The Effect of Initial Charge on the Steady-State Operating Performance of a Capillary Assisted Thermosyphon

2005 ◽  
Author(s):  
V. Tudor ◽  
M. Cerza ◽  
A. N. Smith ◽  
C. T. Conroy
Keyword(s):  
Flat Plate ◽  
Electric Propulsion ◽  
Operating Temperature ◽  
Working Fluid ◽  
Cold Plate ◽  
Capillary Pumped Loop ◽  
Forced Circulation ◽  
Fill Ratio ◽  
Initial Charge ◽  
Wick Structure

The future capabilities of naval ships will be directly related to the electronic components used in advanced radar systems, fire control systems, electric propulsion and electric weapons. Modern electronics continue to grow in speed and functionality but shrink in size and mass, causing the power density to dramatically increase. Thermal management is becoming a major issue for the modern electronic Navy. An experimental investigation on the effect of liquid charge in a capillary assisted thermosyphon (CAT) loop for the shipboard cooling of electronics components has been conducted. The employed CAT loop differs from the capillary pumped loop or loop heat pipe system, in that the basic cooling loop is based on a thermosyphon. A wick structure located on the walls of the evaporator plate provides the capillary assistance needed to spread the working fluid (i.e. water) across the flat plate evaporator in the areas under the heat sources. This differs from a capillary pumped loop in that the wick structure does not produce a significant capillary pumping head from the liquid return to the vapor outlet side of the evaporator. The forced circulation in the CAT loop is caused by a gravity head between the condenser cold plate and the flat plate evaporator. The influence of the liquid charge on the CAT loop performance was studied for a fixed sink temperature and a range of heat inputs from 250W to 1000W. The initial liquid charge was varied from 50 ml to 200 ml (i.e. 16% to 24% evaporator fill ratio). The evaporator fill ratio was defined in this study as the ratio of the initial charge to the total volume of the evaporator. The condenser cold plate cooling water flow rate was set to 63.088 ml/sec. The CAT flat plate evaporator performed very well under this range of heat inputs, sink temperature, and initial charges. The experimental results obtained indicated that as heat input and the liquid charge increased or decreased above/below an optimum value, the operating temperature in the evaporator increased. The CAT loop flow dynamics also changed as a function of the initial liquid charge. Overall these effects did not hinder the thermal performance as measured by the internal operating temperature of the evaporator. An optimal charge was observed at an evaporator fill ratio of 40% (i.e. 125ml).

Investigation of a Capillary Assisted Thermosyphon (CAT) for Shipboard Electronics Cooling

Volume 4 ◽  
2004 ◽  
Author(s):  
E. H. Larsen ◽  
M. Cerza ◽  
A. N. Smith ◽  
C. Thomas Conroy
Keyword(s):  
Flat Plate ◽  
Heat Input ◽  
Power Dissipation ◽  
Water Flow Rate ◽  
Cooling Water ◽  
Electronics Cooling ◽  
Working Fluid ◽  
Cold Plate ◽  
Capillary Pumped Loop ◽  
Forced Circulation

As microprocessors shrink in size and increase in power dissipation levels, the current need for advanced electronics cooling techniques is paramount since power dissipation levels are rapidly exceeding the capabilities of forced air convection cooling. This paper reports an investigation of using a capillary assisted thermosyphon for the shipboard cooling of electronics components. The capillary assisted thermosyphon differs from the capillary pumped loop or loop heat pipe system in that the basic cooling loop is based on a thermosyphon. The capillary assist comes from the fact that there is a wicking structure in the flat evaporator plate, however, the wicking structure is there to spread the working fluid across the flat plate evaporator in the areas under the heat sources. This differs from a capillary pumped loop in that the wick structure does not produce a capillary pumping head from the liquid return to the vapor outlet side of the evaporator. In fact, the liquid return and vapor outlet are almost at the same pressure. The forced circulation in the thermosyphon is caused by a gravity head between the condenser cold plate and the flat plate evaporator. An experimental facility for conducting research on capillary assisted thermosyphon was developed. In order to simulate the shipboard cooling water encountered at various locations of the ocean, the heat sink temperature of the facility could be varied. A vertical flat plate, CAT evaporator was designed and tested under thermal sink temperatures of 4, 21 and 37°C. The condenser cold plate cooling water flow rate varied from 0.38 to 3 GPM. The heat input varied from 250 to 1500 W evenly spread over the area of the evaporator. The CAT flat plate evaporator performed very well under this range of heat inputs, sink temperatures, and cold plate flow rates. The main result obtained showed that as heat input increased the amount of subcooling between the evaporator vapor outlet line and liquid return line increased. This subcooling did not hinder thermal performance as measured by the internal operating temperature.

Start Up and Transient Response to Power Input of a Capillary Assisted Thermosyphon for Shipboard Electronics Cooling

2010 ◽  
Author(s):  
V. Tudor ◽  
M. Cerza
Keyword(s):  
Steady State ◽  
Flat Plate ◽  
Transient Response ◽  
Flow Rate ◽  
Heat Input ◽  
Electric Propulsion ◽  
Electronics Cooling ◽  
Working Fluid ◽  
Cold Plate ◽  
Start Up

The future capabilities of naval ships will be directly related to the electronic components used in advanced radar systems, fire control systems, electric propulsion and even electric weapons. The next generation of naval warships will fall under the concept of an all electric ship, where turbines convert all the power produced by the engine into electricity. This electrical power can then be distributed given the ship’s mission and operating profile. The current need for advanced electronics cooling techniques is paramount since power dissipation levels are rapidly exceeding the capabilities of forced air convection cooling. This paper reports an experimental investigation of the start-up and transient response to heat load change of a capillary assisted thermosyphon (CAT) for the shipboard cooling of electronics components. The capillary assisted thermosyphon differs from a capillary pumped loop or loop heat pipe system in that the basic cooling-loop is based on a thermosyphon. The capillary assist comes from the fact that there is a wicking structure in the flat evaporator plate. The wicking structure allows uniformly spread of the working fluid across the flat plate evaporator in the areas under the heat sources as well as providing additional capillary pumping assist to the loop. A vertical flat plate, CAT evaporator was designed and tested under a fixed thermal sink temperature of 21°C. The condenser cold plate cooling water flow rate was fixed as 3.785 liters per minute (i.e. 1 gpm). The heat input varied from 250 to 1000W — evenly spread over the area of the evaporator. The CAT flat plate evaporator performed very well under this range of heat inputs, sink temperature, and cold plate flow rate. The main result obtained showed that the CAT loop reached steady state operation within 10 min. to 15 min. The average plate temperature did not exceed 70°C for the maximum heat input of 1000W. The CAT evaporator operating temperature increased with increasing heat input for all conditions tested and reached 60°C at 1000W. The continuous and stable operation of the CAT loop during start-up, steady-state and during transient/sudden heat input variations indicates that the CAT loop is a viable solution for high flux electronics components cooling.

The Effect of Ship Tilt and Pitch on a Capillary Assisted Thermosyphon (CAT) for Shipboard Electronics Cooling

2003 ◽  
Author(s):  
E. H. Larsen ◽  
A. N. Smith ◽  
M. Cerza ◽  
C. Thomas Conroy
Keyword(s):  
Flat Plate ◽  
Heat Input ◽  
Power Dissipation ◽  
Cooling Water ◽  
Electronics Cooling ◽  
Working Fluid ◽  
Cold Plate ◽  
Capillary Pumped Loop ◽  
Flat Evaporator ◽  
Vertical Flat Plate

As microprocessors shrink in size and increase in power dissipation levels, the current need for advanced electronics cooling techniques is paramount. Power dissipation levels are rapidly exceeding the capabilities of forced air convection cooling. This paper reports an investigation of using a capillary assisted thermosyphon (CAT) for the shipboard cooling of electronics components. The CAT differs from the capillary pumped loop (CPL) or loop heat pipe (LHP) system in that the basic cooling loop is based on a thermosyphon. The capillary assist comes from the fact that there is a wicking structure in the flat evaporator plate. The wicking structure is there to spread the working fluid across the vertical flat plate evaporator to the areas under the heat sources. This differs from a capillary pumped loop in that the capillary pumping action of the wick structure does not produce the sole pumping head from the liquid return to the vapor outlet side of the evaporator. In fact, the liquid return and vapor outlet are almost at the same pressure. The forced circulation in the thermosyphon is caused by a gravity head between the condenser cold plate and the flat plate evaporator. An experimental facility for conducting research on a CAT was developed. In order to simulate the shipboard cooling water encountered at various locations of the ocean, the heat sink temperature of the facility was varied. A vertical flat plate, CAT evaporator was designed and tested with a thermal sink temperature of 21° C. The condenser cold plate cooling water flowrate was set at 3.8 lpm. The heat input was held constant at 1500 W for the independent tilt and pitch cases. For the extreme tilt and pitch combined case, the heat input varied from 400 to 2000 W. The flat evaporator plate was tilted from side to side over a range +/− 45 degrees from vertical and the plate was pitched fore and aft over a range of +/− 45 degrees. This tilt and pitch orientation was to simulate that orientation which a ship might undergo in various sea states. In addition an extreme case which consisted of a 45 degree tilt and a 45 degree pitch was tested and compared to the normal vertical geometry. Results indicate that the CAT loop was very robust and handled all geometric orientations with minimal degradation in operating temperature performance.

An Investigation of Flat-Plate Oscillating Heat Pipes

2010 ◽  
Author(s):  
Peng Cheng ◽  
Scott Thompson ◽  
Joe Boswell ◽  
Hongbin Ma
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Flat Plate ◽  
Heat Transfer Performance ◽  
Operating Temperature ◽  
Pure Water ◽  
Heat Pipes ◽  
Copper Plate ◽  
Working Fluid ◽  
Transfer Performance

The heat transfer performance of flat-plate oscillating heat pipes (FP-OHPs) was investigated experimentally and theoretically. Two layers of channels were created by machining grooves on both sides of copper plate, in order to increase the channel number per unit volume. The channels had rectangular cross-sections with hydraulic diameters ranging from 0.762 mm to 1.389 mm. Acetone, water and diamond/acetone, gold/water and diamond/water nanofluids were tested as working fluids. It was found that the FP-OHP’s thermal resistance depended on the power input and operating temperature. The FP-OHP charged with pure water achieved a thermal resistance of 0.078°C/W while removing 560 W with a heat flux of 86.8 W/cm2. The thermal resistance was further decreased when nanofluid was used as the working fluid. A mathematical model predicting the heat transfer performance was developed to predict the effects of channel dimension, heating mode, working fluid and operating temperature on the thermal performance of the FP-OHP. Results presented here will assist in optimization of the FP-OHP and provide a better understanding of heat transfer mechanisms occurring in an OHPs.

Experimental Investigation of a Flat-Plate Oscillating Heat Pipe With Groove-Enhanced Minichannels

2020 ◽  
Vol 12 (6) ◽  
Author(s):  
Matthew J. Rhodes ◽  
Scott M. Thompson
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Heat Pipe ◽  
Operating Temperature ◽  
Operating Conditions ◽  
Working Fluid ◽  
Oscillating Heat Pipe ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Wide Range

Abstract The thermal and capillary performance of a groove-enhanced, or “microchannel-embedded,” flat-plate oscillating heat pipe (MC FP-OHP) was experimentally investigated while varying heating width, orientation, working fluid and operating temperature. The copper MC FP-OHP possessed two layers of 1.02 × 1.02 mm2 square channels, with the center 14 channels possessing two embedded microchannels (0.25 × 0.13 mm2) aligned coaxially with the primary minichannels. A FP-OHP without embedded microchannels, but with deeper minichannels (DC FP-OHP), was also tested for comparison. The FP-OHPs were filled with Novec 7200 or water (both at 80% ± 2% by volume), and the heating widths were varied between full-width and localized configurations: 38.71 cm2 and 14.52 cm2, respectively. Experimental results demonstrate that the MC FP-OHP is significantly less sensitive to operating orientation and can perform with less detriment as heat flux increases. The MC FP-OHP has a lower startup heating requirement and provides more fluid wetting along the FP-OHP structure—which is advantageous for pumping liquid from the evaporator to the condenser. The MC FP-OHP has enhanced convective heat transfer during operation, as it was observed to have similar or lower thermal resistances to that of the DC FP-OHP for a wide range of operating conditions. The groove-enhanced minichannel within the MC FP-OHP also provides for enhanced heat transfer because there being more thin-film evaporation sites and vapor–liquid mixing between the minichannel and microchannels.

First and Second Law Analysis of a Flat Plate Collector Working With Nanofluids

2018 ◽  
Author(s):  
M. T. Nitsas ◽  
I. P. Koronaki ◽  
L. Prentza
Keyword(s):  
Flat Plate ◽  
Second Law Of Thermodynamics ◽  
Climatic Conditions ◽  
Working Fluid ◽  
Second Law ◽  
Inlet Temperature ◽  
Water Tank ◽  
Systems Quality ◽  
Typical Day ◽  
Flat Plate Collector

The utilization of solar energy in thermal energy systems was and always be one of the most effective alternative to conventional energy resources. Energy efficiency is widely used as one of the most important parameters in order to evaluate and compare thermal systems including solar collectors. Nevertheless, the first law of thermodynamics is not solely capable of describing the quantitative and qualitative performance of such systems and thus exergy efficiency is used so as to introduce the systems’ quality. In this work, the performance of a flat plate solar collector using water based nanofluids of different nanoparticle types as a working fluid is analyzed theoretically under the climatic conditions in Greece based on the First and Second Law of Thermodynamics. A mathematical model is built and the model equations are solved iteratively in a MATLAB code. The energy and exergy efficiencies as well as the collector losses coefficient for various parameters such as the inlet temperature, the particles concentration and type are determined. Moreover, a dynamic model is built so as to determine the performance of a flat plate collector working with nanofluids and the useful energy that can be stored in a water tank. The exergy destruction and exergy leakage are determined for a typical day in summer during which high temperatures and solar intensity values are common for the Greek climate.

Heat Transport Limitation of a Triangular Micro Heat Pipe

2003 ◽  
Author(s):  
D. Sugumar ◽  
Kek Kiong Tio
Keyword(s):  
Heat Pipe ◽  
Heat Transport ◽  
Operating Temperature ◽  
Working Fluid ◽  
Transport Capacity ◽  
Condenser Section ◽  
Micro Heat Pipe ◽  
Evaporator Section ◽  
Higher Temperature ◽  
Specific Temperature

A micro heat pipe will operate effectively by achieving its maximum possible heat transport capacity only if it is to operate at a specific temperature, i.e., design temperature. In reality, micro heat pipe’s may be required to operate at temperatures different from the design temperature. In this study, the heat transport capacity of an equilateral triangle micro heat pipe is investigated. The micro heat pipe is filled optimally with working fluid for a specific design temperature and operated at different operating temperatures. For this purpose, water, pentane and acetone was selected as the working fluids. From the numerical results obtained, it shows that the optimal charge level of the micro heat pipe is dependent on the operating temperature. Furthermore, the results also shows that if the micro heat pipe is to be operated at temperatures other than its design temperature, its heat transport capacity is limited by the occurrence of flooding at the condenser section or dryout at the evaporator section, depending on the operating temperature and type of working fluid. It is observed that when the micro heat pipe is operated at a higher temperature than its design temperature, the heat transport capacity increases but limited by the onset of dryout at the evaporator section. However, the heat transport capacity decreases if it is to be operated at lower temperatures than its design temperature due to the occurrence of flooding at condenser end. From the results obtained, we can conclude that the performance of a micro heat pipe is decreased if it is to be operated at temperatures other than its design temperature.

Theoretical Considerations of Combined Thermal and Mass Transfer From a Vertical Flat Plate

1956 ◽  
Vol 23 (2) ◽  
pp. 295-301
Author(s):  
E. V. Somers
Keyword(s):  
Mass Transfer ◽  
Flat Plate ◽  
Fluid Motion ◽  
Practical Case ◽  
Forced Circulation ◽  
Evaporation And Condensation ◽  
Mass Transfer Processes ◽  
Convective Thermal ◽  
Theoretical Considerations ◽  
Vertical Flat Plate

Abstract In free-convective processes involving both thermal and mass transfer, since the driving force for the fluid motion has its source solely in the density difference from ambient, it is necessary to consider the thermal and mass-transfer processes simultaneously in solving any given problem. The present problem involves evaporation and condensation phenomena associated with free-convective thermal and mass transfer from a wetted isothermal vertical flat plate to a gas at an ambient temperature and mass concentration different from that on the plate. This problem presents itself in the practical case of vaporization cooling of equipment without forced circulation of the ambient gas.

scholarly journals The Effect of Sink Temperature on a Capillary Pumped Loop Employing a Flat Evaporator and Shell and Tube Condenser

2001 ◽  
Author(s):  
M. Cerza ◽  
R. C. Herron ◽  
M. J. Harper
Keyword(s):  
Flat Plate ◽  
Heat Input ◽  
Heat Sink ◽  
Cooling Water ◽  
Large Degree ◽  
Heat Fluxes ◽  
Capillary Pumped Loop ◽  
Flat Evaporator ◽  
Conducting Research ◽  
Tube Condenser

Abstract An experimental facility for conducting research on capillary pumped loop (CPL) systems was developed. In order to simulate shipboard cooling water encountered at various locations of the ocean, the heat sink temperature of the facility could be varied. A flat plate, CPL evaporator was designed and tested under various heat sink temperatures. The sink temperature ranged from 274.3 to 305.2 K and the heat input varied from 250 to 800 W which corresponds to heat fluxes up to 1.8 W/cm2. The CPL flat plate evaporator performed very well under this range of heat input and sink temperatures. The main result obtained showed that a large degree of subcooling developed between the evaporator vapor outlet line and liquid return line. This condensate depression increased with increasing heat input.

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