Cooling Fluid Temperature Research Articles

Impact of two-stage turbocharging architectures on pumping losses of automotive engines based on an analytical model

Present work presents an analytical study of two-stage turbocharging configuration performance. The aim of this work is to understand the influence of different two-stage-architecture parameters to optimize the use of exhaust manifold gases energy and to aid decision making process. An analytical model giving the relationship between global compression ratio and global expansion ratio is developed as a function of basic engine and turbocharging system parameters. Having an analytical solution, the influence of different variables, such as expansion ratio between HP and LP turbine, intercooler efficiency, turbochargers efficiency, cooling fluid temperature and exhaust temperature are studied independently. Engine simulations with proposed analytical model have been performed to analyze the influence of these different parameters on brake thermal efficiency and pumping mean effective pressure. The results obtained show the overall performance of the two-stage system for the whole operative range and characterize the optimum control of the elements for each operative condition. The model was also used to compare single-stage and two-stage architectures performance for the same engine operative conditions. Benefits and limits in terms of breathing capabilities and brake thermal efficiency of each type of system have been presented and analyzed.

Numerical analysis of heat and mass transfer during absorption of hydrogen in metal hydride based hydrogen storage tanks

In this paper, hydriding in a cylindrical metal hydride hydrogen storage tank containing HWT5800 (Ti 0.98Zr 0.02V 0.43Fe 0.09Cr 0.05Mn 1.5) is numerically studied with a two-dimensional mathematical model. The heat and mass transfer of this model is computed by finite difference method. The effects of supply pressure, cooling fluid temperature, overall heat transfer coefficient and height to the radius ratio of the tank (H/R) on the hydriding in the hydrogen storage tank are studied. It is found that hydride formation initially takes place uniformly all over the bed and hydriding processes take place at a slower rate at the core region. Supply pressure, cooling fluid temperature and overall heat transfer coefficient play significant roles during the absorption of hydrogen. At the H/R = 2 both maximum bed temperature and the average bed temperature are the highest, and the hydride bed takes the longest time to saturate.

Analytical and numerical models for estimates of power loads from calorimetric measurements

The total power loads applied to inertially cooled components are commonly calculated starting from calorimetric measurements as cooling fluid temperature increase and flow rate during and after the power load application. In this paper, some generalizations to the standard models of measure interpretation are introduced. A method is presented to take into account the effect of thermal conduction and radiation between the component and the surrounding material. It consists in evaluating the conduction and convection thermal resistances and the radiation heat flux by Computational Fluid Dynamics (CFD) numerical models. An analytical model permits to use these evaluations to obtain, from the measured convection flux, the corresponding fluxes by conduction and radiation. Sometimes the durations of pulses and duty cycles are such that the calorimetric measurements after one pulse are actually influenced by the previously applied pulse. A correction factor is introduced to cancel this systematic error. The cooling down phase can be long compared to the duty cycles between the pulses, and consequently the signals cannot be completely recorded till the thermal equilibrium. In order to evaluate the total heat flux on a component also in this case, a model is presented which considers a proper extrapolation curve to estimate the integral of the energy exhausted by the cooling systems. As an example, the models introduced in the paper have been used to interpret experimental measurements carried out on the RADI experiment at IPP Garching and some results are presented in the paper.

Numerical simulation of coupled heat and mass transfer in metal hydride-based hydrogen storage reactor

In this paper, a numerical investigation of two-dimensional heat and mass transfer during absorption of hydrogen in a cylindrical metal hydride bed containing MmNi 6.4Al 0.4 is presented. By considering the variation in cooling fluid temperature along the axial direction (variable wall temperature), the changes in hydrogen concentration, hydride equilibrium pressure, and average hydride bed temperature at different axial locations are presented. The average bed temperature profiles and hydrogen storage capacities at different supply pressures showed good agreement with the experimental data reported in the literature. As the absorption progresses, the change in cooling fluid temperature along the axial direction is found to decrease and becomes unchanged at the end of the absorption process. The effect of variable wall temperature on hydrogen absorption rate for different supply pressures and hydride bed thicknesses are presented. The effect of variable wall temperature on absorption time is found to be significant for the hydride beds of thickness of above 7.5 mm. For a supply pressure of 20 bar, the maximum difference in absorption time between variable wall temperature and constant wall temperature boundary conditions is about 300 s for 17.5 mm bed thickness.

Parametric studies on a metal hydride based hydrogen storage device

In this paper, a two-dimensional computational investigation of coupled heat and mass transfer process in an annular cylindrical hydrogen storage device filled with MmNi 4.6 Al 0.4 is presented using a commercial software FLUENT 6.1.22. Hydrogen storage performance of the device is studied by varying the operating parameters such as hydrogen supply pressure and absorption temperature. Further, the effects of various bed parameters such as hydride bed thickness and overall heat transfer coefficient on the storage performance of the device are also studied. The average temperature of the hydriding bed and hydrogen storage capacity at different supply pressures showed good agreement with the experimental data reported in the literature. It is observed that as the hydriding process is initiated, the absorption of hydrogen increases rapidly and then it slows down after the temperature of the hydride bed increases due to the heat of the reaction. At any given absorption temperature, the hydrogen absorption rate and hydrogen storage capacity are found to increase with the supply pressure. The variation in the hydrogen absorption capacity, rate of reaction and temperature profiles at different supply pressures from 5 to 35 bar in steps of 5 bar are presented. Further, the effects of overall heat transfer coefficients from 750 to 1250 W/m 2 K and cooling fluid temperatures from 288 to 298 K on hydrogen storage capacity are also investigated. It is shown that the heat transfer rate enhances the hydriding rate by accomplishing a rapid reaction. At the supply condition of 35 bar and 298 K, MmNi 4.6 Al 0.4 stores about 13.1 g of hydrogen per kg of alloy.

A novel design of a heat exchanger for a metal-hydrogen reactor

A metal-hydride reactor equipped by a spiral heat exchanger is experimentally studied. The inserted exchanger provides significant insights into the problem of minimizing the total storage time by manipulating the operating parameters. Performance studies are carried out by varying the supply pressure, volume of the tank, absorption temperature, and overall heat transfer coefficient. At any given absorption temperature, hydrogen absorption rate and storage capacity are found to increase with supply pressure. Cooling fluid temperature is found to have a significant effect on hydrogen storage time and higher values of the overall heat transfer coefficient yields better rates of absorption and desorption. Hydriding time mainly depends on the successful heat removal from the bed. A reactor equipped with an exchanger that provides more heat transfer area significantly reduces hydriding time.

Numerical study of ice melting inside rectangular capsule under cyclic temperature of heat transfer fluid

The periodic melting of encapsulated ice for cold thermal energy storage has been investigated numerically. A horizontal rectangular container is used as a storage capsule, since warm coolant fluid (glycol) flows over the upper and lower walls of the capsule, melting the ice. The enthalpy method is employed to model the phase change at the two moving interfaces. The effect of cyclic time variant coolant fluid temperature on the heat transfer efficiency and the corresponding energy stored has been investigated. Also, the influence of the convection heat transfer coefficient and coolant fluid temperature on the melting behavior has been studied and reported. The results show that the coolant fluid temperature markedly affects the melting behavior rather than the convection heat transfer coefficient.

Analytical solution of the non-uniform heat exchange in a reactor cooling coil with constant fluid flow

An analytical solution of the partial differential equation describing the enthalpy balance of the cooling fluid in a batch exothermic reactor has been developed for a constant flow. Thanks to an analytical integration on position, the simulation of the process can be performed with one independant variable (time) and without any approximation on the profile of the cooling fluid temperature. Comparisons are made with the well-known approximate method of segmentation into finite volumes at uniform temperature. The proposed method requires the integration of one ordinary differential equation (ODE) instead of the system of N + 1 ODEs used in the N finite volumes method. It is shown in simulations that a small number of finite elements (one to six) leads to a large inaccuracy in the results, however, it is commonly used. Finally the analytic method is applied as a zeroth order approximation to the case of a time varying flow. Comparisons are also made with the finite elements method and shown very good simulation results.

Practical heat transfer model for oxygen‐fed ozone generators

Abstract Heat dissipation has a bad influence on ozone production reactor performance. In order to enhance our understanding of influence of operating parameters, a heat transfer model has been developed. Model predictions are in qualitative agreement with experimental results obtained on oxygen‐fed cold plasma reactors. Moreover, incidences of the local climate and of the cooling fluid temperature level on the ozone production cost are emphasized.

Periodic steady-state heat transfer in cooling panels

A slab is considered to be exchanging heat internally with a fluid flowing through pipes embedded in the slab and externally by convection and radiation with the ambient surroundings in a periodic fashion. In practice, such cases are encountered in panel cooling of buildings, in which the heat produced within or inserted into a room is absorbed by a cold fluid flowing through pipes imbedded in the roof slab of the room. A method is developed for predicting the performance of such systems, which is based on a finite-difference solution of the transient two-dimensional heat conduction differential equation within the roof slab containing the cooling pipes. The boundary conditions on the upper surface are periodic, i.e., it is assumed that the daily cycle of the ambient temperature and the incident solar radiation are repeated on consecutive days, thus leading to a periodic steady-state solution. In the case of floor slabs, the problem becomes steady-state unless intermittent operation is to be examined. A parametric study is presented, in which the effect is examined of the most important parameters, including the pipe spacing and the cooling fluid temperature.

Thermal model for the local microwave hyperthermia treatment of benign prostatic hyperplasia.

A system for the noninvasive localized, hyperthermia treatment of benign prostatic hyperplasia was investigated. The system uses a microwave transrectal antenna with a water cooled jacket to achieve localized hyperthermia. The purpose of this study is to model the temperature rise in the prostate and in the surrounding tissue during treatment. The SAR distribution for the transrectal probe is measured in a muscle tissue equivalent phantom. The SAR information is used with a finite element solution of the bioheat transfer equation to give the temperature rise during the treatment. Also the finite element solution is further used to determine the effect of the microwave power, the cooling fluid temperature and the blood perfusion on the tissue temperature rise. The results of the solution are compared to temperature measurements in a canine protocol. It was found that the maximum temperature rise in the tissue during treatment is 44 degrees C at a depth of 2 cm from the rectal mucosa.

Major factors affecting the reaction rate in metal hydride beds

A thorough study of the 13 major factors affecting the reaction rate in hydride beds (bed reaction rate) is carried out by using the computer program called SCUT. A MlNi 4.5Mn 0.5 (Ml stands for lanthanum-rich misch metal) cylindrical hydride bed surrounded by a coaxial water cell is taken as an example in the study. The related data required in the analyses are all taken from our experiments. The study shows that heating or cooling fluid temperature, bed void fraction, radius of hydride bed, effective thermal conductivity of bed and metal hydride density have severe influences on the reaction rate in metal hydride beds.

An analysis of thermal warpage in injection molded flat parts due to unbalanced cooling

AbstractTo illustrate the potential effect of unbalanced cooling on warpage of flat parts, a simplified two‐part analysis is presented. First a computational model for amorphous polymers cooling in an injection molding cavity is presented. The simulation is a finite difference solution of the one‐dimensional, transient heat conduction equation with constant material properties. Plastic and mold temperature profiles are calculated through the cooling cycle and the transients from cycle to cycle are included. Temperatures are predicted for both sides of the mold allowing asymmetrical cooling to be analyzed. The model is verified analytically and is in agreement with published data. Secondly, a simplified method of predicting the thermal warpage of a fiat part from calculated temperature profiles is discussed and illustrated. The relative effects on calculated part warpage of asymmetric mold geometry and cooling fluid temperature are predicted with this analysis method. The sensitivity of warpage to these design factors is illustrated for an example part.