Heat Transfer

Provide descriptive (~ 0.5 - 1 page) answer(s) to each of the following questions (use Figures and provide sample calculation for each law wherever feasible to illustrate your response). Your answers should not be too mathematical/complex but at a level that an engineering under- graduate student can understand.

Question 5 Draw a diagram and explain the operation of an evacuated heat pipe solar collector. What features are used to improve its performance?

Question 6 The solar collector with the performance curve depicted in your solar homework is used to heat water over a 4 hour period. The collector has an area of 16 m² and the storage tank has a volume of 250 gallons. The water in the storage tank is initially 18°C and the ambient air temperature is 10°C. Assume that the water moving through the collector has an average temperature of 50°C for the purposes of calculating the solar collector efficiency. The flow rate through the collector is 0.5 L/s. The average global radiation incident on the collector is 620 W/m² over the 4 hours. Determine: a. The average solar collector efficiency. b. The rate of heat absorbed by the collector, in kW. c. The exit temperature of the water from the collector, in °C. d. The total energy absorbed by the collector, in kJ. e. The average temperature of the water in the tank after 4 hours, in °C.

3. It is solar noon on the winter solstice and the sun is 50 degrees above the horizon at a location in the northern hemisphere. Match the terms with the corresponding angles for this instance. Altitude Angle 50 degrees Zenith Angle 40 degrees Azimuth Angle Declination Angle

1. Consider the electric hot water heater in the figure below. The tank is insulated with 6cm thick layer of insulation with a kinsul-0.03 W/m-°C. The convection heat transfer coefficients on the inner and outer surfaces of the heater are 50 and 12 W/m²-°C, respectively. Determine the cost of electricity required per year to maintain a water temperature of 55°C if the surrounding air temperature is at 27°C. Assume a cost of electricity of 0.12 $/kW-hr. Neglect radiation heat transfer and the thermal resistance of the tank. Assume the flow of water to be zero. Also neglect the heat transfer from the top and bottom of the tank.

2. A 10cm long, 3cm wide, and 1cm thick rectangular cross-section aluminum fin (k=237 W/m-°C) is attached to a hot surface of 100°C. The convection heat transfer coefficient is 15 W/m²-°C and the surrounding air is maintained at 30°C. a. Assume a very long fin and calculate the rate of heat transfer from the fin. b. Is the assumption from part a. valid? Why? c. Find the heat transfer using an alternative method. Assume no radiation heat transfer.

1. (2 pts) Short-answer and Multiple-choice Problems A. When Bi << 1, which of the following is approximately true for the temperature, 7, of the object being transiently cooled? Explain your reasoning. a. T = f(t) only b. T = f(t) and one spatial dimension c. T = f(t, x,y,z) B. Consider a plate of material X, originally at To, that is exposed to fluid at T<To and a given heat-transfer coefficient h at time t = 0. If the plate is now replaced with material Y with a higher thermal conductivity but the same plate size and given heat-transfer coefficient, how will the time for the center of the plate to cool to a given value change with the new material Y? C. Cite two reasons that insulation is used for chemical engineering process equipment. D. Consider a hot oven with an insulated door exposed to a cold room. If the room temperature was increased but all other variables were not changed, would (i) the heat loss to the room increase, decrease, or not change? (ii) the temperature of the outside surface of the door increase, decrease or not change? Explain your reasoning.

4. (12 pts) An infinite long fin with rectangular cross section is exposed to the ambient air with T-40 "C and the heat transfer coefficient of 10 W/(m2K). The fin is fabricated from stainless steel with a thermal conductivity of 17 W/(m K). The fin length, width, and thickness are 90 cm, 5 cm and 0.3 cm. respectively. The fin base temperature 7,280 °C. Determine the heat lost by the fin (unit in W). abou

The heat pump CoP1 and CoP3 evaluated around 11-12 mins are expected to be different. Submit a file (Word, PDF or image) in which you explain the possible sources of discrepancy (max 100 words).

PROBLEM 1 Problem 10.5. A circular heater plate with 80 mm diameter is placed in a tank containing liquid nitrogen at 1 MPa pressure and 80 K temperature. The upward facing side of the plate is maintained at 100 K. Find the heat transfer rate between the heater and liquid nitrogen. For liquid nitrogen properties, you may assume: p = 745.6 kg/m³, Cp = 2.122; ‚μ = 104 x 10-6N.2, k = 0.122- kJ kg.K m². 0.0072 K-¹. W m.K , Pr = 1.80,ß =