A system mean void fraction model for predicting various transient phenomena associated with two-phase evaporating and condensing flows

Wedekind, G. L.; Bhatt, B. L.; Beck, B. Terry

doi:10.1016/0301-9322(78)90029-0

Cited by 89 publications

(32 citation statements)

References 12 publications

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“…The average condensing and evaporating pressures ( Figure 5) and average outlet temperatures of condenser and evaporators (cabinet evaporator or SF evaporator) have been used to obtain the refrigerant density along the liquid and vapour lines. To compute the refrigerant charge in the evaporators, a mean void fraction of 85% has been considered, as recommended by Wedekind et al [26]. Table 4 summarizes the inner volumes of distribution lines and evaporators, as well as the refrigerant charge contained in those elements when operating with R-134a or R-507A.…”

Section: Refrigerant Charge Reductionmentioning

confidence: 99%

Conversion of a Direct to an Indirect Refrigeration System at Medium Temperature Using R-134a and R-507A: An Energy Impact Analysis

et al. 2018

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This work presents the experimental evaluation of energy consumption and refrigerant charge reduction when a commercial direct expansion refrigeration system is converted into an indirect system. The evaluation (with R-134a and R-507A) used a commercial cabinet with doors for medium temperature and a single-stage refrigeration cycle using a semi-hermetic compressor and electronic expansion valve; 24-h energy consumption tests were performed at laboratory conditions for each refrigerant and configuration at three heat rejection levels (23.3, 32.8 and 43.6 • C), maintaining an average product temperature inside the cabinet of 2 • C. The work analyses the impact of the conversion on temperature and pressure indicators, as well as, in the energy performance of each element. For R-134a the refrigerant charge was reduced in a 42.9%, but the energy consumption rose by 22.0%-22.8%; for R-507A the charge reduction was of 32.8% with an increase in energy consumption of between 27.7% and 38.7%.

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Section: Refrigerant Charge Reductionmentioning

confidence: 99%

Conversion of a Direct to an Indirect Refrigeration System at Medium Temperature Using R-134a and R-507A: An Energy Impact Analysis

et al. 2018

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“…The model assumptions are: fluid properties in each control volume are considered constant in each time period; the heat transmitted in the two-phase region is assumed to be only taken up by the saturated liquid, thus the heat transfer only occurs in the liquid zone (V l ); no thermal capacity and mass storage in vapour zones are considered; the refrigerant pressure drop along the evaporator is neglected; kinetic and potential energy variations are not taken into account; and the vapour-liquid volume relations for two-phase flow presented by Wedekind et al (1978) are used for connecting the liquid and vapour saturated volumes in the two-phase region.…”

Section: Mathematical Model Of the Evaporatormentioning

confidence: 99%

“…Dynamic modelling of refrigeration and air conditioning systems came about in 1978 from the work by Wedekind et al (1978) on two-phase flow dynamic performance in heat exchangers. From this, and following the evolution of computers and the energy problem in a parallel fashion, several dynamic modelling works started to emerge.…”

Section: Introductionmentioning

confidence: 99%

A dynamic mathematical model of a shell-and-tube evaporator. validation with pure and blend refrigerants

Llopis¹,

Cabello²,

Navarro-Esbrí³

et al. 2007

Int. J. Energy Res.

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SUMMARYThis work presents a mathematical model of a shell-and-tube evaporator based on mass continuity, energy conservation and heat transfer physical fundamentals. The model is formulated as a control volume combination that represents the different refrigerant states along the evaporator. Since the model is based on refrigerant and secondary fluid states prediction, it can be easily adapted for modelling any type of evaporator. The strategy of working with physical fundamentals allows the steady-and dynamic-state analysis of any of its performance variables. The paper presents a steady-state validation made with two pure refrigerants (HCFC-22, HFC-134a) and with a zeotropic blend (HFC-407C), and a dynamic validation with transient experimental tests using HCFC-22. The model prediction error is lower than 5% and it is well in accordance with actual dynamic behaviour.

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“…The MB model was first pioneered by Wedekind et al (1978). This approach uses the concept of a mean void fraction (MVF), calculated from the local void fraction and defined as the cross-sectional area occupied by the vapour in relation to the total area of the flow channel.…”

Section: Introductionmentioning

confidence: 99%

Effect of mean void fraction correlations on a shell-and-tube evaporator dynamic model performance

Navarro-Esbrí

Milián²,

Mota-Babiloni

et al. 2015

Science and Technology for the Built Environment

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A system mean void fraction model for predicting various transient phenomena associated with two-phase evaporating and condensing flows

Cited by 89 publications

References 12 publications

Conversion of a Direct to an Indirect Refrigeration System at Medium Temperature Using R-134a and R-507A: An Energy Impact Analysis

Conversion of a Direct to an Indirect Refrigeration System at Medium Temperature Using R-134a and R-507A: An Energy Impact Analysis

A dynamic mathematical model of a shell-and-tube evaporator. validation with pure and blend refrigerants

Effect of mean void fraction correlations on a shell-and-tube evaporator dynamic model performance

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