Removing Excess Heat

All BU produce heat as a result of metabolic processes, and so the major problem faced by many BU is the removal of excess heat. BU that are not provided with the ability to rid themselves of waste heat will eventually die. We have already seen in Section 2.7 that BU may lose heat by conduction, convection, radiation, and evaporation. Of these, conduction is not usually significant because BU 

FIGURE 6.5.1 Hot hydrothermal pools in Kamchatka, Russia, are a fitting environment for thermophilic bacteria and archaea. (From Hoffmann, R., Am. Sci., 89, 20, 2001. With permission.) 

Convection heat loss may or may not be significant. Tissue and organ BU depend upon the convection of the blood flow to maintain a constant and uniform internal thermal environment. We often think of blood as heating the tissues through which it flows, but a heat balance requires that for the blood to heat some tissues it must cool others. The brain and liver are two organs for which blood cooling is especially important. 

Cattle adapted to colder climates store fat under the skin and between muscle fibers. This fat is poorly vascularized and acts as insulation against heat loss. Hot-weather adapted cattle, however, store most of their fat in the gut, around body organs, and in humps on their backs. These cattle can lose much more heat to the environment than if they had the insulating fat layer underneath their skin. 

Convection is also important for microbes bathed by a water-based medium and for plants in the air. Each has such a small capacity to generate heat compared to the capacity to transfer heat by convection that they exist at the same temperature as their surrounding fluids. The temperatures of biomes and ecosystems can also be considered to be determined by the temperature of the air and water around them. 

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Elevated pressures are required to keep water in the Hquid state. Liquid water cataly2es oxidation so that reactions proceed at relatively lower temperatures than would be required if the same materials were oxidi2ed in open flame combustion. At the same time, water moderates oxidation rates by providing a medium for heat transfer and removing excess heat by evaporation. 

Liquid cooled internal combustion engines require a circulating coolant to remove excess heat. While water is an effective heat transfer fluid, it has serious shortcomings as an engine... 

This formula is able to remove excess heat from the Qi level, especially from the Lung and Stomach. The manifestations are high fever without chill, perspiration, dry mouth and thirst, a red face, irritability, shortness of breath, a red tongue with a yellow coating and a rapid and forceful pulse. 

The lift pipe design was tapered to a larger diameter at the top. This minimized the effects of erosion and catalyst attrition, and also prevented the instantaneous total collapse of circulations when the saltation concentration, or velocity, of solids is experienced (i.e. the slump velocity-that velocity below which particles drop out of the flowing gas stream). In a typical operation, 2 % to 4 % coke can be deposited on the catalyst in the reactor and burned in the regenerator. Catalyst circulation is generally not sufficient to remove all the heat of combustion. This facilitated the need for steam or pressurized water coils to be located in the regeneration zone to remove excess heat. 

Three types of UV system configurations are usually applied in drinking water disinfection unsubmerged, closed channel submerged, and open channel submerged operations. In unsubmerged operation, the water flows inside of a transparent tube, while the UV lamp is outside of the tube. Special design must be applied to remove excess heat accumulated in the system. 

Cooling towers are used in many industrial areas to cool water to remove excess heat produced by fuel combustion or by other reactions. Nowhere is more cooling water used than in the production of electricity from nuclear fission. In virtually every cooling tower application, cool water is taken from a surface source (river, estuary, or lake) and is returned to its source heated up. The introduction of warmed water to its source disrupts marine plant and animal life and also catalyzes chemical reactions. These have the effect of increasing the concentrations of toxic chemicals in water, which is often taken up for drinking use downstream... 

Since the reaction of sulfur with dry air is exothermic, the sulfur dioxide must be cooled to remove excess heat and avoid reversal of the reaction. 

If the mean surface temperature is independent of metabolic rate, a heat exchange mechanism other than convection or radiation must be responsible for removing excess heat generated when a subject exercises. One s attention turns immediately to sweating, a phenomenon which has been studied in many laboratories. For subjects in equilibrium with the environment, the sweat rate is directly proportional to the total heat production rate. Perhaps this is expected because regulating central temperature by controlling the blood flow rate to skin, and, thus, the skin temperature is relatively ineffective. As the skin temperature rises, the difference between the central temperature and the skin temperature... 

Measurement of Temperature Inside the Capillary The use of NECEEM for measuring temperature inside the capillary has been demonstrated experimentally by measuring koff as a function of temperature for the interaction between SSB protein and fluorescently labeled ssDNA (Berezovski and Krylov, 2004). The calibration curve was built with a verified Beckman MDQ CE instrument, which uses a liquid heat exchanger to remove excess heat efficiently from the capillary. This calibration curve was then used to measure the temperature inside the capillary in a custom-built instrument with the capillary exposed to the ambient atmosphere at 20°C. It was found that the temperature inside the capillary was 15°C higher than the ambient temperature. As affinity interactions are very sensitive to temperature, the unjustified assumption that the capillary temperature... 

Heat is a form of energy indicated by temperature. Temperature extremes affect how well people work and how much work they can do. The human body is always producing heat and must remove excess heat in order to maintain body proper temperature. In the same way that excessive heat can affect process equipment and process safety, heat can also affect the human body and its proper functioning. During the summer, especially in geographic areas subject to hot summers, heat can become a serious safety hazard to a process technician. 

Sweating is the body s principal method for removing excess heat. Sweat consists of water and electrolytes (salts). An individual at rest and not under stress, sweats about one liter per day. The sweating rate for an individual under stress of heavy woric or high temperatures is about four liters in four hours. The body must replace water and electrolytes to prevent heat stress or sickness. This is why many people who try to walk out of stranded situations in a desert with only a few liters of water fail and die. They do not realize how profusely they will sweat and how dehydrated they will become. In the pages that follow, we will take a closer look at temperature hazards the process technician may be exposed to in the processing industry. 

Practically all extruders have a barrel cooling system, such as air fans or water circulators, to remove excess heat from the polymer. However, it is best that the unwanted heat not be added to the polymer in the first place. Therefore, when the temperature controller in an extruder cooling system (or zone) calls for cooling often, or all the time, it indicates inefficiency in the system. 

Control rooms housing electrical equipment should be pressurized with clean filtered air and entrances should preferably be fitted with two sets of interlocked doors to seal the factory environment, with only one operable door at a time. All electrical cabinets and consoles should be pressurized with fan units fitted with filters and due care should be taken to ensure that there is sufficient air available to remove excess heat from the cabinets. 

Heat input is the driving force for fractionation. For a simple fractionation column, heat input comes from feed and bottom reboiling, while heat is removed from products and the overhead condenser. For a complex fractionation column, multiple products are produced, while pump-arounds are located to remove excess heat in the column and recover this heat for process usage. 

Pump-Around Many fractionation towers have pump-arounds to remove excess heat in the key sections of the tower. The effect of increasing pump-around rate is reduced internal reflux rate in the trays above the pump-around, but increased internal reflux rate below the pump-around. Thus, change in pumparound duty affects fractionation. On the other hand, pump-around rates and return temperature have effects on heat recovery via the heat exchanger network. It is not straightforward in optimizing pump-around duties and temperamres since the effects on both fractionation and heat recovery can only be assessed in a simulation model. An APC application incorporated with process simulation should be able to handle this optimization. 

Cooling garment One of three methods Removes excess heat ... 

Many modem FCC units are designed to process significant amounts of vacuum residue. These units use catalyst coolers (e.g., steam coils) in the regenerator or a second regeneration zone to remove excess heat from the unit. This is because vacuum residue generates substantially more coke than conventional FCC feeds, and excess heat is generated when the extra coke is burned away from catalyst. 

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