Showing papers on "Heat pipe published in 2020"

Recent progress in phase change materials storage containers: Geometries, design considerations and heat transfer improvement methods

Abstract: The potential for phase change materials (PCMs) has a vital role in thermal energy storage (TES) applications and energy management strategies. Nevertheless, these materials suffer from their low thermal conductivity and hence heat transfer enhancement techniques should be applied to enhance their thermophysical properties. This review focuses on the geometrical configurations of PCM containers and their design considerations, aims to improve the performance of TES systems. Various methods for enhancing heat transfer of PCMs (the main challenge in container design) include microencapsulated PCMs, insertion of fins, the combination of fins and nanoparticles, the use of metal foams and graphite, and the doping of high photothermal materials are also extensively discussed as well. Moreover, this paper highlights various designs of PCM-finned storage systems and discusses deeply their key parameters to find out the suitable design for optimum melting and solidification rate of PCM. The reviewed results showed that the rectangular PCM container is the effective container for the bulk storage due to its high melting rate and storage efficiency. Moreover, the use of longitudinal finned geometry within PCM integrated triplex tube heat storage units significantly achieved better heat transfer performance compared to the other finned geometries. Additionally, the improvement of the heat transfer of PCM by the deployment of fins is more effective than the hybrid combination of fins and nanoparticles. Further optimization and experimental studies are recommended to explore new hybrid compound intensification techniques such as the triple combination of fins, expanded graphite, and heat pipes with multiple PCMs that augment the thermal performance of TES systems.

Thermal management analysis using heat pipe in the high current discharging of lithium-ion battery in electric vehicles

Abstract: Thermal management system (TMS) for commonly used lithium-ion (Li-ion) batteries is an essential requirement in electric vehicle operation due to the excessive heat generation of these batteries during fast charging/discharging. In the current study, a thermal model of lithium-titanate (LTO) cell and three cooling strategies comprising natural air cooling, forced fluid cooling, and a flat heat pipe-assisted method is proposed experimentally. A new thermal analysis of the single battery cell is conducted to identify the most critical zone of the cell in terms of heat generation. This analysis allowed us to maximize heat dissipation with only one heat pipe mounted on the vital region. For further evaluation of the proposed strategies, a computational fluid dynamic (CFD) model is built in COMSOL Multiphysics® and validated with surface temperature profile along the heat pipe and cell. For real applications, a numerical optimization computation is also conducted in the module level to investigate the cooling capacity of the liquid cooling system and liquid cooling system embedded heat pipe (LCHP). The results show that the single heat pipe provided up to 29.1% of the required cooling load in the 8C discharging rate. Moreover, in the module level, the liquid cooling system and LCHP show better performance compared with natural air cooling while reducing the module temperature by 29.9% and 32.6%, respectively.

Thermal evaluation of a heat pipe working with n-pentane-acetone and n-pentane-methanol binary mixtures

Abstract: In the present study, a set of experiments were accomplished to appraise the thermal performance and heat transfer of n-pentane-acetone and n-pentane-methanol mixtures inside a gravity-assisted thermosyphon heat pipe. Pure n-pentane, acetone and methanol were also tested as the carrying fluid to produce some reference data. The heat pipe was manufactured from copper with length and diameter of 290 and 20 mm, respectively. The effect of multiple factors covering the input heat to the evaporator section, the filling ratio of the carrying fluid, heat pipe tilt angle and also the type of the carrying fluid on temperature distribution and thermal performance of the heat pipe was investigated. The results demonstrated that the thermo-physical properties of the carrying fluid were the key factor controlling the heat pipe efficiency. The vapour pressure and boiling temperature of the carrying fluid controlled the thermal efficiency of the system such that for n-pentane-acetone, the highest thermal efficiency was obtained. Also, it was identified that the filling ratio of the system is a key operating factor such that the value of the filling ratio was small for the evaporative carrying fluid (binary mixtures), while it was large for the non-evaporative carrying fluids. Also, heat pipe tilt angle was impressed by the type of the carrying fluid; the optimum tilt angle was 55 degree for the binary mixtures, while it was 65° for the pure liquids.

Investigation, Development and Experimental Analyses of a Heat Pipe Based Battery Thermal Management System

Abstract: In this paper, the performance of a heat pipe based thermal management technique for batteries has been investigated experimentally. In this regard, a test rig was developed and used to demonstrate the effectiveness of flat heat pipe (heat mat) technology at controlling and maintaining the temperature of a prototype battery module, which consisted of sixteen prismatic lithium-titanate (LTO) cells. Test results were obtained which proved the ability of the technology to keep the battery cells at an optimal temperature, during cycling representative of real-world operation, from either a cold or hot start. The heat mat was shown to efficiently absorb the heat generated by the cells and transfer it effectively to an external cooling medium of either water or refrigerant. In conclusion, it was demonstrated that the maximum cell temperature is significantly reduced and the overall temperature uniformity of the module is greatly improved, when compared to a module with no thermal management. The maximum cell temperature was kept below 28 °C and the module temperature uniformity was maintained at +/−1 °C. By using test cycles that generated a quasi-steady-state heat load from the cells, it was shown that approximately 60% of the heat generated by the cells was removed by the heat mat. The results obtained from this work demonstrate that heat mat technology can improve battery performance and longevity by reducing the degradation and ageing process and cell imbalances, that result from high cell temperatures and module/pack-level temperature non-uniformity.

Phase change material/heat pipe and Copper foam-based heat sinks for thermal management of electronic systems

Abstract: Phase change material (PCM) has been extensively used for their thermal management but due to low conductivity that hinders the performance of a system. Since heat pipe and porous materials both have high thermal conductivities, they can be used to form hybrid system with PCM which significantly enhance the heat transfer capability of PCM. In current research of heat pipe, copper foam (pore density 40PPI and porosity 93%) and PCM based heat sinks are used to inspect the thermal performance of heat sink with respect to time by varying heat fluxes. ‘‘RT-35HC” PCM, copper foam and gravity assisted heat pipe with and without cooling fan are used in experimental investigation. The results showed after 6000 s when charging ends hybrid cooling (Foam-PCM-HP) with fan have maximum temperature reduction i.e. 47%, 51% and 54% at heat flux of 2, 2.5 and 3 kW/m2 respectively. Similarly, for discharging hybrid cooling with fan showed excellent cooling results at all heat fluxes.

CFD modeling of a thermal energy storage based heat pipe evacuated tube solar collector

Abstract: The increase in greenhouse gases makes it necessary to utilize renewable energy sources such as solar energy. The most important component of any solar system is solar collector. Among various types of solar collectors, evacuated tube solar collector (ETC) has attracted many attentions especially for the application in solar water heating systems (SWHs). However, due to the intermittency in solar intensity, the ETCs may not work at their maximum functionality. In this study, the computational fluid dynamics (CFD) modeling of a heat pipe ETC (HPETC) with and without the integration of phase change materials (PCMs) is performed. In order to cross-validate the obtained results from CFD and recent experimental analysis, the boundary conditions are set as the field-testing data. In phase-I, the 3D model of commercially available HPETC is simulated, while in phase-II, the HPETC integrated with the PCM is developed. The selected type of PCM is Tritriacontane paraffin (C33H68) with melting point of 72∘C. The simulation results show an acceptable agreement with the experimental data with an average deviation of 4.80% and 2.04% for phase-I and phase-II, respectively. The result from this study can be a benchmark for further optimization of HPETCs in thermal energy storage systems.

Condensation, evaporation and boiling of falling films in wickless heat pipes (two-phase closed thermosyphons): A critical review of correlations

Abstract: With the objective of estimating the thermal resistance of a two-phase closed thermosyphon (TPCT), the work presented is a state of the art of condensation and falling film evaporation/boiling correlations. A deep analysis of up-to-date reported equations dealing with falling film heat transfer is carried out and recommendations are provided to select the most suitable and reliable correlations. Mechanisms such as filmwise condensation and Nusselt theory, falling film development in the thermal entry length (TEL), film thickness, appearance of waves and turbulence, two-phase flow interaction and entrainment with the shear stress at the liquid-vapour interface, falling film evaporation and boiling, in addition to film breakdown, are comprehensively explained and discussed. For all sections, the advised correlations are reported in a clear and simple way using tables. The objective of this paper is to cover sufficient knowledge on the falling film dynamic in thermosyphons to ease the prediction of heat transfer coefficients. This paper can be taken as a starting point for thermosyphon users in the study of falling film heat transfer in wickless heat pipes.

ETEKINA: Analysis of the potential for waste heat recovery in three sectors: aluminium low pressure die casting, steel sector and ceramic tiles manufacturing sector

Abstract: In the framework of the ETEKINA project, waste energy streams have been analysed at an aluminium automotive parts production facility in Spain, at a steel foundry in Slovenia and at a ceramic tile production unit in Italy. The aim is to recover more than 40% of the waste heat contained in the exhaust streams and reuse it within the industrial plant rather than emitting it to the atmosphere. To select the applications where the profitability of heat recovery can be demonstrated, the flow rates and temperatures of the applicable exhaust streams have been measured and analysed to select the processes for waste heat recovery and it's re-used in the three industrial plants. The demonstration of the cost-effective waste heat recovery is to be made by using heat pipe heat exchangers (HPHEs) and the processes whereby the heat recovery installations will be erected have already been selected. HPHEs were selected as a heat recovery technology due to their advantages and key features over convectional heat exchangers considering space restrictions, pressure drop limitations, and other waste stream challenges. The challenges include high temperature of the waste and the heat sink streams, fluctuations in the waste stream flow rate and temperature, presence of corrosive moisture such as sulphuric acid in the waste stream, and the presence of particles in the waste stream which can cause fouling leading to failure of convectional technologies. Furthermore, HPHEs are maintenance-free and can have payback period of less than three years.