Method to evaluate heat leakage of vertical cryogenic vessels at different liquid levels

Based on finite time thermodynamics, an irreversible combined thermal Brownian heat engine model is established in this paper. The model consists of two thermal Brownian heat engines which are operating in tandem with thermal contact with three heat reservoirs. The rates of heat transfer are finite between the heat engine and the reservoir. Considering the heat leakage and the losses caused by kinetic energy change of particles, the formulas of steady current, power output and efficiency are derived. The power output and efficiency of combined heat engine are smaller than that of single heat engine operating between reservoirs with same temperatures. When the potential filed is free from external load, the effects of asymmetry of the potential, barrier height and heat leakage on the performance of the combined heat engine are analyzed. When the potential field is free from external load, the effects of basic design parameters on the performance of the combined heat engine are analyzed. The optimal power and efficiency are obtained by optimizing the barrier heights of two heat engines. The optimal working regions are obtained. There is optimal temperature ratio which maximize the overall power output or efficiency. When the potential filed is subjected to external load, effect of external load is analyzed. The steady current decreases versus external load; the power output and efficiency are monotonically increasing versus external load.

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Performance Analysis and Optimization for Irreversible Combined Carnot Heat Engine Working with Ideal Quantum Gases

Entropy ◽

10.3390/e23050536 ◽

2021 ◽

Vol 23 (5) ◽

pp. 536

Author(s):

Lingen Chen ◽

Zewei Meng ◽

Yanlin Ge ◽

Feng Wu

Keyword(s):

Power Output ◽

Thermal Efficiency ◽

Combined Cycle ◽

Quantum Gases ◽

Carnot Cycle ◽

Leakage Loss ◽

Optimal Power ◽

Heat Leakage ◽

Working Medium ◽

Ideal Quantum

An irreversible combined Carnot cycle model using ideal quantum gases as a working medium was studied by using finite-time thermodynamics. The combined cycle consisted of two Carnot sub-cycles in a cascade mode. Considering thermal resistance, internal irreversibility, and heat leakage losses, the power output and thermal efficiency of the irreversible combined Carnot cycle were derived by utilizing the quantum gas state equation. The temperature effect of the working medium on power output and thermal efficiency is analyzed by numerical method, the optimal relationship between power output and thermal efficiency is solved by the Euler-Lagrange equation, and the effects of different working mediums on the optimal power and thermal efficiency performance are also focused. The results show that there is a set of working medium temperatures that makes the power output of the combined cycle be maximum. When there is no heat leakage loss in the combined cycle, all the characteristic curves of optimal power versus thermal efficiency are parabolic-like ones, and the internal irreversibility makes both power output and efficiency decrease. When there is heat leakage loss in the combined cycle, all the characteristic curves of optimal power versus thermal efficiency are loop-shaped ones, and the heat leakage loss only affects the thermal efficiency of the combined Carnot cycle. Comparing the power output of combined heat engines with four types of working mediums, the two-stage combined Carnot cycle using ideal Fermi-Bose gas as working medium obtains the highest power output.

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Effects of internal irreversibility and heat leakage on the finite time thermoeconomic performance of refrigerators and heat pumps

Energy Conversion and Management ◽

10.1016/s0196-8904(99)00129-6 ◽

2000 ◽

Vol 41 (6) ◽

pp. 607-619 ◽

Cited By ~ 67

Author(s):

Ali Kodal ◽

Bahri Sahin ◽

Tamer Yilmaz

Keyword(s):

Finite Time ◽

Heat Pumps ◽

Heat Leakage ◽

Internal Irreversibility

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Comparative study on thermodynamic characteristics of composite thermal insulation systems with liquid methane, oxygen, and hydrogen

Journal of Thermal Science and Engineering Applications ◽

10.1115/1.4052343 ◽

2021 ◽

pp. 1-18

Author(s):

Xiafan Xu ◽

Jianpeng Zheng ◽

Hao Xu ◽

Liubiao Chen ◽

Junjie Wang

Keyword(s):

Comparative Study ◽

Thermal Insulation ◽

Thermodynamic Characteristics ◽

Calculation Model ◽

System Structure ◽

Insulation System ◽

Optimal Position ◽

Heat Leakage ◽

Cryogenic Liquids ◽

Liquid Methane

Abstract Composite passive insulation technology has been proved to be an effective method to reduce heat leakage into the cryogenic storage tank. However, the current related research mainly focused on liquid hydrogen (LH2). The thermophysical properties of different cryogenic liquids and the thermal insulation materials at different temperatures are significantly different, so whether the results related to LH2 are applicable to other cryogenic liquids remains to be further determined. In fact, the insulation technology of LH2 itself also needs further study. In this paper, a thermodynamic calculation model of a composite insulation system including hollow glass microspheres (HGMs), multilayer insulation (MLI), and self-evaporating vapor cold shield (VCS) has been established. The accuracy of the calculation model was verified by the experimental results, and a comparative study on thermodynamic characteristics of the composite thermal insulation system with liquid methane, liquid oxygen (LO2), and LH2 was carried out. The results show that the heat leakage reduction of the proposed system for liquid methane, LO2 and LH2 is 25.6%, 29.7% and 64.9% respectively compared to the traditional SOFI+MLI system (1*10−3 Pa). The type of liquid and the insulation system structure has a relatively large influence on the VCS optimal position. While for a specific insulation system structure, the insulation material thickness, storage pressure, and hot boundary temperature have a weak influence on the VCS optimal position.

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Modeling and performance analysis of energy selective electron (ESE) engine with heat leakage and transmission probability

Science China Physics Mechanics and Astronomy ◽

10.1007/s11433-011-4473-z ◽

2011 ◽

Vol 54 (11) ◽

pp. 1925-1936 ◽

Cited By ~ 13

Author(s):

ZeMin Ding ◽

LinGen Chen ◽

FengRui Sun

Keyword(s):

Performance Analysis ◽

Transmission Probability ◽

Heat Leakage ◽

And Performance

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Comprehensive study on boil-off gas generation from LNG road tankers under simultaneous impacts of heat leakage and transportation vibration

Fuel ◽

10.1016/j.fuel.2020.117876 ◽

2020 ◽

Vol 275 ◽

pp. 117876

Author(s):

Xingchun Wang ◽

Yiling Xu ◽

Sujing Wang ◽

Qiang Xu ◽

Thomas C. Ho

Keyword(s):

Gas Generation ◽

Heat Leakage ◽

Comprehensive Study

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Energy Saving through Efficient BOG Prediction and Impact of Static Boil-off-Rate in Full Containment-Type LNG Storage Tank

Energies ◽

10.3390/en13215578 ◽

2020 ◽

Vol 13 (21) ◽

pp. 5578

Author(s):

Mohd Shariq Khan ◽

Muhammad Abdul Qyyum ◽

Wahid Ali ◽

Aref Wazwaz ◽

Khursheed B. Ansari ◽

...

Keyword(s):

Storage Tank ◽

Liquid Level ◽

Unequal Distribution ◽

Strong Function ◽

Heat Leakage ◽

Simulation Results ◽

Lng Tank ◽

The Impact ◽

Lower Liquid ◽

Vapor Temperature

Boil-off gas (BOG) from a liquefied natural gas (LNG) storage tank depends on the amount of heat leakage however, its assessment often relies on the static value of the boil-off rate (BOR) suggested by the LNG tank vendors that over/under predicts BOG generation. Thus, the impact of static BOR on BOG predictions is investigated and the results suggest that BOR is a strong function of liquid level in a tank. Total heat leakage in a tank practically remains constant, nonetheless the unequal distribution of heat in vapor and liquid gives variation in BOR. Assigning the total tank heat leak to the liquid is inappropriate since a part of heat increases vapor temperature. At the lower liquid level, BOG is under-predicted and at a higher level, it is over-predicted using static BOR. Simulation results show that BOR varies from 0.012 wt% per day for an 80% tank fill to 0.12 wt% per day at 10% tank fill.

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