scholarly journals Heat transfer mode shift to adiabatic thermalization in near-critical carbon dioxide under terrestrial conditions

2021 ◽  
Author(s):  
Anatoly Parahovnik ◽  
Yoav Peles
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Acoustic Waves ◽  
Reduced Pressure ◽  
Piston Effect ◽  
Mode Shift ◽  
Transfer Mode ◽  
Sensing Technology ◽  
Critical Opalescence ◽  
Microgravity Conditions

Abstract Heat transfer via acoustic waves is referred to as adiabatic thermalization or the piston effect. Until now, adiabatic thermalization was believed to be a secondary effect that mostly occurs under microgravity conditions and is readily overpowered by mixing due to gravitational forces. However, this work revealed that in microsystems, adiabatic thermalization is a dominant heat transfer mechanism. A substantial shift in thermalization modes from vaporization to acoustic waves was observed through critical opalescence temperature measurements of carbon dioxide (CO2). The contribution of the piston’s effect increased from 4.3–77.6% when the reduced pressure increased from 0.86 to 0.99. The findings are used to explain the observed heat transfer enhancement that occurred concurrently with the reduction in the void fraction. Revealing the nature of the piston effect to enhance heat transfer will advance copious technological fields like space exploration, fusion reactors, data centers, electronic devices, and sensing technology.

scholarly journals The Piston Effect inside a microchannel with Carbon Dioxide near Critical conditions

2022 ◽  
Author(s):  
Uday Manda ◽  
Anatoly Parahovnik ◽  
Yoav Peles
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Acoustic Waves ◽  
Temperature Increase ◽  
Fluid Model ◽  
Heated Surface ◽  
Rapid Expansion ◽  
Critical Conditions ◽  
Pressure Waves ◽  
Piston Effect

Abstract Heat transfer near the critical condition of Carbon Dioxide due to thermo-acoustic waves in a 100-µm high microchannel was numerically studied. The temperature at a point farthest away from the heated surface was compared between computational fluid dynamics (CFD) models and a pure conduction model. The comparison revealed that the CFD model predicted a temperature increase furthest from the surface much faster than the time constant required for such increase purely by conduction. It is believed that another heat transfer process, termed the piston effect (PE), which is associated with pressure waves in the fluid, was responsible for this increase. Explicit unsteady methodology in the fluid model indicated that propagation of pressure waves due to a rapid expansion of the boundary layer and the associate change in the fluid density distribution resulted in this temperature raise. It was confirmed that natural convection wasn’t responsible for the temperature increase under quiescent conditions. In addition, it was discovered that the PE is significant for certain forced convection conditions.

Heat Transfer to Carbon Dioxide in the Immediate Vicinity of the Critical Point

1969 ◽  
Vol 91 (1) ◽  
pp. 16-20 ◽  
Author(s):  
N. M. Schnurr
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Critical Point ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Reduced Pressure ◽  
Circular Duct ◽  
Heat Transfer Coefficients ◽  
Thermodynamic Critical Point

Local heat-transfer coefficients are measured for carbon dioxide very near the thermodynamic critical point for flow through an electrically heated circular duct. The experiments cover a range of fluid bulk temperatures spanning the transposed critical temperature and of pressure from 1075 to 1110 psia (reduced pressure from 1.003 to 1.03). The data are correlated by the equation Nuz = 0.0266 Rez0.77 Prw0.55 where the Prandtl number is evaluated at the wall temperature and Nusselt and Reynolds numbers are evaluated at a variable reference temperature. The dominant heat transfer mechanism is found to be turbulent forced convection. There is evidence that free convection effects are also present.

scholarly journals The effect of reduced pressure on carbon dioxide flow boiling heat transfer in minichannels

2018 ◽  
Vol 70 ◽  
pp. 02012
Author(s):  
Dariusz Mikielewicz ◽  
Blanka Jakubowska
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Carbon Dioxide ◽  
Boiling Heat Transfer ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Phase Flow ◽  
Two Phase ◽  
Reduced Pressure ◽  
Flow Boiling Heat Transfer

In the paper presented are the results of the study on the effect of reduced pressure on flow boiling heat transfer data in minichannels as well as conventional ones. That effect renders that most of heat transfer correlations fail to return appropriate results of predictions. Mostly they have been developed for the reduced pressures from the range 0.1-0.3. The special correction has been postulated to the in-house model of flow boiling and condensation which modifies the two-phase flow multiplier as well as the temperature gradient in pool boiling. Four two-phase flow multiplier models were tested for this purpose, i.e. due to Friedel, Tran, Müller-Steinhagen and Heck and finally its in-house modification for applicability to minichannels. The model has been tested against a large selection of experimental data collected from various researchers to investigate the sensitivity of the in-house developed model. The collected experimental data came from various studies from literature and were conducted for the full range of quality variation and a wide range of mass velocity and saturation temperatures. In the work are presented the results of calculations obtained using the in-house developed semi empirical model on selected experimental flow boiling data related to carbon dioxide.

scholarly journals The flame spectrum of carbon monoxide

1940 ◽  
Vol 176 (967) ◽  
pp. 505-521 ◽  
Keyword(s):  
Carbon Dioxide ◽  
Carbon Monoxide ◽  
Electronic State ◽  
Excited Electronic State ◽  
Combustion Process ◽  
Wave Number ◽  
Band Spectrum ◽  
Liquid Form ◽  
Triangular Form ◽  
Reduced Pressure

The spectrum of the flame of carbon monoxide burning in air and in oxygen at reduced pressure has been photographed on plates of high contrast which display the band spectrum clearly above the continuous background. Greater detail has been obtained than has been recorded previously and new measurements are given. The structure of the spectrum has been studied systematically. It is shown that the bands occur in pairs with a separation of about 60 cm. -1 , this separation being due probably to the rotational structure. Various wave-number differences are found to occur frequently, and many of the strong bands are arranged in arrays using intervals of 565 and 2065 cm. -1 . The possible origin of the spectrum is discussed. The choice of emitter is limited to a polyatomic oxide of carbon, of which carbon dioxide is the most likely. The spectrum of the suboxide C 3 O 2 shows some resemblance to the flame bands, but this molecule is improbable as the emitter on other grounds. A peroxide C0 3 is also a possibility, but no evidence for the presence of this has been obtained from experiments on the slow combustion of carbon monoxide. Carbon dioxide in gaseous or liquid form is transparent through the visible and quartz ultra-violet, and the flame bands are not obtained from CO 2 in discharge tubes. Comparison with the Schumann-Runge bands of oxygen shows that it is possible that the flame bands may form part of the absorption band system of CO 2 which is known to exist below 1700 A if there is a big change in shape or size of the molecule in the two electronic states. The electronic energy levels of CO 2 are discussed. Since normal CO 2 is not built up from normal CO and oxygen, an electronic rearrangement of the CO 2 must occur after the combustion process. Mulliken has suggested that the molecule in the first excited electronic state, corresponding to absorption below 1700 A, may have a triangular form. The frequencies obtained from the flame bands are compared with the infra-red frequencies of CO 2 . The 565 interval may be identified with the transverse vibration v 2 , indicating that the excited electronic state is probably triangular in shape. The 2065 interval cannot, however, be identified with the asymmetric vibration v 3 with any certainty. If the excited electronic state of CO 2 is triangular, then molecules formed during the combustion by transitions from this level to the ground state may be “vibrationally activated”. This is probably the reason for many of the peculiarities of the combustion of carbon monoxide.

Comparison of Existing Supercritical Carbon Dioxide Heat Transfer Correlations for Horizontal and Vertical Bare Tubes

2012 ◽  
Author(s):  
Prabu Surendran ◽  
Sahil Gupta ◽  
Tiberiu Preda ◽  
Igor Pioro
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Wall Temperature ◽  
Statistical Error ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Bulk Fluid ◽  
Heat Transfer Correlations ◽  
Supercritical Carbon

This paper presents a thorough analysis of ability of various heat transfer correlations to predict wall temperatures and Heat Transfer Coefficients (HTCs) against experiments on internal forced-convective heat transfer to supercritical carbon dioxide conducted by Koppel [1], He [2], Kim [3] and Bae [4]. It should be noted the Koppel dataset was taken from a paper which used the Koppel data but was not written by Koppel. All experiments were completed in bare tubes with diameters from 0.948 mm to 9 mm for horizontal and vertical configurations. The datasets contain a total of 1573 wall temperature points with pressures ranging from 7.58 to 9.59 MPa, mass fluxes of 400 to 1641 kg/m2s and heat fluxes from 20 to 225 kW/m2. The main objective of the study was to compare several correlations and select the best of them in predicting HTC and wall temperature values for supercritical carbon dioxide. This study will be beneficial for analyzing heat exchangers involving supercritical carbon dioxide, and for verifying scaling parameters between CO2 and other fluids. In addition, supercritical carbon dioxide’s use as a modeling fluid is necessary as the costs of experiments are lower than supercritical water. The datasets were compiled and calculations were performed to find HTCs and wall and bulk-fluid temperatures using existing correlations. Calculated results were compared with the experimental ones. The correlations used were Mokry et al. [5], Swenson et al. [6] and a set of new correlations presented in Gutpa et al. [7]. Statistical error calculations were performed are presented in the paper.

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