A water cooler of storage capacity 120 litres can cool water at a constant rate of P in a closed circulation system. The water from the cooler is used to cool an external device that generates constantly 3 kW of heat (thermal load). The temperature of water fed into the device cannot exceed 30°C and the entire stored 120 litres of water is initially cooled to 10°C. The entire system is thermally insulated. The minimum value of P (in watts) for which the device can be operated for 3 hours is: (Specific heat of water is 4.2 kJkg⁻¹K⁻¹ and density of water is 1000 kgm⁻³)<p></p>

A water cooler of storage capacity 120 litres can cool water at a constant rate of P in a closed circulation system. The water from the cooler is used to cool an external device that generates constantly 3 kW of heat (thermal load). The temperature of water fed into the device cannot exceed 30°C and the entire stored 120 litres of water is initially cooled to 10°C. The entire system is thermally insulated. The minimum value of P (in watts) for which the device can be operated for 3 hours is: (Specific heat of water is 4.2 kJkg⁻¹K⁻¹ and density of water is 1000 kgm⁻³)

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