Search

Paraffin wax is applied to a solar water heater (SWH) as a thermal energy storage material due to its high energy density. Several previous studies have shown that integrating water and paraffin wax in the SWH tank can increase the thermal energy storage capacity. However, the thermal stratification of thermosyphon-type SWHs with horizontal tanks has not been explicitly disclosed. This paper investigates the thermal stratification of water inside the SWH tank containing paraffin wax. Paraffin wax was filled into a cylindrical capsule. The capsules were then put into the SWH tank and arranged parallel to the axis of the tank. The experiment was conducted for the duration of the charging process. The solar radiation intensity, the water, and the paraffin wax temperature were recorded. The resulting data was accustomed to graph the evolution of water and paraffin wax temperature. Based on the graph, thermal stratification was formed visually inside the tank. Stratification analysis was conjointly performed with the Richardson number calculation. The calculation shows that the value of Richardson's number is more than one. These results explain that thermal stratification occurs in the SWH tank. The addition of capsules containing paraffin wax can maintain thermal stratification. [ABSTRACT FROM AUTHOR]

Water use as a heat storage material in solar water heaters (SWH) has disadvantages, including its low energy density, which requires a large volume of thermal energy storage. Phase-change material (PCM) is a latent type of heat storage material that has the advantage of being a high energy density. Therefore, PCM is quite interesting to be applied to SWH systems. In the operation of SWH, it is necessary to know the characteristics of hot water usage. This paper aimed to determine the characteristics of a continuous and gradual discharging method on SWH that applies PCM. This study used a thermosyphon type of SWH. The tank was placed horizontally on the top side of the collector with a volume of 60 liters. Twenty-four cylindrical capsules containing paraffin wax were inserted into the tank. Thermocouples were installed on the waterside and the PCM side. Continuous and gradual methods were carried out in the discharging experiment. Experiments using a continuous discharging method given information that water temperature decrease continuously in the tank. Experiments with a gradual discharging method showed PCM's contribution, which can transfer thermal energy to the water. The gradual discharging method explained that the SWH system produced hot water that can be used for bathing as many as five people every day with water temperatures of 45 °C at an average solar radiation intensity of 514.89 W/m2. The use of PCM makes a positive contribution to the thermal energy storage in the tank. [ABSTRACT FROM AUTHOR]

The weakness of an outdoor solar water heater (SWH) experiments is the difficulty in determining its thermal behavior. The fluctuation of solar radiation intensity causes the supply of energy received by SWH also fluctuate. The result is that the thermal behavior of the SWH cannot be known for specific parameters. This paper aims to investigate the thermal behavior of an active type SWH containing paraffin wax using the constant heat flux method. A phase change material (PCM) inserted into the capsule. The capsules were arranged in a tank to form a heat exchanger (HE). The thermocouples were mounted both on the waterside and the PCM side. The solar simulator installed on the top of the collector, and the SHW system placed indoors. The heat flux and water flow were set at 1000 W/m2 and 2 LPM, respectively. The temperatures of water and PCM for 143 minutes charging recorded. The data obtained were used to analyze the thermal behavior of water and PCM. The results showed that the average heating rate of water and PCM was 0.227 °C/min and 0.205 °C/min, respectively. The value of this adjacent average heating rate shows that HE has functioned well in removing heat energy from water. The accumulated thermal energy produced was 13.08 MJ. Indoor experiments can reveal the thermal behavior of the SWH-PCM systems. [ABSTRACT FROM AUTHOR]

In the present paper, a multi-objective design optimization of a herringbone wavy fin-and-tube condenser by means of entropy generation minimization technique is presented. The objectives are to minimize the dimensionless entropy generation number associated with the heat transfer with finite temperature difference, and the fluid friction with finite pressure drop as two objective functions using Non-dominated Sort Genetic Algorithm-II (NSGA-II) technique. The results of optimal design are presented in a set of multiple optimum solutions, called 'Pareto-optimal' frontier and a final optimal solution was selected. It was found that both entropy generation rates associated with finite temperature difference and the finite pressure drop of the condenser were in optimum state. Therefore, modeling and optimization of the condenser dimensions have provided an optimal set of values for decision makers to freely select the desired heat transfer surface area and condenser volume by fully considering the specific requirements and constraints of the condenser design. [ABSTRACT FROM AUTHOR]

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]

A performance analysis based on exergetic performance coefficient (EPC) criterion was carried out for a dualevaporator vapor compression refrigeration system. The influence of the condensing and evaporating temperature on the EPC, the coefficient of performance (COP), the second law efficiency and the destruction of exergy will be presented. It is found that the evaporating and condensing temperatures have strong effects on EPC in the system. Condensing temperature increases will decrease EPC, COP, and second law efficiency, while evaporating temperature increases will increase the EPC, COP, and second law efficiency. The EPC increases and the total exergy destruction decreases with decreasing temperature difference between the evaporator and refrigerated space and between the condenser and ambient temperature. The EPC can be used for selection of optimal design parameters and the procedures given in this paper for exergy analysis of a dual evaporator vapor compression refrigeration systems has been applied to actual systems. [ABSTRACT FROM AUTHOR]

A performance analysis based on exergetic performance coefficient (EPC) criterion was carried out for a dualevaporator vapor compression refrigeration system. The influence of the condensing and evaporating temperature on the EPC, the coefficient of performance (COP), the second law efficiency and the destruction of exergy will be presented. It is found that the evaporating and condensing temperatures have strong effects on EPC in the system. Condensing temperature increases will decrease EPC, COP, and second law efficiency, while evaporating temperature increases will increase the EPC, COP, and second law efficiency. The EPC increases and the total exergy destruction decreases with decreasing temperature difference between the evaporator and refrigerated space and between the condenser and ambient temperature. The EPC can be used for selection of optimal design parameters and the procedures given in this paper for exergy analysis of a dual evaporator vapor compression refrigeration systems has been applied to actual systems. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on thermal behaviors of phase change material (PCM) during melting process in annulus cylinder. The inner cylinder was functioned as PCM storage, the outer cylinder was designed as shell, and both were made of acrylic. The PCM Storage was heated on its surface by circulating hot water as heat transfer fluid (HTF) in the shell. The variations of HTF temperature are 60, 65, 70°C and its mass flow rate is maintained at 4 liter per minutes. Thermal analysis of the melting process over time is given to provide more specific information of temperature contour change during the process. Solid--liquid melting process is shown by sequential photographs taken by the digital camera during the process in axial and radial direction. The results indicate that at the beginning of melting process, the heat transfer is dominated by conduction between inner wall of PCM storage and solid PCM. When the PCM has melt, convection holds important role in the heat transfer due to density gradient of the liquid PCM. Increasing of 5°C temperature is able to reduce about 34% of the total melting time. [ABSTRACT FROM AUTHOR]

The use of commonly used vapor compression cycle cold storage in fishing vessel is facing limitations to be widely applied in Indonesian fishermen since it consumes more energy and requires large space. Thermoelectric refrigerator is believed to be a promising option due to its simple design and low energy requirement. However, the Coefficient of Performance (CoP) of the system in current development is relatively low. Although many researches have been conducted to increase the CoP of the system But there is still lack of studies focused on effects of the important variables to cold storage performance. The present study aimed to investigate the effect of input voltage on thermoelectric cold storage chamber temperature in the form of transient behaviors. As a result, it was found that the increase of input voltage significantly affected the cooling performance, although in 6 V input voltage, the result is only a bit lower than 12 V with much lower energy use. In addition, the time needed to get steady state in 12 V was the fastest compared to the other input voltages. Those results can be used as design consideration of a portable thermoelectric cold storage. [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]