E. Calculations (47 score) 1. A double-glazed window is composed of two layers of 5 mm thick glass and the air gap betwe

[answerhappygod]

E Calculations 47 Score 1 A Double Glazed Window Is Composed Of Two Layers Of 5 Mm Thick Glass And The Air Gap Betwe 1 (48.7 KiB) Viewed 38 times

E. Calculations (47 score) 1. A double-glazed window is composed of two layers of 5 mm thick glass and the air gap between them. The thickness of the air layer is 6 mm. Assume that the indoor temperature is 20 °C and the surface convective heat transfer coefficient is 10 W/(m² K), and the outdoor temperature is -15 °C and the surface convective heat transfer coefficient is 15 W/(m²K). Please determine the heat flux through the double-glazed window. [Without considering the natural convection in the air gap, it is assumed that the thermal conductivity of glass is 0.78 W/(mK) and that of air is 0.025 W/(mK)] (10 score) 2. The junction point of the thermocouple can be approximated as a sphere with diameter of 1 mm, the density of the thermocouple material is 8500 kg/m³, the heat capacity is 400 J/(kg K), and the thermal conductivity is 20 W/(mK). The initial temperature of the thermocouple is 20°C, and it is suddenly put into the air flow with temperature of 100°C. The convective heat transfer coefficient of the thermocouple surface and the air flow is 90 W/(m²K). Try to calculate (1) the time required for 3/4 the thermocouple temperature reaching to 50°C; (2) If the diameter of the contact point of the thermocouple is changed to 0.5 mm, after the same time, what is the indicated temperature of the thermocouple? (12 score) 3. As shown in the figure below, surface 1 temperature T₁-560K, emissivity =0.8, surface 2 temperature T-280K, emissivity -0.4, cylindrical surface 3 is the adiabatic surface, the view factor X₁-0.308. Try to calculate: (1) the net radiation loss of surface 1; (2) The temperature of adiabatic surface 3. (13 score) -0.3m -0.6m 4. A parallel double-tube type heat exchanger in which oil is cooled from 100 °C to 60 °C and water is heated from 20 °C to 50 °C, the flow rate of water is 720 kg/h. The specific heat of oil is 2.131 kJ/(kg-K), the specific heat of water is 4.174 kJ/(kg K), the overall heat transfer coefficient of heat exchanger is 350 W/(m²K) Please try to calculation: (1) the mass flow of oil and the area of the heat exchanger. (2) If the water inlet and outlet switch, the outlet water temperature can rise to 55°C, oil and water flow, specific heat, inlet temperature and heat exchange area and other conditions are unchanged, please determine the effectiveness and number of transfer unit (NTU). (12 score)