RCL 556/MEE 456 –Project 3 Assignment The Scenario: A utility company is forming to sell the waste heat from the solar-driven Brayton cycle you analyzed in a previous project. The utility company will own the heat exchanger to transfer heat from the Brayton power cycle, and also the supply and return piping system to a second heat exchanger that will be owned by a city (see the system schematic on Page 3). The heat will be sold to the city based on use through HX2. The city will then distribute hot water to its customers who connect to the city's district cooling network. The utility company has hired you to determine a feasible pipe design and heat exchanger size (HX1). The Assignment: Your overall task is to determine the piping and heat exchanger design that results in the lowest simple economic payback period based on energy revenue and basic operating costs. Problem Details: A schematic of the system concept is shown in the figure on Page 2. Other data are as follows: Climate:  The average annual air temperature at this location is 25°C.  Assume an average wind velocity of 5 m/s for convection coefficient calculations. Pipelines:  Supply and return pipelines will be installed above ground. Pipe burial was not considered practical due to numerous subsurface obstructions.  Assume that the exterior of the pipe carrier jacket includes an aluminum reflective coating of negligible thermal resistance. This coating also serves as a radiation barrier such that solar heat gain and nocturnal radiation losses are negligible.  The heat transfer fluid is water with a mass flow rate of 100 kg/s.  Pipe costs (installed) are listed in the following table: Carrier Pipe Jacket Installed Cost (DN in mm) (DN in mm) ($/m) 50 150 $120 100 200 $160 150 250 $210 200 300 $260 250 350 $320 300 400 $410 350 450 $460 400 500 $530 500 600 $750 600 700 $1,030 650 750 $1,170 700 800 $1,290 750 850 $1,440 800 900 $1,580 RCL 556/MEE 456 –Project 3 Assignment Heat Exchanger 1 (HX1):  Assume an overall heat transfer coefficient (U) of 750 W/m2-K.  The 'hot' fluid is CO2 and the 'cold' fluid is water.  Assume an installation cost of this type of heat exchanger as a function of area (A) in m2 defined by the following empirical equation: Cost (in $US) = 2×EXP(8.202 + 0.01506×lnA + 0.06811×(lnA)2)  Assume the heat exchanger is adiabatic (i.e., no heat losses to the surroundings). Heat Exchanger 2 (HX2)  The utility company is contracted to provide water to HX2 at a temperature no less than 100°C.  The design T across HX2 should NOT be greater than 7°C.  Assume the heat exchanger is adiabatic (i.e., no heat losses to the surroundings). Determine the (and show your work): (a) carrier pipe and jacket diameters you recommend, (b) temperature of the water leaving HX1, (c) temperature of the water entering HX1, (d) temperature of the water leaving HX2, (e) pressure drop experienced by the water in the supply pipeline, (f) ideal mechanical power required to move the water through the pipe system (ignore minor losses through fittings, valves, heat exchangers), (g) area required for HX1, (h) effectiveness of HX1, (i) heat loss from the supply pipeline to the ambient air, (j) heat transferred to the cooling district through HX2, (k) cost of the supply and return pipelines, (l) annual revenue through sale of the thermal energy at HX2, assuming a selling price of $25/MWh, and 4000 hours per year, (m) annual pumping costs, assuming 4000 hours per year, a combined pump and motor efficiency of 60%, and an electrical energy cost of $0.10/kWh, and (n) simple payback period (in years) only based on items (k) through (m) . What to Submit: A PDF (or Word, but preferably PDF) file with:  Pasted EES code (or other calculation method you used),  Answers to the questions (a) through (n), and Hints:  Begin with analysis of the SUPPLY pipeline (i.e., pipeline from HX1 to HX2). This will give you the exiting water temperature at HX1.  Once you have the exiting water temperature at HX1, you have enough information to apply the LMTD heat exchanger analysis of HX1.  For simplicity, a reasonable engineering approximation is to assume the same heat loss from the return pipeline as that from the supply pipeline. RCL 556/MEE 456 –Project 3 Assignment Heat Exchanger HX1 UA = ? q  From Previous Project: • Gas power (Brayton) cycle using supercritical CO2. • q̇ = 2765 kW • ṁ CO2 = 10 kg/s. • T 4 = 343 C, P4 = 7000 kPa • T D = 100 C 4 D Heat Exchanger HX2 Above-ground piping • Supply and return, closed-loop • Fluid = water • ṁ = 100 kg/s • 3 km distance (HX1 to HX2) • Steel carrier pipe, insulated, with rigid plastic outer jacket and reflective aluminum coating • T a = not less than 100 C, • T a-b = 7 C maximum • Pipe design = ? Heat losses = ? • Pumping power = ? District Cooling Utility (using thermally-driven heat pumps installed in buildings) This Project: b a SUPPLY RETURN