Heat Transfer Techniques Research Articles

Enhancement technique of heat transfer using inserted twisted tape

Enhancements in heat transfer systems are being applied for recovery of heat in domestic as well as industrial applications in many areas. These are done by generating turbulence and swirl motion in the flow by inserting inserts to reduce the thermal resistance of heat transfer. This paper presents the experimental and numerical results of heat transfer enhancement of cooling of a confined space by inserting twisted tape in a pipe buried in concrete under the floor. The Reynolds number is fixed to 15000. Thirteen cases are considered varying the configurations and designs of twisted tapes and the effects of different types of perforations and slots on twisted tapes are studied. Water as the test fluid flowed in pipe inserted with twisted tapes. Heat is transferred from a heating plate to water along the pipe length through concrete to simulate the heat transfer from a room and the water temperature rise is studied. To validate the experimental results, ANSYS-FLUENT is used as the CFD tool with a Standard k-ε turbulence flow model and the SIMPLE algorithm is implemented. Flow physics behaviour is displayed using velocity and temperature profiles inside the pipe. Insertion of twisted tapes shows that the heat transfer is enhanced due to swirling action, friction and turbulence. The experimental differences in inlet and outlet water temperature validated the CFD simulation results. The temperature distribution on a single twisted tape with increasing twist ratio is found to be the most efficient for heat transfer enhancement of the cooling floor surface with a water temperature rise of 1.62 ºC along a pipe length of 1.8 m.

Study of Natural Convection of Lithium-Ion Battery Module Employing Phase Change Material

When the Lithium-ion battery operates at high temperature, it would bring about short circuit; if it reaches a critical temperature, it will explode. It is important to reduce its maximum temperature by appropriate heat transfer technique. When it operates without an external force for cooling, it needs natural convection technique to take away heat dissipation. Therefore, this study numerically examines three-dimensional transient natural convection of cylindrical lithium-ion batteries inside a rectangular pack with air between cylinders. The heat transfer technique in this study applies PCM (phase change material) between cylinders without or with fin array on top changing distance between cells. The results indicated that for no fin array, the package adopting the PCM could achieve the peak temperature 14.2 °C smaller than the package adopting the air. However, the package adopting the PCM with fin array vertical to the top of the package can best enhance average Nusselt number by 120% compared with using air and no fin array. Replacing the air by the PCM can keep the peak temperature of the batteries within the desirable operation range.

Status, Challenges, and Potential for Machine Learning in Understanding and Applying Heat Transfer Phenomena

AbstractMachine learning (ML) offers a variety of techniques to understand many complex problems in different fields. The field of heat transfer, and thermal systems in general, are governed by complicated sets of physics that can be made tractable by reduced-order modeling and by extracting simple trends from measured data. Therefore, ML algorithms can yield computationally efficient models for more accurate predictions or to generate robust optimization frameworks. This study reviews past and present efforts that use ML techniques in heat transfer from the fundamental level to full-scale applications, including the use of ML to build reduced-order models, predict heat transfer coefficients and pressure drop, perform real-time analysis of complex experimental data, and optimize large-scale thermal systems in a variety of applications. The appropriateness of different data-driven ML models in heat transfer problems is discussed. Finally, some of the imminent opportunities and challenges that the heat transfer community faces in this exciting and rapidly growing field are identified.

A comprehensive experimental and numerical estimation of thermal contact conductance

Realizing perfect contact between any two surfaces is impossible due to the presence of microscopic irregularities in material surfaces. Therefore, for true thermal analysis of multiple components systems knowledge of thermal contact conductance (TCC) between two solid bodies is essential. Estimation of TCC for different applications has been carried out in this paper by inverse heat transfer technique. A novel stochastic Jaya algorithm has been developed for this purpose and its performance has been evaluated for different heat conduction problems like the estimation of TCC with two metals contact (case-1), periodically contacting surfaces (case-2), multilayer wall surfaces (case-3), and simultaneous estimation of TCC and boundary heat flux (case-4). The experiment has also been conducted to determine the efficacy of this new algorithm for real-life situations. Different parameters like population size, sensor location from the interface, and errors in measured temperature data are taken into consideration. The population size of 5 candidate solutions for case-1, 60 candidate solutions for case-2, and 50 candidate solutions for case-3 and case-4 is found to be suitable for estimation. The results are accurate with the root mean square (RMS) error of 12.62 W/m2K even when the sensors are located 50 mm far away from the interface. Although errors in measurements deteriorate the performance of the Jaya algorithm, it still gives stable results (RMS = 2.90 W/m2K at σ = 0.3). Jaya algorithm is found to be an accurate and promising algorithm for inverse problems.

18th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery (ISROMAC18)

Abstract The 18th ISROMAC symposium was supposed to be held in Honolulu, Hawaii (USA), at the Hawaii Convention Center in April 2020. However, due to the COVID19 pandemic, the organizing committee was forced to postpone the symposium and finally decided to organize it online from November 23 to 26, 2020. In these extraordinary circumstances, the conference was held online successfully and was attended by 190 participants, including academic and industrial researchers from 19 countries in America, Asia, Europe, and Oceania. 137 papers were presented in the symposium, divided into 20 sessions focusing on different topics related to rotating machinery. A wide breath of topics related to the dynamics of rotating machinery was presented, including compressors, turbines, pumps and other fluid machinery, multi-phase flows, cavitation, rotor-dynamics, heat transfer, combustion, aero-acoustics, CFD and experimental techniques applied to turbomachines.

Numerical Studies on Thermo-Hydraulic Characteristics of Turbulent Flow in a Tube with a Regularly Spaced Dimple on Twisted Tape

Heat transfer augmentation is an important concern due to the increase in heat management problems in thermal systems. There are many techniques for enhancement of heat transfer, by active and passive techniques. A commonly used passive technique to enhance heat transfer is by inserting twisted tapes in tubes. This work presents a numerical study on Nusselt number, friction factor, and thermal performance characteristics through a circular pipe built-in with/without dimples on twisted tape. The analysis results for a turbulent flow range of 4500≤Re≤20000 are obtained with a twist ratio of the strip is 3.0. The analysis is carried for full-length tape with constant heat flux. The governing equations are numerically solved by a finite volume method using the RNG κ–ε model. The simulation results of Nusselt number versus Reynolds number of the plain, plain twisted tape and dimple twisted tape tube with the experimental data give a variation of 4.15%, 3.89%, and 7.65%. The friction factor of the dimple twisted tape tube is 60 to 70% higher than that of the plain twisted tube at different Reynolds numbers. The thermal performance factor of the dimple twisted tape and plain twisted tape tube is 30 to 35% respectively higher than that of the plain tube. Due to thermal performance factor is above unity yields a promising heat transfer enhancement. By the present study, an optimum geometrical parameter can be selected for use in heat exchangers.

Numerical simulation on performance evaluation among metal and oxide based nanofluids for power savings application of a circular tube

The advancement of heat transfer techniques is a challenge to the researcher in this era. Implementation of nanotechnology is one of the potential techniques which enhance the heat transfer rate in a significant amount. Subsequently, nanotechnology can reduce the requirement of pumping power. However, suspension of nanoparticle with liquid to produce a new working fluid called nanofluid which has better thermal and fluid dynamic properties in comparison to pure liquid is introduced as a typical nanotechnology technique in the heat transfer area. In this study, the thermal performance of two categories of nanofluids metal-based (Cu-water and Ag-water) and oxide-based (Al2O3-water, CuO-water, BeO-water) with 1–5% volume fractions have been analysed for the laminar flow region of a circular tube which is fully developed under 2D control volume finite element method. The heat transfer was analysed for a range of Reynolds numbers from 100 to 1000 with a constant heat flux of 500 W/m2 applied on the tube wall. For evaluating the performance among nanofluids, the Figure of Merits (FOM), pumping power, Nusselt number enhancement ratio, and heat transfer coefficient ratio of the base fluid and nanofluids have been calculated and compared. The computational results show that in terms of Nusselt number and heat transfer coefficient, all nanofluids provide higher enhancement compared to pure water. Meanwhile, for this higher enhancement, nanofluids required significantly power pumping power in comparison to pure water. However, the power has been saved 86.26% for Ag-water nanofluid, 72.84% for Cu-water, 42.36% for CuO-water, 40.99% for Al2O3-water, and 26.58% for BeO-water. Between the mentioned two categories of nanofluids, metal-based nanofluids provide the highest heat transfer enhancement and lowest pumping power requirement compared to oxide-based because of their higher thermal conductivity and other fluid and thermal properties. For clearing the enhancement of heat transfer rate over-pumping power, a dimensionless number FOM has been calculated whereas metal-based nanofluids provide the highest value of FOM (1.863 for Ag-water nanofluid) in comparison to oxide-based (1.266 for BeO-water). In the meantime, the comparison between nanofluids also reveals that among all the nanofluids, metal-based Ag-water nanofluids provide the highest heat transfer enhancement and oxide-based BeO-water provide the lowest heat transfer enhancement in terms of pumping power requirements. Lastly, the study concluded that suspension of metal-based nanoparticles with base fluid has better capability to save pumping power (86.26% for Ag-water nanofluid) by providing the highest enhancement of heat transfer rate whereas oxide-based nanoparticles show the lowest capability to save pumping power (26.58% for BeO-water) compared to the base fluid.

The Impact of Active and Passive Thermal Management on the Energy Storage Efficiency of Metal Hydride Pairs Based Heat Storage

Two-tank metal hydride pairs have gained tremendous interest in thermal energy storage systems for concentrating solar power plants or industrial waste heat recovery. Generally, the system’s performance depends on selecting and matching the metal hydride pairs and the thermal management adopted. In this study, the 2D mathematical modeling used to investigate the heat storage system’s performance under different thermal management techniques, including active and passive heat transfer techniques, is analyzed and discussed in detail. The change in the energy storage density, the specific power output, and the energy storage efficiency is studied under different heat transfer measures applied to the two tanks. The results showed that there is a trade-off between the energy storage density and the energy storage efficiency. The adoption of active heat transfer enhancement (convective heat transfer enhancement) leads to a high energy storage density of 670 MJ m−3 (close to the maximum theoretical value of 755.3 MJ m−3). In contrast, the energy storage efficiency decreases dramatically due to the increase in the pumping power. On the other hand, passive heat transfer techniques using the bed’s thermal conductivity enhancers provide a balance between the energy storage density (578 MJ m−3) and the energy efficiency (74%). The utilization of phase change material as an internal heat recovery medium leads to a further reduction in the heat storage performance indicators (142 MJ m−3 and 49%). Nevertheless, such a system combining thermochemical and latent heat storage, if properly optimized, can be promising for thermal energy storage applications.

Experimental Characterization of Two-Phase Cold Plates Intended for High-Density Data Center Servers Using a Dielectric Fluid

Abstract High-performance computing (HPC) data centers demand cutting edge cooling techniques like direct contact liquid cooling (DCLC) for safe and secure operation of their high-power density servers. The two-phase flow boiling heat transfer technique is widely believed to address the heating problem posed by HPC racks. In this study, a novel liquid-cooled cold plate containing microchannel and jet impingement arrangement was characterized for its two-phase flow and thermal behavior. A sophisticated bench top setup involving a mock package was developed to carry out the experiments in a controlled fashion using a dielectric fluid Novec/HFE-7000. Two-phase flow boiling in cold plates which has a strong dependency on surface phenomena were carefully studied at various levels of inlet pressure, subcooling, flow rates, and heat flux levels to the mock package. A resistance network was invoked to determine the average heat transfer coefficient at various exit qualities estimated by the energy balance equation. While the results make it evident that, the high heat generating components can be kept at operable conditions using the two-phase cooling; a deeper insight at the outcomes could pave way for more energy efficient cold plate designs. The experiment was carried out with a large heated surface of 6.45 cm2 and maximum dissipated heat flux was around 63.6 W/cm2 corresponding to chip power of 410 W. Base temperature was kept below 75 °C and pressure drop did not exceed 21 kPa.

HEAT TRANSFER ENHANCEMENT USING PASSIVE TECHNIQUE: REVIEW

Preserving and saving energy have never been more important, thus the requirement for more effective and efficient heat exchangers has never been more important. However, in order to pave the way for the proposal of a truly efficient technique, there is a need to understand the shortcomings and strengths of various aspects of heat transfer techniques. This review aims to systematically identify these characteristics two of the most popular passive heat transfer techniques: nanofluids and helically coiled tubes. The review indicated that nanoparticles improve thermal conductivity of base fluid and that the nanoparticle size, as well as the concentrations of the nanoparticles plays a major role in the effectiveness of the nanofluids. Regarding the helically coiled tubes, it was discovered that the use of a coiled tube produces secondary flows, which ultimately improves the heat transfer enhancement. The third part of the review focused on microchannels and microtubes. This is mainly due to the growing need and requirement of smaller and more compact thermal cooling systems. Thus, ultimately the result of the review indicates that a combination of all these three techniques can lead to a compact and minimized heat exchanger that uses the benefits obtained from both nanofluids and helically coiled tubes in order to improve the heat transfer rate of the thermal systems.

자동차 시동용 LFP 배터리 팩의 혹한기 시동성 향상을 위한 열선 시스템 적용에 따른 열 유동 해석

A numerical simulation for evaluating thermal performance was performed to determine the possibility of replacing existing lead-acid 12 V batteries with lithium-ion batteries. In batteries used for starting vehicles, low-temperature (≤–20℃) starting performance and lifespan decrease significantly. Therefore, a lithium iron phosphate (LFP) battery system with a relatively high energy density at low temperatures was studied. A system for self-energy heating was designed to improve operability under cold-weather conditions. In particular, the battery pack case, battery cell array, and heating system of the proposed system were designed to be compatible. Furthermore, a thermal performance simulation was performed using computational fluid dynamics and heat transfer techniques based on the estimated thermal properties of each component. The results showed that the self-heating LFP battery pack system reached its startable temperature (–3℃) after 75 s when 249 W of power was applied in a low-temperature (–20℃) environment.

A review on effect of various artificial roughness on heat transfer enhancement in a channel flow

Heat transfer improvement plays a vital role in several industrial applications as well as in the transportation sector such as gas turbines, heat exchangers, various cooling devices, and combustor liners. The extensive research to enhance the heat transfer rate in various sectors has been carried out to achieve the objectives such as (i) to increase the system efficiency, (ii) to reduce thermal load, (ii) to reduce consumption of non-renewable energy, (iii) to reduce the production of emission, (iv) to develop new green technologies, (v) to lower energy prices for the consumer. The heat transfer in various sectors has been carried out by adopting three different ways (i) increasing the surface area of the heat transfer systems, (ii) enhancing the fluid properties, (iii) by adding extra surface on the heat transferring surface. This article aims to deliver a comprehensive review of the current research on heat transfer enhancement techniques by using artificial roughness elements such as rib tarbulator, fin, and dimple. It includes various types of rib tarbulators, fins, and dimples used for heat transfer enhancement of gas turbine blades of the power plant, combustion liners as well as solar air heaters. The physical mechanism responsible for heat transfer enhancement in various artificial roughness elements has been discussed and compared. The challenges and difficulties associated with the heat transfer techniques have been discussed. The parameters such as dimple depth, channel height to dimple imprint diameter, pitch, the density of artificial roughness element, arrangement of artificial roughness, relative roughness pitch, relative roughness height, angle of attack on flow, mass flow rate, Reynolds number on thermal performance, thermohydraulic performance, flow structure, friction characteristics have been studied and compared. From the comprehensive review, it may be recommended that the teardrop shape dimple can be used for further enhancement of heat transfer as compared to other artificial roughness elements. In the future, this teardrop may be used to enhance the heat transfer in the solar thermal system and some other relevant thermal systems.

Heat Transfer and Pressure Drop in Transitional Flow: A Short Review

In the present work, an effort has been made to present the short review of all the numerical as well as experimental studies done in the field of heat transfer and pressure drop in the transitional flow regime. The experimental and numerical studies on transition flow are reported. Though, there are several challenges to do experiments in transition flow regime. Various techniques are also discussed and summarized. Results show that the techniques prove outstanding performance, but few methods quiet suffer from high pressure drop. As per discussion, new viewpoints on the current research gaps and future research ways have been providing for the development of heat transfer techniques.

State of the Art of Phase Change Material (PCM) for the Purpose of Heat Storage and Transfer in Cylindrical and Rectangular/Square Shells/Tubes – A Review

The state of the art of the PCM’s reveals enabled characteristics that opens the door for multiple heat transfer and storage phenomena. The PCM absorbs, stores, and releases the energy during its phase change thus it most widely helps in latent heat transfer techniques. Nowadays Nano-fluid and Nano-phase change materials are replacing the general phase change materials because of its high heat transfer and storage capability. Further, varieties of passive heat transfer techniques such as heat exchangers of shell/tube type of various patterns and geometries are utilized to optimize the thermal energy. The artificial neural network is embedded in the system to recognize the pattern for faster processing. In this article, the PCM heat storage and transfer techniques are critically reviewed in comparison with the Cylindrical and Rectangular/Square shells/tubes based on the effect of parameters such as solidification/melting performance, enthalpy, fluid flow pattern in the liquid molten state, types of PCM used, etc. The numerical/analytical and experimentation techniques are categorized based on the results of various researcher and conclusion is established.

Evaluation of Microstructural Deterioration for a Directionally Solidified Ni-Based Superalloy by X-ray Computed Tomography

The evaluation of the microstructural deterioration was carried out by x-ray computed tomography for the first-stage blades, manufactured using a directionally solidified Ni-based superalloy (Ni-SA) retired from a land gas turbine, after service. The x-ray computed tomography was used to analyze the whole blade as well as, a segment of the top of blade with the purpose for obtaining results in a micrometer scale, which can be contrasted with the results of microstructural characterization. In order to evaluate the internal deterioration of the component, it was necessary to determine the in-service operation conditions of first-stage blades. Thus, the temperature distribution in the component during the start-up cycle was obtained, considering a transitory regime and using the conjugate heat transfer technique by means of Fluent ANSYS software. Besides, the mechanical stresses present in the component were calculated using finite element method implemented in ANSYS software. The main results of this work identified that the presence of cracking in the blade is associated with the occurrence of creep microcavities and coarsened particles of MC-type carbides, which showed debonding from the γ-matrix of the Ni-SA. The origin of the cracking was determined to occur in the cooling channels of the component.

Augmented Heat Transfer Techniques in Laminar Flow

Augmented Heat Transfer Techniques in Laminar Flow

A novel method of enhancing convective heat transfer by dynamic controlling rib

New and efficient mixing heat technology is increasingly demanded for many industrial fields. This paper proposed a novel technique of enhancing convective heat transfer by dynamic controlling rib and investigated several cases of vibration rib controlling flow. The study results of heat transfer coefficient, temperature and turbulent intensity indicate that dynamic flow control is an efficient heat transfer enhancement technique. The dynamic flow control breaks through the current enhancement heat transfer technologies such as general stationary rib and other vortex generators, and achieves a better heat transfer effect. Comparing traditional rib technologies, vibration rib does not only increase heat transfer performance but leads a lower flow resistance. More importantly, it can be dynamically adjusted to achieve better flow turbulence. As a conclusion, the enhancement heat transfer performance can be timely dynamically adjusted to meet the different heat transfer demand by changing timely the frequency and amplitude of vibration rib, which achieves the optimization of whole system thermal protection. New enhancing heat transfer technique effectively improve the comprehensive heat transfer performance, and provides a reference for intelligent thermal control protection system

Study of laminar convection heat transfer in single-side-heating small-scale cooling channel with vibration cylinder

Traditional enhancing convective heat transfer methods are mainly based on the flow turbulence by vortex generators, however, with increasingly heat transfer needs, traditional stationary vortex generators have not met the cooling demand. Thus, active flow control technique is proposed to better enhance convective heat transfer performance. The vibration cylinder is set as a vortex generator to achieve fluid flow disturbance aiming to enhance heat transfer. This method did not change the structure of the channel wall but introduced the built-in vibration source to achieve flow perturbations. New cooling technique is achieved by adjusting vibration cylinder to achieve active flow control and thermal control management. Several test Cases are built to analyze influence of cylinder vibration on convective heat transfer. The investigation indicates that the heat transfer coefficient can be improved by a maximum 14.69%, and comprehensive heat transfer performance is improved by 16.13% than the traditional stationary cylinder channel. Finally, the cylinder vibration can better improve the cooling performance and maintain a smaller pressure drop change. The study aims to propose a new enhancing heat transfer technique of active flow control to improve current heat exchangers performance.

Novel inverse heat transfer methodology for estimation of unknown interfacial heat flux of a continuous casting mould: A complete three-dimensional thermal analysis of an industrial slab mould

Accurate quantification of interfacial heat flux between the continuous casting mould and slab/billet is essential for the design and development of the products as well as operation and quality control of the casting process. Apart from empirical correlations, inverse heat transfer methods are typically employed to predict the heat flux variation by assuming a one-dimensional variation of heat flux along the casting direction. The assumption of one-dimensional heat flux often leads to significant error especially in determining the corner heat flux which affects the shrinkage behaviour and thereby, the quality of the products of casting. Previous studies have recognized this error and assumed this error of heat flux as a constant deviation to account for the longitudinal and transverse variation of heat flux. In this work, a novel methodology has been presented to predict the variable interfacial heat flux of a three-dimensional mould domain by estimating the parameters of a characteristic heat flux profile using an inverse heat transfer technique based on Salp Swarm Algorithm (SSA). This methodology uses limited experimental data or on-site plant recorded data. Representative cases of billet and slab moulds have been considered based on the available plant data. Results indicate that the mould corner heat flux is considerably different from that of the typically assumed value of 67% of the centre heat flux as reported in the literature with deviation reaching as high as 56% near the meniscus for a slab casting mould. The proposed methodology is simple to implement and is recommended for studies aimed towards realistic estimation of unknown boundary heat flux in a continuous casting process.

Computational and statistical analysis on the U‐tube heat exchanger with different passes configuration: Taguchi method

AbstractIn the present study, the passive technique of heat transfer in which single pass and double passes are included in a simple U‐tube heat exchanger is analyzed. The computational fluid dynamics (CFD)‐based parametric analysis is carried out to optimize the parameters affecting the temperature drop and heat transfer achieved from the U‐tube heat exchanger. ANSYS Fluentv20 is used for the CFD analysis, and the RNG k‐ɛ model and energy equation were considered to define the turbulence and heat transfer phenomena. The Taguchi method is used to formulate the experimental work and analyze the working parameters of the U‐tube heat exchanger, such as hot and cold mass flow rate and hoRenew Energyt inlet temperature and cold inlet temperature. For the U‐tube heat exchanger, four operating parameters are considered at four different levels in the Taguchi method. The best combination of parameters for achieving a maximum temperature drop is A4B1C2D3, and it is A3B4C1D2 in case of heat transfer. A U‐tube single‐pass heat exchanger is more effective as compared with other U‐tube heat exchangers (zero‐ and double‐pass). Experimental results are provided to validate the suitability of the purpose of the approach.