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3.15 The heating rate that a heat pump delivers to a living space of tempera- ture 20°C is 5 kW. The coefficient of performance of the heat pump is COP = 2. The temperature of the ambient is 0°C. (a) What is the electrical power required by the heat pump? (b) What is the rate at which the heat pump draws heat from the ambient? (c) What is the highest COP value that the heat pump may attain? (d) Is the operation of this heat pump violating the second law of thermodynamics?

A system is being designed to remove heat from a server rack in a data center. The figure below provides a schematic of this system. A pump circulates water through a heat sink in the rack to remove 5000 W of heat. To keep the electronics below the temperature at which damage may occur, the water leaving the server rack will be limited to 80 °C. That temperature will result in the most optimal system, so you can assume that it is the temperature of the water leaving the server rack. This water is then circulated to a heat exchanger that can be modeled as a counter flow model with a stream of air to remove the heat. Air with an inlet temperature of 20 C at a mass flow rate of 0.1 kg/s is blown through this heat exchanger. Your task is to determine the size of the air-to-water heat exchanger (i.e., its area) and the mass flow rate of water to minimize the life cycle cost of the system. The cost, which is dominated by the first cost of the heat exchanger and the energy to run the pump,…

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A constant temperature of -125 C must be maintained in a cryogenic experiment, although it gains 120 W due to heat transfer. What is the smallest motor you would need for a heat pump absorbing heat from the container and rejecting heat to the room at 20 C

Q.2 The following data relates to the office air conditioning plant having maximum seating capacity of 25 occupants : Recirculated air Room Outside air 4) to = 34°C tm = 28°C ta2 = 24°C $2 = 50% Mixing Coil Outside design conditions: 34°C DBT, 28°C WBT Inside design conditions: 24°C DBT, 50% RH Solar heat gain= 9120 W Latent heat gain per occupant= 105w Sensible heat gain per occupant=90w Lightening load= 2300 W Sensible heat load from other sources= 11630 W Infiltration load= 14 m³/min Assuming 40% fresh air and 60% of recirculated air passing through the evaporator coil and the by-pass factor of 0.15. Draw the process on psychrometric chart and find the dew point temperature of the coil and capacity of the plant.

3. An automobile engine delivers 25hp to the driveshaft with the thermal efficiency of 30%. The fuel has a heat content of 40 000kJ/kg. Calculate the rate of fuel consumption (kg/hr) and the heat rejected (kW) through the radiator and exhaust.

refrigerator. It is given that Q2 + Q4 3 Q1. Calculate the C.O.P. of the .refrigerator In figure shown, (E) is a heat engine with efficiency of 0.4 and ( R) is a Q3 Q1 Q2 C.O.P-5.00 O C.O.P=5.50 C.O.P=5.05 O C.O.P=5.55 O R.

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In an absorption refrigerator, the energy driving the process is sllPplied not as work, but as heat from a gas flame. (Such refrigerators commonly use propane as fuel, and are used in locations where electricity is unavailable. *) Let us define the following symbols, all taken to be positive by definition:                     Qf = heat input from flame                      Qe = heat extracted from inside refrigerator                      Qr = waste heat expelled to room                      Tf = temperature of flame                                         Te temperature inside refrigerator                                           Tr = room temperature Explain why the "coefficient of performance" (COP) for an absorption refrigerator should be defined as Qc/Qf.

In an absorption refrigerator, the energy driving the process is sllPplied not as work, but as heat from a gas flame. (Such refrigerators commonly use propane as fuel, and are used in locations where electricity is unavailable. *) Let us define the following symbols, all taken to be positive by definition:                     Qf = heat input from flame                      Qe = heat extracted from inside refrigerator                      Qr = waste heat expelled to room                      Tf = temperature of flame                                         Te temperature inside refrigerator                                           Tr = room temperature Use the second law of thermodynamics to derive an upper limit on the COP, in terms of the temperatures Tf, Te, and Tr alone.

27. If the system shown below is used to run a refrigerator, which of the following is true for the x to z step? pressure volume y Z A. The work is negative and heat is added to the system B. The work is positive and heat is added to the system C. The work is negative and heat is removed from the system D. The work is positive and heat is removed from the system 28. Refer to the y to z step in the PV diagram of the previous question. If heat was added to the system, which of the following must also be true? A. W 0 C. W = 0, and AU = 0 D. W = 0, and AU 0, and AU = 0

Separate streams of air and water flow through the compressor and heat exchanger arrangement shown in the figure below, where im =0.8 kg/s and T6 = 30°C. Steady-state operating data are provided on the figure. Heat transfer with the surroundings can be neglected, as can all kinetic and potential energy effects. The air is modeled as an ideal gas. Air P1 = 1 bar T = 300 K P4= 9 bar T4 = 800 K4 "cvA Compressor A Compressor B P2= 3 bar +2 T2= 600 K 3+ P3= P2 T3= 450 K www -Heat exchanger T6, P6= P5 Water Ts= 20°C Ps = 1 bar Determine: (a) the total power for both compressors, in kW. (b) the mass flow rate of the water, in kg/s.

An open system is often referred to as control volume, which is a properly selected region in space in which mass and energy can flow across the boundaries as figure 1.2. The boundary of a open thermodynamic system is called the control surface Across the Boundaries E = Yes F 0 = Yes w =Yes Control surface ass YES W CONTROL VOLUME energy YES Figure 1.2. A cooling/heating radiator is an example of such a system – give two more examples of such a system.

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The figure below depicts a water supply pump drawing from a reservior. Water is withdrawn from the reservoir with water surface elevation of 200-feet (Point #1 in the figure), by a pump whose inlet eye (Point #2 in the figure) is located 6-feet above the water surface elevation. The reservoir water temperature is 80° F, and the pump delivers 2 cubic feet per second of water from a steel inlet pipe 8 inches in diameter. What is the Net Positive Suction Head available for the condition just described. 1

After graduation, you take a job with the Acme energy services company. Your first job is to purchase high efficiency heat pumps. The heat pumps employ mechanical power and a heat engine to provide heat at TH = 100°C. A low temperature heat sink at TC = 20ºC is also available. A salesman shows you two models. Performance data for each model operating at steady state are provided in the Figure below

Q4. Electric heater wires are installed in a solid wall having a thickness of 8 cm and k=2.5W/m. Cº. The right face is exposed to an environment with h-50W/m². Cº and T% =30C°, while the left face is exposed to h=75W/m². C° and Too =50C°. What is the maximum allowable heat-generation rate such that the maximum temperature in the solid does not exceed 300-C? Not a2T (BEST WISHES)