Investigation Of Thermal Performance Research Articles

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 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.

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.

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.

Numerical investigation of the long-term thermal performance of a novel thermo-active foundation pile coupled with a ground source heat pump in a cold-climate

The potential to drastically reduce the high upfront cost and the additional land requirement of installing the ground heat exchanger of a ground source heat pump (GSHP) system has led to an increasing interest in thermo-active foundation piles. This study numerically investigates the long-term thermal performance of a novel offset pipe thermo-active foundation pile in a GSHP system for residential space heating and cooling. The pile is a fully enclosed helical steel pile that is 18.288 m deep and 0.139 m in diameter with eccentrically placed inlet and outlet pipes. A thoroughly validated numerical model coupled with realistic normalized building load profiles was employed for the analysis. Four installation configurations (pile beneath a basement, pile beneath a surface-level concrete slab, pile installed at the ground surface level, and pile buried underground) were considered. In addition, the potential of the pile to meet three realistic normalized building load profiles (maximum heating load: 0.3 tons, 0.4 tons, and 0.6 tons) was investigated. The long-term study results indicate that the ground thermal imbalance causes an average ground temperature drop of −0.18 K/year, −0.25 K/year, −0.41 K/year for the three load profiles. Moreover, the ground thermal imbalance causes the system heating COP to decrease by 0.006/year, 0.011/year, and 0.021/year for the 0.3-ton, 0.4-ton, and 0.6-ton maximum load profiles, respectively. Results further show that installing the pile under the basement gives the best overall performance regarding heating COPs and heat pump operability. When used as a retrofit solution for an existing building, burying the pile underground gives the best performance compared to installing it at the ground surface level.

Real‐time thermal performance investigation of a thermal energy storage integrated direct absorption solar collector under tropical climate

AbstractIn the last two decades, metallic particles of nano sizes (~10−9 m) have been tested profoundly in volumetric absorption solar collectors (VASC) due to their excellent optical properties and broadband absorption in the entire solar spectrum. However, very limited studies are available for understanding the performance of integrated energy storage VASC systems using nanofluids. For the experimental work presented here, a hybrid nanofluid of gold nanoparticles in Azadirachta indica leaves extract has been synthesized by chemical route. The prepared hybrid nanofluid has shown good absorption in 400 to 700 nm wavelength range and hence achieved high photo‐thermal conversion efficiency for tested VASC system. Furthermore, commercially available paraffin wax is used as a phase change material (PCM) in thermal energy storage (TES) and further integrated with VASC to analyze the thermal performance of the system even after sunshine hours. The real‐time experiments were conducted using different working fluids, and at three mass flow rates, that is, 0.008 kg/s, 0.016 kg/s, and 0.033 kg/s, respectively, during mild winter days in the tropical climate of India. The study revealed a photo‐thermal efficiency enhancement of about 17.1% when hybrid heat transfer fluid was used in the VASC system with TES as compared to base fluid water but without TES. During the heating period, the maximum thermal gain of the hybrid nanofluid was observed to be about 15°C higher than the ambient temperature at mass flow rate of 0.033 kg/s. Thermal efficiency enhancement of about 23.8%, 24%, and 24.1% was observed with hybrid nanofluid compared to base fluid water at a mass flow rate of 0.008 kg/s, 0.016 kg/s, and 0.033 kg/s, respectively, when PCM was kept inside the tank. Furthermore, a maximum zero loss efficiency of 83.8% was estimated at an optimal mass flow rate of 0.033 kg/s for the TES‐integrated VASC system.

Experimental investigation of thermal performance of three configurations evaporative cooling systems (ECS) using synthetic grass wet media materials

Space cooling of buildings using evaporative cooling is a passive strategy that can provide thermal comfort for occupants and conserve energy. In this paper, an innovative evaporative cooling wet media material in the form of synthetic grass fibre mat was introduced to evaluate experimentally its effectiveness in Direct Evaporative Cooling (DEC), Indirect Evaporative Cooling (IEC), and Dew point evaporative cooling (DPEC). A laboratory evaporative cooling module was constructed and tested using a fully instrumented test rig and was subject to environmentally controlled conditions of air temperature and relative humidity (RH) commensurate to those prevailing in hot and dry climates like the Middle East. The wet bulb effectiveness and cooling capacity of evaporative coolers equipped with the new wet media material were evaluated experimentally. The results show that these evaporative coolers performance correlate well with current technology. For instance, the ambient air temperature is reduced by as much as 12.9 °C, 10.2 °C, and 10.3 °C for direct, indirect, and dew point modes, respectively. It was also shown that DEC achieved effectiveness 20 % higher than indirect evaporative coolers. The work demonstrated that the new wet media can be a viable alternative to organic and non-organic counterparts.

Experimental investigation and artificial neural network-based modelling of thermal barrier engine performance and exhaust emissions for methanol-gasoline blends

In recent years, due to environmental concerns and the depletion of fossil fuels, alternative fuel use and alternative emission reduction methods have gained importance in the automotive industry. In addition, methanol is used as an alternative fuel in gasoline engines with coated piston engines. This study first presents an experimental investigation of engine performance and exhaust emissions for a partially thermal barrier lined piston engine operating on methanol-gasoline blends. In the second phase the obtained data is then used to develop an Artificial Neural Network (ANN) based model to predict engine performance and exhaust emissions for methanol-gasoline blends. The developed ANN model was trained and validated using MATLAB. The results of the experimental study showed that the use of methanol-gasoline blended fuel in the engine provides better engine performance and reduced exhaust emissions compared to gasoline fuel. According to the results obtained, an increase of 3.7 % in effective power and a decrease in NOx and HC emissions by 19 % and 18 %, respectively, compared to the STD case when both coating and alternative fuel are used in the engine. With the established ANN models, engine performance parameters and exhaust emission parameters were predicted with 99 % and 98 % accuracy respectively.

Investigation of thermal performance and entropy generation rate of evacuated tube collector solar air heater with inserted baffles and metal foam: A CFD approach

This study investigates the impact of metal foam embedding into evacuated tube collector solar air heaters with inserted baffle (IBMF-ETC-SAH) on the device thermal performance using a computational fluid dynamics (CFD) approach. A three-dimensional model is employed to analyze the system under steady-state conditions. The key finding of this study is that the utilization of metal foam leads to a substantial increase in thermal performance, with an average improvement of approximately 300 %. The investigation examines the influence of metal foam porosity and pores per inch (PPI) on the performance of the IBMF-ETC-SAH across Reynolds numbers ranging from 6000 to 18,000. The results indicate that increasing the PPI from 20 to 40 at a constant porosity of 0.93 has negligible effects on device performance. However, the pressure drop increases by 48 % for a PPI of 40 compared to a PPI of 20. Furthermore, reducing the porosity from 0.95 to 0.9 leads to a 7 % enhancement in thermal performance. The IBMF-ETC-SAH exhibits a significant decrease in the total global entropy generation rate (EGR) compared to the device without metal foam. The maximum value of total EGR for the IB-ETC-SAH case is 2.32 times higher than the corresponding values for the IBMF-ETC-SAH case.

Experimental investigation of thermal performance of vertical multitube cylindrical latent heat thermal energy storage systems

The multitube design in the shell-and-tube type latent heat thermal energy storage (LHTES) system has received intensive attention due to its promising benefits in enhancing heat storage efficiency. In this paper, single and multi-tube shell LHTES systems were experimentally investigated. First, this study experimentally compared the thermal characteristics between a multiple-tube heat exchanger (MTHX) and a single-tube heat exchanger (STHX). The STHX’s geometrical parameters coincided with a virtual cylindrical domain in the MTHX, being similar to the single-tube model formulated by simplifying the numerical solution to investigate the MTHX. The experimental data was then used to validate the simplified numerical model commonly used in the literature that converted the multi-tube problem to a single-tube model by formulating a virtual cylindrical domain for each tube in the MTHX system. The results showed that there was a noticeable difference in the thermal characteristics between the actual STHX and the virtual cylindrical STHX domain in the MTHX system. The comparison indicated that the simplified numerical model could not accurately reflect the thermal performance of the MTHX system. An experimental study or three-dimensional numerical modelling was required for the thermal analysis of the multi-tube problems. Second, the effect of tube number in the MTHX was experimentally investigated. It was found that an increase in tube number boosted both charging and discharging rates without inhibiting the natural convection. The five-tube configuration decreased the total charging and discharging duration by 50% compared to the two-tube one. Finally, the effect of heat transfer fluid (HTF) operating parameters on the system performance was evaluated on the five-tube MTHX system. The results revealed that the adoption of higher HTF temperature considerably improved the charging performance. The charging time decreased by up to 41% with the HTF temperature increasing from 70 to 80 °C. Meanwhile, a variation in the HTF flow rate from 5 to 20 L/min showed a more pronounced influence on charging than on discharging due to the different dominant heat transfer mechanisms.

Thermal performance investigation of membrane-assisted radiant cooling system for localised outdoor cooling hub

Heat waves pose increasing threats to human well-being, especially in urban areas, and staying safe beyond comfort during heat waves is a crucial issue. Localised cooling hubs may provide thermal stress relief in the outdoor environment. For outdoor cooling applications, conventional air conditioning systems are not effective but energy-intensive, and the membrane-assisted radiant cooling system can be a potential alternative, which directly treats the radiant loads while minimising the convective heat loss to the ambient. In the present study, a numerical model is developed to analyse the heat transfer behavior of membrane-assisted radiant cooling for outdoor applications, considering the effect of solar and long-wave radiation and wind parameters. As the transmissivity of the membrane material plays a crucial role in reducing the amount of solar heat, the performances of three types of membranes, i.e., non-selective, mid-infrared selective, and sky-window selective, were compared and analysed at different times on a typical summer day in Hong Kong. The results indicate that the sky-window selective membrane, which allows only transmission of infrared in the 8–15 µm wavelength range, saves energy up to 44 % and 47% compared with mid-infrared selective and non-selective membranes, respectively. In the outdoor application, the equivalent convective heat transfer coefficient of the cooling panel can be reduced in the range of 2.2 W/m2K to 2.6 W/m2K. It is observed that, when the panel is not exposed to direct solar radiation, there is no advantage in using the mid-infrared selective membrane over the non-selective membrane. However, under direct solar radiation, a non-selective membrane-assisted cooling panel demonstrates poor performance, absorbing solar heat flux 2.27 times higher compared to MIR-selective membrane-assisted panel.

Thermal performance investigation and optimization of a novel v-shaped finned latent heat storage unit

The low thermal conductivity of phase change materials limits the thermal performance of heat storage devices, hindering their widespread application in engineering. To address this challenge, this paper focused on the fin design of a horizontal triplex-tube latent heat storage device. A novel V-shaped fin with a secondary arrangement is proposed. Numerical simulation is employed to investigate the effects of fin angle, fin length, and heat transfer fluid temperature on the thermal performance of the storage system. Moreover, the fin parameter is optimized by the response surface method. The results demonstrate that, compared to traditional rectangular fins, both the primary and secondary V-shaped fins can significantly enhance the thermal performance. The secondary V-shaped fin has the most significant effects, reducing the melting time of the phase change material by 48.5%, and increasing the average heat storage rate by 83.46%. Additionally, the thermal performance of the heat storage unit exhibits a trend of initially increasing and then decreasing with the increase of fin angle and length, suggesting the existence of optimal structural parameters. Consequently, the optimized secondary V-shaped fin reduces the melting time by 52.9% and increases the average heat storage rate of phase change materials by 104.48%.

Numerical Investigation of Thermal and Hydraulic Performance in an Interrupted Microchannel Heat Sink with Aluminum Oxide Nanofluid

Numerical Investigation of Thermal and Hydraulic Performance in an Interrupted Microchannel Heat Sink with Aluminum Oxide Nanofluid