16 research outputs found
Surrogate models for the magnitude of convection in droplets levitated through EML, ADL, and ESL methods
Fluid flow and heat transfer in levitated droplets were numerically
investigated. Three levitation methods: electro-magnetic levitation (EML),
aerodynamic levitation (ADL), and electro-static levitation (ESL) were
considered, and conservative laws of mass, momentum, and energy were applied as
common models. The Marangoni effect was applied as a velocity boundary
condition, whereas heat transfer and radiation heat loss were considered as
thermal boundary conditions. As specific models to EML, the Lorentz force, and
Joule heat were calculated based on the analytical solution of the
electromagnetic field. For the ADL model, besides the Marangoni effect, the
flow driven by the surface shear force was considered. For ADL and ESL models,
the effect of laser heating was introduced as a boundary condition. All the
equations were nondimensionalized using common scales for all three
levitations. Numerical simulations were performed for several materials and
droplet sizes, and the results were evaluated in terms of the Reynolds number
based on the maximum velocity of the flow in the droplet. The order of
magnitude of Reynolds numbers was evaluated as for EML,
for ADL, and for ESL. Based on the
simulation results, we proposed simple formulas for predicting the Reynolds
number of droplet internal convection using combinations of nondimensional
numbers determined from the physical properties of the material and the driving
conditions. The proposed formulas can be used as surrogate models to predict
the Reynolds numbers, even for materials other than those used in this study
Analysis of Defogging Performance, Thermal Comfort, and Energy Saving for HVAC System Optimization in Passenger Vehicles
The heating, ventilation, and air-conditioning (HVAC) system in a vehicle is used for both defogging the windshield and ensuring the thermal comfort of passengers. A challenge is that energy savings in the HVAC system lead to decreased system performance. The three objective functions, i.e. defogging performance, thermal comfort, and energy savings, these must be considered in parallel to find the optimized control strategy. In the present study, a transient numerical simulation of the in-vehicle environment is performed and the dependency of performance on the air flow rate and supplied air temperature is analyzed. The criteria of defogging performance and thermal comfort are determined as the constrained conditions. The results show a trade-off relationship between the air flow rate and air temperature in defogging performance and thermal comfort; however, their sensitivities depend on the conditions and the time elapsed. As for transient defogging performance, the air flow rate has greater impact than airflow temperature. The air flow rate and the air temperature are comparable in their effects on equivalent temperature, which is employed as the index of the thermal environment. The blowing condition range that fulfills the criteria makes a transition to a low-energy condition with time elapsed. A control strategy for the air flow rate and temperature is derived considering the transient and steady-state conditions
Analysis of gravity effect on human blood flow and skin temperature through postural change
The blood flow of human body has much impact on the thermo-physiological response. When person change the posture, the gravity acts changes its direction and thus the blood flow can be changed. It is hypothesized that the gravitational effects of postural changes affect blood flow and skin temperature, which in turn affect comfort. To verify this, in the present study, a subject experiment focusing on postural changes was conducted for two conditions (Case 1 and Case 2). In the Case 1 experiment, the subjects were asked to raise their hands for 10 minutes after 30 minutes of rest in the chair-sitting position. As a result, significant skin temperature change were observed in the upper arm, forearm, and hand. The largest skin temperature change was observed in the hands, which showed a decrease in skin temperature of approximately 1.2 °C. The change had influence on the whole-body average value. In Case 2, the subjects were placed in the supine position for 10 minutes after 30 minutes of rest in the chair position. As a result, a decrease in skin temperature of approximately 1 °C was observed on the hands and 0.5 °C in the foot was observed