Multi-Section Heat Exchanger for Waste Heat Recovery
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Solution Overview
Problem
In waste heat recovery systems, particularly in Rankine cycles, the need to regulate the temperature of the vaporized working fluid and the waste heat stream often conflicts, posing challenges in heat exchanger design due to sensitivity of working fluids to elevated temperatures and requirements for catalytic after-treatment or exhaust gas recirculation, which complicates efficient heat transfer and emission reduction.
Innovation Solution
A heat exchanger design incorporating a combination of cross-counter and parallel flow paths within plate assemblies, with specific heat exchange sections arranged to manage temperature gradients and prevent thermal breakdown, allowing for controlled heat transfer from exhaust gases to the working fluid while maintaining the working fluid within safe temperature ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If heat transfer efficiency is maximized by increasing temperature differential, then heat recovery efficiency improves, but working fluid temperature exceeds safe operating limits causing thermal breakdown
Solution Approach 1:
The heat exchanger is divided into multiple plate assemblies arranged in series, creating staged heat transfer zones. Each plate assembly transfers a portion of the total heat, progressively heating the working fluid while maintaining temperature control at each stage and preventing thermal breakdown.
Solution Approach 2:
Different plate assemblies are positioned to handle different temperature zones. The first plate assembly handles high-temperature heat transfer from exhaust gases, while subsequent assemblies handle lower temperature stages, with each zone optimized for its specific temperature range to protect the working fluid.
2Object-generated harmful factors
If exhaust gas temperature is reduced for catalytic after-treatment, then emission control improves, but available heat energy for recovery decreases
Solution Approach 1:
Heat extraction is performed preliminarily before the exhaust gas enters the catalytic after-treatment system. The plate assemblies recover maximum heat from the high-temperature exhaust stream first, then the cooled exhaust gas proceeds to catalytic treatment, ensuring both energy recovery and emission control are achieved.
3Productivity
If heat exchange area is increased to improve heat transfer, then heat recovery efficiency improves, but device complexity and size increase
Solution Approach 1:
Each plate assembly serves multiple functions: it acts as a heat transfer surface, a flow distributor, and a structural support element. The plates are designed with integrated features that combine several functions into single components, reducing overall device complexity while maintaining high 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 design enhances heat recovery efficiency by optimizing temperature control, preventing thermal breakdown, and reducing NOx emissions by effectively managing the temperature of the exhaust gas and working fluid, thereby improving the overall efficiency of waste heat recovery systems.
Implementation Method 1
heat transfer from exhaust gases to the working fluid
Implementation Method 2
cross-counter and parallel flow paths within plate assemblies
Implementation Method 3
vaporized by receiving the waste heat
Implementation Method 4
thermal energy produced as a byproduct of a fuel-consuming process that would otherwise be wasted (e.g. discharged to the ambient as a waste stream) is captured and converted to useful work
Data Source
AI summary
A heat exchanger and a method are provided to vaporize a working fluid using a heat sourcing fluid. The heat exchanger includes a first section, a second section, and a third section. A first portion of the heat sourcing fluid passes through the first section, in counter-flow with the working fluid. A second portion of the heat sourcing fluid passes through the second section, in co-flow with the working fluid. Both the first and second portions pass through the third section, in overall counter-flow with the working fluid. The working fluid passes sequentially through the third section, the first section, and the second section. The heat exchanger and/or the method may be used in a Rankine cycle for waste heat recovery or in a refrigerant cycle.