Heal sink

Isothermal reactor. The reactor can be operated with a larger heal sink if an excessive amount of heat is liberated by the reaction. 

Another source of heat generation in a medium is exothermic chemical re actions that may occur throughout the medium. The chemical reaction in this case serves as a heal source for the medium. In the case of endothermic reactions, however, heal is absorbed instead of being released during reaction, and thus the chemical reaction serves as a heal sink. The heat generation term becomes a negative quantity in this case. 

A 40-W power transistor is to be cooled by attaching it to one of tlie commercially available heal sinks shown in Table 3-6. Select a heat sink that tvill allow the case temperature of the transistor not to exceed 90°C in the ambient air at 20°C. 

Consider an I8 cm X 18-cm multilayer circuit board dissipating 27 W of heat. The board consists of four layers of 0.2-mm-lhick copper (k — 386 W/m °C) and three layers of 1.5-mm-thick epoxy glas.s (k = 0.26 W/m "C). sandwiched together, as shown in the figure. The circuit board is attached to a heal sink om both ends, and the temperature of the board at those ends is 35°C. Heat is considered to be uniformly generated in the epoxy layers of the board at a rate of 0.5 W per 1-cm X... 

Heal sinks willi (a) widely spaced and (b) closely packed fins. 

When the heat sink involves closely spaced fins, the narrow channels formed tend to block or suffocate the fluid, e.specially when the heat sink is long. As a result, the blocking action produced overwhelms the extra buoyancy and downgrades the heat transfer characteristics of the heat sink. Then, at a fixed power setting, the heat. sink runs at a higher temperature relative to the no-shroud case. When the heal sink involves widely spaced fins, the... 

The oplimuin fin spacing for a vertical heal sink and the Nus-sell number for optimally spaced fins is... 

C Why are heal sinks with closely packed fins not suitable for natural convection heat transfer, although they increase the heat transfer surface area more ... 

C Consider a heat sink with optimum fin spacing. Explain how heal transfer from this heat sink will be affected by (fl) removing some of the fins on the heat sink and (6) doubling the number of fins on the heal sink by reducing the fin spacing. The base area of the heat sink remains unchanged at all limes. 

Contact a manufacturer of aluminum heal sinks and obtain their product catalog for cooling electronic components by natural convection and radiation. Write an essay on how to select a suitable heal sink for an electronic component when its maximum power dissipation and maximum allowable surface temperature are specified. 

C (diamond) Cutting tools and wear-resistant coatings heal sink in laser diodes optical components... 

Deeqf heat removal Fmced cue throu SG ornatural cure to pool active passive 0 heat removal via Turbine condenser to heal sink Reactor pool heat removal to heat sink or to ambient air... 

HEAT SINK. I. In thermodynamic theory, a means by which heal is stored, or is dissipated or transferred from the system under consideration. 

Discussion This transistor can be used at higher power levels by attaching it to a heat sink (which lowers the thermal resistance by increasing the heat transfer surface area, as discussed in the next example) or by using a fan (vrhich lowers the thermal resistance by increasing the convection heal transfer coefficient). 

As we have discussed earlier, the buoyancy force is caused by the density difference between the healed (or cooled) fluid adjacent to the surface and tiie fluid surrounding it, and is proportional to this density difference and the volume occupied by the warmer fluid. It is also well knowu ll at whenever Iwc bodies in contact (.solid--solid, solid-fluid, or fluid-fluid) move relative to cacf other, a friction force develops at the contact surface in the direction opposite ic that of the motion. This opposing force slows down the fluid and thus reduce the flow rate of the fluid. Under steady conditions, the airflow rate driven b buoyancy is established at the point where these two effects balance each othet The friction force increases as more and more solid surfaces are introduced, se tiously disrupting the fluid flow and heat transfer. For that reason, heat sink with closely spaced fins are not suitable for natural convection cooling. 

Natinal convection flow through a channel foimned by two parallel plates as shown in Fig. 9-16 is commonly encountered in practice. When the plates arc hot (Tj > r,), the ambient fluid at enters the channel from the lower end, rises as it is healed under the effect of buoyancy, and the heated fluid leaves the channel from the upper end. The plates could be the fins of a finned heat sink, or the PCBs (printed circuit boards) of an electronic device. The plates can be approximated as being isothermal (Tj = constant) in the first case, and isoflu.x = constant) in the second case. 

Heat transfer media are classified as coolants (heat sinks) when heat is transferred to them from process streams, and as heal sources when heat is transferred from them to process streams. Process design includes the selection of appropriate heat transfer media, data for which are listed in Table 13.1, where the media are ordered by temperature range of application. 

It is believed that soluble borates can esterify the OH groups of cellulose and promote char formation similar to that of phosphorus. For example, a comparison of the performance of ammonium pentaborate, which decomposes and releases boric acid, and ammonium polyphosphate, which releases polyphosphoric acid, showed some similarity. Borates and boric acid also release some water, which provides a heat sink. Sodium borate and boric acid or anhydride or their mixtures are low-melting solids. Their viscous glassy melts can cause intumescence by evolved decomposition gases, mostly water, or they can just cover the surface of the pyrolyzing polymer or char, healing cracks and providing a barrier to heat and decomposition products. 

Anaerobic constructed wetlands promote bac-terially mediated sulfate reduction. These reactions have the potential to remove metals, as well as high concentrations of sulfate, from mine drainage. A growing concern associated with the use of wetlands to attenuate metals is the potential for the wetland soils to become latent sinks of toxic metals (Gopal, 1999). Heal and Salt (1999) monitored aconstructed-wetland system impacted by acidic metal-rich drainage from ironstone mine-spoils. Mine waters (pH 2.7,247 mg total iron)... 

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