To study and evaluate the effects of hot and cold fluid flow rate and flow configurations on the rate of heat transfer through thin walled tubes. To determine the overall heat transfer coefficient for the double pipe heat exchanger for countercurrent flow and parallel (or co-current) flow.
The heat exchanger consists of two thin wall copper tubes mounted concentrically on a panel. The flow of water through the center tube can be reversed for either countercurrent or parallel flow. The hot water flows through the center tube, and cold water flows in the annular region.
• Valves are used to set up desired flow conditions (rate and direction). Set the hot water valve in the correct position to achieve either countercurrent or parallel flow.
• Thermometers and thermocouples are placed near the entrance, midpoint and exit of each pipe. The thermometer should give coarse readings compared to the thermocouple. The thermocouples are connected to a selector switch on the front of the panel.
• The flow meter has a direct read scale in ft3 /min. The flow meter does not read zero at zero flow due to rubber offset. The flow meter can read either the cold or hot water flow rate by turning the appropria te valves.
• A synopsis of operation is as follows: Open or close the appropriate valves to set hot water flow at 0.2 ft3/min in countercurrent configuration. (All globe valves should be totally opened or totally closed.) The metering valves at the outlets should be used to control flow rates. Before beginning cold water flow, temporarily close valve#1 to conserve hot water. Set valve positions for cold water flow at 1.0 ft3/min, then resume hot water flow (open valve#1) Allow the system to reach steady state before taking measurements (1-2 min). Take at least three readings of temperature and cold water flow before changing to new cold water flow rate. Examine cold water flows of 0.8 ft3/min and 0.6 ft3/min. The two heat exchanger groups must work together once the flow has been initiated because the adjustment of flow in one group will affect the other team’s flows. You must communicate when you are ready to change flow rates.
Once you have taken readings for all three rates of cold water flow, reverse the direction of the hot water flow (to the parallel flow configuration) by opening and closing appropriate hot water valves. Collect parallel flow data at cold water flow rate of 0.6 ft3/min only.
• Continuing in parallel flow configuration and 0.6 ft3/min cold water flow, increase hot water flow to 0.4 ft3/min. Collect temperature data.
• Reverse direction of hot water flow (back to countercurrent flow configuration). Collect data at 0.6 ft3/min cold water flow. Take additional readings at cold water flow rates of 0.8 and 1.0 ft3/min.
Considering the heat exchanger given in the figure the continuous, steady-state heat duty is given by,
Q is the heat duty (rate of heat transfer)
m is the flow rate of the stream (mass or molar)
Hin is the enthalpy of the stream entering (per unit mass or mole)
Hout is the enthalpy of the stream leaving (per unit mass or mole)
●Heat is transferred to or from process streams using other process streams or “heat transfer media”. In a heat exchanger design, every effort is made to exchange heat between process streams and thereby minimize the use of heat transfer media (referred to as utilities).
●Heat transfer media are classified as “coolants (heat sinks)” when heat is transferred to them from process streams, and as “heat sources” when heat is transferred from them to process
The objective of this experiment is to study the working principles of a concentric tube heat exchanger operating under parallel and counter flow.
Up to this point we have learned how to analyze conduction and convection heat transfer in various systems with different geometries. This information, however, is not very useful unless it can be applied to practical situations. For this reason we shall devote this experiment to a prototypical application of heat transfer analysis known as a heat exchanger.
A heat exchanger is a device that efficiently transfers heat from a warmer fluid to a colder fluid. A device we are probably all familiar with is the automobile radiator. Other applications for heat exchangers are found in heating and air conditioning systems. Heat exchangers are categorized in many ways, but the two most common practices are, by the method of construction, and by the flow arrangements. The analysis for designing an effective heat exchanger is very important; after all who’d want to be caught on the side of a deserted desert road with an overheated engine!
In this experiment we studied a concentric tube heat exchanger with parallel and counter flow. For the analysis of this heat exchanger we needed to find important quantities such as the heat transfer coefficient, power emitted, absorbed, and lost, the log mean temperature difference, and the overall efficiency to compare the two types of flow.
In this experiment, our aim is to demostrate the working principles of concentric tube heat exchanger operating under paralel and counter flow conditions and the observe the effect of flow rate and hot water temperature variation the performance charasteristics of a concentric tube heat exhanger.
A heat exchanger is used when it is necessary to transfer heat from one fluid to another without mixing the fluids. Two types of heat exchangers, parallel flow and counter flow, will be examined in this lab. The parallel flow heat exchanger has the hot and cold fluids flowing in the same direction whereas the two fluids flow in the opposite direction with a counter flow exchanger. The effect of flow rate variation on the performance characteristics of a counter flow heat exchanger will be studied also.
In section 4.1, we examined a variety of heat exchange equipment used in the food process industry. There are a number of different geometrical configurations used in designing heat exchange equipment, such as tubular, plate, and scraped surface heat exchangers. The primary objective in using a heat exchanger is to transfer thermal energy from one fluid to another. Recall from previous discussionenergy in a fluid, if its temperature changes from T1 to T2, may be expressed as;
Shell and tube heat exchangers are among the more confusing pieces of equipment for the process control engineer. The principle of operation is simple enough: Two fluids of different temperatures are brought into close contact but are prevented from mixing by a physical barrier. The temperature of the two fluids will tend to equalize. By arranging counter-current flow it is possible for the temperature at the outlet of each fluid to approach the temperature at the inlet of the other. The heat contents are simply exchanged from one fluid to the other and vice versa. No energy is added or removed.
Since the heat demands of the process are not constant, and the heat content of the two fluids is not constant either, the heat exchanger must be designed for the worst case and must be controlled to make it operate at the particular rate required by the process at every moment in time. The heat exchanger itself is not constant. Its characteristic changes with time. The most common change is a reduction in the heat transfer rate due to fouling of the surfaces. Exchangers are initially oversized to allow for the fouling which gradually builds up during use until the exchanger is no longer capable of performing its duty. Once it has been cleaned it is again oversized.
“Çalışmadan, yorulmadan ve üretmeden, rahat yaşamak isteyen toplumlar; evvela haysiyetlerini, sonra hürriyetlerini daha sonra da istiklal ve istikballerini kaybetmeye mahkumdurlar.” Mustafa Kemal ATATÜRK