Numerical simulation of tissue freezing by liquid nitrogen based cryoprobe

A model is presented to simulate the cooling processes during tumor cryosurgery with different kinds of flows through the cryoprobe. The heat flux between the cryoprobe wall and the tumor, the heat transfer coefficient under different inflow conditions are obtained numerically. The impact of the inlet mass flow rate, gas volume fraction on these parameters is investigated. It is found that the heat transfer coefficient decreased significantly when inflow changed from two-phase annular flow to droplet flow, and to gas flow. The inlet gas volume fraction and flow velocity only significantly affect the freezing ability of the probe when the inflow is gas or in droplet phase. Simulation of the tumor temperature profiles under different flow conditions show that the heat transfer coefficient is a crucial parameter in temperature prediction during cryosurgery. Results indicate that when the cryoprobe wall is assumed at a constant temperature conventionally, the cooling effect could be overestimated. It would be more reasonable to use the constant wall heat transfer coefficient to simulate the cooling progress under a specific flow.     

Modeling the heat transfer problem for the novel combined cryosurgery and hyperthermia system

A multidimensional, finite element analysis (FEA) for the freezing, holding, rewarming and heating processes of biological tissues during the cryosurgery process of the new Combined Cryosurgery/Hyperthermia System is presented to theoretically test its validity. The tissues are treated as nonideal materials freezing over a temperature range, and the thermophysical properties of which are temperature dependent. The enthalpy method is applied to solve the highly nonlinear problem. It was found that when the same boundary condition and the same target tissue presented, the novel Cryosurgery/Hyperthermia System could supply the target tissue an approximative cooling rate, a much lower minimal temperature, a much greater warming rate, and a much greater thermal gradients compared with that of the simplified Endocare system. The numerical simulation indicates that the novel combined cryosurgery and hyperthermia system can provide an excellent curative effect in the corresponding cryotherapy. And the most attractive feature of this FEA framework is that it can be easily mastered by the surgeon without in-depth theory of heat transfer to analyze the cryosurgery process beforehand due to the friendly GUI (graphical user interface) of Ansys software.     

前列腺低温微创治疗及器件的研究

利用低温冷冻破坏前列腺增生或肿瘤组织治疗疾病具有许多的优点,如出血少、痛苦小,有时甚至不需要麻醉。前列腺冷冻术可采用两种方法,即穿刺式和接触式。穿刺式就是将探针直接插入病灶组织中心,予以冷冻,主要用于较小的病灶;接触式就是将探针冷冻区接触病灶组织表面予以冷冻,主要用于较小的前列腺增生或不规则的肿瘤等,有时也可将二者结合使用。冷冻术最大的优点还在于可防止肿瘤细胞的扩散。文中详细介绍前列腺冷冻治疗的机理、冷冻探针的结构特点及临床应用效果。     

高温相变储能换热器中传热模型的研究

1前言利用相变材料在发生相变时有很高的潜热释放或吸收的特点，将相变材料作为储热介质用于相变储能换热器中，可以大大地提高热储存的容量。本文研究的这种壳管式相变储能换热器壳内布置换热管，管壳之间填充高温储热材料，管内通以空气作为热交换流体提取储存在相变材料中的热量。定义输出功率为单位时间内热交换流体所提取到的热量，那么输出功率就成为评价这类换热器换热性能的指标。2理论模型的建立下面几点，概括了求解本文相变储能装置中传热问题的特点：a．相变储能换热器的壳侧填充的AI-Si合金属高温相变储能材料，实验始末其温…     

临床低温外科装置

低温冷冻在临床上可用来杀死各类肿瘤组织,冷冻治疗具有许多优越性,如手术过程出血少、痛苦小.文中介绍低温外科装置的工作过程及装置结构,分析冷冻探头的传热过程.最后根据临床应用,对装置的工作压力、冷冻速率、复温速率等重要参数进行讨论.     

Regenerative heat exchanger with a periodic change in the airflow direction for room ventilation

This paper presents the results of experimental research of heat transfer in air-to-air regenerative heat exchanger with periodic change of flow direction. The temperatures of the airflow and the material of regenerative packing in different sections have been obtained. The temperature efficiency of the heat exchanger has been determined at different flow rates. The developed mathematical model of the regenerative heat exchanger is described. It is shown that the model fairly well describes the experimental results. Based on numerical studies the dependence of thermal efficiency of the heat exchanger on the airflow rate is determined. It is shown that changing the ratio of the oppositely directed flow rates, it is possible to regulate the temperature of the air flowing into the room. The possibility of using the model for optimizing the operational and design parameters of heat exchanger is demonstrated.     

Experimental and numerical investigation on the exergy and entransy performance of a novel plate heat exchanger

There has been increased attention on various types of plate heat exchangers because of their high efficiency and compactness. This article presents an investigation of heat transfer and fluid flow performance of a novel plate heat exchanger based on numeric studies and experimental tests. Parameters of the novel plate heat exchanger are analyzed and discussed. The thermo-hydraulic transfer performance of different plate heat exchangers is comprehensively analyzed using the exergy and entransy principle. The results indicate that the novel plate heat exchanger has better thermo-hydraulic transfer performance than the smooth plate heat exchanger. The result of this study provides a paradigm for the optimal design of plate heat exchangers.     

Thermal-exergetic behavior of a vertical double-tube heat exchanger with bubble injection

The use of air bubbles as a heat transfer improvement technique for heat exchangers has been proposed by some researchers. The vertical motion of tiny bubbles because of density difference with liquid provides extra vibration, eddies, turbulences, and consequently further heat transfer rate. The variety of affected parameters, such as injection method, air mass flow rate, bubbles size, number of perforations that forms bubbles, etc., has added to the complexity of this phenomena so that any change in the said parameters significantly influences the thermal-exergetic behavior of the heat exchanger. The quality and quantity of the impact of bubbles on the thermal performance of heat exchangers are different for any type of them. Moreover, each type of heat exchanger requires a specific injection method depending on the heat exchanger structure. In the present research, an injection way is proposed for vertical double-tube heat exchangers, and the effect of bubbles on thermal-exergetic characteristics is experimentally studied and discussed, which have not been performed before. Nondimensional exergy destruction, number of heat transfer units, and effectiveness are the main evaluated parameters in the present paper. Results showed a significant thermal improvement of the heat exchanger under the bubble injection.     

Different methods to calculate heat transfer coefficient in a double-tube heat exchanger: A comparative study

An experimental study performed to compare the results of different methods used in the literature for the calculation of heat transfer coefficient in double-tube heat exchangers. Then, a new fundamental approach was proposed which used the temperature profile and the local heat transfer coefficients. In this method, the heat transfer coefficient has been calculated for the total length of the heat exchanger including developing and fully developed regions. Numerous experimentations have been conducted in a double-tube heat exchanger. A significant difference observed between the results obtained from the suggested approach and those of the previous methods.     

液氮汽车的无霜换热器的数值分析

提出新型高效液氮汽车主换热器的数学模型 ,并对其传热特性进行动态模拟仿真 ,得到新型无霜换热器空气侧、氮气侧以及换热器管壁的温度分布 ,三者自身的温度分布 ,三者相互影响情况比较合理。氮气的出口温度为 2 93.0 5 K。与设计要求温度 2 93.15 K基本一致     

Experimental Investigation on Heat Transfer Characteristics of a Gas-to-Gas Counterflow Microchannel Heat Exchanger

Heat transfer characteristics of a gas-to-gas counterflow microchannel heat exchanger have been experimentally investigated. Temperatures and pressures at inlets and outlets of the heat exchanger have been measured to obtain heat transfer rates and pressure drops. The heat transfer and the pressure drop characteristics are discussed. Since the partition wall of the heat exchanger is thick compared with the microchannel dimensions, a simple heat exchange model with constant wall temperature is proposed to predict the heat transfer rate. The predicted heat transfer rate using the constant wall temperature model agrees well with the experimental results.     

低温工况下翅片管换热器的设计计算

采用分段模型将气化压力高于介质临界压力的翅片管换热器内低温介质的气化过程分为液相、气相两个传热区。同时考虑气化过程中翅片管表面结霜情况,对低温介质在翅片管换热器内的吸热气化过程进行传热分析,给出了适合各分区传热特性的计算关联式,为工程设计提供参考。     

Heat Transfer Characteristics in a Double-Pipe Heat Exchanger Equipped with Coiled Circular Wires

An experimental investigation has been carried out to study the enhancement in heat transfer coefficient by inserting coiled wire around the outer surface of the inner tube of the double-pipe heat exchanger. Insulated wires, with a circular cross-section of 2 mm diameter, forming a coil of different pitches (p = 6, 12, and 20 mm), were used as turbulators. The investigation is performed for turbulent water flow in a double-pipe heat exchanger with cold water in the annulus space for both parallel and counter flows. The experiments were performed for Reynolds numbers ranging from 4,000 to 14,000. The experimental results reveal that the use of coiled circular wires leads to a considerable increase in heat transfer coefficients compared with a smooth wall tube for both parallel and counter water flows. The mean Nusselt number increases with Reynolds number and pitch. The convective heat transfer coefficient for a turbulent water flow increases for all coiled wire pitches, with the highest enhancement of about 450% for counter flow and 400% for the parallel flow. New correlations for mean relative Nusselt numbers at different coiled wire pitches are provided.     

考虑冷热刀刀头温度响应对制定肿瘤治疗计划的影响

本文对冷热联合治疗肿瘤过程中在体生物组织的温度响应进行了深入的数值研究。组织被当作非理想材料,在一定的温度范围内冷冻和融化,并且考虑了未冻结组织和未损伤组织区域的血液灌注及代谢产热的影响。对比考虑和不考虑冷热刀刀头温度响应两种情形的计算结果表明,拟定治疗计划中若不考虑刀头温度响应,则有可能会造成冷热剂量的不足,从而无法彻底杀灭肿瘤。     

Experimental Effectiveness Investigation of Liquid-to-air Membrane Energy Exchangers under Low Heat Capacity Rates Conditions

The liquid-to-air membrane energy exchanger is a novel membrane base energy exchanger that allows both heat and moisture transfer between air and a salt solution using a membrane. The heat and mass transfer performance of a single one is significantly dependent on two dimensionless parameters: number of heat transfer units and the ratio of heat capacity rates between solution flow and airflow (Cr^*). In this study, the effectiveness of a small-scale liquid-to-air membrane energy exchanger under low Cr^* conditions (i.e., Cr^* < 1) that has been not investigated previously is experimentally and numerically tested.     

低温微创手术治疗探头周围组织温度分布研究

采用低温方法对人体深部肿瘤进行杀伤时,既要求对肿瘤组织有最大的杀伤效果,又要保证正常组织,特别是一些重要器官组织,能免受冷冻伤害。文中对冷冻治疗探头形成冰球的大小、以及冻结界面周围组织温度分布进行传热分析和测试,以给出安全区和危险区的范围,这可以为外科手术医生设计低温手术方案提供参考依据。     

变截面折流杆换热器的流动与传热分析

本文在折流杆换热器的基础上,采用数值计算的方法,以水为流动介质,对不同折流杆间隔的折流杆式换热器进行流动与传热特性的分析。同时,本文设计了一种新型的变截面折流杆式换热器,对换热器进行优化,结果表明,变截面折流杆换热器比等截面折流杆换热器的综合性能最多高13%～14%。     

An Experimental Investigation of Forced Convection Heat Transfer from a Coiled Heat Exchanger Embedded in a Packed Bed

Forced convection heat transfer from a helically coiled heat exchanger embedded in a packed bed of spherical glass particles was investigated experimentally. With dry air at ambient pressure and temperature as a flowing fluid, the effect of particle size, helically coiled heat exchanger diameter, and position was studied for a wide range of Reynolds numbers. It was found that the particle diameter, the helically coiled heat exchanger diameter and position, and the air velocity are of great influence on the convective heat transfer between the helically coiled heat exchanger and air. Results indicated that the heat transfer coefficient increased with increasing the air velocity, increasing helically coiled heat exchanger diameter, and decreasing the particle size. The highest heat transfer coefficients were obtained with the packed-bed particle size of 16 mm and heat exchanger coil diameter of 9.525 mm (1/4 inch) at a Reynolds number range of 1,536 to 4,134 for all used coil positions in the conducted tests. A dimensionless correlation was proposed for Nusselt number as a function of Reynolds number, particle size, coil size, and coil position.     

斜向流换热器壳程流场均匀化研究

传统弓形折流板换热器壳程流体横向流动时存在流动阻力和传热死区大等缺点。为克服上述不足,研究开发了一种新型高效节能的斜向流管壳式换热器,采用导向型折流栅替代传统弓形折流板,倾斜流道内流体斜向冲刷换热管束。考察和对比了斜向流换热器和弓形折流板换热器壳程主流区的流体流速分布和变化规律,证实了导向型折流栅具有显著的控涡均化壳程流场和提高壳程流体整体流速的作用,有助于减小壳程压降,增大有效换热面积,为管壳式换热器结构改良提供了参考依据。