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Heat exchanger is a device that used to transfer heat between two fluids. Heat exchanger performance depends on the fluid's Nusselt number. The greater the fluid's nusselt number, the greater heat transfer will be. There are several ways to enhance Nusselt number such as adding twisted tape in tube and using nanofluids as working fluids. But by using the method mentioned before it can also increase the pressure drop along the pipes. So it must to be examined is it worth the enhance in heat transfer compared to increase of pressure drop that happen. This article try to modeling parallel heat exchanger that use twisted tape with twist ratio 7.35, 5.25, 4.72 and nanofluids with volume fraction 0 %(base fluid) 0.1% and 0.3% from the experiment that had done. Nanofluid assumed as homogenic fluid and have characteristic as studied in previous research. From simulation using ANSYS Fluent showed that the usage of twisted tapes with twist ratio 7.35, 5.25, 4.72 increase the Nusselt number by 131.88 %, 142.271 %, 145.82 % and increase the pressure drop by 232.52 %, 280.23 %, 304.50 % respectively compared to usage of plain tube with base fluid, furthermore the usage of nanofluids with fraction volume 0.1 % and 0.3% increase the Nusselt Number by 6.72 %, 13.85 % and pressure drop by 14.01 %, 37.09 % respectively compared to usage of plain tube with base fluid. From simulation also showed that twisted tape with twist ratio 7.35 and using base fluid as working fluid give the highest thermal performance compared to the others. [ABSTRACT FROM AUTHOR]

The purpose of this study is to observe the effect on the performance of a double pipe-concentric heat exchanger as the effect of the addition of twisted tape insertions and nanofluids TiO2/TermoXT 32 as the working fluid. Experiments were carried out on a test rig that consists of two pipes with an inner pipe diameter of 38.1 mm for the inside pipe and inner pipe diameter of 75.2 mm for the outside pipe. The working fluid, nanofluids, were constantly flowed and maintained at a low temperature of 20°C. The flow rate was varied at 10 LPM; 12 LPM; 14 LPM; 16 LPM; 18 LPM; and 20 LPM. Twisted tape insertions which are used in the experiment were made of Aluminum and have three variations of twist ratio which are 7.35; 5.25; and 4.72. The nanofluids TiO2/TermoXT 32 has 3 volume fraction variations of 0% (base fluid); 0.1%; and 0.3%. The results showed that the addition of twisted tape insertions led to the increased heat transfer rate. This increment was indicated by the increase of Nusselt number for each measurement planning. The increase of Reynolds number was followed by the increase of heat transfer rate. Moreover, the increasing volume fraction of nanofluids TiO2/TermoXT 32 also influenced the performance of heat exchanger. The highest heat transfer rate was demonstrated by the highest Nusselt number that observed on the twist ratio of 4.72 and Reynolds number of 20 LPM. On top of that, the volume fraction of 0.3% also produced the optimal Nusselt number. The experiments showed the best-operating conditions were found in the specification of 0.3% nanofluids volume fraction with 4.72 twisted tape ratio. [ABSTRACT FROM AUTHOR]

Latent heat storage (LHS) has been widely used for energy storage. Compare to sensible heat storage, LHS has several benefits because of its high energy density, small unit sized and operating at low temperature. This paper is aimed to investigate the melting characteristic of phase change material (PCM) implemented in concentric double pipe heat exchanger. The investigation is carried out by both simulation as well as validation. The simulation is conducted using ANSYS FLUENT with double pipe shape of heat storage. The geometrical shape of the storage is double pipe heat exchanger, the PCM is stored in the inner tube meanwhile hot water is circulated in the outer tube. The dimension of the inner tube are 5 cm of diameter and 50 cm length. The diameter of outer tube is 10 cm and 60 cm length. The hot liquid is circulated from the inlet port and withdrawing from the outer port. The inlet and outlet ports are located away at the distance of 5 cm from the edge of the outer tube. The inlet and outlet ports are constructed at the bottom and upper part of the outer tube. The simulation is carried out at temperature 60oC of the hot liquid and flow rate at 4 liters per minute. The validation is also conducted at the same configuration with that on the simulation. The tweaked parameters are number of mesh and mushy-zone value. Results revealed that validation is numerically accepted at deviation less than 5% for melting time deviation. The validation is obtained at number of mesh is 144,000 and mushy-zone value is 1.4x107. On the evaluation of temperature distribution similarity, all of coefficient correlation are obtained greater than 0.8 between simulation and experiment. Being a valid simulation model, it is enabled to be enhanced for predicting melting of phase change materials on the heat energy storage system. [ABSTRACT FROM AUTHOR]