共查询到19条相似文献,搜索用时 187 毫秒
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本文提出了一种OTEC(OTEC,Ocean Thermal Energy Conversion)增温再热朗肯动力循环,通过第二类吸收式热泵提升热源品质,在热力循环中创造一个相对高温区,与表层温海水共同对朗肯循环的湿工质进行过热,保证了透平出口干度,提升了循环的平均吸热温度,实现了单一热源下的梯级加热和能级匹配,系统效率得到较大的提升。论文构建了OTEC增温再热朗肯动力循环热力学模型,对比了增温再热朗肯动力循环与传统循环的热力性能,并分析了热泵子循环的最佳增温温度。结果表明:增温再热的效果与OTEC循环工质有较大关联,且存在最佳增温温度;对于采用R134A等近似等熵工质的OTEC循环,增温再热的热力性能提升不明显;而对于CO2等工作在亚临界区间的工质而言,增温再热可使热效率提升19.63%41.71%;对于NH3等过热需求较大工质而言,增温再热具有显著的提升效果;其中NH3工质的提升幅度最高,最佳增温温度为42.5°C,OTEC循环热效率可由2.34%提升至4.25%,升幅达84.45%。 相似文献
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本文选择含离子液体体系TFE-[BMIm][Br]作为吸收式制冷循环的工质体系,基于文献数据给出了计算TFE-[BMIm][Br]热物性模型,建立并联双效吸收式制冷循环的模拟程序,分别考察了四种双效并联制冷流程中溶液换热器的热交换效率、蒸发温度、吸收温度以及发生温度对系统性能、溶液循环倍率以及系统操作压力的影响.探索新工质对TFE-[BMIm][Br]的可行性,确定了TFE-[BMIm][Br]双效并联吸收式制冷循环的适宜的运行操作范围以及适宜的流程方案. 相似文献
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以核电站乏燃料水池散热及太阳能热利用等为应用背景,实验分析了R134a作为工质的分离式热管在不同热源温度和不同充液率条件下的换热特性。在热源温度从40℃以5℃间隔递增到65℃的条件下,共进行了6组不同的充液率实验,分别为43.7%,51.7%,60.1%,68.5%,75.2%,82.9%。实验结果表明,系统充液率达到68.5%以后,换热量和换热系数随着充液率的增加波动小,存在最佳充液率区间,并且管内蒸发温度和换热量随着热源温度的升高而升高。与氨工质关于蒸发段换热系数和换热量两方面进行数据分析对比,结果表明随着充液率的增加,两种工质在管内换热系数和换热量上存在较大差异。 相似文献
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基于量子主方程和半群逼近方法,研究以许多无相互作用的自旋-1/2系统为工质的、由两个绝热和两个等磁场过程组成的不可逆量子制冷循环的一般性能特性。导出循环的性能系数、制冷率和输入功率等重要性能参数的表达式。应用数值求解,对受有限循环时间约束的制冷率进行了优化,计算了最大制冷率和相应的最佳性能参数,确定了性能系数的最佳区域和工质温度及两个等磁场过程时间的优化范围。进而详细分析了高温下循环的优化性能,所得结果被进一步推广,以致可直接用来描述由自旋-J系统为工质的量子制冷循环的性能。 相似文献
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《工程热物理学报》2021,42(9):2243-2249
通过实验研究了氨–水–溴化锂三元工质的对氨吸收式制冷系统的影响。实验测试了发生温度100~130℃,蒸发温度-16~-4℃和冷却水温度22~33℃工况下的系统性能系数,发现适用于氨吸收式制冷的最佳溴化锂浓度为15%,与氨吸收式制冷系统相比,性能系数最高提升了10%。溴化锂最为第三工质对系统的影响是整体的,使用三元工质可以降低精馏负荷与回流比,提高热能利用效率同时降低了发生压力,有利于提升性能系数;但其不利影响体现在会降低浓溶液中氨的浓度,导致系统循环倍率上升,不利于提升性能系数。合理使用氨–水–溴化锂三元工质是不增加系统复杂度提高氨吸收式制冷性能有效方式。 相似文献
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热漏、内不可逆性和传热规律对卡诺热泵最优性能的影响 总被引:1,自引:0,他引:1
1引言有限时间热力学研究的基本模型为内可逆模型,而实际装置往往存在热漏、摩擦、涡流等不可逆损失。本文基于一种普遍传热规律qOC凸(T)n,建立了包括上述不可逆因素的不可逆模型,导出热泵供热率与供热系数的最佳特性关系。该关系包括不同传热规律和不同损失项的模型下的多种结果。2不可逆热泵模型考虑工作于两恒温热源问的定常态流热泵,其循环满足如下条件:(1)该循环由两个等温过程和两个绝热过程组成,这四个过程一般为不可逆。(2)传热是在有限温差下进行。设高、低温侧热源和工质工作温度分别为:TH、TL、THC、TLC,这… 相似文献
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Taking into account the finite-rate heat transfer in the heat-transfer processes, heat leak between the two external heat reservoirs, regenerative loss, regeneration time, and internal irreversibility due to dissipation of the cycle working substance, an irreversible magnetic Ericsson heat-pump cycle is presented. On the basis of the thermodynamic properties of magnetic materials, the performance characteristics of the irreversible magnetic Ericsson heat-pump are investigated and the relationship between the optimal heating load and the coefficient of performance (COP) is derived. Moreover, the maximum heating load and the corresponding COP as well as the maximum COP and the corresponding heating load are obtained. Furthermore, the other optimal performance characteristics are discussed in detail. The results obtained here may provide some new information for the optimal parameter design and the development of real magnetic Ericsson heat-pumps. 相似文献
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An irreversible model of an Ericsson cryogenic refrigeration cycle working with an ideal Fermi gas is established, which is
composed of two isothermal and two isobaric processes. The influence of both the quantum degeneracy and the finite-rate heat
transfer between the working fluid and the heat reservoirs on the performance of the cycle is investigated, based on the theory
of statistical mechanics and thermodynamic properties of an ideal Fermi gas. The inherent regeneration losses of the cycle
are analyzed. Expressions for several important performance parameters such as the coefficient of performance, cooling rate
and power input are derived. By using numerical solutions, the cooling rate of the cycle is optimized for a given power input.
The maximum cooling rate and the corresponding parameters are calculated numerically. The optimal regions of the coefficient
of performance and power input are determined. Especially, the optimal performance of the cycle in the strong and weak gas
degeneracy cases and the high temperature limit is discussed in detail. The analytic expressions of some optimized parameters
are derived. Some optimum criteria are given. The distinctions and connections between the Ericsson refrigeration cycles working
with the Fermi and classical gases are revealed.
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This paper deals with the performance analysis and optimization for irreversible heat pumps working on reversed Brayton cycle
with constant-temperature heat reservoirs by taking exergetic efficiency as the optimization objective combining exergy concept
with finite-time thermodynamics (FTT). Exergetic efficiency is defined as the ratio of rate of exergy output to rate of exergy
input of the system. The irreversibilities considered in the system include heat resistance losses in the hot- and cold-side
heat exchangers and non-isentropic losses in the compression and expansion processes. The analytical formulas of the heating
load, coefficient of performance (COP) and exergetic efficiency for the heat pumps are derived. The results are compared with
those obtained for the traditional heating load and coefficient of performance objectives. The influences of the pressure
ratio of the compressor, the allocation of heat exchanger inventory, the temperature ratio of two reservoirs, the effectiveness
of the hot- and cold-side heat exchangers and regenerator, the efficiencies of the compressor and expander, the ratio of hot-side
heat reservoir temperature to ambient temperature, the total heat exchanger inventory, and the heat capacity rate of the working
fluid on the exergetic efficiency of the heat pumps are analysed by numerical calculations. The results show that the exergetic
efficiency optimization is an important and effective criterion for the evaluation of an irreversible heat pump working on
reversed Brayton cycle. 相似文献
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A new model of a quantum refrigeration cycle composed of two adiabatic and
two isomagnetic field processes is established. The working substance in the
cycle consists of many non-interacting spin-1/2 systems. The performance of
the cycle is investigated, based on the quantum master equation and
semi-group approach. The general expressions of several important
performance parameters, such as the coefficient of performance, cooling
rate, and power input, are given. It is found that the coefficient of
performance of this cycle is in the closest analogy to that of the classical
Carnot cycle. Furthermore, at high temperatures the optimal relations of the
cooling rate and the maximum cooling rate are analysed in detail. Some
performance characteristic curves of the cycle are plotted, such as the
cooling rate versus the maximum ratio between high and low ``temperatures'
of the working substances, the maximum cooling rate versus the ratio between
high and low ``magnetic fields' and the ``temperature' ratio between high
and low reservoirs. The obtained results are further generalized and
discussed, so that they may be directly applied to describing the performance
of the quantum refrigerator using spin-$J$ systems as the working substance.
Finally, the optimum characteristics of the quantum Carnot and Ericsson
refrigeration cycles are derived by analogy. 相似文献
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针对高热流密度激光介质散热问题,利用实验方法研究了以十二烷基硫酸钠水溶液作为工质的喷雾冷却传热特性。结果表明,在特定的热流密度范围内,随着热流密度的增加,加热面温度不升反降,称之为热逆转。热逆转现象对对流换热系数的提升作用可高达94.0%,提升大小与热流密度有关。热逆转对应的热流密度区间为80~130 W/cm2,与浓度关系较小。热逆转现象与实验过程有关,该现象仅在热流密度逐渐升高的过程中出现,降低和任调热流密度过程中未发现此现象。热逆转具体原因还有待研究。 相似文献
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工质变比热条件下内燃机循环普适特性 总被引:4,自引:0,他引:4
用有限时间热力学的方法分析空气标准不可逆内燃机循环,导出了考虑工质变比热情况下,存在摩擦及传热损失时,由两个加热过程、两个放热过程和两个绝热过程组成的普适的空气标准不可逆内燃机循环的功率与压缩比、效率与压缩比以及功率和效率的最佳特性关系,同时由数值计算分析了工质变比热和循环过程对循环性能的影响特点,比较了工质恒、变比热时循环性能差异。所得结果包含了不可逆往复式Diesel、Otto、Brayton、Atkinson、Dual和Miller 循环的性能特性。 相似文献
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The fundamental optimal relation between heating load and coefficient of performance (COP) of a generalized irreversible Carnot
heat pump is derived based on a new generalized heat transfer law, which includes the generalized convective heat transfer
law and generalized radiative heat transfer law, q ∝ (ΔT
n
)
m
. The generalized irreversible Carnot heat pump model incorporates several internal and external irreversibilities, such as
heat resistance, bypass heat leakage, friction, turbulence and other undesirable irreversibility factors. The added irreversibilities
besides heat resistance are characterized by a constant parameter and a constant coefficient. The effects of heat transfer
laws and various loss terms are analysed. The heating load vs. COP characteristic of a generalized irreversible Carnot heat
pump is a parabolic-like curve, which is consistent with the experimental result of thermoelectric heat pump. The obtained
results include those obtained in many literatures and indicated that the analysis results of the generalized irreversible
Carnot heat pump were more suitable for engineering practice than those of the endoreversible Carnot heat pump. 相似文献
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The heating of solid surfaces using consecutive laser pulses is studied and the temperature field inside slabs with different thermal properties is predicted. A Gaussian beam intensity distribution is assumed at the irradiated surface and axisymmetric heating situation is accommodated in the numerical simulations. The materials selected include titanium, stainless steel, tantalum, nickel, and aluminum. A control volume approach is introduced to discretize the governing equation of heat transfer. It is found that temperature rise in the early heating period is higher than that in the later heating period. The temperature difference between two consecutive pulses is higher in the heating cycle than that corresponding to the cooling cycle of the consecutive pulses. 相似文献