Latent Thermal Energy Storage Device Research Articles

Experimental and analytical study on continuous frozen/melting processes of latent thermal energy storage driven by bubble flow

It is emphasized direct contact method that introduced to the frozen/melting processes has a high value of development due to the role for mitigating thermal stratification, reducing phase separation and enhancing heat transfer efficiency. However, the absence of fixed solid heat transfer walls can lead to discontinuous switch and difficult-to-control problem during frozen/melting processes. In this paper, the latent thermal energy storage device driven by bubble flow is experimentally investigated. With the usage of low melting point paraffin and the pattern of free expansion in a cabinet, continuous switch between the frozen and the melting process can be realized. Phase change processes, temperatures, heat transfer efficiency, volume change and pressure drops are measured and analyzed. A dynamic analytical model to describe the processes is also developed based on the ε - NTU method. The results show that the heat transfer efficiency can reach to 0.8 at least in all the experimental cases. Moreover, this study records the pressure difference of the gas flow, predicts the required input mechanical work and analyses the volumetric heat transfer coefficient, which help to reveal feasibility of the device.

Experimental and numerical investigations of latent thermal energy storage using combined flat micro-heat pipe array–metal foam configuration: Simultaneous charging and discharging

Simultaneous charging and discharging (SCD) of the latent thermal energy storage (LTES) can improve the flexibility of solar thermal systems and ensure the continuity of energy supply. Experiments and numerical simulation are conducted in this study to reveal the SCD thermal behavior of LTES device using flat micro-heat pipe array–metal foam composite structure. The effects of heat transfer fluid (HTF) temperature, volumetric flow, initial phase change material (PCM) state, and metal foam are analyzed. Results show that PCM absorbs heat from hot HTF or releases heat to cold HTF at the beginning depending on the PCM and HTF temperatures. The SCD eventually reaches an approximate steady state, cold HTF exchanges heat directly with hot HTF, power and PCM temperature remain unchanged. Low cold HTF temperature quickly reaches steady state and low final PCM temperature but has no influence on steady state power. PCM initial state and metal foam porosity do not affect the steady state power and final PCM temperature. However, they affect the time to reach steady state. Metal foam pore density has no obvious effect on SCD. SCD has more stable discharging performance than single discharging, especially when the cold HTF temperature is high.

Numerical and experimental investigations of latent thermal energy storage device based on a flat micro-heat pipe array–metal foam composite structure

Latent heat thermal energy storage (LHTES) is crucial in the application of renewable energy and waste heat recovery. A novel LHTES device with a flat micro-heat pipe array (FMHPA)–metal foam composite structure is designed in this study to obtain excellent heat transfer performance. An evaluation standard called integrated power is proposed to assess and compare the structural advantages of the LHTES device with others. Performances of FMHPA, temperature distribution, effort of inlet temperature and velocity of heat transfer fluid (HTF) are also studied in the experiments. A three-dimensional numerical model is developed to investigate the effort of porosity and pore density of metal foam on the charging process. Results show that the FMHPA–copper foam composite structure improves the performance of the LHTES device. This structure exhibits stronger heat transfer performance than that of other devices. The increasing inlet temperature of HTF has a better promotion effect on power than raising HTF velocity. High porosity is conducive to natural convection but detrimental to heat conduction. High pore density is disadvantageous to natural convection and does not affect heat conduction. • Strengthen of flat micro-heat pipe arrays and metal foam are studied. • The temperature distribution of PCM are experimentally studied. • The effect of temperature and velocity of HTF are experimentally studied. • The porosity and pore density of copper foam are numerically studied. • An evaluation standard is proposed to evaluate the structural advantages.

Investigation on charging enhancement of a latent thermal energy storage device with uneven tree-like fins

The charging intensification of latent thermal energy storage (LTES) devices has an important meaning for solar energy applications. For a more uniform temperature and faster melting rate of LTES devices, uneven tree-like fins are applied and optimized here. Numerical research of melting behaviors in tree-like finned LTES devices is performed with a particular focus on fin layouts. The melting interface transformation and transient temperature distribution in four LTES devices are examined. Moreover, the roles of fill angle and central-angle gradient in melting performance are studied for the optimization of uneven tree-like fins. The results indicate that uneven tree-like fins considerably improve energy charging performance since the heat conduction enhancement exceeds the free convection suppression. Compared with uniform tree-like fins, the uneven tree-like fins lead to a more uniform temperature distribution and consistently faster melting rate by the synergetic improvement of free convection and heat conduction in LTES devices. More significantly, the optimal fill angle and the central-angle gradient are suggested to be 300° and 8° for maximizing the melting performance. Correspondingly, the complete melting time of the optimal LTES devices with heterogeneous and gradient tree-like fins respectively decrease by 49% and 46% compared to LTES devices with uniform tree-like fins.

Investigation of charging and discharging characteristics of a horizontal conical shell and tube latent thermal energy storage device

In this study, a numerical model to analyse the charging and discharging characteristics of a horizontal shell and tube type Latent Heat Storage (LHS) prototype is presented. The system comprises of Sodium Nitrate as phase change material (PCM) in the shell side and flow of air as heat transfer fluid (HTF) in the tube side. The effective heat capacity approach is followed while solving the fluid flow and energy interactions in the PCM. The design is optimized by modifying a cylindrical shell into a conical shell heat exchanger system. The optimized values of diameters at inlet and outlet of the conical shell are found to be 98.6 mm and 54 mm, respectively having a cone angle of 3.4°. A performance comparison is made with a cylindrical shell system of equivalent storage capacity. 3-D numerical simulations performed on the proposed system revealed that an innovation in the design leads to enhanced heat transfer rate caused by uniform melting throughout the system. Further, the conical shell model is numerically simulated for various operating parameters such as inlet HTF velocity and temperature. Also, the effect of fins attached on the HTF tube on the performance of the system is analysed. With the advent of advanced heat exchanger design, there is a greater scope of obtaining higher heat transfer rates employing the proposed conical shell and tube LHS system.

Fast and experimentally validated model of a latent thermal energy storage device for system level simulations

Latent storages utilising phase change materials (PCM) to store thermal energy offer a considerably higher energy density at a nearly constant temperature level in comparison to sensible storage systems. Despite this advantage, only a few latent storage technologies have been integrated successfully to the market. This may be due several engineering challenges and in particular the lack of a computationally fast and accurate mathematical model to facilitate the optimal incorporation of latent heat storages into an energy system. The presented study fills this gap and proposes a new, fast and experimentally validated mathematical modelling approach for latent heat storage units. The numerical model proposed combines high accuracy, low computational effort and numerical stability. The validation was performed with two different commercial latent storage units supplied by Sunamp Ltd. with a nominal phase change temperatures of 34 °C and of 58 °C. Both units use a salt hydrate based phase change material in combination with a fin-tube heat exchanger. The proposed model may be used for both fast system level performance investigations as well as latent storage design for a given application. It may therefore be implemented in commercial software packages such as TRNSYS [1] or Simulink [2].

Experimental investigation on the heat transfer performance of a latent thermal energy storage device based on flat miniature heat pipe arrays

An experimental latent-thermal energy storage device (LTESD) with a flat miniature heat pipe array (FMHPA) as a core heat transfer element is designed. Multihole flat pipes are utilized as a heat supply and heat removal loop for the passage of heat transfer fluid (HTF). Experiments are performed at different HTF volume flow rates and inlet temperatures to investigate the performance of the thermal storage unit consisting of FMHPA and vertical fins and to observe the change in the temperature of phase-change materials, such as lauric acid. The effects of heating/cooling section length and thermal resistance are also examined. Results indicate that LTESD works stably and efficiently and the respective storing and releasing power are 1299 and 1120 W under standard operating conditions of 2 L/min at 70 °C and 2 L/min at 15 °C.