Question

A refrigeration plant chills water and delivers it to a heat exchanger some distance away, as shown in Fig. 9-17. The supply water temperature is ti°C, and the return water temperature is t2. The flow rate is w kg/s, and the pipe diameter is D m. The cooling duty at the heat exchanger is 1200 kW, and the arithmetic mean temperature, (fi 2)/2, must be 12°C in order to transfer the 1200 kW from the air. The pump develops a pressure rise of 100,000 Pa that may be assumed independent of flow rate. The equation for pressure drop m a circular pipe iS 2 D 2 where f-0.02 L = 2100 m ρ 1000 kg/m3 The specific heat of water is 4.19 kJ/(kg K). The three major costs associated with the choice of ti, w, and D are Cost of the pipe, 150,000D dollars Present worth of lifetime pumping costs, 500w dollars Present worth of lifetime chilling costs. 60,000-4000% dollars

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