CONSIDER THE FLOW OF HOT WATER FROM THE BOILER TO THE SHOWERING CAN IN YOUR HOUSE, FOR A COMMERCIAL STEEL PIPE OF ID 40, ONE INCH IN DIAMETER (2.54 cm). WATER RUNS THROUGH THIS TUBE OF Ti = 90 C (Kac = 40 W/mc). THE EXTERNAL DIAMETER IS De=3.34 cm, WHILE THE INTERNAL IS OF Di =2.66 cm. THE THICKNESS OF THE TUBE IS et =.33 cm. HE INTERNAL HEAT TRANSFER COEFFICIENT, BY WHERE HOT WATER PASSES IS hi = 600 W/m2-c, WHILE THE EXTERNAL COEFFICIENT IS HE = 10 W/m2-c. THE TEMPERATURE OF ENVIRONMENT IS AT Ta = 20 C. CALCULATE THE HEAT LOSSES WHEN THE PIPE IS FIND NAKED. TAKING INTO ACCOUNT THAT A WATT OF ENERGY COSTS $.05, AND WITH THE PURPOSE OF SAVING A LITTLE MONEY, AND OF PROTECT THE ENVIRONMENT, DO YOU CONSIDER CONSERVING THE HEAT BY MEANS OF TWO ALTERNATIVES.

a).- CHANGE THE STEEL PIPE FOR A PVC ONE, (Kpvc = .35 W/ m C,)

b).- ISOLATE THE STEEL TUBE WITH A LAYER OF ASBESTOS OF eas =3 cm. (Kas = .15 W/ m-C ).

WHAT PERCENTAGE OF HEAT CAN BE SAVED WITH EACH ONE? OF THESE ALTERNATIVES?

WHICH ALTERNATIVE WOULD YOU CHOOSE, AND WHY?

***** the solution must be raised by means of ecs. of heat transport in cylindrical walls in series. First solve for the different resistances (R1 , R2 and R3 ), and then set up the eqs. transfer for each layer. From one of those you will get the heat flux qr . ******