A Numerical and Optimization Study of Compressible Phase-Change Heat Transfer in a Part-Unit-Cell Model of a Pulsating Heat Pipe (PHP)

2016 ◽  
Author(s):  
Nikhilesh Ghanta ◽  
Arvind Pattamatta
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Objective Function ◽  
Cell Model ◽  
Unit Cell ◽  
Working Time ◽  
Working Fluid ◽  
Optimal Point ◽  
Multi Objective ◽  
Optimization Study

The heat transfer capacity of a PHP is tremendously high and is finding many applications such as in electronic cooling. In order to maximize its heat transfer potential, the working parameters of a PHP have to be set to the right values. The present work deals with the optimization study of a part-unit-cell model of a Pulsating Heat Pipe (PHP) comprising of a single meniscus oscillating between evaporator and adiabatic sections. The parameters considered for this study are the effective length of the evaporator section, the evaporator temperature and the fluid fill ratio. All the numerical studies on PHP till date make the approximation of incompressibility of working fluid. However, recent experimental studies by M.Rao et al. [1] have shown the importance of compressibility effects on the working of a PHP. The present work involves a compressible phase change heat transfer model, based on the Volume-of-Fluid solver. The compressible model is incorporated into open source CFD solver OpenFOAM. This solver is validated in stages by Ghanta and Pattamatta [2] and the part-unit cell of the PHP is validated against the existing experimental results of M. Rao et al [1] and contrast is made with an incompressible solver, to emphasise the importance of considering the compressibility effects. Following validation of the compressible phase change solver, a parametric study explaining the effects of the above mentioned parameters on the objective functions and working of the PHP is performed, which forms the basis for the optimization presented in this work. Accordingly, the ratio of evaporator to the adiabatic length (Le/La) is varied between 2 and 10, the evaporator superheat between 5 and 20 and the fluid filling ratio is varied between 35–80 %. A multi-objective optimization problem is set-up taking the maximum vapour pressure attained and working time (the time for which the working fluid is in contact with the part unit cell of the PHP) as the objective functions. Models are created using two different methods — Kriging and Response Surface Approximation (RSA). The models are optimized using multi-objective Genetic Algorithm, coded in MATLAB. Both the models used predicted the same optimum values, with a variation of 0.01%. The optimum values point at a fluid fill ratio of 79.5%, evaporator excess temperature of 7.89 and an evaporator section of length seven times that of the adiabatic section. The same is also validated with results of numerical simulation at the optimal point. In majority of the works presented so far, the maximum vapour pressure alone is taken as a benchmark for the performance of the PHP. To elucidate the importance of considering working time as an objective function, a single objective optimization study was also performed, with only the maximum pressure as the objective function. The results of single objective optimization showed a deviated optimal point, with similar optimal pressure value as that of multi-objective optimization, but working time reduced by half. Hence by not considering the working time of PHP as an objective function, the optimal point generated results in only half the maximum heat transfer that can otherwise be attained with different parameters.

Thermal Performance of Water-Based Suspensions of Phase Change Nanocapsules in a Natural Circulation Loop

2013 ◽  
Author(s):  
C. J. Ho ◽  
Chi-Ming Lai
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Natural Circulation ◽  
Pure Water ◽  
Circulation Loop ◽  
Core Material ◽  
Working Fluid ◽  
Outer Diameter ◽  
Natural Circulation Loop ◽  
Water Based

Experiments were conducted to investigate the heat transfer characteristics of water-based suspensions of phase change nanocapsules in a natural circulation loop with mini-channel heat sinks and heat sources. A total of 23 and 34 rectangular mini-channels, each with width 0.8 mm, depth 1.2 mm, length 50 mm and hydraulic diameter 0.96 mm, were evenly placed on the copper blocks as the heat source and heat sink, respectively. The adiabatic sections of the circulation loop were constructed using PMMA tubes with an outer diameter of 6 mm and an inner diameter of 4 mm, which were fabricated and assembled to construct a rectangular loop with a height of 630 mm and a width of 220 mm. Using a core material of n-eicosane and a shell of urea-formaldehyde resin, the phase change material nanocapsules of mean particle size 150 nm were fabricated successfully and then dispersed in pure water as the working fluid to form the water-based suspensions with mass fractions of the nanocapsules in the range 0.1–1 wt.%. The results clearly indicate that water-based suspensions of phase change nanocapsules can markedly enhance the heat transfer performance of the natural circulation loop considered.

scholarly journals Dustproof cooling of the electrical box

2018 ◽  
Vol 180 ◽  
pp. 02072
Author(s):  
Patrik Nemec ◽  
Katarína Kaduchová ◽  
Milan Malcho
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Phase Change ◽  
Thermal Performance ◽  
Working Fluid ◽  
Cooling Method ◽  
Box Space

In present are electrical boxes cooled by air through the intake hole on the bottom electrical box to the box space with electrotechnical elements and exhaust through the hole at the top to the surrounding by natural convection. This cooling method is effective but operate with the risk of contamination electrotechnical elements by dust sucking from surrounding air. The goal of this work is solution of the dustproof cooling of the electrical box by natural convection. The work deal with design of the device with the heat transfer by the phase change of the working fluid and experimental measuring its thermal performance at the cooling electrotechnical elements loaded by heat 1 200 W in the dustproof electrical box.

Microscale Boiling Heat Transfer Near the Meniscus

2005 ◽  
Author(s):  
Brenda E. Haendler ◽  
David C. Walther ◽  
Dorian Liepmann ◽  
Albert P. Pisano
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Temperature Profile ◽  
Infrared Camera ◽  
Intake Manifold ◽  
Working Fluid ◽  
Bulk Temperature ◽  
Heating Source ◽  
Portable Power ◽  
Insight Into

Results are presented experimentally measuring the localized temperature profile due to microscale boiling of a silicon-Pyrex bonded wafer with a 100 μm deep, 500 μm wide and six mm long microchannel. Experiments were performed using an infrared camera equipped with a magnifying lens. By using a camera, the dynamic temperature profile is shown from the inside channel all the way out to where the temperature of the wafer reaches the bulk temperature of the heating source. Temperature profiles are shown for both water and methanol as the working fluid applying between five and twenty degrees Celsius of superheat to the bulk wafer. Using these results, a discussion of the relevant heat transfer modes and nondimensional numbers is given to gain insight into the range of influence that phase change in a microchannel has on the temperature of the wafer. Additionally, discussion is given about modeling of microscale phase change using a commercial fluid dynamics software package. The importance of these results with respect to implementation into the fuel intake manifold for a micro engine based portable power system is also discussed.

On Development of a Semi-Mechanistic Wall Boiling Model

2013 ◽  
Author(s):  
Saurish Das ◽  
Hemant Punekar
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Thermal Stresses ◽  
Cooling System ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Wall Heat Transfer ◽  
Cooling Systems ◽  
Transfer Phenomenon

In modern cooling systems the requirement of higher performance demands highest possible heat transfer rates, which can be achieved by controlled nucleate boiling. Boiling based cooling systems are gaining attention in several engineering applications as a potential replacement of conventional single-phase cooling system. Although the controlled nucleate boiling enhances the heat transfer, uncontrolled boiling may lead to Dry Out situation, adversely affecting the cooling performance and may also cause mechanical damage due to high thermal stresses. Designing boiling based cooling systems requires a modeling approach based on detailed fundamental understanding of this complex two-phase heat and mass transfer phenomenon. Such models can help analyze different cooling systems, detect potential design flaws and carry out design optimization. In the present work a new semi-mechanistic wall boiling model is developed within commercial CFD solver ANSYS FLUENT. A phase change mechanism and wall heat transfer augmentation due to nucleate boiling are implemented in mixture multiphase flow framework. The phase change phenomenon is modeled using mechanistic evaporation-condensation model. Enhancement of wall heat transfer due to nucleate boiling is captured using 1D empirical correlation, modified for 3D CFD environment. A new method is proposed to calculate the local suppression of nucleate boiling based on the flow velocity, and hence this model can be applied to any complex shaped coolant passage. For different wall superheat, the wall heat fluxes predicted by the present model are validated against experimental data, in which 50-50 volume mixture of aqueous ethylene glycol (a typical anti-freeze coolant mixture) is used as working fluid. The validation study is performed in ducts of different sizes and shapes with different inlet velocities, inlet sub-cooling and operating pressures. The results are in good agreement with the experiments. This model is applied to a typical automobile Exhaust Gas Recirculation (EGR) system to study boiling heat transfer phenomenon and the results are presented.

Exploration of Phase Change Within a Capillary Flow Driven Square Micro-Channel Using Lattice Boltzmann Method and Experimental Boundary Conditions

2015 ◽  
Author(s):  
E. Borquist ◽  
G. Smith ◽  
L. Weiss
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Boundary Conditions ◽  
Phase Change ◽  
Lattice Boltzmann ◽  
Capillary Flow ◽  
Working Fluid ◽  
Micro Channel ◽  
External Work ◽  
Boltzmann Method

Previously published research examined the overall efficiency of heat transfer through a copper plated micro-channel heat exchanger. However, since the device is sealed and composed entirely of copper, understanding the phase change, temperature field, and density field of the working fluid is difficult empirically. Given that the efficiency was shown to be greatly increased by the working fluid phase change, this understanding within the device is important to designing devices of greater efficiency and different working fluids. One method of determining device and component performance is numerical modeling of the system. Fluids that undergo phase change have long frustrated those attempting to successfully numerically model systems with acceptable stability. Over the past twenty years, the lattice Boltzmann method (LBM) has transformed the simulation of multicomponent and multiphase flows. Particularly with multiphase flows, the LBM “naturally” morphs the phase change interface throughout the model without excessive computational complexity. The relative ease with which LBM has been applied to some multicomponent/multiphase systems inspired the use of LBM to track phase change within the previously recorded experimental boundary conditions for the copper plated heat exchanger. In this paper, the LBM was used to simulate the evaporation and condensation of HFE-7200 within a capillary flow driven square micro-channel heat exchanger (MHE). All initial and boundary conditions for the simulation are exactly those conditions at which the empirical data was measured. These include temperature and heat flux measurements entering and leaving the MHE. Working fluid parameters and characteristics were given by the manufacturer or measured during experimental work. Once the lattice size, initial conditions, and boundary conditions were input into MATLAB®, the simulations indicated that the working fluid was successfully evaporating and condensing which, coupled with the capillary driven flow, allowed the system to provide excellent heat transfer characteristics without the use of any external work mechanism. Results indicated successive instances of stratified flow along the channel length. Micro-channel flow occurring due to capillary action instead of external work mechanisms made differences in flow patterns negligible. Coupled with the experimentally measured thermal characteristics, this allowed simulations to develop a regular pattern of phase interface tracking. The agreement of multiple simulations with previously recorded experimental data has yielded a system where transport properties are understood and recognized as the primary reasons for such excellent energy transport in the device.

scholarly journals Two-Dimensional Model of a Space Station Freedom Thermal Energy Storage Canister

1994 ◽  
Vol 116 (2) ◽  
pp. 114-121 ◽  
Author(s):  
T. W. Kerslake ◽  
M. B. Ibrahim
Keyword(s):  
Heat Transfer ◽  
Energy Storage ◽  
Free Convection ◽  
Phase Change ◽  
Thermal Energy ◽  
Heat Engine ◽  
Space Station ◽  
Working Fluid ◽  
Two Dimensional ◽  
Liquid Salt

The Solar Dynamic Power Module being developed for Space Station Freedom uses a eutectic mixture of LiF-CaF2 phase-change salt contained in toroidal canisters for thermal energy storage. This paper presents results from heat transfer analyses of the phase-change salt containment canister. A two-dimensional, axisymmetric finite difference computer program which models the canister walls, salt, void, and heat engine working fluid coolant was developed. Analyses included effects of conduction in canister walls and solid salt, conduction and free convection in liquid salt, conduction and radiation across salt vapor-filled void regions, and forced convection in the heat engine working fluid. Void shape and location were prescribed based on engineering judgment. The salt phase-change process was modeled using the enthalpy method. Discussion of results focuses on the role of free convection in the liquid salt on canister heat transfer performance. This role is shown to be important for interpreting the relationship between ground-based canister performance (in 1-g) and expected on-orbit performance (in micro-g). Attention is also focused on the influence of void heat transfer on canister wall temperature distributions. The large thermal resistance of void regions is shown to accentuate canister hot spots and temperature gradients.

scholarly journals Multi-objective optimization of CuO based organic Rankine cycle operated using R245ca

2019 ◽  
Vol 116 ◽  
pp. 00062 ◽  
Author(s):  
Parth Prajapati ◽  
Vivek Patel
Keyword(s):  
Heat Transfer ◽  
Thermal Efficiency ◽  
Heat Exchangers ◽  
Waste Heat ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Working Fluid ◽  
Multi Objective Optimization ◽  
Multi Objective ◽  
Source Fluid

The present work deals with multi objective optimization of nanofluid based Organic Rankine Cycle (ORC) to utilise waste heat energy. Working fluid considered for the study is R245ca for its good thermodynamic properties and lower Global Warming Potential (GWP) compared to the conventional fluids used in the waste heat recovery system. Heat Transfer Search (HTS) algorithm is used to optimize the objective functions which tends to maximize thermal efficiency and minimize Levelised Energy Cost (LEC). To enhance heat transfer between the working fluid and source fluid, nanoparticles are added to the source fluid. Application of nanofluids in the heat transfer system helps in maximizing recovery of the waste heat in the heat exchangers. Based on the availability and cost, CuO nanoparticles are considered for the study. Effect of Pinch Point Temperature Difference (PPTD) and concentration of nanoparticles in heat exchangers is studied and discussed. Results showed that nanofluids based ORC gives maximum thermal efficiency of 18.50% at LEC of 2.59 $/kWh. Total reduction of 7.11% in LEC can be achieved using nanofluids.

scholarly journals Heat Transfer Enhancement in Microchannel Flow: Presence of Microparticles in a Fluid

2010 ◽  
Author(s):  
Awad B. S. Alquaity ◽  
Salem A. Al-Dini ◽  
Evelyn N. Wang ◽  
Shahzada Z. Shuja ◽  
Bekir S. Yilbas ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Pressure Drop ◽  
Phase Change ◽  
Constant Heat Flux ◽  
Working Fluid ◽  
Microchannel Flow ◽  
Carrier Fluid ◽  
Volume Fractions ◽  
Energy Equations

In the present study, a numerical model was developed for laminar flow in a microchannel with a suspension of microsized phase change material (PCM) particles. In the model, the carrier fluid and the particles are simultaneously present, and the mass, momentum, and energy equations are solved for both the fluid and particles. The particles are injected into the fluid at the inlet at a temperature equal to the temperature of the carrier fluid. A constant heat flux is applied at the bottom wall. The temperature distribution and pressure drop in the microchannel flow were predicted for lauric acid microparticles in water with volume fractions ranging from 0 to 8%. The particles show heat transfer enhancements by decreasing the temperature distribution in the working fluid by 39% in a 1 mm long channel. Meanwhile, particle blockage in the flow passage was found to have a negligible effect on pressure drop in the range of volume fractions studied. This work is a first step towards providing insight into increasing heat transfer rates with phase change-based microparticles for applications in microchannel cooling and solar thermal systems.

Sign in / Sign up

Export Citation Format

Share Document