Search Results (8)

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

Within the realm of industrial energy conservation, the optimization of heat exchanger performance is paramount for the augmentation of energy utilization efficiency. This investigation employs computational fluid dynamics (CFD) simulations to elucidate the effects of an innovative DNA-Inspired Slotted Insert (DSI) on the convective heat transfer and pressure drop characteristics within heat exchange tubes. The study provides a thorough analysis of fully turbulent flow (Re = 6600–17,200), examining the effects of various DSI pitches, key lengths, and geometries. The findings reveal that the DSI instigates a three-dimensional spiral flow pattern, which is accompanied by an escalation in the Nusselt number (Nu) and friction factor (f) with increasing Reynolds numbers. An inverse relationship between Nu and both pitch and key length is observed; conversely, f exhibits a direct correlation with these parameters. The study identifies an optimal configuration characterized by a pitch of 10 mm and a key length of 1.5 mm, with square keys demonstrating superior heat transfer performance relative to other geometrical configurations. This research contributes significant design and application insights for double-helical inserts, which are pivotal for the enhancement of heat exchanger efficiency. Full article

An experimental study was carried out to assess the thermal performance of a few evacuated tube solar collectors (ETSCs) for water heating. The thermal performance of two kinds of ETSC (heat pipe ETSC and direct-flow ETSC) was investigated using an indoor experimental apparatus in lab testing conditions with a solar simulator. Several experimental tests were carried out for the heat pipe ETSC system under different operating conditions, such as the solar intensity (300, 500, and 1000 W/m²) and the tilt angle (0°, 30° and 90°) of the ETSC and the water flow rate (0.6, 1.2, and 2.4 LPM). Moreover, four configurations of direct-flow ETSC (U tube, double U tubes, coaxial tubes, and helical tube) were examined and compared to the conventional heat pipe ETSC. The results of the experiment proved that the ETSC system presents a great performance at higher solar irradiance and lower water flow rates, and the experiments indicated that with a 30° tilt angle, the ETSC reaches the maximum thermal efficiency of 36%. Furthermore, compared to the conventional heat pipe ETSC and the other proposed configurations of direct-flow ETSCs, the helical tube-based ETSC has a better thermal efficiency, 69%, and can be considered a greater potential heat exchanger that can be integrated in ETSCs. To the best of our knowledge, it is the first time this helical tube type been integrated into the ETSC and tested under these conditions. Full article

The hydrothermal behavior in a helical double-tube heat exchanger is numerically estimated. A new type of swirl generator with two sections, including; outer curved blades and a semi-conical section with two holes in the inner section, is employed. Two geometrical factors, containing the length (L₁) and the position of the swirl generator (S), are used for investigation. The calculations were performed by a commercial FVM code, ANSYS FLUENT 18.2. The numerical outcomes show that a shorter length of the swirl generator leads to a better hydrothermal behavior. Accordingly, the model with L₁ = 100 mm at $\dot{\mathrm{m}}$ = 0.008 kg/s achieves the maximum thermal performance by about 17.65, 53.85, and 100% enhancement compared to the models L₁ = 200, 300 mm, and without swirl generator. Among the different studied positions of the swirl generator, the maximum heat transfer coefficient and average Nusselt number in entire mass flow rates belong to the case with position S = 0.3π mm. Moreover, the thermal performance of the case with S = 0.3π mm is higher than cases with S = 0.1π mm, S = 0.5π mm, and without swirl generator by about 11.11, 53.84, and 100%, respectively. Full article

Due to the high enthalpy of fusion in water, ice storage systems are known as one of the best cold thermal energy storage systems. The phase change material used in these systems is water, thus it is inexpensive, accessible, and completely eco-friendly. However, despite the numerous advantages of these systems, the phase change process in them is time-consuming and this leads to difficulties in their practical application. To solve this problem, the addition of nanomaterials can be helpful. This study aims to investigate the compound heat transfer enhancement of a cylindrical-shaped unit equipped with double helically coiled coolant tubes using connecting plates and nano additives as heat transfer augmentation methods. Complex three-dimensional numerical simulations are carried out here to assess the best heat exchanger material as well as the impact of various nanoparticle types, including alumina, copper oxide, and titania, and their concentrations in the PCM side of the ice storage unit. The influence of these parameters is discussed on the charging rate and the temperature evolution factor in these systems. The results suggest that using nano additives, as well as the connecting plates, together is a promising way to enhance the solidification rate by up to 29.9%. Full article

The purpose of this research is to evaluate the effect of twist in the internal tube in a tube-in-tube helical heat exchanger keeping constant one type of ridges. To meet this goal, a Computational Fluid Dynamic (CFD) model was carried out. The effects of the fluid flow rate on the heat transfer were studied in the internal and annular flow. A commercial CFD package was used to predict the flow and thermal development in a tube-in-tube helical heat exchanger. The simulations were carried out in counter-flow mode operation with hot fluid in the internal tube side and cold fluids in the annular flow. The internal tube was modified with a double passive technique to provide high turbulence in the outer region. The numerical results agree with the reported data, the use of only one passive technique in the internal tube increases the heat transfer up to 28.8% compared to smooth tube. Full article

The heat transfer in double pipe heat exchangers is very poor. This complicates its application in absorption cooling systems, however, the implementation of simple passive techniques should help to increase the heat and mass transfer mainly in the absorber. This paper carried out a simulation and its experimental comparison of a NH₃-H₂O bubble absorption process using a double tube heat exchanger with a helical screw static mixer in both central and annular sides. The experimental results showed that the absorption heat load per area is 31.61% higher with the helical screw mixer than the smooth tube. The theoretical and experimental comparison showed that the absorption heat load difference values were 28.0 and 21.9% for smooth tube and the helical mixer, respectively. These difference values were caused by the calculation of the log mean temperature difference in equilibrium conditions to avoid the overlap of solution temperatures. Therefore, the theoretical and experimental results should be improved when the absorption heat is included in the heat transfer equation or avoiding the operation condition when output is lower than input solution temperature. Full article

In vertical closed-loop systems, it is common to use single or double U-tube heat exchangers separated by longitudinal spacers. In addition, the helical-shaped pipe is another configuration that requires lower drilling lengths but it is less used. The aim of the present research is to study the influence of these components on the total efficiency of a borehole heat exchanger (BHE). Thus, the differences between using single/double U-tubes (with or without spacers) and helical pipes are analysed in terms of efficiency. Through different laboratory tests, a small vertical closed-loop system was simulated in order to analyse all these possible configurations. The grouting materials and the temperatures of the ground were modified at the same time in these tests. Regarding the heat exchange process between the ground and the heat carrier fluid, it must be highlighted that the best results were obtained for the helical-shaped pipe configuration. Some of the improvements offered by this heat exchanger typology with respect to the vertical configuration is that a lower drilling depth is required even it requires a larger diameter. This leads to significant economic savings in the performing drilling process. Finally, it is also worth noting the importance of using spacers in vertical U-tubes and that no improvements have been found regarding the use of single or double configuration of U-tubes. Thanks to the laboratory results derived from this study it is possible to establish the optimum behaviour pattern for the entire vertical closed-loop systems. Full article