A schematic diagram of a water heater using solar energy is shown below. Oil is circulated...

 

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A schematic diagram of a water heater using solar energy is shown below. Oil is circulated through the closed circuit using a pump. Oil is heated up in the solar collector and is then passed to the water storage tank in which heat is exchanged between the heated oil and the cold water in the tank, then the oil returns back the solar collector for further heating. The circulation of oil continues until the water set temperature is reached. Assume that the solar irradiance is constant with time and it is equal to 1000 W/m?, the efficiency of the collector is 75%, the surface area of the collector is 1 m2, the amount of water to be heated is 10 kg, the specific heat of water is 4.18 kJ/kgK, the initial temperature of water and oil is 25°C, the heat transfer coefficient by from the oil to the water is 10 W/m²K, the surface area of the heat exchanger pipes is 0.2 m2 and of diameter 1 cm. The circulated oil is thermal oil that is used in cooling of transformers, and its mass flow rate is 0.3 kg/s. It is required to heat the water in the storage tank to 50°C. Determine, a. How long it will take to heat up the water in the storage tank from 25°C to 50°C. b. Draw the temperature of the water in the tank versus time. c. How much will be the heating time if the oil mass flow rate is decreased to 0.1 kg/ s and if it is increased to 0.5 kg/s. Q solar T oil in, Tank T oil out, Collector Solar collector Storage Tank T oil in. Collector T oil out, Tank Pump Control unit Figure 1: closed loop solar collector system Marking criteria 1- Writing down the set of equations (5 p) 2- Solving one iteration (2 p) 3- Solving parts a, b and c (3 p) A schematic diagram of a water heater using solar energy is shown below. Oil is circulated through the closed circuit using a pump. Oil is heated up in the solar collector and is then passed to the water storage tank in which heat is exchanged between the heated oil and the cold water in the tank, then the oil returns back the solar collector for further heating. The circulation of oil continues until the water set temperature is reached. Assume that the solar irradiance is constant with time and it is equal to 1000 W/m?, the efficiency of the collector is 75%, the surface area of the collector is 1 m2, the amount of water to be heated is 10 kg, the specific heat of water is 4.18 kJ/kgK, the initial temperature of water and oil is 25°C, the heat transfer coefficient by from the oil to the water is 10 W/m²K, the surface area of the heat exchanger pipes is 0.2 m2 and of diameter 1 cm. The circulated oil is thermal oil that is used in cooling of transformers, and its mass flow rate is 0.3 kg/s. It is required to heat the water in the storage tank to 50°C. Determine, a. How long it will take to heat up the water in the storage tank from 25°C to 50°C. b. Draw the temperature of the water in the tank versus time. c. How much will be the heating time if the oil mass flow rate is decreased to 0.1 kg/ s and if it is increased to 0.5 kg/s. Q solar T oil in, Tank T oil out, Collector Solar collector Storage Tank T oil in. Collector T oil out, Tank Pump Control unit Figure 1: closed loop solar collector system Marking criteria 1- Writing down the set of equations (5 p) 2- Solving one iteration (2 p) 3- Solving parts a, b and c (3 p)