Studies on Condensation of Refrigerants in a High Aspect Ratio Microchannel and in a Novel Micro-Groove Surface Heat Exchanger: Development of Micro-Condensers in Compact Two Phase Cooling Systems

2007 ◽  
Author(s):  
Serguei Dessiatoun ◽  
Sourav Chowdhury ◽  
Ebrahim Al-Hajri ◽  
Edvin Cetegen ◽  
Michael Ohadi
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Temperature Drop ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Groove Surface ◽  
Heat Transfer Coefficients ◽  
Surface Condenser ◽  
Two Phase Cooling

Three different refrigerants, R134a, R245fa and HFE7100 were analyzed as working fluids for two-phase cooling of high heat flux electronics in a 0.7 mm hydraulic diameter 190 mm long high aspect ratio minichannel and in a newly developed micro-groove surface condenser. The latter comprised of a micro-groove surface with rectangular grooves of 84 μm in hydraulic diameter with an aspect ratio of 10.6 and headers that directed the refrigerant flow into the grooves. It was concluded that in the minichannel R245fa provides higher heat transfer coefficients compared to R134a with a significantly higher pressure drop. The saturation temperature drop in the same channel created a significant temperature drop for HFE7100 that make the application of such minichannels for cross-flow condensers with this fluid unpractical. The microgroove surface condenser provided significantly higher heat transfer coefficients compared to the minichannel condenser. The pressure drop in the micro-groove surface condenser was extremely low and imposed just 1C temperature drop on HFE7100 at it highest heat flux. The mass flux of refrigerant in the micro-groove surface condenser is significantly lower compared to conventional mini and microchannel condensers. In its current configuration, the microgroove surface condenser benefits from the possibility of an increase in mass flux resulting in a significant increase in heat transfer coefficient and just a moderate increase in pressure drop.

Two-Phase Pressure Drop and Boiling Heat Transfer in a Single Horizontal Microchannel

2006 ◽  
Author(s):  
Cheol Huh ◽  
Moo Hwan Kim
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Local Flow ◽  
Heat Transfer Coefficients ◽  
Phase Pressure

With a single microchannel and a series of microheaters made with MEMS technique, two-phase pressure drop and local flow boiling heat transfer were investigated using deionized water in a single horizontal rectangular microchannel. The test microchannel has a hydraulic diameter of 100 μm and length of 40 mm. A real time observation of the flow patterns with simultaneous measurement are made possible. Tests are performed for mass fluxes of 90, 169, and 267 kg/m2s and heat fluxes of from 100 to 600 kW/m2. The experimental local flow boiling heat transfer coefficients and two-phase frictional pressure gradient are evaluated and the effects of heat flux, mass flux, and vapor qualities on flow boiling are studied. Both the evaluated experimental data are compared with existing correlations. The experimental heat transfer coefficients are nearly independent on mass flux and the vapor quality. Most of all correlations do not provide reliable heat transfer coefficients predictions with vapor quality and prediction accuracy. As for two-phase pressure drop, the measured pressure drop increases with the mass flux and heat flux. Most of all existing correlations of two-phase frictional pressure gradient do not predict the experimental data except some limited conditions.

Heat Transfer and Pressure Drop Simulation of CO2-Hydrate Mixture in Tube

2017 ◽  
Vol 25 (01) ◽  
pp. 1750005 ◽  
Author(s):  
Benedict Prah ◽  
Rin Yun
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Volume Fraction ◽  
Flow Characteristics ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Mixture Flow ◽  
Heat Transfer Coefficients ◽  
Two Phases ◽  
Energy Equations

The formation of CO2 hydrate during CO2 transportation presents a complex two-phase flow within tube. A two-dimensional CFD model for CO2 hydrate mixture flow in tube is derived based on the Eulerian multiphase flow modeling approach in which the two phases consist of CO2 gas and CO2 hydrate particles. A coupled Eulerian multiphase and nonisothermal flow model without phase-change is developed based on COMSOL Multiphysics built-in application modes. The model couples the mass, momentum, and energy equations for the two phases to solve the temperature and flow characteristics of the CO2 hydrate mixture flow in tube. CO2 hydrate particles are found to settle down during flow even under high velocity operation. The pressure drop increased linearly with inlet volume fraction from 1.29[Formula: see text]kPa for 0.1–5.2[Formula: see text]kPa for 0.5, and the related overall heat transfer coefficients of the CO2 hydrate mixture computed from the model ranged from 980 to 4000[Formula: see text]W/m2K with variation of CO2 hydrate volume fraction.

Impact of Turbulator Design on the Heat Transfer in a High Aspect Ratio Passage of a Turbine Blade

2014 ◽  
Author(s):  
S. Naik ◽  
S. Retzko ◽  
M. Gritsch ◽  
A. Sedlov
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Transfer Coefficient ◽  
High Aspect Ratio ◽  
Transfer Coefficients ◽  
Average Heat ◽  
Heat Transfer Coefficients ◽  
Trailing Edges

The trailing edge region of gas turbine blades is generally subjected to extremely high external heat loads due to the combined effects of high mach numbers and gas temperatures. In order to maintain the metal temperatures of these trailing edges to a level, which fulfils both the part mechanical integrity and turbine performance, highly efficient and reliable cooling of the trailing edges is required without increasing the coolant consumption. In this paper, the heat transfer and pressure drop characteristic of three different turbulator designs in a very high aspect ratio passage have been investigated. The turbulator designs included angled and tapered ribs, broken discrete ribs and V-shaped small chevrons ribs. The heat transfer and pressure drop characteristics of all the turbulator configurations was initially investigated via numerical predictions and subsequently in a scaled experimental perspex model. The experimental study was conducted for a range of operational Reynolds numbers and the TLC (thermochromic liquid crystal) method was used to measure the detailed heat transfer coefficients on all surfaces of the passage. Pressure taps were located at several locations within the perspex model and both the local and average heat transfer coefficients and pressure loss coefficients were determined. The measured and predicted results show, that for all cases investigated, the local internal heat transfer coefficient, which is driven by the highly three dimensional passage flows, is highly non-uniformly within the passage. The highest overall average heat transfer was obtained for the angled and tapered turbulator. Although the average heat transfer coefficient of the discrete broken turbulator and the small chevron turbulator were slightly lower than the baseline case, they had much higher pressure losses. In terms of the overall non-dimensional performance index, which incorporates both the heat transfer and the pressure drop, it was found that the angled and tapered turbulator gave the best overall performance.

scholarly journals A Novel Generator Design Utilised for Conventional Ejector Refrigeration Systems

Energies ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7705
Author(s):  
Anas F. A. Elbarghthi ◽  
Mohammad Yousef Hdaib ◽  
Václav Dvořák
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Working Fluid ◽  
Convection Coefficient ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
Cold Fluid ◽  
Cold Stream

Ejector refrigeration systems are rapidly evolving and are poised to become one of the most preferred cooling systems in the near future. CO2 transcritical refrigeration systems have inherently high working pressures and discharge temperatures, providing a large volumetric heating capacity. In the current research, the heat ejected from the CO2 gas cooler was proposed as a driving heating source for the compression ejector system, representing the energy supply for the generator in a combined cycle. The local design approach was investigated for the combined plate-type heat exchanger (PHE) via Matlab code integrated with the NIST real gas database. HFO refrigerants (1234ze(E) and 1234yf) were selected to serve as the cold fluid on the generator flowing through three different phases: subcooled liquid, a two-phase mixture, and superheated vapour. The study examines the following: the effectiveness, the heat transfer coefficients, and the pressure drop of the PHE working fluids under variable hot stream pressures, cold stream flow fluxes, and superheated temperatures. The integration revealed that the cold fluid mixture phase dominates the heat transfer coefficients and the pressure drop of the heat exchanger. By increasing the hot stream inlet pressure from 9 MPa to 12 MPa, the cold stream two-phase convection coefficient can be enhanced by 50% and 200% for R1234yf and R1234ze(E), respectively. Conversely, the cold stream two-phase convection coefficient dropped by 17% and 37% for R1234yf and R1234ze(E), respectively. The overall result supports utilising the ejected heat from the CO2 transcritical system, especially at high CO2 inlet pressures and low cold channel flow fluxes. Moreover, R1234ze(E) could be a more suitable working fluid because it possesses a lower pressure drop and bond number.

Heat Transfer in Rotating, Trailing Edge, Converging Channels With Smooth Walls and Pin-Fins

2020 ◽  
Author(s):  
Izzet Sahin ◽  
I-Lun Chen ◽  
Lesley M. Wright ◽  
Je-Chin Han ◽  
Hongzhou Xu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Rotation Number ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Heat Transfer Coefficients ◽  
Pin Fins ◽  
Cooling Passage

Abstract The heat transfer and pressure drop characteristics of a rotating cooling channel that has an angled trapezoidal cross-section and converges from the hub to tip in both the streamwise and spanwise directions are experimentally investigated. The channel is oriented 120° with respect to the direction of rotation to model the geometry of an internal, trailing edge cooling passage. Both the leading and trailing sides of the channel are divided into three and six regions in the spanwise and streamwise directions, respectively. The copper plate method is used to obtain regionally averaged heat transfer coefficients. The pressure drop is measured utilizing pressure taps placed at the inlet and outlet of the channel. Experiments were conducted with the inlet Reynolds number ranging from 10,000 to 40,000. The rotational speed varies from 0 rpm to 300 rpm, resulting in the highest rotation number of 0.21. The effects of full pin-fins on the heat transfer and pressure drop characteristics are obtained and compared to the smooth surface converging channel results. The impact of the convergence, which causes variations of flow and geometric parameters through the passage, such as aspect ratio, Reynolds number, and rotation number, on the heat transfer coefficients and pressure drop are addressed. Results show that due to the 120° channel orientation, rotation has a positive impact on the leading and trailing surface heat transfer. Furthermore, the convergence decreases the aspect ratio while increasing Reynolds number. The convergence significantly enhances heat transfer on both the leading and trailing surfaces along the streamwise and spanwise directions. The convergence also reduces the rotation effect in the streamwise direction for a given mass flow rate.

Heat Transfer in Rotating, Trailing-Edge, Converging Channels With Smooth Walls and Pin-Fins

2021 ◽  
Vol 143 (7) ◽  
Author(s):  
Izzet Sahin ◽  
I-Lun Chen ◽  
Lesley M. Wright ◽  
Je-Chin Han ◽  
Hongzhou Xu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Rotation Number ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Heat Transfer Coefficients ◽  
Pin Fins ◽  
Cooling Passage

Abstract The heat transfer and pressure drop characteristics of a rotating cooling channel that has an angled trapezoidal cross section and converges from the hub to the tip in both the streamwise and spanwise directions are experimentally investigated. The channel is oriented 120 deg with respect to the direction of rotation to model the geometry of an internal, trailing-edge cooling passage. Both the leading and trailing sides of the channel are divided into three and six regions in the spanwise and streamwise directions, respectively. The copper plate method is used to obtain regionally averaged heat transfer coefficients. The pressure drop is measured using pressure taps placed at the inlet and outlet of the channel. Experiments were conducted with the inlet Reynolds number ranging from 10,000 to 40,000. The rotational speed varies from 0 rpm to 300 rpm, resulting in the highest rotation number of 0.21. The effects of full pin-fins on the heat transfer and pressure drop characteristics are obtained and compared to the smooth surface converging channel results. The impact of the convergence, which causes variations of flow and geometric parameters through the passage, such as aspect ratio, Reynolds number, and rotation number, on the heat transfer coefficients and pressure drop are addressed. Results show that due to the 120 deg channel orientation, the rotation has a positive impact on the leading and trailing surface heat transfer. Furthermore, the convergence decreases the aspect ratio while increasing the Reynolds number. The convergence significantly enhances heat transfer on both the leading and trailing surfaces along the streamwise and spanwise directions. The convergence also reduces the rotation effect in the streamwise direction for a given mass flow rate.

Effects of Pressure and a Microporous Coating on HFC-245fa Pool Boiling Heat Transfer

2013 ◽  
Author(s):  
Gilberto Moreno ◽  
Jana R. Jeffers ◽  
Sreekant Narumanchi
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Reduced Pressure ◽  
Heat Transfer Coefficients ◽  
Hfc 134A ◽  
Microporous Coating ◽  
Two Phase Cooling

A study was conducted to experimentally characterize the pool boiling performance of hydrofluorocarbon (HFC)-245fa. The motivation for this research is to characterize the performance of candidate refrigerants for potential use in automotive power electronics two-phase cooling systems. The HFC-245fa pool boiling experiments were conducted using horizontally oriented 1-cm2 heated surfaces to quantify the effects of pressure and a microporous-enhanced coating on heat transfer coefficients and critical heat flux (CHF) values. Experiments were carried out at pressures ranging from 0.15 MPa to 1.1 MPa (reduced pressure range: 0.04–0.31). To enhance boiling heat transfer, a copper microporous coating was applied to the test surfaces. The coating was found to enhance heat transfer coefficients by as much as 430% and CHF by approximately 50%. Increasing pressure decreased the magnitude of the heat transfer coefficient enhancements but had minimal effect on CHF enhancements. The experimental data were then used to generate correlations for the boiling heat transfer coefficients and CHF values. Finally, the performance of HFC-245fa was compared to the performance of hydrofluoroolefin (HFO)-1234yf and HFC-134a at conditions of equivalent saturation temperatures and reduced pressures.

Evaporation Heat Transfer Characteristics on the Outside of Horizontal Smooth, Herringbone and Enhanced Surface 1EHT Tubes

2015 ◽  
Author(s):  
Jian-jun Sun ◽  
Jing-xiang Chen ◽  
David J. Kukulka ◽  
Kan Zhou ◽  
Wei Li ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Smooth Tube ◽  
External Diameter ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Mass Fluxes ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
Enhanced Surface

An experiment investigation was performed using R410A in order to determine the single-phase and evaporation heat transfer coefficients on the outside of (i) a smooth tube; (ii) herringbone tube; and (iii) the newly developed Vipertex enhanced surface 1EHT tube; all with the same external diameter (12.7 mm). The nominal evaporation temperature is 279 K, with inlet and outlet qualities of 0.1 and 0.8. Mass fluxes ranged from 10 to 40 kg m−2s−1. Results suggest that the 1EHT tube has excellent heat transfer performance but a higher pressure drop when compared to a smooth tube. Evaporation heat transfer coefficient for the 1EHT is lower than the herringbone tube and the pressure drop is almost the same.

Forced Convective Boiling of Refrigerant HCFC123 in a Mini-Tube

2010 ◽  
Author(s):  
Koichi Araga ◽  
Keisuke Okamoto ◽  
Keiji Murata
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Pool Boiling ◽  
Constant Heat Flux ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Convective Boiling ◽  
Frictional Pressure Drop ◽  
Heat Transfer Coefficients

This paper presents an experimental investigation of the forced convective boiling of refrigerant HCFC123 in a mini-tube. The inner diameters of the test tubes, D, were 0.51 mm and 0.30 mm. First, two-phase frictional pressure drops were measured under adiabatic conditions and compared with the correlations for conventional tubes. The frictional pressure drop data were lower than the correlation for conventional tubes. However, the data were qualitatively in accord with those for conventional tubes and were correlated in the form φL2−1/Xtt. Next, heat transfer coefficients were measured under the conditions of constant heat flux and compared with those for conventional tubes and for pool boiling. The heat transfer characteristics for mini-tubes were different from those for conventional tubes and quite complicated. The heat transfer coefficients for D = 0.51 mm increased with heat flux but were almost independent of mass flux. Although the heat transfer coefficients were higher than those for a conventional tube with D = 10.3 mm and for pool boiling in the low quality region, they decreased gradually with increasing quality. The heat transfer coefficients for D = 0.30 mm were higher than those for D = 0.51 mm and were almost independent of both mass flux and heat flux.

Experimental Study of Evaporation Heat Transfer Characteristics and Pressure Drops of R410A and R134a in a Multiport Mini-Channel

2009 ◽  
Author(s):  
Jatuporn Kaew-On ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
R 134A

The evaporation heat transfer coefficients and pressure drops of R-410A and R-134a flowing through a horizontal-aluminium rectangular multiport mini-channel having a hydraulic diameter of 3.48 mm are experimentally investigated. The test runs are done at refrigerant mass fluxes ranging between 200 and 400 kg/m2s. The heat fluxes are between 5 and 14.25 kW/m2, and refrigerant saturation temperatures are between 10 and 30 °C. The effects of the refrigerant vapour quality, mass flux, saturation temperature and imposed heat flux on the measured heat transfer coefficient and pressure drop are investigated. The experimental data show that in the same conditions, the heat transfer coefficients of R-410A are about 20–50% higher than those of R-134a, whereas the pressure drops of R-410A are around 50–100% lower than those of R-134a. The new correlations for the evaporation heat transfer coefficient and pressure drop of R-410A and R-134a in a multiport mini-channel are proposed for practical applications.

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