Lab Report Gas Diffusion Essays

Lab Report Gas Diffusion Essays Lab Report Gas Diffusion Paper Lab Report Gas Diffusion Paper A lump of sugar added to a cup f black coffee eventually dissolves and then diffuses uniformly throughout the coffee. Perfume presents a pleasant fragrance which is imparted throughout the surrounding atmosphere. These are examples of mass transfer. Mass transfer plays a very important role in many industrial processes: the removal of pollutants from plant discharge streams by absorption, the striping of gases from wastewater, neutron diffusion within nuclear reactors, the diffusion of adsorbed substances within the pores of activated carbon, the rate of catcalled chemical and biological reactions, and air conditioning are typical examples.. Mass transfer takes place in either gas phase or liquid phase or in both cases simultaneously. When a liquid evaporates into a still gas, vapor is transferred from the surface to the bulk of gas as a result of the concentration gradient. This process continues until the gas is saturated and the concentration gradient is reduced to zero. In a still fluid or in a fluid flowing under streamline conditions in a direction of right angles to the concentration gradient, the transfer is affected by random motion of the molecules. Molecular diffusion or molecular transport can be defined as the transfer or movement of individual molecules wrought a fluid by means of the random, individual movements of the molecules. Whenever a particular molecule of this mixture diffuses, it must diffuse through other molecules; consequently, in almost every practical example there are at least two components present and possibly more. The molecular diffusion process is shown schematically in the below figure. A random path that molecule A might take in diffusing through B molecules from point (1) to (2) is shown. If there are a greater number of A molecules near point (1) than at (2), then, since molecules diffuse randomly in direction, more A molecules will diffuse from (1) o (2) than from (2) to (1). The net diffusion of A is from high-to-low concentration regions. Molecule A Molecule B Diffusion is explained in this experiment through the First Picks Law. The first Picks Law states that the molar diffusion flux of A in B at a certain direction (say Z), is proportional to the negative of the concentration gradient of A in that direction: [pica Molar diffusion flux is defined as the molar diffusion flow rate (nab) per cross sectional area unit of diffusion (L): [pica First Picks law is turned to an equation by introducing a coefficient named effusion coefficient of Main B or diffusivity of A in B, DAB: [pica] (1) where [pica is the molar flux of A in the z is the diffusion coefficient of A in B. Its dimension is LET-1 and thus the unit is mm/s, and [pica]is the concentration gradient in z direction. Equation (1) is applicable for only general cases. If the diffusion occurs for either one kind of molecules into a gas composed of molecules of the same mass velocity and free paths, the equation is incomplete. Since the rate of transfer of A in a mixture of two components, A and B, will be determined not only by the rate of diffusion of A, but also by the behavior of B, Picks Law can be presented in another form. The molar flow rate A per unit cross sectional area, due to molecular motion is given by: [pica (2) where AN is the molar rate of diffusion of A per unit area, DAB is the diffusion coefficient of A in B, CA is the molar concentration of A, y is the distance in the direction of diffusion. The corresponding rate of diffusion of B is given by: If the total pressure and the total molar concentration is constant, [pica and[pica] must be equal and opposite and therefore A and B tend to diffuse in opposite directions. In many processes B will neither remain stationary nor effuse at an equal and opposite molar rate of A. Exact calculations relating to this type of problems are difficult. If turbulent flow of fluid occurs, eddy diffusion takes place in addition to molecular diffusion and the rate of diffusion is increased as denoted below: [pica(4) where DE is eddy diffusivity. Its value increases if turbulence increases and is more difficult to evaluate than the molecular diffusivity. In the case where diffusion takes place in a stationary gas the rates of diffusion of A and B are given by: Applying the ideal gas law does this: where P is the systems pressure T is the systems temperature R is molar gas constant [pica (8) as concentration of substance, C is also equal to the ratio of mole, n of the substance to its volume, V . If a surface is introduced on which A is absorbed but B is not absorbed, a partial pressure gradient will be set up, causing A to diffuse towards and B away from the surface. Given this process to continue for a short interval, A will be absorbed at the surface and B will tend to diffuse away. Thus a total pressure gradient will be produced causing a bulk motion of A and B towards the surface, in addition to the transfer by diffusion. Since there is no net motion of B, the bulk rate or flow must exactly balance its transfer by diffusion. Thus the bulk rate of flow of B The bulk flow of B is accompanied by a bulk flow of A as below: Bulk flow of A = [pica The total rate of transfer of A is obtained by summing the transfers by diffusion and bulk flow. By adding equation (5) and (9), the total transfer, AN is given by: AN = [pica(5) + (9) = [pica] (10) This relation shown by equation (10) is known as Stefan Law. Integration of equation (10) between two positions denoted by suffixes 1 and 2 gives us the results as below: [pica] AN = (11) (12) 13) where the suffix m denotes the logarithmic mean value of the quantity at the positions 1 and 2. There are several ways by which the diffusion coefficient, D can be determined. In Winkle method, the liquid contained in a narrow diameter vertical tube which is maintained at a constant temperature and a vapor free gas, is passed through the top of the tube rapidly enough to ensure that the partial pressure of the vapor remains approximately zero (Figure 1). Gas Stream (Figure 1) The rate of mass transfer is given by: AN= [pica Where CA = the saturation concentration at the interface and L is the effective stance through which mass transfer is taking place. But considering the evaporation of the liquid. AN = [pica Where (L = the density of the liquid. Thus, Integrating and putting L = LO at t = 0, evaporation of the liquid, AN= [pica] [pica] Finally, the following equation is obtained: A graph of Chip] versus L-LO yields a straight line with gradient ,s= (pica and intercept of 0 3. METHODOLOGY When performing the experiment, the Gaseous Diffusion Apparatus is referred. 1 . Capillary tube, R is washed with detergent that is provided and cleansed with distilled water. Then, it is rinsed with a little of acetone liquid. The cleaning process is done with a syringe. 2. With another syringe, acetone is filled into the capillary tube, R until it reaches the height of 35. Mm. This is done carefully to ensure that no air bubble is trapped inside the tube. 3. The tube is inserted into the metal nut, N until the top part of the tube hangs on the nut. 4. Slowly, the tube is screwed into the upper plat, with its T part perpendicular to the microscope, M. 5. Vacuum tube, V is inserted at one end of the T part of capillary tube, R. 6. The vertical height of microscope, M is adjusted until the capillary tube, R can be seen in the microscope, M. The distance of the object lens to the tank is adjusted. 7. When the meniscus level is determined, the fernier scale is aligned to the unmovable scale. 8. When the lens is adjusted, the air pump, P and heater are switched on. 9. The temperature controller is adjusted to maintain the temperature at ICC.

Sun Bear Facts (Helarctos malayanus)

Sun Bear Facts (Helarctos malayanus) The sun bear (Helarctos malayanus) is the smallest species of bear. It gets its common name for the white or golden bib on its chest, which is said to represent the rising sun. The animal is also known as the honey bear, reflecting its love of honey, or the dog bear, referring to its stocky build and short muzzle. Fast Facts: Sun Bear Scientific Name: Helarctos malayanusCommon Names: Sun bear, honey bear, dog bearBasic Animal Group: MammalSize: 47-59 inchesWeight: 60-176 poundsLifespan: 30 yearsDiet: OmnivoreHabitat: Southeast Asia rainforestsPopulation: DecreasingConservation Status: Vulnerable Description The sun bear has short black fur with a pale crescent-shaped bib that may be white, cream, or golden. It has a short, buff-colored muzzle. The bear has small, round ears; an extremely long tongue; large canine teeth; and large, curved claws. The soles of its feet are hairless, which helps the bear climb trees. Adult male sun bears are 10% to 20% larger than females. Adults average between 47 and 59 inches long and weigh between 60 and 176 pounds. The sun bear has curved claws and an extremely long tongue. Freder / Getty Images Habitat and Distribution Sun bears live in the evergreen tropical rainforests of Southeast Asia. Their habitat includes northeastern India, Bangladesh, Myanmar, Thailand, Malaysia, Cambodia, Vietnam, Laos, southern China, and some Indonesian islands. There are two subspecies of sun bear. The Bornean sun bear only lives on the island of Borneo. The Malayan sun bear occurs in Asia and on the island of Sumatra. Diet Sun bears, like other bears, are omnivores. They feed on bees, hives, honey, termites, ants, insect larvae, nuts, figs and other fruit, and sometimes flowers, plant shoots, and eggs. The bears strong jaws easily crack open nuts. Sun bears are hunted by humans, leopards, tigers, and pythons. Behavior Despite its name, the sun bear is largely nocturnal. It relies on its keen sense of smell to find food at night. The bears long claws help it climb and also tear open termite mounds and trees. The bear uses its extremely long tongue to lap up honey from bee hives. Male bears are more likely than females to be active during the day. Although relatively small, sun bears are known to be fierce and aggressive if disturbed. Because they live in the tropics, the bears are active year-round and do not hibernate. Reproduction and Offspring Sun bears reach sexual maturity around 3 to 4 years of age. They can mate at any time of the year. After a gestation period of 95 to 174 days, the females gives birth to one or two cubs (although twins are uncommon). Newborn cubs are blind and hairless and weigh between 9.9 and 11.5 ounces. Cubs are weaned after 18 months. In captivity, male and female bears socialize and jointly care for young. In other bear species the female raises her cubs on her own. The lifespan of highly reclusive wild sun bears is unknown, but captive bears live up to 30 years. Sun bear cubs are born blind and furless. Christian Aslund / Getty Images Conservation Status The IUCN classifies the sun bears conservation status as vulnerable. Bear populations are decreasing in size. The sun bear has been listed on CITES Appendix I since 1979. Threats While it is illegal to kill sun bears throughout their range, commercial hunting is among the species greatest threats. Sun bears are poached for their meat and gall bladders. Bear bile is used in traditional Chinese medicine and is also an ingredient in soft drinks, shampoo, and cough drops. Despite their temperament, sun bears are also illegally captured for the pet trade. The other significant threat to sun bear survival is habitat loss and fragmentation due to deforestation and human encroachment. Forest fires also affect sun bears, but they tend to recover providing there is a neighboring population. Sun bears are kept in captivity for their commercial value and for conservation. They are farmed for their gall bladders in Vietnam, Laos, and Myanmar. Since 1994, the species has been part of a captive-breeding program with the Association of Zoos and Aquariums and the European breed registry. The Bornean Sun Bear Conservation Centre in Sandakan, Malaysia rehabilitates sun bears and works toward their conservation. Sources Brown, G. Great Bear Almanac. 1996. ISBN:978-1-55821-474-3.Foley, K. E., Stengel, C. J. and Shepherd, C. R. Pills, Powders, Vials and Flakes: The Bear Bile Trade in Asia. Traffic Southeast Asia, Petaling Jaya, Selangor, Malaysia, 2011.Scotson, L., Fredriksson, G., Augeri, D., Cheah, C., Ngoprasert, D. Wai-Ming, W. Helarctos malayanus (errata version published in 2018). The IUCN Red List of Threatened Species 2017: e.T9760A123798233. doi:10.2305/IUCN.UK.2017-3.RLTS.T9760A45033547.enServheen, C.; Salter, R. E. Chapter 11: Sun Bear Conservation Action Plan. In Servheen, C.; Herrero, S.; Peyton, B. (eds.). Bears: Status Survey and Conservation Action Plan. Gland: International Union for Conservation of Nature. pp. 219–224, 1999.Wong, S. T.; Servheen, C. W.; Ambu, L. Home range, movement and activity patterns, and bedding sites of Malayan sun bears Helarctos malayanus in the Rainforest of Borneo. Biological Conservation. 119 (2): 169–181, 2004. doi:10.1016/j.biocon.2003.10. 029