Numerical Investigation of Thermal Resistance in a Rectangular Flux Channel With Non-Uniform Heat Convection in the Sink Plane

Author(s):  
Masood Razavi ◽  
Alireza Dehghani-Sanij ◽  
Yuri S. Muzychka

Thermal analysis of electronic devices is essential for designing thermal management systems and for assuring a perfect working condition. In order to have a precise thermal analysis, thermal spreading resistance should be calculated. In this paper, a numerical study is conducted on the thermal resistance of a 2D flux channel with a non-uniform convection coefficient in the heat sink plane. For this purpose, the Finite Volume Method (FVM) is used. As a case study, a 2D flux channel with a discrete specified heat flux and convection edges is assumed. Also, the heat transfer coefficient in the sink boundary condition is determined symmetrically using a hyperellipse function. This function can model a wide variety of different distributions of a heat transfer coefficient from a uniform cooling to the most intense cooling in the central region. All results are compared and validated with the COMSOL commercial software package. The proposed method is useful for thermal engineers for modeling different flux channels with different properties and boundary conditions such as the variable heat transfer coefficient.

2014 ◽  
Vol 1070-1072 ◽  
pp. 1705-1708
Author(s):  
Xiao Lu Wang ◽  
Da Yu Huang

In this paper, condensation mechanism of the Freon refrigerants outside spiral grooved tube is discussed. The heat transfer coefficient of Freon refrigerants condensation outside spiral grooved tube is obtained. A calculation example of heat transfer coefficient on the tube bundle of condenser with baffle bars is presented. It shows the excellent thermal performance of the spiral groove tubes compared to smooth tubes.


2015 ◽  
Vol 137 (11) ◽  
Author(s):  
M. Razavi ◽  
Y. S. Muzychka ◽  
S. Kocabiyik

In this paper, thermal resistance of a 2D flux channel with nonuniform convection coefficient in the heat sink plane is studied using the method of separation of variables and the least squares technique. For this purpose, a two-dimensional flux channel with discretely specified heat flux is assumed. The heat transfer coefficient at the sink boundary is defined symmetrically using a hyperellipse function which can model a wide variety of different distributions of heat transfer coefficient from uniform cooling to the most intense cooling in the central region. The boundary condition along the edges is defined with convective cooling. As a special case, the heat transfer coefficient along the edges can be made negligible to simulate a flux channel with adiabatic edges. To obtain the temperature profile and the thermal resistance, the Laplace equation is solved by the method of separation of variables considering the applied boundary conditions. The temperature along the flux channel is presented in the form of a series solution. Due to the complexity of the sink plane boundary condition, there is a need to calculate the Fourier coefficients using the least squares method. Finally, the dimensionless thermal resistance for a number of different systems is presented. Results are validated using the data obtained from the finite element method (FEM). It is shown that the thick flux channels with variable heat transfer coefficient can be simplified to a flux channel with the same uniform heat transfer coefficient.


Author(s):  
Jin-Cherng Shyu ◽  
Shu-Kai Jheng

A 120 mm × 53 mm × 19 mm horizontally-oriented pico projector in which both a pin-fin array and a piezoelectric fan were installed was tested to measure the thermal resistance at various heating powers. The operating frequency of the 40 mm × 10 mm aluminum piezoelectric fan ranged from 242 Hz to 257 Hz. The heat transfer coefficient of the pin-fin array was also estimated based on a thermal resistance network of the pico projector. The results showed that the thermal resistance of the pico projector which had a piezoelectric fan vibrating at a specific frequency would not monotonically reduce as the heating power increased. The heat transfer coefficient of the 1.5-mm-wide pin-fin array was higher than that of the 2.0-mm-wide pin-fin array at a given fan tip velocity ranging from 0.26 m/s to 0.76 m/s. The highest heat transfer coefficient of the 1.5-mm-wide pin-fin array reached approximately 21 W/m2K, while the highest heat transfer coefficient of the 2.0-mm-wide pin-fin array was approximately 16 W/m2K. A correlation between Nusselt number of the pin-fin array and Reynolds number was also developed in this study in a form of Nu = 0.3526Re0.1774.


Author(s):  
Thomas E. Dyson ◽  
James R. Winka ◽  
David B. Helmer

Many analyses in the literature have assessed the appropriate manner in which to scale an experimental test rig to represent film-cooled engine components. For conventional testing using low conductivity models, the key parameters are the mainstream Reynolds number, scaled coolant flow rate, and the adiabatic film effectiveness. The few studies that have sought scaling parameters for conjugate testing have identified that one must additionally match the heat transfer coefficient ratio between the internal and external surfaces and external Biot number. However, these analyses have focused on blade or nozzle regions with single or sparse film rows. The validity of this scaling approach to regions or components with substantial bore cooling contributions is unclear — for example the showerhead and/or platform of a blade or nozzle, or a component like a shroud. The present analysis outlines the drivers for potential departure from the accepted scaling. A numerical study is performed to assess potential errors due to the traditional scaling. The results of the analysis demonstrate that the additional parameter, the ratio of bore cooling to external heat transfer coefficient, is more appropriate in the near hole region especially in cases where film cooling is not significant.


Author(s):  
Дуаиссиа Омар Хадж Аисса

To determine the required oil pumping through the GTE rotor support, an accurate calculation of the heat flow from the engine to the GTE bearing chamber is necessary. The complexity of the mathematical description of thermo-hydraulic processes is associated with the presence of a multiphase mixture in the bearing chamber, consisting of oil, going for lubrication and cooling of the support elements, and air, used for seals pressurization. The work is devoted to the issues of numerical study of the effect of regime parameters on the heat transfer coefficient in the bearing chamber of the GTE. For these purposes, the methodology based on conservation laws and CFD modeling methods is applied. The change in the heat transfer coefficient in the characteristic sections of the chamber is considered. The influence of the oil film distribution around the circumference of the chamber is shown.


2018 ◽  
Vol 26 (7) ◽  
pp. 112-123
Author(s):  
Jalal M. Jalil ◽  
Ghada A. Aziz ◽  
Amjed A. Kadhim

Experimental and numerical study of fluid flow and heat transfer in microchannel airflow is investigated. The study covers changing the cooling of micro-channel for the velocities and heater powers. The dimensions of the microchannel were, length = 0.1m, width = 0.001m, height = 0.0005 m. The experimental and numerical results were compared with the previous paper for velocities up to 20 m/s and heater powers up to 5 W and the comparison was acceptable. In this paper, the results were extended numerically for velocities up to 60 m/s. The numerical solution used finite volume (SIMPLE algorithm) to solve Navier Stokes equations (continuity, momentum and energy). The results show that the heat transfer coefficient increases up to 220 W/m2 oC for velocity 60 m/s.


2020 ◽  
Vol 22 ◽  
pp. 78-84
Author(s):  
S. Niemyі

The safety of passenger transportation is not only to prevent accidents but also to ensure the conditions of health and efficiency of passengers and driver and the comfort of moving, which is guaranteed by the microclimate in the bus and the driver's workplace. One of the principal indicators of the microclimate is the air temperature in the cabin. The purpose of the work is to develop and substantiate the method of calculating the temperature of the bus interior.Unorganized air exchange due to body leaks (infiltration) influence on the thermal regime of the bus interior. Air exchange due to body leaks depends linearly on the speed of the bus. Heat loss through the structural elements of the body linearly depends on the outside air temperature.The calculation of the thermal state of the bus interior, in principle, is reduced to the estimation of the calorific value of the liquid heater, taking into account all heat losses in the cabin. The method of calculation developed on two indicators: experimentally defined coefficient of heat transfer of a body of the city bus and its inverse size, the calculated value of thermal resistance of unit of the area of salon of the bus. The thermal regime of the interior of a city bus in the conditions of winter operation is significantly influenced by heat exchange through the openings of open doors at short-term service stops. As for long-distance coaches, open the passenger door is much less. Therefore at the operation of buses of the specified class, it is necessary to give in salon-fresh air which needs to be heated.Since there are statistics on heat transfer of the body of city buses, the temperature of their cabins proposes to be calculated by the heat transfer coefficient of the bus body.In this method, the calculation depends on the heat transfer coefficient of the body. The supply and heating of air for ventilation are not taken into account, as the passenger door carries out air exchange in the cabin during bus stops.As calculations have shown, heat losses primarily depend on the temperature difference between the outside air and in the cabin. However, statistics on heat transfer of intercity (tourist) bus bodies are not currently available in the available publications. The temperature condition of intercity buses must correspond to the following calculations, inverse to the heat transfer coefficient of the body - thermal resistance per unit area of the bus.The method of calculating the temperature of the bus interior is substantiated. For city buses should be based on the calculation of heat transfer coefficients body. The temperature condition of intercity buses must be calculated from the thermal resistance per unit area of the bus interior. We proved that heat losses in the cabin of intercity buses, compared to city buses, are much lower due to the absence of heat losses at service stops at the exit and entry of passengers, which account for more than half of all heat losses. To reduce heat loss, the use of double-glazed windows instead of single panes has a particularly significant effect.


2016 ◽  
Vol 850 ◽  
pp. 299-306
Author(s):  
Zhen Hu Duan ◽  
Xuan Du ◽  
Hou Fa Shen ◽  
Bai Cheng Liu

Large steel ingots are the important material for the equipment manufacturing industry. It is still difficult to predict and control the macrosegregation in ingot. In this paper, the cooling curves at the surface of ingot and temperature variation of the mold were measured. The carbon distribution was measured through the local region dissection of ingot. Then, based on the definite the heat transfer coefficient at the interface of mold/ingot, a two-phase model with consideration of the motion of equiaxed grains is applied for the prediction of macrosegregation in 160-t steel ingot formed during the solidification. The results indicate that the heat transfer coefficient at the interface of mold/ingot decreases sharply after starting solidification and then varies slowly. Negative segregation at the bottom of ingot forms due to the interaction of solidification interface and equiaxed grains deposition during solidification. The positive segregation appears in the riser with thanks to the solidification shrinkage and the floating enriched solute. Finally, the results of the predicted and the measured are in good agreement.


2021 ◽  
Vol 2069 (1) ◽  
pp. 012145
Author(s):  
S Juricic ◽  
S Rouchier ◽  
J Goffart

Abstract Verification of the actual thermal performance of a building envelope after renovation is likely to become a useful key for performance contracting in the frame of heavy retrofit operations in buildings. Some existing methods such as the co-heating method, use on-site measurements to estimate the Heat Transfer Coefficient, or its inverse the overall thermal resistance. Although reliable and accurate, they need several days to several weeks of undisturbed measurements which can be rather inconvenient for building occupants and quite expensive in terms of operational costs. This paper investigates perturbation methods to design a 24-h heat input signal that would ensure an accuracy similar to or better than other perturbation methods to estimate an overall thermal resistance of the building envelope. The paper first studies 256 different squared heating signals in a numerical methodology to determine common characteristics of high-scoring 24-h signals. An experimental campaign in a wooden-framed house tested one of the high-scoring signals. The experimental results showed estimation errors higher than expected but consistent with the literature.


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