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Mechanical Engineering Principles and Practives IIIExpt.8 – Bare and Lagged Pipes Apparatus De La Salle UniversityCollege of EngineeringMechanical Engineering DepartmentExperiment 8Bare & Lagged Pipe ApparatusDate Performed: June 6, 2011 Date Submitted: June 27, 2011 Instructor:Subject/Section: LBYME16 / Group Number: 2 Submitted by: Amparo, Carlos ManuelCuyco, KevinDelos Santos, Dann Presentations :________________ Data and Results:________________ Analysis and Conclusion :________________ Answers to Questions:________________ Total:________________ Remarks _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ Instructor’s Signature: ________________ Mechanical Engineering Principles and Practives IIIExpt.8 – Bare and Lagged Pipes Apparatus OBJECTIVES :A.To determine the combined radiation and convection coefficient (hr +hc) at various temperaturesfrom different surfaces:1.85% Magnesia insulation2.Pipe painted with aluminum paint3.Pipe painted with black paint4.Bare pipe5.Foam insulationB.To determine the efficiency of these insulating materials.C.To compare the experimentally determined (hc + hr) with those calculated from empiricalequations. THEORY AND ANALYSIS :A good pipe covering, in addition to being a good insulator, should be fire proof, water proof,vermin proof, odorless and light in weight. It should also be mechanically strong and should suffer noloss of insulating value with age. Asbestos and carbonate magnesia are the most commonly used pipe-covering materials.The only logical method for testing commercial pipe covering is, of course, to mount thosecoverings on pipes of the size for which they were intended. Two general methods for heatmeasurement have been used. For steam-pipe coverings, the most natural method is to fill the covered pipe with steam, to measure the heat content of the steam entering and leaving the test section, and tocondense and weigh the steam. A dead-end pipe is ordinarily used, the pipe itself acting as the steamcondenser. The second and more accurate method is to supply and measure the heat electrically. Thismethod eliminates the “end correction”. When covering pipe ends with heavily insulated caps andmaintaining separately heated end sections adjacent to the caps at the same temperature as the testsection, the heat from the main test section cannot travel along the pipe and must escape radiallythrough the covering under test.Heat escapes from a pipe, or other surface, to the room in two ways: (1) by conduction trough anair film, and then by convection in the bulk of the air; and (2) by direct radiation to the cooler walls of the room. Mechanical Engineering Principles and Practives IIIExpt.8 – Bare and Lagged Pipes Apparatus That proportion of the heat which is lost by conduction and convection can be calculated by theequation:q c = h c A(t s – t g )and that proportion which is lost by radiation may be expressed by simplified equation:q c = h r A(t s – t w )where:q c = heat transferred from surface to room by conduction and convection, Btu/hr q r = heat transferred from surface to room by radiation Btu/hr h c = coefficient of heat transfer by conduction and convection, Btu/(hr sq ft ft o F)h r = coefficient of heat transfer by radiation, Btu/(hr-sq ft o F)A = surface areat s = temperature of the surface o Ft g = temperature of the air o Ft w = temperature of the walls of the room o Fthe convection coefficient h c can be evaluated from equation:h c =0.42 (Δ t/d) 0.25 and:h r = 0.173 p (_t s _ )4 – (_t w _) 4 100 100ΔtSubstituting can result in:q = q c + q r = (h r + h c )(A)(t s – t w )andq = (h c + h r )(A)(Δt)where:q = total heat transfer from the surface by conduction and convection, and by radiation, Btu/hr (h c + h r ) = combined coefficient of heat transfer A = surface area, sq ft Mechanical Engineering Principles and Practives IIIExpt.8 – Bare and Lagged Pipes Apparatus Δt = temperature difference, surface to room o FThe lagging efficienct of a pipeline with insulation can be calculated from the equation:L.E. = q B – q L x 100q B where:q B = heat loss from bare pipeq L = heat loss from logged pipeSince the heat loss is proportional to the quantitiy of condensate collected, thenL.E. = W B – W L x100W B Where W B and W L are the quantities of condensate from the bare and logged pipes, respectively. APPARATUS :For determining the heat loss from bare and lagged pipes, heat is supplied by the deadcondensation of steam, and surface temperatures are measured by means of a portable thermocouple potentiometer. The test section consists of four 10 feet lengths of one-inch standard steel pipemounted with a slope of 0.63 inches per foot in a framework of welded two-inch steel angles. One of the lengths is bare and the other are covered with asbestos insulation, aluminum paint, black paint,and foam insulation. The test pipes are connected to a common header into which steam is introducedeither directly from the main or from a line containing a reducing valve. The steam condensate isdrained from the opposite ends of the pipes through plug-type valves and is collected in beakers andmeasured.1.5 pcs. Beaker 1000 ml capacity2.1 pc. Stopwatch3.1pc. Graduated cylinder 1000ml capacity4.18 pcs. Thermometer 0-360C ᵒ SET-UP OF THE EXPERIEMENT :
