optimizing the channel cross-sectional shape to enhance flow velocity and reduce pressure drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the inner diameter of the outer pipe is made larger than the outer diameter of the inner pipe to form an outer-side channel, then the channel cross-sectional area increases, but the flow velocity of the refrigerant drops and heat-exchanging performance deteriorates
Solution Approach 1:
The outer-side channel is segmented into multiple circumferential channels by providing groove portions that extend in the longitudinal direction. This segmentation divides the single large channel into multiple smaller channels, increasing the flow velocity while maintaining the total cross-sectional area for heat exchange.
Solution Approach 2:
The groove portions extend in the longitudinal direction (adding a dimensional element), creating ridges that partition the circumferential space. This dimensional addition transforms a single large channel into multiple narrower channels, improving flow velocity without sacrificing overall heat exchange area.
2Area of stationary object
If the groove portions are made deeper to increase contact surface area, then heat-exchanging performance improves, but the channel cross-sectional area decreases and pressure drop increases
Solution Approach 1:
The depth of the groove portions is optimized to a specific range (0.5mm to 2.0mm) to achieve the desired balance. This parameter optimization ensures sufficient contact surface area for heat exchange while maintaining adequate channel cross-sectional area to minimize pressure drop and energy loss.
3Productivity
If the double pipe configuration is used to improve heat-exchanging performance, then heat exchange efficiency increases, but the device complexity increases
Solution Approach 1:
The inner pipe is nested within the outer pipe, with groove portions formed on the outer surface of the inner pipe. This nested configuration achieves complex heat exchange functionality through a relatively simple structural arrangement, minimizing device complexity while maximizing heat-exchanging performance.
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 improves heat-exchanging performance by increasing the contact surface area and flow velocity in the outer-side channels while minimizing pressure drops, both in the outer-side and inner-side channels, thereby enhancing the overall efficiency of the heat exchanger.
Implementation Method 1
effect heat exchange between a fluid that flows in the interior of the inner pipe and a fluid that flows between the inner pipe and the outer pipe
Implementation Method 2
the inner pipe comprises a plurality of protruding parts extending in a longitudinal direction and curved to protrude toward an outer-circumference side; the protruding parts are helically offset in the longitudinal direction
Data Source
AI summary
A double pipe for a heat exchanger includes an inner pipe disposed in an outer pipe. In a straight-pipe portion of the double pipe, the inner pipe has a plurality of protruding parts extending in a helically offset manner along a longitudinal direction, an inner-circumferential surface of the outer pipe directly contacts the protruding parts, and outer-side channels are partitioned at a plurality of locations in a circumferential direction of the double pipe. The protruding parts are curved to protrude radially outward. In a cross section of the straight-pipe portion orthogonal to the longitudinal direction, the inner-circumferential surface of the outer pipe is circular, and an average value of D/L values of all the outer-side channels is 0.09-0.20, wherein D is defined as a maximum depth of each of the outer-side channels and L is defined as an arc length of each of the outer-side channels in the circumferential direction.