Blanka Jakubowska

Analytical Model With Nonadiabatic Effects for Pressure Drop and Heat Transfer During Boiling and Condensation Flows in Conventional Channels and Minichannels

In this paper a method developed earlier by the authors is applied to calculations of pressure drop and heat transfer coefficient for boiling flow and condensation flow with account of nonadiabatic effects for some recent data collected from the literature. The first effect, the modification of interface shear stresses in an annular flow pattern, is considered through incorporation of the so-called “blowing parameter.” The mechanism of modification of shear stresses at the vapor–liquid interface for such case is presented in detail in the paper. In the case of annular flow it contributes to thickening and thinning of the liquid film, which correspond to condensation and boiling, respectively. There is also another influence of the wall heat flux, where it is influencing the bubble nucleation in the case of the bubbly flow pattern. As a result, a modified general form of the two-phase flow multiplier, applicable both to boiling flow and condensation flow, is obtained, in which the nonadiabatic effects are clearly pronounced. The obtained model of the two-phase multiplier, incorporating the nonadiabatic effects, is additionally used in predictions of the heat transfer coefficient.

Calculation method for flow boiling and flow condensation of R134a and R1234yf in conventional and small diameter channels

Abstract The paper presents the results of calculations performed using the authors′ model to predict the heat transfer coefficient during flow boiling for two refrigerants R134a and R1234yf. The experimental data from various past studies have been collected and the calculations have been conducted for the full range of quality variation and a wide range of mass velocity. The aim of the study was to test the sensitivity of the in-house flow boiling and flow condensation model. The importance of taking into account the surface tension as the parameter exhibiting its importance in case of the flow in minichannels, as well as the influence of the reduced pressure were analysed. The obtained numerical results show good consistency with those recorded in the experiments.

Wpływ właściwości czynników chłodniczych na straty egzergii w pompie ciepła

Artykul poświecony jest wplywowi wystepujących w pompie ciepla strat egzergii na jej efektywnośc energetyczną, a co za tym idzie koszty funkcjonowania instalacji. Autorzy prezentują tu metodologie obliczeniową, ktora moze byc zastosowana w procesach projektowania ukladow cieplno-przeplywowych. Obliczenia zostaly wykonane na podstawie typowego ukladu powietrznej pompy ciepla pracującej w klimacie środkowo-europejskim. Ponadto w artykule wykonano analize techniczno-ekonomiczną pompy ciepla z wykorzystaniem wybranych czynnikow roboczych, ktore mogą byc stosowane w przyszlości.