A refrigeration unit is cooling a space to -5°C by rejecting energy to the atmosphere at 20°C. It is desired to reduce the temperature in the refrigerated space to a value of -25°C. Calculate (a) the coefficient of performance for the initial condition assuming a Carnot refrigerator, and (b) the minimum fractional increase in work required for the same amount of energy removed, (that is, find the ratio of the new work to the initial work).

In the following problem, consider the human body as a heat engine with efficiency e = 0.2 that can take in energy as food Qh, perform work W, and generate heat Qc. This heat expelled from our muscles (Qc) is an important component of maintaining a constant body temperature, which necessitates a balance of energy intake and output. In order to calculate the energy intake Qh, you will use the table above listing activity factors for selected activities, for a person with a BMR of 1440 kcal/day. For example, the energy required to stand per hour would be (fstand)(BMR) = (1.7)(1440 kcal/day) (1day/24 hours) = 102 kcal/h. For each scenario, calculate the 24 h number of bowls of cereal that must be consumed per hour (1 bowl = 100 kcal) to perform the required activity (Qh) Determine whether you have an energy deficit or surplus by considering the heat generated by your muscles (Qc), the heat loss from conduction, and the heat loss/gain from radiation We will consider heat loss from…

Q4/ A particular power plant operates with a heat source reservoir at 350 °C and a heat sink reservoir at 30 °C. It has a thermal efficiency equal to 55% of the Carnot engine therma' efficiency for the same temperatures. 1. What is the thermal efficiency of the plant? 2. To what temperature must the heat source reservoir be raised to increase the thermal efficiency of the plant to 35%?

Consider the refrigerator shown in Figure. If the compressor consumes 850 W of power and the COP of the refrigerator is 2.5 determine. The mass flow rate of the refrigerant The rate of heat rejected to the kitchen air Condenser Expansion Xvalve Wn Compressor Evaporator 100 kPa 100 kPa x0.2 -26°C