PUMPS Thermal Systems Laboratory Samuel A. Santiago Pérez Modesto González David Alvarado

OUTLINE Objective Introduction Theory Pumps Pump Characteristics Duty Point Affinity Laws Cavitation NPSH Pump Configuration Experimental Procedure

OBJECTIVE To better understand the performance characteristics of centrifugal pumps by monitoring the system behavior of a Pump Circuit. To be able to characterize a parallel and series connection of a pair of pumps to improve design knowledge in the area.

INTRODUCTION Pumps are the most efficient means of transport for any type of fluid from point A to B. The centrifugal pump is the most commonly used in the market given its low operating and maintenance costs. The principle of operation consists of fluid entering the inlet of the pump which is mechanically forced through the outlet with and added pressure caused by the impeller.

THEORY

PUMPS First Law of Thermodynamics as applied to a pump system: In this equation the w represents the power supplied by the pump. The head loss in a pipe circuit falls into two categories:  Due to viscous resistance extending throughout the total length of the circuit  Due to localized affects such as valves, sudden changes in area of flow and bends

PUMPS As w can also be represented by the actual head it can be referred to as the energy per unit of weight. If pipe inlet and outlet diameters are similar, then the kinematic head will be zero. Therefore calculation for the actual head H can be made by measuring differential pressure. Usually potential and kinematic heads are relatively small compared to the pressure head. Pressure Head Kinematic Head Potential Head

PUMP CHARACTERISTICS This graph shows the curves which pertain to different performance characteristics of pumps. Usually the actual head (h a ) is plotted against flowrate (Q).

PUMP CHARACTERISTICS A more specific type of graph which provides various efficiency curves as well as bhp lines. This type of graph can typically be found in manufacture information relating a given pump.

DUTY POINT The duty point of a pump is where the flowrate and head match the required application parameters. Centrifugal pumps generally operate where the pump head matches the resistance of the pipeline.

AFFINITY LAWS Affinity Laws are utilized to relate several pump performance characteristics (flowrate, head, power, etc.). These laws help extrapolate to predict pump performance and are useful to modify pumps for required applications.

CAVITATION OF PUMPS Cavitation is the development of bubbles or cavities in low pressure areas around pump impellers. The appearance of the phenomenon in pumps can cause great losses in efficiency and even destruction of the pump.

NET POSITIVE SUCTION HEAD (NPSH) The NPSH is responsible for the pump not causing cavitation. It is the minimum pressure required to keep the fluid from cavitation. There are two types of NPSH, actual and required. For a pump to work without cavitation

PUMP CONFIGURATIONS A pump connected in series adds the head of the system at the same flowrate. A pump connected in parallel will add the flowrates at a same head.

EXPERIMENTAL PROCEDURE

1. SINGLE PUMP CHARACTERIZATION A pump containing an outlet valve will be to operate at its maximum velocity. Data collection will consist of pressure drop and other readings which will be recorded ten times for different valve settings. Pump Head (H), Efficiency (η) and Power (P) will be compared in relation to volumetric flow. 2. SINGLE PUMP CHARACTERIZATION II A pump will be operated at four different speeds. Data collection will consist of pressure drop and other readings which will be recorded ten times for different valve settings. Pump Head (H), Efficiency (η) and Power (P) will be compared in relation to rotational speed. The use of affinity Laws can help predict pump behavior with comparison to experimental data.

3. PUMP SUCTION A pump’s inlet valve will be controlled as to limit the amount of intake till the pump is no longer able to draw water from the feed line. 4. DUTY POINT To find the duty point a pump will have a set outlet setting while a variation of speed will produce the system curve of the pump. The point is found by plotting the pump head with the system head.

5. PUMP CONFIGURATION (SERIES/PARALLEL) Two pumps will be configured in each setting to evaluate the differences in head and flowrate capabilities and how each is affected by the other.