Armfield Engineering Education
HEAT TRANSFER AND THERMODYNAMICS
HT17 Unsteady State Heat Transfer - Issue 6
Analytical solutions are available for temperature distribution
and heat flow as a function of time and position for simple solid shapes
which are suddenly subjected to convection with a fluid at a constant temperature.
Simple shapes are provided together with appropriate classical transient-temperature/heat
flow charts which allow a fast analysis of the response from actual transient
measurements. Each shape is allowed to stabilise at room temperature then
suddenly immersed in a bath of hot water at a steady temperature. Monitoring
of the temperature at the centre of the shape allows analysis of heat flow
using the appropriate transient-temperature/heat flow charts provided.
An independent thermocouple mounted alongside the shape indicates the temperature
of the water adjacent to the shape and provides an accurate datum for measurement
of the time since immersion in the hot water.
Ordering Specification
• A small scale accessory designed to allow exercises to be performed
in unsteady state heat transfer.
• Comprises an electrically heated water bath, variable speed recirculation
pump, set of solid thermal shapes and a shape holder.
• The shapes supplied comprise a rectangular slab, long cylinder and
sphere. Two of each shape are supplied, manufactured from brass and stainless
steel. Each shape is instrumented with a thermocouple at the centre of each
shape.
• Analytical transient-temperature/heat flow charts are supplied for
each of the shapes.
• The water bath is 3kW. The water bath includes an integral flow
duct and a thermocouple to measure the water temperature.
• The circulating pump ensures that hot water flows past the solid
shape under evaluation at constant velocity during the test. It is a variable
speed DC pump.
• The accessory is mounted on a PVC baseplate which is designed to
stand on the bench top and connect to the Heat Transfer Service Unit without
the need for tools.
• A comprehensive instruction manual is supplied.
Technical Details
The equipment consists of a heated water bath together with set of instrumented shapes. Three simple shapes are supplied, namely, a rectangular slab, a long solid cylinder and a solid sphere. Each of the shapes incorporates a thermocouple to measure the temperature at the centre of the shape. Each of the shapes is duplicated in brass and stainless steel which have different thermal conductivities. Measurements taken on a shape in one material can be used to confirm the conductivity of a similar shape constructed from a different material. Transient-temperature/ heat flow charts are supplied for each of the shapes.
The water heating bath has a capacity of 30 litres and is heated by an electric heating element having a rating of 3.0kW. A thermostat allows the water to be heated to a predetermined temperature before taking measurements. The large volume of water in the bath ensures that any change in the temperature of the water, as the measurements are taken, is minimal.
The electrical supply to the heating element is protected by a combined RCD/circuit breaker for operator safety. A circulating pump mounted alongside the water bath draws water from the bath and returns it at the base of a vertical cylindrical duct which is located inside the water bath at the centre. A holder ensures that each of the shapes is quickly and correctly positioned within the vertical duct for measurements to be taken. The upward flow of water at constant velocity past the shape ensures that the heat transfer characteristic remains constant and also ensures that the water surrounding the shape remains at a constant temperature.
The circulating pump operates from the variable 24V DC supply on the HT10X. The velocity of the water can be varied by adjusting the voltage supplied to the pump. A thermocouple located in the water bath allows the temperature of the water to be monitored and adjusted to the required temperature before immersing the shapes. Each of the shapes can be attached to a holder which eliminates the need to touch the shape when its temperature has stabilised in air and accurately positions the shape inside the water bath while transient measurements are taken. A thermocouple mounted on the shape holder contacts the hot water at the same instant as the solid shape and provides an accurate datum for temperature/time measurements.
All temperatures are measured using K-type thermocouples, each fitted with a miniature plug for direct connection to the service unit HT10X. The accessory is designed to be used in conjunction with the HT10X Heat Transfer Service Unit and is assembled on a mounting plate to stand on the bench top alongside the HT10X.
Experimental Capabilities
• Bodies of different size, shape and material are allowed to stabilise
at room temperature then dropped into the hot water bath. The change in
temperature of each body is monitored using HT17-304 Educational Software
or suitable chart recorder connected to the HT10X
• Using analytical temperature/heat flow charts to analyse the results
obtained from different solid shapes
• Using the results obtained from one shape to determine the conductivity
of a similar shape constructed from a different material
• Investigating the effect of shape, size and material properties
on unsteady heat flow
Essential Armfield Equipment
HT10X Heat Transfer Service Unit
Optional Armfield Accessories
HT10X-304 Educational Software with USB interface
requirements
Electrical supply
HT17-A: 220/240 V /1ph/50Hz @ 13A
HT17-B: 120V/1ph/60Hz @ 26A
HT17-G: 220V/1ph/60Hz @ 13A
Shipping Specification
Volume: 0.17m3
Gross Weight: 14kg
Overall dimensions
Height: 0.67m
Width: 0.60m
Depth: 0.40m
|
 |
|---|
