Chapter 10: Flows, Pumps, and Piping Design Fluid distributions by pipes using a pump are essential to all heating and cooling systems. w is the work requirement to produce the change between the inlet and outlet (the work could be provided by a pump, but also by other means). Fluid flow basics Energy per unit mass Fluid flow basics Pump

Fluid flow basics   Fluid distributions by pipes using a pump are essential to all heating and cooling systems. Each term has the unit of pressure Each term has the unit of length, referred to as head Pumping work, negative

Discussion on 10-1a and 10-1c   In EE system, the gc in both equations is the constant of proportionality in Newton’s second law. gc F = m·a/gc = m·g/gc ≈ m, g ≈ gc. gc is primarily used to equalize both sides under the condition of F = m at standard conditions. The above two equations appear to be the same. However, the interpretation is difference. For the second one, the unit of each term is ft; but the unit of the first equation is energy per mass, as shown below: A force of one pound (1 lbf) is the force that gives a pound mass (1 lbm) an acceleration equal to the standard acceleration of gravity on Earth (32.2 ft/s2).

Fluid flow basics   Total pressure: Total head

Lost head   Correlations are needed to compute friction factor

Lost head   When the friction factor becomes independent of the Reynolds number.

Lost head   When the friction factor becomes independent of the Reynolds number.

Lost head   The term of Schedule is used to indicate the wall thickness of a pipe.

Friction Loss of Water Flow

Friction Loss of Water Flow

System characteristics From Eq. 10-1C: Lost head plus mechanical energy gain across the flow system Pumping power 2 1 a b 2 1 w is the work requirement in terms of head to produce the change (the work could be provided by a pump, but also by other means). When flow rate is zero, pressure difference, velocity difference, and head loss are all zero.

System characteristics

Centrifugal pumps  

Centrifugal pumps   The total head Between the inlet and outlet of the pump, not including the pipeline

Centrifugal pumps   If the static pressure of the fluid entering a pump approaches the vapor pressure of the liquid too closely, vapor bubbles will form in the impeller passages. This condition is detrimental to pump performance, and the collapse of the bubbles is noisy and may damage the pump. This phenomenon is known as cavitation. The amount of pressure in excess of the vapor pressure required to prevent cavitation is known as the required net positive suction head (NPSHR), determined by the actual testing of each model. The vapor pressure here is the saturation pressure corresponding to the fluid inlet temperature

Centrifugal pumps  

Combined system and operating point Piping system Piping system, mechanical energy requirement for the fluid, based on the energy balance over the piping system. Pump, energy balance between the pump inlet (suction) and outlet (discharge ) only. Both Hp are related to pump power input to the fluid, one obtained through the piping system, the other through the pump.

Combined system and operating point Piping system from 1 to 2, the change of valve condition may cause a similar effect as the change of pipe length.

Combined system and operating point

Affinity Laws   For a constant impeller diameter The affinity laws may be used to generate a new pump head characteristic. n: new, o: old

Multiple pump arrangement Parallel arrangements are the most common because the variation in the system flow rate is usually the variable of interest.

Multiple pump arrangement

Piping system fundamentals Basic Open-loop system

Basic closed-loop systems The expansion tank is to accommodate the volume change of the fluid due to a changed in thermal conditions.

Pipe sizing criteria Where possible, the pipes should be sized so that drastic valve adjustments are nor required.

Pipe sizing Basic

Pipe sizing Basic ft is the friction factor to be found in Table 10-2 For both inlets and outlets, if there is no contraction/expansion, ft is the friction factor to be found in Table 10-2 Basic ft NOT ft ft NOT ft Theta is the converging/diverging angle of the inlet port or outlet port of the gate valve ft NOT ft ft NOT ft

Pipe sizing Basic Reservoir

Pipe sizing

Lost head for valves, check valves, and strainers in term of coefficient Cv