scholarly journals Thermal Assessment of Laminar Flow Liquid Cooling Blocks for LED Circuit Boards Used in Automotive Headlight Assemblies

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1202
Author(s):  
Muhsin Kilic ◽  
Mehmet Aktas ◽  
Gokhan Sevilgen
Keyword(s):  
Numerical Model ◽  
Pressure Drop ◽  
Laminar Flow ◽  
Mass Flow ◽  
Thermal Performance ◽  
Cover Plate ◽  
Coolant Fluid ◽  
Liquid Cooling ◽  
Flow Rates ◽  
Mass Flow Rates

This research work presents a comparative thermal performance assessment of the laminar flow cooling blocks produced for automotive headlight assembly using a high power Light Emitting Diode (LED) chip. A three-dimensional numerical model with conjugate heat transfer in solid and fluid domains was used. Laminar flow was considered in the present analysis. The validation of the numerical model was realized by using the measured data from the test rig. It was observed that substantial temperature variations were occurred around the LED chip owing to volumetric heat generation. The cooling board with lower height performs better thermal performance but higher pressure drop for the same mass flow rates. The cooling board with the finned cover plate performs better thermal performance but results in an increased pressure drop for the same mass flow rates. Increasing the power of the LED results in higher temperature values for the same mass flow rates. The junction temperature is highly dependent on the mass flow rates and LED power. It can be controlled by means of the mass flow rate of the coolant fluid. New Nusselt number correlations are proposed for laminar flow mini-channel liquid cooling block applications.

scholarly journals Net-exergetic, hydraulic and thermal optimization of coaxial heat exchangers using fixed flow conditions instead of fixed flow rates

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Tobias Blanke ◽  
Markus Hagenkamp ◽  
Bernd Döring ◽  
Joachim Göttsche ◽  
Vitali Reger ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Mass Flow ◽  
Flow Rate ◽  
Heat Exchangers ◽  
Circular Ring ◽  
Flow Conditions ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Pipe Radius

AbstractPrevious studies optimized the dimensions of coaxial heat exchangers using constant mass flow rates as a boundary condition. They show a thermal optimal circular ring width of nearly zero. Hydraulically optimal is an inner to outer pipe radius ratio of 0.65 for turbulent and 0.68 for laminar flow types. In contrast, in this study, flow conditions in the circular ring are kept constant (a set of fixed Reynolds numbers) during optimization. This approach ensures fixed flow conditions and prevents inappropriately high or low mass flow rates. The optimization is carried out for three objectives: Maximum energy gain, minimum hydraulic effort and eventually optimum net-exergy balance. The optimization changes the inner pipe radius and mass flow rate but not the Reynolds number of the circular ring. The thermal calculations base on Hellström’s borehole resistance and the hydraulic optimization on individually calculated linear loss of head coefficients. Increasing the inner pipe radius results in decreased hydraulic losses in the inner pipe but increased losses in the circular ring. The net-exergy difference is a key performance indicator and combines thermal and hydraulic calculations. It is the difference between thermal exergy flux and hydraulic effort. The Reynolds number in the circular ring is instead of the mass flow rate constant during all optimizations. The result from a thermal perspective is an optimal width of the circular ring of nearly zero. The hydraulically optimal inner pipe radius is 54% of the outer pipe radius for laminar flow and 60% for turbulent flow scenarios. Net-exergetic optimization shows a predominant influence of hydraulic losses, especially for small temperature gains. The exact result depends on the earth’s thermal properties and the flow type. Conclusively, coaxial geothermal probes’ design should focus on the hydraulic optimum and take the thermal optimum as a secondary criterion due to the dominating hydraulics.

scholarly journals Applying the Concepts of Efficiency and Effectiveness to Analyze the Influence of the Number of Passes in the Shell and Tubes Condenser Thermal Performance

2021 ◽  
Vol 8 (1) ◽  
pp. F1-F10
Author(s):  
E. Nogueira
Keyword(s):  
Heat Exchanger ◽  
Mass Flow ◽  
Thermal Performance ◽  
High Mass ◽  
Saturated Steam ◽  
Inlet Temperature ◽  
Flow Rates ◽  
Efficiency And Effectiveness ◽  
Mass Flow Rates ◽  
Number Of Passes

The work analyzes the influence of the number of passes in a shell and tubes condenser heat exchanger, with an inlet pressure of R134a refrigerant in the shell equal to 1.2 MPa. The fluid that circulates in the tubes is water or water-based nanofluid with a fraction of aluminum oxide nanoparticles (Al2O3), and the methodology used subdivides the heat exchanger into three distinct regions: the overheated region, the saturated region, and the subcooled region. The main parameters used to analyze the thermal performance of the heat exchanger were efficiency and effectiveness. Efficiency in the superheated steam region is close to 1.0. There is scope for increasing thermal effectiveness, which can be improved with more significant passes in the tube. The saturated steam region process is efficient for lower mass flow rates of the fluid in the tube, but it is ineffective. However, it is highly effective for high mass flow rates. There is ample scope for increasing effectiveness in the subcooled region. Still, the fluid inlet temperature in the pipe and the work refrigerant pressure are the limiting factors for greater heat exchange in the subcooled region.

An Analytical and Experimental Evaluation of the Pressure-Drop Losses in the Stirling Cycle

1970 ◽  
Vol 92 (2) ◽  
pp. 182-187 ◽  
Author(s):  
P. A. Rios ◽  
J. L. Smith
Keyword(s):  
Heat Exchange ◽  
Pressure Drop ◽  
Mass Flow ◽  
Experimental Evaluation ◽  
Successive Approximations ◽  
Flow Rates ◽  
The Real ◽  
Stirling Cycle ◽  
First Approximation ◽  
Mass Flow Rates

An analysis of the effects of pressure drop in the heat-exchange components of a Stirling cycle has been made and successfully applied to an experimental refrigerator. Data are presented for the indicated work per cycle for each cylinder of the machine. Two successive approximations to the real cycle are used. The first approximation is a Stirling cycle with two adiabatic cylinders and is used to compute the mass flow rates at each location. The second approximation uses these flow rates to obtain the pressure-drop losses in the heat-exchange components. The correlation between measured and calculated pressure-drop losses and individual cylinder work substantiates the validity of the analysis.

scholarly journals Study on heat transfer and pressure drop characteristics in marine S-CO2 power cycle hybrid heat exchangers

2020 ◽  
Vol 185 ◽  
pp. 01082
Author(s):  
Jiawei Wang ◽  
Yuwei Sun ◽  
Mingjian Lu ◽  
Xinping Yan
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Mass Flow ◽  
Heat Exchangers ◽  
Great Influence ◽  
High Energy ◽  
High Energy Density ◽  
Flow Rates ◽  
Power Cycle ◽  
Mass Flow Rates

The S-CO2 power cycle has the advantages of compact structure and high energy density, which can be used to recover the waste heat of ship exhaust, thus improving the energy efficiency of ships and reducing emissions. The hybrid heat exchangers with etched plates and fins can be used as the heat transfer device of S-CO2 and exhaust, its heat transfer and pressure drop characteristics have a great influence on S- CO2 power cycle performance. In this study, a CFD model of the hybrid heat exchangers was established. The effects of different exhaust inlet temperatures, inlet mass flow rates and inlet pressures on the heat transfer and the pressure drop characteristics were analyzed by Fluent. The results show that the inlet temperatures and inlet mass flow rates of exhaust have a great influence on the heat transfer characteristics of the hybrid heat exchanger. The inlet mass flow rates and inlet pressures of exhaust have a great influence on the pressure drop characteristics of the hybrid heat exchangers. In the design of the hybrid heat exchangers, the status of the exhaust need to be considered to ensure efficient operation of the heat exchangers. The study can provide guidance for the design of the hybrid heat exchangers.

Applications of Performance Tables on Steady State Analysis of Multipass Parallel Cross Flow Heat Exchanger

2017 ◽  
Vol 28 ◽  
pp. 53-72
Author(s):  
Karthik Silaipillayarputhur ◽  
Ali Al-Saif ◽  
Musab Al-Otaibi
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Heat Exchanger ◽  
Mass Flow ◽  
Thermal Performance ◽  
Rate Ratio ◽  
Cross Flow ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Operational Phase

In this paper, steady state sensible performance analysis on multi pass parallel cross flow exchanger was considered. The inputs to the heat exchanger were described through meaningful physically significant parameters such as number of transfer units, capacity rate ratio and dimensionless input temperature. The inputs to the heat exchager were varied systematically and a parametric study was conducted to determine the thermal performance at each individual pass of the heat exchanger. Heat exchanger’s thermal performance was described through the discharge temperatures that were expressed in a dimensionless form. The results from the study were presented in the form of performance tables. The performance tables employed meaningful and industry recognized dimensionless input parameters and the heat exchanger‘s performance was described through dimensionless discharge temperatures at every pass of the heat exchanger. The developed performance tables shall serve two critical aspects. First, it will help the heat exchanger designers to readily choose an optimum heat exchanger. An undersized heat exchanger shall not deliver the requirements and likewise an oversized heat exchanger shall add unnecessary weight and cost. This aspect was clearly observed in this study as indefinetly increasing the number of transfer units (or surface area) beyond a threshold value didn’t enhance the heat transfer. By employing the performance tables as a guide, the heat exchanger designers can quickly ascertain the performance of the heat exchanger without having to perform simulations and/or lengthy calculations. Second, during operational phase of the heat exchanger, the performance tables can be used to understand the performance variation of the heat exchanger with respect to mass flow rates and/or can help the engineers to choose appropriate mass flow rates for the required heat transfer. The highest heat exchanger performance was observed at the lowest capacity rate ratio and likewise the lowest heat exchanger performance was observed at the highest capacity rate ratio. In-addition, during the operational phase, the performance tables can help to detect an underperforming heat exchanger and can help the engineers to schedule maintenance activity on the heat exchanger equipment.

Numerical study on flow characteristics of rotor pumps including cavitation

2014 ◽  
Vol 229 (14) ◽  
pp. 2626-2638 ◽  
Author(s):  
Yingyuan Liu ◽  
Leqin Wang ◽  
Zuchao Zhu
Keyword(s):  
Numerical Model ◽  
Mass Flow ◽  
Volume Fraction ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Two Dimensional ◽  
Flow Rates ◽  
Factors Affecting ◽  
Remarkable Effect ◽  
Mass Flow Rates

This work is purposed to study the flow characteristics of rotor pumps including cavitation. First, a simplified two-dimensional numerical model is developed and computing strategies of the numerical analysis for cavitation are set up, including the selection of cavitation model and its parameters. Second, the reliability and accuracy of the two-dimensional numerical model are verified by experimental results. Then, several factors affecting the cavitation are discussed, including the rotational speeds, pressure differences, clearance sizes, and inlet pressures. For different rotational speeds and pressure differences, the mass flow rates with cavitation are a little larger than that without cavitation, but the amplitudes of the mass flow rates with cavitation are much larger than that without cavitation. Meanwhile, the volume fraction of the water vapor increases with the increasing speeds and the decreasing pressure differences. However, compared with the influence of rotational speeds, the influence of the pressure differences on the vapor contents is relatively smaller. Regarding the clearance size, the smaller the clearance size is, the stronger the cavitation will be. Furthermore, the clearance size between two rotors has a larger effect on the cavitation than that between rotor and pump case. For inlet pressure, it has a little effect on the mass flow rates when cavitation is not considered, but it presents a remarkable effect for the model with cavitation. In addition, the peaks of the volume fractions of vapor and the mass flow rates generally offset backward with the decreasing inlet pressures.

Experimental and Numerical Study of the Pressure Drop in Transonic Micronozzle Flows Across Multiple Flow Regimes

2016 ◽  
Author(s):  
Juan E. Gomez Herrera ◽  
Rodion Groll
Keyword(s):  
Pressure Drop ◽  
Mass Flow ◽  
Slip Flow ◽  
Slip Boundary Condition ◽  
Navier Stokes ◽  
Lower Mass ◽  
Flow Rates ◽  
Slip Boundary ◽  
Accommodation Coefficients ◽  
Mass Flow Rates

In the present work, the behavior of a millimeter-scale cold-gas thruster operating with the noble gases neon, argon, krypton and xenon is investigated both experimentally and numerically. In the experimental setup, the cold-gas thruster operates under vacuum conditions and the pressure drop in the system is measured at several fixed mass flow rates ranging between 0.178 mg/s and 3.568 mg/s. The estimated Knudsen numbers for all the studied cases are above the continuum flow limit 0.01. At the higher mass flow rates the studied flows are in the slip-flow regime while at the lower mass flow rates, the transition regime is reached. The experimental pressure results are compared with numerical simulations based on the compressible Navier-Stokes equations with a no-slip boundary condition and with simulations based on the Direct Simulation Monte Carlo (DSMC) method. At high values of Kn, the pressure results of the Navier-Stokes based simulations show high deviations from both the DSMC and the experimental results. This is a consequence of the discrepancy between the no-slip boundary condition used for the Navier-Stokes simulations and gas rarefaction effects in the micronozzle becoming dominant at the lower mass flow rates. Based on the comparison between the experimental results and the Navier-Stokes based simulations, a Knudsen-dependent correcting function with four gas-independent accommodation coefficients is developed. The accommodation coefficients allow the accurate estimation of the actual pressure drop along the nozzle based on usually computationally inexpensive Navier-Stokes simulations with no-slip boundary conditions. The flexibility of the proposed approach is advantageous for the study of experimental setups operating at a large range of mass flow rates, where several flow regimes might exist, provided that a rigorous numerical distinction between continuum, slip-flow and transition regime is not essential.

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