Jen-Chieh Cheng

ENHANCEMENT OF HEAT TRANSFER FROM SURFACE-MOUNTED BLOCK HEAT SOURCESIN A DUCT WITH BAFFLES

A numerical analysis was carried out to study the performance of mixed convection in a horizontal duct with two heated blocks mounted on the bottom plate and baffles arranged on the up plate. The effects of the dimensionless height of baffle H b , the dimensionless distance between the block and baffle D , and the number of baffle N on the flow structure and heat transfer characteristics were investigated for the system at various Reynolds number Re and ratio of Grashof number to square of Reynolds number Gr/Re 2 . With the two baffles installed at D 1 =0 and D 2 =0, results show that the maximum augmentation in the average Nusselt number of the second heated block exceeds 320% for H b1 = H b2 =0.4, Pr = 0.7, 100 h Re h 1,000, and 0 h Gr/Re 2 h 10, while the maximum augmentation is about 130% for the first heated block. When a single baffle is located between the two heated blocks, the heat transfer performance of both the first and second heated blocks can be significantly promoted. However, only the heat transfer performance of the second heated block can be enhanced, as the baffle is installed behind the second heated block.

Thermal Interaction and Chimney Effects on Natural Convective Cooling Performance of Heat Generating Blocks Mounted on a Board in a Two-Dimensional Cabinet

This study aims to investigate numerically the effect of thermal interaction between the air streams inside and outside a cabinet on the cooling performance of heat generating blocks mounted on a board in the two-dimensional square cabinet. Moreover, air vents are proposed to construct in the cabinet wall; the thermal buoyant force can induce air to flow through the cabinet. Great efforts are performed to rigorously investigate the chimney effect of air vents on heat transfer enhancement of heat generating blocks in the cabinet. The computation domain covers the cabinet and the surrounding area, and the temperature and velocity fields of the cabinet and surrounding area are solved simultaneously. Results show that the thermal interaction and air vents can significantly affect the cooling performance of heat generating blocks. The maximum difference in hot spot temperatures of the blocks for the situations with and without consideration of thermal interaction can be up to 44%, as Pr = 0.7, 104 ≦ Ra ≦ 106 and 10 ≦ K bf = K pf = K wf ≦ 100. When three vents are constructed in the cabinet wall, the hot spot temperature can be reduced by 45%. On the other hand, the difference in the hot spot temperatures for cases with two and three air vents is within 6%.

Characteristics and Enhancement of Heat Transportation From a Block Heat Source Module in Three-Dimensional Cabinets to an Ambient Natural Convective Air Stream

This study aims to numerically investigate the natural convective heat transfer characteristics and cooling performance enhancement for a module comprised of a board and arrays of discrete heat generating blocks in three-dimensional cabinets. The objective of this study has three aspects. First, efforts are performed to investigate the influence of thermal interaction between the air streams inside and outside the cabinet on the natural convective heat transfer characteristics for the heat source module. Second, attention is given to investigate the cooling performance enhancement of the module by installing plate fins onto the back surface of board. Finally, the cooling performance enhancement of the module by constructing air vents in the cabinet wall is conducted. The computation domain covers the cabinet and surrounding area, so that the temperature and velocity fields of the cabinet and surrounding are solved simultaneously. The results show that the maximum difference in hot spot temperatures of the heat source module for the situations with and without consideration of thermal interaction can be up to 22.7 as Pr = 0.7, 104 ≤ Ra ≤ 106, K bf = K pf = K wf = 100, K Ff = 8000, and the ranges of other parameters listed in the text. When plate fins are installed onto the back surface of the board, the hot spot temperature can be reduced by 25.5%. Furthermore, the reduction in hot spot temperature is about 47.8% when air vents are constructed in the cabinet wall.

Enhancement of heat transfer from block heat sources mounted on a short board to air stream in a channel by constructing slots in the board

ABSTRACT Aiming to enhance the performance of laminar forced convection in a two-dimensional channel containing a short board mounted with block heat sources, this study proposes a method of constructing slots in the board. The effects of the slot position, board location, and Reynolds number on the flow structure, temperature distribution, and heat transfer coefficient are investigated numerically. Results show that when the stream approaches and passes the short board, the streamlines and isotherms may deflect strongly in the regions near the leading and trailing edges of the board. Comparing the results for the situations without and with slots in the board, the maximum enhancements of the average Nusselt numbers are about 81%, 57%, and 55% for the front, top, and rear surfaces of blocks, respectively, when Pr = 0.7, 50 ≤ Re ≤ 500, L e = 0.5, L a = L f = 1, H b = L b = 0.3, D b = 0.7, D f = 0.1, 0 ≤ L s ≤ 0.2, 0.1 ≤ D a ≤ 0.4, and 0.2 ≤ C 2 ≤ 0.5. In addition, the convective transfer behaviors are more sensitive to the variation of slot position when the spacing between the board and bottom channel plate C 2 is smaller.

Heat transfer from block heat sources mounted on the wall of a 3D cabinet to an ambient natural convective air stream

ABSTRACT In this study the physical system under consideration is a three-dimensional (3D) cabinet with arrays of block heat sources mounted on one of the walls of the cabinet. The block heat sources dissipate heat to the surrounding cabinet through conjugate conduction and natural convection. The results illustrate that the difference in hot spot temperature (θH) for situations with and without consideration of thermal interaction between the system and its surrounding area is higher for smaller Rayleigh number (Ra), and can be up to 94.73% with Ra = 105. In addition, heat transfer characteristics depend strongly on the dimensionless heat conductivity of the cabinet wall (Kwf), heat conductivity of the block (Kbf), and length of cabinet (Cx). The maximum reduction in θH is 70.01% when Kwf varies from 10 to 1,000, 12.7% for 10 ≦ Kbf ≦ 1,000, and 30.07% for 0.5 ≦ Cx ≦ 1. The variation in hot spot temperature of blocks is not sensitive to cabinet angle (Φ).

Conjugate natural convective heat transfer from photovoltaic cells on the bottom wall of a horizontal cabinet to ambient air stream

This study proposes a model to investigate the detailed behaviors of natural convective cooling of photovoltaic cells mounted discretely on the bottom wall of a horizontal cabinet. The numerical computation domain covers the cabinet and surrounding area, so that the temperature and velocity fields of the combined regions are solved simultaneously. Results show that the temperature differences among the photovoltaic cells can be up to 28% for all the investigated cases when 106 ≦ Ra ≦ 108, 1000 ≦ Kef ≦ 6300, Cx = 7.5 and N = 6. The maximum difference in hot spot temperatures of photovoltaic cells is about 26% among the cases with various Kef.