In the present paper, the numerical analyses of the heat charge and discharge processes of the latent heat energy storage (LHTES) system designed for the recovery of the exhaust waste heat energy of the SI engine presented. In the LHTES system as phase change material (PCM), the charge and discharge ability of paraffin wax commercially identified with code RT27 were analyzed depending on time. Two closed-loop fluid circulation system consisting of two heat exchangers (HESs) was designed, someone connected to the exhaust path of SI engine for waste heat recovery, and the other used for the charging and discharging of waste heat energy in the PCM. To transfer the waste heat from the hot exhaust gases to the PC, cold water was used as the heat carrier fluid. In the numerical analysis, the exhaust gas temperature and flow rate values of a single-cylinder, air-cooled having a stroke volume of 476.5 cm3 SI engine operated with gasoline at 1600 rpm engine speed and 1/2 throttle position were used. As a result, at designed LHTES system and numerical analysis performed for RT27 paraffin wax under boundary conditions, the process of heat charge (melting) completed at 8000.sec with 93% liquid-fraction, while the process of heat discharge (solidification) completed at 55000.sec with 15% liquid-fraction.

Bu çalışmada buji ateşlemeli bir motorunun egzoz atık ısı enerjisinin geri kazanımı için tasarlanan termal enerji depolama (TED) sisteminin erime ve katılaşma süreçlerinin sayısal analizleri gerçekleştirilmiştir. TED sisteminde termal enerjiyi gizli ısı olarak depolayan ve ticari olarak RT35 koduyla tanımlanan parafin mumu faz değişim malzemesi (FDM) olarak kullanılmıştır. TED sistemi için iki ısı eşanjöründen oluşan iki kapalı devre sıvı sirkülasyon sistemi tasarlanmıştır. Isı eşanjörlerinden ilki, atık ısı geri kazanımı için buji ateşlemeli motorunun egzoz yoluna, diğeri ise FDM kabında atık ısı enerjisinin şarjı ve boşaltılması için kullanıldı. FDM kabı içerisinde, RT35'in erime ve katılaşma süreçlerinde kullanılmak üzere serpantin tipi iki adet ısı eşanjörü iç içe konumlandırılmış. Sayısal analizlerde, tek silindirli ve buji ateşlemeli bir motorda gerçekleştirilen deneysel çalışmadan elde edilen egzoz gazının sıcaklık ve debi değeri kullanılmıştır. Sayısal analizler sonucunda, tasarlanan gizli ısı TED sistemi ve kabul edilen sınır şartları altında RT35'in erime işleminde 13375.sn'de %98 sıvı oranına ulaşılarak 1136 kJ'ün gizli ısı enerjisi olarak depolanabildiği, katılaşma işleminde ise 49775.sn'de %18 sıvı oranı ile 945 kJ'lük enerjisinin geri salınabildiği tespit edilmiştir.

This article presents numerical and experimental results on the melting process of phase change material (PCM) in a latent heat storage (LHTES) system designed to recover the exhaust waste heat energy of a SI engine. In the LHTES system as PCM, three different paraffin waxes, commercially identified by the codes RT27, RT35, and RT55, were used. A closed-loop liquid circulation system with two heat exchangers was designed with one connected to the exhaust line of the SI engine and the other used in the melting of the PCMs. Water was used as the heat carrier fluid to melt the PCMs with hot exhaust gases. In addition, an experimental study was conducted on a single-cylinder, air-cooled SI engine fueled by gasoline with a stroke volume of 476.5 cm3, using RT55 in the designed LHTES system. By comparing the experimental results with the analysis results, the validity of the numerical model is ensured. According to the experimental temperature results in the center of the PCM container, the error of the numerical results is approximately 7.8%, while there is a difference of 0.4 units and 2.1% in terms of PCM heat exchanger efficiency and total heat energy stored, respectively. At the end of the analyses (1440th second), performed under the same boundary conditions in the LHTES system design, the storing heat energy is as follows: 1829 kJ by 88.8% liquid fraction for RT27, 1556 kJ by 86% liquid fraction for RT35, and 1843 kJ by 83.9% liquid fraction for RT55. In addition, the PCM heat exchanger efficiency for RT27, RT35, and RT55 is 11%, 9.4%, and 11.1%, respectively.

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