A review of performance enhancement of PCM based latent heat storage system within the context of materials, thermal stability and compatibility

TLDR: In this article, the authors focused on the classification of various paraffins and salt hydrates, and provided an understanding on how to maximize thermal utilization of PCM and how to improve the phase transition rate, thermal conductivity, latent heat storage capacity and thermo-physical stability.

About: This article is published in Energy Conversion and Management.The article was published on 2016-05-01 and is currently open access. It has received 484 citations till now. The article focuses on the topics: Thermal energy storage & Heat transfer.

Figures

Table 2 Comparison of various PCM groups.

Table 1 Key design properties of PCM for storage purposes.

Table 5 A list of compatible PCM with container material.

Table 6 Performance enhancement using multiple PCM [98]

Table 4 Thermo-physical properties of Salt Hydrates

Frequently asked questions

Q1. What is the way to increase solidification rate of a lhs system?

Encapsulation 906 having higher thermal conductivity, lower temperature at external surface and smaller diameter of 907 capsule can increase solidification rate of LHS system. 

Q2. What can be controlled by adding suitable thickener and nucleating agents?

Salt hydrates faces phase segregation and supercooling, 876 which can be controlled by adding suitable thickener and nucleating agents. 

Q3. What are the two main causes of the melting of PCMs?

It is noticed that conduction heat transfer and natural convection are responsible for melting behaviour of 880 PCMs in containers with different shapes. 

Q4. What is the effect of encapsulation on the performance of PCM?

Encapsulation ensures 726 the sustainability of true composition of PCM that can be altered by connection with surrounding, reduces the 727 possibility of surrounding reaction with PCM, improves thermal and mechanical stability, improves heat transfer 728 rate and compatibility with hazardous PCMs that cannot be exposed to surrounding such as building temperature 729 control, food storage and blood transport applications. 

Q5. What is the effect of random type of carbon fibers on the thermal performance of paraffin wax?

in case of small mass fraction of carbon fibers, the randomly oriented carbon fibers 663 dampened the natural convection and thus resulted in lower melting rate than pure paraffin. 

Q6. What was the effect of fins on the thermal conductivity of PCM?

It was noticed that an increase in fins number, thickness and 470 height amplified the thermal conductivity in lower portion of PCM causing enhanced heat transfer rate and 471 melting rate. 

Q7. What is the effect of the inclusion of high density additives on the storage capacity of PCM?

the inclusion 892 of high density additives can reduce storage volume for PCM in container and it can lead to loss in 893 storage capacity. 

Q8. What is the way to improve the thermal performance of PCM?

The melting and solidification rate of PCM can be enhanced significantly by incorporating high thermal 891 conductivity additives as it will increase the thermal conductivity of LHS system. 

Q9. What is the possibility that the additives can settle at the bottom of the container?

640Due to higher density of metal particles and metal structures, there is a possibility that the additives can settle at 641 the bottom of container and increasing the weight of container. 

Q10. How long did the inclusion of graphite keep the water temperature above 54 o C?

The inclusion of 822 encapsulated PCM-graphite maintained the temperature of water top layer in storage tank above 54 o C for 10-12 823 hours. 

Q11. What is the critical external radius for copper, PVC and glass?

As 855 constant mass of PCM resulted in constant internal radius of 0.05m, the critical external radius for copper, PVC 856 and glass were found to be 17.46 m, 0.003 m and 0.054 m, respectively. 

Q12. How did Shin et al. investigate the thermal performance of sodium acetate trihydrate?

the inclusion of expanded graphite increased the thermal conductivity of hydrated salts 594 to 3.643 W/mK. 595H.K. Shin et al.[87] investigated the thermal performance enhancement of sodium acetate trihydrate by 596 inserting various weight percentages of expanded graphite. 

Q13. What is the way to test the stability of the PCMs?

Before using industrial grade PCMs, it is advised to run the repeated thermal 878 cycle test to check the stability of thermo-physical properties. 

Q14. How many cycles should be used to test the stability of the PCMs?

Murat and Khamid [15] suggested that prior to 130 commercial development; the PCMs should be subjected to at least 1000 thermal cycles to examine the long 131Page | 16term stability. 

Q15. What are the advantages of using a double pipe as heat storage?

the double pipe with graphite 525 matrix, double pipe with fins and compact heat exchanger can be utilized as heat storage containers. 

Q16. What is the effect of the number of fins on the thermal performance of a LHS?

In addition, the number of fins in a LHS system can affect the thermal 534 storage capacity of container due to small volume for PCM. 

Q17. How much did the addition of graphite reduce the melting time?

the addition of 13%wt. of expanded 837 graphite reduced the melting and solidification time by 60% and 40%, respectively. 

Q18. How many dimensions of fins were recommended for the simulated PCM?

the recommended values for number of fins, dimensionless thickness and 473 dimensionless height were 7, 0.1 and 0.8, respectively.