Investigation Of Thermal Performance Research Articles

Investigation of thermal performance of modified vertical rectangular fin array in free convection using experimental and numerical method

Heat transfer by free convection from fin array is influenced by modification in size and shape of the fins as well as interruption in fluid flow. The objective of heat sink is the thermal management of electronic devices by removing excessive heat and improve the lifespan of the device. The paper investigates the thermal performance of free convection heat transfer with vertical heat sink by providing slits along the vertical surface of the fins. For the evaluation purpose two different arrangements viz. plain fin and slitted fin are selected. Fins are made from high thermal conductivity aluminium material and five dissimilar heat inputs are selected for study. The experimental and numerical findings are confirmed using the theoretical correlations available from the literature.The effect of number of slits and width of slits is investigated on convective heat transfer coefficient. Numerical study is used to understand the flow patterns around the vertical fin surface. It has been observed that the presence of slits on the surface appreciably improves the thermal performance of vertical fin array.

Experimental investigation and analytical prediction of a multi-channel flat heat pipe thermal performance

Recently, multi-channel flat heat pipes have been developed to improve the heat recovery from flat surfaces, such as solar panels and batteries. In this paper, the thermal performance of a multi-channel flat heat pipe is experimentally investigated and analytically predicted. The multi-channel heat pipe studied transmits heat from silicone flat heaters to a water flow circulating inside a cooling manifold. The manifold heat sink is a flat aluminium surface comprising channels in which water recovers thermal energy by forced convection. The impact of the water flow rate on the working temperature of the heat pipe is investigated. To predict the performance and working temperature of the multi-channel flat heat pipe, a theoretical model has been developed. The thermal model considers the two-phase heat transfer in a multi-channel heat pipe geometry. It is shown that the heat pipe working temperature decreases with the water flow rate as a result of a reduced forced convection resistance of the manifold. Finally, the analytical multi-channel flat heat pipe model developed is compared with experimental data. It is shown that the thermal model, considering both cooling manifold and the multi-channel heat pipe geometry, is able to predict the heat pipe working temperature evolution within 7%.

Thermal performance investigations of the melting and solidification in differently shaped macro-capsules saturated with phase change material

Abstract The storage of phase change material in the macro-capsules used for a latent thermal energy storage system significantly enhances the thermal performance compared to the conventional shell and tube heat exchanger. The geometrical shape and dimensions of these capsules have a major impact on the melting and solidification characterization. Most of the research is, however, carried out using a spherical capsule only. Hence, the influence of the differently shaped macro-capsules is required to be evaluated to obtain thermal performance enhancement. An experimental setup is developed to validate numerical observations. The primary objective of the present study is to visualize the phase change phenomenon and compare the thermal behavior of differently shaped capsules (spherical, cubical, triangular, and plus-shaped) during the melting and solidification processes. Results show that the triangular capsule exhibits better thermal performance with melting and solidification time of 41 min and 133 min, respectively. In addition, the increase in the heat transfer fluid temperature increases the melting rate. Furthermore, it is found that the 27% reduction in the capsule size decreases melting and solidification time by 12.19 and 19.17%, respectively. Hence, the capsule size has more influence on the solidification process compared to the melting process.

Experimental and thermal performance investigations on sensible storage based solar air heater

Abstract The thermal performance of the solar collector for air heating purpose is investigated with and without packed bed through experimental and theoretical methods. A simple flat plate solar air heater was developed with 2m2 corrugated absorber plate and integrated with porous pebble bed in the airflow path to act as a sensible heat storage medium. The experimental studies were carried out for different mass flow rates of air from 0.014 to 0.087 kg/s with the increment of 0.0095 kg/s. Steady-state theoretical models have been established to predict the thermal performance of the air heaters and the results indicated that they are well enough to predict the outlet air temperature with acceptable error percentage. The collector with packed bed storage medium is more efficient than without packed bed in terms of energy efficiency as well as in reducing temperature fluctuation of air at the outlet of the collector. The energy and exergy efficiency of the collector with packed bed veried from 20.35% to 50.92% and +3.97% to −2.807% for the airflow rates 0.014 kg/s to 0.087 kg/s respectively. Solar collectors with packed bed are capable to deliver the hot air in the range of 45 to 60 °C for a longer period and which can be preferred for achieving a better quality of the dried products as well as for space heating applications.

Design and thermal performance investigation of a box cooker with flexible solar collector tubes: An experimental research

Abstract In recent years, solar cookers have been technologically promoted by most of the national governments as renewable and sustainable cooking system round the globe. In the present article, a solar box cooker (SBC) has been developed for fast response and uninterrupted cooking process. For this purpose, a cylindrical copper tube infused with thermal energy storage (TES) has been designed and tested under a modified SBC. Experimental study has been carried out on three different TES materials such as; grainy carbon powder, paraffin wax and specific mixture of carbon powder and paraffin. Specifically, twelve TES filled tubes have been brought into the use for experimentation at three different configurations. Results indicate that the modified cooker has better performance in terms of efficiency (53.81%), overall heat loss coefficient (5.11 W/m2°C), cooking power (68.81 W) and heat transfer coefficient (56.78 W/m2°C) in comparison with a conventional SBC and other designs using different TES materials. PCM infused tubes are low in cost and flexible to carry with SBC for outdoor cooking. It can easily be carried anywhere along with cooker. This novel configuration enables a fast response cooking with an enhanced efficiency irrespective of climatic conditions. The total cost of SBC is estimated about $39.11.

A Novel Approach for Energy Efficiency Prediction of Various Natural Draft Wet Cooling Towers Using ANN

Cooling tower is crucial equipment in the cool-end system of power plant and the natural draft counter-flow wet cooling tower (NDWCT) gets wide application. The artificial neural network (ANN) technique is becoming an effective method for the thermal performance investigation of cooling towers. However, the neural network research on the energy efficiency performance of NDWCTs is not sufficient. In this paper, a novel approach was proposed to predict energy efficiency of various NDWCTs by using Back Propagation (BP) neural network: Firstly, based on 638 sets of field test data within 36 diverse NDWCTs in power plant, a three-layer BP neural network model with structure of 8-14-2 was developed. Then the cooling number and evaporation loss of water of different NDWCTs were predicted adopting the BP model. The results show that the established BP neural network has preferable prediction accuracy for the heat and mass transfer performance of NDWCT with various scales. The predicted cooling number and evaporative loss proportion of the testing cooling towers are in good agreement with experimental values with the mean relative error in the range of 2.11%–4.45% and 1.04%–4.52%, respectively. Furthermore, the energy efficiency of different NDWCTs can also be predicted by the proposed BP model with consideration of evaporation loss of water in cooling tower. At last, a novel method for energy efficiency prediction of various NDWCTs using the developed ANN model was proposed. The energy efficiency index (EEI) of different NDWCTs can be achieved readily without measuring the temperature as well as velocity of the outlet air.

Empirical Thermal Performance Investigation of a Compact Lithium Ion Battery Module under Forced Convection Cooling

Lithium ion batteries (LiBs) are considered one of the most suitable power options for electric vehicle (EV) drivetrains, known for having low self-discharging properties which hence provide a long life-cycle operation. To obtain maximum power output from LiBs, it is necessary to critically monitor operating conditions which affect their performance and life span. This paper investigates the thermal performance of a battery thermal management system (BTMS) for a battery pack housing 100 NCR18650 lithium ion cells. Maximum cell temperature (Tmax) and maximum temperature difference (ΔTmax) between cells were the performance criteria for the battery pack. The battery pack is investigated for three levels of air flow rate combined with two current rate using a full factorial Design of Experiment (DoE) method. A worst case scenario of cell Tmax averaged at 36.1 °C was recorded during a 0.75 C charge experiment and 37.5 °C during a 0.75 C discharge under a 1.4 m/s flow rate. While a 54.28% reduction in ΔTmax between the cells was achieved by increasing the air flow rate in the 0.75 C charge experiment from 1.4 m/s to 3.4 m/s. Conclusively, increasing BTMS performance with increasing air flow rate was a common trend observed in the experimental data after analyzing various experiment results.

Cellulose nanofibril (CNF) based aerogels prepared by a facile process and the investigation of thermal insulation performance

Herein, a facile method on fabricating aerogels with hierarchical porous structures was created by freeze-drying the cellulose nanofibril (CNF)/methyltrimethoxysilan (MTMS)/fumed silica (FS) suspension. FS was introduced for its porous structure, which could improve the thermal insulation performance of freeze-dried aerogels. The as-prepared aerogels were hydrophobic with improved mechanical properties (elastic recovery rate was up to 99.7%) and reduced thermal conductivity (0.027 Wm−1 K−1 at 25 °C). Most importantly, the addition of FS was proved to improve the thermal insulation stability of cellulose aerogels efficiently in different values of relative humidity (RH) and temperatures. The thermal conductivity of pure CNF aerogel conditioned at 25 °C and 95% RH was 196% higher than that of the fully-dried one, while the increase was 56% for the composite aerogel. Besides, at 30% RH, the thermal conductivity increased by 24% for the pure CNF aerogel when tested from 20 to 60 °C while only a 2% increase for the composite aerogel. Moreover, when tert-butanol was used as the solvent to optimize the distribution of the pores of freeze-dried aerogels, their thermal insulation performance was further improved. Our work provides easily available CNF/MTMS/FS ternary aerogels, which are stable in thermal conductivity in the changing environment.

Enhanced photothermal conversion performances with ultra‐broad plasmon absorption of Au in Au/Sm2O3 composites

AbstractLanthanide oxides are ideal candidates as photothermal conversion agents owing to their larger photon energy and advantages in biomedical applications. However, the small absorption cross section of rare earth is not conducive of absorbing near infrared light, which will affect the photothermal conversion efficiency of lanthanide oxides. Herein, Au particles are successfully introduced into Sm2O3 to form Au/Sm2O3 composites. The investigation of broadband emission and thermal performances in Sm2O3 and Au/Sm2O3 composites confirm the ultra‐broad plasmon absorption of Au induced thermal effect is in favor of the formation of broadband emission, meanwhile, enhances the photothermal conversion capability of Au/Sm2O3 composites. The temperature increases of the Au/Sm2O3 composites are 5.5°C and 19.6°C compared to Sm2O3 particles under the irradiation of near infrared laser with power density of 11.5 and 29.0 mW/mm2, respectively. In additional, the enhanced photothermal conversion effect is confirmed by the alcohol volatilization experiment and visual infrared thermal images. We present here an idea for enhancing the photothermal conversion capabilities of lanthanide oxides and highlight the promise of using this kind of materials for photothermal therapy.

Thermal and Energy-Efficiency Assessment of Hybrid CLT–glass Façade Elements

Façade elements are a building component that satisfies multiple performance parameters. Among other things, “advanced façades” take advantage of hybrid solutions, such as assembling laminated materials. In addition to the enhanced mechanical properties that are typical of optimally composed hybrid structural components, these systems are energy-efficient, durable, and offer lighting comfort and optimal thermal performance, an example of which is the structural solution developed in collaboration with the University of Zagreb and the University of Ljubljana within the Croatian Science Foundation VETROLIGNUM project. The design concept involves the mechanical interaction of timber and glass load-bearing members without sealing or bonding the glass-to-timber surfaces. Following earlier research efforts devoted to the structural analysis and optimization of thus-assembled hybrid Cross-Laminated Timber (CLT)-glass façade elements, in this paper, special focus is given to a thermal and energy performance investigation under ordinary operational conditions. A simplified numerical model representative of a full-size building is first presented by taking advantage of continuous ambient records from a Live-Lab mock-up facility in Zagreb. Afterwards, a more detailed Finite Element (FE) numerical analysis is carried out at the component level to further explore the potential of CLT–glass façade elements. The collected numerical results show that CLT–glass composite panels can offer stable and promising thermal performance for façades similar to national and European standard requirements.

Investigation of Mechanical, Thermal and Melt Flow Performance of Polycarbonate Hybrid Composites Containing Mica Flakes and Glass Fiber

Investigation of Mechanical, Thermal and Melt Flow Performance of Polycarbonate Hybrid Composites Containing Mica Flakes and Glass Fiber

Experimental Investigation of Thermal Performance of a Solar Chimney Provided with a Porous Absorber Plate


 Experimental investigation of the influence of inserting the metal foam to the solar chimney to induce natural ventilation are described and analyzed in this work. To carry out the experimental test, two identical solar chimneys (without insertion of metal foam and with insertion of metal foam) are designed and placed facing south with dimensions of length× width× air gap (2 m× 1 m× 0.2 m). Four incline angles are tested (20o,30o,45o,60o) for each chimney in Baghdad climate condition (33.3o latitude, 44.4o longitude) on October, November, December 2018. The solar chimney performance is investigated by experimentally recording absorber plate and air temperatures and velocity of air. Results indicated that the using metal foam absorber plate lead to reducing the mean temperature of absorber plate by 6.7 °C as a result, the values of chimney outlet air temperature increased. The daily solar chimney efficiency enhanced by 58.7% and the useful energy received also increased. The existence of metal foam caused higher air velocity at the exit and increasing in the ventilation rate that the maximum ventilate rate obtained from the solar chimney is 5.96 1/hr for 27 m3 volume of room at solar irradiance of 730 W/m2 for chimney incline angle of 60o. The results of the experimental work show that the addition of metal foam to the solar chimney as an absorber plate is an efficient method to enhance the characteristics of heat transfer and the thermal performance of the solar chimney in the weather condition of Iraq.

Numerical Investigation of Thermal Performance of Micro-Pin Fin with Different Arrangements

The impact of micro-pin fins on heat transfer performance in this study is analyzed numerically. Navier-Stokes equations are solved by steady-state three dimensions turbulent forced convection. Various numbers of micro-pin fins with in-line configuration and different micro-pin fins configurations such as staggered configuration additionally to the in-line configuration are explored. In addition, comparison between micro-pin fins duct and smooth duct is studied. Results illustrate that the thermal performance was enhanced by 7.9 - 9.3% with increasing the number of micro-pin fins from 902 to 1312 and by 10.2 - 11.1% with increasing the number from 902 to 1640. Also, displays that the heat transfer performance in the staggered configuration is slightly better than the in-line configuration by 2.6 - 4.2% with the same micro-pin fins number. Moreover, the micro-pin fins duct gave an increase of 30.24% in heat transfer performance relative to the smooth duct.

Numerical Investigation of Thermal Performance for Air Solar Collector with Multi Inlets

Over the years, there has been rigorous modification of solar collectors for the thermal needs of the era to be efficiently served. A variety of design innovations have paved their way into the invention of novel ways of securing more solar energy as useful heat. Primarily, this study investigates the effects of multi air inlets on the transfer of heat between air flow and the absorber of flat plate collector. Computational Fluid Dynamics was employed to simulate a flat plate collector with 1, 2 and 3 inlets to evaluate the thermal performance with more than one inlet. The results showed that the 3 inlets case has the highest exit temperature followed by 2 inlets and then 1 inlet. Also higher exit air temperature can be obtained for higher heat flux and slower inlet velocity.

Environmental Heat Stress on Indoor Environments in Shallow, Deep and Covered Atrium Plan Form Office Buildings in Tropics

Environmental heat stress on buildings through façades contributes to indoor overheating and thus increases demand for energy consumption. The study analyzed the problem, heat gain risk, of modern air-conditioned multi-level office buildings in tropics, for example Colombo. Plan form, orientation, sectional form and envelope were identified and theorized to understand design interventions to reduce the risk of getting heat stress on indoor environments. On-site thermal performance investigations in multi zones of identified three typical built forms, namely; shallow, deep and covered atrium plan forms, quantified the heat stress. Reaching the daytime indoor and surface temperature in peripheral zones of multi-story office buildings during air conditioning “off-mode” up to 38 °C–42 °C was seen as a critical heat stress situation to be addressed through building design. Shading or insulation on façades to control environmental heat gain and manipulation of building section for night ventilation to remove internal heat developed during the daytime are discussed. However, the significance of the plan form depth was found to be a main contributor in dealing with heat transfer to indoor space. Deep plan form was found to be more effective in controlling environmental heat transfer to indoor space across the plan depth.

Efficient design of curved solar air heater integrated with semi-down turbulators

Recent investigations reveal that curved solar air heaters (SAH) thermo-hydrodynamically performs better in comparison to flat SAH design. Further, it has been observed that down-configurations of turbulators or extended surfaces on the flat plate solar collector significantly enhance the thermal performance. However, scientific literature on thermal performance investigations with down-configurations of ribs in curved SAH are rare. In the paper, we systematically investigate using experimentally validated computational fluid dynamics model for different shapes of down-configuration of ribs. It was observed that half-trapezoidal and quarter-circular shape ribs shows maximum increase in thermal performance i.e. 17% and 16%, respectively, however frictional loss for quarter-circular ribs was observed to be less by about 10% when compared to trapezoidal shape ribs. The exergy recovery is maximum for trapezoidal and circular shape ribs and it is about 35% more than the smooth flat SAH. A new correlation has been developed for Nusselt number variation which has the form as Nu=f[Re,erH] where er is the height of quarter-circle groove. Observed data from the model matches well with the prediction from the developed correlation.

Assessment of thermo-hydraulic performance of inward dimpled tubes with variation in angular orientations

This paper presents a numerical investigation and assessment of thermal and hydraulic performance of dimpled tubes of varying topologies at constant heat flux of 10kW/m2 and Reynolds numbers ranging from 2300 to 15,000. The performance of the tubes consisting of conical, spherical and ellipsoidal dimples with equivalent flow volumes were compared using steady state Reynolds Averaged Navier Stokes simulations. The ellipsoidal dimples, in comparison to other dimple shapes, demonstrated large increment in heat transfer rate. The variation in the orientation of the ellipsoidal dimples was examined to further improve thermal and hydraulic performances of the tube. A 45° inclination angle of ellipsoidal dimple, from its major axis, increased the thermo-hydraulic performance by 58.1% and 20.2% in comparison to smooth tube and 0° ellipsoidal dimpled tube, respectively. Furthermore, Large Eddy Simulations (LES) were carried out to investigate the role geometrical assistance to fluid flow and heat transfer enhancement for the 45° and 90° ellipsoidal dimpled tubes. LES results revealed a flow channel of connected zones of wakes which maximized fluid-surface contact and therefore enhanced the thermal performance of the tube. In addition, correlations for Nusselt number and friction factor for all angular topologies of ellipsoidal dimpled tube have been proposed.

Thermal performance investigation of the miniature revolving heat pipes using artificial neural networks and genetic algorithms

The miniature revolving heat pipes (MRVHPs) are promising candidates for the cooling structure design of rotating machines, however, the relation between the thermal performance of MRVHPs and their thermophysical properties is still absent. Therefore, MRVHPs are tested in various operational conditions firstly. And then, a power-law empirical correlation is developed based on experimental data, Ku, Ja, Pr, Bo and Fr are determined as main effective dimensionless parameters, while the structural parameters of MRVHPs Di/R, Le/Lc, Le/Leff and filling ratio φ are considered as well. However, the prediction accuracy is not satisfactory enough. Considering ANNs have been widely used in varied applications and demonstrated to be particularly credible in system modeling and identification, therefore, a BPNN model which parameterized by GA is developed for thermal performance prediction of the MRVHPs. The experimental data are divided into training data set and testing data set. Ja, Pr, Bo, Fr and φ are regarded as inputs, while Ku is output. The results show that the established GA-BPNN model could predict thermal performance of MRVHPs with a very good accuracy. Comparing with the predicted results of semi-empirical correlation, the square of correlation coefficient (R2) is increased by 13.265%. Meanwhile, the evaluation method for the optimal filling ratio of the MRVHPs under specified working conditions is developed and an acceptable accuracy is obtained.

Parametric Study on Integrated Thermal and Mechanical Performance of Molten Salt Receiver for Solar Tower Power Plant

In this study, the mathematical and numerical models of a receiver tube are established for the integrated thermal and mechanical performance investigation of molten salt solar receiver. Effects of four parameters on heat transfer performance and thermal strain of the receiver are studied. The results indicate that when other parameters are settled, a smaller tube internal diameter can lead to a higher convection heat transfer coefficient and a smaller thermal strain. As the tube wall thickness increases, the convection heat transfer coefficient and thermal strain both increase. With the inlet molten salt flow velocity increased, the convection heat transfer coefficient increases and the thermal strain decreases. Similar to the effect of inlet flow velocity of molten salt, a higher inlet molten salt temperature can also improve the convection heat transfer coefficient and reduce the thermal strain. The thermal efficiency of the receiver can be improved by increasing the inlet flow velocity of molten salt, or by reducing the receiver tube internal diameter, tube wall thickness, or inlet molten salt temperature. All results have revealed the effect laws of the four parameters on the thermal and mechanical performances of the receiver tube, which may be helpful for the further research and development of molten salt solar receiver for solar thermal power plant.

Comparative Thermal Performance in SiO2-H2O and (MoS2-SiO2)-H2O over a Curved Stretching Semi-Infinite Region: A Numerical Investigation

The investigation of Thermal performance in nanofluids and hybrid nanofluids over a curved stretching infinite region strengthens its roots in engineering and industry. Therefore, the comparative thermal analysis in SiO2–H2O and (MoS2–SiO2)–H2O is conducted over curved stretching surface. The model is reduced in the dimensional version via similarity transformation and then treated numerically. The velocity and thermal behavior for both the fluids is decorated against the preeminent parameters. From the analysis, it is examined that the motion of under consideration fluids declines against Fr and λ. The thermal performance enhances for higher volumetric fraction and λ. Further, it is noticed that thermal performance prevailed in (MoS2–SiO2)–H2O throughout the analysis. Therefore, (MoS2–SiO2)–H2O is better for industrial and engineering uses where high heat transfer is required to accomplished different processes of production.