In this study, laminar convective heat transfer over two heated wall-mounted cubes is investigated.Two cubes, which are under constant heat flux, are placed in different tandem and staggeredarrangements ...In this study, laminar convective heat transfer over two heated wall-mounted cubes is investigated.Two cubes, which are under constant heat flux, are placed in different tandem and staggeredarrangements on a base plate. This problem is studied for different streamwise and spanwisedistances between two cubes in different Renolds number （Re）, by using finite-volume method.Effects of these parameters are considered on flow and heat transfer characteristics. The resultsshow that the temperature distribution is strongly dependent on flow structure and varies with anychange of flow pattern in different arrangements of cubes. In addition, it is observed that the dragcoefficient, which is influenced more by pressure forces, in staggered arrangement, is greater thantandem arrangement. Results show that by increasing the spanwise distance the amount of meanNusselt number （Nu） of Cube 2 becomes the same as Cube 1.展开更多
Theoretical and experimental study has been performed on heat transfer of airwater two phase laminar annular flow through a uniformly heated vertical small tube. Analysis ascertains that the mechanism of heat transfer...Theoretical and experimental study has been performed on heat transfer of airwater two phase laminar annular flow through a uniformly heated vertical small tube. Analysis ascertains that the mechanism of heat transfer is the evaporation of a very thin liquid film attached on the tube wall. The predictions of analytical solutions are quite good compared with the experimental results.展开更多
A three-dimensional thermoregulation mathematical model of temperature fluctuations for the human body is developed based on predecessors＇ thermal models. The following improvements are necessary in real situations：...A three-dimensional thermoregulation mathematical model of temperature fluctuations for the human body is developed based on predecessors＇ thermal models. The following improvements are necessary in real situations： ellipsoids and elliptical cylinders are used to adequately approximate body geometry, divided into 18 segments and five layers; the core layer consists of the organs; the pulsation of the heart cycle, the pulsatile laminar flow, the peripheral resistance, and the thermal effect of food are considered. The model is calculated by adopting computational fluid dynamics（CFD） technology, and the results of the model match with the experimental data. This paper can give a reasonable explanation for the temperature fluctuations.展开更多
The building sector consumes much energy either for cooling or heating and is associated to greenhouse gas emissions. To meet energy and environmental challenges, the use of ground-to-air heat exchangers for preheatin...The building sector consumes much energy either for cooling or heating and is associated to greenhouse gas emissions. To meet energy and environmental challenges, the use of ground-to-air heat exchangers for preheating and cooling buildings has recently received considerable attention. They provide substantial energy savings and contribute to the improvement of thermal comfort in buildings. For these systems, the ground temperature plays the main role. The present work aims to investigate numerically the influence of the nature of soil on the thermal behavior of the ground-to-air heat exchanger used for building passive cooling. We have taken into account in this work the influence of the soil nature by considering three types of dry soil: clay soil, sandy-clay soil and sandy soil. The mixed convection equations governing the heat transfers in the earth-to-air heat exchanger have been presented and discretized using the finite difference method with an Alternate Direction Implicit (ADI) scheme. The resulting algebraic equations are then solved using the algorithm of Thomas combined with an iterative Gauss-Seidel procedure. The results show that the flow is dominated by forced convection. The examination of the sensitivity of the model to the type of soil shows that the distributions of contours of streamlines, isotherms, isovalues of moisture are less affected by the variations of the nature of soil through the variation of the diffusivity of the soil. However, it is observed that the temperature values obtained for the clay soil are higher while the sandy soil shows lower temperature values. The values of the ground-to-air heat exchanger efficiency are only slightly influenced by the nature of the soil. Nevertheless, we note a slightly better efficiency for the sandy soil than for the sandy-clayey silt and clayey soils. This result shows that a sandy soil would be more suitable for geothermal system installations.展开更多
Based on the principle of field synergy for heat transfer enhancement, the concept of physical quantity synergy in the laminar flow field is proposed in the present study according to the physical mechanism of convect...Based on the principle of field synergy for heat transfer enhancement, the concept of physical quantity synergy in the laminar flow field is proposed in the present study according to the physical mechanism of convective heat transfer between fluid and tube wall. The synergy regulation among physical quantities of fluid particle is revealed by establishing formulas reflecting the relation between synergy angles and heat transfer enhancement. The physical nature of enhancing heat transfer and reducing flow resistance, which is directly associated with synergy angles α, β, γ, φ, θ and ψ, is also explained. Besides, the principle of synergy among physical quantities is numerically verified by the calculation of heat transfer and flow in a thin cylinder-interpolated tube, which may guide the optimum design for better heat transfer unit and high-efficiency heat exchanger.展开更多
Theoretical investigations have been performed on the convective heat transfer for incompressible laminar flow of gases through microtube and parallel-plates micropassages with constant wall temperature. Considering t...Theoretical investigations have been performed on the convective heat transfer for incompressible laminar flow of gases through microtube and parallel-plates micropassages with constant wall temperature. Considering the change in thermal conductivity and viscosity of gas in wall adjacent region from the kinetic theory, mathematical models are built for both of the micropassages. The dimensionless temperature distribution and the corresponding heat transfer characteristics are simulated numerically, and the results discussed briefly.展开更多
Modeling results are presented for the laminar flow and heat transfer within a circular tube connected coaxially with a d c arc plasma torch. In order to determine the correct boundary conditions at the tube in...Modeling results are presented for the laminar flow and heat transfer within a circular tube connected coaxially with a d c arc plasma torch. In order to determine the correct boundary conditions at the tube inlet, the computational domain is extended to include both the circular tube and the arc plasma torch. Computational results show that the gas static pressure in the tube increases at first and then decreases slowly, while the heat flux to the tube wall decreases monotonically with increasing distance from the tube inlet. Comparison of some computed results with corresponding experimental data is also given.展开更多
文摘In this study, laminar convective heat transfer over two heated wall-mounted cubes is investigated.Two cubes, which are under constant heat flux, are placed in different tandem and staggeredarrangements on a base plate. This problem is studied for different streamwise and spanwisedistances between two cubes in different Renolds number （Re）, by using finite-volume method.Effects of these parameters are considered on flow and heat transfer characteristics. The resultsshow that the temperature distribution is strongly dependent on flow structure and varies with anychange of flow pattern in different arrangements of cubes. In addition, it is observed that the dragcoefficient, which is influenced more by pressure forces, in staggered arrangement, is greater thantandem arrangement. Results show that by increasing the spanwise distance the amount of meanNusselt number （Nu） of Cube 2 becomes the same as Cube 1.
文摘Theoretical and experimental study has been performed on heat transfer of airwater two phase laminar annular flow through a uniformly heated vertical small tube. Analysis ascertains that the mechanism of heat transfer is the evaporation of a very thin liquid film attached on the tube wall. The predictions of analytical solutions are quite good compared with the experimental results.
基金Project supported by the National Basic Research Program of China(Grant No.2010CB734101)the National Natural Science Foundation of China(Grant No.51705332)
文摘A three-dimensional thermoregulation mathematical model of temperature fluctuations for the human body is developed based on predecessors＇ thermal models. The following improvements are necessary in real situations： ellipsoids and elliptical cylinders are used to adequately approximate body geometry, divided into 18 segments and five layers; the core layer consists of the organs; the pulsation of the heart cycle, the pulsatile laminar flow, the peripheral resistance, and the thermal effect of food are considered. The model is calculated by adopting computational fluid dynamics（CFD） technology, and the results of the model match with the experimental data. This paper can give a reasonable explanation for the temperature fluctuations.
文摘The building sector consumes much energy either for cooling or heating and is associated to greenhouse gas emissions. To meet energy and environmental challenges, the use of ground-to-air heat exchangers for preheating and cooling buildings has recently received considerable attention. They provide substantial energy savings and contribute to the improvement of thermal comfort in buildings. For these systems, the ground temperature plays the main role. The present work aims to investigate numerically the influence of the nature of soil on the thermal behavior of the ground-to-air heat exchanger used for building passive cooling. We have taken into account in this work the influence of the soil nature by considering three types of dry soil: clay soil, sandy-clay soil and sandy soil. The mixed convection equations governing the heat transfers in the earth-to-air heat exchanger have been presented and discretized using the finite difference method with an Alternate Direction Implicit (ADI) scheme. The resulting algebraic equations are then solved using the algorithm of Thomas combined with an iterative Gauss-Seidel procedure. The results show that the flow is dominated by forced convection. The examination of the sensitivity of the model to the type of soil shows that the distributions of contours of streamlines, isotherms, isovalues of moisture are less affected by the variations of the nature of soil through the variation of the diffusivity of the soil. However, it is observed that the temperature values obtained for the clay soil are higher while the sandy soil shows lower temperature values. The values of the ground-to-air heat exchanger efficiency are only slightly influenced by the nature of the soil. Nevertheless, we note a slightly better efficiency for the sandy soil than for the sandy-clayey silt and clayey soils. This result shows that a sandy soil would be more suitable for geothermal system installations.
基金Supported by the National Basic Research Program of China (Grant No. 2007CB206903)National Natural Science Foundation of China (Grant No. 50721005)
文摘Based on the principle of field synergy for heat transfer enhancement, the concept of physical quantity synergy in the laminar flow field is proposed in the present study according to the physical mechanism of convective heat transfer between fluid and tube wall. The synergy regulation among physical quantities of fluid particle is revealed by establishing formulas reflecting the relation between synergy angles and heat transfer enhancement. The physical nature of enhancing heat transfer and reducing flow resistance, which is directly associated with synergy angles α, β, γ, φ, θ and ψ, is also explained. Besides, the principle of synergy among physical quantities is numerically verified by the calculation of heat transfer and flow in a thin cylinder-interpolated tube, which may guide the optimum design for better heat transfer unit and high-efficiency heat exchanger.
基金the National Natural Science Foundation of China (Grant No. 59995550-3).
文摘Theoretical investigations have been performed on the convective heat transfer for incompressible laminar flow of gases through microtube and parallel-plates micropassages with constant wall temperature. Considering the change in thermal conductivity and viscosity of gas in wall adjacent region from the kinetic theory, mathematical models are built for both of the micropassages. The dimensionless temperature distribution and the corresponding heat transfer characteristics are simulated numerically, and the results discussed briefly.
文摘Modeling results are presented for the laminar flow and heat transfer within a circular tube connected coaxially with a d c arc plasma torch. In order to determine the correct boundary conditions at the tube inlet, the computational domain is extended to include both the circular tube and the arc plasma torch. Computational results show that the gas static pressure in the tube increases at first and then decreases slowly, while the heat flux to the tube wall decreases monotonically with increasing distance from the tube inlet. Comparison of some computed results with corresponding experimental data is also given.
