Hot water at 160 ⁰C is passing through a pipe, and it is lagged with a plastic covering. The coefficient of thermal conduction of the plastic is 0.2 Wm-1K-1 and the heat transfer coefficient is 16 Wm-2K-1. The ambient temperature surrounding the pipe is 25 ⁰C. Determine the critical radius and hence the maximum heat loss. Calculate the heat loss for varying thicknesses of lagging and plot this against the thickness. From the graph, estimate an optimal thickness of lagging and explain your reasons. You can use Excel for the calculations and plotting.

A w=40 mm square computer CPU is air cooled with fans shown in the figure below. The surrounding air in the case has convection coefficient h = 100 W/m2⋅K and temperature T∞ = 30oC. If the aluminum heat sink (k = 230 W/m⋅K) on your computer has N = 20 exposed equally-spaced rectangular fins of thickness t =1 mm and length Lf = 15 mm: a) Calculate the overall efficiency ηo of the fins b) Given that the CPU is generating QCPU = 90 W, determine the temperature of the CPU, assuming the CPU is a uniform temperature and well-insulated on its sides. Ignore thermal contact resistance and fin array base resistance

1. Calculate the overall heat-transfer coefficient (U=?) for a frame construction wall made of brick veneer (120-lbm/ft³) with 3-in. fiberglass insulation bats between the 2x4 wood studs (softwood) that are 16-in. on center. The wind velocity is 15-mph. Fill out the table below also utilizing materials data from the textbook. Also, calculate the total heat loss if the referenced wall was 9-ft tall and 35-ft in length set in Ohio, Clevland @ 99% winter OAT with an indoor setpoint of 75°F. Hint: 2x4 wood studs are 16-in. on center and 2-in. thick by 4-in. deep thus the empty space between each stud is 14-in. Remember use R = L/K & R = 1/C for materials. Between Frame (R-Value) At Framing (R-Value) Outside Surface 4-in. Face Brick (k=middle value) 1/2-in. Sheathing reg. density 3-in. Insulation Batt 2"x4" Wood Studs (k=middle value) 1/2-in. Gypsum Board Inside Surface Total (R-Value): ● U = ● Q= Btu/(hr-ft²-F) Btu/h Heat Loss

A thick-walled cylindrical tubing of hard rubber (k=0.151 W/m*K) having an inside radius of 5 mm and an outside radius of 20 mm is being used as a temporary cooling coil in a bath. Ice water is flowing rapidly inside, and the inside wall temperature is 275 K. The outside surface temperature is 300 K. A total of 20 W must be removed from the bath by the cooling coil. How many meter of tubing are needed?