Effect of heater and condenser orientations on fluid flow behaviour in a two-phase natural circulation loop

A Numerical investigation on the influence of heater and condenser orientation and its location on steady state performance of a Two Phase Natural Circulation Loop (TPNCL) is presented. In the present study, four possible orientations are considered in TPNCL namely, Vertical Heater and Vertical Condenser (VHVC), Vertical Heater and Horizontal Condenser (VHHC), Horizontal Heater and Horizontal Condenser (HHHC) and Horizontal Heater and Vertical Condenser (HHVC). An in house MATLAB code is developed to solve the systems of equations. Homogeneous equilibrium model (HEM) is used in two phase regions. It is observed that steady state mass flow rate of the loop is significantly influenced by the developed pressure gradient in the riser and downcomer sections, as well as available vapour quality in the riser section. Moreover, it is also noticed that condenser position and orientation significantly effects the thermo-hydraulic characteristic of loop compared with heater orientation.

EXPERIMENTAL STUDY TO DETERMINE THE LOCAL CONDENSATION HEAT TRANSFER COEFFICIENTE FOR R134A FLOWING THROUGH A 4.8 MM INTERNAL DIAMETER SMOOTH HORIZONTAL TUBE

Refrigerant fluid R134a is commonly one of the most utilised invapour compression cycles wordlide, wheter in dommestic HVAC orautomotive regrigeration systems. This paper’s goal is toexperimetnally determine the fluid local condensation Heat TransferCoefficient (HTC), in several flor regimes. In this work, the mass fluxwas equal to 200, 250 and 300 kg/(m2s) and the fluid flowedthrough a smooth, horizontal 4.8 mm internal diameter aluminiumpipe, during which its vapour quality varied along the entire qualityrange. A purpose built test rig was developed, in which fluidconditions were constantly monitored and controlled. Throughmeasurements in temperature and pressure, an energy balance wasused to calculate experimentally the local heat transfer coeeficient.Average results for the unit quality range equalled to 3781 , 3459 and3944 W/m2K for saturation temperature equal to 30 C and theaforementioned mass velocities. Likewise, at 35C the averages HTCfound were 2903, 3141 and 3898 W/m2K at the same mass fluxrates. Later on, the experimental results were compared to tencommonly used HTC correlation found in relevant references,with Chato’s correlation returning the best fitting.

Technique for flowrate calculation of cryogenic two-phase flows in Venturi flowmeters without separation

A technique for calculating the flowrate of cryogenic two-phase flows in separationless flowmeters based on a venturi is proposed. The technique takes into account the equation of state of the two-phase medium, that is changes in density, mass vapour quality and temperature of cryogens two-phase flows against pressure in the venturi. It is shown that without an accounting of the flow parameters evolution, an additional flowrate error appears and therefore it is impossible to correctly determine the sensitivity and measurement range of the flowmeter. The most optimal measurement range of the pressure drop is chosen as well as a method of the flowrate measuring by the temperature difference across the venturi is proposed. The problem of determining the flowrate of two-phase cryogenic flows is topical for accelerator, aerospace and gas-transport engineering.

Impact of Channel Geometries and Flow Patterns On Micro-Channel Heat Sink Performance

Demand for greater capability of electronic devices in very small volume for compactness has affected huge augmentations in heat indulgence at all stages of device, electronic wrapping, test section and system. Latest cooling systems are hence needed to eliminate the released heat while maintaining compactness of the device. The micro-channel heat sink (MCHS) is ideal for this situation as it consists of channels of micron size which offers an extended surface area to volume ratio of approximately 15.294 m2 / m3 compared to 650 m2 / m3 for a typical heat compact exchanger. A comprehensive review has been done for consequence of heat flux (qo ), mass flux (G), vapour quality (x) and channel geometries at flow patterns and heat dissipation of MCHS. The study show that to increase the rate of heat transfer by using different channel geometries like converging-diverging, segmented etc. compared to conventional rectangular micro-channels has given better cooling effect The Flow patterns like bubbly, slug flow are associated with nucleate boiling dominated in low vapour quality and annular flow also given the significant effect on heat transfer in higher vapour quality region

Condensation of Novec 649 refrigerant in pipe minichannels

The paper presents the results of experimental investigation of Novec 649 refrigerant condensation in tube minichannels. This is a low-pressure refrigerant. This investigations are basis for flow structures visualization during condensation in pipe minichannels. The local and the average values of pressure drop (Δp/L) and heat transfer coefficient α in the whole range of the changes of vapour quality (x = 1 ÷ 0) were calculated. On the basis of the obtained test results there was illustrated the influence of the vapour quality x, the mass flux density G and the inner diameter of channel d changes on the studied parameters. These results were compared with the calculation results based on the dependencies of other authors.

An investigation of heat transfer coefficient during refrigerants condensation in vertical pipe minichannels

This article presents the results of experimental research of heat transfer coefficient in air cooled vertical pipe minichannels during R404A, R407C and R410A high-pressure refrigerants condensation. The study determined local and average heat transfer coefficient values in full range of vapour quality, x = 0 ÷ 1. On the basis of experimental investigations, the dependence of heat transfer on the vapour quality x, mass flux density G and minichannel's internal diameter dw was obtained.