Lower Heat Transfer Rate Research Articles

Backfill thermal properties improvement using granular phase change materials and graphite

Phase change materials (PCMs) are ideal for thermal energy storage due to latent heat release or absorption at target temperatures. Hence, adding PCMs into backfill materials of ground heat exchangers for example, can enhance the borehole thermal energy storage capacity and the corresponding shallow geothermal system performance. However, the heat transfer efficiency between the borehole and surrounding ground might be reduced because of the low thermal conductivity of PCMs. Incorporating additives with high thermal conductivity can reduce the lowering effect of PCMs on the overall thermal conductivity of the mixture while maintaining a desirable thermal capacity. This work mixes encapsulated PCMs (EPCMs), graphite and recycled glass fines, aiming to develop green backfill materials with excellent thermal properties. The heat capacity and thermal conductivity of the mixtures with different fractions of the components are measured in a laboratory. The measured data agree with simulated results. Better thermal properties can be achieved with specific fractions of components, and the findings could help geothermal systems design for better energy utilisation.
 Geothermal energy is one of the promising renewable energy sources and its utilisation can be an alternative to fossil fuels. A geothermal system requires a ground source heat exchanger with pipes installed inside a borehole, and backfill materials filling the gap between the pipe heat exchanger and the ground. Thus, the thermal properties of backfill materials are essential to the geothermal energy extraction process and influence the corresponding shallow geothermal system performance [2]. PCMs are used to improve the thermal storage capacity of backfill materials because they can absorb and release heat at a relatively constant temperature [1]. To avoid problems of leakage and volume change of PCMs during a phase change, encapsulated PCMs (EPCMs) are better suited in backfill materials [5]. However, mixtures including PCMs may hinder heat transfer because of their low thermal conductivity. Therefore, other additives with high thermal conductivity can be used to resist the low heat transfer rate [3]. Even though the thermal properties of backfill materials are fundamental to the geothermal energy extraction process, their dependence on the amount of added PCMs and other additives has not been investigated yet. This work mixes EPCMs, graphite and recycled glass fines, aiming to develop green backfill materials with excellent thermal properties. The heat capacity (), thermal conductivity () and thermal diffusivity () of the mixtures with different fractions of the components are measured in a laboratory.
 SEM images of materials used, recycled glass fines, EPCMs and graphite, are shown in Figure 1(a). Cylindrical containers with a diameter of 44 mm and a height of 57 mm are used to prepare samples of mixtures. Each sample has the controlled volume fractions of components indicated by Figure 1(b) while keeping a constant overall porosity of 0.47. A decagon KD2 Pro thermal analyzer with a dual thermal needle measures the thermal properties of samples kept at 4 °C when EPCMs are in the solid phase and 45 °C when EPCMs are in the liquid phase. The geometrical mean model is used for theoretical estimations of values for comparison against experimental results [4].
 
 The thermal conductivity () of the mixtures increases with increasing graphite volume while decreasing with increasing EPCMs volume, as shown in Figure 1(c). The difference between under solid EPCMs and liquid EPCMs is limited. The heat capacity () rises with increasing EPCMs volume but declines with the increase of graphite volume, and it is higher when EPCMs are liquid than solid. It can be observed that a trade-off between the improvement of and the reduction of exists. Hence, the thermal diffusivity (), which depends on the ratio of to , is also investigated as presented in Figure 1(d). It decreases with the increase of EPCMs volume but grows with increasing graphite volume. Besides, it is higher under solid EPCMs than that under liquid EPCMs. This indicates the backfilling materials have a faster thermal response to the change of surrounding temperature under solid EPCMs.

Evaluation of feasibility and performance of foamed Fire-Resistant coating materials

A preliminary study found high-performance cement mortar, geopolymer mortar, and magnesium phosphate cement mortar (MPCM) have the potential as new fire-resistant materials. In this study, foam was added to these three fire-resistant materials to further improve their rheological, mechanical, and fire-resistant performance and reduce costs. Systematic design and experimental programs were conducted. The results showed the addition of foam enhanced workability, adhesiveness, and fire resistance, allowing the materials to withstand higher temperatures and further delay heat transfer. A mixture of 70% MPCM and 30% foam was identified as the optimum design, which could withstand 1000 °C with low heat transfer rates.

Development of Nusselt number and friction factor correlations for double-pass solar air heater duct

A solar air heater exhibits a low heat transfer rate due to the formation of a laminar thermal boundary layer across the absorber plate. Furthermore, the artificial roughness contributes to the intensification of turbulence along the absorber plate, which interrupts and breaks the thermal boundary layer. Keeping in this view, a three-dimensional simulation is performed to investigate the heat transfer and frictional characteristics of a double-pass solar air heater with semicircular tubes and perforated baffles as artificial roughness. This numerical investigation is performed for the parameters considered in the study: tube amplitude ratios (a/H) from 0.2 to 0.5, baffle height ratios (e/H) from 0.4 to 0.8, open area ratios (β) from 13 % to 30 % and Reynolds number (Re) from 3000 to 19000. The experimental testing rig is designed to validate numerical results corresponding to e/H of 0.4, an open area ratio of 30 %, a/H of 0.3, and Reynolds number varying from 3000 to 15000. Numerical results are found to be in good agreement with the experimental results, with a maximum absolute percentage error of 1.82 % and 5.28 % for the Nusselt number (Nur) and friction factor (fr), respectively. The maximum Nusselt number is observed as 274.29 at Reynolds number of 19,000 and e/H of 0.8; however, the maximum friction factor is observed as 0.6290 at Reynolds number of 3000 and e/H of 0.8 at a constant value of open area ratio of 30 % and a/H of 0.3. Within the range parameters studied, the maximum THPP value is reported to be 2.51 at Reynolds number of 3000, β of 30 %, e/H of 0.4, and a/H of 0.3. Further, correlations for the Nusselt number and friction factor in the function of a/H, e/H, open area ratio, and Reynolds number have been derived based on simulation results.

An analysis of different cutting strategies to improve tool life when machining Ti-5Al-5V-5Mo-3Cr alloy

Ti-5Al-5V-5Mo-3Cr is a near-beta titanium alloy generally employed in the production of high strength parts. Its high tensile strength and light weight, compared to Ti-6Al-4V, make it a suitable choice for landing gear parts and advanced structural components. However, due to its high strength-to-weight ratio, mechanical strength at elevated temperatures, and oxidation resistance, the cutting zone experiences high cutting temperatures, which, combined with a low rate of heat transfer during the machining process, consequently, generates stress, causing premature tool failure. In this paper, several distinct experimental approaches were applied, different machining condition combinations (tools and coolants) were compared, cutting tool wear performance was diagnosed, and, finally, optimized cutting parameters were identified. The main objective of this research was to understand how these parameters affect tribological behavior when machining Ti-5Al-5V-5Mo-3Cr. One of the PCD tools possessed the longest life under high pressure coolant of 28 %–170 % longer than the other tool materials. The main wear mechanism was a combined abrasion, adhesion/attrition, diffusion, and oxidation. Optimizing cooling conditions can affect cutting forces substantially, minimizing residual stress, improving the surface roughness, and reducing the work-hardening during machining. Therefore, the results show that the combination of coolant and cutting tool material leads to longer tool life and improved surface integrity.

A novel design for faster hydrogen storage: A combined semi-cylindrical and central return tube heat exchanger

Metal hydrides (MH) have recently attracted significant interest for hydrogen storage as they provide large storage capacity and a high degree of safety. The main disadvantage, however, is that storage speed is compromised by their low rate of hydrogen absorption. One possible way to accelerate the absorption reaction, and thus improve storage performance regarding incoming hydrogen transfer speed, is to increase the heat transfer rate inside the storage system. Among internal heat exchangers, using helical coil and semi-cylindrical coil heat exchangers significantly improves the heat transfer performance inside the storage system because of the secondary circulation. However, the central area of the storage system still has a lower heat transfer rate as this area is far away from the heat transfer fluid. For this purpose, the development of a heat exchanger structure is considered for the new achievement of this study. A semi-cylindrical coil heat exchanger incorporating a central return tube (SCHE-CR) is first developed from a semi-cylindrical coil heat exchanger (SCHE) to improve heat exchange rate at the MH central area. The tube size's effect on absorption is analysed. Further, a combination of internal and external heat exchangers is considered for further improvement of MH storage performance. The operating parameters of the heat transfer fluid for various heat exchanger configurations are investigated to determine optimal values. Results from numerical simulations indicate that absorption duration reduces by 30 % in the SCHE-CR case compared to the SCHE. Increasing the tube diameter of SCHE-CR results in a 40 % faster absorption reaction. Using SCHE-CR with a cooling jacket reduces the absorption duration by 51 % compared to the SCHE-CR. Among other operating conditions, the operating temperature of the cooling fluid is found to significantly affect the hydrogen absorption reaction with up to a 36 % enhancement of the absorption rate. However, the heat transfer coefficient between cooling fluid and MH, is not found to have a significant effect, as the improvement of the absorption rate is only 8 %. The new MH reactor configuration would be beneficial to improve heat exchange in MH storage applications.

Heat and mass transfer analysis of non-Newtonian radiative nanofluid flow driven by the combined action of peristalsis and electroosmosis

The present numerical investigation uncovers the flow, heat, and mass transfer of ethylene glycol-based nanofluid (BN-EG) led by the combined impacts of peristaltic pumping and electroosmosis. The thermal conductivity of carrier liquid is deemed to change with temperature. Further, the features of electric field, Ohmic heating, radiative heat flux, mixed convection, and magnetic field are taken. Mathematical modeling is conducted under the assumption of lubrication theory. The nonlinear-coupled equations are addressed numerically by implementing Shooting method. The effective results of all physical constraints linked with the flow model are vigilantly studied and highlighted through various curves. The observations obtained from current analysis reveal that temperature augments with higher electroosmotic parameter. However, the Joule heating parameter increases the rate of heat transmission, while a lower rate of heat transfer is perceived for the radiation parameter. An increment in Helmholtz–Smoluchowski velocity increases the velocity profile. Pressure gradient rises in a forward way when electrical field favors peristaltic flow. Concentration of nanomaterial considerably declines when concentration Grashoff number is assigned higher values.

Solidification of nanoparticle-based PCM in a fin-aided triplex-tube energy storage system for cooling applications

Accomplishing a better solidification rate to enhance the Thermal Energy Storage (TES) systems' performance is crucial. One such storage system is the Triplex-tube heat exchanger (TTHX), which is preferable due to its larger heat exchanger area that makes the phase change rate faster. The present study demonstrates a combination of different heat transfer enhancement techniques to improve the performance of the TTHX system. The heat transfer performance of the entire solidification process in the heat exchanger is numerically studied. The system is designed for low-temperature cooling applications with water as PCM placed in between the annulus region of the TTHX. Fins have been employed to enhance the low heat transfer rate due to the poor thermal conductivity of the water as PCM. The effect of incorporating maximum fin length between the annulus region on the discharging performance is evaluated. In this regard, two fin arrangements – attached and detached are investigated. The influence of different cooling methods, namely both-side, inside and outside, are evaluated for mentioned fin arrangements in terms of the required solidification time, liquid–solid interfaces, and heat transfer rate. The impact of including CuO nanoparticles on the thermal and flow structure under different volume fractions is investigated. The results demonstrate that detached fins perform superior under a given heat transfer fluid temperature among other fin cases. In comparison, both-side cooling expedites the process better than other cooling methods. Inclusion of 7% nanoparticles along with fins results in an even faster freezing process, which helps to reduce full solidification time in all cases by nearly 29% and 25% in attached and detached fins, respectively.

Hybrid-nanofluid mixed convection in square cavity subjected to oriented magnetic field and multiple rotating rough cylinders

In this study, mixed convective hybrid-nanofluid flow in a partially heated square cavity with two rotating rough cylinders in presence of an external magnetic field is numerically investigated. A pair of rotating rough cylinders is placed at different locations inside the cavity. The cavity is permeated by an external magnetic field at different inclination angles. Maxwell's thermal conductivity model is modified incorporating Brownian motion of hybrid nanoparticles. The conservation equations of the flow and thermal fields are simulated using finite element method. The effects of different influential parameters such as cylinders rotation velocity (0 ≤ ω ≤ 50), Hartmann number (0 ≤ Ha ≤50), hybrid nanoparticle volume fraction (0% ≤ φ ≤ 5%) and magnetic inclination angle (0° ≤ α ≤ 135°) on the flow and thermal fields are explored via streamlines, isotherms and bar charts of average Nusselt number. The simulated results ensure that mixed convective flow is accelerated with cylinders rotation speed but declines with higher magnetic field strength and hybrid-nanoparticle volume fraction. Heat transfer enhancement is recorded up to 261.29% at highest rotating speed of rough cylinders (ω: 0–50, φ = 1%, Ha = 10). Enhancement of heat transfer rate is found decreasing for increasing magnetic field strength. Lowest heat transfer rate is occurred at highest magnetic field impact (Ha = 50) which is 144.62% less than that of heat transfer in absence of magnetic field (Ha = 0). Optimum heat transfer is found for 5% hybrid nanoparticle volume fraction which is 101.2% more compared to base fluid water. The presence of triangular rough components accelerates the fluid flow and heat transfer rate significantly. In addition, 48.89% more heat transfer is obtained for rotating rough cylinders with triangular components compared to smooth cylinders. Moreover, maximum heat transfer is achieved at magnetic inclination angle of 90°. It is also observed that the flow and thermal fields strongly depend on the cylinders arrangements.

Case study for enhancing concentration of waste dilute sulfuric acid by microwave flash evaporation: modelling, heat transfer, energy consumption and process optimization

The ameliorative microwave flash evaporation system (MFE) was utilized to concentrate and distillate waste sulfuric acid, the system may overcome the problems of equipment corrosion, product pollution, high energy consumption, long process flow, and low heat transfer rate during recovery process of waste sulfuric acid. The dilute sulfuric acid with mass fraction of 75 wt% was used as experimental medium, 5 experimental cases was generated to verify the effects of MFE with the conditions of different volume, microwave power and depressurization rate. Experimental results demonstrated that the sulfuric acid could be concentrated to mass fraction of 85–95%, and the heating efficiency was among 30% to 80%, heat transfer volume coefficient was among 100 J/K·L-1 to 500 J/K·L-1 with the combination of vacuum and microwave heating during flash evaporation process. Thermal process analysis indicated that the interaction among experimental factors affected concentration and distillation process. At last, we gave the modeling and process optimization method for concentrating sulfuric acid through MFE process based on analyzing those experimental cases.

Dual dynamical jumps on Lie group analysis of hydro-magnetic flow in a suspension of different shapes of water-based hybrid solid particles with Fourier flux

In recent times, the mixture of liquids has been referred to as “hybrid modelling.” Ternary hybrid models are advantageous for different systems such as production industries, aerosol particle processing, and experimental instrument design, to name a few. The regulating partial differential equation (PDE) for nonlinear systems is changed into a system of associate nonlinear (ODE) In this study, ordinary differential equations report utilizing new similarity scaling symmetry transformations produced via Lie group transformations analysis. Using a BVP4C with a shooting method approach, the resulting system is numerically resolved (MATLAB). For Cases: 1 CNT, Graphene, Aluminium oxide, Cases: 2 Cooper oxide, Magnesium oxide, and Zirconium oxide with different nanosized particle morphologies including platelet, cylindrical, and spherical, the rate of heat transmission and the magnetohydrodynamic flow of incompressible fluid friction were studied. It is observed that Nusselt number transfer is having more transmission rate in case-1 Al2o3+GNT+CNTwith water than in case-2 Mgo+Zro2+Cuowithwater, This shows that, due to the Case-1 hybrid nanofluid mixture's improved heat transmission rate, it can be used for cooling as well as other applications where a faster heat transfer rate is necessary, including rapid charging batteries. Where there is a lower heat transfer rate than in instance 1, the case-2 hybrid nanofluid mixture can be used. Even in cancer treatment also nanoparticles will be useful to kill the cancer cell by injecting the nanoparticles into the human body. In order to predict the outcomes of a response variable, a statistical technique known as multilinear regression analysis (MLR) makes use of a variety of explanatory variables.

한옥의 내화 및 방충 성능 개선에 관한 연구

This paper is a study on the fire resistance of wood and securing the performance of insects, which are still emerging as problems in order to convert the various advantages and excellence of hanok into modern architectural methods. To verify the research results, the test was conducted by applying it to the building materials of hanok, and the results of the research were summarized as follows.
 First, wood with fire resistance regulations is relatively safe from fire. Wood has a very low heat transfer rate and a relatively low ignition temperature on the surface is a relatively safe material compared to other materials because when a fire breaks out, the carbonized part of the surface additionally blocks heat transfer and prevents the inside from being carbonized.
 Second, in the case of hanok, the standard of the member that can be used as a fireproof material is 460mm×600mm long in the case of beams, 360mm in diameter, 3,600mm high in the case of cylinders, and 300mm×300mm high in each column.
 Third, in order to prevent insects such as termites, insect repellent paint is directly applied to wood, a building material, to show the performance of the room. In comparison to existing termite damage prevention methods such as fumigation, soil treatment, and termite colony removal systems, insect repellent paints show excellent performance in difficulty, cost, use of eco-friendly products, and room effects.

Comprehensive performance enhancement of conformal cooling process using thermal-load-based topology optimization

Conformal cooling technology is widely used in the thermal management for injection molding process. However, the overall design of cooling channel layout needs to be optimized due to non-uniform thermal load, limited design freedom and other factors. This paper presents a novel procedure for conformal cooling channel design by using thermal-load-based topology optimization. Unlike previous approaches that focused on optimizing the channel configuration or geometric parameters, the current work applies multiphysics topology optimization on the entire cooling area. The objective is to obtain the optimal channel layout with both low pressure drop and high heat transfer rate. A serious of optimized planar results are converted to three-dimensional channels that conform to the specific injection casting and are applied to injection molding process in a simulation software environment. For a given thin-plate casting, compared with the conventional parallel cooling process, the steady state average temperature and maximum temperature difference are decreased by 0.53 K and 2.20 K, respectively, and the pressure drop of coolant is decreased by 25.40%. For castings where non-uniform thermal loads are considered, the average temperature and pressure drop are decreased up to 1.45 K and 27.55%, respectively. The results for both sheet castings and cylindrical castings have demonstrated the stability, flexibility, and rationality of the proposed procedure. In addition, the conceptual design of cooling channels based on thermal load is expected to be applied to more potential thermal engineering fields.

Conjugated non-Newtonian phase change process in a shell and tube heat exchanger: A parametric-geometric analysis

The present study aims to better knowledge of the phase change process in shell and tube heat exchangers in the presence of thick tubes, porous medium, and Carreau- Yasuda non-Newtonian fluid. It is the first time that this combination has been presented in the literature. It is believed that considering the phase change process of RT-35 as a Carreau-Yasuda non-Newtonian one in the presence of porous medium and copper pipes can create a challenge in the field. The continuity and momentum equations along with the horizontal and vertical directions, the heat equation for RT-35 as a non-Newtonian Carreau–Yasuda fluid, and the heat equation for thick tubes were determined and transformed into their non-dimensional forms, which were then solved using the finite element method. The effects of non-dimensional numbers such as Stefan number, porosity parameter, Rayleigh number, and Effect of rheological behavior of fluid have been determined. Reaching better performance via using porous medium and center- a to- center distance of double pipes, as well as a number of the pipes, are the ideas to conduct the present study. The results were reported as the average Nusselt number, melting fraction of the PCM, the average velocity of the non-Newtonian fluid, streamlines, and isotherms, all as functions of non-dimensional time. The results indicated that higher values for the porosity parameter led to lower heat transfer rates, which in turn weakened the PCM melting front. It was also found that changing the center-to-center distance between the hot tubes influenced melting front propagation.

Preparation, Characterization, Stability and Thermophysical Properties of Bio, Non-Bio (Metallic and Non-Metallic) and Hybrids Nanofluids: A Review

Traditional heat transfer base fluids, such as ethylene glycol, ethanol, kerosene, oil, methanol, water etc. are normally used to enhance the heat transfer performance in many industrial applications. These traditional heat transfer fluids have many limitations. One of the limitations is the poor thermophysical properties of each of the base fluids and this results in a lower heat transfer rate in Thermal Engineering systems. Nanofluids are considered a new generation heat transfer fluid with higher thermal conductivity. Nanofluids have enhanced thermophysical properties compared to single-phase traditional heat transfer fluids. This paper highlights detailed reviews of the various methods of preparation, characterization, stability and thermophysical properties of bio, non-bio and hybrids nanofluids. Thermophysical properties such as density, viscosity, thermal conductivity and specific heat capacity from different works of literature were summarized, discussed and presented. There are many different parameters to be considered while investigating the thermophysical properties of nanofluids. Density and specific heat capacity are strongly dependent on the material type while the viscosity and thermal conductivity are highly affected by temperature and concentration. The most influential parameters on thermophysical properties of nanofluids are material type and temperature. The majority of the literature revealed that bio nanofluids have low viscosity values and hybrids have high thermal conductivity values. The novelty of this review paper is the presentation of the various methods of synthesizing, characterization, stability and factors affecting the thermophysical properties of metallic, non-metallic and hybrid nanofluids.

Three-dimensional analysis of the thermal and hydraulic performance of finned and un-finned tubes in a staggered array

• Novel type of leeward cut fin is compared with a conventional circular fin. • Fin spacing was varied to evaluate thermo-hydraulic behaviour. • Leeward cut fin gives lower heat transfer rate and pressure drop than circular fin. • Performance study suggests the potential of leeward cut fins for material saving. A novel type of finned tube obtained by removing the downstream section of the conventionally used complete circular finned tube (CCFT) is studied. The resulting novel type of finned tube obtained is termed leeward cut finned tube (LCFT). The thermal and hydraulic behaviour of these novel finned tubes is compared with CCFT and un-finned tubes. Leeward cut fins are specifically studied to check their capability to give equivalent heat transfer like that of complete circular fins. This study is carried out in the Reynolds number range 4330 ≤ Re ≤ 8790 and fin spacing range 2 ≤ s ≤ 4 mm . The transition SST model is implemented to solve the RANS equations. Heat transfer coefficient at the downstream section of fins is found to be less than the upstream section; hence, it can be advantageous to remove some portion of the downstream section of the fin. The leeward cut finned tubes give a lower value of heat transfer rate and pressure drop when compared with complete circular finned tubes. The heat transfer Colburn factor j for leeward cut fins is higher than CCFT and un-finned tubes. The friction factor is the lowest for CCFT and the highest for un-finned tubes. Analysis of the effect of fin spacing showed an increment in heat transfer rate and a decrease in pressure drop when fin spacing is increased from 2 to 4 mm. The studied geometries are evaluated based on their thermo-hydraulic performance parameters ( PEC and Z/E ). The performance evaluation criterion PEC for LCFT is higher than CCFT by 30–46 % at fin spacing of 2 mm, whereas for spacing of 4 mm, it is 21–23 % higher. The ratio of heat transfer rate per unit temperature difference to power provided to the heat exchanger Z/E is lower for LCFT than CCFT by 5–8 % for fin spacing of 2 mm, whereas for fin spacing of 4 mm, it is lower by 9–12 %. Based on the results, CCFT performs better than LCFT, but they have more fin material requirements (∼50 %). Hence, the LCFT can be seen as a potential novel type of fin to give equivalent heat transfer with the advantage of material savings.

A review on materials processing using microwave radiation

Welding is one among the most popular industrial production techniques. The traditional welding procedure has several disadvantages, such as increased energy consumption, longer melting periods and low heat transfer rate. Innovative welding processes are being developed to alleviate the shortcomings of traditional welding methods. Recently, a revolutionary method called microwave joining has emerged. It may be used to treat a diverse variety of materials, including metal matrix composites, polymers, alloys, ceramics, metals, powder metallurgy, material joining, coatings and claddings. This research explored the introduction of microwave welding with hybrid technology and contributions from other researchers, which shed light on numerous research prospects in the field of microwave welding. The welding setup, the technique, and step-by-step welding operation were all thoroughly addressed. Finally, Conclusions were discussed, as well as future recommendations.

Convective heat transfer enhancement in a quarter-circular enclosure utilizing nanofluids under the influence of periodic magnetic field

A coupled one-component numerical model is applied to analyze the transient natural convective hydro-thermal incidents of different nanofluids occupied with a quarter circular vicinity. A sinusoidal magnetic arena is preferred in the transverse direction to examine the magnetization phenomena. The circular arc of the geometry domain is cold and the lowest wall is heated whereas the vertical wall of the arena is kept thermally insulated. During numerical computation, herein considered Water (H 2 O), Kerosene (Ke), Engine Oil (EO) as base fluids and Copper (Cu), Cobalt (Co), and Iron Oxide (Fe 3 O 4 ) as nanoparticles. The dimensionless transports equations are solved numerically by applying the Galerkin weighted residual based finite element method. The outcomes spectacle that heat transfer rate augmented significantly with the increasing values of the Rayleigh number ( Ra ), nanoparticles volume fraction (φ), and period of the magnetic field (λ), whereas an intensification in the Hartmann number ( Ha ) lessens the total heat transfer rate. For nine sorts of nanofluids, the average heat transfer rate is computed along the bottom wall, and found that the heat transfer rate of Co-Kerosene nanofluid is considerably greater than other eight sorts of nanofluids. Finally, it is observed that the Cu-Kerosene nanofluid provides the high heat transfer rate whereas Cu-EO has the low rate of heat transfer for distinct thermal boundary conditions. The numerical results could be useful in assessing heat transfer features of solar collectors, and electronic devices.

Influence of fin configuration on the thermal performance of nanoparticle-enhanced latent heat storage system

Storing the thermal energy using the materials' latent heat capacity is a prominent and well-established technique; these materials are termed phase-change materials (PCMs). For low-temperature applications mostly organic PCMs are available. These PCMs possess very less thermal conductivity, which results in a low rate of heat transfer. To overcome this problem usage of fins and the addition of nanoparticles (NPs) to PCM are two potential methods. In the present study, three-dimensional numerical analysis of melting and solidification is performed on the radial, spiral, and longitudinal finned PCM-based shell and tube heat exchangers with the addition of NPs to PCM. Numerical analysis is carried out with various volume fractions of NPs in the PCM. Based on the study it is observed that the PCM-based heat exchanger with radial fins has the lowest melting time, average temperature, and energy storage ratio. For longitudinal fins melting time is maximum and it also has the maximum average temperature and energy storage ratio. It is observed that the addition of NPs showed a significant effect on the phase change process. For all the selected geometries the average exergy efficiency is not more than 4.4% during solidification.

Thermoeconomic analysis of a waste heat recovery system with fluctuating flue gas scenario

The performance and economy of a waste heat recovery system featuring a fin tube heat exchanger (FTHE) and an organic Rankine cycle system with a fluctuating flue gas were investigated. The output power of this system increased with the temperature and mass flow rate of the flue gas (m˙f), which had positive and negative effects, respectively, on the effectiveness (εFT) of the FTHE. Furthermore, εFT increased with the evaporation temperature (Teva). The system performance and economy can be increased and decreased, respectively, through an increase in Teva, especially for as the m˙f less than the design conditions. A method in which the flow rate of the working fluid is restricted through adjustment of the rotation speed of the expander is proposed to reduce the heat absorbed by the evaporator when the evaporation temperature increases. At a low evaporation heat transfer rate, when the rotation speed of the expander decreased from 1350 to 900 rpm, the evaporation pressure increased from 1.36 to 1.77 MPa, and system efficiency and output power increased by 1.0% and 204.7 W, respectively. Finally, results of the experiment confirmed that increasing evaporation pressure can increase system performance under low heat transfer rate.

Thermal comfort in a building with Trombe wall integrated with phase change materials in hot summer and cold winter region without air conditioning

Trombe wall and phase change materials (PCMs) are two effective ways to regulate indoor thermal comfort. However, Trombe wall surfers from overheating in summer and PCMs suffer from low heat transfer rate caused by the limited thermal conductivity. To compensate the shortcomings of the two methods, this paper proposed a Trombe wall system integrated with PCMs. Based on a light-weight building envelope in Changsha, China, the thermal comfort of 10 kinds of Trombe wall systems with PCMs with a melting temperature of 18–28 ℃ were studied. Taking the integrated indoor discomfort duration (ID), integrated indoor discomfort degree-hour (IDH), indoor air temperature (Tin), PCM liquid fraction (γ) and heat flux across wall (q) as evaluation indexes, the indoor thermal comfort was assessed in hot summer and cold winter region. Results show that the Trombe wall helped PCMs complete the phase change process effectively. Trombe wall with PCM25 next to the wall inner surface possessed the lowest annual ID and IDH, as 2877 h and 12,974 ℃· h, respectively. Compared with the values in a traditional building, the ID and IDH were reduced by 7.01% and 14.14%. In order to give full play to the heat storage and heat release of the Trombe wall with PCMs, PCMs with phase change temperature 7℃ lower than the peak ambient temperature in summer or 8℃ higher than the winter night temperature was recommended according to regional climate conditions.