Heat dissipation

while the corresponding value for flooded batteries is slightly above The difference is due mainly to the additional electrolyte in flooded 

A battery reaches a stable temperature when heat generation balances heat dissipation, i.e., when dQgjdt = dg /dt. When heat generation exceeds heat dissipation, thermal runaway may result. 

The dissipation of heat from a battery to its surroundings normally proceeds via three mechanisms (i) heat flow through the components of the battery and the container walls (ii) heat radiation (iii) free convection of air. In practice, the cooling of a battery takes place mainly through the side walls of the container. The bottom surface is usually in contact with a solid surface, which attains the same temperature as the battery and then ceases to be an effective heat sink. The upper surface plays little part in heat exchange the lid has no direct contact with the electrolyte, and the intermediate layer of gas, which has low thermal conductivity, hinders heat exchange. 

The quantity of heat per unit area (W m ) that can be conducted through the battery wall per unit time is given by 

The quantity of the heat lost per unit area (W m per unit time by the radiation 

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The majority of polymer flow processes involve significant heat dissipation and should be regarded as nou-isothermal regimes. Therefore in the finite element modelling of polymeric flow, in conjunction with the equations of continuity... 

These ion lasers are very inefficient, partly because energy is required first to ionize the atom and then to produce the population inversion. This inefficiency leads to a serious problem of heat dissipation, which is partly solved by using a plasma tube, in which a low-voltage high-current discharge is created in the Ar or Kr gas, made from beryllium oxide, BeO, which is an efficient heat conductor. Water cooling of the tube is also necessary. 

Ferrites aHowing for operation at frequencies well above 1 MH2 have also become available, eg, 3F4 and 4F1 (Table 6). Other newer industrial power ferrites are the Siemens-Matsushita N-series (28,97) the TDK PC-series (28,100), and the Thomson B-series (28,103). While moving to higher frequencies, the ferrites have been optimized for different loss contributions, eg, hysteresis losses, eddy current losses, and resonance losses. Loss levels are specified at 100°C because ambient temperature in power appHcations is about 60°C plus an increase caused by internal heat dissipation of about 40°C. 

Reoxidation occurs when the metallic iron in hot DRI reacts with oxygen in the air to form either Ee O or Ee202. The reaction continues as long as the DRI remains hot and sufficient oxygen is avadable. Because reoxidation reactions are exothermic and DRI is a good insulator, it is possible that once reoxidation begins inside a pde, the DRI temperature increases and accelerates the reoxidation rate. Although the inner core of the pde may reach temperatures up to the fusion point of iron, the maximum temperature of the outer parts of the pde will be much lower because of heat dissipation. 

Cases can be classified as either hermetic or nonhermetic, based on their permeabiUty to moisture. Ceramics and metals are usually used for hermetic cases, whereas plastic materials are used for nonhermetic appHcations. Cases should have good electrical insulation properties. The coefficient of thermal expansion of a particular case should closely match those of the substrate, die, and sealing materials to avoid excessive residual stresses and fatigue damage under thermal cycling loads. Moreover, since cases must provide a path for heat dissipation, high thermal conductivity is also desirable. 

Leads serve as the input—output interconnections between the component package and the mounting platform. Sometimes leads also aid in the dissipation of heat generated in the package. In the case of plastic packages, leads are formed from the leadframe, which also acts as a heat-dissipation path and a mechanical support for the die. 

Dye sublimation requires more heat dissipation and a longer (>10 ms) heating period to make a dark mark than does thermal transfer. Carehil manipulation of heating time and temperature can proportion mark size and dye content to cover a wide density range (0 to ca 2 optical density). 

Thermal conductivity of a fabric is related to its air permeabiUty, or movement of air between the interstices of the yam and fabric. For fabrics of a given thickness, the one that has greater air permeabiUty allows greater heat dissipation by convection. Thus thermal insulation falls as air velocity rises. 

The total heat released is the sum of the entropy contribution plus the irreversible contribution. This heat is released inside the battery at the reaction site. Heat release is not a problem for low rate appHcations however, high rate batteries must make provisions for heat dissipation. Failure to accommodate heat can lead to thermal mnaway and other catastrophic situations. 

Resistance Heating of Contacts. The contact material, contact area, and heat dissipating abihty, as well as the heat dissipating abihty of the stmcture to which the material is attached, limit the amount of current that a contact can transport. Excessive current heats and softens the metal contact. This softening results in an increase in the surface area of the contact and a corresponding reduction in contact resistance. 

W. R. Grace Co. dielectric and conductive adhesives, encapsulants, heat dissipating materials, manufacturing aid coatings... 

Example 6 Cooling Tower Determine water consumption and amount of heat dissipated per 1000 ftVmin of entering air at 90 F drydsulb temperature and 70 F wet-bulb temperature when the air leaves saturated at 110 F and the makeup water is at 75 F. 

A possible way to restrict the temperature rise is the use of a material having a high specific heat. An increase in the weight would be futile, as it would require more material and prove to be a costly proposition. A motor s constructional features should be such as to provide good heat dissipation through its body. 

Note 2 Since no system can be heal adiabatic in practice there is a ce.rtain amount of heat dissipation from the impregnated windings to the stator core and housing. This heat dissipation is considered as 15% of the total heat generated as in lEC 60079-7. 

They arc fabricated of two power tran.si.stor.s and arc used as a single transistor and are suitable only for control circuits. They arc used to reduce the control cuiTcnt requirement and hence cause lesser heat dissipation, particularly during switching operations. 

S Healing effect Low heat dissipation due to low voltage drop across the device (up to I V only)... 

This is similar to (a) above but each busbar now is mounted horizontally. Due to obstruction in heat dissipation, this arrangement requires a higher derating. It is also prone to collecting dust and provides a habitable surface for lizards and rodents etc. Therefore this is not a recommended configuration. 

This is similar to (a) except that now they are in the same plane and are not one below the other. Although heat dissipation would be slightly better than (b), this too is not a recommended configuration. 

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