Nonsteady thermal bending of multilayered plates with internal cooling

We have derived approximate analytical expressions to estimate the nonsteady values of temperature and thermal bending for multilayered plates with internal cooling.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 57, No. 6, pp. 1005–1010, December, 1989.     

Axial strain calculation using a low-pass digital differentiator in ultrasound elastography

In ultrasound elastography, tissue axial strains are calculated from the gradient of the estimated axial displacements. However, the common differentiation operation amplifies the noises in the displacement estimation, especially at high frequencies. In this paper, a low-pass digital differentiator (LPDD) is proposed to calculate the axial strain from the estimated tissue displacement. Several LPDDs that have been well developed in the field of digital signal processing are presented. The corresponding performances are compared qualitatively and quantitatively in computer simulations and in preliminary phantom and in vitro experiments. The results are consistent with the theoretical analysis of the LPDDs.     

Automatic ultrasound determination of thermal coagulation front during laser tissue heating

Thermal therapies using laser, microwaves, radio frequency radiation, and high intensity focused ultrasound have shown great promise for minimally invasive treatment of benign and malignant lesions. To treat tissue effectively and safely, techniques that could monitor the advancement of coagulation front during treatment are highly desirable. This paper presents a noninvasive ultrasound technique for automatically determining the propagation of coagulation damage front during laser tissue heating. The basic assumption underlying this technique is that when coagulation is taking place in a tissue, owing to thermally induced structure changes in tissue, the waveform of echo signal scattered from that treated region should be changing accordingly. We first track echoes scattered from many small tissue regions during heating using a cross-correlation echo-tracking technique. We then use the waveform-change information to determine the position of coagulation front via an automatic calculation procedure. To test our technique, we carried out 35 experiments in which we irradiated fresh canine liver samples with a Nd:YAG laser (1064-nm wavelength) at various light fluence (62 to 167 W/cm(2)) and exposure time (20 to 350 s). A 13-mm diameter 10-MHz broadband single-element spherical focused ultrasound transducer was used to detect the thermal coagulation front. The root mean square difference between ultrasonically and visually determined coagulation depths was 0.77 mm. This good agreement between visually inspected and ultrasonically determined coagulation depths shows the potential of our technique for monitoring coagulative tissue damage during thermal therapy.     

Experimental evaluation of a prototype cylindrical section ultrasound hyperthermia phased-array applicator

A prototype 64-element, 75 degrees cylindrical-section ultrasonic phased-array hyperthermia applicator has been designed and constructed. The ability of this applicator to focus ultrasonic energy at its geometric focus is verified in a water medium. The array is then driven by excitation vectors obtained using the pseudoinverse pattern synthesis method to generate shifted-focus and multiple-focus field patterns. Experimental results of single and multiple-focus patterns at 500 kHz are given and are in good agreement with theory. The results indicate that the main beam in single-focus patterns is generally insensitive to errors in the phases and amplitudes of the particle velocities of the array elements. The effect of such errors is largely exhibited in the sidelobes which, for all practical purposes, remain at levels acceptable for hyperthermia. This is true for both the geometric focus and shifted foci.     

Temperature control for a long distance cooling channel using a microcomputer

Conventional control systems developed so far for long distance cooling channels, are not yet capable of local-temperature control, local-pressure control or sequential control, since thermodynamic properties of supercritical helium show an order of magnitude change and strong nonlinearity for applied pressure and temperature of cables and magnets.In this paper, a new temperature control method for long distance cooling channels using a microcomputer is proposed. This method is controllable without the necessity to consider the thermodynamic properties of supercritical helium, because a type of learning control method is adopted.     

Materials selection for a cooling plate using control area diagrams

Merit indices are used to rank materials and are of fundamental importance in materials selection. Traditionally, merit indices have only been available for elementary design cases. In the present paper merit indices are generalised to cooling systems where heat flow and strength are design criteria in a materials optimisation framework. A cooling tube and a cooling plate are considered. A new concept, merit exponent is used that is related to the merit indices. A definition of the merit exponent is given also for cases with many design variables. In each design case a number of merit exponents are involved. It is a nontrivial task to identify which they are and when each of them is applicable. For this purpose control area diagrams (CAD) are used. A CAD is a diagram with the controlling properties on the axes, and areas where one or more constraints are active. For the cooling systems the controlling properties are heat conductivity and strength. The active constraints define the relevant merit exponent. The constraints involve the controlling properties and geometrical variables. Principles are established for how to set up the CAD and to derive the merit exponents.     

EAST内冷屏降温过程瞬态温度场和热应力分析

基于EAST内冷屏降温过程的安全问题,验证目前50K控制温差的合理性。运用有限元软件ANSYS计算了降温过程中冷氦流在50K进出口温差下内冷屏的温度场和热应力分布,以及总应力的大小,计算结果表明当前的控制参数是合理的。     

Inducing and imaging thermal strain using a single ultrasound linear array

For the first time, the feasibility of inducing and imaging thermal strain using an ultrasound imaging array is demonstrated. A commercial ultrasound scanner was used to heat and image a gelatin phantom with a cylindrical rubber inclusion. The inclusion was successfully characterized as an oil-bearing material using thermal strain imaging.     

Heat transfer of a conical tube with internal cooling by a swirling air jet

The results of an experimental investigation of local heat transfer during flow of turbulent semibounded jets in a conical tube beyond an annular swirler installed at the inlet are presented.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 30, No. 1, pp. 18–26, January, 1976.     

Experimental study of thermal condition in a room with hydronic cooling radiant surfaces

This paper presents a new approach for experimental analysis of chilled or heated ceiling systems and its environment (ventilation, windows and thermal loads distribution). The work is aimed at giving a better insight to crucial parameters as the contact thermal resistance, fin effectiveness of ceiling panels, mass flow rate, supply water temperature, thermal load distribution, fenestration and ventilation system effects on the radiant ceiling capacity and comfort conditions. The experimental methodology and its discussion are also presented. A test chamber is adapted in a way to reproduce as good as possible the characteristics of a hospital room with a cooling ceiling system. The convection and radiation heat transfer coefficients to room and losses through the ceiling void are also studied. Experimental data are used to fit the uncertain parameters mentioned and improve the capacity and performance of the ceiling system, but also to evaluate the design of this HVAC system and the applicable control strategies.     

Performance of a galvanothermomagnetic cooling element under steady-state thermal conditions

The galvanothermomagnetic effect in a cylindrical cooling element is analyzed, with the nonuniform temperature distribution taken into account.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 1, pp. 75–81, January, 1981.     

Spallation of a substrate by thermal shock and thermal expansion differential during splat cooling

The manufacture of metal-matrix composite materials by spray deposition is a very attractive process, but impaired by the spallation that may take place after impact of molten metal droplets on the fibers. In this work, the spallation of a quartz substrate was investigated through video and acoustic measurements and through temperature measurements of the splat surface. The time scales pertaining to the fracture mechanisms are examined from acoustic measurements of the spallation. The spall formation mechanism was quantified by analyzing the geometric configuration of the splats and spalls under varying conditions of droplet superheat, droplet size, and droplet or substrate material. Furthermore, the thermal contact resistance between the splat and the substrate was evaluated by matching the measured temperatures of the top or bottom surface of the splat with numerical results from a heat conduction model with phase change.     

Development of an ejector cooling system with thermal pumping effect

This paper presents a feasibility study of an ejector cooling system (ECS) that utilizes a multi-function generator (MFG) to eliminate the mechanical pump. The MFG serves as both a pump and a vapor generator. The MFG is designed based on the pressure equilibration between high and low pressures through heating and cooling process. In this design, an ECS that contains no moving components and is entirely powered by heat can be practicable. A prototype using refrigerant R141b as working fluid was constructed and tested in the present study. The experimental results showed that the system coefficient of performance (COP_o) was 0.218 and the cooling capacity was 0.786 kW at generating temperature (T_G) 90 °C, condensing temperature (T_C) 32.4 °C and evaporating temperature (T_E) 8.2 °C. While taking into account the extra heat needed for the MFG operation, the total coefficient of performance (COP_t) is 0.185. It is shown that a continuous operation for the generation of cooling effect in an ECS with MFG can be achieved. This cooling machine can be very reliable since there is no moving part.     

Optimal control of thermal fluid flow using automatic differentiation

The aim of this study is to present a method for numerical optimal control of thermal fluid flow using automatic differentiation (AD). For the optimal control, governing equations are required. The optimal controls that have been previously presented by the present authors’ research group are based on the Boussinesq equations. However, because the numerical results of these equations are not satisfactory, the compressible Navier–Stokes equations are employed in this study. The objective is to determine whether or not the temperature at the objective points can be kept constant by imposing boundary conditions and by controlling the temperature at the control points. To measure the difference between the computed and target temperatures, the square sum of these values is used. The objective points are located at the center of the computational domain while the control points are at the bottom of the computational domain. The weighted gradient method that employs AD for efficiently calculating the gradient is used for the minimization. By using numerical computations, we show the validity of the present method.     

Noninvasive transesophageal cardiac thermal ablation using a 2-D focused, ultrasound phased array: a simulation study

This simulation study proposes a noninvasive, transesophageal cardiac-thermal ablation using a planar ultrasound phased array (1 MHz, 60 x 10 mm2, 0.525 mm interelement spacing, 114 x 20 elements). Thirty-nine foci in cardiac muscle were defined at 20, 40, and 60-mm distances and at various angles from the transducer surface to simulate the accessible posterior left atrial wall through the esophageal wall window. The ultrasound pressure distribution and the resulting thermal effect in a volume of 60 x 80 x 80 mm3, including esophagus and cardiac muscle, were simulated for each focus. For 1, 10, and 20-s sonications with 60 degrees C and 70 degrees C peak temperatures in cardiac muscle and without thermal damage in esophageal wall, the transducer acoustic powers were 105-727, 28-117, 21-79 W and 151-1044, 40-167, 30-114 W, respectively. The simulated lesions (thermal dose in equivalent minutes at 43 degrees C > or = 240 minutes) at these foci had lengths of 1-6, 3-11, 3-13 mm and 3-15, 5-19, 6-23 mm, respectively, and widths of 1-4, 2-7, 3-9 mm and 3-9, 4-13, 4-17 mm, respectively. As a first step toward feasibility, controllable tissue coagulation in cardiac tissue without damage to the esophagus was demonstrated numerically.     

Progressive thermal desorption of vapor mixtures from a preconcentrator with a porous metal foam internal architecture and variable thermal ramp rates

A vapor preconcentrator has been designed with the porous polymer (Tenax) packed into a highly porous metal foam to facilitate thermal conductivity and temperature uniformity throughout the bed of the preconcentrator during heating. Vapors were desorbed using linear temperature programming from room temperature to a maximum temperature of 170 or 200 degrees C; the programmed duration of the thermal ramp was varied from 10 to 180 s. The partial separation of vapor mixtures that are thermally desorbed from the preconcentrator has been examined in terms of a metric for resolution, using methyl ethyl ketone, toluene, and dimethyl methylphosphonate as a test mixture. Vapors desorbed as a sequence of partially separated overlapping peaks, as observed with a polymer-coated flexural plate wave sensor. It was shown that vapor mixture resolution improved as the total time of the thermal ramp was extended from 30 to 120 s. In this way, the preconcentrator serves to act as a preseparator in addition to its usual functions for sampling, signal modulation, and improving sensitivity. Overlapping peaks were modeled, and peak areas were extracted using an exponentially modified Gaussian model. Peak areas were independent of the thermal ramp rate. Uses of such preconcentrators with multivariate detectors, such as sensor arrays, are discussed.     

The thermal state of a porous wall under conditions of transpiration cooling

Results of numerical experiment are used for analysis of fields of temperature in a laminar boundary layer, in a porous wall, and in a cooling gas delivery chamber, as well as for analysis of heat transfer and of distribution of the temperature difference between the cooling gas and the porous wall frame and cooling efficiency. It is demonstrated that heat transfer between a porous wall of finite thickness and a high-temperature gas flow differs significantly from heat transfer with preassignment of the same intensity of injection and of the homogeneous thermal boundary condition directly on the surface subjected to flow. One of the reasons for this is the formation of wall temperature variable along the boundary layer.     

横流板式间接蒸发热回收装置的优化研究

运用遗传算法对横流板式间接蒸发热回收装置的经济性进行分析,建立优化设计数学模型,并对新、排风风量均为540m^3／h的横流板式间接蒸发热回收装置进行优化求解,探讨其经济性随各结构参数的变化规律。研究结果表明：遗传算法可以很好地实现横流板式间接蒸发热回收装置的优化;得到横流板式间接蒸发热回收装置的优化结构;随各结构参数的变化,目标函数呈抛物线的变化规律。该研究对于横流板式间接蒸发热回收装置的设计有一定的参考价值。     

Determining thermal parameters in the cooling of a small-scale high-pressure freezing vessel

High-pressure supported freezing processes need a more efficient refrigeration technique to be applied at industrial level. A cooling method consisting in the circulation of a refrigerant in ebullition around the product in the vessel has been tested on a lab-scale prototype built for that purpose. The cooling kinetic of a mixture of ethanol, ethylene glycol and water (a usual pressurizing medium) was followed, recording temperatures in the whole sample. A mathematical model has been developed to describe heat transfer during cooling of the sample in the vessel. The heat transfer coefficient between the refrigerant and the vessel was determined by a fitting procedure between the numerical simulation results and the experimental measurements. This model should be used to predict the cooling kinetics in other conditions (other products, larger vessels) and to optimise the process.