Solids Deposition during “Cold Flow” of Wax−Solvent Mixtures in a Flow-loop Apparatus with Heat Transfer

2009 ◽  
Vol 23 (6) ◽  
pp. 3184-3194 ◽  
Author(s):  
Hamid O. Bidmus ◽  
Anil K. Mehrotra
Keyword(s):  
Heat Transfer ◽  
Solvent Mixtures ◽  
Flow Loop ◽  
Cold Flow ◽  
Solids Deposition

Numerical Analysis of Heat Transfer in the Concentric Heat Exchanger

2013 ◽  
Vol 275-277 ◽  
pp. 572-575
Author(s):  
Hung Chien Chen ◽  
Tzu Chen Hung ◽  
Yi Feng Chen
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Three Dimensional ◽  
Flow Channel ◽  
Computational Time ◽  
Space Length ◽  
Flow Paths ◽  
Cold Flow ◽  
Angle Space ◽  
Fin Thickness

The computational fluid dynamics (CFD) software is used to compute three-dimensional concentric heat exchanger in this research. In order to reduce the burden of the computational time, the concentric heat exchanger is simplified sector of 5° for the regular arrangement of internal shape. The working fluids for hot flow and cold flow are helium and molten salt individually. The arrangements for hot and cold flow paths within a heat exchanger is opposite. This study is mainly focused on the distribution of field for the two layers of concentric heat exchanger. The width of the flow channel as well as the length, pitch, thickness and angle of fin have been changing to analyze the effectiveness-NTU method. The results showed that the best heat transfer of fin thickness, angle, space, length, and flow channel are under 5mm, 5°, 8mm, 44mm, and 12mm, respectively.

Thermal Management of Time-Varying High Heat Flux Electronic Devices

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
T. David ◽  
D. Mendler ◽  
A. Mosyak ◽  
A. Bar-Cohen ◽  
G. Hetsroni
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Heat Fluxes ◽  
Vapor Quality ◽  
Flow Loop ◽  
Pin Fin ◽  
The Heat Transfer Coefficient

The thermal characteristics of a laboratory pin-fin microchannel heat sink were empirically obtained for heat flux, q″, in the range of 30–170 W/cm2, mass flux, m, in the range of 230–380 kg/m2 s, and an exit vapor quality, xout, from 0.2 to 0.75. Refrigerant R 134a (HFC-134a) was chosen as the working fluid. The heat sink was a pin-fin microchannel module installed in open flow loop. Deviation from the measured average temperatures was 1.5 °C at q = 30 W/cm2, and 2.0 °C at q = 170 W/cm2. These results indicate that use of pin-fin microchannel heat sink enables keeping an electronic device near uniform temperature under steady state and transient conditions. The heat transfer coefficient varied significantly with refrigerant quality and showed a peak at an exit vapor quality of 0.55 in all the experiments. At relatively low heat fluxes and vapor qualities, the heat transfer coefficient increased with vapor quality. At high heat fluxes and vapor qualities, the heat transfer coefficient decreased with vapor quality. A noteworthy feature of the present data is the larger magnitude of the transient heat transfer coefficients compared to values obtained under steady state conditions. The results of transient boiling were compared with those for steady state conditions. In contrast to the more common techniques, the low cost technique, based on open flow loop was developed to promote cooling using micropin fin sinks. Results of this experimental study may be used for designing the cooling high power laser and rocket-born electronic devices.

Internal Condensing Flows Inside a Vertical Pipe: Experimental/Computational Investigations of Effects of Constrained and Natural Exit Conditions

2005 ◽  
Author(s):  
A. Narain ◽  
A. Siemionko ◽  
J. H. Kurita ◽  
T. W. Ng ◽  
N. Kim ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Power Plants ◽  
Computational Simulation ◽  
Vertical Tube ◽  
Film Condensation ◽  
Flow Loop ◽  
Transfer Rates ◽  
Application Systems ◽  
Condensing Flows ◽  
Internal Condensing Flows

The flow and heat transfer rates inside a condenser depend on the specification of inlet, wall, and exit conditions. For steady/quasi-steady internal condensing flows (that involve compressible vapor at low Mach Numbers), the vapor’s ability to change its density — and hence interfacial mass transfer rates and associated locations of the interface — allows the flow to have a rather significant dependence on exit conditions. Both experimental and direct computational simulation results presented here show that this is indeed the case for flows of pure vapor experiencing film condensation on the inside walls of a vertical tube. In applications, the totality of boundary conditions are determined not only by the condenser; but also by the flow-loop (or the system) — of which the condenser is only a part. Therefore, the results outlined here should contribute towards a better understanding of the behavior (particularly the extent to which vapor compressibility effects affect the flow regimes of operation — i.e. annular, plug/churn, etc.) and response (transients due to start-up, system instabilities, etc.) of condensers in application systems (e.g. Rankine Cycle power plants, Capillary Pumped Loops, Looped Heat Pipes, etc.). In this connection, an experimental example of a relevant system instability is presented here. In summary, the experimental results presented here, and computational results presented elsewhere, reinforce the fact that there exist multiple steady solutions (with different heat transfer rates) for different exit conditions and that there also exists a “natural” steady solution for straight vertical condensers (circular and rectangular cross-sections).

Convective Flow and Heat Transfer Inside a Beta Type Stirling Engine Based on Control Volume Finite Element Method

2016 ◽  
Author(s):  
Ramla Gheith ◽  
Houda Hachem ◽  
Nessrine Zahi ◽  
Fethi Aloui ◽  
Sassi Ben Nasrallah
Keyword(s):  
Heat Transfer ◽  
Control Volume ◽  
Stirling Engine ◽  
Engine Compartment ◽  
Heat Transfer Characteristics ◽  
Cold Flow ◽  
Flow And Heat Transfer ◽  
Compression And Expansion ◽  
Instantaneous Temperature ◽  
Control Volume Finite Element

In this manuscript, a beta type Stirling engine is numerically modulated. The flow and heat transfer characteristics are finely considered in each engine compartment. The PV diagram is plotted to determine the produced work by the engine. The instantaneous temperature in compression and expansion spaces present a larger variations that recorded in all treated heat exchangers. It is observed that the porous media dumps the oscillations. The temperature evolution is plotted for 100 successive Stirling cycles in order to observe its stability in each Stirling compartments. During the first 10 cycles, the regenerator temperature is influenced by the cold flow pumped by the cooler. It reaches thermal equilibrium after only 10 cycles. From this point, the regenerator temperature undergoes a slight increase to stabilize at 1.05 * Ta.

On-Sun Testing of a High Temperature Bladed Solar Receiver and Transient Efficiency Evaluation Using Air

2018 ◽  
Author(s):  
Jesus D. Ortega ◽  
Sagar D. Khivsara ◽  
Joshua M. Christian ◽  
Pradip Dutta ◽  
Clifford K. Ho
Keyword(s):  
Heat Transfer ◽  
Light Trapping ◽  
Heat Fluxes ◽  
Heat Transfer Fluid ◽  
Test Facility ◽  
Flow Loop ◽  
Solar Absorptance ◽  
Cfd Models ◽  
Efficiency Increase ◽  
Solar Receiver

Prior research at Sandia National Laboratories showed the potential advantages of using light-trapping features which are not currently used in direct tubular receivers. A horizontal bladed receiver arrangement showed the best potential for increasing the effective solar absorptance by increasing the ratio of effective surface area to the aperture footprint. Previous test results and models of the bladed receiver showed a receiver efficiency increase over a flat receiver panel of ∼ 5–7% over a range of average irradiances, while showing that the receiver tubes can withstand temperatures > 800 °C with no issues. The bladed receiver is being tested at various peak heat fluxes ranging 75–150 kW/m2 under transient conditions using Air as a heat transfer fluid at inlet pressure ∼250 kPa (∼36 psi) using a regulating flow loop. The flow loop was designed and tested to maintain a steady mass flow rate for ∼15 minutes using pressurized bottles as gas supply. Due to the limited flow-time available, a novel transient methodology to evaluate the thermal efficiencies is presented in this work. Computational fluid dynamics (CFD) models are used to predict the temperature distribution and the resulting transient receiver efficiencies. The CFD simulations results using air as heat transfer fluid have been validated experimentally at the National Solar Thermal Test Facility in Sandia National Labs.

An Experimental Study on the Effect of Configuration of Multiple Microchannels on Heat Removal for Electronic Cooling

2010 ◽  
Author(s):  
Jingru Zhang ◽  
Shaurya Prakash ◽  
Yogesh Jaluria ◽  
Lei Lin
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Heat Removal ◽  
Electronic Cooling ◽  
Heat Sinks ◽  
Flow Loop ◽  
Labview Software ◽  
Chemical Etch ◽  
Potential Applications

This paper presents the design, fabrication, and characterization of three different configurations of multiple microchannel heat sink devices to improve their overall cooling efficiency for potential applications in electronic cooling. A fabrication and packaging process based on standard UV-lithography, wet etching, and bonding was developed to allow a rapid parametric study. An anisotropic chemical etch with potassium hydroxide, water, and isopropanol is used to fabricate microchannels on (110)-oriented silicon wafers. PDMS (Polydimethylsiloxane) was tested as the cover of microchannels due to its mechanical flexibility. It is transparent so that the microchannel flow can be visualized using a microscope. An open flow loop, which consists of syringe pump and a power supply, was designed to test the heat sinks with different configurations. Temperature data were collected at different locations by a Data Acquisition (DAQ) system and recorded by Labview software to investigate the heat transfer characteristics of the heat sink. Three heat sinks, with different configurations, were tested. They all included microchannels of width 50 μm, depth 60 μm, and fin width 200 μm. Some Typical results on heat transfer are presented, along with discussion on the efficiency for heat removal.

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