Hot water (cph = 4188 J/kg*K) with mass flow rate of 2.5 kg/s at 100 deg C enters a thin- walled concentric tube counterflow heat exchanger with a surface area of 23 m^2 and an overall heat transfer coefficient of 1000 W/m2*K. Cold water (cpc = 4178 J/kg*K) with mass flow rate of 5 kg/s enters the heat exchanger at 20 deg C, determine (a) the heat transfer rate for the heat exchanger and (b) the outlet temperatures of the cold and hot fluids.

Two coaxial cylinders, r1 = 3.5 cm, r2 = 8cm, of equal length (3.5 m) are placed inside a very large room maintined at 350 K. Suppose that the inside cylinder is maintained at 520 K, outside at 636K, determine the net heat transfer at surface 2 when the emissivities are ε1=0.37 and ε2=0.56.

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1. Oil enters the tube side of a shell-and-tube heat exchanger with a flow rate of 5.04 kg/s (c, = 2.09 kJ/kg-K; p = 900 kg/m3) and it is cooled from 366.5 K to 344.3 K by 2.02 kg/s of water entering at 283.2 K. The overall heat-transfer coefficient U, is 340 W/m2-K. The tubes have an outside diameter of 60.33 mm and inside diameter of 52.50 mm (use outside diameter for surface area, use inside diameter for mass flow rate in tubes). The velocity of the oil is 0.100 m/s. Calculate the number tubes and tube passes if space constraint limits the tube length to be 1.50 m and lesser and shell pass is only 1. Figure 10-8 | Corection-factor plot for exchanger with one shell pass and two, four, or any multiple of tube passes. 12

Steam in a heating system flows through a 1-m long tube whose outer diameter is D1 = 3 cm andwhose walls are maintained at a temperature of Tb = 120 °C. Circular fins (k = 46 W/m. °C) of outer diameter D2 = 6 cm and constant thickness t = 2 mm are attached to the tube, as shown in the figure. The space between the fins is 3 mm, and thus there are 200 fins per meter length of the tube.Heat is transferred to the surrounding air at Tꚙ = 20 °C, with a combined heat transfer coefficient of h = 90 W/m2. °C. Determine:a. No fin area: Ano fin = ____ m2b. Unfin area: Aunfin = ____ m2c. Fin area: Afin = _______ m2d. Fin efficiency = ______e. Qno,fin = ______ Wf. Qtotal, fin = ______ Wg. Overall fin effectiveness =

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4- Consider a wall (20x40) cm [k=12 w/m °C is heated by convection on one side and cooled by convection on the other side. What is the heat transfer. Draw he temperature curve the through the wall. L = 2 m AX=0.05 m ºC, Too2 = 20 °C, T, = 100 h₁ = 30 w/m²K, h₂ = 13 w/m² K

Heat Transfer 176 Convection Ex. 3.15: air at 101.325 kPa and 308 K (35 °C) flows across a 50 mm diameter cylinder at a velocity of 50 m/s. The cylinder surface is maintained at a temperature of 423 K (150 °C). Estimate the heat loss per unit length of the cylinder. Data: The physical properties of air at the film temperature of 365.5 K are: H= 2.14 x 10-5 kg/(m-s), p = 0.966 kg/m³, k = 0.0312 W/(m-K) and Npr 0.695.

À wall of area 30 m² having a density of 1500 kg/m', thermal conductivity 30 W/m.K, and specific heat capacity 4 kJ/kg.K. The temperature distribution across a wall 0.5 m thick at a certain instant of time is given as T(x) = 30-5 x-7x The wall is generating a uniform heat (q.) of 1000 W. (1) Find the rate of heat transfer entering and leaving the wall (in W). (2) Find rate of energy stored in Watt. (3) Find (dFT/dx²) (4) Derive the change in temperature with respect to time equation (time rate of temperature change)- remember to substitute the value of (d T/dx²) from (part 3) and values of all other properties into final equation. %3D

10.33 Saturated steam at 0.2 bar condenses with a convec- tion coefficient of 6000 W/m²2 · K on the outside of a brass tube having inner and outer diameters of 16 and 19 mm, respectively. The convection coefficient for water flowing inside the tube is 5000 W/m². K. Esti- mate the steam condensation rate per unit length of the tube when the mean water temperature is 30°C.