Shiuh-Ming Chang

Application of the hybrid method to inverse heat conduction problems

Abstract The hybrid method involving the combined use of the Laplace transform method and the finite element method is considerably powerful for solving one-dimensional linear heat conduction problems. In the present method, the time-dependent terms are removed from the problem using the Laplace transform method and then the finite element method is applied to the space domain. The transformed temperature is inverted numerically to obtain the result in the physical quantity. The estimation of the surface heat flux or temperature from transient measured temperatures inside the solid agrees well with the analytical solution of the direct problem without Becks sensitivity analysis and a least square criterion. Due to no time step, the present method can directly calculate the surface conditions of an inverse problem without step by step computation in the time domain until the specific time is reached. In addition, it is also not necessary to compute all the nodal temperatures at each time step when the present method is applied to an inverse problem. It is worth mentioning that a little effect of the measurement location on the estimates is shown in the present method. Thus, it can be concluded that the present method is straightforward and efficient for such problems.

Thermal interaction between laminar film condensation and forced convection along a conducting wall

SummaryA theoretical analysis is presented to investigate the thermal interaction between laminar film condensation of a saturated vapor and a forced convection system separated by a heat conducting wall. In this work, the effect of the wall thermal resistance is considered. It is assumed that the countercurrent boundary layer flow is formed on the two sides. Governing boundary layer equations together with their corresponding boundary conditions for film condensation and forced convection are all cast into dimensionless forms by using the non-similarity transformation. The resulting system of equations is solved by using the local non-similarity method in conjunction with the fourth order Runge-Kutta method in conjunction with the Nachtsheim-Swigert iteration scheme. The total heat flux through the wall and the wall temperature distribution are determined. The present results show that the effect of the forced convection Prandtl number Prc is not negligible for large values of the thermal resistance ratioA*, and the effect ofA* and Prc on the overall heat transfer through the wall is more pronounced than that of the Jakob number and film Prandtl number.

Numerical simulation for conjugate problem of natural convection on both sides of a vertical wall

The present analysis is presented to predict the heat transfer rate between two natural convection systems at different temperatures separated by a vertical plate, where the effects of one-dimensional heat conduction along the plate and transverse heat conduction will be discussed. Thus, the countercurrent boundary layer flow is formed on the two sides. Governing boundary layer equations with their corresponding boundary conditions for these two natural convection systems are cast into dimensionless forms by using the non-similarity transformation. The resulting system of equations is solved by using the finite difference approximation for the heat conduction equation and the local non-similarity method in conjunction with the Nachtsheim-Swigert iteration scheme for boundary layer equations. Excellent agreement between the present results predicted by using the approximation of heat conduction along the plate and reliable experimental data is obtained. This implies that the present analysis provides accurate prediction for such problems.

COUPLING BETWEEN LAMINAR FILM CONDENSATION AND NATURAL CONVECTION ON OPPOSITE SIDES OF A VERTICAL PLATE

SUMMARY Theoretical analyses which incorporate one-dimensional heat conduction along a plate and transverse heat conduction approximations are presented to predict the net heat transfer between laminar film condensation of a saturated vapour on one side of a vertical plate and boundary layer natural convection on the other side. It is assumed that countercurrent boundary layer flows are formed on the two sides. The governing boundary layer equations of this problem and their corresponding boundary conditions are all cast into dimensionless forms by using a non-similarity transformation. Thus the resulting system of equations can be solved by using the local non-similarity method for the boundary layer equations and a finite difference method for the heat conduction equation of the plate. The plate temperature and the heat flux through the plate are repetitively determined until the solutions for each side of the plate match. The predicted results show that the effect of Prc is not negligible for larger values of A* (thermal resistance ratio between natural convection side and condensing film side) and the approximation of transverse heat conduction overpredicts the plate temperature for lower values of Rt (thermal resistance ratio between plate and condensing film). However, no significant differences are observed between the two different approximations for higher values of Rt.

Couple-Stress Fluid Improves Dynamic Response of Gear-Pair System Supported by Journal Bearings

A systematic analysis of the dynamic behavior of a gear-bearing system with nonlinear suspension, couple-stress fluid flow effect, nonlinear oil-film force, and nonlinear gear mesh force is performed in the present study. The dynamic orbits of the system are observed using bifurcation diagrams plotted using the dimensionless rotational speed ratio as a control parameter. The onset of chaotic motion is identified from the phase diagrams, power spectra, Poincare maps, Lyapunov exponents and fractal dimension of the gear-bearing system. The numerical results reveal that the system exhibits a diverse range of periodic, subharmonic, quasiperiodic, and chaotic behaviors. The couple-stress fluid would be a useful lubricating fluid to suppress nonlinear dynamic responses and improve the steady of the systems. The results presented in this study provide some useful insights into the design and development of a gear-bearing system for rotating machinery that operates in highly rotational speed and highly nonlinear regimes.

Integrated Assessment for Trapezoid and Square Types PEMFC Bipolar Plate by Field Synergy Principle

This study is to investigate integrated assessment on the flow channel and glove in channel of bipolar plate for PEMFC. We used two software Multiphysics and Moldex3d 9.1 to simulate these characteristics of gas flow pattern, filling, packing, cooling and warpage. In order to get better performance on bipolar plate with fiber orientation for different types like square and trapezoid fuel cell bipolar plate, the field synergy principle is used to determine the better type of channel shape of bipolar plate of fuel cell The result shows trapezoid channel of fuel cell bipolar plates with fiber orientation in injection molded fuel cell bipolar plates will get better quality for both simulations. The effects of fiber orientation is also discussed in this paper.

The Optimization Comfortness of Air Craft by Field Synergy Principle

This study is to investigate heat transfer, thermal comfort of captain in the specified airplane cabin by field synergy principle using turbulence flow to simulate input wind temperature and position, input wind u, v, w, passenger temperature, his position and thermal load. In this research, we use COMSOL software to analyze velocity and temperature fields and comfort impact of input position of wind. The results show that field synergy angle can indicate low angle increase better comfort of captain in the specified airplane cabin.

The Freezer Optimization of Input Fan Location by Field Synergy Principle

The principle of field synergy is to simulate the freezer optimization of input fan location in this study. The parameters U, V, W and input position of fan are calculated to simulate ooptimization of fan position of freezer. Temperature and velocity fields are simulated by COMSOL Multiphysics software. Freezing degree is calculated by field synergy mean square root method in this research. The simulation result shows that field synergy angle decreases while freezing degree increases. It is very obvious that the best input position of fan leads lower field synergy angle.

Comfort Design of Air Condition for MRT by Field Synergy Principle

The comfort design of air condition for MRT by field synergy principle is to be investigated in this study. Comfort design of temperature and velocity fields are simulated by COMSOL Multiphysics software. Comfort design of air condition is calculated by field synergy mean square root method in this research. The numerical simulation result shows that field synergy angle decreases while comfortness of degree increases for MRTs comfort of air condition. The present results show that the method in this research is very powerful to find optimization of air condition for MRT.

The Submarine Air Condition Optimization by Field Synergy Principle

The air condition optimization of submarine by field synergy principle is to be investigated in this study. Temperature and velocity fields of submarine are simulated by COMSOL Multiphysics software. Comfortness of degree is calculated by field synergy mean square root method in this research. The simulation result shows that field synergy angle decreases while comfortness of degree increases. The present results show that the research is very powerful to find optimization of air condition for submarine.