Heat Transfer in Vertically Aligned Phase Change Energy Storage Systems

1999 ◽  
Vol 121 (2) ◽  
pp. 98-109 ◽  
Author(s):  
H. T. El-Dessouky ◽  
W. S. Bouhamra ◽  
H. M. Ettouney ◽  
M. Akbar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Energy Storage ◽  
Phase Change ◽  
Transfer Coefficient ◽  
Storage Systems ◽  
Flow Direction ◽  
Vertically Aligned ◽  
Bottom To Top

Convection effects on heat transfer are analyzed in low temperature and vertically aligned phase change energy storage systems. This is performed by detailed temperature measurements in the phase change material (PCM) in eighteen locations forming a grid of six radial and three axial positions. The system constitutes a double pipe configuration, where commercial grade paraffin wax is stored in the annular space between the two pipes and water flows inside the inner pipe. Vertical alignment of the system allowed for reverse of the flow direction of the heat transfer fluid (HTF), which is water. Therefore, the PCM is heated from the bottom for HTF flow from bottom to top and from the top as the HTF flow direction is reversed. For the former case, natural convection affects the melting process. Collected data are used to study variations in the transient temperature distribution at axial and radial positions as well as for the two-dimensional temperature field. The data is used to calculate the PCM heat transfer coefficient and to develop correlations for the melting Fourier number. Results indicate that the PCM heat transfer coefficient is higher for the case of PCM heating from bottom to top. Nusselt number correlations are developed as a function of Rayleigh, Stefan, and Fourier numbers for the HTF flow from bottom to top and as a function of Stefan and Fourier numbers for HTF flow from top to bottom. The enhancement ratio for heat transfer caused by natural convection increases and then levels off as the inlet temperature of the HTF is increased.

scholarly journals Experimental and Theoretical Investigation of the Natural Convection Heat Transfer Coefficient in Phase Change Material (PCM) Based Fin-and-Tube Heat Exchanger

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 716
Author(s):  
Saulius Pakalka ◽  
Kęstutis Valančius ◽  
Giedrė Streckienė
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Energy Storage ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Convection Heat Transfer Coefficient

Latent heat thermal energy storage systems allow storing large amounts of energy in relatively small volumes. Phase change materials (PCMs) are used as a latent heat storage medium. However, low thermal conductivity of most PCMs results in long melting (charging) and solidification (discharging) processes. This study focuses on the PCM melting process in a fin-and-tube type copper heat exchanger. The aim of this study is to define analytically natural convection heat transfer coefficient and compare the results with experimental data. The study shows how the local heat transfer coefficient changes in different areas of the heat exchanger and how it is affected by the choice of characteristic length and boundary conditions. It has been determined that applying the calculation method of the natural convection occurring in the channel leads to results that are closer to the experiment. Using this method, the average values of the heat transfer coefficient (have) during the entire charging process was obtained 68 W/m2K, compared to the experimental result have = 61 W/m2K. This is beneficial in the predesign stage of PCM-based thermal energy storage units.

A Natural Convection Fin with a Solution-Determined Nonmonotonically Varying Heat Transfer Coefficient

1981 ◽  
Vol 103 (2) ◽  
pp. 218-225 ◽  
Author(s):  
E. M. Sparrow ◽  
S. Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Transfer Coefficient ◽  
First Principles ◽  
Numerical Solutions ◽  
Flow Direction ◽  
Operating Conditions ◽  
Fluid Temperature ◽  
Wide Range

A conjugate conduction-convection analysis has been made for a vertical plate fin which exchanges heat with its fluid environment by natural convection. The analysis is based on a first-principles approach whereby the heat conduction equation for the fin is solved simultaneously with the conservation equations for mass, momentum, and energy in the fluid boundary layer adjacent to the fin. The natural convection heat transfer coefficient is not specified in advance but is one of the results of the numerical solutions. For a wide range of operating conditions, the local heat transfer coefficients were found not to decrease monotonically in the flow direction, as is usual. Rather, the coefficient decreased at first, attained a minimum, and then increased with increasing downstream distance. This behavior was attributed to an enhanced buoyancy resulting from an increase in the wall-to-fluid temperature difference along the streamwise direction. To supplement the first-principles analysis, results were also obtained from a simple adaptation of the conventional fin model.

Experimental Study of Cylindrical Latent Heat Energy Storage Systems Using Lauric Acid as the Phase Change Material

2012 ◽  
Author(s):  
Chang Liu ◽  
Robynne E. Murray ◽  
Dominic Groulx
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Energy Storage ◽  
Phase Change ◽  
Latent Heat ◽  
Storage Systems ◽  
Heat Energy ◽  
Hot Water ◽  
Energy Storage Systems ◽  
Water Flows

Phase change materials (PCMs) inside latent heat energy storage systems (LHESS) can be used to store large amounts of thermal energy in relatively small volumes. However, such systems are complicated to design from a heat transfer point of view since the low thermal conductivity of PCMs makes charging and discharging those systems challenging on a usable time scale. Results of experiments performed on both a vertical and a horizontal cylindrical LHESS, during charging, discharging and simultaneous charging/discharging, are presented in this paper. Both LHESS are made of acrylic plastic, the horizontal LHESS has one 1/2″ copper pipe passing through its center. The vertical LHESS has two 1/2″ copper pipes, one through which hot water flows, and the other through which cold water flows. Each of the pipes has four longitudinal fins to enhance the overall rate of heat transfer to and from the PCM, therefore reducing the time required for charging and discharging. The objective of this work is to determine the phase change behavior of the PCM during the operation of the LHESS, as well as the heat transfer processes within the LHESS. Natural convection was found to play a crucial role during charging (melting) and during simultaneous charging/discharging (in the vertical LHESS). However, during discharging, the effect of natural convection was reduced in both systems.

Modeling of Intramatrix Heat Transfer in Thermal Energy Storage for Asynchronous Cooling

2017 ◽  
Author(s):  
Andrea Helmns ◽  
Van P. Carey
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Energy Storage ◽  
Phase Change ◽  
Transfer Coefficient ◽  
Phase Change Material ◽  
Thermal Energy ◽  
Overall Heat Transfer Coefficient ◽  
The Matrix ◽  
Change Material

In this paper, we investigate sensible and latent heat transfer through heat exchanger matrix structures containing phase change material (PCM) in the interstitial spacing. The heat transfer is driven by a temperature difference between fluid flow passages and the phase change material matrix which experiences sensible heat transfer until it reaches the phase change material fusion point; then it undergoes melting or solidification in order to store, or reject, energy. In prior work, a dimensionless framework was established to model heat transfer in a thermal energy storage (TES) device much like effectiveness-NTU analysis methods for compact heat exchangers. A key difference, however, is that in TES units, the overall heat transfer coefficient, U, within the phase change material matrix varies spatially in the unit and with time during storage or extraction. Determination of a mean U for these processes is a key challenge to applying the effectiveness-NTU analysis to design of a TES unit. This paper assesses and identifies strategies for determining the matrix overall heat transfer coefficient in a TES unit from model predictions or experiments. The sensitivity of the TES energy efficiency to the matrix overall heat transfer coefficient is also explored, and the implications for some typical applications are discussed.

scholarly journals A numerical model and validation of phase change material integrated thermoelectric radiant cooling panel

2019 ◽  
Vol 111 ◽  
pp. 01001
Author(s):  
Hansol Lim ◽  
Hye-Jin Cho ◽  
Seong-Yong Cheon ◽  
Soo-Jin Lee ◽  
Jae-Weon Jeong
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Numerical Model ◽  
Surface Temperature ◽  
Phase Change ◽  
Transfer Coefficient ◽  
Phase Change Material ◽  
Overall Heat Transfer Coefficient ◽  
Radiant Cooling ◽  
Change Material

A phase change material based radiant cooling panel with thermoelectric module (PCM-TERCP) is proposed in this study. It consists of two aluminium panels, and phase change materials (PCMs) sandwiched between the two panels. Thermoelectric modules (TEMs) are attached to one of the aluminium panels, and heat sinks are attached to the top side of TEMs. PCM-TERCP is a thermal energy storage concept equipment, in which TEMs freeze the PCM during the night whose melting temperature is 16○C. Therefore, the radiant cooling panel can maintain a surface temperature of 16◦C without the operation of TEM during the day. Furthermore, it is necessary to design the PCM-TERCP in a way that it can maintain the panel surface temperature during the targeted operating time. Therefore, the numerical model was developed using finite difference method to evaluate the thermal behaviour of PCM-TERCP. Experiments were also conducted to validate the performance of the developed model. Using the developed model, the possible operation time was investigated to determine the overall heat transfer coefficient required between radiant cooling panel and TEM. Consequently, the results showed that a overall heat transfer coefficient of 394 W/m2K is required to maintain the surface temperature between 16○C to 18○C for a 3 hours operation.

scholarly journals Numerical Investigation on the Influence of Surface Flow Direction on the Heat Transfer Characteristics in a Granite Single Fracture

2021 ◽  
Vol 11 (2) ◽  
pp. 751
Author(s):  
Xuefeng Gao ◽  
Yanjun Zhang ◽  
Zhongjun Hu ◽  
Yibin Huang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Rate ◽  
Flow Direction ◽  
Heat Extraction ◽  
Geothermal System ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Heat Transfer Capacity

As fluid passes through the fracture of an enhanced geothermal system, the flow direction exhibits distinct angular relationships with the geometric profile of the rough fracture. This will inevitably affect the heat transfer characteristics in the fracture. Therefore, we established a hydro-thermal coupling model to study the influence of the fluid flow direction on the heat transfer characteristics of granite single fractures and the accuracy of the numerical model was verified by experiments. Results demonstrate a strong correlation between the distribution of the local heat transfer coefficient and the fracture morphology. A change in the flow direction is likely to alter the transfer coefficient value and does not affect the distribution characteristics along the flow path. Increasing injection flow rate has an enhanced effect. Although the heat transfer capacity in the fractured increases with the flow rate, a sharp decline in the heat extraction rate and the total heat transfer coefficient is also observed. Furthermore, the model with the smooth fracture surface in the flow direction exhibits a higher heat transfer capacity compared to that of the fracture model with varying roughness. This is attributed to the presence of fluid deflection and dominant channels.

Sign in / Sign up

Export Citation Format

Share Document