Sometimes we can develop equations and solve practical problems by knowing nothing more than the dimensions of the key parameters in the problem. For example, consider the heal Joss through a window in a building. Window efficiency is rated in terms of "R value," which has units of (ft2 · h · °F)/Btu. A certain manufacturer advertises a double-pane window with an R value of 2,5. The same company produces a. triple-pane window with an R value of 3.4. In either case the window dimensions are 3 ft by 5 ft. On a given winter day, the temperature difference between the inside and outside of the building is 45°F. (a) Develop an equation for the amount of heat lost in a given time period
(b) How much heat (in Btu) is lost through the triple-pane window in one 24-h period?
(c) Suppose the building is heated with propane gas, which costs $3.25 per gallon. The propane burner is HO percent efficient. Propane has approximately 90,000 Btu of available energy per gallon. In that same 24-h period, how much money would a homeowner save per window by installing triple-pane rather than double-pane windows?
(d) Finally, suppose the homeowner buys 20 such triple-pane windows for the house. A typical winter has the equivalent of about 120 heating days at a temperature difference of 45°F. Each triple-pane window costs $85 more than the double-pane window. Ignoring interest and inflation, how many years will it take the homeowner to make up the additional cost of the triple-pane windows from heating bill savings?
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Fluid Mechanics
- As we explained in earlier chapters, the air resistance to the motion of a vehicle is something important that engineers investigate. The drag force acting on a car is determined experimentally by placing the car in a wind tunnel. The air speed inside the tunnel is changed, and the drag force acting on the car is measured. For a given car, the experimental data generally is represented by a single coefficient that is called drag coefficient. It is defined by the following relationship: F, where air resistance for a car that has a listed C, = drag coefficient (unitless) measured drag force (N) drag coefficient of 0.4 and width of 190 cm and height of 145 cm. Vary the air speed in the range of 15 m/sarrow_forwardYou are developing a porous membrane for use in a dialysis system. The membrane must be able to retain both protein and glucose on the inlet side and allow other, smaller molecules to flow through. You have found that the membrane is 0.25 mm thick and contains long, rectangular pores with a width of 0.1 microns. 57% of the 50 cm^2 membrane surface area is covered with pores. A test fluid (viscosity = 1.5 cP, density = 1015 kg/m^3) is passed through the membrane. You can assume that the test fluid has a composition similar to that of blood plasma. An initial test is run at physiological conditions, and you observe that the flow rate of fluid through the membrane is 500 cm^3/min. Given this data, what must the hydrodynamic pressure drop across the membrane in your test system be in pascals?arrow_forwardThermal conductivity k is a measure of the ability of a material to conduct heat. For conduction heat transfer in the x-direction through a surface normal to the x-direction, Fourier’s law of heat conduction is expressed as: Q=-kA.dT/dx where ?̇ is the rate of heat transfer and A is the area normal to the direction of heat transfer. Determine the primary dimensions of thermal conductivity (k). Look up a value of k and verify that its SI units are consistent with your result. Write a set of primary SI units for k.arrow_forwardSurface tension is due to uneven molecular attraction between immiscible fluid media and solid surface. Its importance is governed by dimensionless parameter Which of the Inertia force called Weber number given by We = Surface tension force™ following statements are correct? (i) Surface tension becomes important when the length scale L is small such as in ink jet printing, coating of thin film, oxygenation of water by falling rain drops. (ii) 111 Super-hydrophobicity can be achieved by micro/nano texturing of surface such as in lotus leave, butterfly and dragonfly wing. During oil spill in ocean, oil floats and spreads out due to gravity. By conservation of mass, the oil film becomes thinner as it spreads. Finally, the surface tension force becomes important causing the formation of tiny oil droplets. (A) (B) (C) (D) (i) and (ii) (i) and (iii) (ii) and (iii) All of the abovearrow_forwardPlease answer it correctly and read carefully. SHOW SOLUTION STEP BY STEP PLEASEarrow_forwardplease show steps with explanation of the formulas and calculs for more understanding. Thank you!arrow_forwardYou are the mechanical engineer supervising the layout of a piping system. In a certain portion of the pipe, the specifications are as follows: length of pipe is 10m, inside diameter of 30cm, outside diameter of 30.5cm, maximum allowable speed of 15m/s and a coefficient of 0.003456. If the uncertainties are 0.02mm for length, 0.8mm for the diameters and 0.1mm/s for the velocity, what loss of head will be imminent in this pipe? With all the above uncertainties, what is the total uncertainty in the head loss?arrow_forwardYou are the mechanical engineer supervising the layout of a piping system. In a certain portion of the pipe, the specifications are as follows: length of pipe is 10m, inside diameter of 30cm, outside diameter of 30.5cm, maximum allowable speed of 15m/s and a coefficient of 0.003456. If the uncertainties are 0.02mm for length, 0.8mm for the diameters and 0.1mm/s for the velocity, what loss of head will be imminent in this pipe? In the piping system above, what is the uncertainty in computed head loss contributed by the velocity of the pipe?arrow_forwardYou are the mechanical engineer supervising the layout of a piping system. In a certain portion of the pipe, the specifications are as follows: length of pipe is 10m, inside diameter of 30cm, outside diameter of 30.5cm, maximum allowable speed of 15m/s and a coefficient of 0.003456. If the uncertainties are 0.02mm for length, 0.8mm for the diameters and 0.1mm/s for the velocity, what loss of head will be imminent in this pipe?arrow_forwardQl: The viscosity in industrial measurement continue to use the CGS system of Lunits, since centimeters and grams vield convenient numbers for many fluids. The absolute viscosity () unit is the poise, I poise = 1 gtem. s). The kinematic viscosity (v) unit is the stohes, I stokes = 1 em /s. Water at 20C has u = 001 poise and also V= 0.01 stokes. Express these resalts in (a) SI and (h) BG tanits.arrow_forwardWith the data below solve the problems:arrow_forwardLook up the metric specifications for a car of your choice (body, trunk, engine sizes, and gas consumption) and a home appliance such as an air-conditioning unit (size, cooling capacity, and energy consumption). Convert your findings to U.S. Customary units.arrow_forwardarrow_back_iosSEE MORE QUESTIONSarrow_forward_ios
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