Lab Report_ Coefficient of Performance
docx
School
CUNY LaGuardia Community College *
*We aren’t endorsed by this school
Course
219
Subject
Aerospace Engineering
Date
Dec 6, 2023
Type
docx
Pages
10
Uploaded by EarlDanger3924
Thermodynamics, MAE219
Lab Report: Coefficient of Performance
5/28/2022
Professor Ngabonziza
Objective
To measure the coefficient of performance of a reversible heat pump running in both refrigerator
and heat pump mode.
Introduction
Heat pumps can pump heat out of a building (cooling the space) or into a building (heating the room). If a heat pump is working as an air conditioner or refrigerator, it is absorbing heat from the space to be cooled and rejecting it to the surrounding atmosphere (for example, the surrounding room where a refrigerator is). If a heat pump works as a heater, it absorbs heat from the surrounding cold atmosphere (outside) and uses it to warm the heated space (inside a house). Heat pumps and refrigerators are typically separate systems, but in this experiment, we will use a reversible heat pump that can be used as both a heater and an air conditioner. The amount of energy that a heat pump uses to move a certain amount of heat is called its coefficient of performance. Coefficient of performance of a refrigerator
k
=
Q
cold
W
(
cooling
)
Coefficient of performance of a heat pump
k
=
Q
hot
W
(
heating
)
1
The software DataStudio was used to calculate and display heat flow, power, and work for a reversible heat pump in this experiment. The interface showed the values for the temperatures of the hot and cold blocks, the heating flowing into the hot block (Q
hot
), and the heat flowing out of the cold block (Q
cold)
. Additionally, the real-time power vs. time graph was displayed and the area under this graph is equal to the work done by the peltier.
Equipment
Thermal Efficiency Apparatus
Foam insulators
Banana patch cords
Temperature cables
DC Power Supply (5 V, 1 A minimum)
PASPORT Voltage/Current Sensor
PASPORT Quad Temperature Sensor Setup
Set the switch to the neutral position. Connect the power supply using banana patch cords to the input power terminals.
Attach the heat sink and insulator to the aluminum blocks.
Connect the cables from the temperature ports on the circuit board to the temperature sensor.
Connect the cables from the voltage ports and the current ports on the circuit board to the voltage/current sensor.
Connect the temperature sensor and the voltage/current sensor to the computer. Open DataStudio and launch the file “Coeff of Performance”.
2
Procedure
Refrigerator
Before starting, the knife switch was moved to the neutral position, and the fan turned off.
The DC power was set to 5 volts.
The foam insulator was moved to the cold block, and the heat sink was moved to the hot
block.
The program was started in DataStudio.
Once the temperatures of the blocks were within 0.1 ᵒ
C, the knife switch was closed, and
the program was allowed to run for 10-15 seconds.
3
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
The values for power (W*s) and Q
cold
(J) were recorded.
Heat pump
The foam insulator was moved to the hot block, and the heat sink was moved to the cold
block.
The procedure outlined above for the refrigerator was repeated for the heat pump.
Experimental Results and Discussion
Refrigerator
1.
Use your values for the heat pumped out of the cold block (Qcold) and the area under the Power versus time curve (W) to calculate the Coefficient of Performance, k, for your model refrigerator.
Trial
Q
cold
(J)
W (W*s)
k
1
1.05
0.11
9.55
2
1.05
0.12
8.75
3
1.05
0.14
7.5
Average
9
2.
For real heat pumps k is usually expected to be greater than 1. Is this the case for your model?
Yes, the coefficient of performance k was greater than one for all trials.
3.
Your heat pump can also be thought of as a model air conditioner, a device used to keep
the inside of a building cooler than the outside air. In terms of moving heat, what does 4
an air conditioner do to keep a building cool? (Keep in mind that an air conditioner does not necessarily move air into or out of the building.)
An air conditioner works by absorbing the heat in a room/building and discharging it outdoors. An air conditioner is like a large refrigerator that works by transferring the heat to a working fluid (refrigerant) that absorbs heat in an evaporator and discharges it in a condenser.
4.
Compare your model to a building being cooled by an air conditioner. What does the peltier represent? What does the cold block represent? What does the hot block represent?
The peltier device represents the refrigeration system that transfers heat from one reservoir to another depending on the direction of the current. The cold block represents the building/room being cooled by the AC. The hot block represents the outdoors, where heat is discharged.
5.
If you were selecting an air conditioner to keep your home cool, would you choose one with a high or low coefficient of performance? Explain why.
When choosing an air conditioner for your home, one with a higher COP is preferable. The higher the COP, the less energy is required to cool the space, which means you will have a lower electricity bill.
Heat Pump
5
6.
Use your values for the heat delivered to the hot block (Q
hot
) and the area under the Power versus time curve (W) to calculate the Coefficient of Performance, k.
Trial
Q
hot
(J)
W (W*s)
k
1
0.27
0.12
2.25
2
0.27
0.13
2.08
3
0.28
0.13
2.15
Average
2.16
7.
If you had used a simple resistor (rather than the peltier) to heat the aluminum block, and used the same amount of energy (W), what would have been the maximum amount of heat transferred to the block?
Using a simple resistor heater, the maximum amount of heat transferred to the block would be equal to the amount of electrical energy input. For example, if 0.13 W*s were used to run the system, then 0.13 J of heat would be transferred to the block.
8.
Compare your model to a building being heated by a reversible heat pump. What does the peltier represent? What does the cold block represent? What does the hot block represent?
The peltier device represents the heat pump that transfers heat from one block to another. The cold block represents the outside, where heat is absorbed from. The hot block represents the inside of the building/room that is being heated.
6
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
9.
Why is it important for k to be greater than 1 for a reversible heat pump? Compare this to a simple electrical heater. How much heat is delivered to a building using a simple heater supplied with 100 J of electrical energy? How much heat is delivered to a building
using a heat pump, with k = 2, that uses 100 J of electrical energy to pump heat from outside to inside the building?
It is important for k>1 for a reversible heat pump because a larger value of k means that less electrical energy is required to heat or cool a space. A simple resistance heater using 100 J of energy will supply 100 J of heat to a building. These types of systems have a coefficient of performance of k=1, meaning energy is used at a 1:1 ratio which is not an efficient use of energy. A heat pump using 100 J of energy with k=2 will supply 200 J of energy to a building. This type of system is more efficient because it has twice the heating capacity of the simple resistor while using the same amount of electrical energy input.
7
Refrigerator
8
Heat pump
9
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
Conclusion
The objective of the experiment was achieved and the values for the coefficient of performance of a heat pump and refrigerator seem reasonable. The fan was left on throughout the experiment, which affected the coefficient of performance values.
10