Comparative study of heat transfer and pressure drop during flow boiling and flow condensation in minichannels

Abstract

In the paper a method developed earlier by authors is applied to calculations of pressure drop and heat transfer coefficient for flow boiling and also flow condensation for some recent data collected from literature for such fluids as R404a, R600a, R290, R32,R134a, R1234yf and other. The modification of interface shear stresses between flow boiling and flow condensation in annular flow structure are considered through incorporation of the so called blowing parameter. The shear stress between vapor phase and liquid phase is generally a function of nonisothermal effects. The mechanism of modification of shear stresses at the vapor-liquid interface has been presented in detail. In case of annular flow it contributes to thickening and thinning of the liquid film, which corresponds to condensation and boiling respectively. There is also a different influence of heat flux on the modification of shear stress in the bubbly flow structure, where it affects bubble nucleation. In that case the effect of applied heat flux is considered. As a result a modified form of the two-phase flow multiplier is obtained, in which the nonadiabatic effect is clearly pronounced. Nomenclature A -cross section area, m 2 B -blowing parameter Bo -boiling number, B0 = q Gh LG C -mass concentration of droplets in two phase core C f -friction factor Con -confinement number cp -specific heat, J/kg K d -diameter, m D -deposition term, kg/ms; channel inner diameter, m E -entrainment term, energy dissipation, kg/ms G -mass flux, kg/m 2 s g -gravitational acceleration, m/s 2 h -enthalpy, J/kg hLG -specific enthalpy of vaporization, J/kg h lv -specific enthalpy of vaporization,J/kg mG -mass of vapour phase mL -mass of liquid phasė m -mass flux,kg/s P -perimeter, m p -pressure, Pa Pr -Prandtl number q -density of heat flux, W/m 2 qw -wall heat flux, W/m 2 Re -Reynolds number, Re = Gd µ L ReL -Reynolds number liquid film only ReL = G d (1−x) µ L s = uG/uL -slip ratio u -velocity, m/s u + = u/u h -reduced speed w -velocity, m/s v0 -transverse velocity, m/s x = m G m G +m L

The analysis of thermal and flow characteristics of the condensation of refrigerant zeotropic mixtures in minichannels

“…Figure 9 summarizes the results of experimental studies in comparison to the calculation results obtained using the correlation developed by other authors for the local pressure drop. These were the comparative models due to Friedel [16], Garimella [17], Cavallini [10], Chen [14], Mikielewicz [20], and Zhang and Webb [32]. Discrepancies between own investigation results and the calculation results using mentioned above correlations, were found in the range of 50%.…”

“…The authors of publications [20,21] proposed their own, generalized mathematical model for description of heat transfer and pressure drop during condensation and boiling of refrigerants in the small diameter channels. The analysis covered such refrigerants, as R134a, R404a, R600a, R290, R32, and R1234yf.…”

“…Based on the available research results the authors of the paper compared own mathematical models with correlations of other authors. In articles [20,21] to evaluate the value of heat transfer coefficient and pressure drop during condensation were used correlations due to Thome et Thome [28] presented the calculation model of heat transfer during the condensation of zeotropic mixtures in horizontal channels. He draws attention to three important issues concerning the condensation of mixtures, namely: 1) construction of new two-phase flow maps, 2) difference of heat transfer models of zeotropic mixtures and homogeneous refrigerants, 3) original heat transfer model concerning these mixtures.…”

Study on Transport Packages Used for Food Freshness Preservation based on ANSYS Thermal Analysis

“…Basic theories of heat transfer theory Fourier law is a fundamental law of heat transfer theory (Jaremkiewicz, 2014;Mikielewicz et al, 2014;Vasiliev et al, 2015), which can be described as follow: in phenomena of heat conduction, suppose the heat quantity that passes through the interface in unit time is in direct proportion to the change rate of temperature in vertical direction of the interface as well as to the area of the interface, then the direction of heat transfer is contrary to the direction of the temperature increase (Mikielewicz et al, 2012). According to the Fourier law, the quantity of heat conduction  that passes through one position in unit time should be in direct proportion to the change rate of temperature as well as the area of the position:…”

Study on transport packages used for food freshness preservation based on thermal analysis

“…Fourier law is a fundamental law of heat transfer theory [10][11][12], which can be described as follow: in phenomena of heat conduction, suppose the heat quantity that passes through the interface in unit time is in direct proportion to the change rate of temperature in vertical direction of the interface as well as to the area of the interface, then the direction of heat transfer is contrary to the direction of the temperature increase [13]. According to the Fourier law, the quantity of heat conduction, Φ, that passes through one position in unit time should be in direct proportion to the change rate of temperature as well as the area of the position:…”