Tube Latent Heat Thermal Energy Research Articles

Performance investigation of shell and helical tube heat energy storage system with graphene dispersed erythritol PCM

AbstractExperimental investigation on the thermal performance of a shell and helical tube latent heat thermal energy storage system for medium temperature applications is reported in the article. Commercial grade erythritol having a melting temperature of 120°C was employed as the phase change material (PCM). The thermal conductivity of the erythritol had been usually very low (0.73 W/mK) and it results in low heat transfer rates during both charging and discharging processes. In the study, an attempt was made, this inherent limitation of erythritol, high thermal conductive graphene nanoparticles, which are dispersed into erythritol matrix, referred to as nanoparticle dispersed phase change material (NDPCM). The effect of the addition of graphene nanoparticles on the performance of the storage system such as heat flow rate, overall heat transfer coefficient, charging and discharging efficiency and effectiveness was evaluated and compared with the storage system with only base erythritol during both energy storage and retrieval processes. The efficiency of the NDPCM system increased to 16.29% during the storage period and 28.48% during the retrieval period compared with the base PCM system. Further, it was observed that the effectiveness is about 14% greater at the beginning of the melting process and about 12% greater at the beginning of the solidification process for NDPCM.

Design of non-uniformly distributed annular fins for a shell-and-tube thermal energy storage unit

The shell and tube latent heat thermal energy storage systems are widely recognized as one of the most effective ways to store and utilize solar energy due to their high energy density, constant storage/releasing temperature, structural feasibility and rational price. The application of fins is an effective method to enhance heat exchange through extend the heat transfer surface area. However, there existed strong uneven melting behavior including melting fraction, temperature uniformity in a vertical thermal energy storage unit. To improve its uniformity of melting fraction and temperature, this study designed various conditions for fin pitch and positions in a non-uniform pattern to reduce the inhomogeneity for the melting process. Numerical models were established and validated by the experimental measurement conducted in this study. The effects of fin pitch and position on the thermal performance of the melting process were quantified via analyzing the melting front evolution, temperature and velocity distribution, melting rate and temperature uniformity. Results demonstrated that a 62.8% and 34.4% reduction in full melting time and average temperature difference in the phase change material region was separately obtained for the thermal energy storage unit with non-uniformly distributed annular fins, compared to the original case with uniform fins. Besides, the melting rate uniformity was also improved by 84.7%. The non-uniform design on fin position and pitch give a perspective to enriching the design methods for practical application in engineering.

Charging time and energy storage rate analysis of fin effect inside the horizontal tube for thermal energy storage

Clean energy storage is of vital importance for cleaner production and environmental protection. This present study focuses on the promotion of clean energy storage efficiency in the widely used shell and tube latent heat thermal energy storage unit. The enhancing effects of fin inside the tube on the charging time and energy storage rate are studied. Numerical investigations are performed through the enthalpy based lattice Boltzmann method couple with curved boundary. Three kinds of configurations for one-fin and two-fin are investigated. Results indicated that fin position can effectively impact the enhancing effects. For one-fin, the maximum difference of the enhanced ratio for different fin positions is 15.17% when Ra = 107, while it is 7.52% for two-fin. The optimal fin position varies with different Ra, but with appropriate approximation, it can be concluded that one-fin on the bottom and two-fin on the vertical direction are the optimal fin position for one-fin and two-fin cases. In addition, one long fin shows better enhancing effects than two short fins. Under the same fin length, the average enhanced ratio for one long fin is 41.82%, while it is only 27.03% for two short fins. These results can provide guidance for the fin configuration in the shell and tube latent heat thermal energy storage unit to achieve higher energy storage efficiency. Since this unit is widely used in various clean energy storage systems, the results would also be beneficial for various industrial applications of clean energy storage and utilization.

A numerical study on the combined effect of dispersed nanoparticles and embedded heat pipes on melting and solidification of a shell and tube latent heat thermal energy storage system

Abstract The thermal analysis of melting and solidification processes of Rubitherm 55 in a vertical shell and tube based latent heat thermal storage unit is presented in this study. To resolve the low heat transfer rate issue within the phase change material due to its low thermal conductivity, hybrid enhancement methods are considered. Heat pipes are placed horizontally to act as a bridge between the heat transfer fluid and the phase changed material stored in the shell. In addition, nanoparticles with high thermal conductivity are added to the phase change material. Aluminum oxide, silver, copper and copper oxide are the nanoparticles used for this study. The effects of various parameters, such as the heat pipes quantity, nanoparticles type, and concentration are studied on the overall performance of the system. It was concluded that embedding heat pipes significantly decreases the melting and solidification times. It was also shown that increasing the nanoparticles concentration decreases the melting or solidification time as well as the stored or released energy per unit of mass. However, the significance of the effect of type of nanoparticles was dependent upon the quantity of the heat pipes in the storage unit.

Transient performance analysis of concentrating solar thermal power plant with finned latent heat thermal energy storage

This paper presents the effect of finned multitube shell and tube latent heat thermal energy storage system (LHTES) on the dynamic performance of the Rankine cycle based solar thermal power plant. A widely available phase change material (PCM), sodium nitrate is kept in the shell side. As PCM and HTF have low thermal conductivities, fins are attached on the inner and outer surfaces of the HTF tubes. A simplified thermal resistance network-based energy equation coupled with the enthalpy technique, is developed for analysing heat transfer in the LHTES. The effects of number of fins (Np = 12, 24, 36 and 48) and fin thickness (tf = 1, 2, 3 and 4 mm) on the PCM side of LHTES on the overall performance of the solar power plant for generating electricity after sunset are investigated for an Indian condition on cloudy days. The addition of fins in LHTES is found to reduce the time for continuous power generation. The marginal changes in melt fraction of PCM and turbine output power are found for the number of fins and fin thickness greater than 36 and 2 mm, respectively. The maximum discharge efficiency occurs at the number of fins of 48.

Solidification performance of a latent heat storage unit with innovative longitudinal triangular fins

In this paper, an innovative longitudinal triangular fin was proposed to improve the solidification performance of shell and tube latent heat thermal energy storage (LHTES) device. At first, the solidification behaviors (solid fraction, temperature distribution and solidification time) of two different layouts of innovative fins (Fin-B, Fin-C) were compared with the traditional rectangular fin (Fin-A). Then, the dynamic temperature response of the fins with superior performance were analyzed. In addition, the influences of the fin geometrical parameters, initial temperature and fin materials on the solidification performance were studied and discussed. The results showed that the innovative longitudinal triangular fins can significantly improve the solidification performance of PCM in LHTES, and the Fin-C had better heat transfer efficiency and superior solidification performance among the three types of fins. The solidification time of Fin-C-Ⅰ decreased 38.30% significantly compared with the traditional rectangular Fin-A. Generally, the solidification time decreased by decreasing the initial temperature, or increasing the thermal conductivity and the fin heights. However, the effect of the bottom width of triangular fin on the solidification performance can be neglected. To achieve a faster cooling rate, the recommended temperature difference between the inner wall and PCM was over 20 K.

Latent heat thermal storage with variable porosity metal matrix: A numerical study

Abstract In this paper, a novel design of multitube shell and tube latent heat thermal energy storage system (LHTES) with variable porosity metal matrix in PCM is presented. The shell side of the LHTES contains a phase change material, whereas heat transfer fluid (HTF) flows through seven tubes with internal fins. Metal matrix, as a thermal conductivity enhancer (TCE), is used to augment heat transfer in PCM, however the temperature distribution in PCM is found to be non-uniform along the length of the storage system for constant porosity metal matrix in PCM, which affects the thermal performance of the LHTES. A numerical model is developed to investigate the fluid flow and heat transfer characteristics using the momentum equation and the two-temperature non-equilibrium energy equation coupled with the enthalpy method to account for phase change in PCM. The numerical model is first validated with the experimental results and further extended to identify the effects of geometrical parameters on the temperature distribution in PCM. A relationship between porosity and ratio of length to annular diameter of the storage system is developed for porosity varying from 0.95 to 0.85. It is found that the size of LHTES with variable metal matrix porosity can be reduced for the same effectiveness.

Experimental thermal storage research of organic binary phase change materials in building environment

ABSTRACTThis paper aims to reveal the heat transfer mechanism of low-temperature phase change material (PCM) and design PCM heat storage device in building heating environment. Firstly, low-temperature binary PCMs of lauric acid and stearic acid are prepared, and their thermal properties are investigated by DSC. Then, shell and tube latent heat thermal energy storage units are conducted, and heat transfer experiments are carried out to analyze the heat transfer mechanism of PCM. The results demonstrate that natural convection plays an important role in heat transfer process, and the heat storage efficiency of PCMs can be significantly enhanced by increasing the fin width and improving the inlet heat transfer fluid (HTF) temperature. Furthermore, some proposals are put forward to guide the design of PCM storage device in building heating environment.

Techno-economic analysis of a concentrating solar collector with built-in shell and tube latent heat thermal energy storage

In this paper, the feasibility of a medium temperature, low profile concentrated solar thermal collector integrated with latent heat thermal energy storage (LHTES) is investigated. The proposed modular integrated collector storage (ICS) system consists of six solar receiver units and seven cylindrical shell and tube LHTES tanks. By implementing an innovative optical concentration assembly and an internal linear tracking mechanism, the collector can concentrate beam radiation to the tube receivers during the highest flux hours of a day without any external or rotational motion. The collector's efficiency correlations were obtained experimentally and its integrated performance – with the LHTES units – was evaluated numerically.To demonstrate the potential of this proposed ICS system, an annual analysis was carried out for a characteristic industrial application – a dairy dehydration process that requires a constant 50 kWth of heat in the 120–150 °C temperature range. It was found that adding the storage units will increase the capital costs by ∼10%, but it can increase the annual thermal output of the system by up to ∼20%. A solar fraction of 65% was achievable with some design alternatives, but the optimum techno-economic design had a solar fraction of ∼35% and an annual charging efficiency of nearly 100%. It was also found that if the capital cost of the ICS (collector and LHTES tank) system could be reduced by 50% from an estimated ∼1000 US$/m2 to ∼500 US$/m2 through mass production and/or further design optimizations, this system could provide industrial process heat with a levelized cost of heating (LCOH) of ∼0.065 US$/kWhth.

Experimental Analysis and Numerical Modeling of a Shell and Tube Heat Storage Unit with Phase Change Materials

Thermal storages are part of highly integrated energy systems. The development of accurate and reduced models is critical for efficient simulations on a system-level and the analysis of the storage design, control, and integration. We present the experimental analysis and numerical modeling of a lab-scale shell and tube latent heat thermal energy storage (LHTES) unit with a (latent) storage capacity of about 10–15 kWh. The phase change material (PCM) is a high density polyethylene (HD-PE) with phase change temperatures between 120 and 135 °C. An efficient 2D numeric storage model is derived which accounts for design and material parameters of PCM, storage, and heat transfer fluid (HTF). Different probability distribution functions are used to model the PCM apparent specific heat capacity. From these functions the state of charge (SOC) can be predicted, which indicates the extent to which a LHTES is charged relative to storeable latent heat. Model predictions are fitted to experimental data from thermophys...

Design and feasibility of high temperature shell and tube latent heat thermal energy storage system for solar thermal power plants

A simple shell and tube heat exchanger provides a straightforward design for near-term integration of latent heat thermal energy storage (LHTES) systems in concentrated solar thermal-tower (CST-tower) plants, but currently there is no literature available for this configuration in the 286–565 °C temperature range. Therefore, the primary objective of this work is to evaluate the potential of this configuration for CST-tower plants. In addition, a proper design method of this storage configuration should simultaneously account for the effects of geometric parameters and the number of modules. The present work optimizes these parameters for market ready phase change materials (PCM) that are suitable in the aforementioned temperature range. This optimization consisted of fixing the PCM volume while varying the other geometric parameters (namely, L, L/d, R/ro) simultaneously over a wide range. The goal was to achieve the highest amount of total stored/delivered energy with a minimum heat transfer surface area. This analysis revealed that there was an optimum area between 36 and 63 m2 GJ−1 (or 0.12–0.22 m2 kWhth−1), depending on the PCM employed. This optimum surface area can be obtained with several combinations of geometric parameters, but only certain combinations were found to achieve the highest total stored/delivered energy. The charging and discharging efficiency for the selected PCMs was found to be ∼99% and 75–85%, respectively. Using the optimized designs, the cost of this shell and tube LHTES system was found to vary between 27 and 170 US$ kWhth−1, which indicates that with further development it may be competitive with conventional sensible storage systems (e.g. two-tank molten salts).

Numerical investigation of heat transfer mechanism in a vertical shell and tube latent heat energy storage system

The thermal behavior and heat transfer characteristics of a vertical cylindrical shell and tube latent heat thermal energy storage (LHTES) unit are investigated using a pure thermal conduction model and a combined conduction-convection heat transfer model, respectively. The results from numerical simulation are validated with published experimental data which indicate that the combined convection and conduction model can better describe the energy transfer in the phase change materials (PCMs) during melting process. In contrast, heat transfer by conduction is more significant during the solidification process. In terms of total solidification time, the two models show little difference.