Performance Of Cooling System Research Articles

Qualitative analysis of coupling effect of fluid velocity distribution in microchannels on the performance of the LED water cooling system

PurposeThe purpose of this paper is to ensure adequate thermal management to remove and dissipate the heat produced by a light-emitting diode (LED) and to guarantee reliable and safe operation.Design/methodology/approachA three-dimensional (3-D) computational fluid dynamics (CFD) model was used to analyze the distribution of fluid velocities among microchannels at four different aspect ratios.FindingsThe results showed that at the same inlet flow rate, the larger the aspect ratio of the microchannels, the better the uniformity of the internal fluid velocity and thus better the heat dissipation performance on the surface of the high-power LED chip. In addition, the thermal performance of a high-power LED water cooling system with four different aspect ratios’ microchannel structures is further studied experimentally. Specifically, the coupling effect between the fluid velocity distribution in the microchannels and the heat dissipation performance of a high-power LED water cooling system is qualitatively analyzed and compared with the simulation results of the fluid velocity distribution. The results fully demonstrated that a larger aspect ratio of the microchannels results in better heat dissipation performance on the surface of the high-power LED chip.Originality/valueOptimizing the structural parameters to facilitate a relatively uniform velocity distribution to improve the water cooling system performance may be a key factor to be considered.

Effect of Un-Balanced Water Supply and Nonuniform Pressure Distribution on the Performance of an Adsorption Cooling System

A three-dimensional numerical analysis was conducted to examine the effect on performance of un-balanced heating/cooling water supply and nonuniform pressure distribution in the beds, issues observed in an experiment by our colleague during the development of a 35[Formula: see text]kW prototype finned-tube type adsorption chiller. Case studies were conducted with reference values of [Formula: see text][Formula: see text]m/s, [Formula: see text][Formula: see text]Pa and [Formula: see text][Formula: see text]Pa, and the differences in [Formula: see text][Formula: see text]m/s, [Formula: see text][Formula: see text]Pa and [Formula: see text][Formula: see text]Pa. A remarkable increase in COP was found for the cases of un-balanced heating water supply and nonuniform pressure distribution when the bed was connected to the evaporator. However, after integration of multi-modules, the effect was smoothed out, which removed the worry about the degradation in the overall COP. The effect of un-balanced cooling water supply and nonuniform pressure distribution when the bed was connected to the condenser was not discernible. In all cases, the change in SCP was negligible.

Numerical Investigation on the Thermal Performance of Nanofluid-Based Cooling System for Synchronous Generators.

This paper presents a nanofluid-based cooling method for a brushless synchronous generator (BLSG) by using Al2O3 lubricating oil. In order to demonstrate the superiority of the nanofluid-based cooling method, analysis of the thermal performance and efficiency of the nanofluid-based cooling system (NBCS) for the BLSG is conducted along with the modeling and simulation cases arranged for NBCS. Compared with the results obtained under the base fluid cooling condition, results show that the nanofluid-based cooling method can reduce the steady-state temperature and power losses in BLSG and decrease the temperature settling time and changing ratio, which demonstrate that both steady-state and transient thermal performance of NBCS are improved as nanoparticle volume fraction (NVF) in nanofluid increases. Besides, although the input power of cycling pumps in NBCS has ~30% increase when the NVF is 10%, the efficiency of the NBCS has a slight increase because the 4.1% reduction in power loss of BLSG is bigger than the total incensement of input power of the cycling pumps. The results illustrate the superiority of the nanofluid-based cooling method, and it indicates that the proposed method has a broad application prospect in the field of thermal control of onboard synchronous generators with high power density.

MHD mixed convection flow in the WCLL: Heat transfer analysis and cooling system optimization

In the Water-Cooled Lithium Lead (WCLL) blanket, a critical problem faced by the design is to ensure that the breeding zone (BZ) is properly cooled to avoid the loss of mechanical properties in the structural materials. CFD simulations are performed using ANSYS CFX to assess the cooling system performances accounting for the magnetic field effect in the sub-channel closest to the first wall (FW). Here, intense buoyancy forces (Gr ≈ 1010) interact with the pressure-driven flow (Re ≈ 103) in a MHD mixed convection regime. A constant magnetic field, parallel to the toroidal direction, is assumed with Ha = 8550. The walls bounding the channel and the water pipes are modeled as perfectly conducting. The magnetic field is found to dampen the velocity fluctuations triggered by the buoyancy forces and the flow is similar to a forced convection regime. The PbLi heat transfer coefficient is reduced to one-third of its ordinary hydrodynamic value and, consequently, hot-spots close to the FW are observed, where TMax ≈ 1000 K. Optimization strategies for the BZ cooling system layout are proposed and implemented in the CFD model, thus fulfilling the design criterion.

Theoretical study of thermoelectric cooling system performance

Theoretical study of thermoelectric cooling system performance

Analysis of the multi-stage desiccant cooling system performance in Wrocław (Poland)

In this study, the application potential of desiccant cooling system with indirect evaporative precooling is analyzed for moderate climatic conditions. Wrocław (Poland) was selected as a representative city. On the base of summer season weather parameters different system running modes were proposed such as cooling and dehumidification mode (Mode 1) and only cooling mode (Mode 2). The average month Thermal and Electrical COP were established for selected climatic conditions. It was concluded that proposed system allows to cool the air without occurrence of condensation in Mode 2 with high average monthly electrical COP (COPel = 62.2 in August). On the other hand when dehumidification is needed, system operates in Mode 1 and obtains relatively high average Thermal COP values (COPth = 2.2).

Assessment of numerical models in the evaluation of adsorption cooling system performance

A lab-scale adsorption unit is designed and constructed to investigate its efficacy under typical operating conditions of a practical adsorption cooling system. A detailed coupled heat and mass transfer (CHMT) model and a lumped parameter (LP) model are implemented to estimate the Specific Cooling Power (SCP) of an adsorption cooling system using silica gel/water as the working pair. It is found that the optimal cycle time can be predicted by using the LP model. Results show that the SCP obtained from the CHMT model is always higher than that measured from the experiment because the dynamic effect of the evaporator is not considered. The LP model, with its input parameters estimated by the CHMT, actually produces reliable estimates of the SCP because the evaporator dynamic effect is considered. The difference between the two models is higher at shorter cycle times because the evaporator pressure drop is very high at the beginning of the adsorption process. Without considering this pressure drop, the CHMT yields a higher SCP compared to that calculated from the LP model. In view of the evaporator pressure variation during the adsorption process, a modified CHMT model that considers the evaporator dynamic behavior is developed. It is shown that the modified CHMT model can be used to evaluate the performance of an adsorption bed and to estimate the SCP accurately.

Transmissive microfluidic active cooling for concentrator photovoltaics

We present the design, fabrication, characterization, and field testing of transmissive active cooling for use in a point-focus spectrum-splitting hybrid concentrator photovoltaics/thermal (CPV/T) system. Seven parallel-path 100 μm thick microchannels are made using polydimethylsiloxane and attached to a CPV module containing a 6 × 6 array of 5.5 mm transmissive CPV cells on a sapphire substrate. Water is flowed through the microchannels to actively cool the CPV cells. The total transmittance of the CPV module reduces by 5.2% with the addition of the active cooling microchannels, relative to the module transmission with no microchannels. The peak cell temperature is measured as 69 °C with a thermal resistance of 9.35 K/W at 157 suns, well below the 110 °C maximum allowed temperature. A maximum flowrate of 16.7 g/s is achieved from a 13 psi pressure drop across the microchannels and manifold assembly. The flow characteristics within each microfluidic channel show maximum fluid velocity of 4.3 m/s (Re = 953) with a calculated convection coefficient of 1.7 × 104 W/m2 K (Nu = 5.36). The CPV/T module and cooling system performance was validated during week-long outdoor tests under varying solar conditions up to 250 suns using a 2.7 m2 parabolic dish collector mounted to a two-axis tracking system.

Comparison of the Thermal Performance of Solar Adsorption Cooling System between Egypt and Morocco

This paper presents the thermal performance of a single stage solar adsorption system. The study includes a thermal performance comparison between two different locations in North Africa (Cairo and Casablanca) under different climate conditions. It was found that the solar fraction of the adsorption system is better under Cairo climate due to the relatively low daily solar radiation of Casablanca compared to Cairo. The solar fraction of the cooling plant was investigated theoretically for six months. The effect of the solar collector area and the mass flow rate of the solar loop on the solar fraction were investigated. The solar fraction was computed for 40 and 20 kW auxiliary heater capacity. The required solar collector area for optimum solar fraction was reduced from 140 to 88 m2 with using 20 kW auxiliary heater and reduced to 46 m2 with the 40 kW auxiliary heater using. The results proved that with the mass flow rate of the solar loop increasing from 0.18 to 1.5 kg/s the collector area required decreases from 110 to 60 m2. This study was performed by the TRNSYS simulation using.

Comprehensive review of principle factors for thermal conductivity and dynamic viscosity enhancement in thermal transport applications: An analytical tool approach

In past decades, nanofluid science has been widely investigated for thermal related activities. In thermal transport applications, thermal conductivity and dynamic viscosity are closely related to cooling system performance enhancement. The genuine anomaly behind thermal conductivity and dynamic viscosity enhancement in nanofluid is still undiscoverable. In this paper, comprehensive study on principle factor behind thermophysical property enhancement focusing on thermal conductivity and dynamic viscosity is conducted. Thus, a detailed review of existing experimental results for thermal conductivity and dynamic viscosity enhancement are compiled and discussed in this manuscript. Analytical tool approach such as fishbone diagram and summary tables are used to highlight principle factor for thermal conductivity and dynamic viscosity enhancement. The principal factor which influences the thermal conductivity is shape of the particle, nanofluid preparation, interfacial layer, Brownian motion, particle clustering and aggregation. Meanwhile, the principal factor influencing dynamic viscosity is the physical behavior of the particle, nanofluid preparation, particle clustering and aggregation. The optimum nanofluid should have high thermal conductivity and minimum viscosity. High thermal conductivity is mandatory for maximum heat absorption in thermal transport applications. Meanwhile, minimum viscosity ensures less pressure drop which reduces the power consumption and increases the overall efficiency of the system.

Innovative low-energy evaporative cooling system for buildings: study of the porous evaporator wall

To face the current increase of building cooling demand and the concerns related to climate changes, an energy-efficient evaporative cooling system using porous material has been developed. This article presents the innovative cooling system and a detailed hygrothermal analysis of its main element: the porous evaporator. A mathematical model and an experimental set-up are presented, which enable to determine the suitable material properties for the evaporator and its impact on the overall cooling system performance, focusing on the optimal use of both energy and water. A good agreement is observed between numerical and experimental results, and the evaporative cooling power is estimated from 12 to 72 W/m² of evaporator wall, depending on the evaporator characteristics. A parametric analysis is conducted to select the best material for the evaporative cooling system. An intrinsic permeability of the material of 4 × 10−17 m2 is recommended for this new cooling system.

Predictive simulation-based optimisation of cooling system including a sprinkler tank

Prerequisite for an efficient cooling energy system is the knowledge and the optimal combination of different operating conditions of individual compression and free cooling chillers. The performance of cooling systems depends on its part load performance and its condensing temperature, which are often unknown. Recorded energy data remains unused and manufacturers' data significantly differs from the real performance. For this purpose, manufacturer and real data are combined and continuously adapted to form partial load curve models. This study applied a predictive optimization algorithm to calculate the optimal operating conditions of multiple chillers. A sprinkler tank offers the opportunity to store cold-water for later utilisation. This potential is used to show the load shifting potential of the cooling system by using a variable electricity price as an input parameter of the optimisation. The set points from the optimisation have been continuously validated by a dynamic simulation. Finally, a case study of a plastic processing company evaluated different scenarios against the status quo. Applying an optimal chiller loading and charging strategy of a sprinkler tank increased the energy efficiency of up to 40 % during colder and around 17 % during warmer periods. The total energy savings highly depended on the weather conditions. For the consider fluctuations, the electricity price had only a minor effect.

APPLYING DIRECT EVAPORATIVE COOLING SYSTEM FOR CONTROLLING ENVIRONMENTAL CONDITIONS IN RABBIT HOUSES

Heat stress is a major problem that faces rabbit’s breeders. This problem adversely affects rabbit's growth and reduces the resistance to diseases. The present research was carried out to apply and evaluate the performance of a direct evaporative pad cooling system in rabbit houses to control environmental conditions. The direct evaporative pad cooling system performance was studied as a function of change in pad thickness (10 and 15 cm), water flow rate (3, 5 and 7 L/min.m2) and rabbit stocking density with an approximate average (0.5 and 1.0 rabbit/m2). Performance evaluation of the evaporative pad cooling system was carried out in terms of temperature reduction, cooling efficiency, temperature-humidity index, daily body weight gain and mortality ratio. The experimental results clarified that values of temperature reduction (7.3 and 6.8 oC), cooling efficiency (94.92 and 90.91 %), temperature-humidity index (26.30 and 27.40 oC), daily body weight gain (38.80 and 38 g/rabbit/day) and mortality ratio (0.2 and 0.4 %) are in the optimal limits under conditions of 15 cm pad thickness and 5 L/min.m2 water flow rate for rabbit stocking densities of 0.5 and 1.0 rabbit/m2, respectively.

Design and performance study of dry cooling system for 25 MW solar power plant operated with supercritical CO2 cycle

Dry natural draft cooling towers are mostly employed in thermal power plants in arid areas with no energy consumption and maintenance compared with the mechanical draft cooling system. Different types and shapes of natural draft dry cooling towers (NDDCT) are available in many thermal and nuclear power plant industries. The main purpose of NDDCT is to generate air flow through the finned tube heat exchanger bundles by the influence of buoyancy due to the density difference between the ambient air and the warm air inside the tower. In the present chapter, a one-dimensional MATLAB code is developed to design a NDDCT with detailed specification of finned tube heat exchanger bundles for a 25 MW solar plant operated with supercritical CO2 (sCO2) Brayton cycle. The tower height, the tower inlet and outlet diameters and the number of heat exchanger bundles are evaluated after accomplishing the design requirements. The performance study of an air-cooled heat exchanger is performed for a range of sCO2 inlet temperature from 71 °C to 91 °C, operating pressure from 7.5 MPa to 9 MPa and ambient air temperature from 20 °C to 50 °C. The sCO2 inlet temperature and operating pressure to the heat exchanger significantly affect the cooling system performance. During high ambient temperature period, the cooling potential of NDDCT is significantly reduced.

Numerical Investigation of Small-Scale Adsorption Cooling System Performance Employing Activated Carbon-Ethanol Pair

Adsorber heat exchanger design has great importance in increasing the performance of the adsorption-based cooling system. In this study, a transient two-dimensional axisymmetric Computational Fluid Dynamics (CFD) model has been developed for the performance investigation of finned tube type adsorber using activated carbon and ethanol as the working pair. The operating conditions of the cooling system were 15, 20 and 80 for evaporation, cooling and heating temperatures, respectively. The simulated temperature profiles for different adsorbent thicknesses were validated with those from experimental data measured in our laboratory. Moreover, the error in mass and energy balance were 3% and 7.88%, respectively. Besides, the performance investigation has been performed for cycle time ranging from 600 s to 1400 s. The optimum cycle time was 800 s and the corresponding evaluated specific cooling power (SCP) and coefficient of performance (COP) were found to be 488 W/kg and 0.61, respectively. The developed CFD model will be used for fin height and fin pitch optimization and can be extended to other adsorbent-adsorbate based adsorption cooling system.

Enhancement of the survival probability of a photovoltaic converter–An optimization approach

Maximizing the return on investment of a photovoltaic array requires a power electronics converter with the longest possible operational life. This paper is aimed at presenting a heatsink optimization approach to enhance the survival probability of a high-efficiency 1 kW DC/DC converter, specifically designed for PV applications. A main feature of the enhancement is that it takes into account the meteorological characteristics of the intended installation site: a coastal area with high humidity and cloudiness throughout the year.As a first step, the converter reliability is estimated according to the FIDES procedure, yielding a mean time between failures MTBF = 98.15 FIT. The numerical results pinpoint the diodes as the most failure-prone components, and temperature as the dominant stressor, clearly suggesting that the performance can be improved by resorting to better heatsinks. As a second step, a heatsink optimization problem is established, involving three objective functions: minimization of heatsink thermal resistance and weight, and maximization of the cooling system performance index, The problem is solved using a genetic algorithm, which yields MTBF = 74.09 FIT. The approach takes advantage of the computer tools currently available: mathematical toolboxes to implement the optimization algorithm, user-friendly reliability prediction software, and software packages capable of simulating the thermal behavior of heatsinks with good accuracy.

Enhancement of the Cooling System Performance of the Proton-exchange Membrane Fuel Cell By Baffle-restricted Coolant Flow Channels

The performance of proton-exchange membrane fuel cell cooling system using coolant flow channels enhanced with baffles was numerically investigated. To do this, the maximum temperature of the cooling plate, temperature uniformity and also pressure drop along the flow channels were compared for different cases associated with number of baffles and their dimensions inside the channels. The governing equations by the finite-volume approach in three dimensions were solved. Numerical results indicate that the baffle-restricted cooling flow channels, generally improved the performance of the fuel cell in such a way that a reduced maximum temperature of the cell and a better temperature uniformity in the cooling plates were determined. As the pressure drop increases by incorporating the baffles inside the coolant flow channels, one needs to compromise between the improvement of cooling system performance and the total pressure drop.

CFD Analysis of Hot Air Recirculation in Cooling System of Off Road Vehicle

The demands on cooling system of an off-road vehicle have increased due to charge air cooling, air conditioning and higher horsepower (hp) engines. In order to maximize cooling system performance of an off-road vehicle, the temperature of air entering the cooling system through front grill should be as low as possible, ideally at ambient temperature. Hot air exiting the cooling system which finds its way back to the front grill decreases the system performance. This is called as hot air recirculation. To study hot air recirculation complete vehicle is placed in physical wind tunnel facility. With CFD simulation tool this hot air recirculation can be studied in a virtual wind tunnel. Current paper studies hot air recirculation & quantifies the recirculation using CFD tool. Influence of tail wind velocity on recirculation was studied. The results of simulations were compared with experimental results.

Simulations of Heat Transfer in Thermoplastic Injection Molds Manufactured by Additive Techniques

AbstractThe cost and quality of complex thermoplastic parts manufactured by injection are traditionally limited by the design constraints on the mold cooling system. A possible way to overcome this problem is to produce the mold by additive manufacturing, which makes it possible to freely design the shape and position of the cooling channels. Such molds can have hollow spaces in order to reduce the manufacturing time by Selective Laser Melting and the use of costly materials. The complex geometry resulting from optimized cooling channels and hollow regions makes the prediction of the cooling system performance difficult. This work aims to devise a numerical methodology for the simulation of heat transfer phenomena between the polymer, the mold and the cooling channels. An Immersed Volume approach is chosen, where the different parts of the domain (i.e. the polymer, the cooling channels, the hollow regions and the mold) are represented implicitly and the thermo-mechanical properties of the materials vary smoothly at the interface between the parts. The energy and momentum equations are solved by a stabilized Finite Element method. In order to accurately resolve the large variations of material properties and the steep temperature gradients at interfaces, state-of-the art anisotropic mesh refinement techniques are employed. In a first step, we perform thermal calculations only. We then consider the proper thermo-mechanical coupling in the packing stage, as well as the ejection stage and the thermal contact resistance between the polymer part and the mold, in order to weight their influence on the part and the mold temperatures. The modeling strategy is first validated on a simple geometry of a center-gated disk and compared with experimental measurements. The agreement between the experimental results and the simulation is good. Simulations are then performed on an industrial case which illustrates the ability of the method to deal with complex geometries.

Cooling Performance Analysis of ThePrimary Cooling System ReactorTRIGA-2000Bandung

The conversion of reactor fuel type will affect the heat transfer process resulting from the reactor core to the cooling system. This conversion resulted in changes to the cooling system performance and parameters of operation and design of key components of the reactor coolant system, especially the primary cooling system. The calculation of the operating parameters of the primary cooling system of the reactor TRIGA 2000 Bandung is done using ChemCad Package 6.1.4. The calculation of the operating parameters of the cooling system is based on mass and energy balance in each coolant flow path and unit components. Output calculation is the temperature, pressure and flow rate of the coolant used in the cooling process. The results of a simulation of the performance of the primary cooling system indicate that if the primary cooling system operates with a single pump or coolant mass flow rate of 60 kg/s, it will obtain the reactor inlet and outlet temperature respectively 32.2 °C and 40.2 °C. But if it operates with two pumps with a capacity of 75% or coolant mass flow rate of 90 kg/s, the obtained reactor inlet, and outlet temperature respectively 32.9 °C and 38.2 °C. Both models are qualified as a primary coolant for the primary coolant temperature is still below the permitted limit is 49.0 °C.