2.4 kg/s of a fluid have a specific heat of 0.81 kJ/kg-K enter a counterflow heat exchanger at 0°C and are heated to 400°C by 2 kg/s of a fluid having a specific heat of 0.96 kJ/kg•K entering the unit at 700°C. Show that to heat the cooler fluid to 500°C, all other conditions remaining unchanged, would require the surface area for a heat transfer to be increased by 87,5%

2.4 kg/s of a fluid have a specific heat of 0.81 kJ/kg-K enter a counterflow heat exchanger at 0°C and are heated to 400°C by 2 kg/s of a fluid having a specific heat of 0.96 kJ/kg•K entering the unit at 700°C. Show that to heat the cooler fluid to 500°C, all other conditions remaining unchanged, would require the surface area for a heat transfer to be increased by 87,5%

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter7: Forced Convection Inside Tubes And Ducts

Section: Chapter Questions

Problem 7.17P: Determine the rate of heat transfer per meter length to a light oil flowing through a 2.5-cm-ID,...

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Determine the rate of heat transfer per meter length to a light oil flowing through a 2.5-cm-ID, 60-cm-long copper tube at a velocity of 0.03 m/s. The oil enters the tube at 16C, and the tube is heated by steam condensing on its outer surface at atmospheric pressure with a heat transfer coefficient of 11.3 kW/m K. The properties of the oil at various temperatures are listed in the following table: Temperature, T(C) 15 30 40 65 100 (kg/m3) 912 912 896 880 864 c(kJ/kgK) 1.80 1.84 1.925 2.0 2.135 k(W/mK) 0.133 0.133 0.131 0.129 0.128 (kg/ms) 0.089 0.0414 0.023 0.00786 0.0033 Pr 1204 573 338 122 55
In large steam power plants, the feedwater is often heated in closed feedwater heaters, which are basically heat exchangers, by steam extracted from the turbine at some stage. Steam enters the feedwater heater at 1.6 MPa and 250°C and leaves as saturated liquid at the same pressure. Feedwater enters the heater at 4 MPa and 30°C and leaves 10°C below the exit temperature of the steam. Neglecting any heat losses from the outer surfaces of the heater, determine the ratio of the mass flow rates of the extracted steam and the feedwater heater.
In large steam power plants, the feedwater is often heated in closed feedwater heaters, which are basically heat exchangers, by steam extracted from the turbine at some stage. Steam enters the feedwater heater at 1.6 MPa and 250°C and leaves as saturated liquid at the same pressure. Feedwater enters the heater at 4 MPa and 30°C and leaves 10°C below the exit temperature of the steam. Neglecting any heat losses from the outer surfaces of the heater, determine the reversible work for this process per unit mass of the feedwater. Assume the surroundings to be at 25°C.
Water (cp=4.182 kJ/kg.K, k=0.6405 W/m.K, Pr=3.57, ν=0.5537x10-6 m2/s, ρ=998 kg/m3) flows through a tube (D=0.5 cm) with an average velocity of 0.2 m/s. The average temperatures of the water at the inlet and outlet cross-sections are 20 oC and 79,87 oC, respectively. The uniform heat flux of 0,69 W/cm2 is subjected to the surface of the tube for heating process. Determine the maximum surface temperature [oC] of the tube.
The condenser of a room air conditioner is designed to reject heat at a rate of 15,000 kJ/h from refrigerant-134a as the refrigerant is condensed at a temperature of 40°C. Air (cp = 1005 J/kg·K) flows across the finned condenser coils, entering at 25°C and leaving at 35°C. If the overall heat transfer coefficient based on the refrigerant side is 150 W/ m2·K, determine the heat transfer area on the refrigerant side.
n electric generator at a power plant produces energy by passing superheated steam from a high temperature container (reservoir), through a pipe connected to a series of fans, and then into a low temperature reservoir. As the steam passes across the blades of the fans some of the heat energy of the steam is transformed into mechanical energy, which turns the fans which in turn are connected to a generator, which in turn converts the mechanical energy into electrical energy. If the high temperature steam has a temperature of 412.1 K and the low temperature reservoir has a temperature of 105.4 K, what is the Carnot efficiency of this process?
A shell-and-tube process heater is to be selected to heat water (cp = 4190 J/kg.K) from 20°C to 90°C by steam flowing on the shell side. The heat transfer load of the heater is 600 kW. If the inner diameter of the tubes is 1 cm and the velocity of water is not to exceed 3 m/s, determine how many tubes need to be used in the heat exchanger.
Water (cp=4.182 kJ/kg.K, k=0.6405 W/m.K, Pr=3.57, ν=0.5537x10-6 m2/s, ρ=998 kg/m3) flows through a tube (D=0.5 cm) with an average velocity of 0.2 m/s. The average temperatures of the water at the inlet and outlet cross-sections are 16,21 oC and 78,49 oC, respectively. The uniform heat flux of 0,58 W/cm2 is subjected to the surface of the tube for heating process. Determine the tube length [m].
A fluid at 690 kPa has a specific volume of 0.25 m³/kg and enters an apparatus with a velocity of 15 m/s. Heat radiation losses in the apparatus are equal to 25 kJ/kg of fluid supplied. The fluid leaves the apparatus at 135 kPa with a specific volume of 0.9 m³/kg and a velocity of 300 m/s. In the apparatus, the shaft work done by the fluid is equal to 900 kJ/kg. Does the internal energy of the fluid increase or decrease, and how much is the change?A. 858 kJ/kg (increase)B. 858 kJ/kg (decrease)C. 908 kJ/kg (increase)D. 908 kJ/kg (decrease)
Steam in the condenser of a steam power plant is to be condensed at a temperature 500C (hfg = 2383 kJ/ kg) with cooling water (Cp = 4180 J/kg) from a nearby lake, which enters the condenser at 180C and leaves at 270C. The surface area of the tubes is 42 m2 and the overall heat transfer coefficient is 2400 W/ m2 .0C. Determine: (i) The mass flow rate of cooling water needed (ii) The rate of condensation of steam in the condenser.
In a once-through boiler, feedwater enters through the bottom og tubes, receives heat from combustion of coal, and escapes from the top of the tubes as superheated steam, calculate the heat transfer coefficients of water and superheated steam using the following data: Pressure of feedwater at tube inlet = 27.0 MPa Absolute temperature of feedwater, Tf =563 K Pressure of superheated steam at tube outlet = 24.5 MPa Absolute Temperature of superheated steam, Tg = 838 K Velocity of Feedwater through each tube. Vf = 6 m/s internal diameter of each tube = 63.5 mm Length of pipe = 30m
750 kg of dry saturated steam at a pressure of 160 N/cm2 is generated in a boiler per hour. The temperature of feed water is 28°C and the steam from the boiler enters the super heater after a heat loss of 690 kJ/kg, where it is superheated such that the degree of superheat is 250°C. Determine i) Dryness fraction of the steam at the entry point of the super heater ii) Heat absorbed per hour in the super heater iii) Total heat supplied to the inlet water in the boiler