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Abstract: The satisfactory performance of electrical equipments depends on their operating temperature. In order to maintain these devices within the safe temperature limits, an effective cooling is needed. High heat transfer rate of compact in size and reliable operation are the challenges of a thermal design engineer of electronic equipment. Then, it has been simulated the transient a three-dimensional model to study the heating phenomenon with two assumption values of heat generation. To control for the working of this equipment, cooling process was modeled by choosing one from different cooling technique. Constant low speed fan at one direction of air flow was used for cooling to predict the reducing of heating temperature through working of this equipment. Numerical Solution of finite difference time domain method (FDTD) has been utilized to simulate the temporal and spatial temperature profiles through two processes, which would minimize the solution errors.
1. Introduction
The heat mechanism of heat generation from the electrical equipment through its working and the air around is often described by means of thermal model. Thus, temperature profiles as a function of time and at various locations in the bulk of the material were calculated.
Most of the theoretical work has centered on the solution of the momentum and energy equations to show how the air around was influenced by heat dissipation from this equipment. While Eriksson and Sunden [1] developed a numerical model based on finite volume method with implicit technique for estimating the transient temperature response and cooling rate of an electrical unit with time dependent internal heat generation, the accuracy and reliability of the model were established by considering
experimental case studies. The electrical unit is placed in a closed box with cooling channels on two opposite sides. Measurements of the surface temperatures and cooling rate with time are achieved. Increasing the flow rate has a minor effect on the temperature. When water is used as coolant, the cooling rate is considerably higher than when oil is used as coolant. Natural convection cooling, in particular, results simple, cheap and reliable. In compact, low power consumption electronic equipments, in sealed system or available for the cooling technique of the system. It is also the only way to avoid or reduce the acoustic noise related with fan or liquid pumps characterizing other kinds of cooling systems. More complex cooling technique is necessary only in high power applications. In these cases we have to face with increase of costs and added cooling related space [2].
The present work predicts two models to show how the heat transfer mechanism was happened between a closed casing and air around, which was assumed as electronic equipment. This closed box was heated by heater, which was fixed at the bottom of this box. This position of heater was made as heat source per unit volume of a rectangular closed box. First model predicts the temperatures distribution over all the surfaces of a closed casing. These risings of temperatures were produced by heating with a heat source (heater) at two different values of power 25 W and 70 W respectively. Two approaches were assumed firstly, the effect of natural air around of these heating temperatures as natural convection.
In second model, it has been fixed a fan in cabinet in order to exhaust the air around, and then the heat mechanism was assumed between heating temperature and around air moving by fan (i.e., forced convection). The influences of the thermal properties of box material were taken in two models. The paper is organized as follows: Section 2 discusses the mathematical analysis through heating and cooling. Section 3 discusses results and discussion. Section 4 gives conclusions. Section 5 presents references.
As a computational grid of the three dimensional model (See Fig. 2).
Eq. (6) is referred to as the equation for node (i, j, k), since it is obtained by performing an energy balance on that element. A complete set of equations will be obtained by writing an energy balance for the boundary nodes. Special care must be exercised when handling corner nodes at A, C and D.
Through edge BC, that edge is insulated and subjected the boundary conditions z = 0, when
4. Conclusions
(1) Two models were simulated in this work. First model was predicted to present the spatial and temporal temperatures distribution of rectangular box and all outside corners, and all outside edge planes. The prediction model was unsteady, and in three dimensions with assumption of two values of heat generation in order to show the mechanism of heat transfer through heating process due its work function while the second model was predicted to present the
presentation of the spatial and temporal temperature distribution through both processes.
(2) Numerical solution using the explicit technique, have been performed to the basic 3-dimensional differential equation of heat diffusion in electrical equipment and energy equation of cooling this equipment, utilizing finite difference analysis for the surface and the distributed heat source of rectangular equipment type.
References
[1] D. Eriksson, B. Sunden, Numerical modeling of the cooling of an electrical unit with time-dependent heat generation, in: A.J. Nowak, C.A. Brebbia, R. Bialecki, M. Zerroukat (Eds.), Advanced Computational Methods in Heat Transfer V, Computational Mechanics Publications Southampton, UK and Boston, USA, 1998.
[2] S.J. Kim, S.W. Lee, Air Cooling Technology for Electronic Equipment, CRC Press, Boca Raton, LA, 1996.
[3] R.M. Desmond, R.V. Karlekar, Heat Transfer, 2nd ed., West Publishing Company, Minnesota, United State of America, 1982.
[4] R.H. Hameed, Numerical and experimental study of cooling for an electrical unit, M.Sc. Thesis, University of Babylon, 2010.
[5] W.M. Kays, M.E. Crawford, Convective Heat and Mass Transfer, 3rd ed., McGraw-Hill, 1993.
[6] E.M. Alawadhi, Thermal analysis of a channel containing multiple heated obstacles with localized heat generation, Journal of IEEE Transaction on Components and Packaging Technologies 27 (2) (2004) 327-336.
1. Introduction
The heat mechanism of heat generation from the electrical equipment through its working and the air around is often described by means of thermal model. Thus, temperature profiles as a function of time and at various locations in the bulk of the material were calculated.
Most of the theoretical work has centered on the solution of the momentum and energy equations to show how the air around was influenced by heat dissipation from this equipment. While Eriksson and Sunden [1] developed a numerical model based on finite volume method with implicit technique for estimating the transient temperature response and cooling rate of an electrical unit with time dependent internal heat generation, the accuracy and reliability of the model were established by considering
experimental case studies. The electrical unit is placed in a closed box with cooling channels on two opposite sides. Measurements of the surface temperatures and cooling rate with time are achieved. Increasing the flow rate has a minor effect on the temperature. When water is used as coolant, the cooling rate is considerably higher than when oil is used as coolant. Natural convection cooling, in particular, results simple, cheap and reliable. In compact, low power consumption electronic equipments, in sealed system or available for the cooling technique of the system. It is also the only way to avoid or reduce the acoustic noise related with fan or liquid pumps characterizing other kinds of cooling systems. More complex cooling technique is necessary only in high power applications. In these cases we have to face with increase of costs and added cooling related space [2].
The present work predicts two models to show how the heat transfer mechanism was happened between a closed casing and air around, which was assumed as electronic equipment. This closed box was heated by heater, which was fixed at the bottom of this box. This position of heater was made as heat source per unit volume of a rectangular closed box. First model predicts the temperatures distribution over all the surfaces of a closed casing. These risings of temperatures were produced by heating with a heat source (heater) at two different values of power 25 W and 70 W respectively. Two approaches were assumed firstly, the effect of natural air around of these heating temperatures as natural convection.
In second model, it has been fixed a fan in cabinet in order to exhaust the air around, and then the heat mechanism was assumed between heating temperature and around air moving by fan (i.e., forced convection). The influences of the thermal properties of box material were taken in two models. The paper is organized as follows: Section 2 discusses the mathematical analysis through heating and cooling. Section 3 discusses results and discussion. Section 4 gives conclusions. Section 5 presents references.
As a computational grid of the three dimensional model (See Fig. 2).
Eq. (6) is referred to as the equation for node (i, j, k), since it is obtained by performing an energy balance on that element. A complete set of equations will be obtained by writing an energy balance for the boundary nodes. Special care must be exercised when handling corner nodes at A, C and D.
Through edge BC, that edge is insulated and subjected the boundary conditions z = 0, when
4. Conclusions
(1) Two models were simulated in this work. First model was predicted to present the spatial and temporal temperatures distribution of rectangular box and all outside corners, and all outside edge planes. The prediction model was unsteady, and in three dimensions with assumption of two values of heat generation in order to show the mechanism of heat transfer through heating process due its work function while the second model was predicted to present the
presentation of the spatial and temporal temperature distribution through both processes.
(2) Numerical solution using the explicit technique, have been performed to the basic 3-dimensional differential equation of heat diffusion in electrical equipment and energy equation of cooling this equipment, utilizing finite difference analysis for the surface and the distributed heat source of rectangular equipment type.
References
[1] D. Eriksson, B. Sunden, Numerical modeling of the cooling of an electrical unit with time-dependent heat generation, in: A.J. Nowak, C.A. Brebbia, R. Bialecki, M. Zerroukat (Eds.), Advanced Computational Methods in Heat Transfer V, Computational Mechanics Publications Southampton, UK and Boston, USA, 1998.
[2] S.J. Kim, S.W. Lee, Air Cooling Technology for Electronic Equipment, CRC Press, Boca Raton, LA, 1996.
[3] R.M. Desmond, R.V. Karlekar, Heat Transfer, 2nd ed., West Publishing Company, Minnesota, United State of America, 1982.
[4] R.H. Hameed, Numerical and experimental study of cooling for an electrical unit, M.Sc. Thesis, University of Babylon, 2010.
[5] W.M. Kays, M.E. Crawford, Convective Heat and Mass Transfer, 3rd ed., McGraw-Hill, 1993.
[6] E.M. Alawadhi, Thermal analysis of a channel containing multiple heated obstacles with localized heat generation, Journal of IEEE Transaction on Components and Packaging Technologies 27 (2) (2004) 327-336.