**6. References**


The results are compared with the solution procedure that used only the TDMA solver without a multigrid correction. The TDMA solver with the AC-MG algorithm was capable of efficiently driving the residual down to the level of the computer machine round-off error within 400 AC-MG cycles. The residual was driven down by about twelve orders of

A three-dimensional mathematical model, developed using incompressible laminar Navier-Stokes equations of motion, is capable of predicting correctly the flow and conjugate heat transfer in the microchannel heat sink. The microchannel heat sink model consists of a 10 mm long silicon substrate, with rectangular microchannels, 57 µm wide and 180 µm deep, fabricated along the entire length. A finite volume numerical code with a multigrid technique, based on additive correction multigrid (AC-MG) scheme, that is a highperformance solver, was developed to solve the steady incompressible laminar Navier– Stokes (N-S) equations, over a colocated Cartesian grid arrangement. Higher Reynolds numbers are beneficial at reducing both the water outlet temperature and the temperatures within the heat sink, also at the expense of greater pressure drop. By the magnitude of the mean velocities and the Reynolds numbers obtained from the analytical and numerical methods, the agreement between the two methods is quite good and provides sufficient evidence for validation of the numerical method. The variations of the heat transfer coefficient and the Nusselt number along the flow direction is quite small for this type of microchannel heat sink after the thermal entrance lengths. The heat flux along the channel side walls is higher than along the channel top and bottom walls (almost two orders of magnitude larger than those at the top and bottom walls) due to the short distance between the channel side walls and the large velocity gradient present. The temperature is highest at the channel corner; this is due to the low velocity of the flow and the resulting high concentration of heat flux. The results indicate that the thermophysical properties of the liquid can significantly influence both the flow and heat transfer in the microchannel heat sink. The bulk liquid temperature is shown to vary in a quasi-linear form along the flow

direction for high fluid flow rates, but not for low flow rates (low Reynolds number).

Electronic Devices Letters EDL-2 (1981) 126-129.

Engineering, 7(1), pp. 11–16.

(14) (2003) 2547– 2556.

[1] D.B. Tuckerman, R.F. Pease, "High-Performance Heat Sinking for VLSI, " IEEE

[2] S.P. Jang, S. Kim, K.W. Paik, 2003, "Experimental Investigation of Thermal

[4] H.Y. Wu, P. Cheng, "An Experimental Study of Convective Heat Transfer in Silicon

[5] W. Qu, I. Mudawar, "Analysis of Three-Dimensional Heat Transfer in Microchannel

Heat Sinks," Int. J. Heat Mass Transfer 45 (2002) 3973–3985.

Micro Thermal Sensor Array," Sens. Actuators, A, 105, pp. 211– 224. [3] Y. Chen, S. Kang, W. Tuh, and T. Hsiao, 2004, "Experimental Investigation of Fluid Flow

Characteristics for a Microchannel Heat Sink Subject to an Impinging Jet, Using a

and Heat Transfer in Microchannels," Tamkang Journal of Science and

Microchannels with Different Surface Conditions," Int. J. Heat Mass Transfer 46

magnitude.

**5. Conclusion** 

**6. References** 


**9** 

*China* 

**Compact Heat Exchange Reformer Used for** 

High temperature fuel cell systems are an attractive emerging technology for stationary power generation, especially for the distributed generation [1]. Today, there are mainly two types of high temperature fuel cell systems, including the molten carbonate fuel cell (MCFC) and solid oxide fuel cell (SOFC), which are generally operated at high temperatures ranging from 823K to 1273K. Several advantages of this setup are listed in the references [2]. The main advantages of both fuel cells are related to what could be done with the waste heat and how they can be used to reform fuels, provide heat, and drive engines. Therefore, high temperature fuel cell systems can never be simply considered as fuel cells; instead, they must always be thought of as an integral part of a complete fuel processing and heat

Steam reforming is a well-established industrial fuel process for producing hydrogen or synthetic gas from natural gas, other hydrocarbon fuels, and alcohols [3]. In the high temperature fuel cell systems, the pre-reformer is usually needed for fuel processing. Due to the high endothermic reaction, a great amount of heat must be provided from the outside,

High temperature heat exchangers are widely used in the high temperature fuel cell/gas turbine system, closed cycle gas turbine system, high temperature gas cooled reactors, and other thermal power systems. It is an effective method of improving the whole system efficiency [4]. Compact heat exchangers are generally characterized by extended surfaces with large surface area/volume ratios that are often configured in either plate-fin or tube-fin arrangements [5]. In a plate-fin exchanger, many augmented surface types are used: plainfins, wavy fins, offset strip fins, perforated fins, pin fins, and louvered fins. Offset strip fins, which have a high degree of surface compactness and feasible manufacturing, are very

In general, the high temperature heat exchanger is used to preheat the air or fuel, while the pre-reformer is used to produce hydrogen rich fuel from methane or other hydrocarbons. Fig. 1 shows one of the fuel cell systems, which consists of a direct internal reforming solid oxide fuel cell (DIR-SOFC), a high temperature heat exchanger (HTHE), a low temperature heat exchanger (LTHE), a pre-reformer, a gas turbine, a generator, etc. In order to simplify the system, reduce the cost, and improve the fuel cell system's efficiency, it is suggested that

such as waste heat from the fuel cell, catalyst combustion, etc.

**1. Introduction** 

generating system [2].

widely applied.

**High Temperature Fuel Cell Systems** 

Huisheng Zhang, Shilie Weng and Ming Su

*Shanghai Jiao Tong University* 


Huisheng Zhang, Shilie Weng and Ming Su *Shanghai Jiao Tong University China* 
