Q1: An inventor claims to have a heat engine producing mechanical power that extracts 25 kW of heat at 400 K and rejects 10 kW of heat at 200 K. Is this claim possible? (What is the Carnot efficiency of this? What is the claimed efficiency?)
Q2: For the following problem, use the TRNSYS model for flat plate solar collector. Weather data for Albuquerque, NM are in the TRNSYS database.
A flat plate solar collector supplies heat for an industrial process. The collector system is located in Albuquerque with total area of 60 square meters, incidence angle modifier constant bo of 0.1, and collector slope of 40 degrees. The collector is used 9 hours per day from 8AM to 5PM at the rate of 1500 kg/hr. A storage tank is used to store the hot water with tank volume of 10,000 lit. and tank height of 3m. The heat loss to the ambient air is at 4 kJ/(hr.m2.K), the initial water temperature is at 70 deg.C, and the storage tank is not equipped with heating installation. It can be assumed that the tank is fully-mixed with no stratification effects. Hot water is pumped at the rate of 250kg/hr, 9hr per day from 8AM to 5PM, from the tank to be connected to a heat extractor. The process requires heat at a rate of at least 12 kW at temperature of 80 deg.C for 9 hour per day from 8AM to 5PM. Heat that cannot be supplied by solar energy is supplied with an auxillary natural gas burning heater.
Hint: The heat extractor is modeled as an auxiliary cooling unit by setting the rate of energy removed as the heat extracted.
1. Plot the heat collected in solar collector, heat loss in the storage, additional heat needed using auxillary natural gas heat, and the heat extracted from heat extractor as a function of time for the month of March (TRNSYS has a plot function, plot heat values as a function of time in hours for the month of March).
2. Estimate the solar fraction for the month of March (Solar fraction = heat extracted/(heat collected + heat from auxillary natural gas heater)
3. Estimate the annual solar fraction