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Item type:Publication, Access status: with files , Investigation of refrigerant pipe pressure drop and charge reduction of mobile air conditioning units with R1234yfIn this study, the pressure drop of automotive refrigerant pipes with the refrigerant R1234yf is investigated in detail. For this purpose, 1D and 3D simulations are compared with respect to prediction accuracy using liquid lines from a production car. It is shown that for a combined approach of the methods a very good agreement with the measured values can be obtained, whereas simplified modeling of the line as a straight pipe of equal length significantly underestimates the experimental values. The transition pieces between the pipe and the hose are of particular importance, since they account for up to 85 % of the total pressure drop and therefore result in major errors if neglected. If hoses were eliminated, the lines could be designed smaller, resulting in a charge reduction of up to 56 %.Publicationtype: Journal ArticleScopus© Citations 1 84 562 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Experimental parameter studies on a two-phase loop thermosyphon cooling system with R1233zd(E) and R1224yd(Z)Two-phase loop thermosyphon (TPLT) is a promising technology looking at highly effective electronics cooling. Due to strong coupling between the internal and external parameters, in this study experimental tests in steady-state are carried out using R1233zd(E) and R1224yd(Z) as a working fluid to investigate the respective influences and resulting design requirements. The relationship between the governing thermal and flow equations is presented to facilitate the interpretation of the test results. The study shows a stable flow and cooling performance over a wide range of heat loads and recooling temperatures. The refrigerant charge is identified as one of the main influencing factors, with an optimum being between excessive subcooling and beginning dry-out. Both tested refrigerants lead to basically similar results, showing minor differences regarding thermal performance and system stability.Publicationtype: Journal ArticleScopus© Citations 13 139 788 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Analysis of refrigerant pipe pressure drop of a CO₂ air conditioning unit for vehiclesThis study investigates the pressure drop in refrigerant pipes of a CO₂ automotive air conditioning unit. A test rig to measure the pressure drop of arbitrarily shaped pipes is presented. As boundary conditions at the inlet of the test section, mass flow, pressure and enthalpy of the refrigerant are independently adjustable to values that cover the whole operating range of a CO₂ automotive air conditioning system for cars in the premium segment. Numerical analysis using CFD and a one-dimensional modelling tool is carried out. The pressure drop for the suction pipe reaches values of up to 500 mbar. CFD simulation predicts the pressure drop with an error of 25.7% for single-phase flow whereas the deviation using one-dimensional models is 46.5%. During two-phase flow the error increases to 55.8% with one-dimensional models and 42.4% using CFD.Publicationtype: Journal ArticleScopus© Citations 12 289 740