Here you will find informational articles on topics related to the Excel spreadsheets for civil and mechanical engineering calculations available from the DOWNLOADS page. This includes articles in the clickable categories below: pipe flow calculations, open channel flow, heat transfer/heat exchangers, storm water/hydrology, continuous beam analysis and design, open channel flow measurement, and pipe flow measurement topics. Scroll down on each category page to see all of the articles.
Similar blog articles are available at our companion site, www.EngineeringExcelSpreadsheets.com.
For an Excel spreadsheet for thermal design of a double pipe heat exchanger, click here to visit our spreadsheet store. Read on for information about the use of a spreadsheet for thermal design of a double pipe heat exchanger.
The basic heat exchanger design equation is: Q = U A ΔT_{lm}, where:
In an Excel spreadsheet for thermal design of a double pipe heat exchanger, the heat exchanger equation can be used to calculate the required heat exchanger area for known or estimated values of the other three parameters, Q, U, and ΔT_{lm}. Each of those parameters will be discussed briefly in the next three sections.
The driving force for a heat transfer process is always a temperature difference. For heat exchangers, there are always two fluids involved, and the temperatures of both are changing as they pass through the heat exchanger. Thus some type of average temperature difference is needed. Many heat transfer textbooks (e.g. ref #1 below) show that the log mean temperature difference is the appropriate average temperature difference to use for heat exchanger design calculations. The definition of the log mean temperature difference is shown in the figure above. The meanings of the four temperatures in the log mean temperature difference equation are rather self explanatory as shown in the diagram of a counterflow double pipe heat exchanger at the right.
In order to use the heat exchanger design equation to calculate a required heat transfer area, a value is needed for the heat transfer rate, Q. This rate of heat flow can be calculated if the flow rate of one of the fluids is known along with its specific heat and the required temperature change for that fluid. The equation to be used is shown below for both the hot fluid and the cold fluid:
Q = m_{H} C_{pH} (T_{Hin} - T_{Hout}) = m_{C} C_{pC} (T_{Cout} - T_{Cin}), where
The heat transfer rate, Q, can be calculated in a preliminary heat exchanger design spreadsheet if the flow rate, heat capacity and temperature change are known for either the hot fluid or the cold fluid. Then one unknown parameter can be calculated for the other fluid. (e.g. the flow rate, the inlet temperature, or the outlet temperature.)
The overall heat transfer coefficient, U, depends on the convection coefficient inside the pipe or tube, the convection coefficient on the outside of the pipe or tube, and the thermal conductivity of the pipe wall. See the article, Forced Convection Heat Transfer Coefficient Calculations, for information about calculating the heat transfer coefficients and click here to visit our spreadsheet store, for spreadsheets to calculate the inside and outside convection coefficients and to calculate the overall heat transfer coefficient.
The screenshot below shows a screenshot of an Excel spreadsheet for hthermal design of a double pipe heat exchanger. The image shows only the beginning of the calculations. The rest of the spreadsheet will calculate the length of pipe needed, the length of each pass for a selected number of 180 degree bends, and the pressure drop through the inside of the pipe. Why bother to make these calculations by hand? This Excel spreadsheet is available in either U.S. or S.I. units at a very low cost at in our spreadsheet store.
References
1. Kuppan, T., Heat Exchanger Design Handbook, CRC Press, 2000.
2. Kakac, S. and Liu, H., Heat Exchangers: Selection, Rating and Thermal Design, CRC Press, 2002.
3. Bengtson, H., Fundamentals of Heat Exchangers, an online, continuing education course for PDH credit.
4. Bengtson, H., Heat Exchanger Thermal Design Calculations Spreadsheet, an online blog article
Scroll down for the following blog articles in this category:
Introduction
If you want to obtain an Excel spreadsheet for preliminary design of double pipe and/or shell and tube heat exchangers, click here to visit our download page. Read on for information about the use of an Excel spreadsheet for preliminary heat exchanger design calculations.
The Heat Exchanger Design Equation
The basic heat exchanger design equation is: Q = U A ΔT_{lm}
where:
For design of heat exchangers, the basic heat exchanger design equation can be used to calculate the required heat exchanger area for known or estimated values of the other three parameters, Q, U, and ΔT_{lm}. Each of those parameters will be discussed briefly in the next three sections.
The Log Mean Temperature Difference, ΔT_{lm}
The driving force for a heat transfer process is always a temperature difference. For heat exchangers, there are always two fluids involved, and the temperatures of both are changing as they pass through the heat exchanger. Thus some type of average temperature difference is needed. Many heat transfer textbooks (e.g. ref #1 below) showthat the log mean temperature difference is the appropriate average temperature difference to use for heat exchanger calculations. The definition of the log mean temperature difference is shown in the figure at the left. The meanings of the four temperatures in the log mean temperature difference equation are rather self explanatory as shown in the diagram of a counterflow double pipe heat exchanger at the right.
The Heat Transfer Rate, Q
The heat transfer rate, Q, can be calculated if the flow rate, heat capacity and temperature change are known for either the hot fluid or the cold fluid. Then one unknown parameter can be calculated for the other fluid. (e.g. the flow rate, the inlet temperature, or the outlet temperature.)
The Overall Heat Transfer Coefficient, U
The overall heat transfer coefficient, U, depends on the convection coefficient inside the pipe or tube, the convection coefficient on the outside of the pipe or tube, and the thermal conductivity of the pipe wall. See the article, Forced Convection Heat Transfer Coefficient Calculations, for information about calculating the heat transfer coefficients and click here to visit our download page, for spreadsheets to calculate the inside and outside convection coefficients and to calculate the overall heat transfer coefficient.
An Excel Spreadsheet as a Preliminary Heat Exchange Design Calculator
The Excel spreadsheet template shown below can be used to carry out preliminary design of a double pipe heat exchanger. The image shown only the beginning of the calculations. The rest of the spreadsheet will calculate the length of pipe needed, the length of each pass for a selected number of 180 degree bends, and the pressure drop through the inside of the pipe. Why bother to make these calculations by hand? This Excel spreadsheet and others with similar calculations for a shell and tube heat exchanger are available in either U.S. or S.I. units at a very low cost at www.engineeringexceltemplates.com or in our spreadsheet store.
If you want to obtain an Excel spreadsheet for natural convection heat transfer coefficient calculations, click here to visit our download page. Read on for information about natural convection heat transfer coefficients and Excel spreadsheets to obtain a value for them.
Convection heat transfer takes place between a solid surface and fluid that is at a different temperature and is in contact with the surface. If the fluid is flowing past the surface due to an external driving force like a fan or pump, then the heat transfer is called forced convection. When fluid motion is due to density differences within the fluid (caused by temperature variation), then the heat transfer is called natural convection or free convection.
Newton's Law of Cooling for Natural Convection Heat Transfer
Newton's Law of Cooling [ Q = hA(T_{s} - T_{f}) ] is a simple expression used for the rate for convective heat transfer with either forced or natural convection. The parameters in Newton's Law of Cooling are:
Dimensionless Nusselt, Rayleigh, Grashof, and Prandtl Numbers
Natural convection heat transfer coefficients typically are estimated using correlations of dimensionless numbers, specifically correlations of Nusselt number (Nu) with Prandtl number (Pr), Grashof number (Gr), and/or Rayleigh number (Ra), where Ra = GrPr. The Nusselt, Grashof and Prandtl numbers are defined in the box at the left.
The following sections provide equations for estimating the heat transfer coefficient for several common natural convection configurations.
Natural Convection from a Vertical Plane
The box at the right shows two correlations for convection heat transfer between a vertical plane and a fluid of different temperature in contact with it. The first can be used for all values of Rayleigh number and the second is only for laminar flow, indicated by Ra < 10^{9}. The screenshot image below shows an example of an Excel spreadsheet to calculate the natural convection heat transfer coefficient for a vertical plate using the two equations shown here.
For low cost, easy to use Excel spreadsheet packages for calculating convection heat transfer coefficients for natural convection from a vertical plane, a horizontal plane, an inclined plane, a horizontal cylinder or a sphere in either U.S. or S.I. units, click here to visit our download page.
1. Incropera, F.P., DeWitt, D.P, Bergman, T.L., & Lavine, A.S., Fundamentals of Heat and Mass Transfer, 6th Ed., Hoboken, NJ, John Wiley & Sons, (2007).
2. Lienhard, J.H, IV and Lienhard, J.H. V, A Heat Transfer Textbook: A Free Electronic Textbook
3. Bengtson, Harlan H, Fundamentals of Heat Transfer, an online continuing education course for engineering PDH credit
Excel templates work well for calculation of forced convection heat transfer coefficients, typically based on correlations of Nusselt number in terms of Reynolds number and Prandtl number. Forced convection occurs when a fluid moving past a solid surface with the fluid and the solid being at different temperatures. Newton's Law of Cooling is a simple expression for the rate for convective heat transfer: Q = hA(Ts - Tf), where the parameters are:
The most difficult part of forced convection heat transfer calculations is typically determination of a good value for the heat transfer coefficient, h. The most common way of determining the heat transfer coefficient for a particular forced convection application is through a correlation for Nusselt number (Nu) in terms of Reynolds number (Re) and Prandtl number (Pr). The definitions of these three dimensionless numbers are shown in the box at the right, where:
Excel spreadsheets to calculate forced convection heat transfer coefficients for several common physical configurations are available at our downloads page.