Experimental Investigation on Heat Transfer of CO2 Solid-Gas Two Phase Flow With Dry Ice Sublimation

2009 ◽  
Author(s):  
Xin-Rong Zhang ◽  
Hiroshi Yamaguchi
Keyword(s):  
Heat Transfer ◽  
Gas Flow ◽  
Two Phase Flow ◽  
Horizontal Tube ◽  
Tube Length ◽  
Phase Flow ◽  
Two Phase ◽  
Average Value ◽  
Pressure Fields ◽  
Phase Fluid

From the viewpoint of protecting the ozone layer and preventing global warming, there is now strong demand for science and technology based on ecologically safe ‘natural’ working fluids. A CO2 refrigeration method has been proposed and developed several years ago, using CO2 solid-gas two phase fluid as refrigerant. Heat transfer of the CO2 solid-gas two phase flow in a horizontal tube is important to design of such a refrigeration system. In the present paper, an experiment work is conducted to measure its heat transfer characteristics in the horizontal tube. The results show an average value 310 W/(m2-K) of heat convective coefficient is experimentally obtained, which is much higher than that of gas flow. In the sublimation area, the Nusselt number is observed to increase slowly along the tube length, the phenomena may be physically explained that the sublimation process changes the thermal boundary layer thickness; makes the flow turbulence stronger; or changes the flow and the pressure fields.

Two-Phase Wakes in Adiabatic Liquid-Gas Flow Around a Cylinder

2020 ◽  
Author(s):  
Dohwan Kim ◽  
Matthew J. Rau
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
High Speed ◽  
Gas Flow ◽  
Two Phase Flow ◽  
Water Channel ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Around A Cylinder ◽  
High Heat Transfer

Abstract Small tubes and fins have long been used as methods to increase surface area for convective heat transfer in single-phase flow applications. As demands for high heat transfer effectiveness has increased, implementing evaporative phase-change heat transfer in conjunction with small fins, tubes, and surface structures in advanced heat exchanger and heat sink designs has become increasingly attractive. The complex two-phase flow that results from these configurations is poorly understood, particularly in how the gas phase interacts with the flow structure of the wake created by these bluff bodies. An experimental study of liquid-gas bubbly flow around a cylinder was performed to understand these complex flow physics. A 9.5 mm diameter cylinder was installed horizontally within a vertical water channel facility. A high-speed camera captured the movement of the liquid-gas mixture around the cylinder for a range of bubble sizes. Liquid Reynolds number, calculated based on the cylinder diameter, was varied approximately from 100 to 3000. Time-averaged probability of bubble presence was calculated to characterize the cylinder wake and its effects on the bubble motion. The influence of the liquid Reynolds number, superficial air velocity, and bubble size is discussed in the context of the observed two-phase flow patterns.

The Effect of Channel Diameter on Heat Transfer Characteristics of Two-Phase Flow in Microchannels

2011 ◽  
Author(s):  
Kyosung Choo ◽  
Daniel Trainer ◽  
Sung Jin Kim
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Gas Flow ◽  
Two Phase Flow ◽  
Superficial Velocity ◽  
Phase Flow ◽  
Heat Transfer Characteristics ◽  
Two Phase ◽  
Channel Diameter ◽  
Transfer Characteristics

The heat transfer and fluid flow characteristics of non-boiling two-phase flow in microchannels were experimentally investigated. The effects of channel diameter (140, 222, 334, and 506 μm) on the Nusselt number were considered. Air and water were used as the working fluids. Results were presented for the Nusselt number over a wide range of gas superficial velocity (1.24–40.1 m/s), liquid superficial velocity (0.57–2.13 m/s), and wall heat flux (0.34–0.95 MW/m2). The results showed that the Nusselt number increased with increasing gas flow rate for the 506 μm and 334 μm channels, while the Nusselt number decreased with increasing gas flow for the 222 μm and 140 μm channels. Based on these experimental results, a transition channel diameter of about 235 μm to 260 μm, which distinguishes microchannels from minichannels, was suggested. By observing two-phase flow patterns within the microchannels, viscosity and surface tension were identified as the key factors that caused the heat transfer characteristics to change. In addition, new correlations for the forced convection Nusselt number were developed.

Experimental Investigation and Empirical Correlations of Heat Transfer in Different Regimes of Air–Water Two-Phase Flow in a Horizontal Tube

2016 ◽  
Vol 9 (2) ◽  
Author(s):  
S. A. Nada
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Flow Rate ◽  
Two Phase Flow ◽  
Horizontal Tube ◽  
Flow Regimes ◽  
Phase Flow ◽  
Two Phase

This article reports on the experimental investigation of heat transfer to cocurrent air–water two-phase flow in a horizontal tube. The idea is to enhance heat transfer to the coolant liquid by air injection. Experiments were conducted for different air water ratios in constant temperature heated tube. Visual identification of flow regimes was supplemented. The effects of the liquid and gas superficial velocities and the flow regimes on the heat transfer coefficients were investigated. The results showed that the heat transfer coefficient generally increases with the increase of the injected air flow rate, and the enhancement is more significant at low water flow rates. A maximum value of the two-phase heat transfer coefficient was observed at the transition to wavy-annular flow as the air superficial Reynolds number increases for a fixed water flow rate. It was noticed that the Nusselt number increased about three times due to the injection of air at low water Reynolds number. Correlations for heat transfer by air–water two-phase flow were deduced in dimensionless form for different flow regimes.

Effect of Bubble flow on Heat Transfer Characteristics in Gas-Liquid Two-Phase Flow in a Horizontal Tube Bundle

2020 ◽  
Vol 2020 (0) ◽  
pp. OS12-06
Author(s):  
Kyoya ARAKI ◽  
Hideki MURAKAWA ◽  
Katsumi SUGIMOTO ◽  
Hitoshi ASANO ◽  
Daisuke ITO ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Two Phase Flow ◽  
Tube Bundle ◽  
Horizontal Tube ◽  
Bubble Flow ◽  
Phase Flow ◽  
Heat Transfer Characteristics ◽  
Two Phase ◽  
Transfer Characteristics
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