ASHRAE Research on All-Aluminum Microchannel and Tube and Fin Heat Exchangers Explained
From eSociety, May 2019
An ASHRAE research project set out to develop a corrosion test for all-aluminum microchannel and tube and fin heat exchangers. A standard corrosion test would guide ASHRAE members in selecting the type of heat exchanger alloy system appropriate for a given operating mode and atmospheric corrosion system.
Two tests—an environmental chamber-based test that simulated field conditions and an electrochemical-based test—were developed in this research study. A total of 40 heat exchangers samples (30 thick tube wall and 10 thin tube wall) were tested in various simulated environmental conditions. The final report details the conclusions from the research and suggested some future activity.
Principal investigator Seifollah Nasrazadani, Ph.D., with the University of North Texas, explains the significance and challenges of 1645-RP, Development of New Accelerated Corrosion Tests for All-Aluminum Microchannel and Tube and Fin Heat Exchangers:
1. What is the significance of this research?
ASHRAE 1645-RP provides guidance in designing corrosion test procedures for assessing corrosion resistance of all aluminum microchannel heat exchangers (MCHX). This research signifies the importance of duplicating exact atmospheric conditions and mode of heat exchanger operation when simulating corrosion of such parts in laboratories using accelerated corrosion testing methods. Test parameters used in ASHRAE 1645-RP better simulated atmospheric conditions and included operational parameter (duty cycle) of heat exchangers. To the best of the author’s knowledge, this is the first investigation that simulates operation parameter of heat exchangers.
2. Why is it important to explore this topic now?
High cost of copper alloys, along with desire to use lighter vehicles components (such as radiators) for better fuel efficiency, have enticed the automotive industry to replace copper alloys with aluminum alloys. New designs include microchannel heat exchangers (MCHX) that are very light and provide more efficient heat dissipation.
Enhancement of durability and resistance to atmospheric corrosion of MCHX is the motive for this investigation.
3. What lessons, facts, and/or guidance can an engineer working in the field take away from this research?
In this investigation, a comprehensive literature review of the topic was performed. The results of this literature review are very helpful to engineers and practitioners in the field in designing their own corrosion test procedures for their unique applications. Pros and cons of chambers studies compared to electrochemical tests are provided. Chamber tests allow assessment of a complete MCHX system, whereas electrochemical tests use coupons that are only testing part of the system.
4. How can this research further the industry's knowledge on this topic?
This research educates engineers and practitioners in this field about new testing procedures to include important parameters in atmospheric corrosion and operational parameters of MCHX systems. New analytical methods are provided for pit count, pit depth, and pit density characterization of alloys used in MCHX systems in various corrosive environments.
Data presented in this investigation can help engineers predict the life span of new MCHX systems.
5. Were there any surprises or unforeseen challenges for you when preparing this research?
Yes. We expected to observe MCHX tube wall perforations in reasonably short test durations, but no tube wall perforations were observed, even after 2,500 hours (104 days) of testing. This was attributed to relatively high tube wall thickness (0.5 millimeters). One could get tube wall perforations in a shorter time by using more acidic corrosive electrolytes (electrolytes with low pH levels). However, highly acidic corrosive electrolytes are not dominant in natural atmospheres.
Two technical papers have been submitted for future publication in ASHRAE Transactions.
TC 8.4, Air-to-Refrigerant Heat Transfer Equipment, sponsored the research project.