Numerical determination of the distance between the GPUs where effective cooling is made in computers used in coin mining

Quantification of the heat exchange of chicken eggs

Numerical evaluation of the convective and radiative heat transfer coefficients for preterm neonate body segments inside an incubator

Evaporation heat transfer from the hot water flow to the cold air flow in a horizontal and rectangular flow channel was examined. The water temperature was 35°C ∼ 65°C. The air velocity was 0.02 m/s ∼2.57 m/s. The heat transfer rate from the water flow to the air flow became large with an increase in the air velocity and the water temperature. The evaporation heat transfer was much larger than the convection heat transfer and dominant in the heat transfer. The ratio of the evaporation heat transfer rate to the total heat transfer rate was approximately 0.9 ∼ 0.7 in the present experimental conditions. It showed the slightly decreasing tendency for the air velocity. The evaporation heat transfer coefficient showed strong dependency on the air velocity in both the laminar and the turbulent flow region of the air flow. The convection heat transfer coefficient showed the same tendency for the Reynolds number of the air flow as that for the air single-phase flow in the turbulent flow region although the value was much larger than that of the single-phase flow. In the laminar flow region, the convection heat transfer coefficient was constant as in the single-phase flow when the water temperature was low, although the value itself was much larger than that of the single-phase flow. As the water temperature became high, the convection heat transfer coefficient became large and showing dependency on the Reynolds number of the air flow. As the Reynolds number of the air flow became further small, the convection heart transfer coefficient greatly decreased irrespective of the water temperature.

This study aimed to develop a model using experimentally obtained convective heat and mass transfer coefficients to predict the effect of temperature, humidity, and drying rate on wood drying. Tangential wood samples of Eucalyptus nitens (H. Deane & Maiden) were used in the investigation. The experimental design consisted of two temperature levels (40 °C and 55 °C), two relative humidity levels (55% and 75%), and two air velocity settings (2 m·s−1 and 3 m·s−1). The experiments were conducted under a constant evaporation rate, spanning the maximum and critical moisture content in the wood. A statistical model using multivariate regression was created to predict the convective heat and mass transfer coefficients. The results indicated that the experimental data and empirical correlations exhibited an error margin of 37.77% and 37.86%, respectively. A significant positive correlation was found between the convective heat transfer coefficient and air velocity, temperature, and relative humidity, while the convective mass transfer coefficient showed a significant positive correlation only with air velocity and temperature. The model predicted the convective heat and mass transfer coefficients with high accuracy and statistical significance. Using the proposed method, we successfully obtained both convective coefficients, which enable accurate description of heat and mass flow during the convective drying of Eucalyptus nitens wood.

This article presents an analytical model for analyzing transient heat transfer between a brick particle and air flow during heating in a fluidized bed combustor. Both experimental and theoretical studies were carried out. The experimental investigation provided the temperature distributions at the centers of the spherical particles during heating. These data were presented in the dimensionless form and were compared with the results of the present analytical model The modeling includes two heat transfer coefficient cases. In the first case, heat transfer coefficient is the only convection heat transfer coefficient, and in the second case, it is the sum of the convection and radiation heat transfer coefficients. In the comparison between experimental data and theoretical results, better agreement was found for the second case. The present results indicate that the radiation heat transfer coefficient has a significant effect on transient heat transfer from the single object and should be taken into consideration.

Heat transfer modelling of spherical particles subject to heating in a fluidized bed

It is important in grinding for the fluid to remove heat from the grinding contact zone to avoid thermal damage to the workpiece surface and/or subsurface layers. The cooling effect of grinding fluid can be quantified by a convection heat convective heat transfer coefficient acting in the grinding zone. This article presents values of the convection heat transfer coefficient based on published experimental results for measured grinding temperatures. This article also presents a new convective heat transfer model based on principles of applied fluid dynamics and heat transfer. Predicted values for the convection heat transfer coefficient calculated from the model are compared with results from experiments obtained under a range of grinding conditions and with experimental data obtained from published literature. The results demonstrate that the new convection heat transfer coefficient model improves the accuracy of prediction and helps explain the variation in the value of convection heat transfer coefficient under varying process conditions. The results also show that convection efficiency strongly depends on the grinding wheel speed, grinding arc length and fluid properties. This new model can be readily introduced into current thermal models of the process used to predict and control grinding temperatures.

A detailed model of human thermoregulation and a numerical algorithm to predict thermal comfort is a novel field of research and has wide applications in the auto/transportation industry and in the heating, ventilating, and air-conditioning (HVAC) industry. Anatomically specific convective and radiative heat transfer coefficients for the human body will be required to understand the human thermal physiological and comfort models. It necessitates to create hygienic and thermally comfortable spaces for the best productivity of the users. The physiological nature of thermal comfort during a transient condition such as a physical exercise or travel in an automobile are not yet well understood. In this paper, thermography has been applied to measure the convective and radiative heat transfer coefficients which has not been done before. Three different recovery processes were considered after the running of a human model on a treadmill with a range of speeds starting from 2 miles/hour to 10 miles/hour for stretch of twenty minutes. The recovery process included, (a) fan-assisted cooling with an air velocity of 0.5 m/s for 30 minutes, (b) fan-assisted cooling with an air velocity of 1.5 m/s for 30 minutes, and (c) natural cooling with no assistance of fan for 30 minutes. Thermal images were taken for forehead, trunk, arms, hands, legs of the models and the convective heat transfer coefficient and radiative heat transfer coefficient were calculated. The human models included both male and female, and belonged to two different age groups of less than 15 and above 40 with a total of 24 participants. The results show that though the temperatures, measured using thermography, for various parts of the human body changed locally, the overall calculated radiative heat transfer coefficients matched with the ASHRAE handbook values, and the calculated convective heat transfer coefficient increased with the increase of air velocity, while the models cooled down after the workout. Interestingly, the skin temperature decreased, initially, as the exercise progressed. After the completion of exercise, the skin temperature exhibited a quick rise during the recovery period with a subsequent decrease in the temperature, later. This trend was the same with all different age groups and sex of the models. The results also confirm that thermal images can be relied on for calculating the convective and radiative heat transfer coefficients of the human body to determine the heat transfer rate.

The air flow propelled by an axial flow fan is often assumed to be uniform across the tube bundle of an industrial air-cooled heat exchanger, but the fact is that the air flow is non-uniform in practice to the extent that as much as 35% performance of air-cooled heat exchangers is cut off. Besides the structure of tube bundle, the high flux and low pressure head fan with 1.5 m to 4.5 m in diameter is the primary reason of the air flow maldistribution. CFD was employed to numerically simulate the non-uniform air flow distribution produced by the fan in the radial and flow direction. One axial flow type fan with 3 blades about 2 m in diameter was investigated under the angular speed of 80, 350 revolutions per minute. Given that the uniform velocity is the default for the velocity or mass flow boundary, the boundary of the total pressure inlet and the static outlet was adopted in the present work for axial flow fan simulation. Between the rotating zone and the other zones is the fluid to fluid type interface with frozen rotor. The result showed that the air velocity rises when it comes nearer to the fan either in the upstream or in the downstream direction. The upstream flow decreases more rapidly than the downstream flow, the upstream velocity air at Z=−1.5 m is almost the same with the ambient while the downstream velocity at Z=5.8 m is still 2, 6 times larger than the ambient for 80, 350 RPM respectively. In each plane, the air flow distribution from the rotating center of the fan to the circumference is different from each other plane by the boundary conditions. And the maximum velocity locates at about the radial middle part of the blades. The hub at the central part near the fan causes the concave velocity distribution of the downstream flow. It is the driver mechanism geometry that causes the radial velocity change of the upstream flow. Finally, 3 methods involving the upstream or downstream type and the blade angle of inclination are provided to reduce the air flow non-uniformity.

In the present work, a study on convective heat, mass transfer coefficients and evaporative heat transfer coefficient of the thin layer drying process of ivy gourd is performed. The experiment was conducted in three drying modes such as natural, forced convection solar dryer and open sun drying. The hourly data for the rate of moisture removal, sample temperature, relative humidity inside and outside the solar and ambient air temperature for complete drying have been recorded. The drying air temperature varied from 55, 65, 70 and 75°C, and the air velocity was 1, 1.5 and 2m/s. All the drying experiments had shown a falling rate period. The data obtained from experimentation have been used to evaluate the experimental constant values of C and n by simple regression analysis. Based on the values of "C" and "n", convective and evaporative heat transfer coefficients for ivy gourd were determined. The average convective heat and mass transfer coefficients varied between 2.64 and 8.30W/m2 °C and 0.0025 to 0.0076m/s for temperature ranges, at the different air velocities, respectively. The average evaporative heat transfer coefficient for ivy gourd varied from 181.89 to 421.84W/m2 °C. It was observed that convective and evaporative heat transfer coefficients increase with the increase in drying air temperature. The rate of increment of evaporative heat transfer coefficient is higher than the convective heat transfer coefficient. The intensity of heat and mass transfer during solar drying depends on the drying air temperature and velocity.

In this research paper, the convective heat and mass transfer coefficients are evaluated for khoa drying under natural convection greenhouse mode for different sizes of khoa samples for a given mass.The khoa pieces of dimensions 0.025 × 0.02 × 0.015 m 3 , 0.0375 × 0.03 × 0.015 m 3 , and 0.075 × 0.06 × 0.015 m 3 with total quantity of 100 g are dried in the roof type even span greenhouse with a floor area of 1.2 × 0.8 m 2 .The khoa has been dried at atmospheric pressure till there is almost no variation in its mass is recorded.The experimental data are used to determine the values of the constants in the Nusselt number expression by simple linear regression analysis and, consequently the convective heat transfer coefficients are evaluated.The mass transfer coefficients have also been evaluated.The convective heat and mass transfer coefficients are observed to decrease with the increase in size of the khoa sample and are found more for the khoa pieces having dimension 0.025 × 0.02 × 0.015 m 3 .The experimental error in terms of percent uncertainty has also been evaluated.

Effect of absorption of solar radiation in glass-cover(s) on heat transfer coefficients in upward heat flow in single and double glazed flat-plate collectors

An investigation was conducted to determine the relationship between heat transfer coefficient and molten pool’s geometry. It was accomplished by performing an experimental and numerical investigation using a cylinder dimple with two different serials of geometry: (1) cylinder dimples with fixed print diameter D=50mm and different depth, and (2) cylinder dimples with fixed depth d=10mm and different print diameter. The airflow speed varies from 50m/s to 250m/s in the turbulent regime. The results consist of flow characteristics, mainly velocity profile and heat transfer characteristics, including heat transfer coefficient and Nusselt number along flow direction, were obtained. The comparison was held against the smooth surface. Results showed that a centrally-located vortex was formed due to the flow separation. For heat transfer coefficient, such augmentations are present near the downstream edges and diminutions are present near the upstream edges of dimple rims, both slightly within each depression. It was found that the convection heat transfer coefficients with different geometry parameters have similar distribution along flow direction. A uniform piecewise linear function was built to describe the heat transfer characterizes for different molten pool print diameter.

A theoretical and experimental study of transient heat transfer in the heating of an individual slab product, subjected to an air flow at a temperature of 50°C and a velocity of 1 m/s, is presented. Experimental temperature measurements at the centre of the slab product were made, and the experimental heat-transfer rates were derived from the temperature data. A simplified analytical technique, using the boundary condition of the third kind in transient heat transfer, was used to predict the theoretical heat transfer rates for two cases, the first considering that the heat transfer coefficient is a convective heat transfer coefficient, and the second considering that heat transfer coefficient is the sum of the convective and radiative heat transfer coefficients. The experimental heat-transfer rates were compared with the predictions for two cases, and a very good agreement was obtained.

Supercritical CO<sub>2</sub> can be used as a heat transfer fluid in a solar receiver, especially for a concentrating solar thermal power tower system. Such applications require better understanding of the heat transfer characteristics of supercritical CO<sub>2</sub> in the solar receiver tube in a high temperature region. However, most of the existing experimental and numerical studies of the heat transfer characteristics of supercritical CO<sub>2</sub> in tubes near the critical temperature region, and the corresponding heat transfer characteristics in the high temperature region are conducted. In this paper, a three-dimensional steady-state numerical simulation with the standard <i>k</i>-<i>ε</i> turbulent model is established by using ANSYS FLUENT for the flow and heat transfer of supercritical CO<sub>2</sub> in a heated circular tube with an inner diameter of 6 mm and a length of 500 mm in the high temperature region. The effects of the fluid temperature (823–1023 K), the flow direction (horizontal, downward and upward), the pressure (7.5–9 MPa), the mass flux (200–500 kg·m<sup>–2</sup>·s<sup>–1</sup>) and the heat flux (100–800 kW·m<sup>–2</sup>) on the convection heat transfer coefficient and Nusselt number are discussed. The results show that the convection heat transfer coefficient increases while Nusselt number decreases nearly linearly with fluid temperature increasing. Both fluid direction and pressure have negligible effects on the convection heat transfer coefficient and Nusselt number. Moreover, the convective heat transfer coefficient and Nusselt number are enhanced greatly with the increasing of mass flux and the decreasing of heat flux, which is more obvious at a higher heat flux. The influences of buoyancy and flow acceleration on the heat transfer characteristics are also investigated. The buoyancy effect can be ignored within the present parameter range. However, the flow acceleration induced by the high heat flux significantly deteriorates the heat transfer preformation. Moreover, eight heat transfer correlations of supercritical fluid in tubes are evaluated and compared with the present numerical data. The comparison indicates that the correlations based on the thermal property modification show better performance in the heat transfer prediction in the high temperature region than those based on the dimensionless number modification. And Nusselt number predicted by the best correlation has a mean absolute relative deviation of 8.1% compared with the present numerical results, with all predicted data points located in the deviation bandwidth of ±20%. The present work can provide a theoretical guidance for the optimal design and safe operation of concentrating solar receivers where supercritical CO<sub>2</sub> is used as a heat transfer fluid.