Search Results (12)

Ice energy storage systems have gained significant attention as sustainable solutions for energy management, particularly in applications with fluctuating energy demands. This study aims to compare two different designs, a triple-tube heat exchanger (TTHE) and spherical ice balls, the latter being the most widely used traditional design in the industry. The TTHE design was first analyzed theoretically, then optimized using Computational Fluid Dynamics (CFD) simulations, and validated by the literature. Finally, it was compared with spherical ice balls under identical conditions. The analyses were conducted for an ice storage volume of 1000 kg, with the complete solidification process designed to occur within 8 h. The results indicate that the TTHE reduced solidification time by 25% while simultaneously increasing energy storage by 8%. This study contributes to the advancement of sustainable energy technologies by providing a comparative analysis of spherical ice balls and triple-tube heat exchangers for optimizing ice storage systems. The implementation of a TTHE for thermal storage can lower energy costs, mitigate peak demand, and address the intermittency challenges associated with renewable energy sources. Full article

Geothermal heat pump systems (GHPSs) offer a sustainable and energy-efficient solution for heating and cooling buildings. Ground heat exchanger (GHE) design and configuration significantly impact on the overall performance and installation expenses of geothermal heat pump systems. This paper presents a comprehensive analysis of GHPSs, focusing on their advantages, disadvantages, key components, types, and particularly the various closed-loop GHE configurations. Detailed comparisons highlight how different designs affect thermal performance and installation costs. The findings reveal that helical GHEs offer superior thermal efficiency with reduced drilling requirements and cost savings, while coaxial GHEs, especially those using steel tubes, enhance heat transfer and enable shorter boreholes. Cost-effective options like W-type GHEs provide performance comparable to more complex systems. Additionally, triple U-tube and spiral configurations balance high efficiency with economic feasibility. The single and double U-tube remain the most common borehole geometry, though coaxial designs present distinct advantages in targeted scenarios. These insights support the optimization of vertical GHEs, advancing system performance, cost-effectiveness, and long-term sustainability in GHPS applications. Full article

Flameless combustion has advantages such as low pollution and uniform temperature in the combustion chamber, making it an excellent option for heat exchangers. Previous studies have focused solely on the flameless combustion phenomenon, without considering its interaction with the target being heated. In this study, we conducted experimental and computational fluid analyses on a cylindrical reformer for reverse air injection flameless combustion. Typically, small-scale reformers of 10 kW or less are coaxial triple-tube cylindrical reformers. In contrast, multitubular reformers are used for larger-scale applications, since the heat transfer rate in single-burner cylindrical reformers decreases sharply as the scale increases. Flameless combustion, with high heat transfer efficiency, helps overcome the limitation of premixed burner. Compared with conventional premixed burners, flameless burner decreases the combustion gas outlet temperature by 30% at 25 kW while reducing energy consumption by 24% (owing to the high heat transfer rate) for a given cooling fluid outlet temperature. Furthermore, it is shown that introducing a ring at the combustion chamber exit can enhance combustion gas recirculation. The experimental result was confirmed through computational fluid analysis. It is concluded that for reverse air injection flameless combustion, the combustion gas recirculation rate in the combustion chamber is strongly related to the heat transfer. Full article

Climate change is one of the main problems humanity is currently facing due to the use of fossil fuels. At present, 20% of the total electricity consumed in buildings worldwide is for air conditioning. The development and use of thermally driven cooling systems is very important, since they can be activated by renewable energies, such as geothermal, reducing the consumption of electricity produced by fossil fuels. In this paper, we analyze a geothermal field located in the state of Jalisco, Mexico, with the aim of comparing the performance of different advanced absorption cooling systems driven by a geothermal heat source. The analysis includes the influence of water temperature obtained from an abandoned geothermal well, using a U tube heat exchanger inside the well. The results show that this well can reach temperatures from 59 °C to 190 °C, depending on the depth of the U tube and the insulation thickness. At a T_E = 8 °C, the operating range temperatures were 59–80 °C, 77–110 °C, 135–162 °C, and 180–187 °C for the half-effect, single-effect, double-effect and triple-effect systems, respectively. The maximum cooling potential was 99,334 GW obtained with the double-effect system, followed by 92,995 GW with the triple-effect system, 70,939 GW with the single-effect system, and 38,721 GW with the half-effect system. Full article

Employing phase-change materials (PCM) is considered a very efficient and cost-effective option for addressing the mismatch between the energy supply and the demand. The high storage density, little temperature degradation, and ease of material processing register the PCM as a key candidate for the thermal energy storage system. However, the sluggish response rates during their melting and solidification processes limit their applications and consequently require the inclusion of heat transfer enhancers. This research aims to investigate the potential enhancement of circular fins on intensifying the PCM thermal response in a vertical triple-tube casing. Fin arrays of non-uniform dimensions and distinct distribution patterns were designed and investigated to determine the impact of modifying the fin geometric characteristics and distribution patterns in various spatial zones of the heat exchanger. Parametric analysis on the various fin structures under consideration was carried out to determine the most optimal fin structure from the perspective of the transient melting evolution and heat storage rates while maintaining the same design limitations of fin material and volume usage. The results revealed that changing the fin dimensions with the heat-flow direction results in a faster charging rate, a higher storage rate, and a more uniform temperature distribution when compared to a uniform fin size. The time required to fully charge the storage system (fully melting of the PCM) was found to be reduced by up to 10.4%, and the heat storage rate can be improved by up to 9.3% compared to the reference case of uniform fin sizes within the same fin volume limitations. Full article

Due to the potential cost saving and minimal temperature stratification, the energy storage based on phase-change materials (PCMs) can be a reliable approach for decoupling energy demand from immediate supply availability. However, due to their high heat resistance, these materials necessitate the introduction of enhancing additives, such as expanded surfaces and fins, to enable their deployment in more widespread thermal and energy storage applications. This study reports on how circular fins with staggered distribution and variable orientations can be employed for addressing the low thermal response rates in a PCM (Paraffin RT-35) triple-tube heat exchanger consisting of two heat-transfer fluids flow in opposites directions through the inner and the outer tubes. Various configurations, dimensions, and orientations of the circular fins at different flow conditions of the heat-transfer fluid were numerically examined and optimized using an experimentally validated computational fluid-dynamic model. The results show that the melting rate, compared with the base case of finless, can be improved by 88% and the heat charging rate by 34%, when the fin orientation is downward–upward along the left side and the right side of the PCM shell. The results also show that there is a benefit if longer fins with smaller thicknesses are adopted in the vertical direction of the storage unit. This benefit helps natural convection to play a greater role, resulting in higher melting rates. Changing the fins’ dimensions from (thickness × length) 2 × 7.071 mm² to 0.55 × 25.76 mm² decreases the melting time by 22% and increases the heat charging rate by 9.6%. This study has also confirmed the importance of selecting the suitable values of Reynolds numbers and the inlet temperatures of the heat-transfer fluid for optimizing the melting enhancement potential of circular fins with downward–upward fin orientations. Full article

This work evaluates the influence of combining twisted fins in a triple-tube heat exchanger utilised for latent heat thermal energy storage (LHTES) in three-dimensional numerical simulation and comparing the outcome with the cases of the straight fins and no fins. The phase change material (PCM) is in the annulus between the inner and the outer tube, these tubes include a cold fluid that flows in the counter current path, to solidify the PCM and release the heat storage energy. The performance of the unit was assessed based on the liquid fraction and temperature profiles as well as solidification and the energy storage rate. This study aims to find suitable and efficient fins number and the optimum values of the Re and the inlet temperature of the heat transfer fluid. The outcomes stated the benefits of using twisted fins related to those cases of straight fins and the no-fins. The impact of multi-twisted fins was also considered to detect their influences on the solidification process. The outcomes reveal that the operation of four twisted fins decreased the solidification time by 12.7% and 22.9% compared with four straight fins and the no-fins cases, respectively. Four twisted fins improved the discharging rate by 12.4% and 22.8% compared with the cases of four straight fins and no-fins, respectively. Besides, by reducing the fins’ number from six to four and two, the solidification time reduces by 11.9% and 25.6%, respectively. The current work shows the impacts of innovative designs of fins in the LHTES to produce novel inventions for commercialisation, besides saving the power grid. Full article

Inherent fluctuations in the availability of energy from renewables, particularly solar, remain a substantial impediment to their widespread deployment worldwide. Employing phase-change materials (PCMs) as media, saving energy for later consumption, offers a promising solution for overcoming the problem. However, the heat conductivities of most PCMs are limited, which severely limits the energy storage potential of these materials. This study suggests employing circular fins with staggered distribution to achieve improved thermal response rates of PCM in a vertical triple-tube heat exchanger involving two opposite flow streams of the heat-transfer fluid (HTF). Since heat diffusion is not the same at various portions of the PCM unit, different fin configurations, fin dimensions and HTF flow boundary conditions were explored using computational studies of melting in the PCM triple-tube system. Staggered configuration of fin distribution resulted in significant increases in the rates of PCM melting. The results indicate that the melting rate and heat charging rate could be increased by 37.2 and 59.1%, respectively, in the case of staggered distribution. Furthermore, the use of lengthy fins with smaller thickness in the vertical direction of the storage unit resulted in a better positive role of natural convection; thus, faster melting rates were achieved. With fin dimensions of 0.666 mm × 15 mm, the melting rate was found to be increased by 23.6%, when compared to the base case of 2 mm × 5 mm. Finally, it was confirmed that the values of the Reynolds number and inlet temperatures of the HTF had a significant impact on melting time savings when circular fins of staggered distribution were included. Full article

This study aims to assess the effect of adding twisted fins in a triple-tube heat exchanger used for latent heat storage compared with using straight fins and no fins. In the proposed heat exchanger, phase change material (PCM) is placed between the middle annulus while hot water is passed in the inner tube and outer annulus in a counter-current direction, as a superior method to melt the PCM and store the thermal energy. The behavior of the system was assessed regarding the liquid fraction and temperature distributions as well as charging time and energy storage rate. The results indicate the advantages of adding twisted fins compared with those of using straight fins. The effect of several twisted fins was also studied to discover its effectiveness on the melting rate. The results demonstrate that deployment of four twisted fins reduced the melting time by 18% compared with using the same number of straight fins, and 25% compared with the no-fins case considering a similar PCM mass. Moreover, the melting time for the case of using four straight fins was 8.3% lower than that compared with the no-fins case. By raising the fins’ number from two to four and six, the heat storage rate rose 14.2% and 25.4%, respectively. This study presents the effects of novel configurations of fins in PCM-based thermal energy storage to deliver innovative products toward commercialization, which can be manufactured with additive manufacturing. Full article

Conventional circular double or triple tube type heat exchanger, DHE or THE, is one of the compact heat exchangers; a large number of studies have been performed to improve their heat transfer performance. The authors demonstrated that a petal-shaped special DHE with a large wet perimeter yields a high heat transfer efficiency, η. In this study, the DHE with six or five petals-, five shallow petals-, and circular-inner tubes were used. To further improve the η of the DHE, a THE with a petal-shaped inner tube along with the middle and outer circular tubes were used. Hot water flowed through the inner tube and cold water flowed through the middle and outer tubes as a counter current flow. The heat transfer was approximately equal; however, the flow resistance (pressure loss) of the outer tube of the DHE could be decreased using the middle and outer tubes under the same amount of cold water as the DHE; consequently, the η could be improved. In addition, the effect of changing the flow path of the hot- and cold-water flows on the η was examined. Full article

This paper presents a new air-heating system concept for energy-efficient dwellings. It is a system designed to heat a low-energy building by coupling a heat-recovery ventilation system with a three-fluid heat exchanger located on the chimney of a wood-pellet stove. The proposed work focuses on the heat transfer that occurs between flue gases, the ventilation air and the combustion air within a triple concentric tube heat exchanger with no insulation at its outer surface. The main objective is to predict outlet temperature for the specific geometry of the heat exchanger studied here. Thus, the governing differential equations are derived for a counter-co-current flow arrangement of the three fluids. Then analytical solutions for the steady-state temperature distribution are obtained as well as the amount of heat transferred to the outside. An expression for the effectiveness of the heat exchanger is also proposed. Based on these results, calculations are performed on a case study to predict the fluid temperature distribution along the heat exchanger. Finally, a parametric study is carried out on this case study to assess the influence of the relevant parameters on the effectiveness of the heat exchanger. In addition, computation of heat losses to the outside justifies whether insulation is needed. Full article

In this paper, experimental tests conducted on a new wood-based air-heating system for energy-efficient dwellings are presented. The main objective is to evaluate the resulting outlet temperatures and the amount of heat recovered by the ventilation air in order to assess feasibility and performance of coupling a mechanical ventilation heat-recovery unit and a triple concentric tube heat exchanger integrated into the chimney of a room-sealed wood-pellet stove to heat an entire house. After introducing the context of this work, the three main components of the combined system developed here, the coupling configuration adopted, as well as the protocol used and the sensors implemented on an experimental setup carried out in a laboratory are detailed in turn. Then, the heat transfer rates obtained from measurements for the various fluids as well as the effectiveness of the heat exchangers are presented and discussed. Finally, the resulting outlet temperatures of the three fluids exchanging in the triple concentric tube heat exchanger studied here are compared to those provided by analytical solutions obtained with a mathematical model. It is shown that heat transfer rates are predicted with a relative difference that is lower than 5% compared to experimental values and that such a system enables to cover all or most of heat losses in an energy efficient building. Full article