A stream of warm water is produced by mixing 1 kg/s of cool water at 20°C with1 kg/s of hot water at 80°C. During mixing, heat is transferred to the surroundings at the rate of 30 kJ/s.Determine the temperature of the warm water. Assume the specific heat of water is constant at 4.18 kJ/kg.K .

A 1 m diameter cylinder, 1 m long, is maintained at 800 K and has an emissivity of 0.65. Another cylinder, 2 m in diameter and 1 m long, encloses the first cylinder and is perfectly insulated. Both cylinders are placed in a large room maintained at 300 K. Calculate the heat lost by the inner cylinder.

11.22 A shell-and-tube heat exchanger must be designed to heat 2.5 kg/s of water from 15 to 85°C. The heating is to be accomplished by passing hot engine oil, which is available at 160°C, through the shell side of the exchanger. The oil is known to provide an average convection coefficient of h, = 400 W/m² K on the outside of the tubes. Ten tubes pass the water through the shell. Each tube is thin walled, of diameter D = 25 mm, and makes eight passes through the shell. If the oil leaves the exchanger at 100°C, what is its flow rate? How long must the tubes be to accomplish the desired heating?

The work done when a gas is expanded in a cylinder is -220 J. A heat transfer of 190 J occurs from the surrounding to the gas. Calculate ∆E of the gas in J.

Question 1.2 A helical coil cooler is used to cool 0.5 kg.s¹ of hot oil from 100°C down to 40°C. Cooling water with an inlet temperature of 10°C flows inside the coiled tube. The specific heat of the oil is 2 kJ.kg¹.K¹, the specific heat of the water is 4.2 kJ.kg¹.K¹, and the density of water is 1000 kg.m. a) Determine the lowest possible cooling water flow rate. (0.48 kg.s¹) b) Determine the inside diameter of the tube if a cooling water flow of 1.5 times the minimum is used, and the recommended flow velocity is 1 m.s. Select an appropriate tube from the following standard sizes: Outside diameter (mm) Wall thickness (mm) 30 1.5 35 2.0 40 2.0 45 2.5 50 3.0 c) For a heat transfer coefficient of U = 800 W.m2.K, determine the heat transfer surface area and the tube length of the heat exchanger. The oil inside the tank is mixed by a stirrer and the oil temperature at any location in the tank can be assumed to be equal to the oil outlet temperature. (Area = 4.12 m², length = 39.7 m)

The horizontal roof of a building has an emittance of 0.9. Air temperature is 1°C on a clear night. Sky acts as a black radiation sink at -60°C. If the underside of the roof is well insulated, estimate the roof temperature. Assume a convective heat transfer coefficient of 5 W/m2 K.