Refrigerant performance evaluation including effects of transport properties and optimized heat exchangers

Abstract

Preliminary refrigerant screenings typically rely on using cycle simulation models involving thermodynamic properties alone. This approach has two shortcomings. First, it neglects transport properties, whose influence on system performance is particularly strong through their impact on the performance of the heat exchangers. Second, the refrigerant temperatures in the evaporator and condenser are specified as input, while real-life equipment operates at imposed heat sink and heat source temperatures; the temperatures in the evaporator and condensers are established based on overall heat transfer resistances of these heat exchangers and the balance of the system. The paper discusses a simulation methodology and model that addresses the above shortcomings. This model simulates the thermodynamic cycle operating at specified heat sink and heat source temperature profiles, and includes the ability to account for the effects of thermophysical properties and refrigerant mass flux on refrigerant heat transfer and pressure drop in the air-to-refrigerant evaporator and condenser. Additionally, the model can optimize the refrigerant mass flux in the heat exchangers to maximize the Coefficient of Performance. The new model is validated with experimental data and its predictions are contrasted to those of a model based on thermodynamic properties alone.

Low-GWP refrigerants for medium and high-pressure applications

“…The second round of simulations used a more advanced cycle model, which is referred to as CYCLE_D-HX (Brignoli et al ., 2017). The CYCLE_D-HX model builds on the concept of using temperature profiles of the heat sink and heat source, and the mean effective temperature differences between the refrigerant and heat transfer fluids (Δ T hx ) in the evaporator and condenser (Domanski and McLinden, 1992).…”

“…The isentropic efficiency of the compressor was at about the 70 % level, and it differed between the fluids as it was a function of refrigerant thermodynamic properties (Brignoli et al ., 2017). The more detailed cycle analysis implemented in CYCLE_D-HX yielded fluid COP and Q vol that are different from those obtained from CYCLE_D simulations based on thermodynamic properties alone (Figures 4a and 4b).…”

Performance analysis of fin tube evaporator using various refrigerants

“…The R134a is the most commonly used refrigerant in the refrigerators. It causes difficult inhalation while breathing and it has high global warming effect, and also the power consumption is high [1][2][3][4]. It is necessary to choose an alternate refrigerant for reducing global warming and power consumption.…”

CYCLE_D-HX: NIST vapor compression cycle model accounting for refrigerant thermodynamic and transport properties, version 1.0, user's guide

“…The other cycles may contain a second compressor, one or two economizers, or an intercooler. These advanced cycles do not include the optional liquid-line/suction-line heat exchanger (Brignoli et al, 2017).…”

“…The 'Number of Circuits' remained unchanged in this 'Simulate' run, but it would be altered should the user checked 'Yes' on the radio button instructing the program to 'Optimize the Number of Circuits'. For fair evaluation of alternative refrigerants, it is important to 'Optimize number of circuits' (Brignoli et al, 2017). Figure 15 shows the Cycle Specifications window with the 'Compressor' box allowing the user to select a compressor map from the created list of compressors, create a new compressor map, and edit or delete the exiting selection.…”