Compatibility of Phase Change Materials and Metals: Experimental Evaluation Based on the Corrosion Rate

Abstract

The construction and maintenance of building stock is responsible for approximately 36% of all CO2 emissions in the European Union. One of the possibilities of how to achieve high energy-efficient and decarbonized building stock is the integration of renewable energy sources (RES) in building energy systems that contain efficient energy storage capacity. Phase Change Materials (PCMs) are latent heat storage media with a high potential of integration in building structures and technical systems. Their solid-liquid transition is specifically utilized for thermal energy storage in building applications. The typically quite old example is the use of ice that serves as long-term storage of cold. Large pieces of ice cut in winter were stored in heavily insulated spaces and prepared for cooling of food or beverages in summer. In the contemporary use of the principle, the PCMs for building applications and tested in this study must have a melting range close to the desired temperature in the occupied rooms. As the PCMs need to be encapsulated, several types of metal containers have been developed and tested for their thermal conductivity and resistance to mechanical damage, which enhances the performance of these so-called latent heat thermal energy storage (LHTES) systems. Long-term compatibility of metals with PCMs depends, i.e., on the elimination of an undesirable interaction between the metal and the specific PCM. Heat storage medium must be reliably sealed in a metal container, especially if the LHTES is integrated into systems where PCM leaks can negatively affect human health (e.g., domestic hot water tanks). The aim of this study is to evaluate the interactions between the selected commercially available organic (Linpar 17 and 1820) and inorganic (Rubitherm SP22 and SP25) PCMs and metals widely used for PCM encapsulation (aluminum, brass, carbon steel, and copper). The evaluation is based on the calculation of the corrosion rate (CR), and the gravimetric method is used for the determination of the weight variations of the metal samples. The results show good compatibility for all metals with organic PCMs, which is demonstrated by a mass loss as low as 2.1 mg in case of carbon steel immersed in Linpar 1820 for 12 weeks. The exposure of metals to organic PCMs also did not cause any visual changes on the surface except for darker stains, and tarnishing occurred on the copper samples. More pronounced changes were observed in metal samples immersed in inorganic PCMs. The highest CR values were calculated for carbon steel exposed to inorganic PCM Rubitherm SP25 (up to 13.897 mg·cm−2·year−1). The conclusion of the study is that aluminum is the most suitable container material for the tested PCMs as it shows the lowest mass loss and minimal visual changes on the surface after prolonged exposure to the selected PCMs.

Compatibility Tests between Three Commercially Available Organic PCMs and Metals Typically Used in Fin-and-Tube Heat Exchangers

“…The gravimetric method (experiment) consists of the following steps: Preparation of the sample: samples are cut out, grinded with sandpaper, and cleaned (usually with acetone); Weighing of samples: metal samples are weighed before being put into the test tubes filled with the PCM; Immersion of samples in the PCM: metal samples are placed into tubes filled with the PCM (at a temperature when the PCM is a liquid) and they are completely immersed in the PCM, after which they are kept at a constant temperature (when the PCM is a liquid) [ 7 , 8 , 9 , 10 , 11 ] or are tested in temperature cycles triggering phase transformation processes [ 3 , 4 , 5 , 6 , 13 , 17 ]; Removal of samples from the PCM: metal samples are removed from the PCM after a specified time (e.g., a week, a month, or several months); Sample cleaning-up: metal samples are cleaned and dried after being removed from the PCM; Reweighing of samples: metal samples are weighed and subjected to visual evaluation; Corrosion rate calculation: based on the measurement results, the mass change of the sample and the corrosion rate ( CR ) are determined. …”

“…Immersion of samples in the PCM: metal samples are placed into tubes filled with the PCM (at a temperature when the PCM is a liquid) and they are completely immersed in the PCM, after which they are kept at a constant temperature (when the PCM is a liquid) [ 7 , 8 , 9 , 10 , 11 ] or are tested in temperature cycles triggering phase transformation processes [ 3 , 4 , 5 , 6 , 13 , 17 ];…”

“…Corrosion rate (mg/cm 2 /year), taking into account the weight loss (Δ m ), the surface area of the metal/metal alloy sample ( A ), and the experiment time ( t o − t ), is calculated based on the relationship [ 4 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 17 ]: where …”

“…Bantová et al [ 6 , 17 ] tested the compatibility of organic (Linpar17 and Linpar1820) and inorganic PCMs (SP22 and SP25) with brass, copper, aluminum, and carbon steel. On the basis of visual evaluation, corrosion rate ( CR ), and weight loss, they concluded that all metals showed good compatibility with organic PCMs.…”

Fault Injection with Multiple Fault Patterns for Experimental Evaluation of Demand-Controlled Ventilation and Heating Systems

“…HVAC systems are the main reason for global energy consumption, electricity consumption, and worldwide CO 2 emissions [ 4 ]. For example, the construction and maintenance of building stock are responsible for 36% of the CO 2 emission in the European Union (EU) [ 5 ]. In 2018, the building, construction, and building processes represented 36% of energy consumption, 39% of energy-related CO 2 emissions, and 50% of global electricity consumption [ 4 , 6 ].…”