Similarly, to calculate the power needed to heat or cool a bath to a certain temperature in a given time, you can use this equation: P is the power at which energy is supplied in watts or joules per second.ΔT is the temperature differential in degrees Celcius or Fahrenheit.c is the specific heat capacity of the fluid in joules per kilogram and per Kelvin.m is the mass of the fluid in kilograms.t is heating or cooling time in seconds.To find out how much time it will take to heat a bath to a certain temperature, you can use the following equation: When heating, the power applied is constant, but when cooling, the power (or the cooling capacity) is variable depending on the temperature. You can use the same basic equation when calculating heating or cooling time, although there is a little more work involved for calculating cooling time. In this post, we take a look at the equation for calculating heating or cooling time and the reasons you should look for a system with slightly more power than you think you need. That said, using this equation isn’t entirely reliable, as there are various factors that could throw off the calculation. Thankfully, there is a fairly simple equation you can use as long as you know the mass of the bath fluid, it’s specific heat capacity, the temperature differential, and either power or time. Or, you may want to calculate how much power is required to heat or cool a given volume of fluid in a certain amount of time. The Flow Factor k v defines the friction loss for water at a density of ρ=1000kg/m 3.There are many occasions where it might be helpful to know how much time it will take to heat or cool your system to a certain temperature. The flow factor uses SI-units and is used throughout the world whereas the Flow Coefficient uses imperial units and is mainly used in the United States. The only difference being the units used. The Flow Factor k v and Flow Coefficient C v are very similar. Table 4 - Resistance coefficient for various fittings Fitting Parameter Resistance Coefficient ζ Note Bend 90° R/D=1 0.40 ζ β = ζ 90°β/90° R/D=2 0.30 R/D=4 0.28 R/D=6 0.33 Reducer gradual D 1/D 2=1.2 0.02 ζ refer to w 2ĭ 2=outlet diameter D 1/D 2=1.4 0.04 D 1/D 2=1.6 0.04 D 1/D 2=1.8 0.05 D 1/D 2=2.0 0.06 Reducer gradual D 2/D 1=1.2 0.1 ζ refer to w 1ĭ 2=outlet diameter D 2/D 1=1.4 0.2 D 2/D 1=1.6 0.5 D 2/D 1=1.8 1.5 D 2/D 1=2.0 2.5 Ball valve 0.1-0.2 Full bore Butterfly valve 0.2 Completely open Gate valve 0.1-0.3 Without flow restrictions Gate valve 0.3-1.2 With flow restrictions Gate valve 0.2-2.5 High pressure Globe valve 2-10 Straight Globe valve 1-2 Wye type Globe valve 3-12 Angled Check valve (swing type) 0.4-1.0 Screw down non-return valve 1-8 Check valve (ball type) 0.5-2 Flow Factor kv and Flow Coefficient Cv The friction coefficient is for laminar flow i.e. This procedure has also been included in an easy to use Friction Coefficient Calculator. It show the Darcy-Weisbach friction factor as function of roughness and Reynolds number and is a quick way to quickly determine the friction factor.Īnother possibility is to calculate the friction coefficient using the equations in the next section. One way to determine it is by using The Moody Diagram. It is a function of surface roughness and flow type. The friction coefficient shall be determined in order to calculate the friction loss in the straight pipes. Table 1 - Hydraulic diameter for different pipe shapes Cross section shape Hydraulic diameter Note Circular D h=D i The inner diameter Square D h=a a is the length of a side Rectangular duct (Completely filled) D h=2ab/(a+b) with a being the height and b the width Annulus D h=D out-D in D out = outer diameter and D in=Inner diameter Friction loss in straight pipes Friction Coefficient - Moody Diagram
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