Discharging Characteristics of Graphite Matrix–PCM Composites in a Tube-in-Shell TES System under Different Operating Conditions

Öz

The inherently low thermal conductivity of phase change materials (PCMs) significantly limits their applicability in thermal energy storage (TES) systems. To address this limitation, carbon-based porous matrices are widely utilized to establish highly conductive thermal networks, enhancing overall thermal conductivity, accelerating heat recovery, and improving energy efficiency. In this study, a numerical investigation validated by a small-scale experimental setup is conducted to evaluate the heat recovery performance of a paraffin/graphite matrix composite in an annular geometry with various configurations and operating conditions. Graphite matrices with bulk densities of 23 kg/m³, 50 kg/m³, and 100 kg/m³ are used to encapsulate the paraffin a a storage material. Two-dimensional (2D) and three-dimensional (3D) models were developed, and the effects of varying wall temperatures and inlet parameters (temperature and velocity) on the discharging process were comparatively analyzed. Simulations are performed at three temperature levels (20 °C, 30 °C, and 40 °C), representing practical applications such as tap water, thermal power plant cooling water, and low-temperature geothermal systems. The results indicate that increasing wall or inlet temperatures prolongs the solidification process by reducing the thermal gradient between the PCM and the heat transfer fluid. In contrast, the mass flow boundary condition enhances heat recovery compared to the isothermal wall configuration, resulting in shorter discharge times.

Anahtar Kelimeler

• thermal energy storage
• discharging
• solidification
• energy recovery
• phase change materials
• graphite matrix
• heat transfer enhancement

Etik Beyan

No ethical issues are associated with the publication of this manuscript.

Halkasal Aralık TES Sistemlerinde Grafit Matris-FDM Kompozitlerinin Farklı Çalışma Koşullarındaki Deşarj Karakteristikleri

Öz

Faz değiştiren maddelerin (FDM) düşük ısıl iletkenliği, termal enerji depolama (TED) sistemlerindeki uygulanabilirliğini önemli ölçüde sınırlamaktadır. Bu sınırlamayı gidermek amacıyla, karbon bazlı gözenekli matrisler yüksek iletkenliğe sahip ısıl ağlar oluşturmak için yaygın olarak kullanılmakta; bu sayede toplam ısıl iletkenlik artırılmakta, ısı geri kazanımı hızlandırılmakta ve sistem verimliliği iyileştirilmektedir. Bu çalışmada, farklı konfigürasyon ve çalışma koşulları altında, halkasal geometriye sahip bir sistemde grafit matris-FDM kompozitin deşarj karakteristikleri sayısal olarak incelenmiş ve elde edilen bulgular küçük ölçekli bir deney düzeneği ile doğrulanmıştır. 23 kg/m³, 50 kg/m³ ve 100 kg/m³ yoğunluklara sahip grafit matrisler, parafini depolama malzemesi olarak kapsüllemek için kullanılmıştır. İki boyutlu (2B) ve üç boyutlu (3B) modeller geliştirilmiş; farklı duvar sıcaklıkları ile akışkan giriş parametrelerinin (sıcaklık ve hız) deşarj süreci üzerindeki etkileri karşılaştırmalı olarak analiz edilmiştir. Mevcut çalışmanın özgünlüğü, aynı halkasal grafit matris-FDM kompozit TED ünitesi içerisinde idealleştirilmiş 2B izotermal duvar sınır koşulunun, ITA bölgesi, giriş sıcaklığı, giriş hızı, taşınım ısı transferi ve ITA sıcaklığının eksenel gelişiminin doğrudan dikkate alındığı daha fiziksel olarak temsil edici 3B kütlesel debi sınır koşulu ile karşılaştırılmasında yatmaktadır. Simülasyonlar, musluk suyu, termik santral soğutma suyu ve düşük sıcaklıklı jeotermal sistemleri temsil eden üç farklı sıcaklık seviyesinde (20°C, 30°C ve 40°C) gerçekleştirilmiştir. Sonuçlar, duvar veya giriş sıcaklığındaki artışın, FDM ile ısı transfer akışkanı arasındaki sıcaklık farkını azaltarak katılaşma sürecini uzattığını göstermiştir. Buna karşılık, kütlesel debi sınır şartının uygulanması, izotermal duvar koşuluna kıyasla daha hızlı ısı geri kazanımı sağlayarak deşarj sürelerini kısaltmıştır. Maksimum termal enerji geri kazanım oranı, 100 kg/m3 yığın yoğunluğu, 20°C HTF giriş sıcaklığı ve 0.3 m/s giriş hızı koşulunda elde edilmiştir. Bulgular ayrıca, daha düşük yığın yoğunluklarının kapasite odaklı TES işletimi için daha uygun olduğunu, buna karşılık daha yüksek yığın yoğunluklarının güç odaklı ısı geri kazanım uygulamaları için daha avantajlı olduğunu göstermiştir.

Anahtar Kelimeler

• termal enerji depolama
• deşarj
• kKatılaşma
• enerji geri kazanımı
• faz değiştiren maddeler
• grafit matris
• ısı transferi iyileştirme

Etik Beyan

Bu makalenin yayınlanmasıyla ilgili herhangi bir etik sorun bulunmamaktadır.

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