Investigation on Microheat Pipe Array with Arteries

Abstract

A novel design of microheat pipe array with arteries that can limit the onset of the dryout region is proposed. Additional pipes are inserted between adjacent microheat pipes to improve liquid transportation ability from the condenser section to the evaporator section. These additional pipes have smaller cross-sectional dimensions than the microheat pipe and serve as an artery of the microheat pipe. Because of the liquid pressure difference in the meniscuses between the two ends of the microheat pipe, an additional amount of working liquid can be effectively transported to the evaporator section through these arteries, which definitely improves the performance of the microheat pipe. The working principle and optimal design of the arteries are numerically investigated with a onedimensional steady-state model of the artery microheat pipe array. To verify the idea, a silicon-based artery microheat pipe array and traditional microheat pipe sample with the same dimensional parameters are fabricated by lithographic technique and anodic bonding process. The validation has been carried out by the comparison observation experiments of the novel microheat pipe and the traditional microheat pipe through a microscopic camera. Both the model's numerical solution and the observation results indicate that the artery microheat pipe array can effectively extend thermal working range.Nomenclature A = liquid area in the V-groove of the microheat pipe, m 2 A 0 = area of the cross section, m 2 A 0 L = liquid area in the cross section at the cold end (x 1), m 2 a A = width of the artery, m a = width of the microheat pipe, m B 1 = constant in expression for A 1 B 2 = constant in expression for dR =dx c = constant in expression for a 1 =a f = friction factor g = acceleration due to gravity, m=s 2 K 0 = constant in expression for w L = length of heat pipe, m L h = half of total wetted length, m P = liquid pressure, N=m 2 P = nondimensional liquid pressure P R = reference pressure, N=m 2 Q = heat supplied to the liquid, W=m 2 R = radius of meniscus curvature in the V-grooves of the microheat pipe, m R 0 = radius of meniscus curvature in the V-grooves of the microheat pipe at x 0, m R L = radius of meniscus curvature in the V-grooves of the microheat pipe at x L, m R R = reference radius of meniscus curvature, m V = axial liquid velocity, m=s V A = liquid velocity in the artery, m=s V = nondimensional liquid velocity V R = reference liquid velocity, m=s x = coordinate along the heat pipe, m x = nondimensional coordinate along microheat pipe = half apex angle of V-groove, rad = inclination of substrate with horizontal, rad = contact angle, rad = correction coefficient = fill charge = latent heat of vaporization of coolant liquid, J=kg = viscosity of coolant liquid, kg=ms = density of coolant liquid, kg=m 3 = surface tension of coolant liquid, N=m wA = shear stress between liquid and substrate of the artery, N=m 2 w = shear stress between liquid and substrate of the microheat pipe, N=m 2 = curvature, m 1

MEMS-Based Micro-heat Pipes

“…The effective thermal conductivity evaluated by a 3D simulation was found to be 600 W/(m K), which represented an increase of 300% of the silicon thermal conductivity at high heat flux, demonstrating remarkable heat transfer enhancement. Recently, a novel artery MHP array as illustrated in Figure 9 was proposed by Kang et al [38] to enhance the liquid backflow. Two smaller channels serving as arteries are positioned on both sides of one vein channel which acts as the ordinary MHP, and these channels are connected together at both ends by two connecting channels.…”

“…Because of the two ends' pressure difference of the V-shape grooves in the MHP array, the working liquid gathered at the Figure 9. Schematic diagram of the MHP and artery and working principle [38].…”