Three-dimensional Heat Transfer Model Research Articles

Experimental Validation of a Three-Dimensional Heat Transfer Model Within the Scala Tympani With Application to Magnetic Cochlear Implant Surgery.

The objective of this work is to experimentally validate a three-dimensional (3D) heat transfer model of the scala tympani which will enable accurate predictions of the maximum safe input power to avoid localized hyperthermia when detaching the magnet from the implant electrode array. Experiments are designed using a rigorous scale analysis and performed by measuring transient temperatures in a 3D-printed scala tympani phantom subjected to a sudden change in its isothermal environment and localized heating via a small heat source. The measured and predicted temperatures are in good agreement with an error less than 6 % ( p= 0.84). For the most conservative case where all boundaries of the model except the insertion opening are adiabatic, the power required to release the magnet attached to the implant electrode array by 1 mm 3 of paraffin is approximately half of the predicted maximum safe input power. A 3D heat transfer model of the scala tympani is successfully validated and enables predicting the maximum safe input power required to detach the magnet from the implant electrode array. This work will enable the design of a thermally safe magnetic cochlear implant surgery procedure.

Numerical investigation on fluid flow and convective heat transfer in a microchannel heat sink with fan-shaped cavities and ribs

In the present study, a detailed numerical simulations of liquid flow in microchannel heat sink with four different geometry of ribs: rectangular (RR), backward triangular (BTR), forward triangular (FTR) and diamond (DR) arranged symmetrically inside reentrant fan shaped cavities (FC) on side walls has been conducted and compared with smooth channel (SC) to acquire fluid flow and heat transfer characteristics between Reynolds numbers of 136−588. The local pressure, temperature and heat transfer coefficients were determined to understand the convective heat transfer regimes and to analyze local flow behavior. The three-dimensional conjugate heat transfer model, investigation is done extensively to identify the influence of geometrical parameters towards augmenting thermal performance with parametric optimization. Evolved governing equations are solved by using SIMPLEC algorithm. Attempt has been made to improve heat extraction ability with reasonable pressure drop by replacing the existing simple design of microsink. It is observed that Nusselt number and friction factor are in good agreement with previous experimental data. Based on detailed parametric study, it was found that FC-RR is good in achieving maximum Nusselt number, but due to higher pressure drop penalty giving lower performance. Out of four proposed, FC-DR is conferring upstanding balance between heat transfer, pressure drop and giving the best thermal performance of 1.97 at Re = 391.47.

Effects of solid particle thermal conductivity on heat storage performance of heat storage bed

The thermal properties of particles are important parameters that directly affect the heat storage performance of the solid particle heat storage bed. This paper reports the effects of solid particle thermal conductivity on heat storage performance of heat storage bed. A three-dimensional steady-state heat transfer model of heat storage bed with a single vacancy was established using ANSYS 19.0. The effects of thermal conductivity of particles were studied. With the increase in thermal conductivity of particles, the effect of the vacancy on heat storage particle bed heat transfer performance increases, the affected area size increases, so the heat storage and release performance of heat storage bed decreases. With the increase of thermal conductivity of particles from 0.5 W/ (m·K) to 50 W/ (m·K), the size of the affected region increased from 0.61 times of particle size to 1.82 times of particle size in the direction perpendicular to the heat transfer, and the size of the affected region increased from 1.61 times of particle size to 3.91 times of particle size in upstream of the direction parallel to the heat transfer. At the same time, the size of the affected region increased from 1.69 times of particle size to 3.93 times of particle size in downstream of the direction parallel to the heat transfer. It can provide a basis for improving the thermal resistance theory.

Detection of slags in structural steel sample using InfraRed thermal wave imaging

The estimation of defects in any material is a critical problem in the domain of InfraRed thermography (IRT). The paper presents simulation aspects of three-dimensional heat transfer model for a finite thickness structural steel sample having six different slag inclusions using a low peak power frequency modulated thermal wave imaging (FMTWI) and its digital counterpart digitized frequency modulated thermal wave imaging (DFMTWI) technique. The sample surface is subjected to proposed thermal heat flux and defect analysis was carried out by studying the thermal gradient over the test sample surface. Further, time domain pulse compression approach allowing better defect depth analysis has been discussed to evaluate the correlation coefficients and time delays for the proposed approaches. Results show better performance of the DFMTWI approach with high correlation coefficient values for all the defects with low time delays than the FMTWI approach.

Three-dimensional heat transfer of globe thermometers in indoor environments controlled by radiant systems

The theoretical basis of a globe thermometer is based on the lumped parameter method. In highly heterogeneous radiation environments, e.g., outdoor solar radiation and indoor heavily asymmetric radiation, the lumped parameter assumption is likely to be unreasonable. Asymmetric radiation is the inherent feature of radiant cooling indoor environments. Therefore, it is necessary to evaluate the influence of the asymmetric radiation of radiant cooling indoor environments on the thermal behaviour of globe thermometers. In this study, a three-dimensional heat transfer model for globe thermometers is established. The computational fluid dynamics method and the finite element method are used to solve the thermo-fluid field of the globe thermometer. The proposed theoretical model was validated against the results of experiments performed in a radiant cooling room and the data from existing literature. Some case studies were performed to analyse the thermal behaviour of various globe thermometers with different diameters and materials. The temperatures of metal globe thermometers were found to be uniform, whereas the temperature differences in the 50 mm and 150 mm acrylic globe thermometers were both 1.2 °C. Compared to metal globe thermometers, the air temperature deviations in the 50 mm and 150 mm acrylic globe thermometers were 0.6 °C and 0.4 °C, respectively. Thus, the asymmetric radiation of common radiant cooling indoor environments has a slight effect on the thermal behaviour of acrylic globe thermometers. This study is conducive to understanding the heat transfer mechanism of globe thermometers in indoor environments controlled by radiant systems.

Header impact assessment of double-layer microchannel heat sink in the computational fluid mechanics simulation for CPV thermal management

Thermal management is extremely required for concentrator photovoltaic (CPV) to prevent any thermal stress or physical damage. Yet, offering an adequate, reliable, and practical thermal management system for CPV is still challenging. In this work, the double-layer microchannel heat sink (DL-MCHS) is investigated for CPV cooling. To achieve this objective, a three-dimensional (3D) conjugate heat transfer model for the fluid flow in the DL-MCHS coupled with the thermal model for the solar cell, is done. The assessment of considering the inlet and outlet headers in the computational fluid mechanics (CFD) simulations are highlighted. The results reveal that including headers in the numerical study leads to predicting the accurate thermo-hydraulic performance of the DL-MCHS, especially in the CF. However, slight predicted variations have been obtained when PF operated. Moreover, neglecting the header in the CFD calculations significantly affect the calculated pumping power for both PF and CF operated. The potential of this intensive study demonstrates that there is an obvious difference in the CFD simulation figures when the DL-MCHS attached by headers in the CFD calculations.

Numerical Study of Combustion and Air Supply Characteristics and Structural Optimization of Top Combustion Hot Blast Stoves

The high-temperature hot air of hot blast stoves has an important effect on blast furnace ironmaking; it is one of the crucial factors that are used to assess the performance of hot blast stoves. In this study, a three-dimensional fluid flow heat transfer model combining turbulence, heat transfer, combustion, heat radiation, and heat exchange models was developed to assess the combustion and air supply characteristics of a new type of top combustion hot blast stove. The results indicate that nozzles that are alternately arranged in the same layer of the new hot blast stove caused rapid combustion reactions. In addition, it caused the high-temperature flue gas in the pre-combustion chamber to accelerate toward the combustion chamber, thereby eliminating the “eccentric swirl” of the traditional hot blast stove and improving the heat transfer efficiency and heat storage capacity. However, the “attachment effect” of the fluid still occurred in the new stove type, which led to an unreasonable temperature distribution inside the combustion chamber and regenerator. Therefore, an improved design of a top combustion hot blast stove was proposed in this paper. Using the developed numerical model, the performance of the new design was evaluated and compared with the original one.

Research on the human heat transfer model of Chinese pilots and experimental verification of model correctness

A three-dimensional human heat transfer model has been improved based on Chinese pilots’ anthropometric data. The temperature distribution of pilots can be simulated by this model. The improved model to simulate the variation of temperature distribution over time in pilots is adopted. To verify the model, an experimental study on temperature distribution of human body is carried out in this paper. The human heat transfer model built in the paper considering heat production from food and blood resistance can simulate the temperature distribution of Chinese pilots.

Numerical Evaluation of the Transient Performance of Rock-Pile Seasonal Thermal Energy Storage Systems Coupled with Exhaust Heat Recovery

This study seeks to investigate the concept of using large waste rocks from mining operations as waste-heat thermal energy storage for remote arctic communities, both commercial and residential. It holds its novelty in analyzing such systems with an experimentally validated transient three-dimensional computational fluid dynamics and heat transfer model that accounts for interphase energy balance using a local thermal non-equilibrium approach. The system performance is evaluated for a wide range of distinct parameters, such as porosity between 0.2 and 0.5, fluid velocity from 0.01 to 0.07 m/s, and the aspect ratio of the bed between 1 and 1.35. It is demonstrated that the mass flow rate of the heat transfer fluid does not expressively impact the total energy storage capacity of the rock mass, but it does significantly affect the charge/discharge times. Finally, it is shown that porosity has the greatest impact on both fluid flow and heat transfer. The evaluations show that about 540 GJ can be stored on the bed with a porosity of 0.2, and about 350 GJ on the one with 0.35, while the intermediate porosity leads to a total of 450 GJ. Additionally, thermal capacity is deemed to be the most important thermophysical factor in thermal energy storage performance.

Numerical investigation of heat transfer in the double-layered minichannel with microencapsulated phase change suspension

A three-dimensional heat transfer model of a double-layered minichannel heat sink (MCHS) with microencapsulated phase change material (MPCM) slurry as working fluid was established. The equivalent heat capacity method was used to deal with the phase transition process of microcapsules under turbulent conditions. The flow and heat transfer of MPCM slurries in the minichannel with constant heat flux at the bottom were investigated. In comparison with the single-layered MCHS and the water as working fluid, lower thermal resistance and more pressure drop occur double-layered minichannel with MPCM suspensions of different concentrations, thus, a comprehensive performance factor is defined to evaluated the overall behavior of minichannel, that is related to the thermal resistance and pressure drop. In the presented mode with MPCM suspensions, more than 13.8% higher performance factor occurs than that of water, and more effects on heat transfer happens in the lower channel. The optimized structures of double-layered minichannel are related to the operating conditions.

Three dimensional FE thermal analysis for friction stir welding of low carbon steel

Abstract In this work, a three-dimensional heat transfer model based on Abaqus/CAE 2017 finite element (FE) software package was developed to examine the effect of heat flux from tool shoulder and pin on the temperature distribution during FSW of low carbon steel sheet. Heat flux distribution models for shoulder and pin were developed by assuming the shoulder portion as a surface heat source and the tool pin as a volumetric heat source. These non-uniform heat flux models were embedded in a Fortran code and fed to Abaqus/CAE via DFLUX subroutine. In the FE model, temperature-dependent thermal properties of low carbon steel were incorporated. The influence of traverse speeds (i.e., 300 mm/min, 450 mm/min and 600 mm/min with the constant rotational speed of 450 rpm) on transient thermal history at varying distance from the weld center line was studied. It was observed that the higher heat input increases the peak temperature with a decrease in traverse speed. The transient thermal profile obtained from the FE analysis and experiment were matched fairly well with a percentage error of 6.4% for maximum temperature.

Numerical Simulation of Shallow Geothermal Field in Operating of a Ground Source Heat Pump System—A Case Study in Nan Cha Village, Ping Gu District, Beijing

The inefficient use of single energy and cold accumulation in the shallow geothermal field seriously affect the efficient operation of the ground source heat pump system (GSHPS). The operation of solar-assisted GSHPS can effectively solve the above problems. In this paper, a shallow geothermal utilization project in Nan cha Village, Ping Gu District of Beijing, is chosen as the study area. A three-dimensional numerical model of groundwater flow and heat transfer considering ambient temperature and backfill materials is established, and the level of model integration and validation are novel features of this paper. The thermal response test data in summer and winter conditions are used to validate the model. The results show that increasing hydraulic gradient has a positive impact on the heat exchange. The mixture of sand and barite powder is recognized as a more efficient and economical backfill material. The changes of thermal influence radius, heat balance, and shallow geothermal field are simulated and analyzed by three schemes. It is demonstrated that the thermal influence radius is 5 m, 3.9 m and 3.9 m for Scheme 1, Scheme 2 and Scheme 3, respectively. The ground temperature is always lower than the initial formation temperature in Scheme 1 and Scheme 2; however, under Scheme 3 it is higher than the initial values. The closer the hole wall is, the larger the difference between the initial formation temperature and the ground temperature, and vice versa. The thermal equilibrium of Scheme 1, Scheme 2 and Scheme 3 is −728 × 106 KJ, −269 × 106 KJ and +514 × 106 KJ. Through comprehensive analysis of the above three factors, Scheme 3 is regarded as the most reasonable scheme for a solar system to assist GSHPS.

Performance investigation of zero-building-integrated photovoltaic roof system: A case study in Egypt

The concept of zero-energy buildings was developed due to the high cost of electricity and the availability of renewable energy. This study presents detailed design steps for a zero building using a grid-connected photovoltaic (PV) system with a battery to supply the load demand for a building in Egypt (31.0409°N, 31.3785°E). In the system design, the sizes of the system components are determined, including the sizes of the PV cells, batteries, chargers, and controllers, such that they fulfill the load requirements. Maximum power tracking is designed to achieve maximum utilization of solar energy. In addition, a cooling model for the PV system is introduced to increase its efficiency. The PV performance with and without the thermal absorber is theoretically investigated and compared using a three-dimensional conjugate heat transfer model. A coupled thermal-electrical iterative model is also used to estimate the system’s hourly performance. Findings show that increasing the cooling flow rate for the proposed PV system from 0 L/min to 1 L/min significantly decreases the temperature of the PV module from 60 °C to 41 °C at a solar radiation of 650 W/m2. The theoretical results show that using the PV thermal technology at a coolant flow rate of 2 L/min /module generates the highest electrical power along with enough thermal energy for residential building heating. The outlet warm water from the cooling process has been used household uses to achieve a zero-building theory. This thermal energy can also be used in floor heating radiant systems with high energy efficiency and good thermal comfort. Furthermore, the proposed system can sell 33.5 and 61.9 kWh energy to the grid per day in summer and winter, respectively.

Parametric investigation to optimize the thermal management of pouch type lithium-ion batteries with mini-channel cold plates

The thermal management for the pouch type li-ion battery module holds a pivotal role in preventing the electric and hybrid electric vehicles from thermal runaway or cold-start during on-road or fast charging conditions by improving the battery lifecycle and reliability. In this paper, a straight mini-channel based cold plate is sandwiched between two consecutive batteries to form a battery module, and the coolant is allowed to pass through it. A three-dimensional conjugate heat transfer model is deployed to solve the electrochemical-thermal reaction using commercially available software for a wide variety of design and operating conditions such as mini-channel width, number of channels, coolant type, liquid flow rate, coolant temperature, ambient temperature, and discharge rate. Results indicate that a cold plate containing an even number of channels showcases a higher pressure drop than the odd number of channels due to the flow resistance. With the increase of coolant flow rate, the average temperature of the battery module reduces at the expense of a more considerable pressure drop and increased power consumption. Thermally and statistically, a cold plate comprising 5 number of mini-channels each of width 6 mm, and water as the coolant at an entry temperature of 25 °C with the mass flow rate of 3 × 10−3 kg. s−1 is found ideal for maintaining the temperature of the 20 Ah pouch type LiFePO4 battery module within a desirable range of 25 °C–40 °C for any climatic conditions.

Pyrolysis of single large biomass particle: Simulation and experiments

Pyrolysis and heat transfer characteristics of single large biomass particle were investigated using three-dimensional unsteady heat transfer model coupled with chemical reactions. The consumption of biomass and the production of products were simulated. Some experiments were designed to provide model parameters for simulation calculations. The simulation was verified by pyrolysis experiments of large biomass particle in a vertical tube furnace. The simulation results show the internal heat and mass transfer law during the pyrolysis of large biomass particle. When the biomass particle diameter is between 10 and 30 mm, for every 5 mm increase in particle diameter, the time required for complete pyrolysis will increase on average by about 50 s. When the pyrolysis temperature is between 673 K and 873 K, a slight decrease in the pyrolysis temperature will cause the time required for the biomass to fully pyrolyze to rise significantly. And the phenomenon is more obvious in the low temperature range. The results indicate that the numerical simulation agrees well with the experimental results.

A Three-Dimensional Conjugate Heat Transfer Model of a Turbocharger Turbine Housing

The turbine housing is subjected to thermal load which is essential to be taken into account in the design process. In this paper, a three-dimensional conjugate heat transfer simulation of a wastegated turbine housing has been performed. The model has been validated with data from thermocouple measurements and thermography pictures. Moreover, the effect of ventilation speed on temperature distribution of turbine housing is investigated. As the air velocity increases from 8 to 20 m/s, the turbine housing temperature decreases about 114 K. The wastegate valve could be gradually opened by stepping-up the speed of the engine. The ratio of wastegate flow to the turbine housing gas flow is near 30% for the high rotational speeds and loads. Therefore, the exhaust gas passes through the wastegate channel and the velocity reaches 538 m/s for 2° opening of the wastegate valve. Simulation results show that 1.5 mm decreasing the wall thickness of the volute wall causes 30 Kelvin higher temperature in the turbine housing wall. According to the results of the simulation, the impeller specific work of high gas flow condition was observed to be up to 2.5 times of low mass flow rate operation. Furthermore, the specific amount of gas heat transfer at a closed wastegate condition is significantly higher in comparison to the high gas flow rate and open wastegate condition. In addition, the results show that at low speed and closed wastegate condition, 15 percent of the specific heat transfer occurs before the turbine wheel.

Effect of the single vacancy in particle pile on heat transfer performance of particle pile

This paper reports the effect of a single vacancy on heat transfer of particle pile. A three-dimensional steady-state heat transfer model of particle pile with a single vacancy was established. The effects on the temperature distribution, heat transfer mode and heat flux characteristics of the particle pile were studied. In the area close to the vacancy, the particle temperature distribution is significantly affected, and the average temperature line is significantly deformed. The heat conduction between particles along the Y-direction is the dominant heat transfer mode around the vacancy. Compared with a particle pile without vacancy, the total heat flux at the hot wall decreases by 0.63% and the apparent thermal resistance of the particle pile increases by 0.71%. The size of the region affected by a vacancy on heat transfer was determined. At the X-direction, the size of the region affected by a vacancy is 1.79 times of particle size. Upstream position of vacancy at the Y-direction, the size of the region is 4.03 times of particle size. Downstream position of vacancy at the Y-direction, the size of the region is 3.81 times of particle size. The research results can be used to improve the thermal resistance network theory.

An unsaturated three-dimensional model of fluid flow and heat transfer in NW Sabalan geothermal reservoir

This paper presents a 3D numerical model for the north-west (NW) Sabalan geothermal system, including the unsaturated vadose zone overlying the system, based on a conceptual model derived from data gathered from 10 deep exploration wells. To achieve the goal, the EOS3 (water-air state equation) module of the Tough2 simulator was utilized to develop the model. The model was constructed from a rectangular prism, which is 11.5 km long, 8 km wide, and variable depths ranging from 3.8–5.11 km. The 21 horizontal layers with a thickness range of 100−1000 m were expanded from the maximum height of 4110 to -1000 masl. A total of 22 rock types were distributed within the model based on the availability of rock units and geological structures derived from the exploration wells. The permeability of these rock types varied from 1.0 × 10−17 to 9.0 × 10-13 m2. The model was initially run to match the natural state of the reservoir. A close agreement was obtained between the measured data from the exploration wells, and the model results for subsurface temperatures and pressures. In the calibrated model, a high temperature upflow zone was required in the southeast part of the area (below the exploration sites D and E). This flow rises to the land surface through permeable zones, faults, and fractures, and finally appears on the earth’s surface as hot springs in the northwestern part of the area. This model was then used as the initial model to predict the reservoir performance for the 50 MWe scenario. The results showed that the reservoir can generate about 45 MWe by assigning two makeup wells and remain at this level for more than 30 years.

Experimental study and numerical modeling of heat and mass transfer in rubberwood during kiln drying

Rubberwood (Hevea brasiliensis) is a major raw material used in furniture factories in southern Thailand. Proper kiln drying of the lumber plays a significant role on the efficient utilization of the final product. Overall quality-reducing defects in such a materials are inevitable, unless a correct and proper drying process is used. Therefore, the objective of the present study was to develop a three-dimensional numerical model of heat and moisture transfer during the drying process and to conduct physical experiments in order to compare the results between the two approaches. For this purpose, an innovative kiln dryer was designed in the laboratory which will also contribute to the prevention of defects in the wood. The results show that the samples dried at a temperature of 120 °C experienced faster decreases in their moisture content compared to those dried at temperatures of 100 °C and 80 °C. The drying temperature and moisture content of the samples were successfully predicted by the simulation model created in this investigation and the two approaches demonstrated good agreement for temperature and moisture with root mean square errors of 0.50 and 0.19, standard errors of 0.38 and 0.16, and mean absolute errors of 0.94 and 2.18, respectively. These results will help rubberwood drying facilities prevent wood deformation while reducing the drying time required.

Open manifold microchannel heat sink for high heat flux electronic cooling with a reduced pressure drop

To meet the intensifying demands of electronics cooling the current study proposes an open manifold microchannel heat sink, which substantially reduces the pressure drop of a conventional manifold microchannel heat sink while retaining a low thermal resistance, thin profile (< 2 mm) and planar geometry suited to microfabrication. The open heat sink achieves this by eliminating ineffective nozzle constrictions, specifically by removing channel walls beneath the slot nozzle. Two three-dimensional conjugate heat transfer models are used, including a single microchannel or a single manifold channel pair with hundreds of interconnecting microchannels. The performance of the open geometry is compared to an unmodified baseline geometry. In the microchannel model, the open case showed ideal pressure drop reductions of 45 % to 75 % with a negligible change to thermal resistance, at flow rates between 0.2 L/min and 1.0 L/min. Chamfering the tips of the microchannel walls show similar trends, although to a lesser degree. In the manifold model, the open case showed pressure drop reductions of 25 %, with thermal resistance slightly decreasing at flow rates below 0.58 L/min (-4 % to 1 %) and increasing at flow rates above 0.70 L/min (11 % to 21 %). These changes in thermal resistance were attributed to flow maldistribution, which may be alleviated through optimisation of the manifold convergence profile. At a flow rate of 1.32 L/min, the open geometry achieved a thermal resistance of 0.120 cm2K/W with a pressure drop of 10.3 kPa.