PASCO ET-8782 User Manual

Instructions Experiments Sample Data

Instruction Manual

No. 012-08745A

Energy Tr ansfer–

Thermoelectric

ET-8782

Energy Transfer–Thermoelectric Model No. ET-8782

Table of Conte nts

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Experiment 1:

Conservation of Energy and the First Law of Thermodynamics . . . . . . . . . . . . . . . . . . . . . 9

Experiment 1:

Teachers’ Notes–Conservation of Energy and the First Law of Thermodynamics . . . . . 15

Experiment 2:

Load Resistance and Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Experiment 2:

Teachers’ Notes–Load Resistance and Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Experiment 3:

A Model Refrigerator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Experiment 3:

Teachers’ Notes–A Model Refrigerator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Experiment 4:

Coefficient of Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Experiment 4:

Teachers’ Notes–Coefficient of Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37

Experiment 5:

Teachers’ Notes–Carnot Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Safety. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Technical Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Copyright and Warranty Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Model No. ET-8782 Energy Transfer –T her m oelectri c

Energy Transfer–Thermoelectric

Model No. ET-8782

Included Equipme nt Replace m ent P art N um ber

1. Thermoelectric circuit board

2. Foam insulators (qty. 2)

3. Heat sink

4. Thumbscrew

5. Temperature cables (qty. 2)

6. Banana patch cords (qty. 8)

ET-8782

648-08724

624-013

617-01 8 an d 615-031

PS-2515

SE-7123

7. CD-ROM containing editable experiment instructions and DataStudio

files (not pictured)

Contact Tech Support

Energy Transfer–T herm o el ectri c Introduction

Additional Equipment Required Model Number

DC Power Supply (10 V , 1 A minimum) Temperature Sen sor(s), compatible with 10 kΩ thermistors Voltage and Current Sensor(s) PASCO Computer Interface DataStudio software

Optional Equipment Model Number

Fast Response Temperature Probes Decade Resistance Box

SE-972 0A or equivalent

Various, see note below

See PASCO catalog

PS-2135 (3-pack)

SE-712 2 or equivalent

Note

The most convenient combination of interface and sensors for use with the Thermoelectric circuit board is:

• PS-2001 PowerLink interface

• PS-2143 Quad Te mperature Sensor

• PS-2115 Voltage/Current Sensor

• PS-2135 Fast Response Temperature Probes (3-pack), optional This is the equipment ca lled for by the experime nts in this manual and on the C D-ROM. There are

other options for PASPORT™ and ScienceWorkshop® sensors and interfaces, and stand-alone multimeters. Please contact Tech Support, or see the PASCO catalog or website for details.

Introduction

The Energy T ransfer–Thermoelectric circuit board provides students with a hands-on example of a thermoelectric heat engine. Using measurements from temperature, voltage and current sensors, students will quantitatively study the energy, work and heat flow associated with heat engines, heat pumps and refrigerators.

This manual includes instructions for five e xperime nts with sample data and teachers’ notes. You can photocopy the student instructions or print them from the editable copy of this manual included on the CD-ROM. Experiment #5 is a DataStudio workbook, which contains the student instructions within the DataStudio file.

In addition to the experiments detailed here, the Thermoelectric board is well-suited for selfguided exploration. The following sections will familiarize you with the components of the experimental set-up.

Model No. ET-8782 Introduction

1. Peltier Device with Hot and Cold Reservoirs

The Peltier Device is constructed of two ceramic plates with p and n semiconductors in between. As DC current passes through the device, it pumps heat from one side to the other. Aluminum blocks are fastened to each side of the peltier in thermal contact with the ceramic plates. These blocks add thermal mass to the system and act as the traditional Hot and Cold Reservoirs. When there is a temperature difference across the peltier, it can be s witched to Heat Engine Mode, in which spontaneous heat flow through the device generates an electric current. Do not touch the

hot aluminum block when it is running in Heat Pump Mode. The temperature of this block can reach 90 °C or higher.

Do not allow the peltier device to reach temperatures above 100 ºC. Always monitor the temperature of the hot side whe n the peltier is oper ating in Heat Pump Mode. Operation between

80 °C and 100 °C will shorten the life of the device; if you operate the device in that temperature range, do so for the briefest possible time. You can operate the peltier device without damage at temperatures below 80 °C.

Energy Transfer–T herm o el ectri c Introduction

2. Input Power

Input Power for the board must be supplied from an external DC power supply capable of 1 amp at 10 volts. Connect the power supply via the red and black banana jacks on the right-hand side of the board. Note the polarity: red must be positive. Do not input more than 10 volts.

3. Load Resistors

In Heat Engine Mode, a jumper cable must be connected from the bottom banana jack terminal to one of the terminals labeled A through D. The load resistance depends on how you connect the jumper cables. If, for example, the jumper is connected to terminal A, then all of the resistors ar e in series in the circuit, and the total load resistance is 20 Ω + 7 Ω + 3 Ω = 30 Ω. If the jumper is connected to terminal C, the load resistance is 3 Ω. A second jumper can also be used across a resistor to remove it from the circuit. For example, if the mai n jumpe r from th e bottom connector is plugged into terminal A, and a second jumper is connected between B and D, the total load resistance is 20 Ω; the 7 Ω and 3 Ω resistors are bypassed.

The possible combinations are 3 Ω, 7 Ω, 10 Ω, 20 Ω, 23 Ω, 27 Ω and 30 Ω. If you use a decade resistance box instead of the on-board resistors, you can supply any value you want. You can also connect the jumper from the bottom terminal directly to terminal D, which reduces the load resistance to a few tenths of an ohm (due to the internal resistance of the circuit).

4. Knife Switch

The single pole double throw Knife Switch on the right side of the board is used to select the mode of operation. In Heat Pump Mode, external power is applied to the peltier device, and heat is pumped from the aluminum block on the cold side to the block on the hot side. In Heat Engine Mode, the external power is disconnected, and heat flows back through the peltier, generating electric current through the load resistor.

5. Voltage and Current

Voltage and current sensors connected to the banana jacks at the top of the board will measure voltage across and current through the peltier. Note the polarity when you connect the sensors. A single PASPORT Voltage/Current sensor can be used for both measurements. If you plan to run the peltier without a current sensor, you must connect a jumper between the current terminals to complete the circuit.

From the measured voltage and current, DataStudio will calculate the power supplied to the peltier (in Heat Pump mode ) or power genera ted by the pelti er (in Heat Engine mode). DataS tudio will plot a graph of power versus time, which it will use to calculate input or output energy.

6. Temperature Ports

Each aluminum block has a 10 kΩ thermistor embedded in it. Use the provided Temperature Cables to connect temperature sensors to the thermistors through the hot-side and cold-side

Model No. ET-8782 Introduction

Temperature Ports. The temperature sensor measures the resistance of the thermistor and translates it into a temperature reading. If you are using a PASPORT Quad Te mper ature sensor, you will connect both temperature ports (and up to two additional probes) to a single sensor.

From the measured temperature change, DataStudio will calculate the heat flow into or out of the aluminum blocks.

7. Foam Insulators and Heat Sink

The Foam Insulators are used to insulate one side or both sides of the peltier. For conservation of energy studies, use both insulators to minimize heat exchange with the environment. If needed, you can put a rubber band around them to hold them tightly together .

The Heat Sink, which helps to dissipate heat, fastens to the hot-side aluminum block with the provided thumb screw. For more efficient cooling, the fins of the heat sink should be ver tical. Be

careful when removing the heat sink because it can get very hot.

In some experiments, you will have an insulator on the cold side, and the heat sink on the hot side.

8. Cooling Fan

The Cooling Fan and heat sink act together t o dissipate heat from the hot r eservoir . T he fan is used when demonstrating a refrigerator. You can also use it to cool the aluminum blocks back to room temperature, which is a required initial condition in some experiments.

The fan is operated through a switch in the center of the board and it is powered by the same external power supply that powers the peltier. The fan has a built-in regulator, so it will run at a constant speed when the input voltage is 6 volts or higher. Do not use the fan when the input voltage is below 4 volts.

Energy Transfer–T herm o el ectri c Introduction

9. Temperature Sensor Clamps

When modeling a refrigerator it is useful to observe the heat flow around the heat sink. Two Temper ature Sensor Clamps (one high, one low) are provided to position Fast Response Temper ature Probes (not included) in the air stream from the fan before and after the air has passed through the heat sink.

Model No. ET-8782 Energy Transfer –T her m oelectri c

Experim ent 1:

Conservation of Energy and the First Law of Thermodynamics

Equipment Required Part Number

Thermoelectric circuit board Foam insulators (qty. 2) Banana patch cords (qty. 5) Temperature cables (qty. 2) DC Power Supply (10 V, 1 A minimum) PASPORT Voltage/Current Sensor PASPORT Quad Temperature Sensor PASPORT interface(s) DataStu d io software “Conservation of Energy” configuration file for DataStudio

part of ET -8782

SE-972 0A or eq uiv a le nt

PS-2115

PS-2143

PS-2001 or equivalent

See PASCO catalog

part of ET -8782

Introduction

In this activity you will study the flow of energy in the experimental set-up as you run it through a cycle.

First you will operate the apparatus in Heat Pump mode, in which energy is supplied to the peltier, and the peltier pumps heat from one aluminum block to the other. After a temperature difference has been established between the blocks, you will switch the peltier into Heat Engine mode, in which heat flows from the hot block, through the peltier, and into the cold block. The peltier will convert some of the heat that flows out of the hot block to electrical energy, which it will supply to the load resistor.

During this cycle you will follow the energy as in moves in different forms from the power supply to the peltier (electrical energy), in and out of the aluminum blocks (heat or thermal energy), and into the load resistor (electrical energy). As you do the experiment, bear in mind the law of conservation of energy and the first law of thermodynamics. How do they relate to the transfer of energy within the system?

Set-Up

1. Input Power: Set the Heat Pump/Heat Engine switch to the neutral position (straight up).

Connect the power supply using banana patch cords to the input power terminals on the circuit board as shown in picture below. Note the polarity.

Energy Transfer–T hermo el ectric Conservation of Energy and the First Law of Thermo dyn ami cs

2. Load Resistance: Connect a jumper from

the terminal at the bottom of the board to Terminal B. This makes the load resistance 3 Ω + 7 Ω = 10 Ω.

3. Insulators: Place both foam insulators on

the aluminum blocks.

4. Temperature: Connect the cables from the

temperature ports to the Quad Temperature Sensor . Connect the Cold Side to Channel 1 of the sensor and the Hot Side to Channel 2.

5. Voltage: Connect the voltage leads of the

Voltage/Current Sensor to the Voltage Ports on the board. Note the polarity.

6. Current: Connect separate red and

black banana patch cords from the current input of the Voltage/Current sensor to the Current Ports on the board. Note the polarity.

Ch 2

Temperature

Sensor

Ch 1

Voltage/Current

Sensor

Power Supply

7. Computer: Connect the sensors to the

computer through the PASPORT interface. Open the pre-configured DataStudio file “Conservation of Energy”. The display should look as shown here.

Background

DataStudio has been configured to measure and record the temperature of both aluminum blocks, the voltage and current applied to the peltier during Heat Pump mode, a nd the voltage and current generated by the peltier during Heat Engine mode. From these measured quantities, DataStudio will calculate and display heat flow, power and work. The following sections explain how DataStudio makes those calculations.

Heat vs. Temperature

Each digits display shows the heat ( Q either the hot or cold side of the peltier. The relationship between heat flow and temperature change is given by

hot

or Q

) that flows into or out of the aluminum block on

cold

Q = mc∆T

where:

Model No. ET-8782 Experiment 1: Conservation of Energy and the First Law of Thermo dyn ami cs

Q = heat transferred, m = mass of the aluminum block,

c = specific heat of aluminum = 0.90 J/(g·°C),

∆T = change in temperature.

A positive value of Q may represent heat transferred into or out of the aluminum block, depending on whether the block is on the hot side or the cold side of the peltier, and whether the peltier is operating as a heat pump or a heat engine.

The temperature of each block is measured by the embedded thermistor. DataStudio calculates the heat flow from the measured temperature change, and pre-entered values of m and c. Click on the calculator icon in the tool bar and look at the equations used; note the constants, m and c, in the bottom section of the calculator window. (The mass of each block is about 19 g. If you would like to enter your own value for the mass, measure the blocks with calipers and use the density of aluminum, 2.7 g/cc, to calculate the mass, then enter it in the calculator.)

Input Power and Work Done by the Peltier Heat Pump

In Heat Pump mode, Input Power from the power supply equals the rate at which the peltier does work to pump heat out of the cold reservoir and into the hot reservoir . The Voltage/Current Sensor measures the voltage applied to the peltier, and the current that flows through it. DataStudio calculates the Input Power using the equation: Power = Voltage × Current.

The area under the plot of Input Power versus ti me equals the ener gy supplied to the peltier , which equals the work done by the peltier.

Power Generated and Work Done by the Peltier Heat Engine

In Heat Engine mode, Power Generated is the rate at which the peltier does work on the load resistor . The Voltage/Current sensor measures the voltage across the resistor and the current through it. From these measurements, DataStudio calculates the power supplied to the load resistor . The area under the plot of Power Generated versus time equals the work that the peltier has done on the resistor.

Procedure

Before you start, the aluminum blocks should both be at room temperature. The knife switch should be in neutral position ( s traight up) and the fan should be switched off.

Set the DC Voltage to between 3 and 4 volts. Start data recording, then set the knife switch to Heat Pump. You will see Input Power data appear in the top section of graph. The area under the graph equals

the energy supplied to the peltier, which equals the work done by the heat pump. The Heat Pump digits display shows the heat pumped out of cold reservoir (Q hot reservoir (Q

hot

) and the heat deposited into the

cold

Energy Transfer–T hermo el ectric Conservation of Energy and the First Law of Thermo dyn ami cs

Observe how the temperatures of the aluminum blocks change. Run the peltier in Heat Pump mode for about a minute (or until the cold side appears to reach a

minimum temperature), then switch to Heat Engine mode. Again, observe how the temperatures of the aluminum blocks change. Power Generated data now appears in the bottom section of the graph display . The area under the

graph equals the energy generated by the heat engine and supplied to the load resistor. The Heat Engine digits display shows the heat that has flowed out of the hot reservoir (Q that has flowed into the cold reservoir (Q

cold

) and the heat

hot

Continue to record until the aluminum blocks are close to the same temperature.

Analysis

Hot Reservoir

Heat Pump Mode

In Heat Pump mode the peltier does work to pump heat out of the cold reservoir and into the hot reservoir.

W = work done by the peltier (equal to the area under the Input Power curve),

= heat pumped into the hot reservoir,

hot

= heat pumped out of the cold reservoir.

cold

Cold Reservoir

By the first law of thermodynamics,

hot

= Q

cold

+ W

1) Where did the heat pumped out of the cold reservoir go? Where did the heat pumped into the

hot reserv oir come from? Why was more heat pumped into the hot reservoir than was pumped out of the cold reservoir?

2) Compare your observed values of (Q

+ W) and Q

cold

. If they are not equal, where did the

hot

“lost energy” go?

hot

Heat Pump

cold

3) Write an equation in terms of the “lost energy”, E Q

cold

, and your observed data, W, Q

lost

Heat Engine Mode

In a heat engine, heat flows out of the hot reservoir, some of the heat is converted to work, and the rest of the heat flows into the cold reservoir.

W = work done by the heat engine,

= heat flow out of the hot reservoir,

hot

= heat flow into the cold reservoir.

cold

By the first law of thermodynamics,

and

hot

Hot Reservoir

hot

Heat Engine

cold

Cold Reservoir

Model No. ET-8782 Experiment 1: Conservation of Energy and the First Law of Thermo dyn ami cs

W = Q

4) Compare your observed value of work, W

plot) to the quantity Q

hot

– Q

. Are they equal?

cold

– Q

hot

observed

cold

(which is the area under the Power vs. Time

5) In a real heat engine, only part of the heat that flows out of the two-reservoir system (Q

hot

– Q

) is converted to useful work. In this experiment, the work that you observed (the

cold

useful work) was the work done on the load resistor. Can you account for all of the energy that flowed out of the hot reservoir with your values of W

observed

, Q

and Q

hot

? If not, where

cold

did the “lost energy” go?

6) Calculate the proportion of net heat flow from the aluminum blocks that was converted to useful work;

observed

% of useful work

7) Write an equation in terms of the “lost energy”, E and Q

cold

----------------------------

–

hot

cold

, and your observed data, W

lost

100 %×=

, Q

observed

hot

8) In this experiment the “useful work” was the work done on the load resistor. What was the result of doing work on the resistor? How could you modify the circuit in order to make better use of the work done by the heat engine?

Conservation of Energy

In the Heat Pump phase of the cycle the power supply put energy into the system. Then, in the Heat Engine phase heat flowed out of the hot reservoir and part of it was converted into electrical energy, which was supplied to the load resistor.

9) Calculate the percentage of energy put in during the Heat Pump phase that was recovered as useful work during the Heat Engine phase;

energy generated

% recovere d

---------------------------------------- energy put in

100 %×=

10) Is this a good way to store energy?

Conduction and Heat Flow Through the Insulators

One of the losses of energy in this experiment has to do with heat f low by conduction thr ough the polyethylene foam insulators. The rate of heat flow through the insulator is

T∆

Qit⁄ kA

------ -

where:

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