Transfer Model Simulations Research Articles

Continuous Casting Secondary Cooling: Laboratory Heat Transfer Measurements and Accuracy Considerations by Comparison with the Real Situation

In secondary cooling of continuous casting, it is very important to know the cooling heat flux for the actual spray cooling situation with respect to various parameters like the local position, the nozzle types, distances, and the water and air flow rates, to be able to control the cooling conditions precisely. As heat flux measurements on a casting machine are too challenging, experimental laboratory test rigs are designed and used for measurements by different research groups. Therefore, metal probes of different dimensions and materials are heated up to the desired temperature and then exposed to spray nozzles. The heat flux is usually measured by temperature sensors immersed in the probe body, and then determined from the measured temperature using inverse modelling methods. Herein, the differences between the real and laboratory conditions are focused on using a mathematical heat transfer simulation model. The influence of strand surface temperature, nozzle spray water flow conditions, and Leidenfrost effect are pointed out. A procedure to use heatflux data measured on a test rig for cooling control on a real caster despite the different conditions is proposed.

Experimental Investigation on Process Signature for EDM Processes

Abstract In recent years, the term “process signature” has been introduced by different scientists. Within the framework of determining process signatures, the interaction between material loads resulting in material modifications should be investigated. During recently this idea is adopted to the EDM process. Therefore, as a further step towards this goal, in this work the interaction between the applied thermal loads (including temperature field as well as temporal temperature gradients) and the induced modifications in form of phase transitions and change in the grain size in the heat affected zone (HAZ) during single discharge experiments were analyzed. Due to the nature of the EDM process, namely its high frequency as well as high local and temporal gradients of the applied thermal loads, the in-situ measurement of the thermal loads is not always straightforward and accurate enough. Thereby, the determination of applied thermal loads has been done by using a heat transfer simulation model. Using the obtained results from the experiment and simulations, the microstructure modifications in the HAZ of an eroded workpiece are analyzed, with respect to the temperature gradients induced during a single discharge experiment.

Developing an Accurate Heat Transfer Simulation Model of Alaska Pollock Surimi Paste by Estimating the Thermal Diffusivities at Various Moisture and Salt Contents

Abstract Alaska pollock (AP) surimi paste was prepared (0–3% salt and 76–84% moisture). The density, specific heat, and thermal conductivity were measured and modelled in temperatures between 25 and 90 °C (R 2 > 0.92). The thermal diffusivity (α) function showed a strong dependence on the moisture content and a unique salt dependence at 84% of the moisture content and applied to the heat transfer simulation of surimi paste. The simulation model coupled with the empirical thermal properties accurately predicted the heat penetration curves during heating with RMSE values ranging from 0.43 to 1.22 °C. The salt dependence on thermal diffusivity was identified and modeled only at 84% moisture content. With a model for 84% moisture content, the RMSE value of 3% salt content decreased from 1.11 °C to 0.56 °C. This study demonstrated that an accurate prediction of the heat transfer of the surimi paste needs to be coupled with the nonlinear thermal diffusivity functions.

On Optimal Imaging Angles in Multi-Angle Ocean Sun Glitter Remote-Sensing Platforms to Observe Sea Surface Roughness.

Sea surface roughness (SSR) is a key physical parameter in studies of air–sea interactions and the ocean dynamics process. The SSR quantitative inversion model based on multi-angle sun glitter (SG) images has been proposed recently, which will significantly promote SSR observations through multi-angle remote-sensing platforms. However, due to the sensitivity of the sensor view angle (SVA) to SG, it is necessary to determine the optimal imaging angle and their combinations. In this study, considering the design optimization of imaging geometry for multi-angle remote-sensing platforms, we have developed an error transfer simulation model based on the multi-angle SG remote-sensing radiation transmission and SSR estimation models. We simulate SSR estimation errors at different imaging geometry combinations to evaluate the optimal observation geometry combination. The results show that increased SSR inversion accuracy can be obtained with SVA combinations of 0° and 20° for nadir- and backward-looking SVA compared with current combinations of 0° and 27.6°. We found that SSR inversion prediction error using the proposed model and actual SSR inversion error from field buoy data are correlated. These results can provide support for the design optimization of imaging geometry for multi-angle ocean remote-sensing platforms.

An intergenerational farm transfer: when to start handing over the reins?

This case illustrates a challenging management decision faced by the family farm: when should they bring the younger generation to the farm full-time? Under consideration is a critical trade-off between the firm’s growth and transfer tax implications that drives the farm transfer decision. Industry practitioners and students are asked to use the results of the intergenerational farm transfer simulation model to evaluate this trade-off and provide an effective recommendation. The case can be used as part of succession/estate planning workshops attended by agricultural producers, farm managers, agricultural lenders, as well as in Master’s level courses in agricultural finance and farm management.

An Experimental Study on the Drying-Out Ability of Highly Insulated Wall Structures with Built-In Moisture and Rain Leakage

The recent research on highly insulated structures presents controversial conclusions on risks in moisture safety. This paper addresses these controversial issues through investigating the hygrothermal performance of energy efficient envelope structures under high moisture loads. The experiments consist of built-in moisture and rain leakage tests in mineral wool insulated structures. A heat and moisture transfer simulation model is developed to examine the drying-out ability in both warm and cold seasons. The results show that the energy efficient structures have an excellent drying out ability against built-in and leakage moisture. The difference in the drying ability is limited compared to conventional structures. A critical leakage moisture amount reaching the insulation cavity for a wood frame wall is determined to be between 6.9–20.7 g in a single rain event occurring every other day. Further research is required to target highly insulated structures, particularly addressing water vapor diffusion and convection.

Parallel simulation model for heat and moisture transfer of clothed human body

The heat and moisture transfer performance in clothed human body affects human life quality (e.g., comfort and health) directly. Accurate modeling and highly efficient simulation of the heat and moisture transfer mechanisms in clothed human body is helpful to enhance the human life quality. In this paper, we first describe a heat and moisture transfer simulation model of clothed human body, which comprises the George Fu’s human thermal physiological model and a 3D heat and moisture transfer model in clothing, and the thermoregulation behaviors as well as the heat transfer mechanisms are taken into consideration. Then according to the physiological and geometrical features of human body, a parallel algorithm for the heat and moisture transfer simulation in clothed human body is proposed. The SPMD framework has been utilized for data parallel. At last, case studies with different environment scenes are presented. The visual simulated results are displayed, and the parallel performance is discussed.

Developing a sterilization processing and a grading system to produce a uniform quality of sterilized whole corn (Zea mays L. var. ceratina)

In this study, a grading system for ears of corn was developed to design sterilization process of the ear of corn using fuzzy c-mean (FCM) clustering. Three grades (A, B, and C) of corn found by FCM (the m-value and the c-value were 1.15 and 3, respectively) were used to design the sterilization process of the ear of corn. The heat transfer simulation model was successfully developed to determine the locations of the cold point for the three different grades of corn during sterilization (RMSE = 0.104 °C). Among the 3 different temperature used in this study (111.1, 121.1, and 131.1 °C), 121.1 °C found to be the optimum sterilization temperature based on the analysis of texture properties of corn. The heating time to reach the target F0-value (5 min) for grades A, B, and C was 61, 49, and 36 min, respectively. When the longest heating time (61 min) was applied, the quality of the overheated corn (grades B and C) was significantly decreased (p < 0.05), whereas the quality of the corn at the optimum sterilization condition for each grade showed no significant difference. The heat transfer simulation model was successfully combined with the grading system developed by FCM to optimize the sterilization process of packaged whole corn. The texture properties and sensory attributes of sterilized corn were improved by applying the optimum sterilization processes which was adjusted based on the size and weight of corn ears.

Development of a Novel Image Analysis Technique to Detect the Moisture Diffusion of Soybeans [Glycine max (L.)] During Rehydration Using a Mass Transfer Simulation Model

The change in the moisture content of soybeans during a rehydration process at 25 °C was investigated. Peleg’s equation was suitable for describing the soaking characteristics of the soybean with a R2 value of 0.98. The soaking time to achieve the target moisture content of soybeans (33.33%) was estimated to be 14.59 min by the Peleg model. The mass transfer coefficient (k) for the mass transfer simulation was determined with two calculation steps using the Omoto model and the simulation models. The most suitable k value for the simulation was determined to be 6.0 × 10−7 m2/s, which is higher than the apparent k value obtained from the Omoto model. The diffusion simulation for the internal diffusion of the soybean after soaking was conducted for 180 min and the cross-section of soybeans was analyzed using an image processing technique during the diffusion process. The image analysis detected a moving layer during the diffusion process and the moisture content at the layer was determined to be 32.08% (± 0.34) based on the results of the simulation model.

A general distributed parameter model for ground heat exchangers with arbitrary shape and type of heat sources

The heat and mass transfer simulation model of a ground heat exchanger (GHE) directly affects the design and operation performance of a ground-coupled heat pump system. The GHE models based on the response function (like the Green function and g-function) can achieve a fast calculation speed. However, the heat sources in these models are limited to points or whole boreholes, leading to low calculation accuracy in heat transfer during a short time period and limitation to a certain GHE. A general distributed parameter model for a ground heat exchanger (RF model) is proposed based on the principle of response factors in this paper. A sandbox experimental platform is then built to test the temperatures of typical points in the double-layered soil and to validate the RF model. After that, the calculation of the RF model is simplified by determining suitable positions for the soil boundaries and the numbers of sub pipes and sub soil boundaries. Finally, the RF model is applied in different scenarios to demonstrate its characteristics. The results show that: (1) the RF model is suitable for different kinds of GHEs with arbitrary shape and type of heat sources releasing heat in arbitrary time steps; (2) the RF model has only 0.01 °C and 0.23 °C temperature response errors compared to those from numerical solutions and experiments, respectively; (3) the general RF model has similar accuracy to the numerical solution in calculating the distributed temperatures of the borehole and pipes, heat transfer in the short term, and heat transfer of borehole groups and the energy pile.

Experimental and computational fluid dynamics analysis of a photovoltaic/thermal system with active cooling using aluminum fins

Being the most widespread renewable energy generation system, photovoltaic (PV) systems face major problems, overheating and low overall conversion efficiency. The electrical efficiency of PV systems is adversely affected by significant increases in cell temperature upon exposure to solar irradiation. There have been several ways to remove excess heat and cool down the PV to maintain efficiency at fair levels. A hybrid photovoltaic/thermal system cooled by forced air circulation blown by a PV-powered fan was set up, and a rectangular control volume with cylindrical ends was built at the back of the PV panel where aluminum fins were placed in different arrangements and numbers. During the experiments, temperature and electrical output parameters were measured for three different air velocities (3.3, 3.9, and 4.5 m/s) and two different fin numbers and arrangements (54 pcs shifted and 108 pcs inline) under a constant radiation value of 1350 W/m2. While the electrical efficiency of the panel was reduced by almost 50% and decreased from 12% to 6.8% without active cooling, at 4.5-m/s air velocity and with 108 fins in inline arrangement, the electrical efficiency could be maintained at 11.5%. To compare and verify the experimental results, a heat transfer simulation model was developed with the ANSYS Fluent, and a good fit between the simulation and the test results was obtained.

Jet cooling characteristics for ball bearings using the VOF multiphase model

In a jet cooling ball bearing, the oil is mixed with the air and air-oil two-phase flow field is formed. The flow behaviours and heat transfer characteristics of the two-phase flow are significant for cooling evaluation and temperature control of the bearing. This paper investigates the fluid flow and heat transfer characteristics of a jet cooling ball bearing. The air-oil distribution and temperature distribution inside the ball bearing are calculated. The results indicate that micro bubbles are mixed into the oil at high-speed operation conditions. The highest oil volume fraction position is close to the nozzle and moves along the rotation direction at different speeds. Considering the air-oil two-phase distribution, the heat transfer simulation model using the VOF method is well enough for the present analysis. There is a correlation between the temperature distribution and the air-oil distribution inside the bearing. The lower temperature always appears at the higher oil volume fraction position. Optimizing the cooling mechanism according to the oil volume fraction distribution is helpful to achieve greater cooling effect.

Radiative energy balance of Venus based on improved models of the middle and lower atmosphere

The distribution of sources and sinks of radiative energy forces the atmospheric dynamics. The radiative transfer simulation model described by Haus et al. (2015b) is applied to calculate fluxes and temperature change rates in the middle and lower atmosphere of Venus (0–100km) covering the energetic significant spectral range 0.125–1000µm. The calculations rely on improved models of atmospheric parameters (temperature profiles, cloud parameters, trace gas abundances) retrieved from Venus Express (VEX) data (mainly VIRTIS-M-IR, but also VeRa and SPICAV/SOIR with respect to temperature results). The earlier observed pronounced sensitivity of the radiative energy balance of Venus to atmospheric parameter variations is confirmed, but present detailed comparative analyses of possible influence quantities ensure unprecedented insights into radiative forcing on Venus by contrast with former studies.Thermal radiation induced atmospheric cooling rates strongly depend on temperature structure and cloud composition, while heating rates are mainly sensitive to insolation conditions and UV absorber distribution. Cooling and heating rate responses to trace gas variations and cloud mode 1 abundance changes are small, but observed variations of cloud mode 2 abundances and altitude profiles reduce cooling at altitudes 65–80km poleward of 50°S by up to 30% compared to the neglect of cloud parameter changes. Cooling rate variations with local time below 80km are in the same order of magnitude.Radiative effects of the unknown UV absorber are modeled considering a proxy that is based on a suitable parameterization of optical properties, not on a specific chemical composition, and that is independent of the used cloud model. The UV absorber doubles equatorial heating near 68km. Global average radiative equilibrium at the top of atmosphere (TOA) is characterized by the net flux balance of 156W/m2, the Bond albedo of 0.76, and the effective planetary emission temperature of 228.5K in accordance with earlier results. TOA radiative equilibrium can be achieved by slight adjustments of either UV absorber or cloud mode abundances. Ratios of synthetic spectral albedo values at 0.36µm calculated for different abundance factors of the UV absorber are suggested to provide a possible tool to interpret observed VMC/VEX brightness variations with respect to actual absorber abundances.Atmospheric net heating dominates the low and mid latitudes above 82km, while net cooling prevails at high latitudes at all mesospheric altitudes (60–100km). This radiative forcing field has to be balanced by dynamical processes to maintain the observed thermal structure. A similar but much smaller meridional gradient is also observed at altitudes between 62 and 72km where the unknown UV absorber provides additional heating. At these altitudes, equatorial net heating dominates net cooling from about 07:30h until 16:30h local time. Intermediate altitudes (72–82km) are characterized by net cooling at all latitudes in case of VIRTIS temperature data. This planet-wide net cooling region is not observed when calculations are based on VeRa temperatures, and low latitudes are then characterized by small net heating. When a warm atmospheric layer as detected by SPICAV/SOIR around 100km is considered, strong global average net cooling occurs above 90km that is far away from radiative equilibrium. A weak net cooling layer (1–2K/day) exists at altitudes between 55 and 60km, while very weak net heating (0.1–0.5K/day) takes place near the cloud base (48km). Almost zero net heating prevails in the deep atmosphere below 44km. On global average, the entire atmosphere of Venus at altitudes between 0 and 90km is not far away from radiative equilibrium (usually within±2K/day).Maximum temperature change rate deviations from mean values at each altitude and latitude are defined based on retrieved atmospheric parameter single standard deviations using VIRTIS data. This is an important prerequisite to investigate parameterization approaches for the calculation of atmospheric temperature change rates that can be used in Global Circulation Models. This will be a major topic of future studies on radiative energy balance of Venus’ atmosphere.

ヒートクラスター型地中熱ヒートポンプの熱移動解析

Ground Source Heat Pump (GSHP) is the temperature of the ground is stable throughout the year, COP is higher in cold climates compared to the air heat source heat pump that are affected by the temperature. However, GSHP takes a huge initial costs associated with the installation a number of boring work and heat exchanger. Heat cluster as a new method is able to pump heat from both the soil and groundwater to insert a well pile into the ground. In this method it is possible to greatly reduce the boring work and costs. Heat cluster system will perform heat exchange by actively pumping groundwater into the well pile by the purge pump. Its heat transfer mechanism is not clear. In this study, we tried the development of the underground heat transfer simulation model that contains soil and the flow of groundwater.

Simulation of Power Production from Dry Geothermal Well Using Down-hole Heat Exchanger in Sabalan Field, Northwest Iran

In this research, a simulation was performed for evaluating power production from an abandoned geothermal well as an enhanced geothermal system by injecting a secondary fluid. Abandoned wells, due to lack of fluid or very low transmissivity, are regarded among the low-to moderate-temperature resources that have the potential for heat production without any cost for deep drilling. Accordingly, they are taken as suitable sources of energy. In the present paper, an abandoned geothermal well at Meshkinshahr geothermal field in Sabalan district, northwestern Iran, with 3176 m depth was simulated. The bottom-hole temperature of 148 °C, as well as well casing size, and real thermal gradient for well were applied in the model. A 3D heat transfer simulation model was designed by considering a coaxial pipe as a down-hole heat exchanger between surrounding rocks of the well and injected fluid. Injected fluid to the well with specified pressure and temperature receives heat from rocks surrounding the well, until it reaches the bottom of the well and converts to vapor. The vapor returns to the surface from inner pipe with very low heat loss during its return. The inner pipe is isolated by a thin layer having a low heat conductivity to prevent heat loss from the returned fluid. It was observed that obtained heat in the well depends on temperature profile of the well, injection velocity, and fluid mass flow rate. The model results were optimized by selecting suitable parameters such as inlet injection speed and fluid flow rate to achieve the highest temperature of the fluid returned from the well. A binary power plant was also modeled to determine the extractable power using returned fluid as input using ammonia and isobutene, as working fluids in binary cycle. Finally, electric power of 270 kW was generated from well NWS3 using designed down-hole heat exchanger.

Heat Recovery Process from Packed Bed of Hot Slag Plates

Reduction of CO2 emissions from the steelmaking process is strongly required for prevention of global warming. One promising heat resource that is estimated to have great potential for energy saving is the waste heat of steelmaking slag, which has a temperature of above 1673 K in the molten state. This molten slag can be solidified in a plate-like shape by feeding it on the surface of water-cooled rolls, and the heat of the plate-like slag can be recovered easily in spite of its low heat conductivity. When these hot slag plates are packed in a slag chamber, the heat of the slag can be recovered by heat exchange with a counter current gas flow. Because the efficiency of gas-slag heat transfer changes depending on the shape of the packed slag, it is difficult to estimate the efficiency of slag heat recovery without evaluating the accuracy of the heat transfer coefficient in the bed. In this work, the effect of the slag shape on the accuracy of the heat transfer equation was evaluated by conducting both laboratory-scale and pilot-scale slag heat recovery experiments and performing a fitting analysis by using a slag packed bed heat transfer simulation model. A comparison of the experimental results and calculation results confirmed that the heat transfer coefficient can be estimated by using Johnson-Rubesin’s equation modified by a correction factor in case the packed materials are plate-like. The effect of the correction factor on the efficiency of slag heat recovery at the industrial scale was also estimated.

Seepage Heat Transfer Model and Numerical Simulation of Grate Cooler

Seepage Heat Transfer Model and Numerical Simulation of Grate Cooler

집광형 태양전지를 이용한 난방장치 개발

본 연구는 집광장치와 태양추적장치를 이용함으로서 제한된 면적을 가지는 집광형 태양전지의 발전효율을 증가시키는 연구를 진행하였다. 태양전지에서 발생된 열은 온수나 난방에 사용되도록 흡열기를 이용하여 회수하였다. 이로서 집광형 태양전지를 이용한 시스템은 전기와 열을 동시에 공급할 수 있다. 태양위치에 따른 실시간 추적, 일몰 이후 난방장치의 동쪽방향 원상복귀, 원상복귀후 자동종료는 조도센서와 Simulink 프로그램으로 구현하였다. 흡열기 입구 속도, 핀설치 유무, 입구위치에 따른 흡열기 온도를 해석하였으며 실험결과와 일치하였다.

A physiological systems approach to modeling and resetting of mouse thermoregulation under heat stress

Heat stroke (HS) is a serious civilian and military health issue. Due to the limited amount of experimental data available in humans, this study was conducted on a mouse mathematical model fitted on experimental data collected from mice under HS conditions, with the assumption there is good agreement among mammals. Core temperature (T(c)) recovery responses in a mouse model consist of hypothermia and delayed fever during 24 h of recovery that represent potential biomarkers of HS severity. The objective of this study was to develop a simulation model of mouse T(c) responses and identify optimal treatment windows for HS recovery using a three-dimensional predictive heat transfer simulation model. Several bioenergetic simulation variables, including nonlinear metabolic heat production (W/m³), temperature-dependent convective heat transfer through blood mass perfusion (W/m³), and activity-related changes in circadian T(c) were used for model simulation. The simulation results predicted the experimental data with few disparities. Using this simulation model, we tested a series of ambient temperature treatment strategies to minimize hypothermia and delayed fever to accelerate HS recovery. Using a genetic algorithm, we identified eight time segments (ambient temperature = 27, 30, 31, 29, 28, 28, 27, 26°C) of 110 min total duration that optimized HS recovery in our model simulation.

An active cooling system for photovoltaic modules

The electrical efficiency of photovoltaic (PV) cell is adversely affected by the significant increase of cell operating temperature during absorption of solar radiation. A hybrid photovoltaic/thermal (PV/T) solar system was designed, fabricated and experimentally investigated in this work. To actively cool the PV cells, a parallel array of ducts with inlet/outlet manifold designed for uniform airflow distribution was attached to the back of the PV panel. Experiments were performed with and without active cooling. A linear trend between the efficiency and temperature was found. Without active cooling, the temperature of the module was high and solar cells can only achieve an efficiency of 8–9%. However, when the module was operated under active cooling condition, the temperature dropped significantly leading to an increase in efficiency of solar cells to between 12% and 14%. A heat transfer simulation model was developed to compare to the actual temperature profile of PV module and good agreement between the simulation and experimental results is obtained.