马铃薯在高压直流电场中冻结的实验研究

微能源在食品工业中的应用日益广泛。本文实验研究了不同场强对马铃薯冻结过程及其冻结后无电场下解冻过程的影响,主要考察冻结和解冻曲线,发现高压直流电场场强不同对马铃薯冻结过程的作用有差异,场强较低时延缓冻结,反之则会加速进行,不同场强冻结的马铃薯在解冻过程中即使不加电场解冻,由于前期冻结时电场的作用使后期解冻时存在解冻速度上的差异。     

超声波对脱气与未脱气氯化铵溶液结晶的影响

为了阐明超声波强化饱和溶液结晶的机理,分别研究了超声波对脱气饱和氯化铵溶液与未脱气饱和氯化铵溶液结晶的影响。结果显示,在相同超声波辐射下,脱气饱和氯化铵溶液与未脱气饱和氯化铵溶液的结晶均得到了强化,但未脱气饱和氯化铵溶液白浊化开始时间显著小于脱气饱和氯化铵溶液白浊化开始时间,未脱气氯化铵溶液结晶晶粒比脱气氯化铵溶液结晶晶粒更细小。这表明超声空化以及声场中溶液分子振动引起的能量、温度及密度的波动对饱和溶液的结晶均有影响,但空化是强化饱和溶液结晶的主要因素。     

超声场中声压与空化对冰晶分裂的影响

为了探讨超声波强化冰晶二次成核的机理,利用自行研制的超声波冷却实验台,研究了超声波对未脱气蔗糖稀溶液和脱气蔗糖稀溶液中树枝状冰晶体的影响.实验结果表明:未脱气蔗糖稀溶液中的树枝状冰晶体受超声波辐射2s后已发生分裂,而脱气溶液中的树枝状冰晶体受功率相同的超声波辐射6s后却仍未分裂.说明超声场中冰晶发生分裂的主要原因是空化效应,而不是超声波在溶液中传播所引起的声压.     

接触式超声波辅助平板冷冻对胡萝卜冷冻速率的影响

超声波可以促进晶核形成,缩短冻结时间并且获得较高的冻结品质,但该技术目前多用于液态样品或浸渍冷冻过程,在固体果蔬样品平板冷冻过程中的应用未见报道。本文设计制作了一种接触式超声波辅助冷冻平板,用于固体果蔬的冷冻过程,并进行了三组实验:1)在-1℃施加10 s不同功率(0 W,122.6 W,178.7 W,229.8 W)的超声波;2)在-1℃施加178.7 W超声波,作用0 s,5 s,10 s,15 s;3)在不同阶段(预冷段,相变段,终了段)施加178.7 W的超声波10 s。分别研究了超声波的作用功率、作用时间、作用阶段等参数对胡萝卜冷冻速率的影响,结果表明:在相变阶段作用178.7 W的超声波10 s,能显著降低样品通过最大冰晶生成段的时间tcf和总冻结时间ttf,提高样品的冷冻速率。     

速冻马铃薯在高压直流电场中解冻的实验研究

微能源在食品工业中的应用日益广泛。本文实验研究了不同场强对快速冻结马铃薯的解冻过程和解冻后质量的影响,主要考察解冻曲线、质地特性,液汁流失三方而。研究发现高压直流电场场强不同对马铃薯解冻过程的作用有差异：在150kv／m场强以下时延缓解冻,反之则会加速解冻进行;不同场强对马铃薯解冻前后的质地特性、液汁流失影响较小。     

速冻马铃薯在高压直流电场中解冻的实验研究

微能源在食品工业中的应用日益广泛.本文实验研究了不同场强对快速冻结马铃薯的解冻过程和解冻后质量的影响,主要考察解冻曲线、质地特性,液汁流失三方面.研究发现高压直流电场场强不同对马铃薯解冻过程的作用有差异.在150kV/m场强以下时会延缓解冻,反之则会加速解冻进行;不同场强对马铃薯解冻前后的质地特性、液汁流失影响较小.     

接触角和质量分数对液滴冻结过程的影响

本文通过FLUENT软件的凝固/熔化模型,模拟了接触角及质量分数对纯水和氯化钠溶液在冷表面冻结过程的影响,选择铜片为亲水表面,纳米膜表面为疏水表面,对液滴在不同表面特性条件下的冻结过程进行实验研究。结果表明：液滴在冷表面的冻结特性与接触角、质量分数有关。当溶液质量分数一定时,接触角越小,液滴冻结速度越快,完全冻结时间越短;在冻结过程的初始时刻,接触角越小,液滴底部温度越低;当冻结时刻相同、液滴高度一致时,液滴表面的温度和液相分数均比液滴内部低;接触角相同时,溶液质量分数与液滴的开始冻结温度成反比,与完全冻结时间成正比。对比实验结果与模拟可知,不同质量分数的氯化钠液滴在接触角为60°和100°时,冻结时间的变化趋势一致,但实验值大于模拟值。     

一种岩心样品横波速度的实验室测量方法

准确测量声波在不同类型岩心中的传播速度是岩心声学性质分析的基础。一般实验室利用超声波透射法所测试的岩心样品均为小尺寸岩心样品。在测量小尺寸岩心样品横波波速时,难以消除的纵波余震信号会对横波的识别产生干扰。提出了一个在实验室内测量小尺寸岩心样品中横波波速的"辅助块"超声波透射波测试方案,较好地实现了纵横波的分离,减小了横波波速的测量误差,提高了岩心样品横波波速测试的精度。给出了上述测量方案和测量实例分析,该方法亦可用于一般固体样品中横波波速的测量。     

沉浸速度对小样品在饱和液氮中的淬冷沸腾传热的影响

用沉浸法研究了金属小球以较高速度沉浸入饱和液氮时的淬冷沸腾传热特性。实验用了14个直径为0．1－3.0mm的小球，小球运动速度为2－6m/s，在液氮中的运动距离（称为沉浸距离）为50cm，实验发现，沉浸样品的直径减小和沉浸速度增大，均导致沸腾曲线急剧向上方移动，同时也讨论了沉浸距离对沸腾的影响。     

小样品在过冷液氮中的淬冷沸腾传热

本文用沉浸法研究小样品沉浸入过冷液氮的沸腾传热特性。实验发现，沉浸样品的直径减少、液氮过冷度增大，均导致沸腾的热流密度急剧向右上方移动。当小直径足够小，过冷度足够大时，稳定膜态沸腾段消失了，“Ｍ”形的沸腾曲线变为“Λ”形。     

双频复合超声强化无水葡萄糖溶液结晶成核研究

溶液结晶技术在许多领域有着广泛的应用,其中结晶成核是溶液结晶的关键环节。以无水α-葡萄糖为研究对象,采用双频复合超声(25 k Hz+40 k Hz)强化糖液结晶成核,研究了溶液浓度、超声功率和作用时间对成核速率的影响,对单频和双频作用的晶核形态进行了对比,并采用碘化钾溶液中碘的释放量研究超声空化产额。研究结果表明:在同等条件下,双频复合超声降低了溶液成核的初始浓度,提高了成核速率,同时得到粒度均匀的晶核;双频复合超声的空化产额远高于单频25 k Hz超声和单频40 k Hz超声的空化产额,双频复合超声具有协同作用。双频复合超声强化溶液成核是一种快速、高效、节能的方法。     

CXF-O型超声成核装置的设计及其应用

本文应用ＣＸＦ—Ｏ型超声发生器和磁致伸缩换能器开展了蔗糖溶液成核作用的研究。试验结果说明，超声宣化促进了晶核的形成，其密度与颗粒均匀，优于其它方法的成核效果。     

气体水合物超声结晶实验

实验中将15kHz超声波引入R141b和水体系,反应过程在恒温水浴中进行,对超声探头处于不同位置、不同过冷度情况下分别研究.结果表明在超声启动后5秒内就出现大量水合物浆,成核对过冷度的依赖程度降低,但结晶完成时间随过冷度的增加而减少.在同样条件下,探头位于两相界面处,消耗的能量较低.分析结果认为这可能与超声空化产生的一系列效应有关.     

Study on Enhancement in Gibbsite Precipitation of Bayer Process under 33 kHz Ultrasound

The enhancement of gibbsite precipitation in Bayer process by 33 kHz ultrasound has been studied. From orthomethod experiment, the optimized operating parameters of treatment under 33 kHz ultrasonic cleaner have obtained.Compared with crystallization of Al(OH)3 without treatment of ultrasound, the precipitation time is reduced by 15 h when the precipitation ratio is 45%. From the results of grain size distribution and SEM photographs of gibbsite, it is found that secondary nucleation and agglomeration could be enhanced under 33 kHz ultrasound. The products are same from comparison of X-ray powder diffraction, but the Raman spectrum of sodium aluminate solution under 33 kHz ultrasound is different from that without ultrasound.     

相界面上超声空化气泡聚并、滑移促进的传质

根据超声空化泡在相间特殊运动时周围流体流动特性,以相间传质渗透理论为依据,结合流体动力学原理,在充分研究相界面上气泡行为的基础上,根据界面上超声空化气泡生长过程的动力学行为,导出了相界面上超声空化气泡聚并和滑移促进的传质模型。在此基础上,建立了相界面上气泡滑移、聚并及脱离界面逸出这三种气泡行为共同促进的传质模型,该模型可用于描述超声空化界面等相界面上的传质行为,为超声波强化传质过程提供了理论依据。     

Synthesis of nanocrystals of gadolinium carbonate by reaction crystallization

The formation of nano-sized crystals of gadolinium carbonate via reaction crystallization was studied in a semi-batch crystallizer using gadolinium chloride and ammonium hydrogen carbonate as the reactants. The gadolinium carbonate crystals were formed by the aggregation of primary particles sized about 5 nm. Thereby, the crystallization parameters acting directly on the aggregation of the primary particles, such as the reactant concentrations, non-stoichiometry of the reactants, solution pH, acoustic energy, and agitation speed, were mechanistically investigated. As such, increasing the reactant concentrations enhanced the crystal size due to higher nucleation of the primary particles for the aggregation. Non-stoichiometric reactant concentrations resulted in a significant reduction of the crystal size, due to the adsorption of the excess species on the primary particles. Similarly, the surface charge of the primary particles depended on the solution pH. Thus, the crystal size was reduced when the pH deviated from the neutral point. The acoustic cavitation of the ultrasound was much more effective than the turbulent fluid motion of the agitation in inhibiting the primary particle aggregation. Thus, the crystal size was remarkably reduced, even at a low acoustic energy of 6 watts.     

In vivo acceleration of ultrasonic tissue heating by microbubble agent

The ultrasonic power absorbed by a microbubble in its continuous wave response is estimated through numerically solving a version of the Rayleigh-Plesset equation. At an ultrasonic frequency of 3 MHz, a resonant microbubble, approximately 1.1 microm in radius, showed an absorption cross section of about 0.005 mm2 in its low power response. This estimation predicts that the tissue ultrasonic absorption will be doubled when such microbubbles are delivered to the tissue at a concentration of about eight bubbles/mm3 in tissue. An exteriorized murine kidney was exposed to focused ultrasound at 3.2 MHz in degassed saline, and the tissue temperature change was measured. With an intravenous bolus administration of a microbubble agent, the ultrasonically induced temperature elevation was multiplied by up to five times. The enhancement in temperature elevation gradually decreased as the microbubble agent was eliminated from the body. The experimental results agreed with the prediction in the order of magnitude. This effect may have a potential use to enhance the throughput as well as the selectivity of focused ultrasound treatment.     

Influence enhancement effect of bi-frequency ultrasonic irradiation by TA fluorescence method

Based on a previous research of cavitation effect under bi-frequency ultrasound irradiation, this paper studies bi-frequency irradiations with similar experimental settings. The additional irradiation sources with frequencies of 1.04MHz, 0.8MHz and 1.7MHz are individually combined with the main ultrasonic irradiation source with frequency of 28kHz to form bi-frequency ultrasonic irradiation. The intensity of 28kHz irradiation was fixed at 12.5W/cm2, while the intensity of the ultrasound at the other three frequencies is varied from1 W/cm2 to 18 W/cm2. It turns out that under the influence of the bi-frequency irradiation, the fluorescence intensity is obviously greater than the sum of those at individual frequencies. So the frequency of the additional sonication strikingly influences the fluorescence enhancement effect. For example, the fluorescence enhancement effect of 1.04MHz is stronger than that of 1.7MHz, and the enhancement effect of 0.8MHz is further stronger than that of 1.04MHz. Under the sonic intensity of 7.9W/cm2, the fluorescence intensity of 1.04MHz is approximately twice that of 1.7MHz while the fluorescence intensity of 0.8MHz is approximately 1.5 times that of 1.04MHz.