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EXECUTIVE SUMMARY 2 INTRODUCTION (ABR) 3 ADVANTAGES & DISADVANTAGES 3 SUBSYSTEM DESIGN (KEN) 7 Regulations (EZE) 7 Cost (EZE) 7 Improvements in Design (EZE)(ABR) 7 CONCLUSION (ABD)(KEN) 8 References: 8

Heat pipes were invented around 1963 by George Grover in Los Alamos National Laboratory (Delete This…just adds unnecessary fluff). The heat pipe is considered a closed evaporative-condenser. Heat pipes are special because they transport heat. This happens through the use of a liquid normally referred as “working fluid”. This working fluid is normally water, nitrogen, methanol/alcohol. The pipe absorbs the heat by vaporizing the liquid inside. The vapor is then released to a cooling medium to cool off. Heat pipes can be easily bent or flattened, but it is important to note that this changes can affect fluid flow, temperature, and performance. However, in order for the heat to be removed from the system a heat sink must be added which will allow heat to be released more efficiently from the system to the surface around them.

Advantages of heat sinks

Heat sinks are made and designed to have a large exposed part of the entire device to the surrounding which acts as a cooling medium. The components or the electronic devices that cannot regulate their temperatures are assisted in cooling by heat sinks. Controlling the heat generated by the electronic devices of the circuit reduced the risks of wearing out the device thus preventing premature failure of the entire electronic component (Zhao, & Tan, 2014).

Heat sinks also plays a major task of maintaining thermal stability of the electronic devices and components entangled in a circuit. The ability of heat sinks to stabilize thermal limits in these components is influenced by material, surface treatment and velocity of the surrounding area of the circuit system. Heat sinks are further tailored to meet requirements of other electronic gadgets such as computers. They are used to cover computer's memory to disperse excess heat. More so, heat sinks are not only used to disperse heat but also to provide heat in instances of low temperatures where they release thermal energy for the effective functioning of the circuit. Heat sinks do not produce noise.

Disadvantages of heat sinks

The materials used to manufacture the different types of heat sinks are expensive which makes the entire installation of heat sinks costly. Installation of heat fans is crucial in, in case it is placed downwards of the component, then it will not disperse heat. Thus, component placement and orientation must be considered. Heat pipes are closed containers that are used to evaporate and condense a fluid thus giving off heat.

Advantages of heat pipes

The installation of heat pipes offers a conducive environment since they are passive in their operations. They do not require energy to run and cool systems. Passive element of heat pipes makes them have a long life since there is nothing to wear out (Yang, Yan, & Mullen, 2012). Heat pipes do not have moving parts thus no need for lubrication. Furthermore, they can be tailored and partitioned to enable separate conduit of fluids. This property makes them best suited for laboratory operations where cross-contact of chemicals is a concern. The immobility aspects of heat pipes reduce the cost of maintenance to the system. They are economical in space and can be customized in different sizes of any application.

Disadvantages of heat pipes

Heat pipes have to be adjusted at an angle of around 25° to allow the internal fluid of the heat pipe to flow back to the hot absorber. Capillarity limit of the heat pipes must be attained. The rate at which the fluid flows from the cooling component to the evaporator through the wick must be standardized to maximize the cooling process. Heat pipes must be thoroughly cleaning the inside or else it is subjected to heat which reduces its performance.

The most popular materials used as a heat sink dissipators are Aluminium and Copper-Chromium-Zirconium, due to their combination of its good thermal conductivity around 400 W/m-k, mechanical strength at low and moderate temperatures, and light density 8.9 g/cc made it of interest for use as heat sink material in high heat flux components in actual and future microelectronics. Copper-Chromium-zirconium may be labeled under several names such as Cu-Cr-Zr,and C18150 mainly for commercial purposes. It has fraction of (0.7 to 0.8) mass% chromium and (0.07 to 0.15) mass% zirconium, and cu is recommended as an additive material. Unfortunately, Cu-Cr-Zr has low operational temperature at 500°C, which particularly loses its mechanical property in microstructural modifications. Due to this mechanical loss Cu-Cr-Zr is not well candidate for excessive heat compartment like engines area. and it needs to be machined and skived, or soldered the fins into the heat sink base.

However, Aluminium is more common than copper as heat sink because it is four to six time cheaper than copper and it can be extruded as a heat sink, while copper can not. Aluminium alloy 1050A has one of the highest thermal conductivity value around 220 W/m-K, but has low strength. this make Aluminum 6060 and 603 more commonly favorable which thermal conductivity 166W/m-k and 201 W/m-k respectively, and low density 2.7 g/cc while is they are three time lighter than copper. Moreover, the Aluminum has a higher melting point. These two materials make a great combination for heat dissipation for microcontrollers, as aluminum use as heat sink and copper as heat pipe.

The picture shown below is a combination of two microchips, attached to a copper heat pipe, which is connected to an aluminum alloy heat sink. Only a heat power source of 25 Watts and heat convection coefficient of 100 W/ m^2 k was applied for each microchip. The mesh was chosen as curvature mesh. There was the option of adding bulk temperature so a temperature of 300k was used. This bulk temperature was used because it is equivalent to a typical room temperature (20-23 Celsius). The heat source is coming from the microchips dispersing through the heat pipes. The simulations show that heat travels from the heat pipes to the heat sink. The problem is that heat color gradient is just yellow. There is no visible heat cooling off just yellow. However, no contacts were applied. For example, no thermal resistance between surfaces were applied because the numbers would be too arbitrary.

Designing a thermal management unit becomes more important and critical to optimization. life expectancy and performance is directly related to the electronical devices. therefore, reliability and equipment operation temperature are inversely related. --( Delete this ...doesn’t add value)

--When designing a thermal management unit it is necessary to set various parameters that affect the overall performance of the system. A large budget depends on external conditions surrounding the heat sink. Below a list of some parameters have that have been assumed in SolidWorks simulation for analysis purposes.

· constant fluid temperature.

· steady fluid flow.

· steady heat flow.

· laminar flow for both vapor and liquid.

Before discussing the heat sink design process, it is common terms and concepts need to be define.

· Q: amount of heat transferred in W/m^2,

· Td: Device temperature during maximum heat generating.

· Tp1: Heat pipe temperature closest to the heat source.

· Rp; thermal resistance due to pipe wall.

· Xp: The thermal wall thickness (m).

· kp: the thermal conductivity of the heat pipe material (W/(m*k))

· Ap; the total area of the heat pipe (m^2).

· Tp2: heat pipe temperature closest to the heat source.

· Ts: sink temperature of heat sink. This represent the maximum temperature of the heat sink at the closest location to the heat pipe.

· Ta: Ambient air temperature.

· Rj: Thermal resistance across the interface between two locations. This can be defined as

R=

To begin the thermal management designing, the first step is to determine the heat pipe and the heat sink thermal resistance required to satisfy the thermal criteria. By rearranging the previous equation, the heat sink resistance can be easily obtained as

We assume the analysis for the simulation is

· Constant fluid temperature

· Steady fluid flow

· Steady heat flow

· Laminar flow for both vapor and liquid phase

Regulations (EZE)

There are two main regulations that will govern design, material and fluid selection of heat pipes. Since the heat pipe is considered a pressure vessel, the design and material thickness will have to comply with all of the ASME pressure vessel codes and standards. (Peterson, 1994). To be ASME complicant the designer has to calculate the thickness using the ASME B31.3 Code for calculating pipe thickness.

Where:

P - Maximum expected pressure at design conditions

d - Maximum expected temperature at design conditions

c - Corrosion allowance

S - Allowable stress of material

E - Quality factor

Y - Material Factor

In addition to solving for longitudinal and hoop stresses for the heat pipe. (

The heat transfer fluid will have to comply with all of the environmental regulations and laws for hazardous fluids. For example, in the case that the designer uses mercury, then there will have to be a procedure in the case of failure with the heat pipe.

Major improvement will come by putting both devices and system of heat transfer together as a single unit created a HSHP (Heat-sink & Heat-pipe). In majority of the cases when one takes apart a laptop or other smaller electrical components they have either a heat-sinks or heat-pipes system, which are very effective but the systems still have major heat build up. By finding different ways to incorporate a heat-sink with a heat pipe would help in removing excess heat that was creating and giving the component a more efficient working environment. Other improvements are to place a source of extra feed to the HSHP in reducing heat by cooling it down with the same air around the components. Which can be accomplished by having an electric fan in the system.

Yang, X., Yan, Y. Y., & Mullen, D. (2012). Recent developments of lightweight, high

performance heat pipes. Applied Thermal Engineering, 33, 1-14.

Zhao, D., & Tan, G. (2014). A review of thermoelectric cooling: materials, modeling and

applications. Applied Thermal Engineering, 66(1), 15-24.

Peterson, G.P., 1994. An Introduction to Heat Pipes. Canada: John Wiley & Sons, Inc.

Meeting min intro AbR (mon Adv Ken (sun MAterial Abd (sun Sys And sub Rob sun Cons Eze Monday