A Novel Double-Pipe Heat Storage Unit

2016 ◽  
Author(s):  
A. Rozenfeld ◽  
Y. Kozak ◽  
T. Rozenfeld ◽  
G. Ziskind
Keyword(s):  
Heat Transfer ◽  
Heat Storage ◽  
Solid Phase ◽  
Close Contact ◽  
Contact Melting ◽  
Melting Time ◽  
Water Tank ◽  
Storage Unit ◽  
Double Pipe ◽  
Pipe Heat

This research is an experimental investigation of a double-pipe heat storage unit. The inner pipe of the unit, through which a heat-transfer fluid (HTF) is supplied, is made of aluminum and has an outer helix-like fin. The annular space between the pipes is filled with a phase change material (PCM). Actually, this research presents a novel design of the heat storage unit, which, unlike traditional designs with e.g. radial (circumferential) or longitudinal fins, has a single fin which does not divide the shell volume into separated cells. Moreover, this research focuses on close-contact melting (CCM), a process which is characterized by detachment of the solid bulk from the unit envelope and its sinking towards the hot fin surface. In previous investigations, performed in our laboratory, this effect has been achieved in units with above-mentioned traditional fin configurations. It was demonstrated that CCM reduces the overall melting time, i.e. the rate of unit charging, significantly as compared with commonly encountered melting in which the fins serve just to enlarge the heat transfer area. The experimental system employed in this study includes a vertically-oriented double-pipe heat storage unit and thermostatic baths capable of providing hot or cold HTF. The unit has a transparent Perspex shell which makes visualization possible. The entire unit may be placed in a heated water tank with transparent walls. In the latter case, close-contact melting is achieved by detaching the solid phase from the envelope and thus allowing its gravity-induced motion. Regular melting is compared to CCM and advantages of the latter are demonstrated. Also demonstrated are the advantages of the novel fin, including in solidification. Possible mathematical and numerical modeling of the melting processes is discussed.

Analysis of a Latent Heat Storage Device With Radial Fins

2013 ◽  
Author(s):  
Y. Kozak ◽  
T. Rozenfeld ◽  
G. Ziskind
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Latent Heat ◽  
Close Contact ◽  
Thermal Storage ◽  
Ambient Air ◽  
Contact Melting ◽  
Storage Device ◽  
Melting Time ◽  
Cfd Model

Phase-change materials (PCMs) can store large amounts of heat without significant change of their temperature during the phase-change process. This effect may be utilized in thermal energy storage, especially for solar-thermal power plants. In order to enhance the rate of heat transfer into PCMs, one of the most common methods is the use of fins which increase the heat transfer area that is in contact with the PCM. The present work deals with a latent heat thermal storage device that uses a finned tube with an array of radial fins. A heat transfer fluid (HTF) flows through the tube and heat is conducted from the tube to the radial fins that are in contact with the bulk of the PCM inside a cylindrical shell. The thermal storage charging/discharging process is driven by a hot/cold HTF inside the tube that causes the PCM to melt/solidify. The main objective of the present work is to demonstrate that close-contact melting (CCM) can affect the storage unit performance. Accordingly, two different types of experiments are conducted: with the shell exposed to ambient air and with the shell submerged into a heated water bath. The latter is done to separate the PCM from the shell by a thin molten layer, thus enabling the solid bulk to sink. The effect of the solid sinking and close-contact melting on the fins is explored. It is found that close-contact melting shortens the melting time drastically. Accordingly, two types of models are used to predict the melting rate: numerical CFD model and analytical/numerical close-contact melting model. The CFD model takes into account convection in the melt and the PCM property dependence on temperature and phase. The analytical/numerical CCM model is developed under several simplifying assumptions. Good agreement is found between the predictions and corresponding experimental results.

Enhanced Melting for Transient Thermal Management

2015 ◽  
Author(s):  
T. Rozenfeld ◽  
R. Hayat ◽  
Y. Kozak ◽  
G. Ziskind
Keyword(s):  
Heat Transfer ◽  
Thermal Management ◽  
Phase Change Materials ◽  
Solid Phase ◽  
Close Contact ◽  
Heated Surface ◽  
Contact Melting ◽  
Significant Rise ◽  
Periodic Regime ◽  
Transient Thermal

The present study deals with transient thermal management using phase change materials (PCMs). These materials can absorb large amounts of heat without significant rise of their temperature during the melting process. This effect is attractive for passive thermal management, particularly where the device is intended to operate in a periodic regime, or where the relatively short stages of high power dissipation are followed by long stand-by periods without a considerable power release. Heat transfer in PCMs, which have low thermal conductivity, can be enhanced by fins that enlarge the heat transfer area. However, when the PCM melts, a layer of liquid is growing at the fins creating an increasing thermal resistance that impedes the process. The present work aims to demonstrate that performance of a latent-heat thermal management unit may be considerably affected by achieving a so-called close-contact melting (CCM), which occurs when the solid phase is approaching a heated surface, and only a thin liquid layer is separating between the two. Although CCM was extensively studied in the past, its possible role in finned systems has been revealed only recently by our group. In particular, it depends heavily on the specific configuration of the fins. In the present work, close-contact melting is modeled analytically for a geometry which includes two symmetrically inclined fins. A quasi-steady approach is used for calculating the rate of melting based on the force and energy balances. The results are expressed in terms of the time-dependent melt fraction and Nusselt number, showing their explicit dependence on the Stefan and Fourier numbers. Moreover, the approach used in the present study may be applied to other geometries in which the heated surface is not horizontal or where there are a number of heated surfaces or fins.

Optimization of Fin Parameters to Reduce Entropy Generation and Melting Time of a Latent Heat Storage Unit

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Lokesh Kalapala ◽  
Jaya Krishna Devanuri
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Entropy Generation ◽  
Transfer Rate ◽  
Heat Storage ◽  
Melting Time ◽  
Multi Objective Optimization ◽  
Storage Unit ◽  
Latent Heat Storage ◽  
Multi Objective

Abstract One of the challenges in the design and development of a latent heat storage unit (LHSU) is to increase the charging and discharging rates which are inherently low because of low thermal conductivity of phase change materials (PCM). Out of various heat transfer enhancement techniques, employing annular fins is very simple, efficient and no fabrication complexity is involved. Fin parameters (fin size and number of fins) significantly influence the enhancement in heat transfer rate. Hence, optimization of fin parameters is necessary for the efficient design of an LHSU. While designing an LHSU along with heat transfer rate, entropy generation should also be considered in order to make it exergetically efficient. Therefore, the present study is aimed at multi-objective optimization of annular fin parameters to minimize the melting time and entropy generation. Fin diameter and the number of fins are taken as the variables. The influence of these two variables on the melting time, average Nusselt number, energy stored, and distribution of entropy is presented. The melting rate is increased, and global entropy generation decreased by increasing the number of fins up to 15. An increase in the fin diameter reduced the melting time while entropy generation got increased. For the multi-objective optimization, the multi-objective optimization based on ratio analysis (MOORA) technique is chosen and the optimized values of fin diameter and number of fins are observed to be 80 mm and 15 respectively. Finally, optimized parameters are represented in non-dimensional form to make them applicable for any size of the LHSU.

scholarly journals Diamond-Shaped Extended Fins for Heat Transfer Enhancement in a Double-Pipe Heat Exchanger: An Innovative Design

2021 ◽  
Vol 11 (13) ◽  
pp. 5954
Author(s):  
Muhammad Ishaq ◽  
Amjad Ali ◽  
Muhammad Amjad ◽  
Khalid Saifullah Syed ◽  
Zafar Iqbal
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Exchangers ◽  
Adaptive Finite Element Method ◽  
Transfer Enhancement ◽  
Enhanced Heat Transfer ◽  
Frictional Loss ◽  
Special Cases ◽  
Double Pipe ◽  
Pipe Heat

Heat transfer enhancement in heat exchangers results in thermal efficiency and energy saving. In double-pipe heat exchangers (DPHEs), extended or augmented fins in the annulus of the two concentric pipes, i.e., at the outer surface of the inner pipe, are used to extend the surface of contact for enhancing heat transfer. In this article, an innovative diamond-shaped design of extended fins is proposed for DPHEs. This type of fin is considered for the first time in the design of DPHEs. The triangular-shaped and rectangular-shaped fin designs of DPHE, available in the literature, can be recovered as special cases of the proposed design. An h-adaptive finite element method is employed for the solution of the governing equations. The results are computed for various performance measures against the emerging parameters. The results dictate that the optimal configurations of the diamond-shaped fins in the DPHE for an enhanced heat transfer are recommended as follows: If around 4–6, 8–12, or 16–32 fins are to be placed in the DPHE, then the height of the fins should be 20%, 80%, or 100%, respectively, of the annulus width. If frictional loss of heat is also to be considered, then for fin-heights of 20–80% and 100% of the annulus width, the placement of 4 and 8 diamond-shaped fins, respectively, is recommended for an enhanced heat transfer. These recommendations are for the radii ratio (i.e., the ratio of the inner pipe radius to that of the outer pipe) of 0.25. The recommendations are be modified if the radii ratio is altered.

scholarly journals Investigation of Overlapped Twisted Tapes Inserted in a Double-Pipe Heat Exchanger Using Two-Phase Nanofluid

Nanomaterials ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1656 ◽  
Author(s):  
Mehdi Ghalambaz ◽  
Hossein Arasteh ◽  
Ramin Mashayekhi ◽  
Amir Keshmiri ◽  
Pouyan Talebizadehsardari ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Performance Evaluation ◽  
Heat Exchanger ◽  
Evaluation Criterion ◽  
Twisted Tape ◽  
Performance Evaluation Criterion ◽  
Twisted Tapes ◽  
Double Pipe ◽  
Pipe Heat

This study investigated the laminar convective heat transfer and fluid flow of Al2O3 nanofluid in a counter flow double-pipe heat exchanger equipped with overlapped twisted tape inserts in both inner and outer tubes. Two models of the same (co-swirling twisted tapes) and opposite (counter-swirling twisted tapes) angular directions for the stationary twisted tapes were considered. The computational fluid dynamic simulations were conducted through varying the design parameters, including the angular direction of twisted tape inserts, nanofluid volume concentration, and Reynolds number. It was found that inserting the overlapped twisted tapes in the heat exchanger significantly increases the thermal performance as well as the friction factor compared with the plain heat exchanger. The results indicate that models of co-swirling twisted tapes and counter-swirling twisted tapes increase the average Nusselt number by almost 35.2–66.2% and 42.1–68.7% over the Reynolds number ranging 250–1000, respectively. To assess the interplay between heat transfer enhancement and pressure loss penalty, the dimensionless number of performance evaluation criterion was calculated for all the captured configurations. Ultimately, the highest value of performance evaluation criterion is equal to 1.40 and 1.26 at inner and outer tubes at the Reynolds number of 1000 and the volume fraction of 3% in the case of counter-swirling twisted tapes model.

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