Investigation Of Thermal Performance Research Articles

Experimental investigation of thermal performance in a shell-and-tube phase change thermal energy storage unit with an inner square tube

Experimental investigations of phase change processes in a shell-and-tube latent heat thermal energy storage unit with an inner square tube were carried out. Paraffin OP44E was selected as a phase change material, and the water heated or cooled by constant temperature water tanks flowed into the inner square tube as the heat transfer fluid. Visualization experiments allow for the observation and analysis of the solid-liquid interface during the phase change process. Due to natural convection, the melting interface progresses from top to bottom, while the solidification interface advances from the center outward, as heat transfer is primarily governed by conduction. The experimental results demonstrated that the initial temperature of the PCM has a negligible impact on the thermal performance of the energy storage unit, particularly during the solidification process. The dimensionless analysis reveals the relationships of Nusselt numbers, Stefan numbers, and Reynolds numbers. Furthermore, four stages of conduction, mixed conduction-convection, convective enhancement, and convective attenuation were divided according to the effects of natural convection. Finally, empirical formulas for effectiveness were established to provide guidance for the heat exchanger design.

Study of a nano-coated hydrophilic polymer for indirect evaporative cooler from wetting, thermal and corrosion resistance performance

Hydrophilicity and evaporation rate of the wet channels play crucial effects on the cooling performance of an indirect evaporative cooler (IEC). Thus, great efforts are made to develop high-performance wet surface materials for IECs. However, current studies of hydrophilic coatings focus on the moisture diffusion ability of the material itself or the overall thermal performance of an IEC, with less in-depth research on the internal local thermal and quantitative wetting performance under various operating conditions. In this study, a TiO2/SiO2 nano-coating is applied to polypropylene (PP) by three treatment methods to develop a hydrophilic durable and corrosion-resistant PP for IEC application. Firstly, the hydrophilic durability of various samples was tested for 30 days. Secondly, test rigs were built for wetting and thermal performance investigation. The wetting performance was studied by both the drop-impact interaction test and the falling film experiment. The flow pattern, water film thickness, and wettability ratio were investigated under varying water flow rates, air velocity, and water distribution strategies (continuous spray, intermittent spray). The thermal performance including the internal wall temperature and supply air temperature of non-coated and coated IEC were comparatively tested. Finally, the corrosion resistance ability of samples was tested by acid salt spray. The results show that primer-aided TiO2/SiO2 coating on PP can provide durable hydrophilicity and corrosion resistance. Gaining better water retention ability, the thermal performance of nano-coated IEC can be enhanced under intermittent spray with 1.1 °C lower plate temperature and wet-bulb efficiency improved from 74.4 % to 81.4 % compared to the non-coated one.

Investigation of thermal performance at forced convection in plate-fin heat sink

Interest in studies on more effective and faster heat dissipation in microelectronic equipment has increased in recent years due to the cooling area and equipment size limitations. This study attempts to focus on the effect of different fin geometry parameters on pure forced convection heat transfer. Total surface areas of plate-fin heat sinks were kept constant and were carried out for ten different heat sinks in these analyses. The Ansys-Fluent 2023 R1 commercial package program was used to perform the thermal and hydrodynamic performance analyses. Three-dimensional turbulent forced convection heat transfer analyses at heat sinks were subjected to fluid flow (500≤Re≤3000). The effects of gap between fins, fin thickness, fin height, fin number, and air velocity on the heat transfer and the friction factor were obtained and discussed for heat sinks. It was observed that there was a maximum difference of 0.27 % between the maximum temperatures obtained as a result of this analysis and the experimental study results in the literature. Among the ten cases examined (from Case 1 to Case 10), the highest heat transfer coefficient was obtained in Case 2 (number of fins 6, gap between fins 4 mm, fin height 17 mm and fin thickness 2 mm) at Re = 3000. The heat transfer coefficient of Case 2 was 41.29 % higher than the heat transfer coefficient of Case 4 at Re = 3000; though, the friction factor of Case 2 is 55.93 % higher than Case 4. Also, a useful correlation for the heat transfer coefficient was generated for the fin geometric parameters and Reynolds number.

Experimental Investigation of Thermal Performance of Novel Finned Radiators for Automotive Cooling System

Experimental Investigation of Thermal Performance of Novel Finned Radiators for Automotive Cooling System

Numerical Investigation of Thermal Performance for Turbulent Water Flow through Dimpled Pipe

Dimples are tiny indentations on the surfaces of the body that enhance heat transfer and alter fluid flow characteristics on or within the body. Numerical investigations were conducted to analyse the heat transfer and flow characteristics in a cross-combined dimple tube in the range of Reynolds numbers from 6000 to 14000. The finite volume method recognised a novel enhancement model utilising methods for composite-form surfaces. Compared to a smooth tube working similarly, the effects significantly improve the heat transfer index, performance evaluation criteria, and friction factor. A three-dimensional simulation was conducted to clarify the underlying process by which dimples affect thermal performance. The simulation findings suggest that the dimples effectively enhance heat transfer by altering the temperature distribution and increasing the temperature gradient within the central area of the dimple section. A concave surface profile disrupts the flow and prevents the formation of a stable boundary layer, promoting the mixing of hot and cold fluids. Furthermore, the study investigates how geometric characteristics impact thermal and hydraulic efficiencies, emphasising that larger dimples improve overall thermo-hydraulic performance. Specifically, the heat transfer enhancement achieved an average increase of 17.3%, ranging from 18.03% to 38.6%, surpassing that of the traditional smooth tube.

Numerical Investigation of Thermal Performance of Minichannels with Transversely Patterned Non-Slip and Superhydrophobic Surfaces in Turbulent Flow Conditions

Numerical Investigation of Thermal Performance of Minichannels with Transversely Patterned Non-Slip and Superhydrophobic Surfaces in Turbulent Flow Conditions

Investigation of Thermal Performance of Optimized Tree-Shaped Fins in Latent Heat Storage Units

An innovative tree-shaped fin is proposed to address the problem of low thermal conductivity of phase change materials (PCMs) in latent heat energy storage units. Numerical methods are applied to investigate the thermal properties of the melting process of PCMs. This paper investigates the effects of fin arrangement, fin geometry parameters, and temperature of the heat source on melting characteristics of PCMs in the latent heat energy storage unit. Results show that the melting time of PCMs with the inwardly-tilted fins at the top increases by 21.3% compared to the outwardly-tilted fins at the bottom. The response surface methodology is adopted to obtain the fin parameter combination with lower quality and better performance. The optimal fin dimensions are a thickness of 1.06 mm, a length of 3.38 mm, and a spacing of 12.61 mm. The reduction of the ambient temperature from 35 °C to 30 °C increases the melting time of the latent heat energy storage unit by 85%, and from 35 °C to 40 °C decreases the melting time by 29%.

Advancement in experimental and computational approach for thermal performance investigation of single-tank packed bed thermal energy storage system

Advancement in experimental and computational approach for thermal performance investigation of single-tank packed bed thermal energy storage system

Experimental thermal performance investigation of air-type solar collector with PCM-rod embedded in vacuum tube

Based on an evacuated tube collector, this study designs a direct flow channel, a spiral tube structure, and a PCM-rod, which are combined to form an air-type direct flow evacuated tube collector integrated with a phase change material. In this study, the thermal performance of the proposed collector is tested and a new method of calculating the instantaneous thermal efficiency (η) by the equivalent thermal efficiency of the PCM (ηpcm) was proposed. Meanwhile, the heat storage effect of the PCM-rod and the influence of series or parallel connections and air supply mode on the thermal efficiency are analysed. The results demonstrate that the PCM-rod causes a more gradual temperature change in the collector, and the maximum temperature difference between the inlet and outlet of the collector reached 129.1 °C. When the radiation intensity is weak at 18:00, the outlet temperature of the collector can still reach 70.2 °C, which is 21.8 °C higher than that of the collector without a PCM-rod. At the same time, the use of PCM-rods can effectively improve the η of the collector and exhibit more gradual changes in η, and the maximum η is 285 %. In addition, the ηpcm can reach 225 %, which transfers heat efficiently and plays the role of peak cutting and valley filling. The η of the series-connected collector is lower than that of the parallel-connected collector during the day, but the opposite is true when the radiation intensity is weak. On the other hand, we should choose the upper air supply for the collectors connected in series, and then the lower air supply is more suitable when connected in parallel.

Development of sunflower husk reinforced polypropylene based sustainable composites: An experimental investigation of mechanical and thermal performance

AbstractClimate change, shrinking resources, and rising raw material costs have pushed the industry to create more sustainable, and lightweight materials. Natural fiber composites are materials of interest for replacing conventional materials such as steel. Sunflower husks (SH), among many other natural fibers, are readily accessible as agricultural waste and have advantageous properties. In this study, sunflower husks were mixed with polypropylene (PP) matrix using a twin‐screw extruder, and then tests specimens for experimental characterizations were manufactured through injection molding. The tensile tests revealed that the inclusion of SH into PP decreased the load‐bearing capacity of the composites by around 20% and increased their impact resistance by over 200%, while reducing the ductility by about eight times. Moreover, magnesium hydroxide (Mg(OH)2) was incorporated into the composites as a flame retardant, and it has improved the stiffness and impact resistance of the composites. Besides, incorporation of SH and Mg(OH)2 elevated significantly the glass transition temperature of the composites. The use of Mg(OH)2 delayed 60% the flame retention of the composites observed from UL‐94 HB flammability testing. In summary, they could be suitable for components such as spare wheel wells, seat backs, trunk floor, the acoustic panel behind the door, and airbag housing.

Modification of steel slag to prepare chlorides based composite phase change materials with shape stability for high-temperature thermal energy storage

Using steel slag to prepare high-temperature (>500 °C) PCMs was an effective way to achieve its high value-added utilization as a potential heat storage medium in a variety of applications, such as solar energy storage, power peak shaving, and industrial waste heat recovery. However, the complex solid waste of steel slag might be corrosive to salt-based PCMs at high temperature. To address this issue, steel slag was firstly modified with another solid waste (i.e., CFA), which was then used to microencapsulate NaCl-KCl to prepare shape-stabilized C-PCMs in this work. Thermophysical and mechanical properties of C-PCMs were analyzed. Results showed that CFA modification greatly improved chemical compatibility between steel slag and eutectic salt through phase reconstruction. Steel slag modified with 30 wt% CFA at 1100 °C was identified as the optimum skeleton. The prepared C-PCMs containing 50 wt% salt showed a phase transition temperature of 653 °C with a high latent heat of 139 J/g and an excellent cycling stability. Additionally, its thermal conductivity reached 1.46 W/(m·K), 180 % higher than of pure salt. Compressive strength of the composite could be as high as 119 MPa, superior to other salt-based C-PCMs. A heat storage device was further designed to allow the numerical investigation of thermal performance of the prepared C-PCMs in practical conditions. Attributed by reasonable arrangement of bricks, the heat storage device possessed a uniform temperature distribution over the vertical cross-section of HTF, which contributed to a quick completion of charging and discharging process. This work could potentially lay a foundation for application of steel slag in the field of high-temperature thermal energy storage.

Investigation of thermal performance, drying characteristics and environomical analysis: direct flow evacuated tube solar drying of okra.

A direct flow evacuated tube solar dryer (DF_ETSD), a novel drying system, was used for drying pre-treated okra (Abelmoschus esculentus). The performance of DF_ETSD was analysed by determining thermal profiling, dryer and collector efficiency hourly. The maximum 3-day average ambient temperature, collector outlet temperature and solar radiation were 35.6°C, 66.4°C and 976 W m-2 respectively. The collector efficiency increased as solar radiation increased over time due to a higher temperature difference between the collector outlet and ambient temperature. The maximum collector and dryer efficiency observed were 30.19% and 21.47%, respectively. A pre-treatment of okra was done in hot water at 70, 80 and 90°C for 5min. Okra samples were dried from an initial moisture content of 87.42 ± 1.49% (wb) to a final value of 10.77 ± 1.03% (wb) in 9h. The pre-treatment temperature of 80°C is suitable for maximum drying rate, colour retention and rehydration ratio and minimum water activity, which signifies the longer shelf-life of okra. Midilli and Kucuk model was best fitted (highest R2, lowest χ2 and RMSE) for the control and samples pre-treated at 80°C; however, Verma model was suitably fitted for the sample pre-treated at 70 and 90°C. The payback period of DF_ETSD was found to be 1.27years. Environmental analysis shows the CO2 emission and net CO2 mitigation ranged between 1.24 and 18.65 t and 9.86 and 154.05 t respectively for different selected lifecycles of the dryer. Due to its environmental sustainability and low payback period, the presented drying system is recommended for okra and other fruits and vegetables.

Numerical investigation of the overall thermal and thermodynamic performance of a high concentration ratio parabolic trough solar collector with a novel modified twisted tape insert using supercritical CO2 as the working fluid

Supercritical CO2 (sCO2) is favoured as the next-generation working fluid for advanced high-temperature and high-concentration ratio parabolic trough solar collectors (PTSC) due to the fluid’s low cost, availability and thermal stability at high temperatures. However, the lower thermal transport properties of sCO2 compared to conventional working fluids necessitate heat transfer enhancement of receivers using sCO2. In this study, a combined and extensively validated approach using Monte-Carlo ray tracing for optical analysis and computational fluid dynamics (CFD) for thermal and thermodynamic analysis were used to investigate the overall thermal and thermodynamic performance of a high concentration ratio sCO2-based PTSC with a modified twisted tape (MTT) inserts in the receiver. MTT inserts with twist ratios in the range of 2.0 to 4.0 and width ratios in the range of 0.75 to 0.95 were investigated. Results show enhancement of the heat transfer performance by up to 73% and thermal efficiency by 6%, and reduction of the receiver heat losses and circumferential temperature gradients when the MTT inserts are used. In addition to presenting results using the first law of thermodynamics, this study also considered the second law of thermodynamics by evaluating the entropy generation rates due to heat transfer and fluid friction irreversibilities. Results showed that the use of MTT inserts caused a reduction in the total entropy generation rates, with the lowest irreversibility occurring at a Reynolds number of 1,650,000 for a twist ratio of 2.0 and width ratio of 0.95.

Investigation of Thermal Similarity and Performances of Solar Thermal Air Collector with Heat-Soaked Vehicle Cabin

This article explores the potential of vehicle interiors, which can reach temperatures of up to 120°C due to solar exposure, as efficient solar collectors. Comparative studies have been conducted on the thermal behavior of heat-soaked vehicle cabins and dedicated solar collectors, highlighting their potential benefits in heating, cooling and ventilation. Thermal soak tests reveal a remarkable similarity in thermal performance between the two, with minor temperature variations of up to 5.3°C between the equivalent components. These temperature deviations are mainly due to differences in absorptivity characteristics, in which the black absorber plate exhibits superior absorption capabilities compared to the grey interior cabin surfaces. Integration of ambient air through the inlets on the cabin floor helps with initial cooling of the hot soaked cabin. The collector benefits from a preheated air mixture (comprising heat-soaked cabin air and ambient air), which improves its operating temperatures. This characteristic is attributed to the synergistic integration of the two systems. By decoupling these systems and aligning the properties of the absorber plate, the cabin and the collector could become thermally identical. The potential of the heated vehicle cabin as a power generation source is underscored, which presents opportunities to supplement the energy demand in remote locations. This study illuminates the untapped potential of vehicular solar heat capture, highlighting its feasibility, diverse applications, and significant implications for sustainable energy strategies and community development.

Thermal Performance Investigation of Thermoelectric Cooling System with Various Hot-Side Cooling Methods

Thermal Performance Investigation of Thermoelectric Cooling System with Various Hot-Side Cooling Methods

Experimental and numerical investigations of multi-layered ship engine room bulkhead insulation thermal performance under fire conditions

Abstract The thermal insulation layer of the ship’s engine room bulkhead is typically constructed from multiple layers of mineral wool. This layer is designed to keep the temperature on the surface of the bulkhead below 140°C in case of a fire. However, measuring the inner and external temperatures of each wall panel bulkhead type during a fire can be difficult. To address this issue, this study was conducted to evaluate the multilayer heat transfer capability of the bulkhead insulation in the event of an engine room fire. The study used heat transfer theory, experimental models, and numerical analysis to assess nine bulkhead insulation specimens. These specimens were fabricated from three original specimens and included a 10–30 mm air layer (W-75, W-50, and W-25). The results showed that all improved specimens had better thermal insulation than the originals. Among them, the improved specimens derived from the W-25 specimen exhibited the most significant temperature reduction compared to those derived from the W-75 and W-50 specimens. The results demonstrated a slight difference between the three methodologies, indicating a high level of reliability in the research findings.

Investigation of Thermal Performance of Heat Exchangers of Inclined-Elliptic-Tube Bundle

Passive performance improvement of heat exchangers is cost-effective and crucial for energy efficiency as well as sustainability of thermal systems. In this paper, an investigation is presented on a compact configuration of heat exchanger composed of a bundle of inclined elliptical tubes. The effect of geometrical parameters on the thermal performance of the heat exchanger is investigated for two tube arrangements i.e. inline and staggered configurations. These parameters include longitudinal (SL/a = 3 to 6) and transversal (ST/a = 2.5 to 5.5) pitch ratios. A CFD commercial code is used for simulation of heat transfer and fluid flow. Computations are performed for the Reynolds number range Re = 300-1500. The outcomes indicate higher performance of the staggered arrangement when compared with the inline inclined tubes. The best thermal performance is observed for a staggered configuration with SL/a = 6, ST/a = 5.5 at Re = 1500. Furthermore, correlations are provided for Nusselt number for heat exchangers of inclined elliptic tubes.

Effect of SCWSP-VGs and thermal performance investigation of pillow-plate type heat exchanger (PPHX)

Vortex Generators (VGs) are an innovative heat transfer enhancement in traditional heat exchangers. With this technique, the study investigates the combined impact of upper-lower Staggered Circular Welding Spot Patterns (SCWSP) and VGs, termed SCWSP-VGs, in a periodic enhanced Pillow-plate type heat exchanger (PPHX) using ANSYS Fluent 18.1. Numerical results reveal SCWSP-VGs induce a periodic velocity profile and opposite elliptical recirculation vortex (OERV) turbulence, significantly improving thermo-hydrodynamics compared to smooth enclosures. In addition, the performance of the PPHX is described or presented in the graphical form in terms of Colburn j-factor, Nu/Nu0, f/f01/3, Reynolds analogy factor, normalized drag coefficient ratio (Cx/Cx0)0.33, and (Nu/Nu0)/(f/f0)1/3. The maximum Nu and performance evaluation criterion (PEC) are improved by 41.34% and 1.68 in the dh/XL = 0.076 and 0.043 at Re = 1000, respectively.

Long-term thermal performance investigation of phase change plates (PCPs) employing tunnel lining ground heat exchangers for cool storage

Combining tunnel lining ground heat exchangers (GHEs) and phase change plates (PCPs) to extract and store the geothermal energy is a novel and environment-friendly energy utilization method, and then PCPs can be used for space cooling. However, existing investigations have not focused on the long-term thermal performances of PCPs employing tunnel lining GHEs for cool storage. In the present work, a coupled finite element model of tunnel lining GHEs and PCPs was built to study long-term operation performances of PCPs during the cold energy charging operation period. Numerical modeling and programming (i.e., co-simulation) were employed to realize the continuous cold energy charging operation mode of PCPs employing tunnel lining GHEs for cool storage. The results indicate that the solidification efficiency (i.e., cold energy charging efficiency) of PCPs and phase interface evolution within the PCPs under the long-term cold energy charging mode are affected by the number of times for cool storage (N) and thermal conductivity of the surrounding rock (ksr) compared with the short-term mode. The drop rate of the liquid fraction and solidification efficiency of PCPs decrease with an increase in the number of times for cool storage. At N = 1, there is no obvious difference for the solidification efficiency of PCPs with increasing ksr. The solidification efficiency of PCPs under N = 10 improves by approximately 35.3% as ksr rises by 3 W/(m K). Additionally, the solidification time of PCPs increases linearly with N under ksr = 1.22 W/(m K). However, the solidification time is related parabolically to N under ksr = 2.22, 3.22, and 4.22 W/(m K). Finally, the long-term thermal response of the surrounding rock is analyzed, which also verifies the heat transfer characteristics of PCPs under the long-term cold energy charging mode.

Thermal performance investigation of water-based nanofluids in an ice storage system

In this study, the combined effects of heat transfer enhancement and cost increment of water-based nanofluids in an ice storage system are investigated theoretically. First, a model for describing the ice formation process of water around a helical coil is established, and the model is verified by comparing the simulation and experimental results. Second, the heat transfer performance of water-based Al2O3 nanofluids and multi-wall carbon nanotubes (MWCNT) nanofluids with different nanoparticle volume fractions are simulated with the established model. Although 0.05 v.% M/W shows the best heat transfer performance, it has a higher cost. In this study, an economic analysis of these two nanofluids is conducted, and a benchmark based on economic analysis and heat transfer performance analysis is obtained, comparing the ice-making performance of the two nanofluids. Based on the benchmark point E, the ice-making performance of two nanofluids can be separated into three regions: a low-performance region, an economic region, and a heat transfer region. In the low-performance region, the enhancement effect on heat transfer performance is small. In the economic region, A/W is a more ideal ice-making medium. In the heat transfer region, M/W is a more ideal ice-making medium.